Cardiology Core Curriculum A problem-based approach - part 2 pot

At age 30 years he noticedreduction in his exercise tolerance and was found to have moderatemitral regurgitation, and because of the family history of prematureheart disease he underwent

Cardiac stress tests are designed to quantitate the cardiovascularresponses to controlled incremental increases in metabolic demandsusing conventional protocols Stress tests fall into two categories:physical exercise and pharmacologic Irrespective of the type of stresstest protocol used, the measurements routinely obtained include heartrate and blood pressure, electrocardiograms at each incrementalincrease in workload, and a continuous account of symptoms Stresstesting is frequently performed in combination with imagingtechniques, or various nuclear cardiac imaging techniques, which allowadditional measurements to be made during stress testing, includingventricular contractile performance (i.e ejection fraction, regional leftventricular wall motion, and myocardial perfusion and metabolism).

Exercise stress tests

Exercise stress tests are conducted either on a treadmill or a bicycleergometer Exercise is begun at a low workload that the patient caneasily sustain The workload is then increased in increments at regularintervals predefined by the exercise protocol until the patient:

• achieves the maximum exercise workload of the protocol

• achieves 85% of their predicted heart rate for age and sex

• achieves his or her anaerobic threshold

• develops typical symptoms with electrocardiographic evidence ofischemia

• becomes hypotensive, or

• develops ventricular dysrhythmias

All of these are reasons to terminate any and every stress test,whether exercise or pharmacologic

Pharmacologic stress tests

Pharmacologic stress tests are used in patients who cannot engage

in physical exercise for various reasons They are conducted byadministering a drug that either increases myocardial workload(dobutamine) or vasodilates the coronary microvasculature(dipyridamole or adenosine)

Abnormal findings

Abnormal findings during stress that reflect impaired performance

of the coronary circulation and the myocardium are as follows

• Characteristic electrocardiographic changes occur during exercisewhen the increased myocardial metabolic activity provokesmyocardial ischemia, that is ≥2 mm of planar depression of the STsegments in the electrocardiographic leads that represent thedistribution of the stenotic coronary artery (Figure 2.12).

• Myocardial ischemia is frequently accompanied by a decline in leftventricular contractile performance heralded by hypotension,which denotes proximal severe triple coronary artery stenoses,stenosis of the left main coronary artery, or ventricular dysfunction.Decline in left ventricular contractile function can be detected byimaging studies conducted during or immediately following stress

• The increased cardiac workload associated with stress may provokeabnormalities and non-uniformities of myocardial coronaryperfusion, which may be detected by imaging studies conductedimmediately following stress Alternatively, they may result inelectrical irritability and ventricular arrhythmias that are evidentelectrocardiographically

Baseline ECG

Stress ECG

VL VF

VR VL

Cardiac nuclear imaging

Cardiac nuclear imaging provides important information oncardiac function by employing radiotracer techniques and externaldetection equipment The most frequently used nuclear techniquesare myocardial perfusion imaging, radionuclide angiography, andmetabolic imaging

Cardiac nuclear imaging is based on the detection of γrays emitted

by radiopharmaceutical agents administered to patients andmeasured by large detectors (i.e γ cameras) outside the body Theimages created represent various functions of the heart depending onthe type of radiopharmaceutical employed We briefly discussradiopharmaceuticals and detection systems below

α, β, and γ Both α and β decay involve the emission of particles,whereas γ decay is characterized by the emission of γ rays(electromagnetic radiation) Clinical nuclear imaging is based entirely

on γ emitting radionuclides because γ rays pose the least harmfuleffect to tissues while having sufficient penetrating power to traversethe body tissues and be detected externally

The most widely used radionuclide for clinical testing istechnetium-99m (Tc-99m) This radionuclide is produced by agenerator made of molybdenum-99, which decays to Tc-99m andemits γ rays of 140 KeV (kiloelectron volts) energy Tc-99m decayswith a half-life of 6 hours Another type of radionuclide used incardiac imaging is the positron emitting radioisotope This elementdecays by emitting a “positron” from the nuclei, which is a particle ofthe same energy (511 KeV) as an electron but is positively charged.This particle immediately interacts with an electron in thesurrounding matter in a process known as annihilation Two γ rays ofthe same energy and opposite direction are emitted from that process

An example of a positron emitting radionuclide is fluorine-18, whichhas a half-life of 110 min

The radionuclides above can be attached to other moleculesthat have a known distribution in the body and thus form a

radiopharmaceutical agent An example of a radiopharmaceutical

is Tc-99m sestamibi, which is a myocardial blood flow (MBF) tracermade of two components: the radionuclide (i.e Tc-99m) and thepharmaceutical (i.e sestamibi) Sestamibi distributes in the myocardium

in proportion to MBF, and its distribution pattern can be detectedbecause of the presence of technetium in the molecule In patientswho have suffered heart attacks, abnormal distribution of tracer helps

to define the area of infarction.12

Detection systems

The overall principle of the detection system is based on the theorythat certain types of crystal emit light when struck by γ rays Oneexample of this type of crystal is sodium iodide, which is used in mostclinical scanners The light output of the crystal is amplified manytimes by photomultiplier tubes and by complex electronic circuitry.This light output can be localized to represent a three-dimensionalmap of radionuclide distribution within the myocardium With theaid of computers, this information is digitized and images produced

and displayed on computer screens or x ray film.

Large detectors, called γ cameras, are used to image large parts of thebody The cameras may produce a single image in a given projection(planar technique) with respect to the organ of interest (for example,heart or liver), or multiple projections that can be reconstructed intoimages known as tomograms The advantage of the tomographic method

is that the three-dimensional distribution of the radiopharmaceuticalmay be determined in detail while avoiding the overlap of structuresthat occurs with planar images This technique is called single photonemission computed tomography (SPECT) and is designed to imageradionuclides that emit single photons The other major techniqueavailable is known as positron emission tomography (PET), which is

an imaging method used to detect positron emitting radionuclides.This is a more complex, but more accurate method and is based on aprinciple called coincidence counting Positron emitting isotopesdecay by giving off two γrays in exactly opposite directions, each withthe same energy Using sophisticated electronics, the origin of the

γrays may be localized within the body more precisely, resulting in athree-dimensional map of perfusion or metabolism, depending on thetracer used (see below)

Myocardial perfusion imaging

Myocardial perfusion tracers are used to estimate non-invasivelythe relative amounts of blood flow to various regions of the heart

This test is the most commonly used technique in cardiac nuclearimaging In this section we briefly discuss the various radiotracersavailable for the assessment of regional myocardial perfusion We review

a number of tracers based on the mechanism by which theseradiopharmaceuticals measure MBF

Broadly speaking, there are two major categories of myocardialperfusion tracers (Table 2.1): those that are retained in themyocardium and those that are diffusible

Mechanically retained, or labeled albumin microspheres are notused clinically because they are large particles (15µm in diameter),which if injected intravenously become trapped in the lung capillariesrather than in the myocardium In order to be used as myocardialperfusion tracers, these microspheres must be injected into the leftsided circulation via a catheter placed into the left atrium or ventricle,which involves a more invasive procedure

Tracers retained in the myocardium via non-mechanical means arethe most commonly used perfusion agents in clinical practice Thesetracers are retained in the myocardium in proportion to MBF, andinclude thallium-201 and Tc-99m sestamibi for SPECT imaging, andnitrogen-13-ammonia and rubidium-82 for PET imaging

