Tài liệu Pacemaker implantation docx

The axillary venous approach also eliminates the long-term complications of lead friction at the subclavian muscle or ligament insertion site... The passive fixation lead approach does

Authors: Moses, H Weston; Mullin, James C.

Title: A Practical Guide to Cardiac Pacing, 6th Edition

Copyright ©2007 Lippincott Williams & Wilkins

> Table of Contents > 10 - Pacemaker Implantation

Regardless of the location of implantation, the operating room or the cardiac catheterization laboratory, similar personnel are required: a radiology technician, a scrub-technician/assistant,circulating personnel, and a nurse/nurse anesthetist/anesthesiologist, who is responsible for monitoring hemodynamics and the patient's level of consciousness

The presence of an anesthesiologist or a nurse anesthetist can be an advantage in the rare patient who needs better control of the airway during the implantation In the majority of patients, a team experienced with conscious sedation can do an excellent job in keeping patients comfortable without the need for anesthesia support

The circulating personnel must be competent in the use of a pacing system analyzer In many busy implanting operating rooms/cardiac catheterization laboratories, this person is an

experienced team member, who has the ability to test pacing lead impedance measurements, capture threshold measurements, and sensing measurements Sometimes, this person is a representative of the device company, and can perform an equally acceptable job The

physician must be able to supervise and interpret the data given to him or her by the

pacemaker representative or the staff person responsible for use of the pacing system

analyzer

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Venous Access

Accessing a venous entry site has become quite important in any device implantation

Historically, the cephalic vein cut-down approach has set a high standard for safety and term lead performance (Fig 10-1) Using this cephalic cut-down technique, the risk of

long-pneumothorax is nil and the risk of long-term lead failure due to crush injury through the subclavius muscle/ligament is also eliminated

A much less favorable approach to central venous entry would be the subclavian stick Using landmarks, the subclavian vein can be approached quickly, but the speed of access has to be weighed against the increasing complication rate, particularly with pneumothorax, vascular injury, and bleeding By performing this intrathoracic venous entry, using landmarks of the patient's anatomy, the lead can often be pinned down from the subclavius muscle or ligament and create a friction point leading to late lead failure

A third approach is the axillary vein approach (Fig 10-2) The nomenclature of the subclavianvein changes when the vein exits the thorax

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and passes over the first rib From the medial border of the first rib, seen on x-ray, the vein moves laterally in the extra thoracic portion of the chest The needle is placed into the axillaryvein a few centimeters more lateral than the traditional subclavian vein approach This

approach can be performed using only surface anatomy landmarks, including the visualization

of the lateral portion of the pectoralis minor muscle, the anatomy of the clavicle, and

acromion process of the shoulder A better visualization of the axillary vein can be performed

if a venogram is performed during the access approach By injecting approximately 25 cc of a low osmolar contrast dye into the IV in the patient's forearm, the anatomy of the axillary vein can be seen as the contrast crosses the first rib With the dye column in the axillary vein, the needle can be placed into this vein directly overlying the first rib Generally, the needle can bevisualized as it pushes down onto the surface of the first rib, directly overlying the venous column Then by withdrawing the needle slowly, blood return into the syringe is noted and a soft guidewire can be advanced into the axillary vein, and then manipulated through the venous system to the right heart chambers After performing this technique many times, most operators feel very comfortable using this same technique without seeing the dye column By placing the needle directly overlying the first rib, the operator can develop a “feel†for  for where the vein would be if a dye column was utilized Dye injections

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can then be used only in difficult access situations Using the dye injection approach does give some operators a higher comfort level in performing this accessed technique This technique is also very helpful in patients who have chronic leads in place and the patency of the vein needs to be assessed prior to attempting access.

Figure 10-1 Deltopectoral Groove.

The cephalic vein travels from the arm, through the deltopectoral groove, and joins the subclavian vein It is located easily in most patients

Figure 10-2 Veins in Relation to External Landmarks.

