Figure 4:  .

(A) Schematic drawing of the posterior or "slow pathway" approach to catheter ablation of atrioventricular nodal re-entrant tachycardia (AVNRT). The ablation catheter is positioned anterior to the coronary sinus os. A schematic drawing of the hypothesised re-entrant circuit for AVNRT is also shown. (B) The electrogram of a successful slow pathway ablation site. Also shown are surface leads 1 and V6 and intracardiac recordings obtained from the right atrium, the right ventricle, and the electrode catheter positioned to record a His bundle. The intracardiac electrogram at the ablation site reveals a ventricular electrogram substantially larger than the atrial electrogram, and a distinct deflection consistent with a slow pathway potential immediately after the atrial electrogram. The arrow points to a slow pathway potential.