Tài liệu Pacemaker implantation docx

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 10 Pacemaker Implantation Permanent Pacemaker Implantation Location of Implantation Permanent pacemaker implantation can be done in the cardiac catheterization laboratory or in the operating room Both locations have unique advantages and disadvantages The operating room often has better lighting and thus allows better visualization of the device pocket, but fluoroscopy can be less optimal in the operating room, which generally utilizes a C-arm radiology device Sterility was once thought to be more advantageous than the operating room setting Data support that infection rates tend to be extremely low in both settings Scrub technicians and assistants in the operating room are often equally matched by personnel in busy cardiac catheterization laboratories 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 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 P.134 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 longterm lead performance (Fig 10-1) Using this cephalic cut-down technique, the risk of 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 subclavian vein changes when the vein exits the thorax P.135 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 axillary vein 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 be visualized 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 where the vein would be if a dye column was utilized Dye injections P.136 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, P.137 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 of the 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 Sitespecific 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 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 acute and chronic thresholds This potential disadvantage P.138 P.139 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 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 if possible 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 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 P.140 less than 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 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 mV R wave when assessing ventricular sensing is usually the minimum required R wave When R waves are smaller than 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 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 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 atrial spike 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 P.141 system to allow “slack” so that the lead will not dislodge when the patient stands or takes 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 Newer techniques 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 o'clock to o'clock ventricular epicardial area should be the target for biventricular pacing P.142 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 show excellent 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 P.143 set screws are closed using a special “torque wrench.” This prevents overtightening of 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 a critically 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 P.144 failure of the pacemaker to sense intrinsic heartbeats A postoperative chest x-ray documents positioning of the pacing lead and can be utilized as a baseline test in the future if lead problems occur Generally, a PA and lateral chest x-ray are obtained to confirm lead position and to exclude the possibility of a complication such as pneumothorax or lead dislodgement 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 P.145 Figure 10-6 Position of Atrial and Ventricular leads on the Chest Radiograph Position of atrial and ventricular leads on the chest radiograph The atrial J lead is positioned in the right atrial appendage and travels anteriorly and slightly medially The ventricular lead is in the right ventricular apex A ventricular lead inadvertently placed in the coronary sinus rather than the right ventricular apex can appear to be in good position on the posterior–anterior view on a chest radiograph or fluoroscopy, but on the lateral view would be posterior rather than anterior P.146 When battery depletion occurs, it is important to assess whether the patient's underlying pacing mode is still appropriate When the pacemaker pulse generator is removed, the patient's pacemaker system can be upgraded to a more appropriate pacing mode or even upgraded to a defibrillator system if indicated In addition, the pacing system can be “downgraded” if the patient has developed a permanent form of atrial fibrillation and atrial pacing is no longer required The patient's mode can be switched to a VVI or VVIR mode if chronic atrial fibrillation has occurred since the original implantation Capping the unneeded lead is generally performed at the time of the procedure A small cap made of silicone is placed over the exposed bare metal of the lead and secured with nonabsorbable suture Some