bài giảng NGOAI TÂM THU

QRS is slightly different but still narrow , indicating that conduction through the ventricle is relatively normal Atrial Escape Beats Ectopic Foci and Beats... Paroxysmal Supraventricul

NGOAI TÂM THU

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Automaticity: Alterations in impulse initiation

depolarization and vice versa

 Ischemia, infarction, hypokalemia, beta

agonists enhance phase 4 depolarization

Significance

 Atrial tachycardia, accelerated

idioventricular rhythms, ventricular

tachycardia

Afterdepolarizations and Triggered activity

Afterdepolarizations and

Triggered activity

EAD (Early AD)

• Due to increase in cytosolic Ca2+

• Causes - hypokalemia, hypomagnesemia,

hypoxia, acidosis, bradycardia, class IA and III antiarrhythmics, antihistaminics,

phenothiazines

• Significance - torsades de pointes

DAD (Delayed AD)

• Due to increased Ca2+

• Causes- catecholamines, quinidine, caffiene

• Significance - idioventricular rhythms, digitalis

toxicity

→ → →

Reentrant Mechanism

Reentrant arrhythmias

inexcitable obstacle

propagates through partially refractory

tissue with no anatomic obstacle- leading to circle re-entry( functional re entry)

Disorders of impulse formation

Disorders of impulse conduction

Conduction blocks

• Sino atrial blocks

Atrioventricular blocks

• First degree AV block

• Mobitz type I block

• Mobitz type II block

• Third degree AV block

Intraventricular blocks

• Hemiblocks

• LBBB

Increased/Abnormal Automaticity

Sinus tachycardia

Junctional tachycardia Ectopic atrial tachycardia

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normal ("sinus") beats

sinus node doesn't fire leading

to a period of asystole (sick

sinus syndrome) p-wave has it did not originate in the sinus node, different shape indicating

but somewhere in the atria.

QRS is slightly different but still narrow , indicating that conduction through the ventricle is relatively normal

Atrial Escape Beats

Ectopic Foci and Beats

Paroxysmal Supraventricular Tachycardia (PSVT)

• A single ectopic focus fires near the AV node, which then conducts normally to the ventricles (usually initiated by a PAC)

•The rhythm is always REGULAR

•Prolonged runs of PSVT may result in atrial fibrillation or atrial flutter

• May be terminated by carotid massage

• Treatment: carotid massage, adenosine, Ca ++ channel blockers, ablation

•Adenosine preferred in hypotension, previous IV B-blocker

Note REGULAR rhythm

Multifocal Atrial Tachycardia (MAT)

•Multiple ectopic foci fire in the atria, all of which are conducted normally to the

ventricles

•The rhythm is always IRREGULAR

• P-waves of different morphologies (shapes) may be seen

•Commonly seen in pulmonary disease, acute cardiorespiratory problems, and CHF

• Treatment:

• Ca++ channel blockers, beta blockers, but antiarrhythmic drugs are often ineffective

• potassium, magnesium (McCord et al, Chest 1998) ,

Ectopic Foci and Beats

there is no p wave , indicating that it did not originate anywhere in the atria, but since the QRS complex is still thin and normal looking, we can conclude that the beat originated somewhere near the AV junction.

Junctional

ventricle is relatively normal

Ectopic Foci and Beats

•a "retrograde” p-wave may sometimes be seen

on the right hand side of beats that originate in the ventricles, indicating that depolarization has

QRS is wide and much different looking than the normal beats This indicates that the beat originated somewhere in the ventricles

•They are frequent (> 30% of complexes) or are increasing in frequency

• The come close to or on top of a preceding T-wave ( R on T )

• Three or more PVC's in a row (run of V-tach )

• Any PVC in the setting of an acute MI

• PVC's come from different foci (" multifocal " or "multiformed")

These may result in ventricular tachycardia or fibrillation.

