Introduction

Since the implantation of the first human pacemaker in 1958, electrical myocardial stimulation against various types of rhythm disorders of the heart has become available. Pacemakers were initially introduced for the treatment of heart block and later on for sinus node disease. Currently, they are used for a variety of conditions, including tri-fascicular block and syncope related to a variety of pathologic reflexes. This implies that pacemakers now have an important role as lifesaving devices.¹ They are important tools for improving quality of life in several of the cited conditions; thus pacemaker therapy has become one of the most effective medical treatments. The recent innovation of cardiac resynchronization added another dimension to pacing because combined left and right ventricular stimulation is a useful tool in improving heart function by restoring synchronous ventricular activation and contraction.

The international revised North American Society of Pacing and Electrophysiology and the British Pacing and Electrophysiology Group (NASPE/BPEG) generic (NBG) pacemaker code (Table 37-1) is generally used to address the pacing chamber, the chambers sensed, and the response to sensing as well as to determine if rate modulation and multi-site pacing have been activated.² Figure 37-1 shows electrocardiograms (ECGs) with the three most often used methods of cardiac stimulation. In Figure 37-2, a photograph and the x-ray image of a pacemaker with the most important components are shown. These are the connectors for the electrodes leading to the heart; the pulse generator itself comprises the power source and the electronic circuit that controls the timing, the impulses, and a variety of programmable features. The pacemaker is connected to one or more pacemaker electrodes (epicardiac or endocardiac), which allow conduction of the stimulus from the pulse generator to the myocardium (Figure 37-3). Pacemaker electrodes can be implanted in the right atrium, the right ventricle, and the coronary sinus for left-sided stimulation by venous access or inserted surgically for epicardial access. Electrodes can be unipolar or bipolar.

FIGURE 37-1 Electrocardiograms (ECGs) of the three most commonly used methods of cardiac stimulation. ECG strip A shows AAI pacing, with the pacing spike before the P wave. Note that the pacemaker does not inhibit during ventricular or nodal extrasystoles (beat 5). ECG strip B shows VVI pacing. In beats 2, 5, and 8, pacemaker activity fuses with simultaneous intrinsic or ectopic heartbeats, whereas the pacemaker inhibits on an early ventricular extrasystole (beat 9). ECG strip C shows DDD pacing. The pacemaker behavior in beat 5 clearly demonstrates the advantage of DDD pacing: ventricular synchronized pacing (tracking) on a premature atrial beat. All the other atrial complexes are preceded by a spike.

FIGURE 37-2 Photograph and radiographic image of a biventricular pacemaker. A, Connector block for the electrodes. B and C, Sealed housing containing battery or power source (B) and electronic circuit board (C). D, Conductors (electrodes) leading to the endocardium.

FIGURE 37-3 Pacemaker electrodes. A, Straight endocardiac passive fixation (tined) electrodes (1, 2) and active fixation (screw-in) electrodes (3, 4, 5). One (nonretractable) screw-in lead is covered with a dissolvable coating (4). B, Epicardiac bipolar electrodes. Screw-in electrode (6) and suture-on electrode (7). Middle, Close-up (side view) of a screw-in electrode (6). Right, close-up of a suture-on electrode (7). C, A variety of passive fixation coronary sinus electrodes. Fixation can be achieved by wedging the preshaped distal tip of the electrodes (8, 9, 13, 15) or the small silicone fins or lobes (10, 11, 12) into the vein. Electrode 14 shows an electrode that combines a preshaped tip with deployable lobes.

The third part of the pacemaker system (beside the pacemaker itself and the electrodes) is the pacemaker programmer (Figure 37-4), which usually is not considered as critical for pacemaker operation. However, this tool is used to check the integrity of the pacemaker system and control the functioning of the pacemaker. Nowadays, these programmers have evolved into dedicated computers, which have made possible extensive programming of pacemakers and advanced interrogation of pacemaker diagnostics. This chapter focuses on the essential elements and developments of modern pacemaker follow-up.

