performed with minimal risk to the implanted device in most patients. This was illustrated in a series of 44 patients with implanted devices, including pacemakers and ICDs [16]. Patients were randomly assigned to either monophasic or biphasic shocks. Cardioversion paddles were placed in an anterior-posterior position, at least 8 cm from the device. Serial device interrogations demonstrated small changes in pacing impedances and ventricular sensing immediately after cardioversion that returned to baseline within one week. There were no differences between the effects of monophasic or biphasic shocks. When the patient undergoes surgery requiring electrocautery, the use of bipolar cautery will minimize the electrical field affecting the pacing system. At a minimum, every effort should be made to assure that the current path for the electrocautery will not encompass the pacing system. A full discussion regarding the perioperative management of patients with a permanent pacemaker, including optimal monitoring and pacemaker programming, is presented separately. (See "Perioperative management of patients with a pacemaker or implantable cardioverter-defibrillator".) Magnetic resonance imaging There has been significant debate about when patients with a CIED should be allowed to undergo an MRI study. The risks of scanning patients with permanent pacemakers or ICDs are related to programming changes, asynchronous pacing, activation of tachyarrhythmia therapies, inhibition of pacing output, and induced currents in lead wires leading to heating and/or cardiac stimulation. All aspects of MRI imaging in the CIED patient is https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 12/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate detailed in a professional society consensus document [15]. This subject is discussed in detail elsewhere. Computed tomography Although most patients with implanted cardiac devices can undergo computed tomography (CT) scans without any adverse consequences, direct exposure to high radiograph dose rates during CT examinations can potentially cause transient changes in pacemaker output pulse rate [17]. However, at this time, the evidence for device interference by CT is very limited and should rarely, if ever, limit device patients from undergoing standard CT imaging. Exceptions to this are detailed in a professional society consensus document [15]. Extracorporeal shock wave lithotripsy Extracorporeal shock wave lithotripsy is occasionally performed as a treatment for urinary tract calculi and cholelithiasis [18]. An older concern was that in patients with pacemakers or ICDs that incorporate a piezoelectric crystal for rate- adaptive pacing, the piezoelectric crystal can be shattered by the shock wave. Therefore, if such a sensor is incorporated in a device placed in the abdomen, extracorporeal shock wave lithotripsy is probably best avoided. However, there are now very few devices that incorporate a piezoelectric crystal. There have also been concerns that extracorporeal shock wave lithotripsy may cause significant mechanical forces that can shatter piezoelectric elements, circuitry, or lead connections but this is less well established. For patients who have any significant degree of pacemaker dependence, pacing mode should be reprogrammed to VOO or DOO because of the potential for inhibition of the ventricular pacing circuit due to interference from extracorporeal shock wave lithotripsy. However, in patients with an ICD, one study found that lithotripsy can be performed safely in those with tiered-therapy ICDs; however, it is recommended that antitachycardia therapies be turned "off" and the patient continuously monitored electrocardiographically during the procedure. Following the procedure the device should be interrogated, antitachycardia therapies turned back "on" and confirmation that final programming matches the programmed values prior to the procedure [19]. (See "Kidney stones in adults: Surgical management of kidney and ureteral stones".) PACING STIMULI ABSENT The absence of pacing stimuli is certainly appropriate when there is an intact native rhythm which inhibits pacemaker output. However, in the patient who has a pacemaker, one should usually not observe an absence of pacing stimuli with pauses in the rhythm that are longer than the programmed base rate of the pacemaker. If these pauses occur in the presence of pacing https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 13/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate stimuli that do not capture, this is a noncapture problem. If there are no visible pacing stimuli, then one of several possible system malfunctions have occurred: The malfunction may arise from oversensing by the pacemaker