operators prefer removing the leads, particularly when multiple leads may be required in the future, such as in a patient who may eventually require an ICD and cardiac resynchronization therapy The younger the patient, the more potential benefit to removing the lead Also, an unused lead in the heart is not necessarily totally benign In theory, an MRI or electrocautery device could lead to an electrical circuit occurring within an unused, capped lead that could stimulate ventricular tachycardia or ventricular fibrillation Any potential benefit of removing unused leads must be weighed against risks, which are not negligible Mortality of lead extraction in some series approaches 1% With current international standards in the development of pins, leads, and connectors, compatibility is not a significant problem between the old pacing lead system and the new pacemaker pulse generator Still, these data should be analyzed in patients who are long-lived and may have undergone several device extraction and removal procedures due to battery depletion It is of note that a new International Standard lead with a quadripolar connector is being evaluated and should be available in the future Analyzing lead performance at the time of pacemaker pulse generator replacement is also important A potential lead problem may lead to early battery depletion One example would be a lead insulation fault that has caused a very low pacing impedance measurement and high energy drain from the battery If a lead problem is causing early battery depletion, a new lead should be placed at the time of device extraction and replacement surgery The chronically utilized lead should be evaluated at the time of pacemaker pulse generator extraction and replacement surgery to make sure the manufacturer has not recalled the leads due to higher than expected incidence of lead problems If the patient is showing a high capture threshold at the time of pacemaker pulse generator and replacement surgery, consideration should be given to placing a new lead to prevent recurrent early battery depletion of the pacemaker pulse generator This early depletion would be due to the need for chronic high voltage necessary to capture the heart, not due to rapid drain of the battery in the setting of low impedance despite a good threshold Sensing parameters should also be evaluated at the time of device extraction and replacement surgery It is easier to program around sensing challenges with P.147 the current telemetry available on modern pacemaker pulse generators However, if sensing is so poor that programming cannot solve the sensing issue, a new lead should be placed Extracting the lead can be done, particularly if the lead has not been implanted long term or if the operator has significant experience in removing chronic leads Those operators who have significant experience with extraction techniques often set an arbitrary number of four leads to be the maximum number of leads they will accept in patients with chronic device therapy The risks versus benefits of lead extraction have to be considered, particularly with mortality in some series approaching 1% with lead extraction Capping the lead prevents extraneous electric currents from entering the unshielded wire The disadvantage of capping the lead is that it does increase bulk in the pulse generator pocket The lead can be cut short to eliminate exposed wire Although this does not remove the wire from the venous system in the heart, it does reduce bulk in the pacemaker generator pocket Insulation can be brought over the exposed wire and sealed with medical silicone adhesive This approach is usually well tolerated but can be problematic if the lead needs to be extracted in the future due to the lack of lead available for placing a sheath over the lead The pacemaker pulse generator pocket should be evaluated at the replacement operation Ideally, the incision should be made superior to the pacemaker pulse generator pocket to lower the risk of infection or erosion By placing the device pocket below the incision line, the risk of infection may be smaller When the incision is made directly over the device pocket, particularly in thinner patients, the risk of late infection may be higher When the pulse generator has migrated to an inferior or lateral site, the pacemaker pulse generator can be secured to the pectoralis muscle by using the purposefully placed suture hole in the device header Generally, this securing of the device to the pectoralis muscle is not necessary, particularly if the device pocket has matured at the time of device extraction and replacement surgery Permanent Transthoracic Pacing If the need for permanent pacing is identified when cardiac surgery is performed, direct attachment of the pacing leads to the heart's myocardium is a straightforward matter The appropriate electrode may be sutured to the heart; more commonly, the screw-in lead (refer to Fig 2-6 in Chapter 2) is attached to the bare area of the right ventricle, an