Transcatheter cryoablation of ventricular myocardium in dogs

Surgical cryoablation, a highly effective technique used during antiarrhythmic surgery, produces voluminous, histologically uniform and discreet myocardial lesions. In contrast, radiofrequency (RF) catheter ablation, which as a result of its less invasive nature has largely supplanted antiarrhythmic surgery, produces smaller, histologically heterogeneous myocardial lesions. Since small lesion size and heterogeneity may reduce antiarrhythmic efficacy, we sought to reproduce the large, histologically homogeneous lesions created by surgical cryoablation, using a catheter cryoablation system (Cryogen, Inc., San Diego, CA) in the canine ventricle.

In seven dogs, nineteen ventricular lesions (two right and seventeen left) were created with a 10F cryoablation catheter with either a 2 or 6 mm tip. In one dog AV node ablation was also performed. For each 'freeze', catheter tip nadir temperature, lesion width, depth, and transmurality were recorded, and lesion volume calculated. Average tip nadir temperature was -79.6+/-4.9 degrees C. Cooler nadir tip temperature was associated with deeper (p=.007) and more voluminous lesions (p=.042), and a greater likelihood of lesion transmurality (p=.034). Average lesion volume was 500+/-356 mm(3). No other variables predicted lesion volume or transmurality. Histologically, the catheter cryoablation lesions were sharply demarcated and homogeneous. The single freeze performed at the AV junction produced complete AV block. One complication, catheter rupture following its repetitive use, resulted in a coronary air embolus and death.

Catheter cryoablation of canine ventricular myocardium produced voluminous, discrete, transmural lesions, which might be effective for ablation of ventricular tachycardia. Lesion volume and transmurality were dependent on catheter tip nadir temperature.