FIGURE 37-4 Combined pacemaker and implantable cardioverter defibrillator (ICD) programmer from Boston Scientific Corp. On a programmer device, the following generic key components can be seen: telemetry wand for wireless contact with the pacemaker, electrocardiogram cable, touch screen with pencil, buttons for emergency therapy and to abort therapy, buttons for interrogation and (re)programming, and paper strip printer with print buttons.

Goals of Pacemaker Follow-up

The first goal of the pacemaker clinic is to monitor the patient’s status and verify that the applied pacemaker therapy still meets the needs of the patient. The second goal is to verify that no problems occurred with the implanted device. The third goal is to monitor the battery status of the device and schedule a device replacement in time.

Organization of the Pacemaker Clinic

In the early pacemaker era, follow-up largely was intended to monitor the proper technical operation of the electronic device itself. Over time, pacemakers have evolved into a stable and trustable technology, and they are now equipped with multiple diagnostic tools. Although the proper technical functioning of the pacemaker still is the most critical part of therapy, a shift from pure technical device checkup to clinical rhythm control is often necessary. Therefore modern pacemaker follow-up takes place in a highly specialized, multi-disciplinary environment. There is general consensus about the various aspects of monitoring cardiovascular implantable electronic devices (CIEDs).³ The essential elements of a well-organized pacemaker clinic are summarized below.

Equipment

Routine pacemaker follow-up is often performed in a dedicated pacemaker control room (Figure 37-5), which allows efficient, high-quality device follow-up. This room should be equipped with an examination table, an electrocardiogram (ECG) recorder, pacemaker programmers with appropriate and updated device software, advanced life support material such as external defibrillator with trans-cutaneous pacing capabilities and resuscitation materials, technical documentation, and specifications of pacemakers in use. Computers connected to the hospital network and the Internet, with online access to electronic patient records, the pacemaker database, and remote follow-up web pages, should be available.

FIGURE 37-5 Dedicated pacemaker follow-up room with a variety of programmers. This picture shows how a dedicated pacemaker follow-up room can be arranged. Some essential equipment can be seen: emergency alarm system and telephone, computer and printer facilities connected to the Internet, multiple programmers of different pacemaker manufacturers, defibrillator, fitted with external pacing capabilities, ECG recording system, and patient examination table.

Normal Routine Pacemaker Follow-up

Patient History and Physical Examination

Along with pacemaker functioning, the patient’s physical and general well-being should also be checked. During this examination, the patient should be questioned about symptoms such as syncope, dizziness, shortness of breath, reduced chronotropic competence, palpitations, precordial pain, and any pacemaker-related complaints such as pectoral or diaphragmatic muscle stimulation. Pectoral muscle stimulation is more common in unipolar programmed settings because in this setting the pacemaker is functioning as the anode of the system. An isolation defect of a conductor in this region can also generate this phenomenon.

During inspection of the scar, any signs of impending infection and all other issues should be easily identified by simple inspection of the pocket, a step that should never be skipped. Also, the first signs of necrosis caused by pressure of the pacemaker can or a pacemaker lead can be revealed during this inspection. When the skin is still intact and infection of the pacemaker pocket does not seem present, a relocation or expansion of the pocket can be sufficient; this helps prevent total removal of the pacemaker system when infection does occur. Patient reports of device movement can be verified by further examination.

A routine ECG will show whether the patient has pacing or no pacing in his or her daily life and is often useful to understand data from the programmer.⁹ Also, the ECG will reveal many other features at the atrial and ventricular levels. This is highly important for cardiac resynchronization therapy (CRT) because QRS width and axis can be proof of biventricular pacing versus right or left ventricular stimulation alone and because the axis, in general, tells something about the pacing site (Figure 37-6).¹⁰

FIGURE 37-6 Relationship between the surface electrocardiogram (ECG) and the pacing site on an x-ray. Left, VVI pacemaker with lead in the right ventricular apex in a patient with a mitral valve prosthesis. The ECG shows a positive QRS complex in lead I and negative complexes in leads II and III. Right, The ventricular lead is located in the right ventricular outflow tract. Note the opposite ventricular activation on the corresponding surface ECG (negative QRS complexes in lead I and positive complexes in leads II and III).

