977-75 Variations in the Termination of Atrial Flutter by Premature Beats. Studies in the Sterile Pericarditis Model

Abstract

Variations and incidence of atrial flutter (AFL) termination by single premature beats were evaluated in 26 dogs of the sterile pericarditis model. Single premature beats were introduced during stable AFL at 4 different sites in the AFL reentrant circuit, 2 at areas of slow conduction (ASC sites) and 2 at sites distant from the ASC (distant sites). The coupling interval of delivered premature beats was decremented by 2 ms from the AFL cycle length until AFL termination or local refractoriness was achieved. A multiplexing system was used to record 190 unipolar electrograms from an electrode array placed on the right atrial free wall during AFL. AFL was interrupted by a single premature beat in 38/52 episodes when pacing at distant sites, and in 7/52 episodes when pacing at ASC sites (p < 0.0001). AFL termination was always associated with block of the activation wave front of the premature beat in an ASC. Of the 38 episodes of AFL termination by a premature beat introduced at distant sites, sinus rhythm directly followed in 27 episodes (71%), and an extra non AFL reentrant beat proceded sinus rhythm in 8 episodes (21%). In these 35 episodes (92%), block of the activation wave front of the premature beat was always total block, and no degeneration in the reentrant circuit was observed. In the remaining 3/38 episodes (8%), block of the activation wave front of the premature beat in an ASC was partial block, so that the central line of block of the reentrant circuit was prolonged, resulting in degeneration of the reentrant circuit. Of the 7 episodes of AFL termination by a premature beat introduced at ASC sites, sinus rhythm directly followed in all episodes (100%). In the canine sterile model of AFL: 1) AFL termination by single premature beats was always associated with block of the activation wave front of the premature beat in an ASC; 2) a higher incidence of AFL termination by single premature beats was achieved at distant sites than ASC sites, indicating that not only the coupling interval of the premature beat, but also the direction of the activation wave front plays an important role to cause block in an ASC; 3) AFL termination directly followed by sinus rhythm was most commonly observed during AFL termination by a premature beat; and 4) degeneration in the AFL reentrant circuit associated with an introduction of premature beat was observed in only 8% when paced at distant sites, and 0% when paced at ASC sites.