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.

Refractory ventricular tachycardia treated by a second session of stereotactic arrhythmia radioablation

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Arrhythmia radioablation (STAR) is effective in refractory ventricular tachycardia.

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We report the first cases of successful re-irradiation of arrhythmogenic substrate.

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No radiation toxicity was observed after the second STAR.

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Caution is advised as data on early and late toxicities remain scarce.

Purpose

Stereotactic arrhythmia radioablation (STAR) is an effective treatment for refractory ventricular tachycardia (VT), but recurrences after STAR were recently published. Herein, we report two cases of successful re-irradiation of the arrhythmogenic substrate.

Cases

We present two cases of re-irradiation after recurrence of a previously treated VT with radioablation at a dose of 20 Gy. The VT exit was localized on the border zone of the irradiated volume, which responded positively to re-irradiation at follow-up.

Conclusion

These two cases show the technical feasibility of re-irradiation to control recurrent VT after a first STAR.

Phantom study of stereotactic radioablation for ventricular tachycardia (STRA-MI-VT) using Cyberknife Synchrony Respiratory Tracking System with a single fiducial marker

PURPOSE

Within the STRA-MI-VT phase Ib/II trial (NCT04066517), the aim of this phantom study was to explore the feasibility of Cyberknife treatments on cardiac lesions by tracking as a single marker the lead tip of an implantable cardioverter defibrillator. The residual displacement of the lesion during the tracking was studied, planning margins were found and the dosimetric accuracy of the treatment was checked.

MATERIALS AND METHODS

A lead was inserted into a phantom (EasyCube phantom, Sun Nuclear Co, USA) and then placed on the translating ExacTrac Gating System (BrainLAB AG, Germany). The phantom was rotated, a virtual lesion was identified and its displacement during the tracking was studied. Two plans were compared, calculated on the unrotated volume and on the envelope of the unrotated and the rotated volumes. The plans were delivered using the Cyberknife System (Accuray Inc, USA) and their dosimetric accuracy verified by gamma analysis with gafchromic films.

RESULTS

The residual margin increases enhancing the distance between the lead and the lesion. It is 4 mm for distance 0 cm and 5 mm for distance 5 cm. The coverage is reduced by 3.8% (interquartile range 2.5%-4.7%) when the dose is prescribed on the unrotated volume. All treatment plans are accurate and 3% 3 mm gamma analysis results are greater than 94%.

CONCLUSIONS

Results showed that tracking with a single marker is feasible considering adequate residual planning margins. The volumes could be further reduced by using additional markers, for example by placing them on the patient's skin.

Stereotactic Radiotherapy: An Alternative Option for Refractory Ventricular Tachycardia to Drug and Ablation Therapy

Refractory ventricular tachycardia (VT) often occurs in the context of organic heart disease. It is associated with significantly high mortality and morbidity rates. Antiarrhythmic drugs and catheter ablation represent the two main treatment options for refractory VT, but their use can be associated with inadequate therapeutic responses and procedure-related complications. Stereotactic body radiotherapy (SBRT) is extensively applied in the precision treatment of solid tumors, with excellent therapeutic responses. Recently, this highly precise technology has been applied for radioablation of VT, and its early results demonstrate a favorable safety profile. This review presents the potential value of SBRT in refractory VT.

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.

Stereotactic Ablative Radiotherapy of Ventricular Tachycardia Using Tracking: Optimized Target Definition Workflow

Background and Purpose

Stereotactic arrhythmia radioablation (STAR) has been suggested as a promising therapeutic alternative in cases of failed catheter ablation for recurrent ventricular tachycardias in patients with structural heart disease. Cyberknife^® robotic radiosurgery system utilizing target tracking technology is one of the available STAR treatment platforms. Tracking using implantable cardioverter-defibrillator lead tip as target surrogate marker is affected by the deformation of marker–target geometry. A simple method to account for the deformation in the target definition process is proposed.

Methods

Radiotherapy planning CT series include scans at expiration and inspiration breath hold, and three free-breathing scans. All secondary series are triple registered to the primary CT: 6D/spine + 3D translation/marker + 3D translation/target surrogate—a heterogeneous structure around the left main coronary artery. The 3D translation difference between the last two registrations reflects the deformation between the marker and the target (surrogate) for the respective respiratory phase. Maximum translation differences in each direction form an anisotropic geometry deformation margin (GDM) to expand the initial single-phase clinical target volume (CTV) to create an internal target volume (ITV) in the dynamic coordinates of the marker. Alternative GDM-based target volumes were created for seven recent STAR patients and compared to the original treated planning target volumes (PTVs) as well as to analogical volumes created using deformable image registration (DIR) by MIM^® and Velocity^® software. Intra- and inter-observer variabilities of the triple registration process were tested as components of the final ITV to PTV margin.

Results

A margin of 2 mm has been found to cover the image registration observer variability. GDM-based target volumes are larger and shifted toward the inspiration phase relative to the original clinical volumes based on a 3-mm isotropic margin without deformation consideration. GDM-based targets are similar (mean DICE similarity coefficient range 0.80–0.87) to their equivalents based on the DIR of the primary target volume delineated by dedicated software.

Conclusion

The proposed GDM method is a simple way to account for marker–target deformation-related uncertainty for tracking with Cyberknife^® and better control of the risk of target underdose. The principle applies to general radiotherapy as well.

Long Term Follow-Up of Stereotactic Body Radiation Therapy for Refractory Ventricular Tachycardia in Advanced Heart Failure Patients

Background

Initial studies of stereotactic body radiation therapy (SBRT) for refractory ventricular tachycardia (VT) have demonstrated impressive efficacy. Follow-up analyses have found mixed results and the role of SBRT for refractory VT remains unclear. We performed palliative, cardiac radio ablation in patients with ventricular tachycardia refractory to ablation and medical management.

Methods

Arrhythmogenic regions were targeted by combining computed tomography imaging with electrophysiologic mapping with collaboration from a radiation oncologist, electrophysiologist and cardiac imaging specialist. Patients were treated with a single fraction 25 Gy. Total durations of VT, the quantity of antitachycardia pacing (ATP) and shocks before and after treatment as recorded by implantable cardioverter-defibrillators (ICDs) were analyzed. Follow-up extended until most recent device interrogation unless transplant, death or repeat ablation occurred sooner.