Technical Pacemaker Control

Checkup of the technical integrity is another routine that may be dealt with simply by interrogating the device and printing out or reading a completely automated report. This typically shows the actual battery voltage, the impedance over the system and the leads, and data on pacing and sensing, which are often expressed as histograms or tables (Figure 37-7). At the impending end of (battery) life (EOL, end-of-life, or EOS, end-of-service) an early warning is reported, called the elective replacement index (ERI). At this time, the appointment for elective replacement should be scheduled within a reasonable time, according to the specifications of the device. When the battery is almost completely depleted, the device often reverts to a backup mode, simply delivering single-chamber synchronous pacing and later reverting to asynchronous pacing until no more output is possible (Figure 37-8). The behavior of current lithium iodine batteries is adequately predictable, so when a normal (remote) follow-up scheme is followed, premature battery depletion or asynchronous EOL behavior should no longer appear on pacemaker follow-up. To prolong the generator life, several precautions can be taken during control. One is to use automatic capture; if this is not available, the output should be programmed at a level that ensures safety (usually two to three times the measured threshold), without depleting the energy of the battery.^8,11 Several systems now have an automatic threshold function, a system to verify automatically the sensing the various levels of the pacemaker and automatic sensor optimization capabilities. This may lead to reprogramming, if possible. Otherwise, automatic adjustments may have occurred all the time, and a printout of this function will be generated. It is generally supposed that activation of the automatic features simplifies follow-up without problems for selected patients.¹² These automatic features can always be checked manually, if preferred, during routine follow-up.

FIGURE 37-7 Pacemaker data expressed as histograms. Example of stored pacemaker data. This histogram from a rate-responsive dual-chamber pacemaker (St. Jude Medical, St Paul, MN) describes the paced and sensed rate distribution and the main programmed pacemaker frequencies in beats per minute. Note the limited variation in frequency between 60 and 90 beats/min. Purple indicates when atrial pacing occurs; blue indicates when atrial sensing is present. AP, Atrial paced; VP, ventricle paced; AS, atrial sensed; VS, ventricle sensed; PVC, premature ventricular contraction; tach, tachycardia.

FIGURE 37-8 Subthreshold asynchronous pacemaker stimulation at the end of battery life. The figure shows the asynchronous fixed-rate pacing behavior at the end of life of the battery. The asynchronous fixed-rate pacing without capture can be clearly seen; the pacing spikes (asterisks) on the electrocardiogram do not cause any QRS complexes and show no relation to the underlying intrinsic heart activity (Q).

The integrity of the conductors should also be examined by observing the intracardiac electrogram (IEGM). When diagnostics are available, more appropriate programming of the device can be performed to avoid the unnecessary features. Alternatively, new features can be included to provide more comfort for the patient. In general, it is wise to start the pacemaker therapy by simply providing basic functions, depending on the patient’s indications for a pacemaker. Features such as rest rate or night drop and flywheel or rate smoothing (Figure 37-9) can be activated later, on the basis of the collected pacemaker diagnostics and Holter or histogram information.¹³ These features should be activated only when adequate lower and upper rates are programmed and after correct steepness of the sensor response has been studied, such as by exercise testing or a 6-minute walk test.¹⁴ Furthermore, as it is known, right ventricular apical pacing should be avoided.¹⁵ This can be ensured with programming the pacemaker modus into AAI, a low backup rate in VVI, DDI with a low rate if an atrial lead is necessary, or ventricular lead implantation on alternative sites such as the right ventricular septum or the outflow tract.¹⁶ The alternatives are automatic mode switching algorithms from AAI to DDD or automatic adjustment of the AV delay if the pacemaker system allows it.¹⁷ However, if ventricular pacing is needed, correct programming in DDD mode with adapted AV delay is necessary.^18,19

