7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate Official reprint from UpToDate www.uptodate.com 2023 UpToDate, Inc. and/or its affiliates. All Rights Reserved. Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management : Brian Olshansky, MD : N A Mark Estes, III, MD : Todd F Dardas, MD, MS All topics are updated as new evidence becomes available and our peer review process is complete. Literature review current through: Jun 2023. This topic last updated: Jun 26, 2019. INTRODUCTION Periodic evaluations are required to maintain optimal pacemaker programming as well as to identify any system problems. A review of the common pacing system problems of dual chamber pacemakers and the methods of evaluation and therapy are reviewed here. The malfunctions presented will be limited to those that are manifest on the electrocardiogram. Other complications, such as infections, venous thrombosis and emboli, pacemaker syndrome, and tricuspid regurgitation are discussed elsewhere. (See "Infections involving cardiac implantable electronic devices: Epidemiology, microbiology, clinical manifestations, and diagnosis" and "Cardiac implantable electronic devices: Long-term complications", section on 'Tricuspid regurgitation'.) A more general review of the evaluation and management of single and dual chamber pacemakers and of the modes of cardiac pacing and indications for pacemaker therapy are presented separately. (See "Pacing system malfunction: Evaluation and management" and "Modes of cardiac pacing: Nomenclature and selection" and "Permanent cardiac pacing: Overview of devices and indications".) PACING SYSTEM COMPONENTS The pacing system is comprised of the pulse generator ( picture 1), also called the pacemaker, and the lead or leads that connect the pulse generator to the heart [1]. Either component may https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 1/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate be the source of a clinical malfunction. (See "Permanent cardiac pacing: Overview of devices and indications", section on 'Types of permanent pacemaker systems'.) The phrase "pacing system malfunction" includes problems that might arise from any of the components of the system. Inappropriately programmed pacemaker parameters, although not representing abnormal pacing system function, may yield suboptimal results for the patient. The normal characteristics and unique timing systems and algorithms of a given pacemaker should be examined, as they may be interpreted as malfunction by a clinician who is unfamiliar with the specific pulse generator. Recording system artifacts must always be considered in the differential diagnosis of a pacing system malfunction. DUAL CHAMBER PACING MODES A pacemaker programmed to the DDD mode is capable of pacing and sensing in both the right atrium and right ventricle. Virtually all of the dual-chamber rate-modulated pacing systems can also be programmed to any of the available modes, including DDI, DVI, VDD, and all of the single-chamber modes ( table 1). A review of the normal pacing modes is presented in detail separately. (See "Modes of cardiac pacing: Nomenclature and selection".) LIMITING THE MAXIMAL PACED RATE In dual chamber pacing systems that are capable of tracking P waves, there is a programmable limit placed upon the maximum paced ventricular rate that can occur in response to sensed atrial activity. This is essential because, if there was no limit, the pacemaker could potentially track atrial flutter at the rate of the flutter waves or track atrial fibrillation resulting in a rapid ventricular response. In addition, there may be clinical and physiologic reasons to limit the fastest rate of the pacing system, such as active ischemic heart disease. Total atrial refractory period The total atrial refractory period (TARP) is comprised of the AV interval, during which the atrial sensing circuit is refractory and the post ventricular atrial refractory period (PVARP). The PVARP is a second refractory period that is initiated on the atrial channel by a sensed or paced ventricular event. With early generation dual-chamber unipolar pacing systems, far-field oversensing was relatively common. To prevent this, paced events in one chamber initiated periods of refractoriness in the opposite channel of the pacemaker. In addition, a ventricular depolarization could potentially be sensed in the atrium and, thus, when an R wave is sensed in the ventricle, the PVARP is initiated. https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 2/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate When the interval between successive native atrial complexes is shorter than the TARP, some P waves will not be sensed. Since the pacemaker can only track those atrial depolarizations that are sensed, as