area on the diaphragmatic surface of the ventricle that is invariably free of the fat that otherwise covers most of the chamber Occasionally, the thresholds from this area are not satisfactory, and placement of electrodes in other locations, usually on the left ventricle, is accomplished Pacing thresholds are determined in the same manner as for transvenous pacing Occasionally, permanent pacing wires, attached at the time of open heart surgery, are left above the rectus fascia, P.148 unattached to a pulse generator unit These wires can be located later under local anesthesia, and permanent pacing can be initiated simply by connecting them to a pulse generator unit Myocardial lead placement is always the best option when satisfactory placement of a transvenous lead is not possible because of certain congenital malformations, the presence of a mechanical prosthetic tricuspid valve, or lack of suitable venous access; nor is it the best option in growing children Two approaches for myocardial lead insertion generally are used when the primary objective is to establish myocardial pacing By far the most common approach used is transxiphoid Under a local or light general anesthesia, the xiphoid process is exposed by a short, midline, lower sternal incision The excision of the xiphoid process facilitates exposure of the pericardial surface that is opened, allowing the leads to be attached directly to the bare area of the right ventricle The pacemaker then is placed in a pocket developed in the left upper abdominal quadrant above the rectus fascia Occasionally, an anterior left thoracotomy incision, exposing the left ventricle between the fifth and sixth interspace, is indicated Electrodes are then attached to the left ventricular myocardium and tunneled to the abdominal wall, where they can be attached to a pulse generator (Fig 10-7) Figure 10-7 The Transxiphoid Approach The transxiphoid approach is used to place epicardial pacemaker leads The xiphoid process itself is removed, exposing the bare area of the right ventricle The epicardial screw-in leads can be placed in this area, and the generator itself is placed subcutaneously in the abdomen P.149 Temporary Pacemaker Placement Emergency Transcutaneous Pacing True emergency pacing required for asystole generally requires rapid use of transcutaneous pacing The traditional approach of transvenous pacing generally requires fluoroscopy and often transport of the patient to a fluoroscopy suite, with significant delay The transthoracic approach of placing a needle directly into the heart on an emergency basis carries considerable risk and is often ineffective Therefore, transcutaneous pacing has become commonly used in emergencies This approach, originally developed by Dr P.M Zoll, did not become widely popular initially because of considerable pain associated with the transcutaneous pacemaker The development of large pads that distribute the electric current over a wide surface area and the use of a wide pulse width have reduced the pain of cutaneous nerve and skeletal muscle stimulation and revived interest in this approach (Fig 10-8 and 109) As with other forms of resuscitation, this is not a particularly effective mode of therapy in a patient who has undergone cardiopulmonary resuscitation for a prolonged period and whose asystole is the result of advanced myocardial damage The typical transcutaneous pacing device generates a current that can be increased from approximately 40 mA up to 200 mA The average-sized adult usually can be paced with a current of 40 to 70 mA (a transvenous pacemaker P.150 will usually capture the heart at less than or mA) The higher levels of current are often painful, even with the broad pads disbursing the charge The pulse width is approximately 20 to 30 msec long, compared with a permanent pacemaker with a pulse width of 0.5 msec Generally, the pads are placed on the front and back of the chest so that the current travels across the thorax to stimulate the myocardium (Fig.10-10) Transcutaneous pacing devices are now often integrated with the defibrillator system for use in cardiac arrest Figure 10-8 Transcutaneous Temporary Pacing Current is passed through the thorax of a patient attached to a transcutaneous pacemaker Figure 10-9 Transcutaneous Pacemaker Generator The transcutaneous pacemaker generator is attached to a cable with two pads that are attached to the patient to complete the circuit, with current transmitted across the patient's thorax In this diagram, the output can be adjusted to the minimum amount of current required to effect capture, thereby reducing patient discomfort The pacing rate can also be adjusted The transcutaneous pacemaker generates much current, which creates problems with performing electrocardiography or monitoring The monitor strip on the device itself does not measure the actual pacemaker spike, but rather causes a deflection on the ECG paper during the pacemaker spike, thus avoiding excessive deflection of the ECG stylus