Figure 1.

Patient 1. HD Grid (Abbott Laboratories, Abbott Park, IL) local activation timing map is depicted while mapping in sustained orthodromic atrioventricular tachycardia for this para-Hisian accessory pathway. The HD Grid is positioned at the accessory pathway and near the location of initial successful ablation lesion (green dot), which was slightly superior to the His bundle (yellow dots). The intracardiac electrograms from the HD Grid are shown on the right. CS = coronary sinus; IVC = inferior vena cava; RV = right ventricle; SVC = superior vena cava.