Phase I/II Trial of Electrophysiology-Guided Noninvasive Cardiac Radioablation for Ventricular Tachycardia

Coronary Venous Ethanol Infusion for Treatment of Refractory Ventricular Arrhythmias

BACKGROUND

Coronary venous ethanol infusion/ablation (CVEA) has been utilized to treat ventricular arrhythmias (VAs) refractory to radiofrequency ablation (RFA).

OBJECTIVE

This single-center study aimed to describe acute and subacute-term safety and efficacy of CVEA for the management of refractory VAs.

METHODS

Patients who underwent CVEA for refractory ventricular tachycardia (VT) or premature ventricular complexes (PVCs) at our center were included. Coronary venous anatomy was delineated, and VAs were mapped in epicardial or septal veins in addition to traditional mapping techniques. Ethanol was infused in the target vessel based on anatomy, size of target veins and collateral flow.

RESULTS

Thirty patients (age 61.4 ±12.5 years; 90% men, 80% white) underwent 32 ablation procedures with CVEA for refractory VT (n=20) or PVCs (n=12). Twenty-eight (93%) patients had undergone prior RFA and 28 had failed anti-arrhythmic drugs. In the VT ablation cohort, acute suppression of clinical VT was achieved after CVEA in 15(75%) cases; 1(5%) required additional RFA, 1 was non-inducible at baseline, and 3(15%) remained inducible for clinical VT. During follow-up, targeted VT recurred in 3(15%) and new VTs occurred in 7(35%) cases. In the PVC ablation cohort, acute suppression was achieved in 11(92%) patients. During follow-up, PVC suppression was sustained in these 11 patients with reduction in PVC burden from 24.8±13.9% to 2.1±2.1%. Complications potentially related to CVEA included complete heart block (2), transient left bundle-branch block (1), pericardial effusion (1), and cardiogenic shock (2).

CONCLUSION

CVEA can be effective for management of complex VAs refractory to standard RFA with an acceptable safety profile.

Investigation of cardiac substructure automatic segmentation methods on synthetically generated 4D cone-beam CT images

BACKGROUND

STereotactic Arrhythmia Radioablation (STAR) is a novel noninvasive method for treating arrythmias in which external beam radiation is directed towards subregions of the heart. Challenges for accurate STAR targeting include small target volumes and relatively large patient motion, which can lead to radiation related patient toxicities. 4D Cone-beam CT (CBCT) images are used for stereotactic lung treatments to account for respiration-related patient motion. 4D-CBCT imaging could similarly be used to account for respiration-related patient motion in STAR; however, the poor contrast of heart tissue in CBCT makes identifying cardiac substructures in 4D-CBCT images challenging. If cardiac structures can be identified in pre-treatment 4D-CBCT images, then the location of the target volume can be more accurately identified for different phases of the respiration cycle, leading to more accurate targeting and a reduction in patient toxicities.

PURPOSE

The aim of this simulation study is to investigate the accuracy of different cardiac substructure segmentation methods for 4D-CBCT images.

METHODS

Repeat 4D-CT scans from 13 lung cancer patients were obtained from The Cancer Imaging Archive. Synthetic 4D-CBCT images for each patient were simulated by forward projecting and reconstructing each respiration phase of a chosen "testing" 4D-CT scan. Eighteen cardiac structures were segmented from each respiration phase image in the testing 4D-CT using the previously validated platipy toolkit. The platipy segmentations from the testing 4D-CT were defined as the ground truth segmentations for the synthetic 4D-CBCT images. Five different 4D-CBCT cardiac segmentation methods were investigated: 3D Rigid Alignment, 4D Rigid Alignment, Direct CBCT Segmentation, Contour Transformation, and Synthetic CT Segmentation methods. For all methods except the Direct CBCT segmentation method, a separate 4D-CT (Planning CT) was used to assist in generating 4D-CBCT segmentations. Segmentation performance was measured using the Dice similarity coefficient (DSC), Hausdorff distance (HD), mean surface distance (MSD), and volume ratio (VR) metrics.

