Duration of the A(H)-A(Md) interval predicts occurrence of AV-block after radiofrequency ablation of the slow pathway.

Purpose: Modification of the slow pathway (SP) of the atrio-ventricular node by radiofrequency ablation is the most effective treatment to cure AV nodal reentry tachycardia (AVNRT). However, this therapy may be complicated by AV-block (AVB). We sought to evaluate the predictive value of the A(H)-A(Md) interval-the electrical delay between atrial signals on the His- and the ablation-catheter-upon development of AVB during SP ablation.

Methods: The associations between A(H)-A(Md) interval, occurrence of ventriculo-atrial block (VAB) during junctional activity (JA) and transient or permanent AVB were analyzed retrospectively for 1585 RF applications at the SP in 393 patients diagnosed with AVNRT. The value of A(H)-A(Md) was further tested prospectively in 118 AVNRT patients, who were only ablated at targets with intervals >20 ms.

Results: Forty-six RF deliveries resulted in transient or permanent AV-conduction disturbances. Shorter A(H)-A(Md) intervals were associated with the occurrence of VAB during JA (p < 0.001) and AVB (p < 0.001). A(H)-A(Md) was the strongest predictor for VAB or AVB in multivariate regression analyses, followed by the radiological distance between the catheters. In the prospective study, permanent high-degree AVB was not observed when the A(H)-A(Md) at the ablation site was >20 ms.

Conclusion: The A(H)-A(Md) interval is a better predictor for occurrence of conduction block during ablation for AVNRT than the radiological distance between the His- and the ablation-catheter. The risk of permanent AVB can be minimized, if only sites with an A(H)-A(Md) longer than 20 ms are targeted for ablation.