The retention process takes place during the first few minutes aftertracer injection, and the distribution of activity represents the bloodflow at the time of the injection This characteristic allows us to image

Table 2.1 Summary of tracers used in myocardial perfusion imaging

Retained in myocardium Mechanical retention Technetium-99, * carbon-11†

(based on microsphere or gallium-68 † labeled

Metabolic retention Thallium, * rubidium-82,†

potassium analogs (Na/K energy requiring pump), nitrogen-13 ammonia† (retained as glutamine)

Retained in propor tion Technetium-99 sestamibi

to electrical membrane gradients

Lipophilic Carbon-11 or oxygen-14

butanol†

These tracers may be used in * single photon emission computed tomography (SPECT) and †positron emission tomography (PET).

patients beginning several minutes after the injection, and permitslonger scan times, which improves image resolution Furtherimprovements in resolution are possible using a new acquisitionmethod synchronized to the cardiac cycle, which also providesinformation on left ventricular wall thickening – a measure ofregional function The ability of tracers to remain in the myocardiumfor minutes to hours after administration allows us to performinterventions such as exercise or pharmacologic stress testing inpatients and then image MBF during flexible time intervals afterward.The most typical example is the perfusion study performed withexercise Exercise is performed in the exercise laboratory, adjacent tothe imaging room, with patients using a treadmill or bicycleergometer The perfusion tracer is administered at peak exercise, andthe patient is allowed to recover for a few minutes to an hour(depending on the radioisotope), followed by perfusion imaging.Typically, with thallium agents, a resting scan is performedapproximately 3 hours after the stress imaging, to allow forcomparison with the stress state (Figure 2.13) A smaller dose ofthallium is usually given just before the rest image in order to detectbetter ischemic but viable myocardium Patients with severelyischemic myocardium may be imaged at 24 hours to allow for furtherredistribution of the isotope Using a tracer with a longer half-lifeand higher energy such as technetium sestamibi has an importantpractical advantage in that higher quality images are obtained Thus,the stress intervention can be performed before the restingexamination and, should the stress perfusion images be normal, thiswill eliminate the need for a resting examination.

None of the diffusible tracers are used clinically because ofthe complicated scanning techniques required However, thesetechniques are very accurate for quantifying MBF and are used mainlyfor clinical research An example of this group of agents is oxygen-15water, which is employed with PET scanning

Imaging protocols Myocardial perfusion imaging is usuallyperformed with some form of stress test when used for the diagnosis

of coronary artery disease (CAD) or for evaluation of treatment inpatients with known CAD (for example, angioplasty, bypass surgery,

or medications) Stress testing is necessary to detect regionaldifferences in myocardial perfusion due to occlusive CAD, becauseMBF at rest is not decreased even in the presence of coronary stenoseswith up to 80% reduction in normal vessel diameter By increasingMBF with exercise or coronary vasodilators such as dipyridamole oradenosine, myocardial regions supplied by significantly diseasedcoronary vessels may be detected because of their inability to increaseMBF to a degree similar to that in regions supplied by normal vessels

Given that the radiopharmaceuticals are carried in the blood andextracted by the myocardium, significantly less tracer is distributed toareas supplied by diseased vessels, and therefore the total amount ofradiotracer delivered to these regions is less than to normal areas Thisresult produces a low intensity segment, or defect, on the scan inregions subserved by diseased vessels, and permits not only thedetection of the presence of CAD but also assists with localizing thedisease to specific coronary arteries (Figure 2.14).

The most frequently used stress test in clinical practice is theexercise test With exercise, there is an increment in heart rate,blood pressure, and contractility that increases with myocardialmetabolism, and in turn increases MBF in order to increase oxygendelivery to meet the increased myocardial oxygen demand Anappropriate increment in MBF in response to the oxygen demand can

be reached in those segments of the myocardium that are supplied

by non-stenotic arteries This increment in MBF with maximalexercise or maximal vasodilatation is called the coronary flow reserve,and is approximately three to four times the normal resting MBF

Figure 2.13 A normal thallium per fusion scan is shown that illustrates the three views used for planar clinical cardiac imaging In the shor t axis view the right ventricle is faintly seen to the left of the image, adjacent to the inter ventricular septum The left ventricular (LV) lateral wall is seen to the right of the image In the horizontal long axis image, the LV apex is at the top of the image, and the lateral wall is to the right In the ver tical long axis view, the anteroseptum is seen at the top of the image, and the LV apex is to the right Note the homogeneous intensity pattern in all LV myocardial regions

However, in segments perfused by a stenotic artery there is anadditional resistance in the vessel that prevents an appropriateincrement in MBF Therefore, patients with CAD will not match theirincreased myocardial oxygen demand, resulting in an imbalancebetween oxygen demand and supply and producing myocardialischemia This supply/demand mismatch and ischemia may result in atypical syndrome of retrosternal chest pain associated with sweating,shortness of breath, and radiation of the pain along the left arm to theelbow or fingers (angina) In other patients, there may be few or nosymptoms at all, despite electrocardiographic changes demonstratingmyocardial ischemia (silent ischemia) Under these conditionsnormally perfused myocardium will demonstrate high MBF and theregion supplied by the stenotic vessel will have lower MBF If we inject

a myocardial perfusion tracer at this point, the resulting image will

Figure 2.14 Per fusion defects A transient per fusion defect is seen in the upper panel that is consistent with exercise-induced ischemia During stress, the inferior walls in both the shor t axis and ver tical long axis views exhibit decreased signal intensity, and therefore decreased per fusion, relative to the remaining walls The signal intensity normalizes or reverses in the resting image, demonstrating a reversible defect In the lower panel, a fixed defect in a similar location is shown.

A defect noted on the stress images show no reversibility upon rest, which is consistent with infarction or non-viable tissue Reinjection of a small amount of thallium at the time of rest images improves detection of severely ischemic but viable myocardium

show a regional perfusion imbalance or defect that is not present in aresting image, when MBF would be more comparable.

There are pharmacologic stress tests that can be used to provokethese same transient perfusion defects, which involve the use ofpotent coronary vasodilators or β-agonists that increase myocardial

oxygen consumption in a similar manner to exercise.

Clinical applications The major clinical applications of myocardialperfusion imaging are:

• diagnosis of CAD

• risk stratification in patients with known chronic CAD

• treatment evaluation in patients with known CAD, in particularfollowing revascularization techniques such as percutaneoustransluminal coronary angioplasty or coronary artery bypassgrafting

• risk stratification after acute myocardial infarction

• evaluation of patients with CAD and left ventricular dysfunction

• evaluation of patients with “silent ischemia”

Radionuclide angiography

Ventricular function is most commonly assessed with a techniquecalled multigated image acquisition scanning, which uses a “bloodpool” method approach Blood labeled with technetium-99 remains

in the intravascular space, or blood pool, and provides a means tomeasure the end-diastolic and end-systolic volumes (EDV and ESV,respectively) of the heart non-invasively The ejection fraction, or(EDV – ESV)/EDV, is a common measure of global ventricularperformance If a stress test is performed after baseline imaging, thenthe cardiac “reserve” can be estimated, with a fall in exercise ejectionfraction indicating abnormal reserve

Metabolic imaging

PET scanning is a technique that can assess myocardial perfusionand metabolism somewhat more rigorously than thallium scanning.13

Nitrogen-13-ammonia is a common perfusion isotope, while

18fluorine deoxyglucose is used as the metabolic tracer that evaluatesthe ability of myocytes to use glucose (Figure 2.15) One potentialadvantage to PET scanning is that the study may be performed at rest;however, the use of the above isotopes requires a cyclotron forproduction