PVC's are Dangerous When:

sinus beats V-tach Unconverted V-tach to V-fib

“R on T phenomenon”

time

• hypoxic myocardium - chronic pulmonary disease, pulmonary embolus

• ischemic myocardium - acute MI, expanding MI, angina

• sympathetic stimulation - nervousness, exercise, CHF, hyperthyroidism

• drugs & electrolyte imbalances - antiarrhythmic drugs, hypokalemia, imbalances of calcium and magnesium

• bradycardia - a slow HR predisposes one to arrhythmias

• enlargement of the atria or ventricles producing stretch in pacemaker cells

Causes of Ectopic Foci and Beats

Rhythm ID: Algorithm

•P-Wave: rate and rhythm

•QRS: rate and rhythm -

shape

•P-R Interval: Is AV

conduction normal? P:QRS regular?

•T Wave and QT Interval

•Any unusual complexes?

•IS IT DANGEROUS?

Define “Normal”

•Regular Atrial and Ventricular

Rhythms: 1P : 1 QRS

•Rates: 60-100

•P Morphology: small, round,

regular and positive in Lead II

•QRS Morph: Similar size and

shape

•Positive T waves in Lead II

P-Wave: • 1.SA Node “fires”

• 2 Right and Left Atria Depolarize

AV Node

ABSENT PQRS Complex: Sinus

•Rare and asymptomatic

•Frequent and symptomatic

Is it normal sinus rhythm?

Normal Sinus Rhythm

Implies normal sequence of conduction, originating in the sinus node and

proceeding to the ventricles via the AV node and His-Purkinje system.

EKG Characteristics: Regular narrow-complex rhythm

Rate 60-100 bpm Each QRS complex is proceeded by a P wave

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Sinus Node Rhythms.

• Usually cyclical.

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Fast & Easy ECGs, 2E

Atrial Dysrhythmias

• Originate in the atrial tissue or in

the internodal pathways

• Are among the most common

Atrial Dysrhythmias

•Can diminish the strength of the atrial contraction and

affect ventricular filling time

• This can lead to decreased cardiac output and

ultimately decreased tissue perfusion

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Atrial Dysrhythmias

•Key characteristics include:

• P’ waves (if present) that differ in appearance

from normal sinus P waves

• Abnormal, shortened, or prolonged P’R intervals

• QRS complexes that appear narrow and normal

Premature Atrial Complexes (PACs)

Premature Atrial Complexes (PACs)

•Produce an irregularity in the

rhythm

• P’-P and R’-R intervals are shorter than the P-P and R-R intervals

of underlying rhythm

•Have P’ waves that are upright (in

lead II) preceding each QRS complex but have a different morphology

(appearance) than the P waves of

underlying rhythm

•Followed by a noncompensatory

pause

Noncompensatory Pause

• Is a pause where

there are less

than two full R-R

intervals between

the R wave of the

normal beat which

precedes the PAC

and the R wave of

the first normal

beat which follows

it

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Effect of PACs

•Isolated PACs seen in

patients with healthy hearts

are considered insignificant

Effect of PACs

•May predispose patient with heart

disease to more serious atrial

dysrhythmias:

–atrial tachycardia

–atrial flutter

–atrial fibrillation

•Can serve as an early indicator of an

electrolyte imbalance or congestive heart failure in patients

experiencing an acute myocardial

infarction

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Fast & Easy ECGs, 2E

Every 3 rd

beat is a PAC

Every 4 th

beat is a PAC

Aberrantly Conducted PAC

– For this reason they

can be confused with

PVCs

Treatment of PACs

•Generally do not require treatment

•PACs caused by the use of caffeine,

tobacco, or alcohol or by anxiety,

fatigue, or fever can be controlled

by eliminating the underlying cause

•Frequent PACs may be treated with

drugs that increase the atrial

refractory time

–This includes beta-adrenergic blockers and calcium channel

blockers

Section 2: Abnormal Rhythms Four Basic Categories:

•Irregular rhythms

•Escape rhythms

•Premature beats

•Tachyarrhythmias

1) Irregular Rhythms

•Sinus Arrhythmia

• Not a true arrhythmia, normal variant

• This variability in HR is good!