This can create a misleading situation Even if the pads are not attached to the patient, deflection will occur, giving the appearance that a spike is being generated on the patient It is often difficult to judge from the ECG or rhythm strip whether the heart is actually being captured The patient's pulse can be palpated during the use of the transcutaneous pacemaker, which does not result in any shock if the femoral or carotid pulse is well away from the current between the two electrodes P.151 Putting the hand between the electrodes can result in a shock Palpating the pulse is an effective way of determining whether capture is occurring Figure 10-10 Tracing with an Arterial Line Paced With a Transcutaneous Pacemaker A tracing from a patient with an arterial line, who is being paced with a transcutaneous pacemaker The patient presented with dramatic, severe asystole and responded to transcutaneous pacemaking emergently The patient's blood pressure was about 85/40 and was stabilized with the transcutaneous pacemaker Note the size of the transcutaneous pacemaker spikes, which were greater than 11 cm in height with routine standardization The QRS complex is not easily noted, but to pacing is documented with the arterial line If the massive transcutaneous pacing spike were shrunk down for a routine bedside monitor, the QRS complex would be essentially invisible and monitoring would be difficult The value of arterial monitoring is obvious We encountered a situation in which the transcutaneous pacemaker was believed not to be working because of the virtually invisible QRS complex after the massive spike When the patient is being monitored on a standard ECG monitoring system in an intensive care unit, the gain is generally turned to the lowest possible level because of the large pacemaker spike This can create confusion when the pacemaker is turned off to assess underlying rhythm The patient's baseline may appear to be a straight line or have minor changes resembling P waves that may be QRS complexes Palpating the patient's pulse can help clarify this, as can turning up the gain on the monitor for a more visible QRS signal Also an arterial line or pulse oximeter can document capture Potential problems with transcutaneous pacing include poor capture if the patient is extremely large or has significant transthoracic resistance to electric stimulation Ventricular capture may not be possible with external patches at a pacing amplitude that is comfortable to the patient At the same time, some patients not tolerate even the minimal requirements for pacing thresholds and have requested removal of this type of pacing device P.152 Other considerations for an external pacing device include those situations in which a transvenous pacemaker is absolutely or relatively contraindicated such as tricuspid valve mechanical prosthesis, existing endocarditis or infected endocardial pacemaker lead, or sepsis Our practice has been to place a transvenous pacemaker soon after the transcutaneous pacemaker has stabilized the patient because of potential problems with prolonged transcutaneous pacing Urgent Temporary Pacing When the patient is hemodynamically stable, or if temporary pacemaker placement is urgent but not emergently required, the patient can be brought to the cardiac catheterization laboratory for placement of a temporary pacemaker lead via the femoral venous approach Alternative pacing approaches can utilize the subclavian venous approach or the internal jugular venous approach The pacemaker wire is fluoroscopically manipulated through the P.153 venous system after placement of a sheath The lead is specifically advanced across the tricuspid valve and to the right ventricular apex Capture thresholds, sensing measurements, and other parameters can be identified by using the temporary pacemaker pulse generator Figure 10-11 Location of the Femoral Vein The femoral vein usually can be entered easily just medial to the femoral artery pulse in the femoral crease Although the traditional anterior posterior (AP) projection can be used, the right anterior oblique (RAO) is a safer approach since the pacemaker tip movement toward the right ventricular apex can now be better appreciated Advancing the tip in the AP projection does not identify the apex as well and perforation is a greater risk The temporary device is set with three variables in mind: rate, pulse output, and sensitivity If AV block or sinus rest is intermittent, it is often best to set the rate to a value below the spontaneous ventricular rate, to preserve normal AV synchrony In some situations, however, pacing the heart at a faster rate than baseline in order to assist the maintenance of an adequate blood pressure may be desirable The capture threshold should always be recorded at the time of catheter placement because this value can be compared with later determinations in the event of suspected dislodgement Capture threshold is determined by pacing at a rate faster than the spontaneous