Symptomatic atrioventricular block during biventricular pacing: Facing a double trouble.

Far-field R wave (FFRW) oversensing in atrial channel is known to cause inappropriate automatic mode switch. We describe a case of 63-year-old lady with dual-chamber permanent pacemaker implanted 2 years back for symptomatic infra-hisian complete heart block and normal biventricular function. After 6 months, she underwent upgradation to cardiac resynchronization therapy (CRT-P, Boston Scientific) for right ventricular pacing induced cardiomyopathy. Her LV function normalized after CRT. Later on, FFRW oversensing caused false triggering of an atrial tachycardia, which subsequently opened up an "atrial flutter response" window leading to symptomatic inadvertent atrioventricular block at frequent intervals. Common ways to troubleshoot FFRW oversensing are either by increasing post-ventricular atrial blanking or reducing atrial channel sensitivity. In her case, concomitant P wave under-sensing made the situation more challenging to manage.