the intrinsic atrial rate increases, eventually the device will only track every other P wave (a fixed 2:1 block response). The occurrence of abrupt 2:1 upper rate behavior may sometimes result in symptoms, most commonly sudden fatigue during exercise or strenuous exertion, in those patients who can exercise to a sufficient degree to achieve atrial rates in excess of the 2:1 block point. Contemporary pacemakers are capable of recognizing rapid atrial rates for the purpose of reverting from a tracking to a nontracking mode when the rapid rate is felt to be secondary to a pathologic atrial rhythm. The change in mode is called mode switching. Mode switching requires that the pacemaker be able to detect atrial events occurring within the PVARP even though it does not track these complexes. (See "Modes of cardiac pacing: Nomenclature and selection", section on 'Mode switching'.) When the sensed atrial rate exceeds the trigger rate, there is an automatic change in pacing mode from an atrial tracking mode to a mode incapable of atrial tracking, for example from DDD to VVI or DDI, or DDDR to VVIR or DDIR. To prevent the pacemaker from detecting a paced or sensed ventricular signal on the atrial channel (called a far field R wave), there is a separate timing interval within the PVARP called the post ventricular atrial blanking (PVAB) period during which the atrial sensing circuit is disabled. It is initiated by the ventricular output or ventricular sensed event. Maximum tracking rate timer In an effort to modulate the upper rate behavior, the maximum tracking rate timer is initiated by a paced or sensed ventricular event and must be completed before another ventricular output pulse can be released. Thus, even when a P wave occurs and the AV interval, which was initiated by that sensed atrial event, times out, the release of the ventricular output pulse is delayed until the maximum tracking rate timing period ends. While this limits the maximum tracking rate, it also effectively lengthens the interval from the sensed P wave to the ventricular output pulse (PV interval). If the atrial rate is stable, the next sensed P wave occurs closer to the preceding ventricular paced complex; if sensed, the same series of timers is initiated, and another ventricular paced beat occurs at an even longer PV interval. Eventually, a P wave will coincide with the PVARP, not be sensed, and, hence, not be tracked, resulting in a relative pause. The net effect is group beating at a fixed ventricular rate with a progressively increasing PV interval. The group beating and increasing PV interval are similar to AV nodal Wenckebach second degree AV block. As a result, this form of pacing system function is called pseudo-Wenckebach upper rate behavior [2]. https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 3/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate Other techniques Other techniques are used to modulate the upper rate behavior of the pacemaker, including rate smoothing and fallback [3,4]. RATE MODULATED (RESPONSIVE) PACEMAKERS Rate-modulation capabilities in dual-chamber pacemakers may result in a number of interesting rhythms since the pacing rate will be controlled by either the sensed P wave or the sensor-input to the pacemaker [5-9]. Rate modulated pacing is of particular value to patients with chronotropic incompetence due to either concomitant pharmacologic therapy or intrinsic conduction system disease; these patients will not increase their native heart rate in response to a physiologic stress. Sensors most commonly incorporated to achieve rate-modulation are an accelerometer (activity sensing) or minute-ventilation sensor. With regard to upper rate behavior, there are three definitions: The upper rate limit (URL) is the maximum paced ventricular rate that can occur in any setting. The maximum tracking rate (MTR) is the maximum paced ventricular rate that can occur in response to sensed atrial activity, defined by the total atrial refractory period (TARP). The maximum sensor rate (MSR) is the maximum paced ventricular rate that can occur in response to the sensor input to the pacing system. Both the MTR and MSR are subsets of the URL. While these two timers are often programmed to identical rates, most contemporary pacemakers allow them to be programmed independently. TRUE DUAL CHAMBER SYSTEM MALFUNCTION True pacemaker system malfunctions occur when there is loss of capture at a time when the myocardium is capable of being depolarized, loss of sensing when an appropriate signal occurs during an alert period, or oversensing. (See "ECG tutorial: Pacemakers", section on 'Pacer malfunction'.) Loss of atrial capture True loss of atrial capture in a dual-chamber pacemaker results in effective ventricular pacing only. With complete loss