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Radiation for Ablation of Ventricular Tachycardia
Study Questions:
Can noninvasive mapping of cardiac arrhythmias with electrocardiographic imaging and noninvasive delivery of ablative radiation with stereotactic body radiation therapy eliminate recurrent ventricular tachycardia (VT)?
Methods:
Patients underwent noninvasive delineation of the ventricular scar with magnetic resonance imaging, computed tomography (CT), single-photon emission CT (SPECT), or a combination. Programed stimulation from the indwelling implantable cardioverter-defibrillator was performed to induce VT, and noninvasive electrophysiologic mapping was performed with electrocardiographic imaging. An ablation volume was developed by targeting the ventricular tissue representing the first 10 msec of VT activation. This volume was transferred by the radiation oncologist onto a respiratory-correlated, four-dimensional CT scan. Stereotactic radioablation was performed with a linear accelerator using a cone-beam CT to align the radiotherapy treatment beams with the target volume.
Results:
Five patients with high-risk, refractory VT underwent treatment. The mean noninvasive ablation time was 14 minutes (range, 11-18). During the 3 months before treatment, the patients had a combined history of 6,577 episodes of VT. During a 6-week post-ablation “blanking period,” there were 680 episodes of VT. After the 6-week blanking period, there were four episodes of VT over the next 46 patient-months, representing a reduction of 99.9% from baseline. A reduction in episodes of VT occurred in all five patients. The mean left ventricular ejection fraction did not decrease with treatment. At 3 months, adjacent lung showed opacities consistent with inflammatory changes, which resolved by 1 year.
Conclusions:
Noninvasive treatment with electrophysiology-guided cardiac radioablation may markedly reduce VT burden.
Perspective:
One of the key limitations of VT catheter ablation is frequent inability to reach arrhythmogenic substrate, which in nonischemic cardiomyopathy may be mid-myocardial or epicardial. Even with epicardial access, catheter ablation may not be feasible in certain areas, especially in the outflow tract region. While the authors emphasize the noninvasive nature of this novel approach, its broadest applicability may be for the difficult-to-access myocardial scar. Tissue injury results from damage to the DNA, followed by apoptosis. This is in part responsible for the delayed response to the radioablation. Future studies involving larger numbers of patients should evaluate the degree of collateral damage to the healthy tissue, including the arterial and conduction systems, and potential long-term effects of the radiation.
Keywords: Arrhythmias, Cardiac, Cardiotoxicity, Catheter Ablation, Defibrillators, Implantable, Diagnostic Imaging, Electrocardiography, Electrophysiology, Four-Dimensional Computed Tomography, Heart Conduction System, Heart Failure, Magnetic Resonance Imaging, Primary Prevention, Stroke Volume, Tachycardia, Ventricular, Tomography, Emission-Computed, Single-Photon, Tomography, X-Ray Computed
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