Axillary, subclavian, and internal jugular veins are demonstrated in relation to external landmarks

With improving ultrasound equipment, accessing the axillary vein has become quite routine (Fig 10-3) Companies provide small transducers to perform ultrasound-guided access By placing a sterile sleeve over the ultrasound probe, visualization of the axillary vein and axillary artery can easily be performed Color-flow Doppler adds little to the 2-D

visualization By applying gentle pressure over the vein, the vein will flatten quickly By applying a similar amount of pressure with the transducer over the axillary artery, no change

in the circular appearance of the artery is noted The needle can be visualized as it enters the vein and partially collapses the vein A guidewire is advanced through the needle and then by slowly withdrawing the needle,

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access can be achieved with an introducer sheath (Fig 10-4) This technique has

a rapid learning curve and allows a very lateral entry point into the axillary vein One advantage of the axillary vein approach over the cephalic vein approach is that multiple leads can easily be placed into the axillary vein With an

experienced implanter, pneumothorax can be virtually eliminated by using any

of these axillary vein entry approaches The axillary venous approach also

eliminates the long-term complications of lead friction at the subclavian muscle

or ligament insertion site.

Figure 10-3 Access to the Axillary Vein.

An ultrasound probe is placed within a sterile sleeve and gently introduced into the incision upon the pectoralis fascia, close to the deltopectoral groove No pressure is applied in A InB, light downward pressure is applied compressing the vein, but having no effect on the shape ofthe artery Using a platinum-coated micropuncture needle, the ultrasound images can show the needle advance into the vein safely

One slight disadvantage of axillary vein approach is back bleeding When the lead is smaller than the peel-away sheath diameter, particularly when it is a difference of more than two French sizes, back bleeding can be a challenge When venous pressure is elevated in a patient with congestive heart failure, this can be a particularly noticeable problem A purse string suture with absorbable suture usually eliminates this problem, even when multiple leads are utilized By making separate sticks for each lead introduced, this back bleeding problem is usually minimal When a single access site is used for multiple leads, back bleeding can be a more significant problem and the purse string suture technique is usually required

The ideal combination of a cephalic cut-down technique and the axillary vein technique allows the operator to have the best of both techniques available, particularly when multiple leads need to be placed The subclavian vein approach, despite its speed advantage, should be avoided

Lead Placement

After gaining access, fluoroscopic imaging is utilized to guide the lead to the desired site of pacing Several small studies have shown that site-specific pacing may be advantageous Site-specific pacing generally requires an active fixation lead The alternative approach is to use a passive fixation lead The passive fixation lead approach does limit the implanter in utilizing classic sites of lead implantation: the right atrial appendage for the atrial approach and the right ventricular apex for the ventricular approach

Active fixation leads and passive fixation leads (tined leads) are the two types available for the transvenous approach and both have their pros and cons The active leads typically have a helix, which penetrates the endocardium and “grasps†the cardiac muscle The helix can  for

be exposed or can be part of a mechanism which protrudes from inside the lead out, using a lead mechanism that can extend or retract the helix into the myocardium One of the major advantages of an active fixation lead is that the lead can be isodiametric This means that the lead would have the same diameter from the very tip of the lead all the way back through the body of the lead The reason this is important is that if the lead would ever need to be

extracted, the extraction process would be much easier than a lead that was not isodiametric

In the past, the active fixation lead had greater inflammation of the tip, leading to poorer acuteand chronic thresholds This potential disadvantage

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has been eliminated with the use of steroid eluding tips Chronic thresholds are

no longer a significant factor in the decision regarding active versus passive fixation.

Figure 10-4 Axillary Stick Technique with Peel-away Sheath.

Axillary stick technique with peel-away sheath A needle is placed into the axillary vein (see text for proper positioning), and a guidewire is advanced through the needle into the axillary vein and superior vena cava The needle is removed, and a dilator with a peel-away sheath around it is advanced through the skin into the vein The guidewire and dilator then are removed, leaving the peel-away sheath in place A lead or leads can be advanced through the sheath and placed in the proper position The advantage of the peel-away sheath is that it can

be removed, peeled in half, and discarded The pacemaker lead then is attached to the

generator subcutaneously and the skin is closed

An active fixation lead does make extraction easier, but a disadvantage of an active fixation lead is a higher perforation risk at the time of implantation Passive fixation leads can cause perforation, but this is less likely The “tines†that help fixate the lead to the right atrial  for appendage, endocardium, or the right ventricular endocardium can make extraction

challenging due to the ingrowth of fibrous material at this site in the lead

Mapping is not very useful with passive fixation leads when compared to active fixation leads Passive fixation leads placed into the right atrial appendage can allow far field R wave sensing This causes oversensing, which is a significant disadvantage and should be avoided ifpossible Many operators feel that using active fixation leads can allow a patient to be

mobilized earlier than when passive leads are used This has not been well studied