RESULTS

The mean ± standard deviation DSC for all cardiac substructures for the 3D Rigid Alignment, 4D Rigid Alignment, Direct CBCT Segmentation, Contour Transformation, and Synthetic CT Segmentation methods were 0.48 ± 0.29, 0.52 ± 0.29, 0.37 ± 0.32, 0.53 ± 0.29, 0.57 ± 0.28, respectively. Similarly, the HD values were 10.9 ± 3.6 , 9.9 ± 2.6 , 17.3 ± 5.3 , 9.9 ± 2.8 , 9.3 ± 3.0 mm, the MSD values were 2.9 ± 0.6 , 2.9 ± 0.6 , 6.3 ± 2.5 , 2.5 ± 0.6 , 2.4 ± 0.8 mm, and the VR Values were 0.81 ± 0.12, 0.78 ± 0.14, 1.10 ± 0.47, 0.72 ± 0.15, 0.98 ± 0.44, respectively. Of the five methods investigated the Synthetic CT segmentation method generated the most accurate segmentations for all calculated segmentation metrics.

CONCLUSION

This simulation study investigates the accuracy of different cardiac substructure segmentation methods for 4D-CBCT images. Accurate 4D-CBCT cardiac segmentation will provide more accurate information on the location of cardiac anatomy during STAR treatments which can lead to safer and more effective STAR. As the data and segmentation methods used in this study are all open source, this study provides a useful benchmarking tool to evaluate other CBCT cardiac segmentation methods.

Patient selection, ventricular tachycardia substrate delineation, and data transfer for stereotactic arrhythmia radioablation: a clinical consensus statement of the European Heart Rhythm Association of the European Society of Cardiology and the Heart Rhythm Society

Stereotactic arrhythmia radioablation (STAR) is a novel, non-invasive, and promising treatment option for ventricular arrhythmias (VAs). It has been applied in highly selected patients mainly as bailout procedure, when (multiple) catheter ablations, together with anti-arrhythmic drugs, were unable to control the VAs. Despite the increasing clinical use, there is still limited knowledge of the acute and long-term response of normal and diseased myocardium to STAR. Acute toxicity appeared to be reasonably low, but potential late adverse effects may be underreported. Among published studies, the provided methodological information is often limited, and patient selection, target volume definition, methods for determination and transfer of target volume, and techniques for treatment planning and execution differ across studies, hampering the pooling of data and comparison across studies. In addition, STAR requires close and new collaboration between clinical electrophysiologists and radiation oncologists, which is facilitated by shared knowledge in each collaborator's area of expertise and a common language. This clinical consensus statement provides uniform definition of cardiac target volumes. It aims to provide advice in patient selection for STAR including aetiology-specific aspects and advice in optimal cardiac target volume identification based on available evidence. Safety concerns and the advice for acute and long-term monitoring including the importance of standardized reporting and follow-up are covered by this document. Areas of uncertainty are listed, which require high-quality, reliable pre-clinical and clinical evidence before the expansion of STAR beyond clinical scenarios in which proven therapies are ineffective or unavailable.

From Bench to Bedside: Translational Approaches to Cardiotoxicity in Breast Cancer, Lung Cancer, and Lymphoma Therapies

Cardiotoxicity represents a critical challenge in cancer therapy, particularly in the treatment of thoracic tumors, such as lung cancer and lymphomas, as well as breast cancer. These malignancies stand out for their high prevalence and the widespread use of cardiotoxic treatments, such as chemotherapy, radiotherapy, and immunotherapy. This work underscores the importance of preclinical models in uncovering the mechanisms of cardiotoxicity and developing targeted prevention and mitigation strategies. In vitro models provide valuable insights into cellular processes, enabling the observation of changes in cell viability and function following exposure to various drugs or ionizing radiation. Complementarily, in vivo animal models offer a broader perspective, allowing for evaluating of both short- and long-term effects and a better understanding of chronic toxicity and cardiac diseases. By integrating these approaches, researchers can identify potential mechanisms of cardiotoxicity and devise effective prevention strategies. This analysis highlights the central role of preclinical models in advancing knowledge of cardiotoxic effects associated with common therapeutic regimens for thoracic and breast cancers.

Toward the Use of Implanted Cardiac Leads or the Diaphragm for Active Respiratory Motion Management in Stereotactic Arrhythmia Radioablation

PURPOSE

To investigate the utility of implanted cardiac leads or the diaphragm for active respiratory motion management in stereotactic arrhythmia radioablation by quantifying the relationship between their motions.

