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 ventriculoatrial (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. In the 101 patients with VA _LPS ≥50 ms, a difference in VA interval of <20 ms recorded at the His bundle region and LPS region, ΔVA(H-_LPS), during right ventricular pacing predicted RPS AP with a sensitivity of 97%, a specificity of 85% and a positive predictive value of 91%. When these 2 parameters were used together for prediction of LPS or RPS AP, the sensitivity, specificity, and positive predictive value were 96%, 97%, and 98% for LPS AP, and 97%, 96%, and 91% for RPS AP, respectively. This simple new algorithm using VALps and ΔVA (H-_LPS) during right ventricular pacing successfully discriminates LPS and RPS AP with high sensitivity, specificity, and positive predictive value and could facilitate radiofrequency ablation in patients with posterior paraseptal AP.