Figure 2.15 In this positron emission tomography (PET) image, the per fusion agent nitrogen-13 ammonia ( 13 NH3; upper panels) demonstrates decreased resting blood flow to the lateral wall, as seen in both the short axis and horizontal long axis views The metabolic tracer 2-deoxy-2-[ 18 F]fluoro- D -glucose ( 18 FDG) depicts regions in which the conversion from free fatty acid substrate use (normal metabolism) to glycolytic metabolism (ischemic zones) has occurred High signal intensities in the 18 FDG images (bottom panels) are seen in segments corresponding to the hypoper fused regions, which is indicative of ischemia-related changes in metabolism

Case studies

Case 2.1

A 32-year-old male tax accountant presented with a 2 year history

of progressive shortness of breath on exertion such that he could onlywalk two blocks on flat ground or climb five stairs He had nevercomplained of chest pain or palpitations, and was a non-smoker andnon-drinker

When aged 15 years, at a school sports medical examination, acardiac murmur was detected In his remote past he had sustained twounexplained syncopal episodes that were unrelated to exertion orposture His father, who had always enjoyed good health as an activeathlete and non-smoker, died suddenly from a “heart attack” at age

37 years His father’s death prompted an office visit to a cardiologistwho, in addition to eliciting an ejection systolic murmur at the leftsternal edge, recorded a 12-lead electrocardiogram, which revealedleft ventricular hypertrophy and repolarization abnormalities Aclinical working diagnosis of congenital aortic valve stenosis was

made, and an outpatient two-dimensional echocardiogram wasscheduled, which excluded aortic valve stenosis, but showed leftventricular hypertrophy with normal systolic function, and nofurther recommendations were made At age 30 years he noticedreduction in his exercise tolerance and was found to have moderatemitral regurgitation, and because of the family history of prematureheart disease he underwent cardiac catheterization and coronaryarteriography.

Catheterization demonstrated a cardiac index of 4·1 l/min per m2;ejection fraction 73%; end-diastolic volume index 55 ml/m2;end-systolic volume index 15 ml/m2; left ventricular pressure135/23 mmHg; aortic pressure 102/65 mmHg; a “v” wave in thepulmonary capillary wedge pressure of 41 mmHg; pulmonary arterysystolic pressure 46 mmHg; and right atrial pressure 9/7 mmHg (mean

6 mmHg) Contrast angiography showed a hyperdynamic leftventricle with no segmental wall motion abnormality, grade 3+mitralregurgitation, an enlarged left atrium, and normal coronary arteries

In view of the progressive reduction in exercise capacity, the moderatepulmonary hypertension, and moderately severe mitral regurgitation,

he was referred for mitral valve repair/replacement

Examination Physical examination: the patient was comfortable

lying flat Pulse: 78 beats/min, brisk upstroke, full volume Bloodpressure: 105/60 mmHg in the right arm Jugular venous pulse:normal Cardiac impulse: forceful, double impulse, regular rhythm.First heart sound: normal Second heart sound: reversed splitting.Fourth heart sound was present Apical grade 3/6 holosystolicmurmur radiating to axilla, grade 2/6 ejection systolic murmur atmid-left sternal edge, which increased with Valsalva Chestexamination: normal air entry, no rales or rhonchi Abdominalexamination: soft abdomen, no tenderness, and no masses Normalliver span No peripheral edema Femoral, popliteal, posterior tibial,and dorsalis pedis pulses: all normal volume and equal Carotidpulses: full volume, rapid upstroke, no bruits Optic fundi: normal

Investigations Laboratory findings: normal Electrocardiogram:

sinus rhythm at 78 beats/min, normal intervals and frontal QRS axis,severe left ventricular hypertrophy with small Q waves, and 2 mm STsegment depression and T-wave inversion in leads V4 through V6

consistent with strain or lateral ischemia Chest x ray: mild

cardiomegaly with left atrial enlargement and normal lung fields.24-Hour ambulatory electrocardiographic monitoring: predominantcardiac rhythm was sinus, occasional isolated premature ventriculardepolarizations, and three episodes of non-sustained ventriculartachycardia, with the longest being an 11-beat run at a maximum rate

of 178 beats/min

Transthoracic two-dimensional echocardiogram Asymmetric

hypertrophy of the interventricular septum; a small hyperdynamicleft ventricle; systolic anterior motion of the mitral valve; a 30 mmHgleft ventricular outflow tract gradient in systole at rest, whichincreased to 64 mmHg with Valsalva in late systole; enlarged leftatrium; and moderately severe mitral regurgitation by color flowDoppler velocity mapping

Clinical course The patient underwent mitral valve surgery, from

which he made an excellent recovery and was discharged fromhospital on postoperative day 7 on β-adrenergic blocking agents At

3 month follow up his exercise tolerance had increased to 12 blocks

Answer to question 2 The diagnosis in this patient was hypertrophicobstructive cardiomyopathy This diagnosis was based clinically onthe auscultatory findings of an ejection systolic murmur with a

forceful double apical impulse, brisk pulses with rapid upstroke to thecarotid pulses, and augmentation of the cardiac murmur with Valsalva.The confirmatory two-dimensional echocardiographic findingscomprised asymmetric septal hypertrophy, systolic obliteration of theleft ventricular cavity with supranormal ejection fraction, systolicanterior motion of the mitral valve, with the left ventricular outflowtract gradient at rest increasing with Valsalva in late systole.

Answer to question 3 The genetic pattern of inheritance ofhypertrophic cardiomyopathy is dominant, and the patient should becounseled so that he is cognizant of the likelihood of his progenyhaving the same disease The sudden and unexpected death of hisfather, who was otherwise healthy, suggests that he had died from thesame disease

Answer to question 4 Valsalva increases intra-thoracic pressure andreduces venous return to the heart so that left ventricular end-diastolic volume is reduced and systolic anterior motion of the mitralvalve more easily obstructs the left ventricular outflow tract andthereby augments the systolic gradient

Answer to question 5 The patient was placed on β-adrenergicreceptor blocking agents to reduce augmentation of the systolicoutflow tract gradients in order to prevent or attenuate the increase inleft ventricular outflow tract gradient with exercise, which is at leastpartly mediated by increased catecholamines Another reason is toslow the heart rate, which allows longer diastolic filling and greaterleft ventricular end-diastolic volume Furthermore, β-adrenergicblocking agents may be efficacious in the treatment of non-sustainedventricular tachycardia

Answer to question 6 Non-sustained ventricular tachycardiacorrelates with sudden death, which accounts for the yearly attritionrate of approximately 5–8% of patients with familial hypertrophiccardiomyopathy

Case 2.2

A 47-year-old female Asian immigrant was brought to theemergency room with a dominant sided dense hemiplegia and severeexpressive dysphasia The history obtained from a relative was limitedbut included long-term shortness of breath on minimal exercise and

at night, requiring three pillows to sleep, and weight loss over theprevious 6 months

In early childhood she spent 1 year away from school convalescingfollowing an acute illness, which consisted of a painful migratoryarthralgia with swelling of both knees and ankles but with no otherstigmata She was discouraged from playing games and took penicillintablets once daily until adulthood She remained well and next saw aphysician during the last trimester of her second pregnancy, when shedeveloped an episode of palpitations and became light-headed Whenshe was seen by a cardiologist she was in regular rhythm and in nodistress However, a murmur was detected, which was thought to bedue to increased blood flow velocity associated with the volumeoverload state of pregnancy, and no follow up was arranged.