of atrial capture, the patient may experience symptoms of pacemaker syndrome. If an atrial stimulus fails to depolarize the atrium and following the subsequent ventricular paced depolarization if retrograde conduction is intact, this may lead to sustained retrograde conduction or even induction of an endless loop https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 4/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate tachycardia (ELT). If there is retrograde block, the lack of atrial capture will allow the native atrial rhythm to occur, which will be intermittently tracked, typically appearing as if there were an premature atrial complex (also referred to a premature atrial beat, premature supraventricular complex, or premature supraventricular beat) simply by juxtaposition of the native atrial rate with the paced rhythm. (See "Pacing system malfunction: Evaluation and management", section on 'Pacing stimuli present with loss of capture'.) Loss of atrial sensing The ECG manifestation of a loss of atrial sensing depends on the status of AV nodal conduction and the intrinsic atrial rate. In the presence of complete heart block, loss of atrial sensing will result in AV sequential pacing at the programmed base rate of the pacemaker. P waves will march through the tracing, occasionally being reset when there is atrial capture; at other times, they will render the atrial stimulus ineffective due to functional noncapture resulting in the appearance of fixed AV sequential pacing. In the absence of complete heart block, the intrinsic atrial rate will determine the presentation. If P waves were able to be sensed normally then the ECG would demonstrate consistent intrinsic P wave to V-paced intervals (so called PV or P synchronous pacing). A lack of PV pacing would therefore suggest loss of atrial sensing. If the PR interval is normal, however, the loss of atrial sensing may not be readily apparent from the surface ECG since the pacemaker will be appropriately inhibited by the sensed ventricular events. Safety pacing, in dual-chamber pacemakers, is the delivery of a ventricular output pulse at an abbreviated AV interval, following atrial pacing, if a signal is sensed by the ventricular channel during the early portion of the AV interval (ie, the cross-talk sensing window or ventricular safety pacing interval which follows the relatively short post-atrial ventricular blanking period). It is used to ensure that ventricular depolarization occurs if the sensed event was something other than an intrinsic ventricular depolarization. The abbreviated AV interval is usually in the range of 100 to 110 ms. If the sensed event was indeed an intrinsic ventricular event, the abbreviated AV interval delivers the pacing artifact early enough to prevent the pacing artifact from being delivered in the vulnerable portion of the cardiac cycle. (See "Pacing system malfunction: Evaluation and management", section on 'Pacing stimulus present with failure to sense'.) Loss of ventricular capture Loss of ventricular capture is obvious in the presence of high- grade AV block. Loss of ventricular capture is not as apparent when AV conduction is intact, because the ventricular stimulus may coincide with the onset of the conducted QRS. If the QRS is narrow, it will probably be interpreted as a fusion beat. If the QRS is wide, as with a bundle branch block, one may easily be misled into believing that capture is intact. In either case, if the https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 5/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate pacing artifact coincides with the native depolarization but does not contribute to the activation of that chamber these events would be designated pseudofusion beats. (See "Pacing system malfunction: Evaluation and management", section on 'Pacing stimuli present with loss of capture'.) Loss of ventricular sensing Undersensing on the ventricular channel may not be obvious when high-grade AV block is present, as each P wave is tracked and triggers a ventricular output. Even when AV conduction is intact, undersensing may not be recognized unless the ventricular stimulus occurs well after each native QRS. If the AV interval allows the ventricular stimulus to coincide with the conducted R wave, which may be normal depending upon where sensing actually occurs within the QRS, loss of ventricular sensing cannot readily be identified from the surface ECG. (See "Pacing system malfunction: Evaluation and management", section on 'Pacing stimulus present with failure to sense'.) Ventricular oversensing Oversensing on the ventricular channel will result in inappropriate pacemaker inhibition and rates that are below the programmed base rate. Depending upon where the oversensing occurs, the sensed ventricular event will