Extracardiac ablation of the canine atrioventricular junction by use of high-intensity focused ultrasound

Background-High-intensity focused ultrasound has been applied to internal o rgans from outside the body to ablate tissue. No published study has assess ed the feasibility of ablating cardiac tissue within the beating heart by u se of this type of therapeutic ultrasound. The purpose of this study was to determine whether high-intensity focused ultrasound can be used to ablate the atrioventricular (AV) junction within the beating heart. Methods and Results-Ten dogs were anesthetized and underwent a thoracotomy. The heart was covered with a polyvinyl chloride membrane. The thorax above the membrane was perfused with degassed water, which functioned as a coupl ing medium for the ultrasound. A 7.0-MHz diagnostic ultrasound probe was af fixed to a spherically focused 1.4-MHz high-intensity focused ultrasound tr ansducer with a 1.1X8.3-mm focal zone 63.5 mm from the ablation transducer. The diagnostic ultrasound probe was calibrated such that the location of t he focal zone of the ablation transducer was identifiable on the 2-dimensio nal ultrasound image. Target sites were identified with the diagnostic ultr asound. The maximum ultrasound intensity for ablation (2.8 kW/cm(2)) was de livered to the AV junction only during electrical diastole and for a total of 30 seconds. Complete AV block was achieved in each of the 10 dogs with 6 .5+/-5.6 (range, 3 to 21) 30-second applications of therapeutic ultrasound. Gross inspection showed that the mean lesion volume was 124+/-43 mm(3), wi th a depth of 6.7=/-3.6 mm, a length of 5.7+/-2.5 mm, and a width of 4.7+/- 1.8 mm, Four hours after the dogs were killed, histopathological study demo nstrated a well-demarcated area of necrosis and early inflammation. Conclusions-High-intensity focused ultrasound produces well-demarcated lesi ons and appears to be a feasible energy source to create complete AV block within the beating heart without damaging the overlying or underlying cardi ac tissue. This energy source may allow for a noninvasive approach to ablat ion of cardiac arrhythmias.