Five years later she noted progressive shortness of breath,intermittent palpitations provoked by exertion, and was finallyadmitted for investigation following hemoptysis She declined cardiaccatheterization but agreed to have an echocardiogram and wasdischarged home on digoxin 0·25 mg/day, furosemide 40 mg/day,potassium supplements, and warfarin at a dose to maintain anInternational Normalized Ratio of 2·5–3·0

Examination Physical examination: the patient had a right-sided

neurologic deficit She was only comfortable at 45° Pulse: 152beats/min, irregularly irregular Blood pressure: 95/70 mmHg Jugularvenous pulse: 12 cm at 45° Cardiac impulse: parasternal lift, palpable

P2 First heart sound: loud Second heart sound: split with loud P2 Atapex was opening snap close to P2 Mid-diastolic murmur at apex.Chest examination: normal air entry, basal crepitations Abdominalexamination: enlarged, tender liver No peripheral edema Carotidpulses: normal, no bruits

Investigations Laboratory findings: normal hemoglobin, hematocrit,

white blood cell count, platelets, electrolytes, and creatinine Aspartateaminotransferase 198 U/l (3·3µkat/l); alanine aminotransferase 33 U/l(5·6µkat/l); International Normalized Ratio 1·3 Electrocardiogram:atrial fibrillation at 167 beats/min, right axis deviation, rightventricular hypertrophy, and T-wave and ST-segment depression

throughout the limb and chest leads Chest x ray: cardiomegaly,

enlargement of the left and right atria and main pulmonary artery,prominence of the left atrial appendage, and elevation in the left mainbronchus at the carina Calcification of the mitral annulus, small leftpleural effusion, septal (Kerley B) lines, and cephalization of the upperlobes of the lung were also noted

Echocardiogram Echocardiography demonstrated a heavily calcified,

severely stenotic mitral valve with shortened chordae, andcalcification extending from the valve leaflets to the tips of thepapillary muscles, but with no mitral regurgitation Left ventricularsize, wall thickness, and function were normal The left atrium wasdilated with laminated mural thrombus on the left atrial wall behind

the posterior aortic root The aortic valve was trileaflet and normal,the right atrium and right ventricle were both dilated with moderatetricuspid regurgitation through a normal tricuspid valve A smallhemodynamically unimportant pericardial effusion was present.Doppler assessment revealed a peak gradient across the mitral valve of

28 mmHg (mean 14 mmHg) and a valve orifice area of 0·7 cm2

calculated from the pressure half-time, and a pulmonary artery systolicpressure of 68 mmHg calculated from the tricuspid regurgitant jet

Hospital course The patient was not considered a candidate for

mitral balloon valvuloplasty because of the extensive calcification ofthe valve leaflets and subvalve apparatus, and the presence of leftatrial thrombus She underwent mitral valve replacement with amechanical prosthesis 3 months later when the risk of exacerbatingher neurologic deficit by cardiopulmonary bypass was considered to

be less likely, and she was discharged on warfarin with anInternational Normalized Ratio of 2·9

Questions

1 What are the clinical diagnoses? What was her childhood illnessand the likely rhythm disturbance during pregnancy?

2 What factors contributed to the neurologic event?

3 Explain the auscultatory findings of a loud first heart sound, loud

P2, and the clinical significance of the closeness of the openingsnap to P2

4 Why was the liver enlarged and the liver function tests deranged?

5 Explain the abnormalities on the electrocardiogram

6 Describe the chest x ray findings that support the clinical

Answer to question 2 The factors that contributed to her neurologicevent include mitral valve stenosis with resultant slow flow in theleft atrium, left atrial enlargement, atrial fibrillation, and pooranticoagulant status with an International Normalized Ratio of 1·3.Answer to question 3 The loud first heart sound is due to the closure

of rheumatically thickened mitral valve leaflets; the loud P2is due tothe presence of pulmonary hypertension The closeness of theopening snap to P2relates to the amplitude of left atrial pressure andthe severity of the mitral stenosis, so that the closer the opening snap

is to P2, the more severe the mitral stenosis

Answer to question 4 The liver is enlarged because of systemicvenous hypertension from tricuspid regurgitation, and the derangedliver function tests indicate acute distension of the liver fromcongestive heart failure or from chronic elevation of systemic venouspressure and “cardiac cirrhosis”

Answer to question 5 Atrial fibrillation occurs from atrial dilatationand is part of the natural history of chronic rheumatic heart disease.The right axis deviation and right ventricular hypertrophy are due topulmonary hypertension, and the T and ST abnormalities are digitaliseffects

Answer to question 6 Left atrial enlargement, prominence of the leftatrial appendage and main pulmonary artery, elevated left mainbronchus, intracardiac calcification of the mitral valve apparatus, andcephalization of the upper lobes of the lungs

Answer to question 7 None

Answer to question 8 The patient is postmenopausal and soproblems with subsequent pregnancy are not an issue She is inestablished atrial fibrillation with a dilated left atrium, and willtherefore require anticoagulation Importantly, the primary failurerate of bioprostheses at 10 years is approximately 20%, so she wouldneed to undergo at least two additional valve replacements.Therefore, the use of a durable prosthesis over the long term isdesirable, and thus a mechanical prosthesis is the treatment of choice

Case 2.3

A 59-year-old male business executive was brought to theemergency room complaining of sudden onset of severe central chest

pain (which he graded 10/10) radiating through to his back,associated with diaphoresis and nausea He had never had chest painpreviously and played golf once weekly without any exerciseintolerance or shortness of breath His past medical history included

an arthroscopy for meniscectomy at age 37 years, and hypertensiontreated for 11 years initially with β-adrenergic blocking agents but forthe past 4 years with once daily angiotensin-converting enzymeinhibitor therapy Risk factors for coronary artery disease included afamily history (his father had sustained a myocardial infarction at age

61 years and underwent coronary artery bypass vein grafting; hismother and younger brother had hypertension), he was not diabetic

or a smoker, and had a cholesterol of 230 mg % (5·9 mmol/l)

Examination Physical examination: the patient was in acute

distress, and was cold, clammy, and complaining of pain in hismid-back Pulse: 110 beats/min, normal character Blood pressure:160/100 mmHg in right arm Jugular venous pulse: 8 cm Cardiacimpulse: prominent, displaced to anterior axillary line First heartsound: normal Second heart sound: split normally on inspiration Noadded sounds Decrescendo murmur at upper left sternal border.Chest examination: normal air entry, no rales or rhonchi Abdominalexamination: soft abdomen, no tenderness, and no masses Normalliver span No peripheral edema Pulses absent below femoral on theright, and his right foot was colder than his left Carotid pulses:normal, no bruits Optic fundi: normal

Investigations Laboratory findings: normal electrolytes and

creatinine Two sets of cardiac enzymes normal Electrocardiogram:sinus tachycardia, left axis deviation (–32°), minor QRS widening,left ventricular hypertrophy with non-specific T wave abnormalities

throughout Chest x ray (anteroposterior): widening of the

mediastinum and an “unfolded aorta”, with cardiomegaly but clearlung fields Two-dimensional echocardiogram: mildly dilated leftventricle with concentric hypertrophy; normal systolic function; nosegmental wall motion abnormalities; mild aortic regurgitation bycolor flow Doppler; a dilated aortic root with an intimal flap in theascending aorta, which could be identified as extending to theabdominal aorta from the subxiphoid images; and no pericardialeffusion Magnetic resonance imaging confirmed the diagnosis anddelineated the extent of the disease and the complications

Clinical course Following his echocardiogram, the patient

complained of a further episode of severe interscapular pain onlypartly relieved by intravenous morphine, after which his bloodpressure dropped to a systolic pressure of 70 mmHg Examinationdemonstrated that he could no longer move his legs, his right legremained cold and pulseless, he had a sensory level at his mid-thorax(T9), and had not passed urine since admission, although he was still

mentating normally Heart sounds and aortic regurgitant murmurwere unchanged On his way to the operating room he becameprofoundly hypotensive and developed sinus bradycardia, which wasfollowed quickly by a cardiac arrest from which he could not beresuscitated A postmortem was conducted.