METHODS AND MATERIALS

Seven patients treated with stereotactic arrhythmia radioablation were imaged using 5-Hz biplanar, kV x-ray fluoroscopy for 15-20 seconds under both abdominal compression (AC) and free breathing (FB) conditions. Three-dimensional motion traces for different regions of the heart were acquired by tracking and triangulating the position of all implanted cardiac leads. The heart's respiratory motion was extracted from the total motion (respiratory + cardiac) using a low-pass filter and described in optimized coordinates using principal component analysis. The existence of a relationship between the respiratory motion of different cardiac leads or the diaphragm was quantified using the Spearman rank correlation coefficient. Polynomial correlation models relating PC1 cardiac lead motion to the diaphragm were created and evaluated on the resultant errors.

RESULTS

Eighty-one respiratory motion correlations between different positions of the heart or diaphragm were calculated under both AC and FB. Consistently strong correlations between the respiratory motion of different positions in the heart and the diaphragm required accounting for phase shifts between motions. When accounting for phase shifts, the proportion of strong (>0.7) PC1 respiratory motion correlations was 100% under FB and 92.6% under AC. Linear fitting of cardiac lead motion with the diaphragm resulted in mean absolute PC1 tracking errors of (1.0 ± 0.6) mm under FB and (0.7 ± 0.4) mm under AC.

CONCLUSIONS

The respiratory motion of all combinations of implanted cardiac leads and the diaphragm are moderately to strongly correlated after accounting for phase shifts between motion traces. These phase shifts should be carefully considered to ensure patient safety during respiratory tracking or gating during stereotactic arrhythmia radioablation using cardiac leads or the diaphragm as internal surrogates.

Cardiorespiratory-gated cardiac proton radiotherapy using a novel ultrasound guidance system

Cardiac stereotactic body radiotherapy is a promising noninvasive treatment for patients with refractory ventricular tachycardia. With the aim to prove feasibility of a novel image guided radiotherapy and heart motion gating device, cardiac proton radiotherapy was performed using a porcine model. Using a novel adaptation of γ - H2AX tissue staining techniques, we have been able to localize a radiation beam in large animal tissue to assess targeting accuracy within a defined field. Cardiorespiratory-gated irradiations of the animals were successfully completed and analysis of the γ-H2AX staining intensity of the excised heart after radiation demonstrated radiotherapy was delivered close to or within the expected region. We simulated the irradiated volumes under different gating scenarios, showing significant reduction when using combined cardiorespiratory gating. The results of this study show the feasibility of proton irradiation of the heart left ventricle with a novel ultrasound based cardiorespiratory gating technology with the benefit of reduced irradiation volumes and increased healthy tissue sparing.

Stereotactic arrhythmia radioablation for refractory ventricular tachycardia-The initial Australian experience

BACKGROUND

Stereotactic arrhythmia radioablation (STAR) is a novel, noninvasive technique for the management of refractory ventricular tachycardia (VT).

OBJECTIVE

This retrospective study aimed to assess the feasibility, efficacy, and safety of STAR in an Australian cohort.

METHODS

From February 2020 to August 2023, 12 patients with drug-refractory VT for whom catheter ablation had failed or who were unsuitable for it were treated with STAR in 2 Australian centers. A combination of electrocardiograms, multimodality imaging, and noninvasive or invasive mapping data was used to target the presumed VT substrate. All treatments (25 Gy in 1 fraction) were delivered without anesthesia. Efficacy end points were defined as the number of VT episodes, antitachycardia pacing sequences, VT storms, and shocks 6 months before and after treatment (6-week blanking period). Mortality and adverse event data were collected during 12-month follow-up.

RESULTS

In the 9 patients who survived the blanking period, a significant reduction (64.5%; P = .011) in VT burden and VT storm (71.7%; P = .027) was observed during a 6-month follow-up. However, 66.7% (6/9) of these patients experienced VT recurrence; 3 of 6 patients with recurrence with electrocardiograms available for review had the same VT morphology as before STAR. During a 12-month follow-up, 5 patients died and 3 adverse events were recorded (undersensing of defibrillator lead, increased rate of reflux, and radiation pneumonitis).

