Stereotactic Radiotherapy for the Management of Refractory Ventricular Tachycardia: Promise and Future Directions

Role of Nuclear Imaging in Cardiac Stereotactic Body Radiotherapy for Ablation of Ventricular Tachycardia

Ventricular tachycardia (VT) is a life-threatening arrhythmia common in patients with structural heart disease or nonischemic cardiomyopathy. Many VTs originate from regions of fibrotic scar tissue, where delayed electrical signals exit scar and re-enter viable myocardium. Cardiac stereotactic body radiotherapy (SBRT) has emerged as a completely noninvasive alternative to catheter ablation for the treatment of recurrent or refractory ventricular tachycardia. While there is no common consensus on the ideal imaging workflow, therapy planning for cardiac SBRT often combines information from a plurality of imaging modalities including MRI, CT, electroanatomic mapping and nuclear imaging. MRI and CT provide detailed anatomic information, and late enhancement contrast imaging can indicate regions of fibrosis. Electroanatomic maps indicate regions of heterogenous conduction voltage or early activation which are indicative of arrhythmogenic tissue. Some early clinical adopters performing cardiac SBRT report the use of myocardial perfusion and viability nuclear imaging to identify regions of scar. Nuclear imaging of hibernating myocardium, inflammation and sympathetic innervation have been studied for ventricular arrhythmia prognosis and in research relating to catheter ablation of VT but have yet to be studied in their potential applications for cardiac SBRT. The integration of information from these many imaging modalities to identify a target for ablation can be challenging. Multimodality image registration and dedicated therapy planning tools may enable higher target accuracy, accelerate therapy planning workflows and improve patient outcomes. Understanding the pathophysiology of ventricular arrhythmias, and localizing the arrhythmogenic tissues, is vital for successful ablation with cardiac SBRT. Nuclear imaging provides an arsenal of imaging strategies to identify regional scar, hibernation, inflammation, and sympathetic denervation with some advantages over alternative imaging strategies.

Patient vulnerability in stereotactic arrhythmia radioablation (STAR): a preliminary ethical appraisal from the STOPSTORM.eu consortium

This preliminary ethical appraisal from the STOPSTORM.eu consortium is meant to raise critical points that clinicians administering stereotactic arrhythmia radioablation should consider to meet the highest standards in medical ethics and thus promote quality of life of patients recruited for radiotherapy treatments at a stage in which they experience a significant degree of vulnerability.

Patient-specific quantification of cardiorespiratory motion for cardiac stereotactic radioablation treatment planning

Background

Cardiac radioablation is a new treatment for patients with refractory ventricular tachycardia (VT). The target for cardiac radioablation is subject to cardiorespiratory motion (CRM), the heart's movement with breathing and cardiac contraction. Data regarding the magnitude of target CRM are limited but are highly important for treatment planning.

Objectives

The study sought to assess CRM amplitude by using ablation catheter geometrical data.

Methods

Electroanatomic mapping data of patients undergoing catheter ablation for VT at 3 academic centers were exported. The spatial position of the ablation catheter as a function of time while in contact with endocardium was analyzed and used to quantify CRM.

Results

Forty-four patients with ischemic and nonischemic cardiomyopathy and VT contributed 1364 ablation lesions to the analysis. Average cardiac and respiratory excursion were 1.62 ± 1.21 mm and 12.12 ± 4.10 mm, respectively. The average ratio of respiratory to cardiac motion was approximately 11:1. CRM was greatest along the craniocaudal axis (9.66 ± 4.00 mm). Regional variations with respect to respiratory and cardiac motion were observed: basal segments had smaller displacements vs midventricular and apical segments. Patient characteristics (previous cardiac surgery, height, weight, body mass index, and left ventricular ejection fraction) had a statistically significant, albeit clinically moderate, impact on CRM.

Conclusion

CRM is primarily determined by respiratory displacement and is modulated by the location of the target and the patient's biometric characteristics. The patient-specific quantification of CRM may allow to decrease treatment volume and reduce radiation exposure of surrounding organs at risk while delivering the therapeutic dose to the target.

