Background: Many ablative approaches in or near the orifice of the pulmonary vein (PV) have demonstrated success in eliminating atrial fibrillation. Despite current practice, there are no data regarding the in vivo efficacy and safety of an 8-mm catheter tip for ablation at the PV orifice.
Methods and results: Ten mongrel dogs were studied. Thermocouples were implanted in the atrial muscle of the PV orifice. Intracardiac echocardiography monitored catheter position, tip/tissue orientation, and microbubble formation. Ninety-four ablations were performed for 120 seconds. A temperature discrepancy >10 degrees C between the catheter tip and tissue occurred during 47 (50%) of the ablations. Despite termination of energy delivery, the average tissue temperature remained within 1 degrees C of the achieved steady state for 9 seconds. A temperature discrepancy >10 degrees C was more common in the right superior PV, with oblique catheter positioning, when tissue temperatures were >60 degrees C or 80 degrees C, and with type 1 or type 2 microbubble formation. However, microbubbles were not present in 7 (13%, type 1) and 10 (40%, type 2) ablations with tissue temperatures >80 degrees C. The maximum tissue temperature achieved with non-full-thickness lesions was 47.3+/-7.4 degrees C vs 75.9+/-11.7 degrees C (P<0.0001) for full-thickness lesions.
Conclusions: Marked discrepancies between catheter-tip and tissue temperatures occurred with higher temperatures, prolonged ablation times, and unfavorable catheter thermistor-tissue contact. Also, these data suggest a conservative approach to atrial ablation, because full-thickness lesions were obtained when tissue temperatures reached 50 degrees C to 60 degrees C and the tissue retained high heat levels despite termination of radiofrequency energy. Finally, microbubbles are inconsistent markers of tissue overheating.