HIGH-RESOLUTION MAPPING OF KOCH TRIANGLE USING 60 ELECTRODES IN HUMANS WITH ATRIOVENTRICULAR JUNCTIONAL (AV NODAL) REENTRANT TACHYCARDIA

Background. Recent evidence suggests that atrioventricular junctional reentrant tachycardia (AVJRT) uses a reentrant -circuit that involves the atrioventricular (AV) node, the atrionodal connections, and perino dal atrial tissue. Electrogram morphology has been used to target the delivery of radiofrequency energy to the site of the ''slow pathway,'' a component of this reentrant circuit. The aim of this study was to l ocalize precisely the sites of atrionodal connections involved in AVJR T and to examine atrial electrogram morphologies and their spatial dis tribution over Koch's triangle. Methods and Results. Electrical activa tion of Koch's triangle and the proximal coronary sinus was examined i n 13 patients using a 60-point plaque electrode and computerized mappi ng system. Recordings were made during sinus rhythm (n=12), left atria l pacing (n=8), ventricular pacing (n=12), and AVJRT (n=12). During si nus rhythm electrical activation approached Koch's triangle and the AV node from the direction of the anterior limbus, activating the anteri or part of the triangle before the posterior part. A zone of slow cond uction during sinus rhythm was found within Koch's triangle in 64% of patients. The pattern of atrial activation in Koch's triangle during a nterograde fast pathway conduction was similar to that seen during ant erograde slow pathway conduction. Retrograde fast pathway conduction d uring ventricular pacing and during anterior (typical) AVJRT caused ea rliest atrial activation at the apex of Koch's triangle near the AV no de-His bundle junction. In individual patients the site of earliest at rial activation was similar for both anterior AVJRT and retrograde fas t pathway conduction during ventricular pacing. Retrograde slow pathwa y conduction during ventricular pacing and during posterior (uncommon or atypical) AVJRT caused earliest atrial activation posterior to the AV node near the orifice of the coronary sinus. This posterior or ''sl ow pathway'' exit site was 15+/-4 mm from the His bundle. In individua l patients the site of earliest atrial activation was similar for both posterior AVJRT and retrograde slow pathway conduction during ventric ular pacing. In one patient anterograde and retrograde conduction occu rred via separate slow pathways during AVJRT. Complex atrial electrogr ams with two or more components were observed near the, coronary sinus orifice and in the posterior part of Koch's triangle in all cases. Th ese were categorized as either low or high frequency potentials accord ing to the rapidity of the second component of the electrogram. Low fr equency potentials were present at the site of earliest atrial excitat ion during retrograde slow pathway conduction in 5 of 5 cases (100%) a nd high frequency potentials in 4 of 5 cases (80%). However, both slow and high frequency potentials could be found at sites up to 16 mm fro m the site of earliest atrial excitation. Conclusions. At least two di stinct groups of atrionodal connections exist. The site of earliest at rial activation during anterior AVJRT is similar to that of fast pathw ay conduction during ventricular pacing. This site is close to the His bundle-AV node junction. The site of earliest atrial activation durin g posterior AVJRT is similar to that of slow pathway conduction during ventricular pacing. This site is near the coronary sinus orifice, app roximately 15 mm from the His bundle. The anterograde slow pathway app ears to be different from the retrograde slow pathway in some patients . Double atrial electrograms are an imprecise guide to the site of ear liest atrial excitation during retrograde slow pathway conduction.