Questions

1 What was the differential diagnosis of the patient’s chest pain?

2 What in the clinical history and physical examination made youselect your working diagnosis?

3 Explain the possible mechanisms for aortic regurgitation Did any

of these potential etiologies elucidate the seriousness or emergentnature of the patient’s management? Does any classification of thedisease in question spring to mind?

4 What was the significance of the cold right leg?

5 Why was the patient unable to move his legs, and what was thesignificance of the sensory level at T9?

6 The presence of the intimal flap seen by echocardiography andmagnetic resonance imaging was indicative of what?

7 What additional information was provided by magneticresonance imaging that was unavailable by transthoracic two-dimensional echocardiography?

8 What findings would you anticipate at postmortem examination?Answers

Answer to question 1 Acute myocardial infarction and acute aorticdissection

Answer to question 2 A history of hypertension associated with chestpain radiating to the back does not distinguish between myocardialinfarction and aortic dissection, and the presence of aorticregurgitation is a common feature of type A aortic dissection, butaortic regurgitation may also occur in patients with hypertension.However, the diagnosis of aortic dissection is strongly suggested bythe loss of pulses in the right leg

Answer to question 3 The probable mechanisms for the aorticregurgitation include acute dissection of the ascending aorta,involving the aortic root with prolapse of the valve leaflets, anddilatation of the aortic root due to longstanding systemichypertension Aortic dissections are classified as type A if they involvethe ascending aorta or aortic arch, and as type B if they are limited tothe descending thoracic aorta, usually beginning at the origin of the

left subclavian artery The treatment of acute type A dissection isurgent surgical repair, whereas type B dissections without rupture orcompromise of an organ or limb have a similar outcome with medical

or surgical repair The presence of aortic regurgitation and the dimensional echocardiographic confirmation of type A dissectionnecessitated emergent surgical repair (transesophageal echocardiographywould have been a better choice than transthoracic echocardiography).Answer to question 4 The cold pulseless right leg was caused bydissection and subsequent occlusion of the right common iliac artery,resulting in an ischemic right leg

two-Answer to question 5 The type A dissection had occluded the arteriamagna, which has a mid-thoracic origin and supplies the anteriorspinal arteries to the mid-thoracic cord The anterior spinal arterysupplies the corticospinal (motor), and anterior and lateralspinothalamic tracts (sensory), interruption of which resulted inmotor paralysis of the legs and the sensory level at T9

Answer to question 6 The intimal flap is the dissection between theintimal and medial layers of the aortic wall The free intimal flap isidentified by both two-dimensional echocardiography and magneticresonance imaging

Answer to question 7 The magnetic resonance imaging scandemonstrated the extent of the aortic dissection, the sites of theentrance and exit of the dissection, as well as the occlusion of theright common iliac artery, which were unavailable byechocardiography Because the transesophageal echocardiographyprobe cannot be passed beyond the stomach, the proximal abdominalaorta is the limit of echocardiographic evaluation

Answer to question 8 Postmortem examination demonstratedsimilar anatomic findings in terms of the dissection, but in additionexsanguination caused by rupture of the descending thoracic aortainto the left pleural cavity

Case 2.4

A 48-year-old male physician saw his local physician complaining

of a sensation of heaviness in the chest associated with weakness andlight-headedness that had progressed over the prior 3 weeks The paindid not radiate, but was provoked by anxiety and by decreasingamounts of exertion over the 3 weeks following its onset and wasrelieved quickly by rest He had brought forward his medical

appointment because of an episode the day before in which his chestdiscomfort occurred while at rest reading the newspaper His pastmedical history was unremarkable, with no previous illness oradmissions to hospital His risk factors included a remote smokinghistory (he had quit 15 years previously), no hypertension or diabetes,unknown cholesterol, and a positive family history for early coronarydisease (his father had had two myocardial infarctions at ages 50 and

57 years, one brother had coronary artery bypass graft surgery at age

53 years, and his eldest brother had a myocardial infarction at age

56 years but is now symptom free on medical therapy)

Examination Physical examination: the patient appeared normal.

Pulse: 78 beats/min, normal character Blood pressure: 135/80 mmHg.Jugular venous pulse: normal Cardiac impulse: normal First heartsound: normal Second heart sound: split normally on inspiration Noadded sounds or murmurs Chest examination: normal air entry, norales or rhonchi Abdominal examination: soft abdomen, no tenderness,and no masses Normal liver span No peripheral edema Femoral,popliteal, posterior tibial, and dorsalis pedis pulses: all normal volumeand equal Carotid pulses: normal, no bruits Optic fundi: normal

Investigations Laboratory findings: normal levels of sodium,

potassium, blood urea nitrogen, creatinine, creatine phosphokinase,and creatine kinase-MB Total cholesterol: 285 mg/dl (7·4 mmol/l).Electrocardiogram: sinus rhythm, normal QRS axis and intervals,T-wave flattening in leads V1–V3 Chest x ray: normal heart size and

clear lung fields Stress thallium was performed using a standard (Bruce)protocol The patient developed his typical chest heaviness, becamehypotensive and presyncopal after 3 min exercise, and had 3 mmplanar depression of the ST segments in leads V1 through V4 withmultiple ventricular extrasystoles Thallium scan revealed a largereversible defect involving the whole of the anterior left ventricular walland anterior septum Emergent cardiac catheterization: left ventricularend-diastolic pressure 19 mmHg; no left ventricular angiogram wasperformed, and during intubation of the left coronary artery arterialsystolic pressure dropped to 70 mmHg, so that only limited views of theleft coronary artery were obtained; the right coronary artery wasnormal The patient was referred for urgent cardiac surgery

Clinical course The patient underwent surgery without any

complications and was discharged home on postoperative day 6

Questions

1 What was the underlying reason for the hypotension andpresyncope at such a low workload, the electrocardiographicchanges and electrical instability?

2 What were the likely diagnoses?

3 Explain the significance of the “reversible” defect on the thalliumscan and the urgency for the cardiac catheterization.

