Scientific Data

HRS 2008
San Francisco, CA
AB32-3, pg. S67; May 14-17, 2008

Non-Invasive Approach to Myocardial Ablation: Pathology of Stereotactic Robot Targeted High Energy X-ray Lesions at Potential Arrhythmia Sites

Arjun D. Sharma, MD, Patrick Maguire, M.D., Luis Fajardo, M.D., Douglas Wong, M.D., Thilaka Sumanaweera, PhD and Thomas Fogarty, M.D.

Introduction: We have demonstrated the feasibility of delivering precise doses of radiation to the myocardium at sites relevant to arrhythmias. In this study we correlated the electrophysiologic post ablation findings with histology, at the ablation site and in adjacent areas of the myocardium. The pathology of discrete x-ray radiation induced cardiac lesions has not been previously described.

Methods: Hanford-Sinclair mini swine were used. The non-invasive external beam stereotactic radiosurgery(x-beam, 40-70 Gy) was targeted at the left pulmonary vein ostium, left atrial appendage, or tricuspid valve-IVC isthmus using the Cyberknife (computer controlled robotic arm, directing a linear accelerator). Targeting was done using 64 slice CT scan and fiducials with cardiac and respiratory motion compensation. 8 to 14 weeks following treatment the animals were restudied. The target chamber was mapped pre and post-treatment with CARTO (J&J Biosense). Left ventricular function was assessed by echocardiography. Pathology specimens were taken from the ablation target, as well as surrounding critical structures in the heart.

Results: Pathology at targets show discrete areas of (1-2 cm) fibrosis. Some arteriolar obliteration and inflammation is seen within the ablation zone, but not in surrounding areas. The effect is limited to 1-2 cm in diameter, and shows an abrupt transition zone (2mm), and then normal myocardium. These findings were seen in the cavotricuspid isthmus, left atrial appendage and pulmonary vein ostia. Other areas of the myocardium sampled show no radiation ablation effect. Major epicardial coronary arteries near the ablation lesion demonstrate no radiation pathology.

Conclusions: Roboticly controlled radiation with motion compensation can accurately target the heart, and produce discrete lesions at planned sites where electrophysiologic changes were observed, but spare remote cardiac locations. This is in contrast to inadvertent cardiac exposure during therapeutic radiation. Longer term follow up is planned to look for any potential late effects of ablation.