Results

Fourteen patients (age 50–78, four females) were treated and had an average of two prior ablations. Nine had ACC/AHA Stage D heart failure and three had left ventricular assist devices (LVAD). Two patients died shortly after SBRT, one received a prompt heart transplant and another had significant VT durations in the following months that were inaccurately recorded by their device. Ten of the 14 patients remained with adequate data post SBRT for analysis with an average follow-up duration of 216 days. Seven of those 10 patients had a decrease in VT post SBRT. Comparing the 90 days before treatment to cumulative follow-up, patients had a 59% reduction in VT, 39% reduction in ATP and a 60% reduction in shocks. Four patients received repeat ablation following SBRT. Pneumonitis was the only complication, occurring in four of the fourteen patients.

Conclusion

SBRT may have value in advanced heart failure patients with refractory VT acutely but the utility over long-term follow-up appears modest. Prospective randomized data is needed to better clarify the role of SBRT in managing refractory VT.

Contemporary Management of Complex Ventricular Arrhythmias

Percutaneous catheter ablation is an effective and safe therapy that can eliminate ventricular tachycardia, reducing the risks of both recurrent arrhythmia and shock therapies from a defibrillator. Successful ablation requires accurate identification of arrhythmic substrate and the effective delivery of energy to the targeted tissue. A thorough pre-procedural assessment is needed before considered 3D electroanatomical mapping can be performed. In contemporary practice, this must combine traditional electrophysiological techniques, such as activation and entrainment mapping, with more novel physiological mapping techniques for which there is an ever-increasing evidence base. Novel techniques to maximise energy delivery to the tissue must also be considered and balanced against their associated risks of complication. This review provides a comprehensive appraisal of contemporary practice and the evidence base that supports recent developments in mapping and ablation, while also considering potential future developments in the field.

Case Report: Repeated Stereotactic Radiotherapy of Recurrent Ventricular Tachycardia: Reasons, Feasibility, and Safety

Stereotactic body radiotherapy (SBRT) has been reported as an attractive option for cases of failed catheter ablation of ventricular tachycardia (VT) in structural heart disease. However, even this strategy can fail for various reasons. For the first time, this case series describes three re-do cases of SBRT which were indicated for three different reasons. The purpose in the first case was the inaccuracy of the determination of the treatment volume by indirect comparison of the electroanatomical map and CT scan. A newly developed strategy of co-registration of both images allowed precise targeting of the substrate. In this case, the second treatment volume overlapped by 60% with the first one. The second reason for the re-do of SBRT was an unusual character of the substrate–large cardiac fibroma associated with different morphologies of VT from two locations around the tumor. The planned treatment volumes did not overlap. The third reason for repeated SBRT was the large intramural substrate in the setting of advanced heart failure. The first treatment volume targeted arrhythmias originating in the basal inferoseptal region, while the second SBRT was focused on adjacent basal septum without significant overlapping. Our observations suggested that SBRT for VT could be safely repeated in case of later arrhythmia recurrences (i.e., after at least 6 weeks). No acute toxicity was observed and in two cases, no side effects were observed during 32 and 22 months, respectively. To avoid re-do SBRT due to inaccurate targeting, the precise and reproducible strategy of substrate identification and co-registration with CT image should be used.

Non-invasive Stereotactic Body Radiation Therapy for Refractory Ventricular Arrhythmias: Venturing into the Unknown

Stereotactic body radiation therapy (SBRT) is a promising new method for non-invasive management of life-threatening ventricular arrhythmias. Numerous case reports and case series have provided encouraging short-term results suggesting good efficacy and safety, but randomized data and long-term outcomes are not yet available. The primary hypothesis as to the mechanism of action for SBRT relates to the development of cardiac fibrosis in arrhythmogenic myocardial substrate; however, limited animal model data offer conflicting insights into this theory. The use of SBRT for patients with refractory ventricular arrhythmias is rapidly increasing, but ongoing translational science work and randomized clinical trials will be critical to address many outstanding questions regarding this novel therapy.

Verification of rebuild-up effect on superficial cardiac lesion of ventricular tachycardia using 3-D printed phantom in volumetric-modulated arc therapy planning

The aim of the study was to evaluate dose distributions on the superficial cardiac lesion surrounded by low-density lungs. Volumetric modulated arc therapy (VMAT) technique was applied to optimize the dose distribution using the anisotropic analytic algorithm (AAA) and Acuros XB algorithm (AXB) using the 3-D printed cardiac phantom. We used four full and half arcs with 6-MV and 15-MV photons to investigate the rebuild-up effect near the planning target volume (PTV). Depending on the calculation algorithm (AAA vs. AXB) for full arcs plans, V₉₅ of PTV differed by 27% for 6-MV and 29% for 15-MV, and D₉₅ for 6-MV and 15-MV shows 24% and 30%, respectively. The maximum doses in the AXB plans on PTV were 5.1% higher than those in AAA plans at 6-MV, and 3.8% higher at 15-MV. In addition, half arcs treatment plans showed a very similar tendency with full arcs plans. Film dosimetry showed significant differences from the planned results in the AAA plans. Particularly, the dose mismatch occurred between the cardiac PTV and the left lung interface. In the case of 6-MV plans calculated by AAA, the maximum dose increased from 4.1 to 7.7% in the PTV. Furthermore, it showed that 50% of the width of dose profiles was reduced by 1.3 cm in the 6-MV plan. Conversely, in the case of the plans using the AXB algorithm, the maximum dose increased by 2.0–5.0%. In contrast to the AAA algorithm, the dose patterns at the interface demonstrated a good agreement with the plans. Dose fluctuation on the interface between superficial cardiac lesions and low-density lungs can lead to an error in the estimation of accurate dose delivery for the case of VT SBRT.