FIGURE 37-9 Rate smoothing during atrial fibrillation. On this electrocardiogram strip, a ventricular pacemaker system can be seen to adapt the programmed lower pacing rate (asterisk) to the intermittent fast conduction during atrial fibrillation. This rate-smoothing algorithm prevents the occurrence of long cycles in heart rate and improves the stability of heart rate.

More Advanced Control and Troubleshooting

More advanced fine-tuning of the pacemaker may be necessary; it is often done unexpectedly or may occur when a patient is admitted to the hospital. The reason for such an event might be syncope or a surgical or medical event such as myocardial infarction, which requires reprogramming or renewed programming. It is almost impossible to describe general rules to solve the diverse problems related to pacemakers; each patient deserves an independent, individualized, and tailored approach. For example, pacemaker fine-tuning is required for persistent atrial fibrillation and atrioventricular block in an older adult who is wheelchair dependent rather than for paroxysmal atrial fibrillation and rate-dependent AV block (Figure 37-10) in a young cyclist, even when a comparable pacemaker system could have been implanted.²⁰

FIGURE 37-10 Exercise test revealing rate-dependent atrioventricular (AV) block. The patient with complete heart block (upper strip) was submitted to exercise testing after having palpitations with a VDD pacemaker. After initial correct tracking, a Wenckebach phenomenon was observed, with 2 : 1 AV tracking from 150 beats/min on; during recovery, poor sensing explains the low pacing rate in the ventricle. The lower strip shows the heart rate trend (at right).

Troubleshooting for the pacemaker system is not always easy. A routine ECG or the reading of the programmer may reveal the reasons for the (potential) dysfunction of the pacemaker system. Box 37-2 lists several potential complications and problems that should be solved with more expert knowledge and systematic analysis of the electrograms and surface ECG.

Various IEGM recordings that display noise, high frequency, or other noncardiac signals can help discover interference that may be caused by cellular phones or magnetic fields. Because of improved signal filtering and detection algorithms, pacemaker malfunction caused by such phenomena seems to have become relatively rare.^21,22

Specific problems such as pacemaker-mediated tachycardia (Figure 37-11) require some understanding of the normal conduction behavior of the heart and of the particular pacemaker algorithms designed to avoid them.²³ Some maneuvers may be necessary to provoke or reproduce complaints associated with pacemaker-mediated tachycardia. Pacemaker syndrome is another problem typically associated with (but not limited to) ventricular pacing and retrograde conduction.

FIGURE 37-11 Pacemaker-mediated tachycardia (PMT). After a normally sensed and tracked atrial complex (As, beat 1), retrograde conduction from the ventricle to the atrium occurs (Ar), which is sensed and tracked again and causes PMT. A dedicated algorithm will terminate the PMT (after beat 8), which causes the second pause that in turn, allows a normal atrial complex.

Complaints associated with far-field R-wave sensing or undersensing of supraventricular activity can be resolved by individual adjustment of blanking and refractory periods.²⁴ Marker annotations combined with IEGMs help interpret these problems.

Pectoral and diaphragmatic stimulations require special attention. They can be reproduced during the consultation by asking the patient to recreate the conditions that caused them. They may be solved with reprogramming, or replacement of the unipolar electrode with a bipolar one may be required.

Additional Tests

Other diagnostic tools or additional tests, such as radiographs, Holter monitoring, exercise testing, and echocardiography, are often used to understand or clarify certain pacing-related problems.