Tined or passive leads are typically anatomy dependent Sometimes, placing the tined leads across the tricuspid valve can be challenging due to the leads “grasping†parts of the  for tricuspid valvular structure with the tined tips Some tined leads have very high impedance measurements, a long-term advantage of which is battery longevity (see Chapter 2)

In summary, both tined leads (passive fixation) and active fixation leads have advantages and disadvantages The active fixation is more commonly used

Site-specific pacing enthusiasts can demonstrate that capturing specific areas of the right ventricle or right atrium can allow more rapid activation of the atria or ventricles This can be particularly demonstrated if the His bundle is captured, utilizing site-specific pacing in the high right ventricular septum This particular advantage of active fixation leads may be shown

to have specific clinical advantages in the future

Pacing System Analyzer

Satisfactory lead performance can be assessed by using a pacing system analyzer The

minimum voltage necessary to capture the right ventricle is usually

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less than 1 V a preferably less than 0.5 V This voltage capture threshold is typically assessed utilizing a pulse width set arbitrarily at 0.5 msec The pacing impedance measurement in ohms should be calculated with the pacing system analyzer A stable impedance generally implies a good site of fixation with the distal tip of the lead When the impedance varies significantly, this may imply “micro-dislodgement.†The patient's intrinsically generated  for QRS pattern is also measured This measurement of sensing allows the pacemaker to inhibit voltage output when voltage output is not needed The amplitude of the signal should be of sufficient size Utilizing a 5 mV R wave when assessing ventricular sensing is usually the minimum required R wave When R waves are smaller than 5 mV, oversensing T waves and undersensing R waves can become a problem

Sensing and capture thresholds in the atrium are different The atrial capture threshold should

be less than 1.5 V at 0.5 msec Some active-fixation atrial leads will show a transiently higher threshold of 2 V at 0.5 msec due to acute injury This usually drops in 10 to 30 minutes if followed closely without moving the lead Preferably, when the capture threshold is less than

1 V long-term lead performance is generally acceptable The sensed P wave should be greater than 1.5 mV and should not include oversensing of a far field R wave

When testing the atrial lead, the method used to document atrial capture can be variable Using the surface electrocardiogram recording equipment in the laboratory, a P wave can be visualized after the pacemaker spike With bipolar pacemaker leads, the spike can be very small and difficult to see The presence of a QRS complex occurring regularly after each atrialspike can be used to assess atrial capture This technique is not useful in a patient with

variable conduction across the AV node or in patients who have atrial ventricular heart block Using fluoroscopy to see atrial movement during capture is an unreliable way to document capture

The peel-away sheath used to implant both atrial and ventricular pacemaker leads is generally sized to allow freedom of movement of the lead within the sheath A sheath that also includes

a hemostatic valve at the end can help prevent inadvertent air embolism or back bleeding during the implantation procedure Patients with relatively low venous pressure or patients with sleep apnea, who suddenly inspire deeply, can have significant amounts of air inspired through peel-away sheaths where the hemostatic valve is not in place If a hemostatic valve is not in place in a peel-away sheath, the lead should be placed quickly into the peel-away sheath immediately after entering the vein

After a guidewire is placed into the desired venous structure and fluoroscopically manipulated

to the right heart, the peel-away sheath is advanced over a straight dilator over the guidewire and the dilator and guidewire are quickly removed

After the lead has been placed in the right ventricle or right atrium, experience will dictate how much extra lead should be placed into the venous

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system to allow “slack†so that the lead will not dislodge when the patient stands or takes for

a deep breath Too much straightening of the lead when someone inspires would indicate not enough lead slack On the other hand, too much lead slack can lead to problems with prolapse

of the lead into the right ventricle or inferior vena cava

Once the lead is in place and sensing and capture threshold and pacing impedance

measurements are found to be acceptable, the lead needs to be secured to the pectoralis fascia