Report of AAPM Task Group 290: Respiratory motion management for particle therapy

Dose uncertainty induced by respiratory motion remains a major concern for treating thoracic and abdominal lesions using particle beams. This Task Group report reviews the impact of tumor motion and dosimetric considerations in particle radiotherapy, current motion‐management techniques, and limitations for different particle‐beam delivery modes (i.e., passive scattering, uniform scanning, and pencil‐beam scanning). Furthermore, the report provides guidance and risk analysis for quality assurance of the motion‐management procedures to ensure consistency and accuracy, and discusses future development and emerging motion‐management strategies. This report supplements previously published AAPM report TG76, and considers aspects of motion management that are crucial to the accurate and safe delivery of particle‐beam therapy. To that end, this report produces general recommendations for commissioning and facility‐specific dosimetric characterization, motion assessment, treatment planning, active and passive motion‐management techniques, image guidance and related decision‐making, monitoring throughout therapy, and recommendations for vendors. Key among these recommendations are that: (1) facilities should perform thorough planning studies (using retrospective data) and develop standard operating procedures that address all aspects of therapy for any treatment site involving respiratory motion; (2) a risk‐based methodology should be adopted for quality management and ongoing process improvement.

Management of ventricular arrhythmias in heart failure: Current perspectives

Congestive heart failure (HF) is a progressive affliction defined as the inability of the heart to sufficiently maintain blood flow. Ventricular arrhythmias (VAs) are common in patients with HF, and conversely, advanced HF promotes the risk of VAs. Management of VA in HF requires a systematic, multimodality approach that comprises optimization of medical therapy and use of implantable cardioverter-defibrillator and/or device combined with cardiac resynchronization therapy. Catheter ablation is one of the most important strategies with the potential to abolish or decrease the number of recurrences of VA in this population. It can be a curative strategy in arrhythmia-induced cardiomyopathy and may even save lives in cases of an electrical storm. Additionally, modulation of the autonomic nervous system and stereotactic radiotherapy have been introduced as novel methods to control refractory VAs. In patients with end-stage HF and refractory VAs, an institution of the mechanical circulatory support device and cardiac transplant may be considered. This review aims to provide an overview of current evidence regarding management strategies of VAs in HF with an emphasis on interventional treatment.

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.

SBRT of ventricular tachycardia using 4pi optimized trajectories

PURPOSE

To investigate the possible advantages of using 4pi-optimized arc trajectories in stereotactic body radiation therapy of ventricular tachycardia (VT-SBRT) to minimize exposure of healthy tissues.

METHODS AND MATERIALS

Thorax computed tomography (CT) data for 15 patients were used for contouring organs at risk (OARs) and defining realistic planning target volumes (PTVs). A conventional trajectory plan, defined as two full coplanar arcs was compared to an optimized-trajectory plan provided by a 4pi algorithm that penalizes geometric overlap of PTV and OARs in the beam's-eye-view. A single fraction of 25 Gy was prescribed to the PTV in both plans and a comparison of dose sparing to OARs was performed based on comparisons of maximum, mean, and median dose.

RESULTS

A significant average reduction in maximum dose was observed for esophagus (18%), spinal cord (26%), and trachea (22%) when using 4pi-optimized trajectories. Mean doses were also found to decrease for esophagus (19%), spinal cord (33%), skin (18%), liver (59%), lungs (19%), trachea (43%), aorta (11%), inferior vena cava (25%), superior vena cava (33%), and pulmonary trunk (26%). A median dose reduction was observed for esophagus (40%), spinal cord (48%), skin (36%), liver (72%), lungs (41%), stomach (45%), trachea (53%), aorta (45%), superior vena cava (38%), pulmonary veins (32%), and pulmonary trunk (39%). No significant difference was observed for maximum dose (p = 0.650) and homogeneity index (p = 0.156) for the PTV. Average values of conformity number were 0.86 ± 0.05 and 0.77 ± 0.09 for the conventional and 4pi optimized plans respectively.

CONCLUSIONS

4pi optimized trajectories provided significant reduction to mean and median doses to cardiac structures close to the target but did not decrease maximum dose. Significant improvement in maximum, mean and median doses for noncardiac OARs makes 4pi optimized trajectories a suitable delivery technique for treating VT.

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.

Cardiac stereotactic ablative radiotherapy for control of refractory ventricular tachycardia: initial UK multicentre experience

Background

Options for patients with ventricular tachycardia (VT) refractory to antiarrhythmic drugs and/or catheter ablation remain limited. Stereotactic radiotherapy has been described as a novel treatment option.

Methods

Seven patients with recurrent refractory VT, deemed high risk for either first time or redo invasive catheter ablation, were treated across three UK centres with non-invasive cardiac stereotactic ablative radiotherapy (SABR). Prior catheter ablation data and non-invasive mapping were combined with cross-sectional imaging to generate radiotherapy plans with aim to deliver a single 25 Gy treatment. Shared planning and treatment guidelines and prospective peer review were used.

Results

Acute suppression of VT was seen in all seven patients. For five patients with at least 6 months follow-up, overall reduction in VT burden was 85%. No high-grade radiotherapy treatment-related side effects were documented. Three deaths (two early, one late) occurred due to heart failure.

Conclusions

Cardiac SABR showed reasonable VT suppression in a high-risk population where conventional treatment had failed.

Cardiac radioablation in the treatment of ventricular tachycardia

Cardiac radioablation with SBRT is a very promising non-invasive modality for the treatment of refractory VT and potentially other cardiac arrhythmias. Initial reports indicate that it is relatively safe and associated with excellent responses, particularly in reduction of ICD-related events, need for anti-arrhythmic medications, and resulting in significantly improved quality of life for patients. Establishment of objective criteria for candidates for cardiac radioablation will accelerate the adoption of this important radiation therapy modality in the treatment of refractory VT and other cardiac arrhythmias in the coming years. In addition, in order to develop more prospective safety and efficacy data, treatment of patients should ideally be performed in the context of clinical trials or prospective registries at, or in collaboration with, experienced centers. Taken together, the future of cardiac radioablation is rich and worthy of further investigation to become a standard treatment in the armamentarium against refractory VT.