Radiographic examination of the chest or the pacemaker pocket can be performed to reveal dislocation, fracture, or crush of a pacemaker lead. The incidence of a lead crush is higher in systems in which the lead is implanted via a subclavian venous access, in which the risk of crush between the clavicular bone and the first rib is higher compared with a cephalic venous access. Although lead impedance can reveal a lead fracture, it is difficult and sometimes impossible to confirm lead fractures by radiography because of the bipolar spiral construction of the leads. Insulation defects or lead fractures sometimes cause unpredictable problems because of intermittent conductor contact or leakage current. These phenomena can present as unexpected attacks of dizziness or syncope. IEGMs are often informative, as they might display noise. Radiographs are useful to identify an unknown implanted device. Focused pictures can show the screws in the connector.

Holter studies can be performed when the patient’s complaints cannot be verified with pacemaker diagnostics or when stored pacemaker electrograms are not available.

Exercise tests are useful to evaluate the behavior of the pacemaker if a patient reports difficulty during effort. Also, the effects of reprogramming can be identified and correct pacemaker programming easily confirmed.

Hemodynamic fine-tuning can be done using echocardiography to adjust the A-V interval, the V-V interval (for resynchronization devices), and the intraventricular interval.^15,25 Optimization of cardiac resynchronization devices requires more attention than described here and is discussed in other chapters in this text.

Avoiding Surgery

Some pacemaker-related problems can be resolved by simply reprogramming the pacemaker, but some need invasive procedures. Almost every reprogrammable pacemaker parameter can contribute to a noninvasive resolution of a pacing-related problem. Reprogramming is sometimes effective only in combination with adjustment of the pharmacologic therapy (e.g., class Ic antiarrhythmic drugs increase the pacing threshold). However, on other occasions, invasive procedures may be necessary to understand and solve a pacing-related problem.

Medical Conditions Requiring Adjustment of Pacing

Although a patient may have an indication for pacemaker therapy, it does not mean that the indication will not change over time. Because of several circumstances such as progress of the clinical picture or a new development in the disease, adjustments in the pacemaker therapy may be necessary. Some of the typical factors or effects that necessitate adjustment of the pacemaker therapy are drug therapy, electrolyte disturbances, and cardiac conditions such as angina pectoris, atrial fibrillation, and heart failure.

General Advice to the Patient

Sometimes, the law requires that a patient not drive during the first weeks after implantation or replacement of a pacemaker. The risks involved in driving should therefore be explained. Some physical activities should be restricted for a short time until the wound heals and until the electrodes are fixed in their intended positions. Educational materials for the patient can be helpful in such situations.

Reporting

All the actions taken during the pacemaker checkup should be reported and stored, such as on a dedicated computer or the hospital database. An electronic patient record system would help make the latest follow-up results directly available to the physician. Furthermore, a letter should be sent to the patient’s physician and a new appointment made.

Device Advisories and Safety Alerts

Good databases also allow taking fast action when a device or lead advisory is issued. The affected devices or leads can be easily queried from the database. Alert notifications as well as specific device advisory information from the manufacturer should be added to the concerned patient’s files. The patient should be given clear information from both the manufacturer and the physician. Finally, all the essential technical and clinical information from the device or the lead and information about patients involved in safety advisories should be reported to, or shared with, the relevant government authorities, manufacturers, and other physicians.^26,27 With these efforts, remote monitoring will be of significant assistance.^28,29

Summary

Good clinical care of a patient with a pacemaker demands a well-structured, regular, and methodical long-term follow-up program. The increased pacemaker memory capabilities allow storage of multiple technical and clinical events. A clear understanding of both technical and clinical issues related to pacemaker therapy is necessary. Successful pacemaker follow-up is changing more and more from a pure technical system control to an integrated clinical consultation. IEGM, pacemaker diagnostics, pacemaker Holter information, and real-time measurements should all be analyzed to determine the integrity of the pacemaker system and the efficacy of the applied therapy. Subsequent reprogramming should overcome pacemaker-related problems and contribute to optimal patient care.