IS THE VENTRICULAR EFFECTIVE REFRACTORY PERIOD DIFFERENT WHEN DETERMINED BY INCREMENTAL VERSUS DECREMENTAL SCANNING - THE EFFECT OF PACING CYCLE LENGTH, D-SOTALOL, AND LEVCROMAKALIM

In the clinical setting, the ventricular effective refractory period ( VERP) is determined by an 8-beat drive train (S1S1), followed by a pre mature stimulus (S2), which is decremented in subsequent drive trains until capture is lost. Variation in intertrain pauses and capturing ex tra stimuli disturb steady-state conditions and reduce reproducibility of values found for the VERP. To increase reproducibility, a protocol without intertrain pause and incremental scanning (IS) of st was deve loped. In anesthetized dogs with chronic AV block, determination of th e VERP using IS and decremental scanning IDS) without intertrain pause was compared at 800 and 350 msec pacing cycle length (PCL). The measu rements were repeated after the administration of d-sotalol to lengthe n the VERP and levcromakalim to shorten the VERP. The results showed n o difference between IS and DS at both PCLs with or without medication . Recurrent and abrupt rate changes were avoided during IS, making thi s the protocol of choice when induction of arrhythmias is to be avoide d.