Stereotactic Arrhythmia Radioablation as a Novel Treatment Approach for Cardiac Arrhythmias: Facts and Limitations

Stereotactic ablative radiotherapy (SABR) is highly focused radiation therapy that targets well-demarcated, limited-volume malignant or benign tumors with high accuracy and precision using image guidance. Stereotactic arrhythmia radioablation (STAR) applies SABR to treat cardiac arrhythmias, including ventricular tachycardia (VT) and atrial fibrillation (AF), and has recently been a focus in research. Clinical studies have demonstrated electrophysiologic conduction blockade and histologic fibrosis after STAR, which provides a proof of principle for its potential for treating arrhythmias. This review will present the basic STAR principles, available clinical study outcomes, and how the technique has evolved since the first pre-clinical study. In addition to the clinical workflow, focus will be given on the process for stereotactic radiotherapy Quality Assurance (QA) tests, as well as the need for establishing a standardized QA protocol. Future implications and potential courses of research will also be discussed.

Stereotactic radioablation for the treatment of ventricular tachycardia: preliminary data and insights from the STRA-MI-VT phase Ib/II study

Purpose

We present the preliminary results of the STRA-MI-VT Study (NCT04066517), a spontaneous, phase Ib/II study, designed to prospectively test the safety and efficacy of stereotactic body radiotherapy (SBRT) in patientswith advanced cardiac disease and intractable ventricular tachycardia (VT).

Methods

Cardiac computed tomography (CT) integrated by electroanatomical mapping was used for substrate identification and merged with dedicated CT scans for treatment plan preparation. A single 25-Gy radioablation dose was delivered by a LINAC-based volumetric modulated arc therapy technique in a non-invasive matter. The primary safety endpoint was treatment-related adverse effects during acute and long-term follow-up (FU), obtained by regular in-hospital controls and implantable cardioverter defibrillator (ICD) remote monitoring. The primary efficacy endpoint was the reduction at 3 and 6 months of VT episodes and ICD shocks.

Results

Seven out of eight patients (men; age, 70 ± 7 years; ejection fraction, 27 ± 11%; 3 ischemic, 4 non-ischemic cardiomyopathies) underwent SBRT. At a median 8-month FU, no treatment-related serious adverse event occurred. Three patients died from non-SBRT-related causes. Four patients completed the 6-month FU: the number of VT decreased from 29 ± 33 to 11 ± 9 (p = .05) and 2 ± 2 (p = .08), at 3 and 6 months, respectively; shocks decreased from 11 to 0 and 2, respectively. At 6 months, all patients. showed a significant reduction of VT episodes and no electrical storm recurrence, with the complete regression of iterative VTs in 2/2 patients.

Conclusion

The STRA-MI-VT Study suggests that SBRT can be considered an alternative option for the treatment of VT in patients with structural heart disease and highlights the need for further clinical investigation addressing safety and efficacy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10840-021-01060-5.

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.

Computational ECG mapping and respiratory gating to optimize stereotactic ablative radiotherapy workflow for refractory ventricular tachycardia

BACKGROUND

Stereotactic ablative radiotherapy (SAbR) is an emerging therapy for refractory ventricular tachycardia (VT). However, the current workflow is complicated, and the precision and safety in patients with significant cardiorespiratory motion and VT targets near the stomach may be suboptimal.

OBJECTIVE

We hypothesized that automated 12-lead electrocardiogram (ECG) mapping and respiratory-gated therapy may improve the ease and precision of SAbR planning and facilitate safe radiation delivery in patients with refractory VT.

METHODS

Consecutive patients with refractory VT were studied at 2 hospitals. VT exit sites were localized using a 3-D computational ECG algorithm noninvasively and compared to available prior invasive mapping. Radiotherapy (25 Gy) was delivered at end-expiration when cardiac respiratory motion was ≥0.6 cm or targets were ≤2 cm from the stomach.

RESULTS

In 6 patients (ejection fraction 29% ± 13%), 4.2 ± 2.3 VT morphologies per patient were mapped. Overall, 7 out of 7 computational ECG mappings (100%) colocalized to the identical cardiac segment when prior invasive electrophysiology study was available. Respiratory gating was associated with smaller planning target volumes compared to nongated volumes (71 ± 7 vs 153 ± 35 cc, P < .01). In 2 patients with inferior wall VT targets close to the stomach (6 mm proximity) or significant respiratory motion (22 mm excursion), no GI complications were observed at 9- and 12-month follow-up. Implantable cardioverter-defibrillator shocks decreased from 23 ± 12 shocks/patient to 0.67 ± 1.0 (P < .001) post-SAbR at 6.0 ± 4.9 months follow-up.

CONCLUSIONS

A workflow including computational ECG mapping and protocol-guided respiratory gating is feasible, is safe, and may improve the ease of SAbR planning. Studies to validate this workflow in larger populations are required.

Cardiac stereotactic body radiation therapy for ventricular tachycardia: Current experience and technical gaps

INTRODUCTION

Despite advances in drug and catheter ablation therapy, long-term recurrence rates for ventricular tachycardia remain suboptimal. Cardiac stereotactic body radiotherapy (SBRT) is a novel treatment that has demonstrated reduction of arrhythmia episodes and favorable short-term safety profile in treatment-refractory patients. Nevertheless, the current clinical experience is early and limited. Recent studies have highlighted variable duration of treatment effect and substantial recurrence rates several months postradiation. Contributing to these differential outcomes are disparate approaches groups have taken in planning and delivering radiation, owing to both technical and knowledge gaps limiting optimization and standardization of cardiac SBRT.

METHODS AND FINDINGS

In this report, we review the historical basis for cardiac SBRT and existing clinical data. We then elucidate the current technical gaps in cardiac radioablation, incorporating the current clinical experience, and summarize the ongoing and needed efforts to resolve them.

CONCLUSION

Cardiac SBRT is an emerging therapy that holds promise for the treatment of ventricular tachycardia. Technical gaps remain, to be addressed by ongoing research and growing clincial experience.

