High resistance of atrioventricular node to cryoablation: A great safety margin targeting perinodal arrhythmic substrates

Abstract

Findings from animal studies and small series of patients support the greater safety of cryoenergy over radiofrequency in the ablation of arrhythmic substrates near the AV node. The purpose of this study was to systematically evaluate the electrophysiologic effects of successive cryoenergy applications to the human AV node in order to better define the safety margin of cryothermal ablation. In 15 patients referred for AV nodal ablation, 94 cryomapping and 105 cryoablation applications were delivered through a 6-mm-tip cryothermal ablation catheter (Freezor Xtra, CryoCath) at predefined sites of the triangle of Koch. Temporary effects on AV conduction were observed in 18 (19%) cryomapping and 38 (36%) cryoablation applications. Persistent effects were observed in 9 (9%) cryoablation applications. Persistent effects were associated with cryoablation at the superior third of the triangle of Koch (P = .05), nadir tip temperature < or = -79 degrees C (P = .007), and effect onset time < or =15 seconds (P = .03). Temperature and effect onset time remained statistically significant after multivariate adjustment (P = .01 and .02, respectively). Overall, persistent complete AV block was achieved with cryoenergy in only one patient. In two additional patients, AV conduction remained modified. In the remaining patients, persistent complete AV block was achieved with radiofrequency (median one application per patient). The low rate of persistent AV conduction impairment observed with attempts to cryoablate the AV node supports a great safety margin of perinodal cryothermal ablation.