ventricular rate and gradually turning the output down from or mA to the value at which noncapture occurs Generally the output is then turned back up to at least two times this value Sensitivity setting is usually left in the demand setting and if oversensing occurs it can gradually be made less sensitive The femoral vein is usually the approach chosen in the cardiac catheterization laboratory (Fig 10-11) The femoral vein has a constant relationship with the femoral artery in the inguinal canal It is medial to the femoral artery pulsation and generally accessed a finger's breadth below the inguinal ligament Rarely, the basilic vein is used for access (Fig 10-12) The internal jugular vein is also sometimes used Insertion of temporary pacemakers through the internal jugular vein should be performed only by operators experienced in this technique It does have the potential advantage of greater mobility for a patient requiring temporary pacing (refer to Fig 10-2) Leads available for temporary pacing include the standard bipolar temporary transvenous lead, which can be manipulated easily across the tricuspid valve and into the right ventricle A balloon-tipped electrode does allow fairly easy passage across the tricuspid valve, aided by blood flow The balloon is deflated once it crosses the tricuspid valve, and then placed into the endocardium This lead tends to be more flimsy and less maneuverable with torque The risk of perforation may be lower A third approach is to deliver an active fixation temporary pacemaker lead via a catheter-delivered technique This very small lead has the advantage of being more stable than typical temporary leads and may be an advantage when leads have to be placed long term This small French system has an active coil in the end which can be rotated into the ventricular or atrial endocardium, as needed This technique would be helpful in a patient who needs temporary pacing for several days rather than just for a few hours The technique of this lead delivery through a catheter system is important P.154 to prevent cardiac perforation The catheter is generally positioned over the site of desired pacing and the French lead is then advanced into the myocardium The lead wire is then rotated in a clockwise manner to guide the helix into the endocardium The catheter is then generally carefully pulled back from the lead and either removed or placed into the inferior vena cava if a femoral approach was utilized This delivery catheter can be completely pulled back provided fluoroscopy is adequate to see this very small lead and make sure that adequate lead slack is available to prevent late dislodgement This active fixation lead is a bipolar lead even though the leads are very small When the lead needs to be extracted, it is rotated counterclockwise and gently retracted until the lead becomes free of the endocardium The lead is then completely removed Figure 10-12 Arm Veins The basilic vein provides the most direct route into the subclavian vein from the arm Temporary Pacing After Cardiac Surgery Often after cardiac surgery, temporary pacing wires are fixed directly to the epicardium or buried into the myocardium or both These wires generally exit through the skin of the upper abdomen and are insulated in containers when P.155 not used but are readily available if perioperative pacing becomes desirable Three patterns of wire placement are common The simplest is a single myocardial wire (unipolar lead) that must be used with a ground wire, using a small-gauge wire stitch or metal needle in the adjacent subcutaneous tissue Alternatively, two myocardial leads, usually attached to the anterior right ventricle, may be used This allows bipolar pacing Either wire can be used as the anode (+) or cathode (-); if one wire fails, the system can be converted to a unipolar lead system Finally, two pairs of temporary pacing wires can be used for atrioventricular sequential pacing In this system, a bipolar atrial and bipolar ventricular pair of wires is placed so that maximum cardiac output can be achieved by use with the atrioventricular sequential temporary pulse generator Recording from an atrial lead, when available, can be quite helpful in the diagnosis of tachycardias By attaching an atrial lead to the V lead terminal of a standard electrocardiograph, the large atrial waves can be seen easily and can be used to distinguish among various types of supraventricular arrhythmias These temporary leads are removed simply by pulling them out Hemorrhage is a rare problem References Antonelli D, Rosenfeld T, Freedbert NA, et al Insulation lead failure: is it a matter of insulation coating, venous approach or both? PACE 1998;21:418-421 Astridge PS, Kaye GC, Whitworth S, et al The response of implanted dual chamber pacemakers to 50 Hz extravenous electrical interferences Pacing Clin Electrophysiol 1993;16:1966 Camunas J, Mehta D, Ip J, et al Total pectoral implantation: a new technique for implantation of transvenous defibrillator lead systems