What is a case example of inappropriate sensing due to EMI during the perioperative management of permanent pacemakers (PPMs) and automatic implantable cardioverter-defibrillators (AICDs)?

Updated: Oct 29, 2018
  • Author: Albert H Tsai, MD; Chief Editor: Sheela Pai Cole, MD  more...
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A 70-year-old male patient with a past medical history of hypertension, hyperlipidemia, coronary artery disease (CAD), and aortic stenosis who underwent a triple coronary artery bypass graft (CABG) and bioprosthetic aortic valve replacement 20 years previously presents for left-side video-assisted thoracoscopic surgery (VATS) for evaluation of a left lower pulmonary nodule. The patient has a PPM in place, implanted after his aortic valve replacement because of unresolved complete heart block. 

Preoperative ECG reveals an AV-paced rhythm at 80 beats/min. Chest radiography reveals a 1 × 1 cm left-lower-lobe density and a dual-chamber PPM in the left upper chest cavity. A recent pacemaker interrogation has noted a pacing mode of DDD at 80 beats/min, 98% V-pacing, an underlying heart rate (HR) of 40 beats/min, and 7 years of remaining battery life.

After thoracic epidural placement, the patient undergoes uneventful general anesthetic induction, intubation, and placement of a left radial arterial catheter. As the surgeon makes an incision with the electrocautery, you notice flattening of the arterial line tracing with a corresponding blood pressure (BP) of 68/26 mm Hg, a pulse rate of 38 beats/min, and loss of pulse oximeter plethysmography. The ECG tracing displays Bovie artifact with no discernible QRS waves. The pressure tubing remains patent, withdrawing and flushing easily, and the transducer is at the appropriate position. You obtain a noninvasive measurement of BP, which corresponds to the arterial line pressure.

You immediately instruct the surgeon to stop use of the electrocautery. You then notice the return of the arterial line tracing, with a BP of 134/76 mm Hg and a pulse rate of 80 beats/min. The pulse oximetry tracing also returns and shows an arterial oxygen saturation (SaO2) of 96%. The ECG shows an AV-paced rhythm at 80 beats/min. You call for a magnet to be brought into the room and place it over the PPM. The ECG now shows an AV-paced rhythm at 100 beats/min.

You then instruct the surgeon to resume incision, and the remainder of the intraoperative course proceeds without further incidents. At the end of the case, the magnet is removed, and the patient is brought to the postanesthesia care unit (PACU) after successful extubation. You give the appropriate signout and proceed to your next case. 

Approximately 1 hour later, you are called to reevaluate the patient for a nonfunctioning epidural and 10/10 pain. You notice an HR of 108 beats/min on telemetry, with atrial and ventricular spikes pacing at 100 beats/min. As you are evaluating the patient’s epidural, he suddenly goes into VF and loses consciousness. The arterial line tracing is flat, and you immediately begin chest compressions.

Defibrillator pads are placed, and the patient receives one unsynchronized defibrillation at 200 J, which is followed by the return of spontaneous circulation (ROSC). Telemetry now shows AV pacing at 100 beats/min. After reintubating the patient, you immediately request an emergency electrophysiology consultation for pacemaker interrogation and reprogramming to synchronized pacing. The patient is stabilized and transferred to the intensive care unit (ICU) for further management.


This scenario demonstrates the deleterious effects of inappropriate sensing due to EMI in a pacer-dependent patient, the danger of leaving a patient in asynchronous pacing, and the importance of pacer reinterrogation in the postoperative period.

In this case, preoperative evaluation of the patient’s CIED was carried out appropriately. The pacemaker’s indication, type, mode, and integrity were all identified, as was the patient's pacer dependence. However, appropriate intraoperative interventions for a patient at high risk for experiencing EMI effects were not employed.

Because the patient was pacer-dependent and the pacemaker was in a synchronous pacing mode (DDD), the pacemaker interpreted Bovie artifact as native QRS above its set rate of 80 beats/min and thus was inhibited. The patient’s native underlying rhythm was subsequently unmasked and proved to generate inadequate stroke volume (hypotension), HR (bradycardia), and cardiac output.

Placement of a magnet before incision would (in most cases, with the previously discussed caveats kept in mind) have converted the pacemaker to asynchronous pacing (DOO) with a rate dependent on device brand and battery status, thereby avoiding inappropriate sensing. In addition to magnet therapy, employing a bipolar cautery device, moving the grounding pad as far away from the PPM as possible, reducing Bovie amplitude, and avoiding continuous application of current could reasonably have been considered as means of minimizing EMI risk.

The postoperative complication described above highlights the danger of unmonitored asynchronous pacing resulting in R-on-T phenomenon and underscores the absolute necessity of reinterrogating the pacemaker postoperatively, especially if the pacemaker was manipulated intraoperatively (either during surgical exposure or through magnet therapy). Magnet removal generally causes a CIED to revert to its baseline mode, but confirmation can be obtained only via formal interrogation of the device.

In this case, the PPM failed to revert to synchronous pacing, probably because of physical disturbance resulting from its proximity to the surgical field. The patient remained in asynchronous pacing (DOO at 100 beats/min) and sustained an R-on-T VF when his native HR was raised above 100 beats/min from uncontrolled pain. Even though advanced cardiac life support (ACLS) protocol was initiated immediately and ROSC was obtained in a timely manner, this complication could have been avoided with prompt reinterrogation of the device postoperatively and expeditious identification of the PPM's failure to revert to synchronous pacing.

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