APPARENT EXTENSION OF THE ATRIOVENTRICULAR INTERVAL DUE TO SENSOR-BASED ALGORITHM AGAINST SUPRAVENTRICULAR TACHYARRHYTHMIAS

Rapid ventricular tracking response to supraventricular tachyarrhythmi a is one major limitation to DDD pacing. In a DDDR pacemaker, sensor-b ased algorithms have been used to control these arrhythmias. These inc lude the use of an interim rate limit (conditional ventricular trackin g limit) or a separate maximum tracking and sensor rate limits (discre pant upper rate). These algorithms limit inappropriate ventricular pac ing rate during tracking of pathological supraventricular tachyarrhyth mia and atrial flutter by Wenckebach-like prolongation of the AV inter val. We observed that this may cause an unexpected extension of the AV interval in patients with high atrial rate and intact AV nodal conduc tion. This was due to P wave rate above the conditional ventricular tr acking limit or maximum tracking limit, but AV paced interval prolonga tion was avoided by the occurrence of intrinsic conduction, albeit at an AV interval longer than the programmed AV interval. This might appe ar as failure of ventricular pacing on the ECG. This phenomenon is a m odified form of ''upper rate'' behavior occurring in the AV interval, and should be recognized as a normal behavior rather than pacemaker ma lfunction.