Lower incidence of thrombus formation with cryoenergy versus radiofrequency catheter ablation.

Background: Radiofrequency (RF) catheter ablation is limited by thromboembolic complications. The objective of this study was to compare the incidence and characteristics of thrombi complicating RF and cryoenergy ablation, a novel technology for the catheter-based treatment of arrhythmias.
Methods and Results: Ablation lesions (n=197) were performed in 22 mongrel dogs at right atrial, right ventricular, and left ventricular sites preselected by a randomized factorial design devised to compare RF ablation with cryocatheter configurations of varying sizes (7F and 9F), cooling rates (-1 degrees C/s, -5 degrees C/s, and -20 degrees C/s) and target temperatures (-55 degrees C and -75 degrees C). Animals were pretreated with acetylsalicylic acid and received intraprocedural intravenous unfractionated heparin. Seven days after ablation, the incidence of thrombus formation was significantly higher with RF than with cryoablation (75.8% versus 30.1%, P=0.0005). In a multiple regression model, RF energy remained an independent predictor of thrombus formation compared with cryoenergy (OR, 5.6; 95% CI, 1.7, 18.1; P=0.0042). Thrombus volume was also significantly greater with RF than with cryoablation (median, 2.8 versus 0.0 mm3; P<0.0001). More voluminous thrombi were associated with larger RF lesions, but cryolesion dimensions were not predictive of thrombus size.
Conclusions: RF energy is significantly more thrombogenic than cryoenergy, with a higher incidence of thrombus formation and larger thrombus volumes. The extent of hyperthermic tissue injury is positively correlated with thrombus bulk, whereas cryoenergy lesion size does not predict thrombus volume, most likely reflecting intact tissue ultrastructure with endothelial cell preservation.