of an inappropriate signal that is not visible on the surface ECG. Failure to deliver a pacing stimuli at the appropriate time may result from an open circuit, which may be due to inadequate lead fixation to pacemaker generator at the time of implantation (loose set screw) or lead fracture. A component in the pulse generator may have failed. This is exceedingly rare, and other possibilities should be considered first. Hysteresis and ventricular pacing avoidance algorithms may result in intervals longer than the programmed base rate. Confusion may arise if it is not recognized that one of these features is programmed "on." Applying a magnet over the pacemaker will usually allow one to quickly differentiate an oversensing problem from an open circuit or pulse generator component malfunction: If pacing resumes with a stimulus being present, whether or not there is intact capture, the etiology of the absent pulses is likely oversensing. In unipolar pacing systems, particularly when programmed to a very sensitive setting, oversensing of myopotentials may be more likely to occur. If magnet application fails to eliminate the pauses, the problem is not one of oversensing, but is either a component failure within the pulse generator, an open circuit, or, in the setting of a bipolar coaxial lead, an internal insulation failure. Oversensing Historically, oversensing has been felt to be somewhat more common in the unipolar sensing configuration because the antenna for signal detection is much larger, extending from the housing of the pulse generator to the electrode located within the heart. Bipolar systems, in which both active electrodes are inside the heart, have a much smaller antenna effect and a better signal/noise ratio with respect to electrical noise originating from outside the heart. As a result, bipolar systems can often be programmed to very sensitive settings without encountering oversensing. Internal insulation failure in bipolar coaxial leads has produced repeated make-break contacts between the two conductor coils. Large nonphysiologic electrical transients result, which can be seen by the pacing system and inhibit it, but are not visible on the surface ECG. When this https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 14/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate occurs, reducing the sensitivity will probably not correct the system malfunction, and management will require replacement of the malfunctioning pacing lead. Management Oversensing can usually be corrected by reducing the pacemaker sensitivity (ie, programming the pacemaker to a higher sensitivity number that defines the smallest millivolt amplitude of the signal that the pacemaker can sense). Reducing the sensitivity predisposes to episodes of undersensing if the amplitude of the intrinsic signal is too small, a problem that may be more common with atrial sensing. Careful programming will usually resolve sensing issues, but occasionally less commonly used triggered pacing mode could be considered in a pacemaker-dependent patient. Open circuit The most common cause of pauses due to an open circuit is a conductor fracture. This usually occurs at a point of stress, only becoming manifest months to years post implant. If pauses are recognized in the early post implant period, they are likely due to an inadequately tightened set screw that secures the lead to the pulse generator connector block. A chest radiograph may allow identification of either the location of the conductor fracture or a lead partially pulled out of the connector block, in which case the tip of the terminal pin does not extend through the set screw of the connector block. If either a loose set screw or a conductor fracture is identified, an operative procedure will be required to correct the problem by either replacing the lead or tightening the set screw. Short circuit due to loss of insulation integrity Another potential etiology for failure to output is a breach of the internal insulation in a bipolar coaxial lead. This occurs when both conductors are making intimate contact, allowing the current traveling down the distal conductor to short-circuit to the proximal conductor before it ever reaches the electrodes within the heart. Without any current or only minimal current reaching the heart, the effective output pulse will be subthreshold and may not be visible. Lead impedance measurements Lead impedance measurements, either invasively or via telemetry, will readily differentiate an open circuit, ie, conductor fracture or loose-set screw (very high impedances) from an insulation defect (very low impedances). Management In the case of a loss of insulation integrity, programming the output configuration to unipolar may restore