4 Why did hypotension supervene during left coronaryangiography and not during injection of the right coronaryartery?

5 What were the likely findings of the cardiac catheterization?

6 Why was the patient referred for surgery rather than undergoingangioplasty?

7 What medical therapy, if any, would you institute followinghospital discharge?

Answers

Answer to question 1 Hypotension during stress testing indicatesthat the myocardium cannot meet the increased demands of exerciseand fails to generate a normal blood pressure response This is usuallydue to severe proximal triple vessel disease (left anterior descending,left circumflex, and right coronary artery) or left mainstem coronaryartery stenosis, or severe ventricular dysfunction The impressiveanterior electrocardiographic ST-segment depression demonstratesextensive anterior ischemia at a low workload in the territory of theleft anterior descending coronary artery The electrical instability andventricular ectopy are probably induced by myocardial ischemia.Answer to question 2 Left mainstem coronary artery stenosis orsevere proximal triple coronary artery disease

Answer to question 3 The reversible defect on the thallium scanindicates a large region of left ventricular myocardium that hasseverely reduced perfusion, even during mild exertion, which iscompletely viable and is normally perfused at rest This suggests that

if occlusion of the vessel occurred, then the area at risk for infarctionwould be large The reason for the urgent cardiac catheterization wasthe probable diagnosis of left main coronary stenosis

Answer to question 4 Hypotension supervened during left coronaryartery injection because when the catheter engaged the severelydiseased left coronary artery it completely obstructed flow, resulting

in myocardial ischemia The right coronary artery was normal and thecatheter did not occlude antegrade flow

Answer to question 5 Coronary arteriography demonstrated a 95%stenosis of the left main coronary artery and an 80% tubular stenosis

in the mid left anterior descending artery, with normal left circumflexand right coronary arteries

Answer to question 6 The treatment of left main coronary stenosis isleft internal mammary artery graft to the left anterior descendingartery and saphenous venous graft to the left circumflex artery.Angioplasty is contraindicated for left main disease because of risk forsevere acute global ischemia and for acute dissection and closureshould complications occur.

Answer to question 7 Long-term cholesterol lowering therapy should

be instituted because this reduces the incidence of late cardiovascularevents in patients with coronary artery disease

References

1 Henry WL, DeMaria A, Gramiak R, et al Report of the American Society of

Echocardiography Committee on Nomenclature and Standards in

Two-dimensional Echocardiography Circulation 1980;62:212–7.

2 St John Sutton M, Kotler M, Oldershaw P, eds Textbook of adult and pediatric

echocardiography and Doppler London: Blackwell Science, 1996.

3 Skjaerpe T, Hegrenaes L, Hatle L Noninvasive estimation of valve area in patients with aortic stenosis by Doppler ultrasound and two-dimensional

echocardiography Circulation 1985;72:810–8.

4 Currie P, Seward J, Reeder G, et al Continuous wave Doppler echocardiographic

assessment of the severity of calcific aortic stenosis: a simultaneous

Doppler-catheter correlative study in 100 adult patients Circulation 1985;71:1162–9.

5 Bonow R, Lakatos E, Maron B, Epstein S Serial long-term assessment of the natural history of asymptomatic patients with chronic aortic regurgitation and normal left

ventricular systolic function Circulation 1991;84:1625–35.

6 Chan K, Currie P, Seward J, Hagler D, Mair D, Tajik A Comparison of three Doppler

ultrasound methods in the prediction of pulmonary artery pressure J Am Coll

8 Schiller N, Shah P, Crawford M, et al Recommendations for quantitation of the left

ventricle by two-dimensional echocardiography J Am Soc Echocardgr 1989;2:

358–67.

9 Marvick T, Nemec J, Stewart W, Salcedo E Diagnosis of coronary artery disease using exercise echocardiograph and positron emission tomography: comparison

and analysis of discrepant results J Am Soc Echocardgr 1992;5:231–9.

10 Marcus M, Schelbert H, Skorton D, Wolf G, eds Cardiac imaging: a companion to

Braunwald's heart disease Philadelphia: WB Saunders Co, 1991.

11 Nienaber C, von Kodolitsch Y, Nicholas V, et al The diagnosis of thoracic aortic

dissection by noninvasive imaging procedures N Engl J Med 1993;328:1–9.

12 Zaret B, Beller G, eds Nuclear cardiology: state of the art and future directions St Louis:

Mosby, 1993.

13 Marshall R, Tillisch H, Phelps M, et al Identification and differentiation of resting

myocardial ischemia and infarction in man with positron emission tomography,

18F-labeled fluorodeoxyglucose and N-13 ammonia Circulation 1983;67:766.

CHARLES LANDAU

The advent of improved equipment and techniques plus anincreasing number of non-surgical options for the treatment ofcardiovascular disorders has increased the role of the cardiaccatheterization laboratory in the management of patients with avariety of diseases that affect the vascular and valvular structures ofthe heart

Diagnostic cardiac catheterization

Definitions and overview

The term “cardiac catheterization” refers to the placement ofhollow plastic tubes (catheters) into the chambers of the heart or intothe epicardial coronary arteries with fluoroscopic guidance for thepurpose of acquiring pressure measurements, collecting bloodsamples, and injecting radiographic contrast material in order toopacify coronary arterial and ventricular anatomy The latterprocedures are frequently referred to as arteriography or angiography

A catheterization procedure usually consists, at a minimum, ofacquiring arterial pressures and coronary arteriography

Right heart catheterization involves the passage of a catheter fromthe venous access site via the vena cava to the right atrium, rightventricle, and pulmonary artery Pulmonary capillary wedge pressure(PCWP), a reflection of left atrial pressure as transmitted retrogradethrough the pulmonary vasculature, is determined by advancing thecatheter to a terminal segment of the pulmonary arterial tree.Pressures are measured in each of the chambers, and blood samplesare drawn for the determination of oxygen saturations whenclinically indicated Determinations of cardiac output are also aroutine aspect of this protocol in most catheterization laboratories.When clinically indicated, an endomyocardial biopsy can be takenfrom the right ventricle using a flexible biopsy forceps afterhemodynamic measurements have been acquired

Left heart catheterization denotes the passage of a catheter from thearterial access site retrograde to the left ventricle through the aorticvalve In order to avoid the consequences of systemic emboli, patientsundergoing a left heart catheterization are usually systemically

anticoagulated with heparin Pressure is recorded sequentially in theleft ventricle and then, after pull-back of the catheter, in the ascendingaorta This series of measurements is performed to exclude a pressuregradient across the aortic valve, a finding indicative of aortic stenosis.Following these measurements a ventriculogram is performed with acontrast injection into the left ventricle The images of the opacifiedleft ventricle are used to assess regional wall motion, determineventricular volumes, calculate global left ventricular function as anejection fraction, and assess the presence and severity of mitralregurgitation, which manifests as the appearance of contrast in the leftatrium during ventricular systole as a result of an incompetent mitralvalve Selective coronary angiography is routinely performed afterventriculography, during which the left main and right coronaryarteries are selectively cannulated, followed by contrast injections todefine coronary anatomy, including stenoses and vascular distribution.Right and left heart catheterization combines the componentsdescribed above In addition to the protocols outlined, simultaneousmeasurements of the PCWP and left ventricular pressures are made inorder to evaluate the presence of a pressure gradient across the mitralvalve This is a pathologic finding that is usually indicative of mitralstenosis.