Cardiac radiotherapy induces electrical conduction reprogramming in the absence of transmural fibrosis

Cardiac radiotherapy (RT) may be effective in treating heart failure (HF) patients with refractory ventricular tachycardia (VT). The previously proposed mechanism of radiation-induced fibrosis does not explain the rapidity and magnitude with which VT reduction occurs clinically. Here, we demonstrate in hearts from RT patients that radiation does not achieve transmural fibrosis within the timeframe of VT reduction. Electrophysiologic assessment of irradiated murine hearts reveals a persistent supraphysiologic electrical phenotype, mediated by increases in NaV1.5 and Cx43. By sequencing and transgenic approaches, we identify Notch signaling as a mechanistic contributor to NaV1.5 upregulation after RT. Clinically, RT was associated with increased NaV1.5 expression in 1 of 1 explanted heart. On electrocardiogram (ECG), post-RT QRS durations were shortened in 13 of 19 patients and lengthened in 5 patients. Collectively, this study provides evidence for radiation-induced reprogramming of cardiac conduction as a potential treatment strategy for arrhythmia management in VT patients.

Leveraging Radiobiology for Arrhythmia Management: A New Treatment Paradigm?

Radiation therapy is a well-established approach for safely and non-invasively treating solid tumours and benign diseases with high precision and accuracy. Cardiac radiation therapy has recently emerged as a non-invasive treatment option for the management of refractory ventricular tachycardia. Here we summarise existing clinical and preclinical literature surrounding cardiac radiobiology and discuss how these studies may inform basic and translational research, as well as clinical treatment paradigms in the management of arrhythmias.

Accuracy of electroanatomical mapping-guided cardiac radiotherapy for ventricular tachycardia: pitfalls and solutions

AIMS

To analyse and optimize the interobserver agreement for gross target volume (GTV) delineation on cardiac computed tomography (CCT) based on electroanatomical mapping (EAM) data acquired to guide radiotherapy for ventricular tachycardia (VT).

METHODS AND RESULTS

Electroanatomical mapping data were exported and merged with the segmented CCT using manual registration by two observers. A GTV was created by both observers for predefined left ventricular (LV) areas based on preselected endocardial EAM points indicating a two-dimensional (2D) surface area of interest. The influence of (interobserver) registration accuracy and availability of EAM data on the final GTV and 2D surface location within each LV area was evaluated. The median distance between the CCT and EAM after registration was 2.7 mm, 95th percentile 6.2 mm for observer #1 and 3.0 mm, 95th percentile 7.6 mm for observer #2 (P = 0.9). Created GTVs were significantly different (8 vs. 19 mL) with lowest GTV overlap (35%) for lateral wall target areas. Similarly, the highest shift between 2D surfaces was observed for the septal LV (6.4 mm). The optimal surface registration accuracy (2.6 mm) and interobserver agreement (Δ interobserver EAM surface registration 1.3 mm) was achieved if at least three cardiac chambers were mapped, including high-quality endocardial LV EAM.

CONCLUSION

Detailed EAM of at least three chambers allows for accurate co-registration of EAM data with CCT and high interobserver agreement to guide radiotherapy of VT. However, the substrate location should be taken in consideration when creating a treatment volume margin.

Clinical management of electrical storm: a current overview

The number of patients affected by electrical storm has been continuously increasing in emergency departments. Patients are often affected by multiple comorbidities requiring multidisciplinary interventions to achieve a clinical stability. Careful reprogramming of cardiac devices, correction of electrolyte imbalance, knowledge of underlying heart disease and antiarrhythmic drugs in the acute phase play a crucial role. The aim of this review is to provide a comprehensive overview of pharmacological treatment, latest transcatheter ablation techniques and advanced management of patients with electrical storm.

Proof-of-concept for x-ray based real-time image guidance during cardiac radioablation

Cardiac radioablation offers non-invasive treatments for refractory arrhythmias. However, treatment delivery for this technique remains challenging. In this paper, we introduce the first method for real-time image guidance during cardiac radioablation for refractory atrial fibrillation on a standard linear accelerator. Our proposed method utilizes direct diaphragm tracking on intrafraction images to estimate the respiratory component of cardiac substructure motion. We compare this method to treatment scenarios without real-time image guidance using the 4D-XCAT digital phantom. Pre-treatment and intrafraction imaging was simulated for 8 phantoms with unique anatomies programmed using cardiorespiratory motion from healthy volunteers. As every voxel in the 4D-XCAT phantom is labelled precisely according to the corresponding anatomical structure, this provided ground-truth for quantitative evaluation. Tracking performance was compared to the ground-truth for simulations with and without real-time image guidance using the left atrium as an exemplar target. Differences in target volume size, mean volumetric coverage, minimum volumetric coverage and geometric error were recorded for each simulation. We observed that differences in target volume size were statistically significant (p < 0.001) across treatment scenarios and that real-time image guidance enabled reductions in target volume size ranging from 11% to 24%. Differences in mean and minimum volumetric coverage were statistically insignificant (bothp = 0.35) while differences in geometric error were statistically significant (p = 0.039). The results of this study provide proof-of-concept for x-ray based real-time image guidance during cardiac radioablation.

Recommendations regarding cardiac stereotactic body radiotherapy for treatment refractory ventricular tachycardia

BACKGROUND

Ventricular tachycardia (VT) is a potentially lethal complication of structural heart disease. Despite optimal management, a subgroup of patients continue to suffer from recurrent VT. Recently, cardiac stereotactic body radiotherapy (CSBRT) has been introduced as a treatment option in patients with VT refractory to antiarrhythmic drugs and catheter ablation.

OBJECTIVE

The purpose of this study was to establish an expert consensus regarding the conduct and use of CSBRT for refractory VT.

METHODS

We conducted a modified Delphi process. Thirteen experts from institutions from Germany and Switzerland participated in the modified Delphi process. Statements regarding the following topics were generated: treatment setting, institutional expertise and technical requirements, patient selection, target volume definition, and monitoring during and after CSBRT. Agreement was rated on a 5-point Likert scale. Cutoffs for agreement were defined in analogy to the RAND methodology.

RESULTS

There was strong agreement regarding the experimental status of the procedure and the preference for treatment in clinical trials. CSBRT should be conducted at specialized centers with a strong expertise in the management of patients with ventricular arrhythmias and in stereotactic body radiotherapy for moving targets. CSBRT should be restricted to patients with refractory VT with optimal antiarrhythmic medication who underwent prior catheter ablation or have contraindications. Target volume delineation for CSBRT is complex. Therefore, interdisciplinary processes that should include cardiology/electrophysiology and radiation oncology as well as medical physics, radiology, and nuclear medicine are needed. Optimal follow-up is required.