CONCLUSION

This paper summarizes the initial Australian experience treating refractory VT with STAR. It demonstrates that STAR can significantly decrease the VT and VT storm burden during a 6-month follow-up with an acceptable acute adverse effect profile, albeit with a high VT recurrence rate.

The conversion of electroanatomic maps for compatibility with treatment planning systems in cardiac radioablation target volume definition

BACKGROUND

Cardiac radioablation (CRA) is a new and promising treatment modality for patients with ventricular tachycardia refractory to standard-of-care treatment. Electroanatomic maps are used to define radiation target volumes; however, there is currently no native method to import electroanatomic maps into the treatment planning system (TPS).

PURPOSE

To develop Edico, a semi-automated tool to enable electroanatomic map import into a TPS, by converting electroanatomic maps to a Digital Imaging and COmmunications in Medicine (DICOM) standard. The overall aim is to facilitate target volume delineation and improve workflow efficiency in treating patients.

METHODS

Edico imports voltage and spatial data from electroanatomic maps and sorts these into voxels to be exported in a DICOM format, with each voxel containing the average voltage value of the data that falls within it. Three different rectangular electroanatomic maps were created and processed using Edico to ensure that expected features are maintained through processing. A sensitivity analysis of voxel size was completed using 19 different electroanatomic maps processed at five different sets of voxel dimensions, for a total of 95 resulting voxelized datasets. The coefficient of variation in each populated voxel in the datasets was analyzed to determine which voxel sizes are necessary to ensure that data loss is kept to a minimum throughout processing, despite averaging. Five electroanatomic maps were used to re-contour clinical target volumes and planning target volumes for previously-treated patients with their electroanatomic maps now directly registered to their planning computed tomography (CT) scans.

RESULTS

All three rectangular test electroanatomic maps were processed as expected. All tested voxel sizes resulted in low coefficients of variation overall, with the exception of the largest voxel size of 1.8 × 1.8 × 8 mm. When using Edico, a user should choose voxel dimensions similar to or smaller than those of a planning CT. Of five pairs of clinical and planning target volumes from previously treated patients, adjustments were made to four (80%), retrospectively, using the electroanatomic maps generated using Edico, registered to the patients' planning CTs.

CONCLUSIONS

Edico provides a reliable solution for electroanatomic map import into a TPS and facilitates clinical and planning target volume identification in CRA.

Implementing stereotactic arrhythmia radioablation with STOPSTORM.eu consortium support: intermediate results of a prospective Israeli single-institutional trial

BACKGROUND

Ventricular tachycardia (VT) is a life-threatening arrhythmia originating from the heart's ventricles. Traditional treatments include antiarrhythmic medications, implantable cardioverter-defibrillators (ICDs), and catheter ablation. Stereotactic body radiation therapy (SBRT) targeting the arrhythmogenic focus in the left ventricle-stereotactic arrhythmia radioablation (STAR)-is an emerging treatment and may offer a potential solution for patients with refractory VT.

OBJECTIVE

We designed an interventional prospective clinical trial in Israel aligned with the STOPSTORM.eu consortium's benchmarks, recommendations, and directives to assess the safety and efficacy of STAR in patients with refractory VT.

METHODS

Our phase I/II single-institutional trial was approved by the Ministry of Health of Israel for 10 patients, initially assessing safety in the first 3 patients. We included patients with ICDs experiencing symptomatic monomorphic VT after an inadequate response to previous therapies. The primary endpoints were treatment-related serious adverse events and a reduction in VT burden as assessed by ICD interrogation. Secondary outcomes included a reduction in antiarrhythmic medications and changes in quality of life.

RESULTS

From August 2023 to August 2024, 3 patients underwent STAR treatment. The prescription dose was a single fraction of 25 Gy. Planning target volumes were 47.8, 49.7, and 91.8 cc, and treatment was successfully delivered with no grade 3 or higher adverse events reported. Over a follow-up period of 12 months for the first patient and 8 months for the second one, no VT events were recorded after treatment. The third patient died from progressive heart failure 3 months after treatment. Left ventricular ejection fraction remained stable, and no significant radiation-induced inflammatory changes were noted.

