77 years old man, implanted with a triple chamber defibrillator Consulta CRT-D for mitral valvular cardiomyopathy with left bundle branch block and long PR interval, Routine follow-up 3 months after implantation; Episodes of ventricular detection are recorded; right ventricular lead is implanted on the inter-ventricular septum and is not displaced on the chest X-ray.
Tracing
Episodes of ventricular sensed event in the device memory;
Interrogation of the device and recording of the tracings; EGM1: Atrial EGM, EGM2 : Ventricular EGM (bipolar channel), EGM3 : Ventricular EGM (far-field channel);
This tracing shows a relatively rare case of loss of biventricular pacing after A/V crosstalk following atrial pacing. Atrial pacing starts 2 periods of ventricular protection to avoid crosstalk: 1) A non-programmable post atrial paced ventricular blanking period (that last 30 ms on the new CRT-D platforms); During this period of time, no ventricular detection is possible. 2) A safety window ending 110 ms after the atrial pacing; its duration is not programmable. However, it is possible to deprogram this parameter (programming off); However, this is not desirable because the deactivation of this safety window can lead to asystole in pacemaker-dependent patients or to the loss of the biventricular pacing in non-dependent patients in case of late A/V crosstalk (ventricular detection of the atrial stimulus or atrial depolarization).
This tracing is relatively rare because the crosstalk occurs after the safety window, which was turned on and programmed to run during the AVD. In this particular patient, the post-stimulation atrial depolarization time is significantly prolonged and detected by the ventricular channel more than 110 msec after the atrial stimulus.
Possible solution options are relatively similar to the previous tracing: 1) reposition the right ventricular lead; 2) reprogram the polarity of ventricular sensing (ineffective in this patient) ; or alter the ventricular sensing; In this patient, reprogramming the sensitivity to 0.6 mV eliminated the oversensing; A VF induction was used to validate the correct detection of a ventricular arrhythmias.