FLASH Proton Radiation Therapy Mitigates Inflammatory and Fibrotic Pathways and Preserves Cardiac Function in a Preclinical Mouse Model of Radiation-Induced Heart Disease

PURPOSE

Studies during the past 9 years suggest that delivering radiation at dose rates exceeding 40 Gy/s, known as "FLASH" radiation therapy, enhances the therapeutic index of radiation therapy (RT) by decreasing normal tissue damage while maintaining tumor response compared with conventional (or standard) RT. This study demonstrates the cardioprotective benefits of FLASH proton RT (F-PRT) compared with standard (conventional) proton RT (S-PRT), as evidenced by reduced acute and chronic cardiac toxicities.

METHODS AND MATERIALS

Mice were imaged using cone beam computed tomography to precisely determine the heart's apex as the beam isocenter. Irradiation was conducted using a shoot-through technique with a 5-mm diameter circular collimator. Bulk RNA-sequencing was performed on nonirradiated samples, as well as apexes treated with F-PRT or S-PRT, at 2 weeks after a single 40 Gy dose. Inflammatory responses were assessed through multiplex cytokine/chemokine microbead assay and immunofluorescence analyses. Levels of perivascular fibrosis were quantified using Masson's Trichrome and Picrosirius red staining. Additionally, cardiac tissue functionality was evaluated by 2-dimensional echocardiograms at 8- and 30-weeks post-PRT.

RESULTS

Radiation damage was specifically localized to the heart's apex. RNA profiling of cardiac tissues treated with PRT revealed that S-PRT uniquely upregulated pathways associated with DNA damage response, induction of tumor necrosis factor superfamily, and inflammatory response, and F-PRT primarily affected cytoplasmic translation, mitochondrion organization, and adenosine triphosphate synthesis. Notably, F-PRT led to a milder inflammatory response, accompanied by significantly attenuated changes in transforming growth factor β1 and α smooth muscle actin levels. Critically, F-PRT decreased collagen deposition and better preserved cardiac functionality compared with S-PRT.

CONCLUSIONS

This study demonstrated that F-PRT reduces the induction of an inflammatory environment with lower expression of inflammatory cytokines and profibrotic factors. Importantly, the results indicate that F-PRT better preserves cardiac functionality, as confirmed by echocardiography analysis, while also mitigating the development of long-term fibrosis.

Noninvasive cardiac radioablation for ventricular tachycardia: dosimetric comparison between linear accelerator- and robotic CyberKnife-based radiosurgery systems

BACKGROUND

Few dosimetric comparisons have been published between linear accelerator (LA)-based systems and CyberKnife (CK)-based robotic radiosurgery systems for cardiac radio-ablation in ventricular tachycardia. This study aimed to compare the dosimetry of noninvasive cardiac radio-ablation deliverable on LA with that on CK.

METHODS

Thirteen patients who underwent noninvasive cardiac radio-ablation by LA were included. The prescribed dose was 25 Gy in 1 fraction, and the average planning target volume was 49.8 ± 31.0 cm3 (range, 14.4-93.7 cm3). CK plans were generated for comparison.

RESULTS

Both the CK and LA plans accomplished appropriate dose coverage and normal tissue sparing. Compared with the LA plans, the CK plans achieved significantly lower gradient indices (3.12 ± 0.71 vs. 3.48 ± 0.55, p = 0.031) and gradient measures (1.00 ± 0.29 cm vs. 1.17 ± 0.29 cm, p < 0.001). They had similar equivalent conformity indices (CK vs. LA: 0.84 ± 0.08 vs. 0.87 ± 0.07, p = 0.093) and maximum doses 2 cm from the planning target volume (PTV) in any direction (CK vs. LA: 50.8 ± 9.9% vs. 53.1 ± 5.3%, p = 0.423). The dosimetric advantages of CK were more prominent in patients with a PTV of ≤ 50 cm3 or a spherical PTV. In patients with a PTV of > 50 cm3 or a non-spherical PTV, the LA and CK plans were similar regarding dosimetric parameters. CK plans involved more beams (232.2 ± 110.8 beams vs. 10.0 ± 1.7 arcs) and longer treatment times (119.2 ± 43.3 min vs. 22.4 ± 1.6 min, p = 0.007).

CONCLUSIONS

Both CK and LA are ideal modalities for noninvasive cardiac radio-ablation. Upfront treatment should be considered based on clinical intent.

