Multimodality imaging fusion to guide stereotactic radioablation for refractory complex ventricular tachycardia Alba Santos-Ortega, MD,*† Nuria Rivas-Gandara, MD, PhD,*† Gabriel Pascual-Gonzalez,* Alejandro Seoane, MSc,‡ Raquel Granado, MD,x Victoria Reyes, MDx From the *Arrhythmia Unit, Cardiology Department, Vall d’Hebron University Hospital, Barcelona, Spain, † Faculty of Medicine and Surgery, Universitat Autonoma Barcelona (UAB), Barcelona, Spain, ‡ Medical Physics Department, Vall d’Hebron University Hospital, Barcelona, Spain, and xRadiation Oncology Department, Vall d’Hebron University Hospital, Barcelona, Spain. Introduction KEY TEACHING POINTS Ventricular tachycardia (VT) is associated with a high risk of sudden cardiac death (SCD). The widespread im-  Multimodal imaging technique fusion using ADAS plantation of defibrillators as an SCD prevention strategy 3D (Barcelona, Spain) software enables precise has increased the number of survivors of VT or ventric- noninvasive radioablation planning. ular fibrillation. These arrhythmias represent a difficult- to-treat problem of great magnitude, with catheter  Noninvasive radioablation is an emerging ablation currently being the most accepted therapy.1 technique that is becoming a promising alternative However, despite technical advances in electroanatomical for refractory ventricular arrhythmia treatment. mapping (EAM) and new ablation catheters, the  Ventricular arrhythmias due to intramyocardial arrhythmic recurrence rate is approximately 50%, reentry require special therapeutic management in exposing patients to multiple invasive procedures and which noninvasive radioablation may play a potentially deleterious defibrillator shocks.2 Stereotactic radiotherapy (SRT) is a widely used treatment relevant role. in oncology whose mechanism of cell death involves apoptosis and microvascular damage. Technical advances have allowed the administration of radiation with great preci- sion and are highly effective, with few side effects. In recent Case report years, SRT has emerged as a promising alternative for the Here we report the case of a 71-year-old patient with a med- treatment of refractory ventricular arrhythmias. Studies pub- ical history of hypertension, dyslipidemia, overweight, and lished to date have shown the high efficacy of this therapy in endothoracic multinodular goiter with normal thyroid func- reducing arrhythmic events, up to 94%, with a low rate of tion. After SCD was diagnosed in 1 of his siblings, a family complications.3–5 SRT should be guided by imaging study was conducted, from which he was diagnosed with hy- techniques, and treatments applied to the heart have a pertrophic obstructive cardiomyopathy, observing a mutation delayed effect. in MYBPC3 p.Glu542Gln. Cardiac magnetic resonance im- aging (MRI) revealed severe asymmetric septal hypertrophy (maximum septal thickness, 31 mm), preserved systolic func- tion, and an extensive and diffuse intramyocardial area of KEYWORDS Stereotactic radioablation; Ventricular tachycardia; Intramural fibrosis in the anterior wall, apical segments, and junction ventricular tachycardia; Hypertrophic cardiomyopathy; Multimodality imag- of the left and right ventricles. In January 2019, a single- ing chamber defibrillator was implanted for prevention. (Heart Rhythm Case Reports 2022;8:836–839) One year later, he was admitted to the cardiac intensive Funding Sources: None. Disclosures: Dra Alba Santos-Ortega, Dra care unit with an arrhythmic storm that occurred with multi- Rivas-Gandara, and Gabriel Pascual-Gonzalez report personal fees from Ab- ple defibrillator therapies. Coronary angiography ruled out bott, outside the submitted work. Address reprint requests and correspon- dence: Dr Alba Santos-Ortega, Arrhythmia Unit, Cardiology Department, coronary obstruction. Medical treatment with intravenous Vall d’Hebron University Hospital, Passeig de Vall d’Hebron, 119-129, procainamide and esmolol and subsequent amiodarone was 08035 Barcelona, Spain. E-mail address: asantos@vhebron.net. ineffective. The patient was subsequently referred for cardiac 2214-0271/© 2022 Heart Rhythm Society. Published by Elsevier Inc. This is an open access article https://doi.org/10.1016/j.hrcr.2022.09.008 under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Santos-Ortega