Noninvasive stereotactic radioablation for the treatment of atrial fibrillation: First-in-man experience

Abstract

Purpose: Catheter ablation is an effective therapy for atrial fibrillation (AF). However, risks remain, and improved efficacy is desired. Stereotactic body radiotherapy (SBRT) is a well-established therapy used to noninvasively treat malignancies and functional disorders with precision. We evaluated the feasibility of stereotactic radioablation for treating paroxysmal AF.

Methods: Two patients with drug-refractory paroxysmal AF underwent pulmonary vein isolation with SBRT. After placement of a percutaneous active fixation temporary pacing lead tracking fiducial, computed tomography (CT) angiography was performed to define left atrial anatomy. A tailored planning treatment volume was created to deliver contiguous linear ablations to isolate the pulmonary veins and posterior wall. Patients were treated on an outpatient basis in the radioablation suite. Clinical follow-up was performed through at least 24 months after therapy.

Results: Both patients successfully underwent SBRT planning and treatment without significant early or long-term side effects up to 48 months of follow-up. One patient had AF recurrence after 6 months free of arrhythmia, while the second patient remains free of AF after 24 months with fibrosis detected on MRI scan consistent with the ablation lesion set. An incidentally noted small pericardial effusion occurred in one patient.

Conclusion: Stereotactic radioablation may be feasible for the treatment of drug-refractory AF. Further evaluation is warranted.

Keywords: ablation; atrial fibrillation; new technology; noninvasive ablation; radioablation; stereotactic.

Figure 1

Placement of an internal fiducial point to improve radioablative accuracy. This shallow left anterior oblique projection fluoroscopic image demonstrates the position of the fiducial marker placed via right internal jugular vein access, and affixed to the right side of the interatrial septum, in close proximity to the left atrial target. Compensation for cardiorespiratory motion during radioablation is achieved by the external beam delivery system through tracking of fiducial movement using planar xray

Figure 2

Anatomical considerations in tailoring the radioablative lesion set. Treatment dosing for Patient 2 is displayed on the 3D rendered left atrial volume using the radioablation treatment planning software (Cardioplan, Cyberheart, Inc and Cyberknife, Accuray Inc) Panel A shows a posterior‐anterior projection of the left atrium with the esophagus in situ to demonstrate the arrangement of the lesion set to minimize esophageal dosing. Panel B and C are additional posterior‐anterior and right lateral caudal views with the esophagus removed. Red signifies dosing at or above 90%, green (60%‐90%) and blue (<60%) of the target dose of 25 Gy. LSPV:Left superior pulmonary vein; LIPV:left inferior pulmonary vein; RSPV:right superior pulmonary vein, RIPV:right inferior pulmomary vein; LV:left ventricle

Figure 3

Planning and delivering steretotactic radioablation to the left atrium. Preprocedural CT scan of the chest obtained for patient 1; treatment volume planning requires defining a treatment volume using orthogonal imaging planes. Panel A and B show transverse and sagittal planes through the left atrium demonstrating radioablative isodose contours within and around the planned treatment volume, P, shown bounded by the orange line. Panel C demonstrates the calculated multiple beam angles used to deliver and concentrate radioablative energy within this treatment volume. Panel D shows the proportion of dose delivered to the targeted atrial myocardium and other key nearby visceral tissues as a function of tissue volume; it can be seen that approximately 89% of the target volume received at least 25 Gy

Figure 4

Cardiac magnetic resonance imaging demonstrating left atrial fibrosis in the radioablation treatment zone. Cardiac MRI for Patient 2, performed one year post stereotactic radioablation therapy, is shown. In this four‐chamber view, areas of late gadolinium enhancement (arrows), consistent with fibrosis, are seen within the left atrium septal and laterally consistent with treatment areas