Scientific Data

HRS 2007
Denver, CO
Presented by Arjun Sharma, MD Heart Rhythm. AB31-5, pg S68; May 9-12, 2007

New Non-invasive Therapy for Cardiac Arrhythmias using Stereotactic Radiosurgery: Initial Feasibility Testing

Arjun Sharma, MD, Patrick Maguire, MD, Douglas Wong, MD, Thilaka Sumanaweera, PhD, James Steele, DVM, Philip Peterson, BS, Louis Fajardo, MD, Patricia Takeda, MD and Thomas Fogarty, MD.

Introduction: Catheter based techniques for arrhythmia ablation require intravascular intervention with attendant limitations and potential complications. We examined the feasibility of using externally focused sterotactic radiation to alter cardiac electrophysiologic properties, as this could be used to ablate arrhythmias.

Methods: Externally focused radiation of atrial tissue was studied in Hanford-Sinclair mini swine (n=5)(40-70kg). The radiation (x-rays, 20-60 Gray) was targeted using a computer controlled robotic arm, directing a linear accelerator (Cyberknife). Radiosurgery enables radiation to be precisely delivered over 1-2 fractions. The target was determined using either a surgically implanted fiducial, or 16 slice CT scan. Cardiac and respiratory motion compensation was used. Four to eight weeks post radiation the animals underwent cardiac assessment with CT, TEE and Cardiac mapping with CARTO (Biosense). The animals were then sacrificed and pathology specimens taken.

Results: All animals survived treatment. Radiation effects appeared to be time and dose dependent. Radiation directed at the left superior pulmonary vein resulted in uniform attenuation of signal amplitude, with the remaining signal appearing to be residual far field. Similar signal attenuation was seen in the inferior venacava-tricuspid isthmus in 1 animal which had radiation there. No pulmonary vein stenosis was seen, and there was no damage to valves, nearby ventricular and pulmonary tissue, or esophagus.

Limitations: These animals did not have any spontaneous arrhythmias and thus efficacy of this technique in clinical therapy is unknown, although loss of electrical activity is usually corellated with success of ablation. The longest follow up was 3 months.

Conclusions: External sterotactic radiosurgery produces focused electrophysiologic changes with minimal changes in surrounding tissue. With CT guidance the technique can be wholly non-invasive. The therapy is rapid and can be done in one hour with the energy directed to any cardiac tissue with 1-2 cm accuracy. This new methodology is potentially applicable to any cardiac arrhythmia.