Localization of the ventricular insertion site of concealed left-sided accessory pathways using ventricular pace mapping.

The aim of the present study was to localize the ventricular insertion site of concealed accessory pathway (APs) by using the ventricular pace mapping and examined if the analysis of the timing of retrograde atrial electrogram recorded at the ventricular side of the mitral annulus is useful in identifying the ventricular insertion site of the AP. In 39 patients with concealed left-sided APs, ventricular pacing was delivered along the mitral annulus at a cycle length of 500 ms while measuring the conduction interval from the pacing stimulus to the earliest retrograde atrial electrogram recorded in the coronary sinus (St-A). The ventricular insertion site of the AP was localized by identifying the shortest St-A. Also the interval between the onsets of QRS and atrial electrograms (QRS-A) and presence of continuous electrical activity (CEA) between the ventricular and atrial electrograms were evaluated at each mapping site during atrioventricular reciprocating tachycardia. Initial radiofrequency energy application to the site with the shortest St-A (46 +/- 15 ms) eliminated the AP conduction in all patients, suggesting the accurate localization of the ventricular insertion site by ventricular pace mapping. The QRS-A and the percentage of the presence of CEA at the shortest St-A site were 79 +/- 19 ms and 64%, respectively. However, the earliest retrograde atrial activation site did not coincide with the shortest St-A site in 19 of 39 patients, suggesting an oblique course of AP. Thus, in these 19 patients, there was a significant difference in St-A (47 +/- 16 vs 59 +/- 15 ms, P < 0.0001), QRS-A (83 +/- 13 vs 72 +/- 12 ms, P < 0.0001) and the presence of CEA (32 vs 74%, P < 0.01) between the shortest St-A site and the earliest retrograde atrial activation site, respectively. These indicate that the earliest retrograde atrial activation is not necessarily indicative of the ventricular insertion site of AP. However, ventricular pace mapping was considered to be useful for identifying and ablating the ventricular insertion site of AP, irrespective of the course of AP.