Scientific Data

Boston Symposium Atrial Fibrillation 2008
Boston, MA
Presented by Patrick Maguire, MD

Non-invasive Radiosurgical Ablation of the Myocardium: Pre Clinical Electrophysiology and Histology

P. Maguire, M.D., Ph.D, A. Sharma, M.D., T.J. Fogarty, M.D., Thilaka Sumanaweera, Ph.D, A. Jack.

Objectives: Current ablative treatments for cardiac arrhythmias involve invasive catheter based approaches. The purpose of this study was to determine whether current non-invasive radiosurgical ablation could be applied to effect electrical conduction block 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 signals in the area of the pulmonary veins. The target volume was irradiated in a single isocentric fraction prescribed at 40 Gy to the 80% isodose line. 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 (present pre-treatment). No secondary arrhythmias were observed. Histology revealed focal fibrosis of muscle and calcified material confined to discrete areas of treatment, indicative of tissue injury at 6 months. Other preclinical studies have documented the ability to target and treat the cavotricuspid isthmus and the AV node. Conduction block has been demonstrated. Targeting is refined with the understanding of cardiac motion.

Conclusion: Non-invasive 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 ablation.