Cardiac arrest caused by undersensing of a temporary epicardial pacemaker.

The R-on-T phenomenon is a well-known entity that predisposes to dangerous arrhythmias. Typically, a premature ventricular complex occurring at the critical time during the T wave of the preceding beat precipitates ventricular tachycardia and fibrillation. This phenomenon can occur not only in asynchronous ventricular pacemakers, but also in synchronous pacemakers, if loss of sensing of the intrinsic rhythm becomes evident. A patient who was fitted with a temporary epicardial wire, following cardiac surgery and experienced repeated episodes of polymorphic ventricular tachycardia caused by the R-on-T phenomenon, is described.