A 78-year-old man with hypertrophic cardiomyopathy and ventricular tachycardia, recipient of a Virtuoso DR dual chamber ICD, was seen in the ambulatory department because of shocks received during exercise.
In this patient, whether oversensing is due to crosstalk or double counting of the R wave is unclear. This oversensing occurs when 2 signals are nearly simultaneous. It is likely that the device detected the true ventricular signal, and that the oversensed signal was the sum of the atrial pacing stimulus and ventricular double counting. This can be solved by lengthening the ventricular blanking period. The alternative is to force ventricular pacing. Oversensing was not occurring on the ventricular paced events. This would also eliminate the long PR interval and the summation of 2 signals.
Oversensing of the P wave can occur when the defibrillation coil of an integrated bipolar lead is straddling the tricuspid valve; the P wave is sensed when the PR interval is long and the P wave falls outside the ventricular blanking period. Double counting of the R wave can occur when ventricular conduction is slowed and the duration of the ventricular endocardial signal is longer than the ventricular blanking period.
The VF episode detected via the combined counter (sensed events alternating between TS and FS) triggered a charge to 35 J in 6.2 sec. The first shock was diverted. Because of recurrence of oversensing, an episode of VF is redetected, prompting a second charge and, because the capacitors are partially charged the charge time is shorter and the shock is delivered