Cardiac radioablation of incessant ventricular tachycardia in patients with terminal heart failure under permanent left ventricular assist device therapy-description of two cases

PURPOSE

Cardiac radioablation (cRA) using a stereotactic single-session radioablative approach has recently been described as a possible treatment option for patients with otherwise untreatable recurrent ventricular tachycardia (VT). There is very limited experience in cRA for patients undergoing left ventricular assist device (LVAD) therapy. We present clinical experiences of two patients treated with cRA for incessant VT under long-term LVAD therapy.

METHODS

Two male patients (54 and 61 years old) with terminal heart failure under LVAD therapy (both patients for 8 years) showed incessant VT despite extensive antiarrhythmic drug therapy and repeated catheter ablation. cRA with a single dose of 25 Gy was applied as a last resort strategy under compassionate use in both patients following an electroanatomical mapping procedure.

RESULTS

Both patients displayed ongoing VT during and after the cRA procedure. Repeated attempts at post-procedural rhythm conversion failed in both patients; however, one patient was hemodynamically stabilized and could be discharged home for several months before falling prey to a fatal bleeding complication. The second patient initially stabilized for a few days following cRA before renewed acceleration of running VT required bilateral ablation of the stellate ganglion; the patient died 50 days later. No immediate side effects of cRA were detected in either patient.

CONCLUSION

cRA might serve as a last resort strategy for patients with terminal heart failure undergoing LVAD therapy and displaying incessant VT. Intermediate- and long-term outcomes of these seriously ill patients often remain poor; therefore, best supportive care strategies should also be evaluated as long as no clear beneficial effects of cRA procedures can be shown. For patients treated with cRA under running ventricular rhythm abnormality, strategies for post-procedural generation of stabilized rhythm have to be established.

Phase II Trial of LINAC-Based STereotactic Arrhythmia Radioablation (STAR) for Paroxysmal Atrial Fibrillation in Elderly: Planning and Dosimetric Point of View

Purpose: Approaching treatment for elderly patients with atrial fibrillation is difficult. A prospective phase II trial evaluating LINAC-based stereotactic arrhythmia radioablation (STAR) safety in this population started in 2021. Dosimetric and planning data were reported. Materials and Methods: A vac-lock bag was used for immobilization in the supine position and a computed tomography (CT, 1 mm) was performed. The clinical target volume (CTV) was defined as the area around the pulmonary veins. An internal target volume (ITV) was added to the CTV to compensate heart and respiratory movement. The planning target volume (PTV) was defined by adding 0–3 mm to the ITV. STAR was performed during free-breathing with a PTV prescription total dose (Dp) of 25 Gy/1 fraction. Flattening filter-free volumetric-modulated arc therapy plans were generated, optimized, and delivered by TrueBeamTM. Image-guided radiotherapy with cone-beam CT and surface-guided radiotherapy with Align-RT (Vision RT) were employed. Results: From May 2021 to March 2022, 10 elderly patients were treated. Mean CTVs, ITVs, and PTVs were 23.6 cc, 44.32 cc, and 62.9 cc, respectively; the mean prescription isodose level and D2% were 76.5% and 31.2 Gy, respectively. The average heart and left anterior descending artery (LAD) Dmean were 3.9 and 6.3 Gy, respectively; the mean Dmax for LAD, spinal cord, left and right bronchus, and esophagus were 11.2, 7.5, 14.3, 12.4, and 13.6 Gy, respectively. The overall treatment time (OTT) was 3 min. Conclusions: The data showed an optimal target coverage, sparing surrounding tissue, in 3 min of OTT. LINAC-based STAR for AF could represent a valid non-invasive alternative for elderly patients who were excluded from catheter ablation.

Cardiac motion and its dosimetric impact during radioablation for refractory ventricular tachycardia

INTRODUCTION

Cardiac radioablation (CR) is a noninvasive treatment option for patients with refractory ventricular tachycardia (VT) during which high doses of radiation, typically 25 Gy, are delivered to myocardial scar. In this study, we investigate motion from cardiac cycle and evaluate the dosimetric impact in a cohort of patients treated with CR.

METHODS

This retrospective study included eight patients treated at our institution who had respiratory-correlated and ECG-gated 4DCT scans acquired within 2 weeks of CR. Deformable image registration was applied between maximum systole (SYS) and diastole (DIAS) CTs to assess cardiac motion. The average respiratory-correlated CT (AVG_resp ) was deformably registered to the average cardiac (AVG_cardiac ), SYS, and DIAS CTs, and contours were propagated using the deformation vector fields (DVFs). Finally, the original treatment plan was recalculated on the deformed AVG_resp CT for dosimetric assessment.

