Scientific Data

Accuray Users Meeting 2008
Presented by Douglas Wong, MD

CyberKnife Radiosurgical Ablation of the Myocardium: Pre Clinical Confirmation of Blocked Electrical Conductivity in the Left Atrium

D. Wong, M.D., Ph.D, M.P.H., G. Weidlich, Ph.D., A. Sharma, M.D., J. Adler, M.D., T.J. Fogarty, M.D., P. Maguire, M.D., Ph.D., A. Jack, Community Regional Medical Center, Fresno, California and CyberHeart Incorporated, Menlo Park, California

Objective: Current ablative treatments for cardiac arrhythmias involve invasive catheter based approaches. The purpose of this study was to determine whether current CyberKnife technologies could be applied to block electrical conduction at the left pulmonary veins.

Methods: A healthy Hanford pig was studied. A fiducial was placed between the left superior and left inferior pulmonary veins. Baseline 3-dimensional electroanatomic mapping (CARTO) confirmed good voltage in the area of the pulmonary veins. The MultiPlan System (versions 1.4 and 1.5.1) was used to contour the area of interest (left pulmonary veins) and to derive optimal treatment plans. The target volume was irradiated in a single isocentric fraction prescribed at 40 Gy to the 80% isodose line. Treatment was delivered on a G-4 CyberKnife radiosurgical system with Synchrony image guidance. The animal was euthanized 196 days after treatment. Just prior to euthanasia, inter-atrial electrophysiologic recordings and 3-dimensional electroanatomic mapping (CARTO) were performed. Histologic evaluation of the heart and contiguous organs (esophagus, trachea, aorta, and lungs) were also performed.

Results: No adverse events were observed in the animal studied at 6 months. The animal gained 80 pounds. Electrophysiologic mapping revealed decreased voltage potentials in the target area treated surrounding the pulmonary veins and no electrical signal at the ostia of the pulmonary veins. No secondary arrhythmias were observed. Histology revealed focal fibrosis of muscle and calcified material confined to areas of treatment indicative of tissue injury at 6 months.

Conclusions: Radiosurgery with CyberKnife can be used to target and ablate the left superior and inferior pulmonary veins without detrimental effects. At 6 months decreased or no conduction potentials were observed at the target site, with histology confirming myocardial injury. Further study into the application of radiosurgery for the treatment of cardiac arrhythmias is warranted.