977-70 Spiral Wave of Excitation as a Mechanism of Functional Reentry in the Isolated Atrium. A New Model of Atrial Reentry

BackgroundFunctional reentrant excitation in atrial tissue (i.e., reentry with no central anatomical obstacle) was proposed to be caused by the “leading circle” mechanisms (Allessie's model). According to this concept, there is no excitable gap and the central core of functional conduction block (FCB) results from continuous centripetal invasion of wavefronts that prevent the cells in the core to recover.HypothesisThe mechanism of functional reentry in atrial tissue is caused by a spiral wave with an excitable gap and a central core of FCB caused by the steep curvature of the spiral wave tip.MethodsBlocks of 3.0 by 4.0cm of canine left and right atrial tissues (N=3) were mounted in a tissue bath with endocardial surface up and reentrant activity initiated by premature stimulation and/or by rapid pacing and acetylcholine (10-6 to 10-5M). Isochronal activation maps of the induced reentrant excitation were constructed using 512 bipolar electrodes with 1.6mm interelectrode distance and were also displayed dynamically on the computer screen to visualize the pattern of activation.ResultsTen episodes of both nonsustained and sustained atrial reentry was induced and mapped. The induced reentrant activity was clearly a spiral wave with a rotation period of 184±74 (110 to 350) msec and rotating in a counterclockwise direction in all. The area of FCB in the central core of the spiral wave was caused by the steep curvature of the tip of the spiral wave that was excitable during regular pacing but not excited during the spiral wave activity. Spiral wave activity could be terminated by electrical stimulation indicating the presence of an excitable gap.ConclusionFunctional reentry in normal atrial tissue is caused by a spiral wave of excitation with an excitable gap