Microwave Ablation of the Atrioventricular Junction in Vivo and Ventricular Myocardium in Vitro and in Vivo Effects of Varying Power and Duration on Lesion Volume

Abstract

Catheter ablation in ventricular tachycardia has achieved only limited success using direct current (DC) and radiofrequency (RF) energy, due to either high complication rates or a limited lesion size. Microwave energy represents a possible alternative source of energy for percutaneous ablation of the ventricular myocardium. However, an optimal method for titration of the dose of microwave energy to achieve the desired lesion volume has not yet been established. The safety and efficacy of microwave ablation of the atrioventricular (AV) junction were studied in 11 dogs in vivo. The relationship between lesion size following microwave ablation and the power output of or exposure duration to microwave energy was also examined at disparate sites in each superfused left ventricular epicardium in vitro. To observe the pathologic changes in the myocardium after microwave ablation, microwave ablation of the endocardium of the left ventricle was carried out in 9 dogs in vivo. Complete AV block was achieved in 10 of the above 11 dogs with a mean of 5 applications of microwave energy. The lesion volume in. vitro demonstrated a parallel increase with power (r=0.76) and duration (r=0.81). The mean lesion volume at 30 sec was: at 10W, 0.8±1.6; 20 W, 34.7±10.3; 30 W, 34.7122.4: 40 W, 64.7±64.4; 50 W, 87.2+42.3; 60 W, 85.8138.1; 70 W, 124.7136.5; 80 W, 134.2149.0 mm3. The mean lesion volume at 80 W was: at 15 sec, 32.6137.8; 30 sec, 101.2+46.4; 60 sec, 180.6+80.1; 120 sec, 291.8+122.7; and 180 sec, 459.31204.6 mm3. The ablated lesions showed discrete, homogeneous coagulation necrosis with sharp margins from the adjacent normal myocardium. Microwave energy may thus be more effective than RF energy, and have a lower risk of complications and arrythmogenesis than DC energy when used for ablation in ventricular tachycardia. (Jpn Heart J 35: 175–191, 1994). © 1994, International Heart Journal Association. All rights reserved.