also initiate both a ventricular refractory period as well as a PVARP. This may result in functional atrial and ventricular undersensing with failure to recognize intrinsic P waves and R waves. Atrial oversensing In the DDD mode, oversensing on the atrial channel will be interpreted by the pacemaker as the occurrence of multiple P waves. This may result in periods of more rapidly paced ventricular rhythms as the pacemaker attempts to track what it believes are atrial depolarizations. Symptoms include palpitations from the loss of AV synchrony and salvos of rapid paced ventricular rates or pacemaker syndrome as a result of the effective ventricular pacing. It may also be the initiating trigger for an ELT. Far field R wave sensing (ventricular paced or sensed events) may result in the pacing system interpreting a normal rhythm as a pathological atrial rhythm, and it may initiate the mode switching algorithm with loss of atrial tracking. Examination of the markers and atrial electrogram will help to identify the presence of far field R waves. When these are present, the atrial refractory period and/or the PVAB should be reprogrammed such that detection of these events are prevented. Inappropriate mode switching in the patient with high grade AV block may result in symptoms of pacemaker syndrome. (See "Modes of cardiac pacing: Nomenclature and selection", section on 'Pacemaker syndrome'.) BIVENTRICULAR PACEMAKERS https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 6/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate In patients with significant dyssynchrony due to intrinsic conduction disease, cardiac resynchronization therapy (CRT) with biventricular (BiV) pacing can improve intraventricular synchrony. This is accomplished with an additional pacemaker lead usually implanted via the coronary sinus to stimulate the left ventricle (LV), most commonly its lateral or posterolateral surface. Simultaneous (or sequential) stimulation of the LV and RV pacing leads provides more synchronous activation of the heart than RV pacing alone, which may actually cause dyssynchronous contraction. Among patients with heart failure who are in sinus rhythm, restoration of ventricular synchrony improves cardiac performance, symptoms, and overall survival. The efficacy of CRT in patients with heart failure and chronic AF is less well established, although available evidence suggests a benefit. (See "Cardiac resynchronization therapy in heart failure: Indications and choice of system" and "Cardiac resynchronization therapy in atrial fibrillation".) Dual-chamber biventricular pacemakers are prone to the same problems as dual chamber pacing systems. However, the specific features of device malfunction are in some respects distinct, and therefore merit separate discussion. Pacing system components and pacing mode The components of a BiV pacing system typically include an atrial lead in the right atrium, a right ventricular lead in the right ventricle, and a left ventricular lead that is most often placed in a cardiac vein by way of the coronary sinus ( figure 1). Biventricular pacemakers are usually programmed in DDD or DDDR mode if the patient is in normal sinus rhythm. Atrial events that are sensed or paced trigger an AV interval that is intended to be long enough to optimize the atrial contribution to ventricular filling but short enough to ensure ventricular pacing for the vast majority of the time and ideally near 100 percent. Pacing is necessary if resynchronization is to be achieved. Proper timing of the AV delay may require echocardiographic assessment to maximize the left ventricular outflow tract velocity time integral and left ventricular filling and ejection times. CRT often results in a QRS complex that is narrower than the native QRS complex because of fusion between the two paced signals. However, QRS duration does not always normalize, and some studies have shown a poor correlation between the width of the paced QRS complex and the clinical benefit of BiV pacing. (See "Cardiac resynchronization therapy in heart failure: Indications and choice of system".) CRT malfunction Biventricular pacing systems are prone to the same system malfunctions seen with other types of pacemakers. (See 'True dual chamber system malfunction' above.) https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 7/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate In addition, there are other system problems that are specific to the CRT setting. Since many patients with BiV pacemakers do not require pacing for the standard indications, pacemaker malfunction will not be associated clinically with syncope or "pacemaker syndrome." Instead, loss of ventricular synchrony may result in exacerbation of heart failure. Loss of capture The coronary sinus (left