RESULTS

Motion magnitudes were measured as the mean (SD) value over the DVFs within each structure. Displacement during the cardiac cycle for all chambers was 1.4 (0.9) mm medially/laterally (ML), 1.6 (1.0) mm anteriorly/posteriorly (AP), and 3.0 (2.8) mm superiorly/inferiorly (SI). Displacement for the 12 distinct clinical target volumes (CTVs) was 1.7 (1.5) mm ML, 2.4 (1.1) mm AP, and 2.1 (1.5) SI. Displacements between the AVG_resp and AVG_cardiac scans were 4.2 (2.0) mm SI and 5.8 (1.4) mm total. Dose recalculations showed that cardiac motion may impact dosimetry, with dose to 95% of the CTV dropping from 27.0 (1.3) Gy on the AVG_resp to 20.5 (7.1) Gy as estimated on the AVG_cardiac .

CONCLUSIONS

Cardiac CTV motion in this patient cohort is on average below 3 mm, location-dependent, and when not accounted for in treatment planning may impact target coverage. Further study is needed to assess the impact of cardiac motion on clinical outcomes.

Inflammation and fibrosis characterize different stages of myocardial remodeling in patients after stereotactic body radiotherapy of ventricular myocardium for recurrent ventricular tachycardia

We performed a histological and immunohistochemical analysis of myocardia from 3 patients who underwent radiosurgery and died for various reasons 3 months to 9 months after radiotherapy. In Case 1 (death 3 months after radiotherapy) we observed a sharp transition between relatively intact and irradiated regions. In the myolytic foci, only scattered cardiomyocytes were left and the area was infiltrated by immune cells. Using immunohistochemistry we detected numerous inflammatory cells including CD68+/CD11c+ macrophages, CD4+ and CD8+ T-lymphocytes and some scattered CD20+ B-lymphocytes. Mast cells were diminished in contrast to viable myocardium. In Case 2 and Case 3 (death 6 and 9 months after radiotherapy, respectively) we found mostly fibrosis, infiltration by adipose tissue and foci of calcification. Inflammatory infiltrates were less pronounced. Our observations are in accordance with animal experimental studies and confirm a progress from myolysis to fibrosis. In addition, we demonstrate a role of pro-inflammatory macrophages in the earlier stages of myocardial remodeling after stereotactic radioablation for ventricular tachycardia.

Preclinical models of radiation-induced cardiac toxicity: Potential mechanisms and biomarkers

Radiation therapy (RT) is an important modality in cancer treatment with >50% of cancer patients undergoing RT for curative or palliative intent. In patients with breast, lung, and esophageal cancer, as well as mediastinal malignancies, incidental RT dose to heart or vascular structures has been linked to the development of Radiation-Induced Heart Disease (RIHD) which manifests as ischemic heart disease, cardiomyopathy, cardiac dysfunction, and heart failure. Despite the remarkable progress in the delivery of radiotherapy treatment, off-target cardiac toxicities are unavoidable. One of the best-studied pathological consequences of incidental exposure of the heart to RT is collagen deposition and fibrosis, leading to the development of radiation-induced myocardial fibrosis (RIMF). However, the pathogenesis of RIMF is still largely unknown. Moreover, there are no available clinical approaches to reverse RIMF once it occurs and it continues to impair the quality of life of long-term cancer survivors. Hence, there is an increasing need for more clinically relevant preclinical models to elucidate the molecular and cellular mechanisms involved in the development of RIMF. This review offers an insight into the existing preclinical models to study RIHD and the suggested mechanisms of RIMF, as well as available multi-modality treatments and outcomes. Moreover, we summarize the valuable detection methods of RIHD/RIMF, and the clinical use of sensitive radiographic and circulating biomarkers.