• Usually related to phases of breathing

• Increases with inspiration

• Inspiration stimulates the sympathetic NS to activate the SA node

• Decreases with expiration

• Expiration stimulates the parasympathetic NS to slow down the SA node

Sinus Arrythmia

1) Irregular 2) P wave before each QRS QRS after each P

3) P waves of same morphology 4)QRS narrow

Wandering Atrial Pacemaker

Pacemaker activity “wanders”

from the SA node to other

atrial foci

• Variable p waves shapes (at

least 3 different) and variable

PR intervals

• Variation in RR interval

• Irregular rhythm

• Rate remains normal

• Not tachycardic as atria

suppresses other foci, only one

fires at a time

• Narrow QRS complexes

What’s the

rhythm?

Wandering Atrial Pacemaker

Rate normal or slow 1) Irregular

2) P before QRS, QRS after p 3) Morphology differs (at

least 3 different p waves) 4) Narrow QRS

Multifocal Atrial Tachycardia

(MAT)

• Generally occurs in patients with

pulmonary disease, COPD, digoxin toxicity (similar to WAP)

• Atria lose ability to suppress

2) Escape Rhythms

•Escape-there is an automatic focus which is responding to

a pause in the normal

pacemaker activity

2) Escape Mechanisms

•Escape Beats: appear as one irregular beat

• Atrial escape beat

• Junctional escape beat

• Ventricular escape beat

•Escape Rhythms

• Atrial escape rhythm

• Junctional escape rhythm

• Ventricular escape rhythm

Intrinsic Pacemaker Rates

Sinus rate = 60-100 Atrial rate = 60-80

AV Junction rate = 40-60 Ventricular rate = 20-40

Atrial Escape

•Atria 60-80 BPM

•Occur when SA node doesn’t fire

•Atrial foci steps in to fire

•See p waves, but of different morphology from SA nodes p waves

Atrial escape

• Escape beat will be one irregular beat

• P before QRS, QRS after p, p morphology will look different than the SA node p waves

• Normal rate

• QRS normal

Junctional Escape

• AV Junction 40-60 bpm

• Occur when SA node and

atria fail OR when there is a proximal block in AV node

• P waves may occur if the

impulse travels backward to atria Produces an inverted p wave on EKG before, during,

or after QRS

Ventricular Escape

• Ventricle 20-40 BPM

• Occur when SA, atria, AVN fail

• Wide QRS

What’s that funny

What is the rhythm?

Ventricular Escape Rhythm with rate~25

Slow rate 25

• Regular

• No p waves

• QRS wide

The Basic Categories:

•Override the SA node

• Atrial premature beats

• Junctional premature beats

• Ventricular premature beats

What’s that beat?

PAC

Normal Rate

• One premature beat

• P before QRS, QRS after P wave3) P wave Morphology different 4) Narrow QRS

Premature Ventricular Beats (PVCs)

•Produce a giant (wide) QRS

complex

•May be coupled with normal QRS

complexes

•Bigemeny (every other beat is a PVC)

•Trigemeny (every third beat is a PVC)

•More than 6 PVCs/min is

pathological

•Run of >3 PVCs is VT (more later)

Normal Rate

• Two premature beats

• No p waves

• QRS wide

The Basic Categories:

Premature Atrial Contractions

•Deviation from NSR

• These ectopic beats originate in the atria (but

not in the SA node), therefore the contour of the

P wave, the PR interval, and the timing are

different than a normally generated pulse from the SA node

Premature Atrial Contractions

•Etiology: Excitation of an atrial cell forms an

impulse that is then

conducted normally

through the AV node and ventricles.

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Teaching Moment

•When an impulse originates anywhere in the atria (SA

node, atrial cells, AV node,

Bundle of His) and then is

conducted normally through the ventricles, the QRS will

be narrow (0.04 - 0.12 s).

•Deviation from NSR

• Ectopic beats originate in the ventricles resulting

in wide and bizarre QRS complexes

• When there are more than 1 premature beats and look alike, they are called “uniform” When they look different, they are called “multiform”

•Etiology: One or more

ventricular cells are

depolarizing and the

impulses are abnormally

conducting through the

ventricles.