ventricular) lead of a BiV pacing system is separated from the myocardium by the full thickness of the vein wall and by any epicardial fat that may be encasing the vein. The capture threshold of the left ventricular lead may be higher than that of the right ventricular lead. In contemporary CRT devices, the right and left ventricular leads can be assessed independently if loss of capture is suspected. Loss of capture may be manifested by widening of the QRS complex or by a more subtle change in QRS morphology [10]. It is not always possible to recognize loss of capture based upon the surface ECG alone ( waveform 1). An intracardiac electrogram obtained by interrogating the pacemaker will commonly demonstrate an obvious change. Oversensing Oversensing is the detection of an inappropriate physiologic or nonphysiologic electrical signal. Skeletal muscle potentials generated by isometric contraction of the muscles in close proximity to the pulse generator are the most common etiology of oversensing, although inappropriate sensing of electrical activity in another cardiac chamber is also a potential problem. In a BiV pacing system, oversensing of atrial activity on the ventricular channel results in ventricular inhibition and loss of resynchronization [11]. This can be a result of malposition of the left ventricular lead too close to the AV valve ring. Mechanical lead failure All major electrical malfunctions, including loss of capture, undersensing, and oversensing, can be associated with a breach in lead insulation or conductor failure. A breach in lead insulation causes a marked drop in the measured stimulation impedance, while a conductor coil fracture causes a marked increase in impedance. PACING SYSTEM EVALUATION Whether the system involves a single chamber or dual chamber pacemaker, the process for evaluating the pacing system is similar. A detailed discussion of pacing system evaluation is presented separately. (See "Cardiac implantable electronic devices: Patient follow-up", section on 'PPM evaluation'.) https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 8/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate PACEMAKER DIAGNOSTICS In addition to interrogation of programmed and measured data, which is absolutely essential, all contemporary systems can provide telemetered event markers and endocardial electrograms. When these are available, the clinician should take advantage of them, since they will greatly facilitate the evaluation. A detailed discussion of pacemaker diagnostics is presented separately. (See "Cardiac implantable electronic devices: Patient follow-up", section on 'Follow-up of the patient with a pacemaker'.) SUMMARY AND RECOMMENDATIONS The phrase "pacing system malfunction" includes problems that might arise from any of the components of the system, including the pulse generator ( picture 1), also called the pacemaker, and the lead or leads that connect the pulse generator to the heart. (See 'Pacing system components' above.) True pacemaker system malfunctions occur when there is loss of capture at a time when the myocardium is capable of being depolarized, loss of sensing when an appropriate signal occurs during an alert period, or oversensing. The pacemaker cannot unpredictably alter its manner of function unless there is a component malfunction. Given the overall reliability of the pulse generators, if a bizarre behavior is encountered, one should consider a device eccentricity, a lead problem, or a recording artifact before entertaining the diagnosis of a pulse generator failure. In these more unusual circumstances, if a definitive diagnosis is not reached, it is always helpful to contact the manufacturer's "help-line" prior to invasive troubleshooting. (See 'True dual chamber system malfunction' above.) Biventricular pacemakers are prone to the same problems as dual chamber pacing systems. However, since many patients with biventricular pacemakers do not require pacing for the standard indications, pacemaker malfunction will not be associated clinically with syncope or "pacemaker syndrome." Instead, loss of ventricular synchrony may result in exacerbation of heart failure. (See 'Biventricular pacemakers' above.) ACKNOWLEDGMENT The UpToDate editorial staff thank Dr. David L. Hayes for his past contributions as an author to prior versions of this topic review. https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 9/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Ellenbogen A, Wilkoff BL, Kay GN, Lau CP. Pacemaker troubleshooting and follow-up. In: Clin ical Cardiac Pacing, Defibrillation and Resynchronization Therapy, 3rd ed, Saunders, Philadel phia 2007. p.1005. 2. Barold SS. Upper rate of DDD pacemakers. The view from the atrial side. Pacing Clin Electrophysiol 1988; 11:2149. 