Adequate sensing of ventricular fibrillation?

We present a case of an 81-year-old female patient who was resuscitated after out-of-hospital ventricular fibrillation. Clinical recovery was fine, but cardiological analysis showed a dilated cardiomyopathy with a poor systolic left ventricular function, left bundle branch block and persistent atrial fibrillation. There was no significant coronary artery disease. We prescribed heart failure medication and implanted a biventricular implantable cardioverter-defibrillator (ICD – Medtronic Viva Quad XT CRT-D). Despite medication, atrial fibrillation with a high ventricular rate persisted. To ensure adequate biventricular pacing, she underwent a successful atrioventricular node ablation. Because of a relative low amplitude R wave in the RV tip to RV ring configuration, RV sensing was programmed to