CONCLUSION

Prospective trials and pooled registries are needed to gain further insight into this promising treatment option for patients with refractory VT.

Substrate Modification Using Stereotactic Radioablation to Treat Refractory Ventricular Tachycardia in Patients With Ischemic Cardiomyopathy

OBJECTIVES

This study aimed to determine the feasibility of using radioablation for arrhythmogenic a substrate modification.

BACKGROUND

Stereotactic body radiation therapy (SBRT) is a promising therapy for ventricular tachycardia (VT) refractory to catheter ablation.

METHODS

A total of 6 male patients (median age 72 years) with ischemic cardiomyopathy (left ventricular ejection fraction 20% [interquartile range (IQR): 16%-25%]) and VT refractory to antiarrhythmic medications and catheter ablations underwent SBRT to extensive scar substrate. In addition to electroanatomical mapping, 5 of 6 patients had computed tomography segmentation using MUSIC (Institut Hospitalo-Universitaire l'Institut de Rythmologie et Modélisation Cardiaque, Bordeaux, France). Regions of wall thinning <5 mm, calcification, and intramyocardial fat were targeted for radioablation at 25 Gy.

RESULTS

The median planning target volume was 319 (IQR: 280-330) mL. Device-treated or sustained VT episodes were not significantly reduced by radioablation (median 42 [IQR: 19-269] to 29 [IQR: 0-81]; P = 0.438). However, a reduction in device shocks was observed from 12 (IQR: 3-19) to 0 (IQR: 0-1) (P = 0.046). Over a follow-up period of 231 (IQR: 212-311) days, 3 patients died of end-stage heart failure and 3 of 6 patients had possible adverse events (heart failure exacerbation, pneumonia, and an asymptomatic pericardial effusion).

CONCLUSIONS

Substrate modification using SBRT assisted by computed tomography segmentation is feasible for treatment of VT in patients with ischemic cardiomyopathy. Although a significant reduction in device shocks was observed, suboptimal VT burden reduction and significant mortality rate in this cohort of patients with advanced cardiomyopathy underscore the need to improve mechanistic understanding for antiarrhythmic effects to guide dosing and targeting of scar substrates.

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.

Evaluation of Motion Compensation Methods for Noninvasive Cardiac Radioablation of Ventricular Tachycardia

PURPOSE

Noninvasive cardiac radioablation is increasingly used for treatment of refractory ventricular tachycardia. Attempts to limit normal tissue exposure are important, including managing motion of the target. An interplay between cardiac and respiratory motion exists for cardiac radioablation, which has not been studied in depth. The objectives of this study were to estimate target motion during abdominal compression free breathing (ACFB) and respiratory gated (RG) deliveries and to investigate the quality of either implanted cardioverter defibrillator lead tip or the diaphragm as a gating surrogate.

METHODS AND MATERIALS

Eleven patients underwent computed tomography (CT) simulation with an ACFB 4-dimensional CT (r4DCT) and an exhale breath-hold cardiac 4D-CT (c4DCT). The target, implanted cardioverter defibrillator lead tip and diaphragm trajectories were measured for each patient on the r4DCT and c4DCT using rigid registration of each 4D phase to the reference (0%) phase. Motion ranges for ACFB and exhale (40%-60%) RG delivery were estimated from the target trajectories. Surrogate quality was estimated as the correlation with the target motion magnitudes.

RESULTS

Mean (range) target motion across patients from r4DCT was as follows: left/right (LR), 3.9 (1.7-6.9); anteroposterior (AP), 4.1 (2.2-5.4); and superoinferior (SI), 4.7 (2.2-7.9) mm. Mean (range) target motion from c4DCT was as follows: LR, 3.4 (1.0-4.8); AP, 4.3 (2.6-6.5); and SI, 4.1 (1.4-8.0) mm. For an ACFB, treatment required mean (range) margins to be 4.5 (3.1-6.9) LR, 4.8 (3-6.5) AP, and 5.5 (2.3-8.0) mm SI. For RG, mean (range) internal target volume motion would be 3.6 (1.1-4.8) mm LR, 4.3 (2.6-6.5) mm AP, and 4.2 (2.2-8.0) mm SI. The motion correlations between the surrogates and target showed a high level of interpatient variability.

CONCLUSIONS

In ACFB patients, a simulated exhale-gated approach did not lead to large projected improvements in margin reduction. Furthermore, the variable correlation between readily available gating surrogates could mitigate any potential advantage to gating and should be evaluated on a patient-specific basis.

Case series on stereotactic body radiation therapy in non-ischemic cardiomyopathy patients with recurrent ventricular tachycardia

INTRODUCTION

The efficacy of stereotactic body radiation therapy (SBRT) as an alternative treatment for recurrent ventricular tachycardia (VT) is still unclear. This study aimed to report the outcome of SBRT in VT patients with nonischemic cardiomyopathy (NICM).

METHODS

The determination of the target substrate for radiation was based on the combination of CMR results and electroanatomical mapping merged with the real-time CT scan image. Radiation therapy was performed by Flattening-filter-free (Truebeam) system, and afterward, patients were followed up for 13.5 ± 2.8 months. We analyzed the outcome of death, incidence of recurrent VT, ICD shocks, anti-tachycardia pacing (ATP) sequences, and possible irradiation side-effects.

RESULTS

A total of three cases of NICM patients with anteroseptal scar detected by CMR. SBRT was successfully performed in all patients. During the follow-up, we found that VT recurrences occurred in all patients. In one patient, it happened during a 6-week blanking period, while the others happened afterward. Re-hospitalization due to VT only appeared in one patient. Through ICD interrogation, we found that all patients have reduced VT burden and ATP therapies. All of the patients died during the follow-up period. Radiotherapy-related adverse events did not occur in all patients.