capture. Part of the current flow down the distal conductor is shunted to the proximal conductor when it reaches the short circuit. If the insulation abnormality is in the outer portion of a bipolar lead, programming to a unipolar configuration excludes the abnormality and current flows between the inner electrode and the pulse generator "can." Restoration of capture may convert a potential emergency to a problem that can be managed electively. However, reestablishment of pacing using polarity https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 15/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate programmability of the pacemaker is not a permanent solution and the malfunctioning lead should be replaced when clinically appropriate. Hysteresis Hysteresis is a feature that can be misinterpreted as a pacing system problem when pacing stimuli are absent. In a pacemaker programmed with hysteresis, the escape interval of the pacemaker is significantly longer than the rate at which it will pace, and thus the escape pacing rate is slower than the automatic basic pacing interval. It is commonly reported as either a ratio of rates (ie, 70/50), which means that the basic rate is 70 bpm but the rate at which the pacemaker will escape to release the first pacing pulse is 50 bpm, or a millisecond addition to the basic pacing interval (ie, 300 msec), which means that the escape interval before the pacing will begin is 300 msec longer than the basic pacing interval. The original goal of hysteresis was to allow the patient who only intermittently and infrequently required pacing support to remain in a normal native rhythm at lower rates when pacing was not required. When AV block developed such that pacing was required, sustained pacing at a very slow rate would be hemodynamically compromising. At these times, hysteresis would allow for the faster paced ventricular rate required. The key to suspecting hysteresis is that the pacemaker is either still inhibited when native heart rates are lower than the programmed base rate, or when pauses occur, they only occur following a native sensed beat. Hysteresis is a programmable parameter in many pacemakers, and, if it is not desired, it can be turned off by programming. Hysteresis does not reflect a malfunction of either the pulse generator or the lead. Recording system artifact Recording system artifacts can also mimic no-output situations. Recording lead disconnections are a fairly common example of such an artifact. They will usually be characterized by an abrupt termination or initiation of a complex in the middle of another complex plus simultaneous failure of the native rhythm coincident with the paced rhythm. Thus, not only does the pacing system appear to fail, but the baseline becomes isoelectric and the patient's sinus mechanism or atrial fibrillation also disappears. Another recording system artifact is an isoelectric native complex, which, although appropriately sensed by the pacemaker causing inhibition, is not seen in the specific lead that is being monitored, resulting in the appearance of excessively long pauses. This occurs rarely and requires a high index of suspicion to recognize. Confirmation requires additional recordings using either different leads or multiple simultaneous leads. https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 16/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate RECORDING SYSTEM ARTIFACTS Many recording system artifacts have already been discussed in the preceding sections, but there are other recording system artifacts that are confusing in single-chamber systems and can render dual-chamber recordings virtually impossible to interpret. The amplitude of the pacing stimulus may provide a wealth of information, but only when recorded with an analog ECG machine. In a stable recording lead, changes in the amplitude of the pacing stimulus commonly reflect varying levels of delivered energy and polarity configuration. It must be stressed that this is only the case with analog recording systems and analog recording systems are now rarely used. The stimulus amplitude will decrease in a partially open circuit, which attenuates the current flow. An insulation defect in a unipolar lead will short-circuit the system, resulting in a decrease in the stimulus amplitude. An insulation defect developing between the proximal conductor and the tissue in a bipolar system will result in a larger stimulus, making it look more like a unipolar system. Beat-to-beat fluctuations in the stimulus raise concerns about a pacing system problem, with special attention directed to the lead. Contemporary ECG recording systems use digital technology, allowing for computer interpretations of the recorded rhythms and 12-lead ECGs. In