STIMULATION OF THE SUMMIT OF THE RIGHT VENTRICULAR ASPECT OF THE VENTRICULAR SEPTUM DURING ORTHODROMIC ATRIOVENTRICULAR REENTRANT TACHYCARDIA

Application of ventricular premature complexes (VPCs) from the right ventricular (RV) apex during orthodromic atrioventricular (AV) reentrant tachycardia has limitations both in the ability to shorten the succeeding atrial cycle length and in helping to identify accessory pathway location. Stimulation from the summit of the RV aspect of the septum during " reentrant tachycardia was investigated as a new technique to improve the diagnostic utility of applying VPCs during AV reentrant tachycardia. VPCs were induced during AV reentrant tachycardia at 10 ms decrements in patients with left free wall (n = 15), posteroseptal (n = S), and right free wall (n = 3) accessory pathways from the RV apex and then from the summit of the RV septum. When the His was refractory, shortening of the atrial cycle length was noted in 13% of patients with left free wall pathways, in 60% of patients with posteroseptal pathways, and in 100% of patients with right free wall pathways with VPCs from the RV apex, and in 47, 100 and 100%, respectively, with VPCs from the summit of the septum. When all VPCs were considered, there was a significant shortening of the atrial cycle length in 67% of patients with left free wall pathways when stimulated from the RV apex, which increased to 93% with summit stimulation. An extrastimulus applied on or after the His effected a significant shortening of the atrial cycle length in no patients with left free wall pathways. The mean maximal shortening of the atrial cycle length when the His was refractory was 4 +/- 11 and 9 +/- 13 ms for left free wall pathways, 29 +/- 30 and 40 +/- 11 ms for posteroseptal pathways, and 35 +/- 15 and 53 +/- 35 ms for right free wall accessory pathway from the apex (p = 0.006) and summit (p = 0.0002), respectively. Stimulation of the summit of the RV septum improves the ability of VPCs to shorten the atrial cycle length during " reentrant tachycardia.