3. Papp, MA, Mason, et al. Use of rate smoothing to treat pacemaker-mediated tachycardias and symptoms due to upper rate response of a DDD pacemaker. Clin Proc Pacing Electrophysiol 1984; 2:547. 4. van Mechelen R, Ruiter J, de Boer H, Hagemeijer F. Pacemaker electrocardiography of rate smoothing during DDD pacing. Pacing Clin Electrophysiol 1985; 8:684. 5. Higano ST, Hayes DL. P wave tracking above the maximum tracking rate in a DDDR pacemaker. Pacing Clin Electrophysiol 1989; 12:1044. 6. Higano ST, Hayes DL, Eisinger G. Sensor-driven rate smoothing in a DDDR pacemaker. Pacing Clin Electrophysiol 1989; 12:922. 7. Higano ST, Hayes DL, Eisinger G. Advantage of discrepant upper rate limits in a DDDR pacemaker. Mayo Clin Proc 1989; 64:932. 8. Hayes DL, Higano ST, Eisinger G. Electrocardiographic manifestations of a dual-chamber, rate-modulated (DDDR) pacemaker. Pacing Clin Electrophysiol 1989; 12:555. 9. Pitney MR, May CD, Davis MJ. Undesirable mode switching with a dual chamber rate responsive pacemaker. Pacing Clin Electrophysiol 1993; 16:729. 10. Yong P, Duby C. A new and reliable method of individual ventricular capture identification during biventricular pacing threshold testing. Pacing Clin Electrophysiol 2000; 23:1735. 11. Lipchenca I, Garrigue S, Glikson M, et al. Inhibition of biventricular pacemakers by oversensing of far-field atrial depolarization. Pacing Clin Electrophysiol 2002; 25:365. Topic 1018 Version 20.0 https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 10/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate GRAPHICS Examples of cardiac pacemaker pulse generators Examples of cardiac pacemaker pulse generators commonly used in practice in 2015. Graphic 104720 Version 1.0 https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 11/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate Types of cardiac pacemakers and NBG codes Code Meaning VOO Asynchronous ventricular pacemaker; no adaptive rate control or antitachyarrhythmia functions VVI Ventricular "demand" pacemaker with electrogram-waveform telemetry; no adaptive rate control or antitachyarrhythmia functions DVI Multiprogrammable atrioventricular-sequential pacemaker; no adaptive rate control DDD Multiprogrammable "physiologic" dual-chamber pacemaker; no adaptive rate control or antitachyarrhythmia functions DDI Multiprogrammable DDI pacemaker (with dual-chamber pacing and sensing but without atrial-synchronous ventricular pacing); no adaptive rate control or antitachycardia functions VVIR Adaptive-rate VVI pacemaker with escape interval controlled adaptively by one or more unspecified variables DDDR Programmable DDD pacemaker with escape interval controlled adaptively by one or more unspecified variables Graphic 79459 Version 1.0 https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 12/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate Pacing leads for cardiac resynchronization therapy Two leads (right atrial and right ventricular leads) permit pacing of the right atrium and right ventricle. The third lead (coronary sinus lead), which is advanced through the coronary sinus into a venous branch that runs along the free wall of the left ventricle, paces the lateral wall and enables synchronized left ventricular contraction. Graphic 79450 Version 5.0 https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 13/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate Loss of LV capture with BiV pacing The top line of this tracing shows one lead from the surface electrocardiogram (ECG). The middle portion of the tracing shows the pacemaker event markers obtained by telemetry. The bottom line of the tracing shows the intracardiac electrogram. The arrow above the tracing indicates the time point at which capture of the left ventricle (LV) by the biventricular (BiV) pacemaker is lost. The changes with loss of capture are subtle in the surface ECG tracing. The event markers and the intracardiac electrogram document the loss of capture. Graphic 71566 Version 2.0 https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 14/15 7/6/23, 10:51 AM Dual chamber pacing system malfunctions of timing, sensing, and capture: Evaluation and management - UpToDate Contributor Disclosures Brian Olshansky, MD Other Financial Interest: AstraZeneca [Member of the DSMB for the DIALYZE trial]; Medtelligence [Cardiovascular disease]. All of the relevant financial relationships listed have been mitigated. N A Mark Estes, III, MD Consultant/Advisory Boards: Boston Scientific [Arrhythmias]; Medtronic [Arrhythmias]. All of the relevant financial relationships listed have been mitigated. Todd F Dardas, MD, MS No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/dual-chamber-pacing-system-malfunctions-of-timing-sensing-and-capture-evaluation-and-management/print 15/15