Transcatheter cryoablation of ventricular myocardium in dogs

Introduction: Surgical cryoablation, a highly effective technique used duri ng antiarrhythmic surgery, produces voluminous, histologically uniform and discreet myocardial lesions. In contrast, radiofrequency (RF) catheter abla tion, which as a result of its less invasive nature has largely supplanted antiarrhythmic surgery, produces smaller, histologically heterogeneous myoc ardial lesions. Since small lesion size and heterogeneity may reduce antiar rhythmic efficacy, we sought to reproduce the large, histologically homogen eous lesions created by surgical cryoablation, using a catheter cryoablatio n system (Cryogen, Inc., San Diego, CA) in the canine ventricle. Methods and Results: In seven dogs, nineteen ventricular lesions (two right and seventeen left) were created with a 10F cryoablation catheter with eit her a 2 or 6 mm tip. In one dog AV node ablation was also performed. For ea ch 'freeze', catheter tip nadir temperature, lesion width, depth, and trans murality were recorded, and lesion volume calculated. Average tip nadir tem perature was -79.6 +/-4.9 degreesC. Cooler nadir tip temperature was associ ated with deeper (p=.007) and more voluminous lesions (p=.042), and a great er likelihood of lesion transmurality (p=.034). Average lesion volume was 5 00 +/- 356 mm(3). No other variables predicted lesion volume or transmurali ty. Histologically, the catheter cryoablation lesions were sharply demarcat ed and homogeneous. The single freeze performed at the AV junction produced complete AV block. One complication, catheter rupture following its repeti tive use, resulted in a coronary air embolus and death. Conclusion: Catheter cryoablation of canine ventricular myocardium produced voluminous, discrete, transmural lesions, which might be effective for abl ation of ventricular tachycardia. Lesion volume and transmurality were depe ndent on catheter tip nadir temperature.