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Teaching Moment

•When an impulse

originates in a ventricle, conduction through the ventricles will be

inefficient and the QRS will be wide and bizarre.

Ventricular Conduction

74

Normal

Signal moves rapidly

through the ventricles

Abnormal

Signal moves slowly through the ventricles

Premature Complexes

•P A C - premature Atrial complex

• P wave upright in front of QRS

Sinus Arrhythmia

• Alternate periods of slower and faster rates

• Rate increases with inspiration and decreases with expiration

• Common in children and young adults

• Accentuated by vagotonic procedures and abolished by

vagolytic procedures

• No treatment required

Atrial Premature Complexes

Rhythm- irregular with incomplete compensatory pause

QRS complex- usually normal unless ventricular aberration

Atrial Premature Complexes

PACs are of 3 types:

 Premature P wave with normal QRS

Ectopic focus with different morphology from

sinus P wave

 Premature P wave with no QRS

P waves occur very early

AV node in refractory period

 Premature P wave with aberrant

ventricular conduction

Impulse reaches the bundle branch when only one has fully recovered

Atrial Premature Complexes

• Increased incidence with age

• More common in patients with chronic

rheumatic valvular disease, coronary artery disease, CHF, hyperthyroidism

• Little clinical significance

• Frequent APCs may trigger more

serious supraventriculr arrhythmias

e.g atrial fibrillation, flutter, PSVT

• Treatment – rarely necessary

Junctional Rhythm

• AV node and sites above and below it act as pacemaker

• Heart rate- variable, 40 to 180 bpm

• Rhythm- regular

• P/QRS- 1:1

• QRS complex- usually normal

Junctional Premature Contraction.

restoration of sinus rhythm.

Junctional Escape Beat.

Junctional Rhythm (contd.)

Types

• High nodal rhythm- impulse reaches atrium

before ventricles, P precedes QRS, short PR interval

• Mid nodal rhythm- impulse reaches atrium

and ventricle at the same time, P lost in QRS

• Low nodal rhythm- impulse reaches

ventricles before atrium, P follows QRS

Common in patients under anaesthesia(20%) especially with halogenated anaesthetic

agents

Junctional Rhythm (contd.)

Treatment

• Usually reverts spontaneously, no

treatment required

• If associated with hypotension &

poor perfusion – t/t with atropine/ ephedrine/ isoproterenol

• Dual chamber electrical pacing

Ventricular Arrhythmias

EMS Professions Temple College

Analyze the Rhythm

Premature Ventricular Complexes (PVCs)

•Definitions

• Early depolarization of the ventricles

• Occur as a result of automaticity or reentry

• A PVC is a characteristic of an underlying ECG rhythm

• PVC is not the name of a dysrhythmia

Premature Ventricular Complexes

Premature Ventricular Complexes (PVCs)

•Characteristics

• Complex is earlier than expected

• Wide QRS (wide is not always ventricular)

• OFTEN has a compensatory pause

• Usually irregular

• Not preceded by a P wave

• T wave opposite deflection

• May or may not result in perfused beat

Premature Ventricular Complexes (PVCs)

•More Terms to Know

• Unifocal, Multifocal

• R on T Phenomenon

• Bigeminy, Trigeminy, Quadrigeminy, Couplet

Premature Ventricular Complexes (PVCs)

•PVCs are not always

dangerous

•Common for some people

•Consider treating PVCs if:

• >6/minute associated with:

• Severe Chest pain

• Hypotension, Decreased Perfusion

• Shortness of Breath

Premature Ventricular Complexes

Ventricular arrhythmias

conduct more slowly so

the QRS is wide (greater

Premature Ventricular Contractions (PVCs)

• Irritable focus causes ventricles to depolarize before the

SA node fires

• Premature beat that has a wide QRS

• QRS and T wave of a PVC usually point in opposite direction from one another

• “Bad PVCs” – more than 6/minute, coupled, multifocal,

and on or near the T wave of the previous sinus beat