CONCLUSIONS

SBRT therapy reduces the number of VT burden and ATP sequence therapy in NICM patients with VT, which had a failed previous catheter ablation. However, the efficacy and safety aspects, especially in NICM cases, remained unclear.

First Asian population study of stereotactic body radiation therapy for ventricular arrhythmias

We report the first Asian series on stereotactic body radiation (SBRT) for refractory ventricular arrhythmia (VA) in Taiwanese patients. Three-dimensional electroanatomic maps, delayed-enhancement magnetic resonance imaging (DE-MRI), and dual-energy computed tomography (CT) were used to identify scar substrates. The main target volume was treated with a single radiation dose of 25 Gy and the margin volume received 20 Gy using simultaneous integrated boost delivered by the Varian TrueBeam system. Efficacy was assessed according to VA events recorded by an implantable cardioverter-defibrillator (ICD) or a 24-h Holter recorder. Pre- and post-radiation therapy imaging studies were performed. From February 2019 to December 2019, seven patients (six men, one woman; mean age, 55 years) were enrolled and treated. One patient died of hepatic failure. In the remaining six patients, at a median follow-up of 14.5 months, the VA burden and ICD shocks significantly decreased (only one patient with one ICD shock after treatment). Increased intensity on DE-MRI might be associated with a lower risk for VA recurrence, whereas dual-energy CT had lower detection sensitivity. No acute or minimal late adverse events occurred. In patients with refractory VA, SBRT is associated with a marked reduction in VA burden and ICD shocks, and DE-MRI might be useful for monitoring treatment effects.

Non-invasive ablation of arrhythmias with stereotactic ablative radiotherapy

Stereotactic ablative radiotherapy (SABR), or stereotactic body radiotherapy (SBRT), has recently been applied in the field of arrhythmia management. It has been most widely assessed in the treatment of ventricular tachycardia (VT) but may also have potential in the treatment of other arrhythmias as well, often termed stereotactic arrhythmia radiotherapy (STAR). The non-invasive delivery of treatment for VT has the potential to spare an often physiologically vulnerable group of patients the burden of long catheter ablation procedures with the potential for prolonged periods of hemodynamic instability. Cardiac SABR also has the capacity to direct ablative therapy at substrate that is inaccessible using current transchatheter techniques. For these reasons cardiac SABR has generated significant enthusiasm as an emerging treatment modality for VT. We consider in review the pre-clinical data pertaining to the use of SABR in cardiac tissue and recent clinical evidence regarding the application of SABR in the field of arrhythmia management.

Dosimetric feasibility of stereotactic ablative radiotherapy in pulmonary vein isolation for atrial fibrillation using intensity-modulated proton therapy

Purpose

To evaluate dosimetric properties of intensity‐modulated proton therapy (IMPT) for simulated treatment planning in patients with atrial fibrillation (AF) targeting left atrial‐pulmonary vein junction (LA‐PVJ), in comparison with volumetric‐modulated arc therapy (VMAT) and helical tomotherapy (TOMO).

Methods

Ten thoracic 4D‐CT scans with respiratory motion and one with cardiac motion were used for the study. Ten respiratory 4D‐CTs were planned with VMAT, TOMO, and IMPT for simulated AF. Targets at the LA‐PVJ were defined as wide‐area circumferential ablation line. A single fraction of 25 Gy was prescribed to all plans. The interplay effects from cardiac motion were evaluated based on the cardiac 4D‐CT scan. Dose‐volume histograms (DVHs) of the ITV and normal tissues were compared. Statistical analysis was evaluated via one‐way Repeated‐Measures ANOVA and Friedman’s test with Bonferroni’s multiple comparisons test.

Results

The median volume of ITV was 8.72cc. All plans had adequate target coverage (V_23.75Gy ≥ 99%). Compared with VMAT and TOMO, IMPT resulted in significantly lower dose of most normal tissues. For VMAT, TOMO, and IMPT plans, D_mean of the whole heart was 5.52 ± 0.90 Gy, 5.89 ± 0.78 Gy, and 3.01 ± 0.57 Gy (P < 0.001), mean dose of pericardium was 4.74 ± 0.76 Gy, 4.98 ± 0.62 Gy, and 2.59 ± 0.44 Gy (P < 0.001), and D_0.03cc of left circumflex artery (LCX) was 13.96 ± 5.45 Gy, 14.34 ± 5.91 Gy, and 8.43 ± 7.24 Gy (P < 0.001), respectively. However, no significant advantage for one technique over the others was observed when examining the D_0.03cc of esophagus and main bronchi.

Conclusions

IMPT targeting LA‐PVJ for patients with AF has high potential to reduce dose to surrounding tissues compared to VMAT or TOMO. Motion mitigation techniques are critical for a particle‐therapy approach.

Clinical Evidence behind Stereotactic Radiotherapy for the Treatment of Ventricular Tachycardia (STAR)-A Comprehensive Review

The electrophysiology-guided noninvasive cardiac radioablation, also known as STAR (stereotactic arrhythmia radioablation) is an emerging treatment method for persistent ventricular tachycardia. Since its first application in 2012 in Stanford Cancer Institute, and a year later in University Hospital Ostrava, Czech Republic, the authors from all around the world have published case reports and case series, and several prospective trials were established. In this article, we would like to discuss the available clinical evidence, analyze the potentially clinically relevant differences in methodology, and address some of the unique challenges that come with this treatment method.

Early Changes in Rat Heart After High-Dose Irradiation: Implications for Antiarrhythmic Effects of Cardiac Radioablation

Background

Noninvasive cardiac radioablation is employed to treat ventricular arrhythmia. However, myocardial changes leading to early‐period antiarrhythmic effects induced by high‐dose irradiation are unknown. This study investigated dose‐responsive histologic, ultrastructural, and functional changes within 1 month after irradiation in rat heart.