A nonabsorbable suture is attached to the pectoralis fascia and a loop from the suture is then placed over the lead collar, close to the entry site Care must be taken not to apply too much tension over the lead collar as this can cause chronic lead injury due to disruption of

insulation or to the conductor itself Suture sleeves help prevent problems with too much tension Alternatively, too little pressure over the lead collar can let the lead slip and cause early lead dislodgement

Cardiac Resynchronization Lateral Wall Lead Placement

Left ventricular epicardial pacing can be achieved through placement of a lead into the

coronary sinus, and then placing the lead out into a lateral vein off of the coronary sinus, onto the surface of the left ventricular epicardium This approach is utilized in patients who have significant intraventricular conduction block and may benefit clinically with cardiac

resynchronization Placing the left ventricular epicardial lead in this way obviates the need for

a surgical approach in placement of a lead directly onto the left ventricular epicardium Newertechniques and experience have shown that the overwhelming majority of patients can have leads placed transvenously onto the left ventricular epicardium

Placement of a left ventricular epicardial lead in this way requires three steps The first step is

to access the coronary sinus with a coronary sinus guide This access can be achieved by using the right anterior oblique view of the AV annulus By placing the coronary sinus sheath past the tricuspid valve, and then withdrawing it to the right atrium while providing

counterclockwise torque, the coronary sinus can generally be entered In patients with severe cardiomyopathy, particularly when they have longstanding atrial fibrillation, this technique is

not as helpful and may require using different types of internal catheters and guidewires to access the coronary sinus.

Once the coronary sinus is engaged with the coronary sinus guide, it is highly recommended that venography be performed Using a balloon occlusive angiographic catheter, the coronary sinus is visualized, using retrograde injection of a 50/50 mixture of a low osmolar iodine contrast medium and saline It is helpful to inflate the balloon to obstruct coronary sinus flow

at the same time fluoroscopy is performed Digital recording of the venography in the RAO view and LAO view allows visualization of the lateral branches The ideal location for

epicardial pacing is generally in the lateral left ventricular epicardium When the left ventricle

is viewed in the LAO view, the 2 o'clock to 4 o'clock ventricular epicardial area should be the target for biventricular pacing

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The second step is to analyze the lateral veins for the best placement to provide long-term lead stability and excellent pacing of the lateral left ventricular epicardium The third step is, lead placement techniques that use lateral vein introducers for direct lead delivery are being developed In addition, some coronary sinus guides have very flexible tips which allow subselected entry into the desired lateral vein Having experience and knowledge of several techniques can aid in more challenging cases

Once the lead is in an ideal location, the lead is tested in a similar manner to right atrial and right ventricular leads Sensing measurements, capture threshold measurements, and lead impedance measurements are made in a similar manner when compared to right atrial and right ventricular leads One additional parameter that has to be assessed is diaphragmatic stimulation When diaphragmatic stimulation is seen, the pacing site is generally found to be unacceptable Many times, when diaphragmatic stimulation is seen only at high pacing outputs in the supine position, diaphragmatic stimulation becomes an issue when the patients return to their hospital room and start to ambulate and change their position Diaphragmatic stimulation occurs because of the phrenic nerve which passes along the left ventricular

epicardium and may be stimulated or when the diaphragm is close to the left ventricular epicardial pacing site

After achieving acceptable pacing capture thresholds, sensing measurements, pacing lead impedance measurements, and no evidence of diaphragmatic stimulation, the lead has to showexcellent stability when removing the coronary sinus guide Two types of guides are

available, a peel-away guide similar to a peel-away sheath and a coronary sinus guide, which requires a cutter to remove the guide from the lead Removing either type of coronary sinus guide requires a careful assessment of fluoroscopy to show lead position during removal of the guide Lead stability must be ensured when removing the guide Placing a preformed stylet into the lead, particularly when the stylet can make it all the way to the end of the lead, helps with lead stability when removing the guide Slight repositioning of the lead during sheath removal may be necessary, particularly if fluoroscopy shows too much slack or too much straightening of the lead during guide removal