Safety and Efficacy of Stereotactic Arrhythmia Radioablation for the Treatment of Ventricular Tachycardia: A Systematic Review

Catheter ablation (CA) is a fundamental therapeutic option for the treatment of recurrent ventricular arrhythmias. Notwithstanding the tremendous improvements in the available technology and the increasing amount of evidence in support of CA, in some patients the procedure fails, or is absolutely contraindicated due to technical or clinical issues. In these cases, the clinical management of patients is highly challenging, and mainly involves antiarrhythmic drugs escalation. Over the last 5 years, stereotactic arrhythmia radioablation (STAR) has been introduced into clinical practice, with several small studies reporting favorable arrhythmia-free outcomes, without severe side effects at a short to mid-term follow-up. In the present systematic review, we provide an overview of the available studies on stereotactic arrhythmia radioablation, by describing the potential indications and technical aspects of this promising therapy.

A case report of long-term successful stereotactic arrhythmia radioablation in a cardiac contractility modulation device carrier with giant left atrium, including a detailed dosimetric analysis

Introduction

Catheter ablation (CA) is the current standard of care for patients suffering drug-refractory monomorphic ventricular tachycardias (MMVTs). Yet, despite significant technological improvements, recurrences remain common, leading to increased morbidity and mortality. Stereotactic arrhythmia radioablation (STAR) is increasingly being adopted to overcome the limitations of conventional CA, but its safety and efficacy are still under evaluation.

Case presentation

We hereby present the case of a 73-year-old patient implanted with a mitral valve prosthesis, a cardiac resynchronization therapy-defibrillator, and a cardiac contractility modulation device, who was successfully treated with STAR for recurrent drug and CA-resistant MMVT in the setting of advanced heart failure and a giant left atrium. We report a 2-year follow-up and a detailed dosimetric analysis.

Conclusion

Our case report supports the early as well as the long-term efficacy of 25 Gy single-session STAR. Despite the concomitant severe heart failure, with an overall heart minus planned target volume mean dosage below 5 Gy, no major detrimental cardiac side effects were detected. To the best of our knowledge, our dosimetric analysis is the most accurate reported so far in the setting of STAR, particularly for what concerns cardiac substructures and coronary arteries. A shared dosimetric planning among centers performing STAR will be crucial in the next future to fully disclose its safety profile.

Treatment Planning for Cardiac Radioablation: Multicenter Multiplatform Benchmarking for the XXX Trial

PURPOSE

Cardiac radioablation is a novel treatment option for patients with refractory ventricular tachycardia (VT) unsuitable for catheter ablation. The quality of treatment planning depends on dose specifications, platform capabilities, and experience of the treating staff. To harmonize the treatment planning, benchmarking of this process is necessary for multicenter clinical studies such as the XXX trial.

METHODS AND MATERIALS

Planning computed tomography data and consensus structures from three patients were sent to five academic centers for independent plan development using a variety of platforms and techniques with the XXX study protocol serving as guideline. Three-dimensional dose distributions and treatment plan details were collected and analyzed. In addition, an objective relative plan quality ranking system for VT treatments was established.

RESULTS

For each case, three coplanar volumetric modulated arc (VMAT) plans for C-arm linear accelerators (LINAC) and three non-coplanar treatment plans for robotic arm LINAC were generated. All plans were suitable for clinical applications with minor deviations from study guidelines in most centers. Eleven of 18 treatment plans showed maximal one minor deviation each for target and cardiac substructures. However, dose-volume histograms showed substantial differences: in one case, the PTV≥30Gy ranged from 0.0% to 79.9% and the RIVA V_14Gy ranged from 4.0% to 45.4%. Overall, the VMAT plans had steeper dose gradients in the high dose region, while the plans for the robotic arm LINAC had smaller low dose regions. Thereby, VMAT plans required only about half as many monitor units, resulting in shorter delivery times, possibly an important factor in treatment outcome.

CONCLUSIONS

Cardiac radioablation is feasible with robotic arm and C-arm LINAC systems with comparable plan quality. Although cross-center training and best practice guidelines have been provided, further recommendations, especially for cardiac substructures, and ranking of dose guidelines will be helpful to optimize cardiac radioablation outcomes.

Feasibility of an Automatic Ultrasonographic Image Acquisition System Associated With an Artificial Intelligence Algorithm for Real-Time Monitoring of Cardiac Motion During Cardiac Radio-Ablation

Background

The management of the cardio-respiratory motion of the target and the reduction of the uncertainties related to patient's positioning are two of the main challenges that stereotactic arrhythmia radio-ablation (STAR) has to overcome. A prototype of a system was developed that can automatically acquire and interpret echocardiographic images using an artificial intelligence (AI) algorithm to calculate cardiac displacement in real-time.

