Algorithm for differentiation of left and right posterior paraseptal accessory pathway.

We studied 196 consecutive patients with posterior paraseptal accessory pathway (AP); 124 showed manifest preexcitation and 72 were concealed AP. Successful ablation was obtained from left-sided approach in 134 patients (left posterior pasaseptal [LPS] group) and from right sided approach in 62 patients (right posterior paraseptal [RPS] group). A ventriculo-atrial (VA) interval of <50 ms recorded at LPS region (VA(LPS)) during right ventricular pacing identified 95 of the 134 patients (71%) with LPS AP with 100% specificity and positive predictive value.