Simulation of Intraoperative Pacemaker Failure

To the Editor We read with interest the article by Wang et al entitled “Simulation of Intraoperative Pacemaker Failure.”1 We wholeheartedly agree that anesthesia providers ought to be trained in appropriate perioperative cardiac rhythm device (usually “cardiac implantable electronic device” or CIED) management and be adept at detecting and understanding common CIED-related problems. We also believe that adverse events in patients with CIEDs undergoing surgery likely are underrecognized and underreported. Consequently, we applaud the authors for developing and publishing this first simulation on this important subject. However, as testamurs of the International Board of Heart Rhythm Examiners and as anesthesiologists who routinely provide comprehensive perioperative CIED management, we believe that these simulation scenarios should be as realistic as possible. Thus, we are concerned that several features of this presentation are inconsistent with actual CIED function, behavior, and terminology. The case stem states that the “consult letter from the cardiac rhythm devices clinic recommends placing a magnet … if necessary … which will cause the pacemaker to pace in DOO mode at 80 beats per minute.” Most importantly, because no appropriately functioning pacemaker (PM) paces at 80 beats per minute (bpm) upon magnet placement, we wonder why this value was chosen.* An 80 bpm magnet rate should raise concern about PM integrity and trigger an immediate consultation to the CIED service. Although not specified as important information in the Canadian position statement,2 the Heart Rhythm Society consensus document,3 or the American Society of Anesthesiologists perioperative advisory,4 we believe that the consult letter should have included the programmed lower rate limit (the 12-lead electrocardiography [ECG] and text suggest that it is 70 bpm), the upper tracking rate, and the maximum sensor rate. The consult letter also should have specified under what circumstances a magnet should be applied. In this scenario, the surgery is inferior to the umbilicus. With appropriate positioning of the monopolar electrosurgical dispersive electrode, this case has little likelihood of electromagnetic interference causing PM oversensing and asystole. Thus, magnet placement is unlikely to be indicated. In cases where the risk of electromagnetic interference is low, use of asynchronous (DOO) pacing has little benefit and might cause harm by inducing ventricular tachycardia with R-on-T pacing.5 Moreover, because the patient’s underlying atrial rate was not specified, a magnet rate lower than the native atrial rate could introduce atrial competition, loss of atrial transport, and hemodynamic embarrassment.6 In the section entitled “Background and Briefing Information,” module (b) attributes the onset of PM-mediated tachycardia to shivering, stating that “pacemaker-mediated tachycardia can develop in a patient who has a rate responsive pacemaker.” The correct term for this behavior is pacemaker-driven tachycardia. Pacemaker-mediated tachycardia (PMT) refers to a very specific phenomenon in which a retrograde atrial event (usually from a premature ventricular depolarization) results in a PM-driven ventricular pace, which again results in a retrograde atrial event. Most of the time, the rate of this behavior is the upper tracking rate. Pacemaker-mediated tachycardia can occur in any dual-chamber tracking mode (DDD, VDD) and does not require rate responsive programming. Most PMs and implanted cardioverter-defibrillators have the ability to detect and abort a PMT; alternatively, placement of a magnet on a PM (capable of asynchronous pacing) but not on an implanted cardioverter-defibrillator can terminate PMT.7 In the section entitled “Debriefing Points,” the best method for determining pacing dependency was not discussed. In general, absolute pacing dependence implies the lack of spontaneous ventricular activity when a CIED is programmed to the VVI mode (AAI for single-chamber atrial devices) at the lowest programmable rate. When CIED interrogation is not possible, pacing dependency might be inferred through history or by examining the ECG. Atrioventricular nodal ablation, the previous placement of a temporary pacing wire, or syncope before CIED implantation likely confirms absolute pacing dependence. Additional clues to pacing dependence include CIED implantation for symptomatic bradyarrhythmia or mental status changes. On the surface ECG, pacing dependence might be rightly assumed if every atrial event, ventricular event, or both are paced. However, ECG inspection has 2 caveats as follows: (1) poor specificity because tracings often fail to show low-voltage pacing spikes, especially on operating room monitors, and (2) overdiagnosis of pacing dependence in patients with cardiac resynchronization therapy because the principal goal of CRT is to purposefully program the device to achieve 100% ventricular pacing.8 In the section on loss of PM capture, why would an external PM fail to affect rhythm? We also do not understand the value of a preoperative echocardiogram9 or the use of a pulmonary artery catheter. Finally, the authors could have included a discussion about chronotropic incompetence, an important contributor to hypotension during subarachnoid block in chronotropically incompetent patients, which often requires an increase in the pacing rate.10 Peter M. Schulman, MD Department of Anesthesiology and Perioperative Medicine Oregon Health & Science University Portland, OR Marc A. Rozner, PhD, MD Departments of Anesthesiology/ Perioperative Medicine and Cardiology University of Texas MD Anderson Cancer Center Houston, TX [email protected]

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