these systems, the signals are digitized for data storage and processing. With the standard pacing pulse being only 0.4 to 0.6 msec in duration, the sampling rate of the standard digital ECG machine may miss the pulse entirely or detect a relatively large deflection associated with the primary pulse or a very small deflection of opposite polarity, which is the recharge pulse. A wide variety of complexes representing the pacing stimulus from a large deflection in one direction to a small deflection in the opposite direction and anything in between might be seen on the digital recording, all of which would be normal. The potential information that is available from an analog recording will be lost with most digital recordings, and the resulting variation in the pacing stimulus amplitude and polarity should not be misinterpreted as indicative of a malfunction. LEAD EXTRACTION https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 17/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate Pacemaker leads may need to be removed from time to time, most often for infection or mechanical lead failure. Lead extraction should be performed by someone trained in the technique. Although complications are lower when laser or electrocautery techniques are utilized, there are inherent potential complications and these should be discussed with the patient prior to the procedure. (See "Cardiac implantable electronic devices: Long-term complications", section on 'Lead extraction'.) SUMMARY Given the sophistication and complexity of contemporary pacemakers, appropriate evaluation may require a significant amount of time. It is imperative to perform a careful evaluation of the entire system with review of all stored data without presupposing that the superficial appearance of "normal" function truly reflects normal pacing system function. 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 either some eccentricity of the specific pulse generator, a lead problem, or a recording artifact before entertaining the diagnosis of a pulse generator failure. ACKNOWLEDGMENT The UpToDate editorial staff thank Dr. David L. Hayes for his past contributions as an author to prior versions of this topic review. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Maisel WH, Moynahan M, Zuckerman BD, et al. Pacemaker and ICD generator malfunctions: analysis of Food and Drug Administration annual reports. JAMA 2006; 295:1901. 2. Maisel WH. Pacemaker and ICD generator reliability: meta-analysis of device registries. JAMA 2006; 295:1929. 3. Hauser RG, Hayes DL, Kallinen LM, et al. Clinical experience with pacemaker pulse generators and transvenous leads: an 8-year prospective multicenter study. Heart Rhythm 2007; 4:154. 4. Maisel WH, Hauser RG, Hammill SC, et al. Recommendations from the Heart Rhythm Society Task Force on Lead Performance Policies and Guidelines: developed in collaboration with https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 18/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate the American College of Cardiology (ACC) and the American Heart Association (AHA). Heart Rhythm 2009; 6:869. 5. Maisel WH, Sweeney MO, Stevenson WG, et al. Recalls and safety alerts involving pacemakers and implantable cardioverter-defibrillator generators. JAMA 2001; 286:793. 6. Thomas D, Becker R, Katus HA, et al. Radiation therapy-induced electrical reset of an implantable cardioverter defibrillator device located outside the irradiation field. J Electrocardiol 2004; 37:73. 7. Kapa S, Fong L, Blackwell CR, et al. Effects of scatter radiation on ICD and CRT function. Pacing Clin Electrophysiol 2008; 31:727. 8. Nemec J. Runaway implantable defibrillator a rare complication of radiation therapy. Pacing Clin Electrophysiol 2007; 30:716. 9. Solan AN, Solan MJ, Bednarz G, Goodkin MB. Treatment of patients with cardiac pacemakers and implantable cardioverter-defibrillators during radiotherapy. Int J Radiat Oncol Biol Phys 2004; 59:897. 10. Gomez DR, Poenisch F, Pinnix CC, et al. Malfunctions of implantable cardiac devices in patients receiving proton beam therapy: incidence and predictors. Int J Radiat Oncol Biol Phys 2013; 87:570. 11. Marbach JR, Sontag MR, Van Dyk J, Wolbarst AB. Management of radiation oncology patients with implanted cardiac pacemakers: report of AAPM Task Group No. 34. American Association of Physicists in Medicine. Med Phys 1994; 21:85. 12. Hurkmans CW, Knegjens JL, Oei BS, et al. Management of radiation oncology patients with a pacemaker or ICD: a new comprehensive practical guideline in The Netherlands. Dutch Society of Radiotherapy and Oncology (NVRO). Radiat Oncol 2012; 7:198. 13. Makkar A, Prisciandaro J, Agarwal S, et al. Effect of radiation therapy on permanent pacemaker and implantable cardioverter-defibrillator function. Heart Rhythm 2012; 9:1964. 