Pacing techniques in the prophylaxis of junctional reentry tachycardia.

Atrial premature beats (APBs) which encounter sufficient AV delay may initiate junctional reentry tachycardia (JRT). This form of initiation may be prevented by rendering part of the reentry circuit refractory by artificial stimulation following an APB which would otherwise initiate JRT. Two such approaches have been suggested: preexcitation pacing, that is, ventricular stimulation with a short AV delay triggered by atrial depolarization; and preemptive pacing, which consists of early atrial stimulation coupled to the initiating APB. We compared these approaches and describe them as follows. Ten patients with JRT (six with atrioventricular reentry and four with AV nodal reentry) were studied. Against a background of regular atrial drive, the range of coupling intervals over which a stimulated APB initiated JRT (tachycardia initiation window) was determined (control). The tachycardia initiation window was also measured when a second atrial stimulus followed the initiating APB 20 ms after atrial recovery (preemptive pacing) or when a ventricular stimulus closely followed the initiating APB with an AV delay of 65 ms (preexcitation pacing). The tachycardia initiation window in response to an isolated APB was also assessed following regular AV pacing with a short (65 ms) AV delay (preconditioning pacing) and the effect of preexcitation pacing following the initiating APB was also assessed after a similar drive (combined preconditioning and preexcitation pacing). All protocols were performed at two basic drive cycle lengths. The results are arranged for the slow and fast drives, respectively, and were as follows: control initiating windows--49.5, 28.5 ms; preemptive pacing initiation windows--151, 38 ms; preexcitation pacing initiation windows--26, 23.5 ms; preconditioning pacing initiation windows--45.5, 35 ms; combined preconditioning and preexcitation pacing initiation windows--10.0, 2.5 ms. Whereas preemptive pacing tended to widen the tachycardia initiation windows (a proarrhythmic effect) the combination of preconditioning and preexcitation pacing considerably reduced the possibility of JRT initiation by an atrial premature beat.