et al Radioablation for Refractory Ventricular Tachycardia 837 Figure 1 Electroanatomical activation mapping during ventricular tachycardia with Abbott EnSite Precision (Abbott, Minneapolis, MN). A: The left image (green arrow) shows epicardial mapping. The right image (yellow arrow) shows endocardial mapping. A significant part of the tachycardia cycle is not repre- sented on any of the electroanatomical maps, suggesting an intramyocardial origin of the tachycardia. B: The left part of the image shows endocardial mapping. On the right, electrocardiogram showing ventricular tachycardia with right bundle brunch block morphology and a superior axis suggestive of an anterolateral left ventricle origin. Low-voltage mesodiastolic electrograms (gray arrow), suggestive of far-field signals, are found on catheter recordings during endocardial map- ping, supporting an intramyocardial origin. ablation. Considering the transmural substrate predicted by intramyocardially (Figure 1B). Extensive radiofrequency MRI, both subxiphoid epicardial and double endocardial ret- ablation during VT was applied from the endocardial and roaortic and transseptal access were achieved. Using a multi- epicardial sides but was ineffective owing to difficult access polar Advisor HD GridÔ catheter and EnSite Precision to this intramyocardial substrate, which was aggravated in (Abbott, St. Paul, MN) EAM system, a voltage map was this patient with severe myocardial hypertrophy. created that showed a very extensive low-voltage area in After evaluating the difficulty of treating VT with conven- the left ventricle, predominantly in the anterior, apical, and tional techniques owing to its intramyocardial substrate asso- lateral epicardium, suggestive of epicardial fat. A VT with ciated with severe ventricular hypertrophy, an alternative a cycle length of 530 ms and the same morphology as the approach consisting of noninvasive radioablation (NIRA) clinical VT was induced (Figure 1A). It was clinically well was considered. Identification of the target area in this case tolerated, which allowed mapping during tachycardia. The was challenging because of its intramyocardial nature. There- activation map showed a macroreentrant circuit in the antero- fore, we used ADAS 3D (Barcelona, Spain) image postpro- lateral area of the left ventricle with endocardial and epicar- cessing software to plan the procedure. This tool allows the dial components. However, only 70% of the tachycardia fusion of 3-dimensional (3D) images (MRI and cardiac cycle was obtained despite mapping of the epicardium and computed tomography [CT]) with the EAM for correct and endocardium, suggesting that the critical isthmus was located precise identification of the area of critical isthmus of the 838 Heart Rhythm Case Reports, Vol 8, No 12, December 2022 Figure 2 ADAS 3D (Barcelona, Spain) reconstruction. A: Cardiac computed tomography (CT) and magnetic resonance imaging (MRI) fusion. The left ventricle is represented in layers corresponding to myocardial depth and this image belongs to the endocardium (10%). Cardiac structures are represented as fol- lows: right ventricle (green), pulmonary artery (purple), aorta (yellow), left atrium (blue), and coronary arteries (white arrow). Red arrow points out intramyo- cardial substrate observed in MRI. B: MRI reconstruction with ADAS shows intramyocardial layer (40%). Grey arrow points out an intramyocardial corridor, corresponding to ventricular tachycardia critical isthmus. C: Cardiac CT / electroanatomical map and radiotherapy planning CT fusion. Area of interest delimited in electroanatomical map is represented (yellow arrow). tachycardia. More importantly, it made it possible to avoid Echocardiography performed in the first few hours re- other nearby structures (eg, coronary arteries, mitral valve), vealed very slight pericardial effusion with a maximum of whose injury could have potential complications 5 mm in the posterior space without hemodynamic compro- (Figure 2A). mise of the cardiac chambers. To plan radiotherapy treatment, 4-dimensional CT was One year later, the patient remained asymptomatic and performed to control for and adjust the respiratory and car- presented no new arrhythmic events or relevant side effects diac