14. Zaremba T, Jakobsen AR, S gaard M, et al. Radiotherapy in patients with pacemakers and implantable cardioverter defibrillators: a literature review. Europace 2016; 18:479. 15. Indik JH, Gimbel JR, Abe H, et al. 2017 HRS expert consensus statement on magnetic resonance imaging and radiation exposure in patients with cardiovascular implantable electronic devices. Heart Rhythm 2017; 14:e97. 16. Manegold JC, Israel CW, Ehrlich JR, et al. External cardioversion of atrial fibrillation in patients with implanted pacemaker or cardioverter-defibrillator systems: a randomized comparison of monophasic and biphasic shock energy application. Eur Heart J 2007; 28:1731. https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 19/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate 17. http://www.fda.gov/medwatch/safety/2008/safety08.htm#ElectronicMedical (Accessed on Ju ne 12, 2012). 18. Platonov MA, Gillis AM, Kavanagh KM. Pacemakers, implantable cardioverter/defibrillators, and extracorporeal shockwave lithotripsy: evidence-based guidelines for the modern era. J Endourol 2008; 22:243. 19. Corzani A, Ziacchi M, Biffi M, et al. Clinical management of electromagnetic interferences in patients with pacemakers and implantable cardioverter-defibrillators: review of the literature and focus on magnetic resonance conditional devices. J Cardiovasc Med (Hagerstown) 2015; 16:704. Topic 1013 Version 32.0 https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 20/25 7/6/23, 11:01 AM Pacing system malfunction: 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/pacing-system-malfunction-evaluation-and-management/print 21/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate Documented sources of electromagnetic interference (EMI) in patients with implanted cardiac devices Source Examples Electromagnetic fields Daily life* Faulty home appliances Metal detectors Anti-theft equipment Slot machines Cellular phones and accessories with strong magnets (eg, wireless charging, magnetic fasteners) [1] Work and industrial environment High voltage power lines Welding equipment Electronic motors while "on" Induction furnaces Degaussing coils Medical/hospital environment Magnetic resonance imaging Defibrillation or cardioversion Device-device interaction (eg, pacemaker and neural stimulator) Radiofrequency ablation Electrocautery Transcutaneous nerve stimulation Therapeutic diathermy Lithotripsy Radiation therapy There are many potential sources of single-beat inhibition. However, single-beat inhibition is not clinically significant and does not merit specific mention. If working at or near the level of the power line. There is no convincing evidence that being under the power lines at ground level will cause interference. Although all welding equipment is capable of causing interference, it most commonly occurs with equipment that operates at 150 amps. Radiation therapy may cause electromagnetic interference but may also result in direct damage to the pulse generator resulting in sudden no output or "runaway." https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 22/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate Reference: 1. Greenberg JC, Altawail MR, Singh G. Life saving therapy inhibition by phones containing magnets. Heart Rhythm; 2021. Reproduced with permission from: Pinski SL, Trohman RG. Interference in implanted cardiac devices, Part I. Pacing Clin Electrophysiol 2002; 25:1367. Copyright 2002 Blackwell Publishing. Graphic 51277 Version 8.0 https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 23/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate Algorithm for cardiac implantable electronic device management in patients undergoing radiation therapy CIED: cardiac implantable electronic device; LOE: level of evidence; EO: expert opinion; NR: nonrandomized. CIED relocation is not recommended for devices receiving a maximum cumulative incident dose of <5 Gy (Class III, LOE B-NR). Reproduced from: Indik JH, Gimbel JR, Abe H, et al. 2017 HRS expert consensus statement on magnetic resonance imaging and radiation exposure in patients with cardiovascular implantable electronic devices. Heart Rhythm 2017; 14:e97. Illustration used with the permission of Elsevier Inc. All rights reserved. Graphic 116359 Version 2.0 https://www.uptodate.com/contents/pacing-system-malfunction-evaluation-and-management/print 24/25 7/6/23, 11:01 AM Pacing system malfunction: Evaluation and management - UpToDate Contributor Disclosures Mark S Link, MD No relevant financial relationship(s) with ineligible companies to disclose. 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/pacing-system-malfunction-evaluation-and-management/print 25/25