Methods

We conducted a single center study enrolling consecutive patients with a history of ventricular arrhythmias (VA) in order to evaluate the feasibility of this automatic acquisition system. Echocardiographic images were automatically acquired from the parasternal and apical views with a dedicated probe. The system was designed to hold the probe fixed to the chest in the supine position during both free-breathing and short expiratory breath-hold sequences, to simulate STAR treatment. The primary endpoint was the percentage of patients reaching a score ≥2 in a multi-parametric assessment evaluating the quality of automatically acquired images. Moreover, we investigated the potential impact of clinical and demographic characteristics on achieving the primary endpoint.

Results

We enrolled 24 patients (63 ± 14 years, 21% females). All of them had a history of VA and 21 (88%) had an ICD. Eight patients (33%) had coronary artery disease, 12 (50%) had non-ischemic cardiomyopathy, and 3 had idiopathic VA. Parasternal, as well as apical images were obtained from all patients except from one, in whom parasternal view could not be collected due to the patient's inability to maintain the supine position. The primary endpoint was achieved in 23 patients (96%) for the apical view, in 20 patients (87%) for the parasternal view, and in all patients in at least one of the two views. The images' quality was maximal (i.e., score = 4) in at least one of the two windows in 19 patients (79%). Atrial fibrillation arrhythmia was the only clinical characteristics associated with a poor score outcome in both imaging windows (apical p = 0.022, parasternal p = 0.014).

Conclusions

These results provide the proof-of-concept for the feasibility of an automatic ultrasonographic image acquisition system associated with an AI algorithm for real-time monitoring of cardiac motion in patients with a history of VA.

Paroxysmal Atrial Fibrillation in Elderly: Worldwide Preliminary Data of LINAC-Based Stereotactic Arrhythmia Radioablation Prospective Phase II Trial

Treatment approach for elderly patients with atrial fibrillation (AF) is difficult. The present prospective phase-II trial evaluated LINAC-based stereotactic arrhythmia radioablation safety in this population. The reported data of the first 5 patients worldwide, showed no side effects, absence of AF episodes and without antiarrhythmic drugs.

Trial Registration:

ClinicalTrials.gov, identifier: NCT04575662.

Recent insights into mechanisms and clinical approaches to electrical storm

Electrical storm, characterized by repetitive ventricular tachycardia/fibrillation (VT/VF) over a short period, is becoming commoner with widespread use of implantable cardioverter-defibrillator (ICD) therapy. Electrical storm, sometimes called "arrhythmic storm" or "VT-storm", is usually a medical emergency requiring hospitalization and expert management, and significantly affects short- and long-term outcomes. This syndrome typically occurs in patients with underlying structural heart disease (ischemic or non-ischemic cardiomyopathy) or inherited channelopathies. Triggers for electrical storm should be sought but are often unidentifiable. Initial management is dictated by the hemodynamic status, while subsequent management typically involves ICD interrogation and reprogramming to reduce recurrent shocks, identification/management of triggers like electrolyte abnormalities, myocardial ischemia, or decompensated heart failure, and antiarrhythmic-drug therapy or catheter ablation. Sympathetic nervous system activation is central to the initiation and maintenance of arrhythmic storm, so autonomic modulation is a cornerstone of management. Sympathetic inhibition can be achieved with medications (particularly beta-adrenoreceptor blockers), deep sedation, or cardiac sympathetic denervation. More definitive management targets the underlying ventricular arrhythmia substrate to terminate and prevent recurrent arrhythmia. Arrhythmia targeting can be achieved with antiarrhythmic medications, catheter ablation or more novel therapies such as stereotactic radiation therapy that targets the arrhythmic substrate. Mechanistic studies point to adrenergic activation and other direct consequences of ICD-shocks in promoting further arrhythmogenesis and hypocontractility. Here, we review the pathophysiologic mechanisms, clinical features, prognosis, and therapeutic options for electrical storm. We also outline a clinical approach to this challenging and complex condition, along with its mechanistic basis.

