Which is the Optimal Testing Method for Identifying an AV Delay that Allows Intrinsic Conduction?

It is desirable to maintain normal, conducted ventricular activation in patients with dual‐chamber pacemakers and preserved atrioventricular (AV) conduction. The shortest AV delay resulting in consistent ventricular inhibition (avoiding ventricular pseudofusion) was determined by a conventional incremental (inside‐out) technique vs the alternate decremental (outside‐in) technique in 20 such patients. Determinations were made in VDD mode in 20 patients and DDD mode (∼10 beats/min faster than the intrinsic rate) in 19. In VDD mode, the shortest AV delay avoiding ventricular pseudofusion was never found during inside‐out testing. It was identical with both methods in 10 patients (50%), and shorter by 10–80 ms (mean 20 ± 20 ms) with the outside‐in method in the remaining 10 (P = 0.004). In DDD mode, the shortest AV delay resulting in consistent ventricular inhibition was found only once during inside‐out testing. It was the same with both methods in 13 patients (68%), and shorter by 10–20 ms (mean 14 ± 5 ms) with the outside‐in method in the remaining 5 (26%, P = 0.18; Fisher's exact test). The shortest sensed AV delay preventing ventricular pseudofusion is most likely to be found with a decremental method (outside‐in). In rare patients, it identifies AV delays resulting in inhibition, while ventricular pacing persists at longer programmable AV delays with the conventional inside‐out approach.