T wave oversensing and low percentage of biventricular pacing in cardiac resynchronization therapy.

The success of cardiac resynchronization therapy (CRT) depends on a high percentage of ventricular pacing. We present the electrocardiography and electrograms of a patient who underwent an implantable cardioverter-defibrillator (ICD) with CRT implantation showing a low percentage of ventricular pacing as a result of T wave oversensing of paced QRS. The patient showed no clinical improvement. We suggest finding a good sensitivity of F waves in induced ventricular fibrillation during ICD implantation in order to overcome the harm of possible oversensing.