Fullscreen Mode

Transmission

While a drop in %CRT associated with alerts for mode switches may suspect atrial fibrillation as the cause, analysis of the real time EGM and (one of) the mode switch episode reveals that there is no evidence of atrial fibrillation. There are however, many oversensed atrial events, especially during the mode switch episode. We see sharp signals with varying amplitudes, non-physiological in nature, suggesting atrial lead dysfunction (conductor failure or isolation rupture). Atrial oversensing are treated by the device as premature atrial events which often occur during refractory periods which can lead to appropriate but also inappropriate inhibition of biventricular pacing (due to non triggering by true atrial events). This is a case of advanced lead failure which has been progressive since a few months; when observing the “AF” and %CRT curve we see a mirror image of increased “AF” associated with decreased %VP. The mode switch episodes also show the major reason why %CRT is low for extended periods; when the mode switch algorithm is activated, the device switches to a non-synchronized mode (VVI). Since the patient (like most CRT patients) has preserved atrioventricular conduction, there are prolonged periods of inappropriate inhibiton of biventricular pacing with the patient’s intrinsic ventricular rate exceedingthe programmed lower rate.

Next steps

Atrial lead dysfunction is quite common and the associated atrial oversensing and inappropriate mode switches can cause a clinically important drop in biventricular pacing. In most cases, the oversensing is paroxysmal and can be overcome by adjusting the sensitivity. But in this case, the atrial lead dysfunction is at an advanced stage, clearly compromising the CRT function. The only real solution to the problem is to change the atrial lead.