Stereotactic Ablative Radiotherapy for the Treatment of Refractory Cardiac Ventricular Arrhythmia

Abstract

A 71-year-old man with coronary artery disease, coronary artery bypass grafting in 2000, baseline ejection fraction of 0.24, and implantation of a single chamber implanted cardioverter defibrillator (ICD) in 2009 for ventricular tachycardia (VT) presented with continuous episodes of nonsustained and sustained VT refractory to sotalol and mexiletine. Despite angioplasty and stent for coronary artery disease, VT continued for 2 years. Medical history included atrial fibrillation and oxygen-dependent chronic obstructive pulmonary disease. Baseline electrocardiogram (ECG) showed atrial fibrillation with a ventricular rate of 82 beats per minute with inferior Q waves and QRS duration of 90 ms. Twelve-lead ECG during VT showed a regular, wide-complex tachycardia at 160 beats per minute (CL 380-400 ms), with a right bundle branch block pattern, superior axis, precordial transition at V3-V4. His ICD log showed numerous VT episodes, with a single morphology seen on intracardiac ventricular electrogram, cycle length 380-411ms. Episodes were nonsustained, pace-terminated, and shock-terminated. As catheter ablation was relatively medically contraindicated, he consented to a Food and Drug Administration and Institutional Review Board-approved compassionate-use protocol of stereotactic arrhythmia radioablation (STAR), noninvasive ablation of VT substrate by stereotactic ablative radiotherapy (SABR) techniques for tumors. STAR therapy was delivered in October, 2012. STAR Planning and DeliveryBaseline echocardiogram showed a dilated left ventricle (LV), ejection fraction of 0.24, with basal inferior aneurysm, and apical and infero-posterior akinesis. Positron emission tomography-computed tomography showed extensive hypometabolic scar in the LV extending between the LV base and the apex, involving the inferior, inferoseptal, and inferolateral walls. A target for STAR was delineated using proprietary visualization and contouring software (CardioPlan™, CyberHeart™, Portola Valley, CA), outlining the target volume corresponding to what would have been the likely catheter ablation volume for this VT substrate based on imaging-defined inferior LV scar and 12-lead ECG QRS morphology during VT, implying a likely inferior LV VT circuit location ( Figure 1A). The target volume was transferred to the radiation treatment planning software (MultiPlan 4.6.0, Accuray, Sunnyvale, CA) of the treatment system (CyberKnife®, Accuray, Sunnyvale, CA), with normal organs delineated, including lungs, esophagus, and stomach.A temporary pacing wire (Oscor, Inc., Miami Lakes, FL) was fluoroscopically placed in the RV apex as an imaging fiducial marker that could be dynamically tracked to compensate for respiratory motion (Synchrony® Respiratory Tracking 9.6.0, Accuray, Sunnyvale, CA). The magnitude of the remaining cardiac motion was determined by fluoroscopy of the fiducial marker during transient breath holds, and the final target volume included an expansion to encompass this residual motion. The finalized target was then used for treatment planning.A...

Stereotactic Arrhythmia Radioablation (STAR) of Ventricular Tachycardia: A Treatment Planning Study

“…In order to determine the ablation volume, a study including ECG during VT, cardiac-gated CT, and cardiac PET-CT were performed before the treatment. The circumferential VT substrate was contoured by the electrophysiologist using CardioPlan software (CyberHeart, Portola Valley, CA) [14]. The target and the images in CardioPlan were then exported to the CyberKnife® treatment planning system (MultiPlan 4.6, Accuray, Sunnyvale, CA), and fused with the treatment planning CT.…”

“…Pre-clinical studies have demonstrated electrophysiologic conduction blockade and histologic fibrosis after SABR to the targeted cardiac conduction pathway, which provided proof of principle for its potential for treating arrhythmias [12-13]. The first STAR of VT was treated at Stanford on a robotic radiosurgery system (CyberKnife®, Accuray, Sunnyvale, CA) in 2012 [14]. The follow-up showed no definite acute or late complications, and a seven-month reduction in VT on a stable antiarrhythmic regimen suggested a possible transient benefit of STAR; however, further investigation is needed.…”

Non-invasive Cardiac Radiation for Ablation of Ventricular Tachycardia: a New Therapeutic Paradigm in Electrophysiology

“…7,18,19 In the largest series, five patients with refractory VT who failed two antiarrhythmic drugs and had either at least one traditional invasive ablation procedure that failed or a contraindication to ablation procedures underwent non-invasive therapy for VT. 7 Of these, four underwent a combined anatomical imaging study and non-invasive ECGI during VT induced by their implanted cardioverter-defibrillator. VT exit points were identified by ECGI and the target volume for radiotherapy defined based on the ECGI or previously defined electro-anatomic maps from prior EP studies.…”

Innovations in Clinical Cardiac Electrophysiology: Challenges and Upcoming Solutions in 2018 and Beyond

“…80 Cardiac and respiratory motion is a major challenge in the accurate delivery of radiotherapy, and a fiducial marker such as a pacing catheter placed adjacent to the area of interest can be utilized to guide therapy. 81 Initial research in swine demonstrated the ability of radiotherapy to form lesions in a variety of locations including the cavotricuspid isthmus, atrioventricular node, and the pulmonary vein-left atrial junction. 82 Additionally, a study in a patient with recurrent ventricular tachycardia demonstrated the feasibility and safety of stereotactic radiotherapy for cardiac ablation.…”

“…82 Additionally, a study in a patient with recurrent ventricular tachycardia demonstrated the feasibility and safety of stereotactic radiotherapy for cardiac ablation. 81 Noninvasive ablation with X-ray radiation therapy is also under active research, with preliminary results expected to be released in the next year for some studies is under active research, with preliminary results expected over the next year for some studies (NCT02919618, NCT02661048).…”