PREDICTION OF ATRIOVENTRICULAR-BLOCK DURING RADIOFREQUENCY ABLATION OF THE SLOW PATHWAY OF THE ATRIOVENTRICULAR NODE

Background Selective radiofrequency (RF) ablation of the slow pathway is an effective treatment for atrioventricular (AV) nodal reentry tach ycardia. A previous report showed that rapid junctional tachycardia (J T) caused by RF associated with loss of ventriculoatrial (VA) conducti on is related to increased risk for AV block. However; this can be dif ficult to detect during energy delivery, and more importantly, it cann ot be measured before the onset of RF energy delivery. The aim of our study was to determine whether measurements made from electrograms cou ld be used to predict the risk of AV block before RF energy is deliver ed. Methods and Results Fifty-eight patients underwent 63 selective sl ow pathway RF ablation procedures. In 46 (26.9%) of 172 JTs caused by RF, VA block was observed, and in 11 this was followed by AV block of various degrees. Electrograms before each application of RF were analy zed for the interval between the atrial signals in the His bundle cath eter and in the distal mapping catheter [A(H)-A(Md)], the interval bet ween the atrial signals in the His bundle catheter and in the proximal coronary sinus catheter [A(H)-A(CS)], the AV ratio, and the presence of a slow pathway potential or a fractionated atrial signal in the dis tal mapping catheter. Mean cycle length (CL) of JT was calculated if i t consisted of at least 10 beats. These parameters were compared betwe en patients with JT who developed VA block and subsequent AV block (gr oup 1), patients with JT and VA block but without subsequent AV block (group 2), and patients with JT without VA block (group 3). The A(H)-A (Md) interval was significantly shorter in group 1 (17+/-8 ms) than in groups 2 (33+/-8 ms, P<.001) and 3 (32+/-10 ms, P<.001), whereas the A(H)-A(Md) intervals of groups 2 and 3 did not differ from each other. CL of JT, A(H)-A(CS) interval, AV ratio, presence of a slow pathway p otential, or a fractionated atrial electrogram were not related to the occurrence of AV block. Conclusions The A(H)-A(Md) interval provides an electrophysiological marker that can be used in addition to the rad iological catheter position to assess the risk for AV block before ons et of RF delivery. CL of JT and occurrence of VA block are not related to the risk of AV block.