Abstract
Epicardial pacemaker wire insertion is standard following cardiothoracic surgery. However, undersensing of pacing wires may cause the R-on-T phenomenon, which induces ventricular fibrillation. We report a case of a male patient with severe mitral regurgitation scheduled for mitral valve replacement who experienced two ventricular fibrillation episodes related to the R-on-T phenomenon caused by undersensing of the epicardial pacing wire. Both undersensing events happened despite an appropriately low sensing threshold. Notably, the stimulated T wave followed the QRS of the premature ventricular contraction (PVC). This case suggests that a PVC’s R wave may be undersensed despite a low sensing threshold. This critical complication may have occurred because pacemakers sense R waves using a slew rate, which is the quotient of voltage over time. As a result, pacemakers may undersense wide QRS waves such as PVCs. Avoiding this dangerous phenomenon completely is not possible using epicardial pacemakers; therefore we recommend carefully adapting epicardial pacing especially when PVC waves occur frequently.
Highlights
Epicardial pacemaker wire insertion is standard following cardiothoracic surgery in most centers [1]
The R-on-T phenomenon is a well-known entity that predisposes to dangerous arrhythmias, including ventricular fibrillation (Vf ), a fatal arrhythmia
We subsequently evaluated the electronically recorded ECG waveforms collected during anesthesia and found that the Vf episodes were induced by the R-on-T pacing
Summary
Epicardial pacemaker wire insertion is standard following cardiothoracic surgery in most centers [1] These wires are valuable in diagnosing and treating cardiac arrhythmias following surgery, maintaining an appropriate heart rate, and may facilitate the reestablishment of circulatory integrity and normal hemodynamics [2]. We report two Vf episodes in a single patient related to the R-on-T phenomenon caused by undersensing of the pacing wire In this case, undersensing occurred despite a sufficiently low threshold, on which the T wave followed the QRS of the PVC, which is an Nakamori et al JA Clinical Reports (2016) 2:3 important finding for anesthesiologists who manage epicardial pacemakers. After 30 min, we attempted atrial asynchronous (AOO) pacing, but the patient’s atrioventricular (AV) node did not completely conduct supraventricular electrical activity and the ECG showed Mobitz type AV block (Fig. 2); we elected to maintain VVI pacing. He was discharged from the ICU on postoperative day 5 and discharged from the hospital without any neurological sequelae on postoperative day 13
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