Undetected ventricular fibrillation in a single-chamber implantable cardioverter-defibrillator: When the far-field channel sees more than the intraventricular channel

Sensing of left ventricular (LV) activity in some devices used for cardiac resynchronization therapy (CRT) was designed primarily to prevent the delivery of an LV stimulus into the LV vulnerable period. Such a sensing function of the LV channel is not universally available in contemporary CRT devices. Recordings of LV electrograms may provide special diagnostic data unavailable solely from the standard right ventricular electrogram and corresponding marker channel. We used the LV sensing function of Biotronik CRT defibrillators to find 3 cases of dissimilar ventricular rhythms or tachyarrhythmias. Such arrhythmias are potentially important because concomitant slower right ventricular activity may prevent or delay implantable cardioverter-defibrillator therapy for a life-threatening situation involving a faster and more serious LV tachyarrhythmia. Dissimilar ventricular rhythms may not be rare and may account for cases of unexplained sudden death with a normally functioning implantable cardioverter-defibrillator and no recorded terminal arrhythmia.

Defibrillation testing is no longer routinely performed after automatic implantable cardioverter-defibrillator (AICD) implantation. However, certain subjects undergoing AICD implantation may be at higher risk of undersensing of ventricular arrhythmias resulting in potentially fatal outcomes. We present the case of a 30-year-old woman with hypertrophic cardiomyopathy (HCM; ‘asymmetric septal hypertophy’ morphologic variant) and prophylactic AICD who experienced an out of hospital cardiac arrest. AICD interrogation revealed undersensing as a result of intermittent high amplitude electrograms during an episode of ventricular fibrillation (VF). The subject underwent replacement and repositioning of the AICD lead along with pulse generator replacement (that utilized a different VF sensing algorithm) with appropriate sensing of VF and successful defibrillation testing. The presence of intermittent high amplitude electrograms during episodes of VF in AICDs using the AGC function should be recognized as a situation that may necessitate interventions to prevent undersensing and consequent delay in therapy.