Extracardiac Ablation of the Canine Atrioventricular Junction by Use of High-Intensity Focused Ultrasound

Abstract

Background-High-intensity focused ultrasound has been applied to internal organs from outside the body to ablate tissue.No published study has assessed the feasibility of ablating cardiac tissue within the beating heart by use 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 coupling medium for the ultrasound. A 7.0-MHz diagnostic ultrasound probe was affixed to a spherically focused 1.4-MHz high-intensity focused ultrasound transducer with a 1.1ϫ8.3-mm focal zone 63.5 mm from the ablation transducer. The diagnostic ultrasound probe was calibrated such that the location of the focal zone of the ablation transducer was identifiable on the 2-dimensional ultrasound image. Target sites were identified with the diagnostic ultrasound. The maximum ultrasound intensity for ablation (2.8 kW/cm 2 ) was delivered 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 6.5Ϯ5.6 (range, 3 to 21) 30-second applications of therapeutic ultrasound. Gross inspection showed that the mean lesion volume was 124Ϯ143 mm 3 , with a depth of 6.7Ϯ3.6 mm, a length of 5.7Ϯ2.5 mm, and a width of 4.7Ϯ1.8 mm. Four hours after the dogs were killed, histopathological study demonstrated a well-demarcated area of necrosis and early inflammation. Conclusions-High-intensity focused ultrasound produces well-demarcated lesions and appears to be a feasible energy source to create complete AV block within the beating heart without damaging the overlying or underlying cardiac tissue. This energy source may allow for a noninvasive approach to ablation of cardiac arrhythmias. (Circulation. 1999;100:203-208.)

Computer-Aided Automatic Delivery System of High-Intensity Focused Ultrasound for Creation of an Atrial Septal Defect

“…HIFU also enables us to create defects in cardiac tissues such as ventricles or cusp of the aortic valve in vitro or ex vivo (Otsuka et al, 2005;Fujikura et al, 2006;Lee et al, 2000;Xu et al, 2004;Strickberger et al, 1999). Particularly in fetal cardiac intervention, less invasiveness of HIFU is effective for the mother as well.…”

“…There is a reported study to try the treatment of arrhythmias using the HIFU delivery triggered by ECG (Strickberger et al, 1999). However, it is difficult to isolate only ECG of fetus from a maternal ECG definitely although fetal ECG monitoring is technically quite demanding because ECG of fetus is obtained only through the mother.…”

Heart ablation using a planar rectangular high intensity ultrasound transducer and MRI guidance

“…Furthermore, in contrast to radiofrequency (RF) waves, therapeutic ultrasound does not require direct contact with target tissue. The use of therapeutic ultrasound to create focal, ablative lesions in the heart has been reported in experimental models [17][18][19].…”

“…Several studies have examined the histological changes related to therapeutic ultrasound ablation in various tissues [20,19,21,22,18,[23][24][25][26][27].…”

“…Therapeutic ultrasound has been used in various in vivo models for heart applications: Strickberger et al in 1999 [18], carried out a study to determine whether therapeutic ultrasound can be used to ablate the atrioventricular (AV) junction within the beating heart. Their study suggested that therapeutic ultrasound produced well-demarcated lesions and appears to be a feasible energy source to create complete AV block within the beating heart without damaging the overlying or underlying cardiac tissue.…”