Indications

In clinical practice the majority of diagnostic cardiaccatheterizations are undertaken primarily for three reasons(Table 3.1)

• To obtain anatomic information regarding the coronary arteriesand left ventricular function

• To quantify hemodynamic abnormalities, including valvularlesions

• To determine the site and magnitude of an intracardiac shunt.Cardiac catheterization should not be undertaken in any patientwho is unable or unwilling to provide informed consent In addition,the procedure is contraindicated in those circumstances that increasethe risks associated with the procedure, such as bleeding diatheses,decompensated congestive heart failure, worsening renal function,systemic infections and untreated hyperthyroidism, and in thoseunwilling to provide informed consent Because catheterizationinvolves radiation exposure, pregnancy should be excluded in women

of childbearing age

Patients refractor y to medical therapy for ischemia

Patients with suspected high-risk anatomy (i.e.

left main or severe three-vessel disease)

To determine the severity

of valvular abnormalities

To assess the severity

of hemodynamic derangements in myocardial or pericardial disease

Equivocal non-invasive evaluation

Persistent chest pain despite negative non-invasive tests Dilated cardiomyopathy Sudden cardiac death Intolerant of medications Limiting angina despite adequate drug therapy Unstable angina

Postmyocardial infarction angina

Positive predischarge exercise test following myocardial infarction Markedly positive exercise test

Diffuse ECG changes (ST depression) during spontaneous episodes

of ischemia Rapid onset pulmonar y edema, presumably due

to ischemia Aor tic stenosis Aor tic regurgitation Mitral stenosis Mitral regurgitation Pulmonic stenosis Dilated cardiomyopathy* Hyper trophic obstructive cardiomyopathy*

Restrictive cardiomyopathy Constrictive pericarditis Left ventricular diastolic dysfunction

Atrial septal defect Ventricular septal defect Aor to-pulmonar y window Patent ductus ar teriosus

*Can also be utilized to assess the efficacy of treatment.

important that it be accomplished in its entirety at the beginning ofcatheterization so that the patient may return to a steady-statecondition for the hemodynamic measurements that follow It isroutine for patients to be premedicated with a combination ofdiazepam and diphenhydramine hydrochloride, or similarmedications, to lessen anxiety and to reduce the severity of an allergicreaction to contrast should one occur In order to detect vagalepisodes, which manifest as a rapid decrement in blood pressureand/or heart rate with the associated symptoms of diaphoresis,nausea, pallor, hyperventilation, yawning, and/or mydriasis, it isessential that vital signs be continuously monitored during thisportion of the procedure The vascular access site is first infused withlidocaine (lignocaine) to achieve local anesthesia.

Vascular access is achieved through either brachial, femoral, or radialsites Femoral access is used most frequently because the larger size ofthe femoral artery decreases the potential for vascular complications.The Seldinger technique is utilized to place a sheath in the femoralartery (for left heart access via the aorta) and/or the femoral vein (forright heart access via the inferior vena cava) A small skin incision ismade and the vascular structure is located using a hollow 18-gaugeneedle Next, a non-traumatic guidewire is introduced through theneedle into the vessel, the needle is removed while leaving the wire inplace, and then a plastic sheath is advanced over the wire into thevascular lumen before removing the wire The sheath, which is ahollow tube 2·0–3·0 mm in diameter and approximately 10 mm inlength, with a proximal one-way valve resting outside the patient toprevent back bleeding, is then used as a conduit through which thelonger catheters are advanced into the heart or its vessels

A similar technique can be used at the brachial site for arterialaccess only because the course of venous structures in the antecubitalfossa is highly variable Alternatively, a cutdown can be performed tovisualize directly the brachial artery with access achieved through anarteriotomy in the superior surface of the artery, which is repaired atthe conclusion of the procedure The advantage of this method overthe Seldinger technique is that a brachial vein can be located and usedfor right heart access The brachial approach is most commonly used

in patients with severe iliofemoral vascular disease in whom arterialaccess may be troublesome or marked by an increased potential forvascular complications Other clinical circumstances that favor thebrachial approach because of difficulties in attaining hemostasisinclude marked obesity, poorly controlled hypertension, or a widepulse pressure (i.e aortic regurgitation) Additionally, the radial arterycan be accessed percutaneously

Following vascular access, catheters are placed in the cardiacchambers of interest and hemodynamic measurements are made

before the injection of any contrast material This strategy is followedbecause intravascular contrast injections alter cardiac physiology andconduction such that measurements made following the administration

of these agents do not reflect the baseline hemodynamics of the patient.Angiography is the final phase of the procedure and involves rapidinfusion of radiopaque contrast material into the ventricle and thenthe coronary arteries Contrast temporarily replaces the bloodvolume, resulting in opacification of the ventricular chamber andcoronary arterial lumen, respectively This technique only providesinformation about the portions of these organs in contact with theblood pool; no direct data regarding the structure of the ventricular orvascular wall is obtained

When the catheterization procedure has been completed,protamine is given to reverse the effects of heparin The vascularsheaths are removed and hemostasis is achieved with direct pressureapplied either manually or with a mechanical device for 15–30 min,depending on sheath size Following hemostasis, the utilized limb isimmobilized for 6–8 hours to permit the clot that has formed at thevascular puncture site to stabilize Alternatively, a vascular closuredevice may be utilized These devices employ either bovine collagen(which is thrombogenic and focally positioned at the puncture site)

or resorbable suture (which is introduced percutaneously through thearteriotomy site created by the sheath) to achieve rapid hemostasiswith minimal compression If successfully deployed, patients canambulate in 2 hours, which facilitates discharge when catheterization

is performed in the outpatient setting

Risks associated with cardiac catheterization

Complications arising from cardiac catheterization are due tovascular access, catheter manipulations, or administration of drugsand contrast material The most serious complications of death,stroke, and myocardial infarction occur in approximately 0·1%,0·07%, and 0·06% of cases, respectively Other complications includeallergic reactions, arrhythmias, cardiac perforation, and vascularcomplications, which occur in 0·5–4% of cases Examples of vascularcomplications include hematoma formation, bleeding, thrombosis,embolism, pseudoaneurysm, and arteriovenous fistula

An additional consideration in patients who will undergoangiography during their procedure is the risk for developing renalinsufficiency from exposure to iodinated contrast material Patientswith pre-existing renal insufficiency, diabetes mellitus, recent (withinthe past 48 hours) contrast exposure, and female gender or advancedage are at increased risk for this complication In patients with

multiple myeloma, contrast exposure is associated with an especiallyhigh incidence of irreversible renal dysfunction.

Hemodynamic measurements

Usually reliable pressure measurements are obtained using a filled system in which the catheter is connected to a pressuretransducer with a short length of tubing The transducer converts thekinetic energy of the pressure signal to an electrical impulse, which isthen recorded on paper or digitized for archiving using optical ormagnetic storage media Pressures are reported in millimeters ofmercury

fluid-The accuracy of the pressures measured is dependent on the systemcomponents The ideal catheter (i.e one that provides the truestreflection of intracardiac pressures) is rigid and possesses a large lumenbecause these characteristics are consistent with the best frequencyresponse These properties must be balanced with those involvingpatient safety because maximizing these characteristics would result in

a catheter with increased risk for cardiac perforation The saline-filledconnection between catheter and transducer must be devoid of blood

or air, either of which can cause dampening of the pressure signal.Reliable pressure references are also required, and this is achieved bycalibrating the system to zero pressure at the level of the heart andagainst a fixed standard, usually a mercury sphygmomanometer.Right heart pressures

Evaluation of right heart pressures begins in the right atrium, wherecare is taken to direct the catheter tip toward the lateral wall of thechamber, away from the tricuspid annulus where a regurgitant jetcould result in a measuring artifact The normal pressure tracingconsists of an “a” wave and a “v” wave, which are analogous to thoseobserved in jugular venous pulsations (Figure 3.1) The “a” waverepresents the pressure increase resulting from atrial contraction atthe conclusion of diastole, and is followed by the X descent The “v”wave represents the pressure increase resulting from upwardmovement of the tricuspid annulus during ventricular systole (whichdecreases the effective size of the atrium) and the continued inflow ofblood into an atrium that is unable to drain in the presence of a closedtricuspid valve The rapid decrement in pressure that results fromopening of the valve is termed the Y descent (Table 3.2) Examples ofconditions that result in an elevated right atrial pressure includeconstrictive pericarditis, restrictive cardiomyopathy, right ventricularinfarction, and right sided congestive heart failure

