Reiterative ventricular fibrillation caused by R-on-T during temporary epicardial pacing: a case report

JA Clin Rep. 2016;2(1):3. doi: 10.1186/s40981-016-0029-6. Epub 2016 Jan 15.


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.

Keywords: Artificial; Cardiac pacemaker; Epicardial temporary pacing; Premature ventricular contraction; R-on-T phenomenon; Slew rate; Undersensing.