Acute and chronic effects of cryoablation of the pulmonary veins in the dog as a potential treatment for focal atrial fibrillation

Background: Atrial fibrillation (AF) may be triggered by premature atrial depolarizations originating in the pulmonary veins (PV). Radiofrequency catheter ablation of PV foci may prevent recurrence of AF, but may cause PV stenosis. Therefore, a safer method for ablation of PV foci is needed. This study evaluated the acute and chronic effects of PV ablation using a cryocatheter ablation (CCA) system, which may be less likely to cause PV stenosis. Methods: CCA was performed by freezing for 5 minutes or more in one or more PVs in 10 anesthetized dogs. Pacing threshold and vessel diameter were measured before and after PV cryoablation. All dogs were restudied at 4.0 +/- 1.64 months (range 2-7) in a manner identical to baseline. Results: CCA was performed in 27 PVs (range 1-4/dog), with a mean freeze time of 8.62 +/- 5.42 minutes per vein (range 5.23-22.06). Mean temperature for all freezes was -65 +/- 5.3degreesC. Mean PV diameter was 6.49 +/- 1.73 vs 6.24 +/- 1.83 mm (p = NS) and mean pacing threshold 1.32 +/- 0.75 vs 9.36 +/- 5.93 mA (p < .01), before vs. acutely after ablation. At followup, at the ablation sites PV diameter (7.02 +/- 1.88 mm) was unchanged from baseline, whereas pacing threshold remained elevated (2.54 +/- 1.44 mA, p < .05 vs baseline). There were no acute or long-term complications. Conclusions: (1) CCA of PVs produced a significant rise in acute and chronic pacing threshold indicating loss of atrial conductivity. (2) CCA of PVs did not cause PV stenosis or other complications. (3) The data suggest that CCA of PVs may be a safe and effective method for treating focal AF.