and implantable cardioverter defibrillator (Part I) Pacing Clin Electrophysiol 1993;16:1380 Da Costa A, Kirkorian G, Cucherat M, et al Antibiotic prophylaxis for permanent pacemaker implantation Circulation 1998;97:1796-1801 Da Costa A, Lelievre H, Kirkorian G Role of the preaxillary flora in pacemaker infections Circulation 1998;97:1791-1795 Davidson NC, Mond HG Ventricular pacing in the presence of tricuspid valve disease PACE 2002;25:129-131 Epstein M, Walsh E, Saul J, et al Long-term performance of bipolar epicardial atrial pacing using an active fixation bipolar endocardial lead (Part II) Pacing Clin Electrophysiol 1998;21:1098 Faust M, Fraser G, Schurig L, et al Educational guidelines for the clinically associated professional in cardiac pacing and electrophysiology (Part I) Pacing Clin Electrophysiol 1990;13:1448 Frumin H, Goodman GR, Pleatman M ICD implantation via thoracoscopy without the need for sternotomy or thoracotomy Pacing Clin Electrophysiol 1993;16:257 Fyke FE III Infraclavicular lead failure: tarnish on a golden route (Part I) Pacing Clin Electrophysiol 1993;16:373 Gallick DM, Ben-Zur UM, Gross JN, et al Lead fracture in cephalic versus subclavian approach with transvenous implantable cardioverter defibrillator systems Pacing Clin Electrophysiol 1996;19:1089-1094 P.156 Gold M Optimization of ventricular pacing: where should we implant the leads? J Am Coll Cardiol 1999;33:324 Greene TO, Portnow AS, Huang SKS Acute pericarditis resulting from an endocardial active fixation screw-in atrial lead Pacing Clin Electrophysiol 1994;17:21 Hayes JJ, Juknavoria R, Maloney JD The role(s) of the industry-employed allied professional, NASPE Policy Statement PACE 2001;24:398-399 Hayes DL, Naccarelli GV, Furman S, et al Report of the NASPE policy conference: training requirements for permanent pacemaker selection, implantation, and follow-up Pacing Clin Electrophysiol 1994;17:6 Jacobs DM, Fink AS, Miller RP, et al Anatomical and morphological evaluation of pacemaker lead compression (Part I) Pacing Clin Electrophysiol 1993;16:434-444 Jamidar H, Goli V, Reynolds DW The right atrial free wall: an alternative pacing site (Part I) Pacing Clin Electrophysiol 1993;16:959 Josephson M, Maloney J, Barold S, et al Task Force 6: training in specialized electrophysiology, cardiac pacing, and arrhythmia management J Am Coll Cardiol 1995;25:23 Levine PA Confirmation of atrial capture and determination of atrial capture thresholds in DDD pacing systems Clin Prog Pacing Electrophysiol 1984;2:465-473 Levine PA Should lead explantation be the practice standard when a lead needs to be replaced? PACE 2002;23:421-422 Magney JE, Flynn DM, Parsons JA, et al Anatomical mechanisms explaining damage to pacemaker leads, defibrillator leads, and failure of central venous catheters adjacent to the sternoclavicular joint PACE 1993;16:445-457 Magney JE, Staplin DH, Flynn DM, et al A new approach to percutaneous subclavian venipuncture to avoid lead fracture or central venous catheter occlusion Pacing Clin Electrophysiol 1993;16:2133 Manolis A, Chiladakis J, Vassilikos V, et al Pectoral cardioverter defibrillators: comparison of prepectoral and submuscular implantation techniques Pacing Clin Electrophysiol 1999;22:469 Ohm O-J, Breivik K, Hammer EA, et al Intraoperative electrical measurements during pacemaker implantation Clin Prog Pacing Electrophysiol 1984;2:1 O'Sullivan JJ, Jameson S, Gold RG, et al Endocardial pacemakers in children: lead length and allowance for growth Pacing Clin Electrophysiol 1993;16:267 Roelke M, O'Nunain SS, Osswald S, et al Subclavian crush syndrome complicating transvenous cardioverter defibrillator systems PACE 1995;18:973-979 Schwaab B, Frohlig G, Alexander C, et al Influence of right ventricular stimulation site on left ventricular function in atrial synchronous ventricular pacing J Am Coll Cardiol 1999;33:317 van Gelder BM, Bracke FALE, ElGamel MIH Adapter failure as a cause of pacemaker malfunction Pacing Clin Electrophysiol 1993;16:1961 Victor F, Leclercq C, Mabo P, et al Optimal right ventricular pacing site in chronically implanted patients J Am Coll Cardiol 1999;33:311 Ward DE, Jones S, Shinebourne EA Long-term transvenous pacing in children weighing ten kilograms or less Int J Cardiol 1987;15:112 Zoll PM Resuscitation of the heart in ventricular standstill by external electric stimulation N Engl J Med 1952;247:768  ... through the thorax of a patient attached to a transcutaneous pacemaker Figure 10-9 Transcutaneous Pacemaker Generator The transcutaneous pacemaker generator is attached to a cable with two pads... chamber pacemakers to 50 Hz extravenous electrical interferences Pacing Clin Electrophysiol 1993;16:1966 Camunas J, Mehta D, Ip J, et al Total pectoral implantation: a new technique for implantation. .. Antibiotic prophylaxis for permanent pacemaker implantation Circulation 1998;97:1796-1801 Da Costa A, Lelievre H, Kirkorian G Role of the preaxillary flora in pacemaker infections Circulation 1998;97:1791-1795