Right ventricular pressure is measured next, after the catheter ispassed through the tricuspid valve Ventricular ectopy may beencountered with this maneuver because of catheter contact with theendocardial surface, and so care must be taken to find a location inthe mid-portion of the chamber so that an accurate pressure recordingcan be taken The operator should carefully observe the morphology

of the waveform because the “dip and plateau” of the diastolicpressure may be the first indication that the patient has constrictive/restrictive physiology Because of the proximity of the right bundle tothe ventricular septum, a transient right bundle branch block can beinduced in up to 5% of patients during catheter manipulations in theright ventricle This complication is well tolerated except in those with

a pre-existing left bundle branch block, in which case all threeconducting fascicles are jeopardized, resulting in complete heart block.The hemodynamic compromise that occurs in this circumstance can

be lessened by placing a temporary pacing catheter in the right

ventricle before right heart catheterization in patients with a leftbundle branch block Alternatively, use of a balloon-tipped catheterinstead of a rigid one may reduce, but does not eliminate, the risk ofcatheter-induced right bundle branch block.

Pulmonary artery pressure is next determined after the catheter ispassed through the pulmonic valve into the proximal pulmonaryarterial tree Because the right ventricular outflow tract is especiallythin, great care must be taken during this portion of thecatheterization procedure to prevent puncture of the right ventricle

If the pulmonary arterial systolic pressure is lower than the rightventricular systolic pressure, then a gradient is present between thetwo chambers This is consistent with a stenotic lesion, which may bevalvular, subvalvular, or supravalvular This finding should beconfirmed with a continuous pressure recording as the catheter ispulled back from the pulmonary artery to the right ventricle

The right heart pressure measurements are concluded with ameasurement of PCWP, which is obtained by advancing the catheteruntil it comes to rest in the distal pulmonary vasculature This can befacilitated by having the patient inspire while the catheter is pusheddistally, and then having the patient cough Adequate catheterposition should be confirmed by drawing an oxygen saturation that

is 95% or greater This establishes that the waveform recorded is not

Table 3.2 Normal values for cardiac catheterization

O2consumption index (ml/min per m 2 )

Cardiac index (l/min per m 2 )

Pulmonar y vascular (dyne·s/cm 5 )

Systemic vascular (dyne·s/cm 5 )

Left ventricular stroke volume index (ml/m 2 )

Left ventricular ejection fraction (%)

110–150 2·7–4·2 0–8 15–30/0–8 15–30/4–12 1–10 100–140/60–90 100–140/3–12 20–120 (0·25–1·5 Woods units)

770–1500 (9·6–18·7 Woods units)

50–90 15–30 35–75 50–80

contaminated by pulmonary arterial pressure, because inclusion ofpulmonary artery blood in the sample would decrease the measuredsaturation to a value below 95% The PCWP is an accurate reflection ofleft atrial pressure, as reflected retrograde through the pulmonaryvenous system.

There are several differences in the morphology of pulmonary arterialpressure and PCWP tracings First, the pulmonary arterial pressure (PA)has a single peak for each QRS complex of the electrocardiogram,whereas the PCWP, like the right atrial pressure tracing, inscribes an “a”and “v” wave for each QRS On those occasions where a large “v” wave

is present, or when the patient has no “a” wave (i.e atrial fibrillation),the pulmonary arterial and PCWP pressures may appear similar, butbecause of the delay in pressure transmission through the pulmonarybed the “v” wave peak occurs later in the cardiac cycle (usually in theregion of the T wave of the electrocardiogram) than the peak of thepulmonary arterial tracing (usually near the end of the QRS complex)

In addition, unlike the PA tracing, “v” waves do not possess a dicroticnotch on the downslope of the pressure waveform Finally, the mean ofthe PCWP is always less than the mean pulmonary arterial pressure.Left heart pressures

In those cases in which an accurate PCWP is not obtainable, leftatrial pressure can be measured directly by passing a catheter from theright atrium, through the interatrial septum, and into the left atrium.This technique, known as transseptal catheterization, requires the use

of a long metal Brockenbrough needle, which is introduced from theright femoral vein Once the needle has punctured the septum, acatheter is usually passed over the needle into the left atrium Thismethod increases the risk for chamber rupture because a sharp object

is deliberately positioned within the cardiac chambers, and so it is notroutinely utilized for pressure measurements Circumstances in whichthe transseptal approach is used include the following: inability toobtain a satisfactory PCWP tracing when this information is vital;mitral valvuloplasty, where balloon dilating equipment must beplaced antegrade across the mitral valve; and procedures in which leftventricular pressure measurements or angiography are critical and theleft ventricle cannot be entered retrograde through the aortic valve,such as severe aortic stenosis or the presence of a tilting disk valveprosthesis in the aortic position Passing a catheter through thesetypes of mechanical valves can result in catheter entrapment In suchcases, the left ventricle is entered by a passing a catheter from theright atrium through the left atrium to the left ventricle

In most situations, left ventricular pressure can be sampled bypassing a catheter across the aortic valve and maneuvering it to a

position where ventricular ectopy is not encountered Because ofdifferences in magnitude between left ventricular systolic anddiastolic pressures, waveforms are usually recorded on two differentscales Left ventricular end-diastolic pressure (LVEDP) is measured atthe time corresponding to the peak of the QRS complex, and is similar

in magnitude to the a wave peak of the PCWP tracing, which alsooccurs temporally at the conclusion of diastole The LVEDP isdependent on factors other than the volume state of the left ventricle,and does not reflect left ventricular pressure during the earlierportions of diastole Consequently, the PCWP is a more accuratereflection of the pressure experienced by the pulmonary vasculature.When left ventricular pressure sampling is completed, pressure ismeasured continuously as the catheter is withdrawn into theascending aorta in order to determine whether a gradient is presentbetween the left ventricle and aorta, a condition consistent with leftventricular outflow obstruction below the valve (as in hypertrophicobstructive cardiomyopathy) or at the level of the aortic valve (aorticstenosis)

Cardiac output

The determination of cardiac output is an important component ofhemodynamic measurements It is the amount of blood ejected by theheart in liters/min, and its value is used in the calculation of vascularresistances, valve areas, and intracardiac shunt magnitudes Because

of the relationship between metabolic demands and body size, it isalso reported as the quotient of cardiac output/body surface area,termed the cardiac index Normal values are listed in Table 3.2 Thetwo most popular methods for measuring cardiac output are the Fickand indicator dilution methods

The Fick principle states that the consumption or release of asubstance by an organ is equal to the product of the blood flowthrough the organ and the concentration difference of the substanceentering and exiting the organ For the purposes of determination ofcardiac output, the organ of interest is the lung and the consumedsubstance is oxygen Transposing the terms of the Fick equationresults in the following relationship

Cardiac output =O2consumption/(pulmonary venous O2concentration – pulmonary arterial O2concentration)The oxygen concentration is calculated as the product of theoxygen saturation (ml O2/dl), the hemoglobin (g/dl), and the oxygencarrying capacity of hemoglobin (1·39 ml O2/g) The result, inmilliliters/deciliter, is multiplied by 10 to convert the concentration