Stereotactic cardiac radiation for ablation (radioablation) for life-threatening ventricular arrhythmia was introduced into clinical practice in 2017.1 In a case series and a small observational study, radioablation was shown to successfully reduce the burden of ventricular arrhythmias with acceptable short term toxicities, by combining electrocardiographic imaging and stereotactic body radiation techniques.23 However, clarity on the indication and proper methodology for radioablation have not yet been clearly established. We recently performed inevitable radioablation to control ventricular tachycardia (VT) and ventricular fibrillation (VF) storm in a patient with apical hypertrophic cardiomyopathy at burnout stage and an implantable cardioverter-defibrillator (ICD). As VT and VF storm was successfully controlled by radioablation, the patient's clinical course has been described in this case report.

A 76-year-old male patient with apical hypertrophic cardiomyopathy at burnout stage and an ICD was admitted for recurrent VT in December 1, 2018. The patient underwent ICD implantation for out-of-hospital cardiac arrest three years prior. Although the patient had been taking sotalol 240 mg/day, the number of fast VT episodes treated by anti-tachycardia pacing increased rapidly for several months, and the patient eventually lost consciousness during ICD charging for shock delivery (Fig. 1). The patient was admitted for radiofrequency catheter ablation (RFCA).

Intracardiac mapping was performed using a 3-dimensional navigation system (CARTO® 3 System, Biosense Webster, Diamond Bar, CA, USA). During a baseline electrophysiologic study, VF was induced by right ventricular pacing at a cycle length of 210 ms and should be terminated by external defibrillation at 150 J. To avoid the risk of VF re-induction, we decided to perform substrate modulation. However, during geometric mapping of the left ventricle (LV), a sustained monomorphic VT of 280 bpm was induced by ventricular premature beats. Electrocardiographic features of both clinically documented and induced VTs suggested that they came from the same arrhythmogenic substrates located in the apical aneurysm (Fig. 2A and B). Activation mapping for the induced VT using a multi-electrode catheter showed the earliest ventricular activation at the septal side of the apical aneurysm with apical-to-basal propagation (Fig. 3A and B). However, the patient's blood pressure dropped to 60/30 mmHg within 4 minutes after induction of the VT, which should be terminated by repeated external cardioversion at 150 J. As the patient refused further ablation, the procedures should be finished after infusion of 300 mg amiodarone to prevent recurrence of hemodynamically unstable VT or VF. However, fast VT and VF requiring ICD shock therapy recurred the next day (Fig. 2C). Although amiodarone at a dose of 20 mg/kg/day was continuously infused in combination with oral flecainide 200 mg/day, ICD shocks were delivered seven times over 24 hours. Because the patient refused any invasive procedures including extracorporeal membrane oxygenation-supported RFCA, cardiac sympathetic denervation, and heart transplantation, we decided to perform stereotactic cardiac radiation for ablation as a rescue therapy after informed consent.

Radioablation was administered under respiratory gating on the first, second, and fifth days with a 6 megavolt X-ray using a linear accelerator (Clinac iX™, Varian Medical Systems, Palo Alto, CA, USA). The gross tumor volume was defined as the LV aneurysm and surrounding myocardium with 1-cm extension from the aneurysmal border to comprise the potential arrhythmogenic substrates and electrical exits of VT and VF. The clinical target volume was generated by combining the gross tumor volume in free breathing and end-expiratory states. The planning target volume consisted of the clinical target volume plus a 1-cm margin in all directions (Fig. 3C). Initially 25–35 Gy in a fraction was planned similarly to the radioablation protocols used in prior clinical studies,23 but 24 Gy in three fractions was adopted due to the excessive gastric irradiation in the single fraction.4

Immediately after the initiation of radioablation, the daily burden of total ventricular arrhythmias and treated VT/VF episodes began to decrease rapidly (Fig. 4A and B). The patient was discharged after two weeks on oral amiodarone 400 mg/day and flecainide 200 mg/day. During the follow-up duration of 6 months, although anti-tachycardia pacing was performed twice, ICD shocks were no longer required (Fig. 1). The LV ejection fraction remained unchanged at 62%–63% after 6 months. Although mild pulmonary fibrosis was noted on chest X-ray, significant cardiac or extracardiac tissue toxicities did not appear.

Animal studies have shown that cardiac radiation of 25–55 Gray induces myocardial tissue damage with fibrosis and reduces conduction velocity similar to that of RFCA.5678 The efficacy and safety of radioablation for ventricular tachyarrhythmia has been recently evaluated in human studies.123910 Compared with conventional RFCA, radioablation is more likely to produce homogenous transmural lesions which can provide greater benefit in electrical and pathologic modulation of the arrhythmogenic substrates.

For stereotactic cardiac radioablation, prior studies used electrocardiographic imaging technology which, by combining cardiac multi-detector computed tomography and 256-electrode surface electrocardiography, can provide information about both the arrhythmogenic substrates and electrical activities of ongoing ventricular arrhythmias. However, it is not yet available in Korea and technically impossible to perform if ventricular arrhythmia is hemodynamically unstable. In the present case, we could define the potential origin of the VT and VF based on the findings of conventional cardiac imaging, electrocardiographic, and electrophysiologic studies.

Stereotactic body radiation was performed using a linear accelerator system widely available in Korea. Suppression of VT and VF storm was instantaneous and the effect of electrical modulation was maintained for at least 6 months without significant radiation toxicities. This case shows that stereotactic cardiac radioablation may be considered as a rescue therapy for scenarios involving VT and VF storm that cannot be controlled by other treatment modalities including antiarrhythmic drug therapy and RFCA.