Stereotactic ablative body radiotherapy for ventricular tachycardia: An alternative therapy for refractory patients

Stereotactic ablative body radiotherapy (SABR) allows the administration of ablative doses of radiation in a focused form with a low probability of side effects and is widely used for cancer treatment. However, in the recent years its usefulness in benign cardiac pathology is being studied. In this study, we aimed to guide the cardiologist in SABR and its applications in treatment of refractory ventricular tachycardia. In this review, we analyzed published literature on PubMed and MEDLINE with papers published in the past 5 years. We included papers in the English language with information about indications, radiotherapy plan, doses and fractionations, and outcomes. All citations were evaluated for relevant content and validation.

Stereotactic radioablation for ventricular tachycardia

Non-invasive stereotactic radioablation of ventricular tachycardia (VT) substrate has been proposed as a novel treatment modality for patients not eligible for catheter-based ablation or in whom this approach has failed. Initial clinical results are promising with good short-term efficacy in VT suppression and tolerable side effects. This article reviews the current clinical evidence for cardiac radioablation and gives an overview of important preclinical and translational results. Practical guidance is provided, and a cardiac radioablation planning and treatment workflow based on expert consensus and the authors' institutional experience is set out.

Use of Stereotactic Radioablation Therapy as a Bailout Therapy for Refractory Ventricular Tachycardia in a Patient with a No-entry Left Ventricle

In patients with mechanical aortic and mitral valves and left ventricular (LV) tachycardia (VT), catheter ablation is technically challenging due to the limited access to the LV. Promising new alternatives to radiofrequency ablation include pulsed-field electroporation, percutaneous or surgical sympathetic neuromodulation, and noninvasive stereotactic radioablation therapy (SBRT). We herein describe the effect of SBRT as a bailout therapy on the management of a challenging VT case in the presence of double left-sided mechanical valves.

The Rapidly-Developing Area of Radiocardiology: Principles, Complications and Applications of Radiotherapy on the Heart

Ventricular arrhythmias are the leading cause of sudden cardiac death. Current treatment strategies for VT, including antiarrhythmic drugs and catheter ablation, have limited efficacy in patients with structural heart disease. Non-invasive ablation with the use of externally applied radiation (cardiac radio-ablation) has emerged as a promising and novel approach to treating recurrent VTs. However, the heart is generally an "organ at risk" for radiation treatments, such that very little is known on the effects of radiotherapy on cardiac ultrastructure and electrophysiological properties. Furthermore, there has been limited interaction between the fields of cardiology and radiation oncology and physics. The advent of cardiac radio-ablation will undoubtedly increase interactions between cardiologists, cardiac electrophysiologists, radiation oncologists and physicists There is an important knowledge gap separating these specialties while scientific developments, technical optimization and improvements are dependent on intense multidisciplinary collaboration. This manuscript seeks to review the basic of radiation physics and biology for cardiovascular specialists in an effort to facilitate constructive scientific and clinical collaborations to improve patient outcomes.

Stereotactic radioablation of ventricular arrhythmias in patients with structural heart disease - A systematic review

BACKGROUND AND PURPOSE

Several studies have suggested stereotactic arrhythmia radioablation (STAR) as a treatment option for patients suffering from therapy-refractory ventricular tachycardia or fibrillation (VT/VF).

MATERIAL AND METHODS

We performed a systematic review of human reports of STAR for structural VT/VF to assess its effectivity and safety. All identified publications were assessed for inclusion. This study adheres to the PRISMA guidelines and was registered on PROSPERO (CRD42020183044).

RESULTS

Thirteen studies were included resulting in a population of 57 patients. Median age was 64 (range 34-83), 31 patients (54%) had ischemic cardiomyopathy and 50 patients (88%) had prior catheter ablation (CA) for VT/VF. A mean planned target volume of 64.4 cc (range 3.5-238) with a mean safety margin of 3.3 mm (0-5) was treated with 25 Gy. Immediately following STAR, four patients (7%) experienced an electrical storm. During a mean follow-up duration of 410 days, all patients suffering from sustained VT/VF prior to STAR (n = 55) had a reduction of their sustained VT/VF-burden after STAR, but recurrence occurred in 41 patients (75%) during follow-up. Forty-six patients (81%) had an adverse effect from therapy, but no treatment-related death occurred. Evidence of scar-formation after STAR either by imaging, invasive mapping or histopathology was found in six of nine examined patients (67%).

CONCLUSION

From the still very limited experience, STAR appears effective and safe in patients with structural heart disease and therapy-refractory sustained VT/VF. It is associated with a significant short-term reduction of sustained VT/VF-burden, but recurrences are common.