CHARACTERISTICS OF THE TEMPORAL AND SPATIAL EXCITABLE GAP IN ANISOTROPIC REENTRANT CIRCUITS CAUSING SUSTAINED VENTRICULAR-TACHYCARDIA

The excitable gap of a reentrant circuit has both temporal (time durin g the cycle length that the circuit is excitable) and spatial (length oi the circuit that is excitable at a given time) properties. We deter mined the temporal and spatial properties of the excitable gap in reen trant circuits caused by nonuniform anisotropy, Myocardial infarction was produced in canine hearts by ligation of the left anterior descend ing coronary artery, Four days later, reentrant circuits were mapped i n the epicardial border-zone of the infarcts with a multielectrode arr ay during sustained ventricular tachycardia induced by programmed stim ulation. During tachycardia, premature impulses were initiated by stim ulation at sites around and in the reentrant circuits, and their condu ction characteristics in the circuit were mapped. All circuits had a t emporal excitable gap in at least part oithe circuit, which allowed pr emature impulses to enter the circuit. Completely and partially excita ble segments of the temporal gap were identified by measuring conducti on velocity of the premature impulses; conduction was equal to the nat ive reentrant wave front in completely excitable regions and slower th an the reentrant wave front in partially excitable regions. In some ci rcuits, a temporal gap existed throughout the circuit, permitting the entire circuit to be reset over a range of premature premature couplin g intervals, although the size of the gap varied at different sites. I n other circuits, the gap became so small at local sites that even tho ugh premature impulses could enter the circuit, the circuit could not be reset. Premature impulses could terminate reentry in circuits that could be reset or not. We also found a significant spatial gap, which was identified by determining the distance between the head oithe circ ulating wave front, which could be located on the activation map, and its tail, which was the site most distal from the head as located by t he site of entry of the premature wave front into the circuit. The spa tial gap could also vary in different parts of the circuit. Therefore, nonuniform anisotropic reentrant circuits have both a temporal and sp atial excitable gap with fully and partially excitable components that change in different parts of the circuit.