Methods and Results

Whole hearts of wild‐type Lewis rats (N=95) were irradiated with single fraction 20, 25, 30, 40, or 50 Gy and explanted at 1 day or 1, 2, 3, or 4 weeks’ postirradiation. Microscopic pathologic changes of cardiac structures by light microscope with immunohistopathologic staining, ultrastructure by electron microscopy, and functional evaluation by ECG and echocardiography were studied. Despite high‐dose irradiation, no myocardial necrosis and apoptosis were observed. Intercalated discs were widened and disrupted, forming uneven and twisted junctions between adjacent myocytes. Diffuse vacuolization peaked at 3 weeks, suggesting irradiation dose‐responsiveness, which was correlated with interstitial and intracellular edema. CD68 immunostaining accompanying vacuolization suggested mononuclear cell infiltration. These changes were prominent in working myocardium but not cardiac conduction tissue. Intracardiac conduction represented by PR and QTc intervals on ECG was delayed compared with baseline measurements. ST segment was initially depressed and gradually elevated. Ventricular chamber dimensions and function remained intact without pericardial effusion.

Conclusions

Mononuclear cell–related intracellular and extracellular edema with diffuse vacuolization and intercalated disc widening were observed within 1 month after high‐dose irradiation. ECG indicated intracardiac conduction delay with prominent ST‐segment changes. These observations suggest that early antiarrhythmic effects after cardiac radioablation result from conduction disturbances and membrane potential alterations without necrosis.

State of the art paper: Cardiovascular CT for planning ventricular tachycardia ablation procedures

In the last 20 years coronary computed tomography angiography (CCTA) gained a pivotal role in the evaluation of patients with suspected coronary artery disease (CAD) as finally recognized by the ESC guidelines on stable CAD. Technological advances have progressively improved the temporal resolution of CT scanners, contemporary reducing acquisition time, radiation dose and contrast volume needed for the whole heart volume acquisition, further expanding the role of cardiac CT beyond coronary anatomy evaluation. Aim of the present review is to discuss use and benefit of cardiac CT for the planning and preparation of VT ablation.

Focus on stereotactic radiotherapy: A new way to treat severe ventricular arrhythmias?

Ventricular tachycardia has a significant recurrence rate after ablation for several reasons, including inaccessible substrate. A non-invasive technique to ablate any defined areas of myocardium involved in arrhythmogenesis would be a potentially important therapeutic improvement if shown to be safe and effective. Early feasibility studies of single-fraction stereotactic body radiotherapy have demonstrated encouraging results, but rigorous evaluation and follow-up are required. In this document, the basic concepts of stereotactic body radiotherapy are summarized, before focusing on stereotactic arrhythmia radioablation. We describe the effect of radioablation on cardiac tissue and its interaction with intracardiac devices, depending on the dose. The different clinical studies on ventricular tachycardia radioablation are analysed, with a focus on target identification, which is the key feature of this approach. Our document ends with the indications and requirements for practicing this type of procedure in 2020. Finally, because of the limited number of patients treated so far, we encourage multicentre registries with long-term follow-up.

Updates in Ventricular Tachycardia Ablation

Sudden cardiac death (SCD) due to recurrent ventricular tachycardia is an important clinical sequela in patients with structural heart disease. As a result, ventricular tachycardia (VT) has emerged as a major clinical and public health problem. The mechanism of VT is predominantly mediated by re-entry in the presence of arrhythmogenic substrate (scar), though focal mechanisms are also important. Catheter ablation for VT, when compared to standard medical therapy, has been shown to improve VT-free survival and burden of device therapies. Approaches to VT ablation are dependent on the underlying disease process, broadly classified into idiopathic (no structural heart disease) or structural heart disease (ischemic or non-ischemic heart disease). This update aims to review recent advances made for the treatment of VT ablation, with respect to current clinical trials, peri-procedure risk assessments, pre-procedural cardiac imaging, electro-anatomic mapping and advances in catheter and non-catheter based ablation techniques.

A case report of successful elimination of recurrent ventricular tachycardia by repeated stereotactic radiotherapy: the importance of accurate target volume delineation

Background

Stereotactic body radiotherapy (SBRT) has emerged recently as a novel therapeutic alternative for patients with ventricular tachycardias (VTs) resistant to convetional treatment. Nevertheless, many aspects related to SBRT are currently unknown.

Case summary

A 66-year-old man with ischaemic heart disease, a history of coronary artery bypass graft surgery and left ventricular dysfunction was referred for recurrent symptomatic episodes of slow VT (108 b.p.m.). The arrhythmia was resistant to antiarrhythmic drug therapy with amiodarone and repeated catheter ablation. The patient was scheduled to SBRT, however, the first session failed to suppress VT recurrences. After 20 months, the patient underwent re-do ablation procedure that revealed a newly developed scar with its core adjacent to the presumed critical part of the VT substrate. Catheter ablation again failed to eliminate VT and the second session of SBRT was scheduled. To improve targeting of the VT substrate for SBRT, we applied our recently developed original method for integration of data from the electroanatomical mapping system with computer tomography images. The second session of SBRT with precise targeting using the novel strategy led within 3 months to the successful elimination of VT.

Discussion

This case report describes a patient in whom the recurrent VT was abolished only by properly targeted SBRT. Above all, the case highlights the importance of precise identification and targeting for SBRT. Our case also documents in vivo, by electroanatomical voltage mapping, the development of SBRT-related myocardial lesion. This represents an important mechanistic proof of the concept of SBRT.

Review of Stereotactic Arrhythmia Radioablation Therapy for Cardiac Tachydysrhythmias

Cardiac tachyarrhythmias are a major cause of morbidity and mortality. Treatments for these tachyarrhythmias include antiarrhythmic drugs, catheter ablation, surgical ablation, cardiac implantable electronic devices, and cardiac transplantation. Each of these treatment approaches is effective in some patients but there is considerable room for improvement, particularly with respect to the most common of the tachydysrhythmias, atrial fibrillation, and the most dangerous of the tachydysrhythmias, ventricular tachycardia (VT) or ventricular fibrillation. Noninvasive stereotactic ablative radiation therapy is emerging as an effective treatment for refractory tachyarrhythmias. Animal models have shown successful ablation of arrhythmogenic myocardial substrates with minimal short-term complications. Studies of stereotactic radioablation involving patients with refractory VT have shown a reduction in VT recurrence and promising early safety data. In this review, we provide the background for the application of stereotactic arrhythmia radioablation therapy along with promising results from early applications of the technology.