movements, and the defibrillator was kept pacing at a related to NIRA. heart rate of 100 beats per minute. Using the ADAS 3D tool, it was possible to combine previous MRI and cardiac CT images with the EAM as well as with the radiotherapy Discussion planning CT (Figure 2B). This is the first reported case in which ADAS 3D image post- To define the area of interest for NIRA, a clinical target vol- processing software was used to plan an NIRA procedure by ume was delimited on the fusion image obtained with ADAS fusing cardiac images with radiotherapy CT images. This 3D software. A margin of 0.3 mm was added to obtain the in- supports the usefulness of NIRA for refractory ventricular ternal target volume, which considers respiratory movements. arrhythmia treatment and its promising application in com- Organs at risk included the lungs, trachea, esophagus, stom- plex arrhythmic substrates assisted by careful multimodal im- ach, medulla, rib wall, liver, aorta, pericardium, anterior de- aging planning. scending coronary artery, left ventricle, and papillary Advances in the recognition and diagnosis of ventricular muscle. A 25 Gy session was applied in the TrueBeamÒ linear arrhythmias have resulted in more complex arrhythmia sub- accelerator (Varian Medical Systems, Palo Alto, CA), with the strates. Despite the latest advances in catheter ablation, we RapidArc technique and treatment verification by cone-beam often encounter great difficulties in treatment in relation to CT (Figure 3), as well as respiratory and heart rate control. anatomical access and target area identification. Character- During the acute phase, the patient presented with mild ization of the 3D VT circuit, as proposed by Tung and col- asthenia. The electrocardiogram taken after NIRA showed leagues,6 showed the presence of intramyocardial reentry in no significant changes compared to the previous ones. Blood a significant percentage of patients (up to 18%). With con- tests performed 8 hours later showed only a minimal increase ventional EAM systems, accurate identification of the slow in cardiac enzymes, which normalized at 24 hours. conduction channels that cause intramyocardial reentry Santos-Ortega et al Radioablation for Refractory Ventricular Tachycardia 839 Figure 3 Noninvasive cardiac radioablation treatment using a TrueBeam (Varian Medical Systems) radiotherapy plan showing the target volume (white arrow) and isodose lines. tachycardias is often challenging. For this reason, the fusion Conclusion of cardiac CT and MRI images using this image postprocess- Here we presented a case in which NIRA allowed successful ing software enables definition of the substrate in 3 dimen- treatment of a patient with a complex arrhythmic sions. In patients with these types of tachycardias, a better substrate that was inaccessible using conventional techniques. understanding of the tachycardia mechanism and more tar- This case highlights the usefulness of cardiac image fusion us- geted treatment is favored. ing ADAS 3D postprocessing software merged with radio- In addition, intramyocardial reentry tachycardias can be therapy CT. It facilitates adequate procedure planning, inaccessible to conventional ablation catheter treatment, allowing radiotherapy to be administered with greater accu- especially in patients with severe myocardial hypertrophy racy and the least possible short- and long-term side effects. or with a septal origin. Radiotherapy seems to be a promising The need for the accurate identification of target areas for alternative for facilitating treatment in deeper areas. Studies radiotherapy application makes us expect great growth in to date have shown high efficacy of radiotherapy treatment this technique for other complex arrhythmic substrate treat- without acute toxicity, with pericarditis and delayed pericar- ment applications in which imaging fusion via specific post- dial effusion (28%) and pneumonitis (11%) being the most processing tools could play a relevant role. frequent complications, with good response to medical treat- ment.4 However, follow-up studies are lacking, which is why the long-term effects of this emerging therapy remain un- References known. Notwithstanding, the fusion of imaging techniques, 1. 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