Feasibility of Catheter Cryoablation in Normal Ventricular Myocardium and Healed Myocardial Infarction

Although novel cryoablation systems have recently been introduced into clinical practice for catheter ablation of supraventricular tachycardia, the feasibility of catheter cryoablation of VT is unknown. Thus, the present study evaluates catheter cryoablation of the ventricular myocardium (1) in healthy sheep and (2) of VT in chronic myocardial infarction (MI). In three healthy sheep, 21 ventricular lesions (12 left and 9 right ventricle) were created with a catheter cryoablation system. Different freeze/thaw characteristics were used for lesion creation. The mean nadir temperature was -84.1 degrees C +/- 0.9 degrees C, mean lesion volume was 175.8 +/- 170.3 mm3, and 5 of 21 lesions were transmural. Lesion dimensions were 7.5 +/- 3.1 mm (width) and 4.2 +/- 2.5 mm (depth). Left ventricular lesions were significantly larger than right ventricular lesions (262 +/- 166 vs 60.5 +/- 91.6 mm3, P=0.0025). There was no difference in lesion volume with respect to different freeze/thaw characteristics. Anatomically (n=3) or electrophysiologically (n=3) guided catheter cryoablation was attempted in six sheep 105 +/- 56 days after MI, three of six animals had reproducibly inducible VT with a mean cycle length of 215 +/- 34 ms prior to ablation. In these animals, five VTs were targeted for ablation. A mean of 6 +/- 3 applications for nine left ventricular lesions were applied, six of nine lesions were transmural. The mean lesion volume was 501 +/- 424 mm3. No VT was inducible in two of three animals after cryoablation using an identical stimulation protocol. Therefore, catheter cryoablation of VT in healed MI is feasible, and no acute complications were observed.