Once the guide is removed and the lead shows good stability and performance, the lead is secured to the lead collar in a manner similar to that described for right ventricular and right atrial leads After all the leads have been placed and leads have been secured to the pectoral muscle, the pocket is generally irrigated with an antibiotic-containing solution

Generator Placement

The pacemaker programmer is brought onto the field after leads have been placed The leads are secured to the header of the pacemaker pulse generator in their selected slots (Fig 10-5) When the lead has been advanced far enough, the lead pin can be seen to protrude beyond the set screw point The

set screws are closed using a special “torque wrench.†This prevents overtightening of  for the set screw pin, preventing damage The attachment of the electrode to the generator is an important step in pacemaker implantation Careful attention to detail can prevent

complications since this connection is the most common source of device

malfunction The tight fit of the lead into the header of the pacemaker pulse generator avoids fluid intrusion into the connection Improper connection of the electrode to the pulse generator, or problems occurring at the connection site, can lead to a variety of pacemaker malfunctions that are generally noticed prior

to the patient leaving the laboratory or after the patient goes to the recovery room.

Figure 10-5 Connection of the Lead to the Generator

This demonstrates the connection of the lead to the generator The upper clear area is termed the header The set screw is somewhat difficult to demonstrate It is actually within the header

as shown in the location indicated by the arrow It is covered by an insulating plastic cover Specially designed torque wrenches can allow the set screw to be tightened onto the lead, without disrupting the insulating material, thus leaving the device sealed from fluids This is acritically important part of implantation and all institutions have anecdotal reports of an improperly set screw The lead may not have been pushed in far enough into the header or the insulation over the set screw can become exposed, leading to a short circuit The connection

of the lead to the header with appropriate stabilization with the set screw and avoidance of insulation problems are the areas of implantation that lead to the most common pacemaker malfunctions The feed-through, which connects the exposed metal portion of the lead to the generator, is also a potential engineering problem

Postoperative Care

Intravenous antibiotics are generally given prior to the device implantation The pre-operative antibiotic is generally given between 30 and 60 minutes prior to the surgical procedure Generally antibiotics are given for the first 24 hours of the procedure to lower the risk of staphylococcus or streptococcus infections Constant monitoring of the heart rhythm is

desirable for the first 24 hours following the device implantation to detect any failure to capture the heart or

Figure 10-6 shows typical positioning of an atrial J lead in the right atrial appendage and a right ventricular lead in the right ventricular apex.

Complications

Surgical complications include hemorrhage at the device pocket and device pocket infection The risk of infection in new implants is approximately 0.5% The risk goes up slightly with lead revision in patients who have chronic scar tissue in the pocket

Device implantations in an age of aggressive antiplatelet therapy can lead to a higher risk of hematoma formation This is particularly true with clopidogrel The combination of both clopidogrel and aspirin can lead to significant platelet dysfunction and cause late hematoma formation

Acute lead dislodgement rates in pacemaker studies are approximately 4%, particularly with atrial leads Increasing ventricular ectopy can be seen after lead placement, but this is

typically a transient phenomenon and generally resolves within a few hours

Despite infection of the device pocket being uncommon, generally device pocket infection implies infection of the entire pacing system and requires device extraction and lead removal Lead extraction is generally straightforward if the lead has just recently been placed and has not had time to become fibrotic If a chronic, long-term lead is in place, then extraction becomes much more problematic Lead extraction techniques have evolved over the past two decades Techniques currently include laser extraction systems, which allow cutting of chronic scar tissue from the surface of the lead to aid in lead extraction Lead extraction techniques have a certain morbidity and mortality associated with this needed procedure Experience in extraction is critical to achieve the lowest morbidity and mortality Because extraction is so operator dependent, high-volume labs tend to have the lowest morbidity and mortality

Generator Change

Battery depletion of a pacemaker pulse generator or other problems with the device may require that the pacemaker pulse generator be removed The most frequent indication for removal of the device is battery depletion Transtelephonic follow-up can detect a drop in magnet rate, diagnosing the elective replacement indicator of the device When this occurs transtelephonically, typically the pacemaker system is interrogated to confirm that the patient has met the elective replacement indicator

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