CONCLUSION

The initial results of this trial suggest that STAR can reduce VT episodes in patients with refractory VT without severe adverse effects. The study highlights the importance of international collaboration and standardization in pioneering new treatments. Further follow-up and additional patient data will be necessary to confirm these findings and evaluate long-term outcomes, including potential adjustments to antiarrhythmic medication regimens.

Cardiac Complications of Radiation Therapy

Radiation therapy is a critical component in managing many malignancies by improving local control and survival. The benefits of radiation may come at the expense of unintended radiation injury to the surrounding normal tissues, with the heart being one of the most affected organs in thoracic radiation treatments. As cancer survivors live longer, radiation-induced cardiotoxicity (RICT) is now increasingly recognized. In this review, we highlight the spectrum and pathophysiology of RICT. We summarize contemporary recommendations for risk stratification, screening, prevention, and management of RICT. We briefly highlight novel applications for radiation to treat some cardiac conditions such as resistant arrhythmias.

Evaluating the Efficacy and Safety of Stereotactic Arrhythmia Radioablation in Ventricular Tachycardia: A Comprehensive Systematic Review and Meta-Analysis

Purpose

Stereotactic arrhythmia radioablation (STAR) has emerged as a promising non-invasive treatment for refractory ventricular tachycardia (VT), offering a novel alternative for patients who are poor candidates for catheter ablation. This systematic review and meta-analysis evaluates the safety, efficacy, and technical aspects of STAR across preclinical studies, case reports, case series, and clinical trials.

Methods and Materials

A systematic review identified 80 studies published between 2015 and 2024, including 12 preclinical studies, 47 case reports, 15 case series, and 6 clinical trials. Data on patient demographics, treatment parameters, and clinical outcomes were extracted. Meta-analyses were performed for pooled mortality rates, VT burden reduction, and acute toxicities, with subgroup analyses exploring cardiomyopathy type, age, left ventricular ejection fraction (LVEF), and treatment modality.

Results

The pooled 6- and 12-month mortality rates were 16% (95% CI: 11-21%) and 32% (95% CI: 26-39%), respectively. VT burden reduction at 6 months was 75% (95% CI: 73-77%), with significant heterogeneity (I2 = 98.8%). Grade 3+ acute toxicities were observed in 7% (95% CI: 4-11%), with pneumonitis being the most common. Subgroup analyses showed comparable outcomes between LINAC- and CyberKnife-based treatments, with minor differences based on patient characteristics and cardiomyopathy type.

Conclusions

STAR demonstrates significant potential in reducing VT burden and improving patient outcomes. While favorable acute safety profiles and efficacy support clinical adoption, variability in treatment protocols underscores the need for standardized practices. Future studies should aim to optimize patient selection, establish robust dosimetric standards, and evaluate long-term safety.

Stereotactic arrhythmia radioablation for ventricular tachycardia: a review of clinical trials and emerging roles of imaging

Ventricular tachycardia (VT) is a severe arrhythmia commonly treated with implantable cardioverter defibrillators, antiarrhythmic drugs and catheter ablation (CA). Although CA is effective in reducing recurrent VT, its impact on survival remains uncertain, especially in patients with extensive scarring. Stereotactic arrhythmia radioablation (STAR) has emerged as a novel treatment for VT in patients unresponsive to CA, leveraging techniques from stereotactic body radiation therapy used in cancer treatments. Recent clinical trials and case series have demonstrated the short-term efficacy and safety of STAR, although long-term outcomes remain unclear. Imaging techniques, such as electroanatomical mapping, contrast-enhanced magnetic resonance imaging and nuclear imaging, play a crucial role in treatment planning by identifying VT substrates and guiding target delineation. However, challenges persist owing to the complex anatomy and variability in target volume definitions. Advances in imaging and artificial intelligence are expected to improve the precision and efficacy of STAR. The exact mechanisms underlying the antiarrhythmic effects of STAR, including potential fibrosis and improvement in cardiac conduction, are still being explored. Despite its potential, STAR should be cautiously applied in prospective clinical trials, with a focus on optimizing dose delivery and understanding long-term outcomes. Collaborative efforts are necessary to standardize treatment strategies and enhance the quality of life for patients with refractory VT.

Pulmonary artery denervation by noninvasive stereotactic radiotherapy: a pilot study in swine models of pulmonary hypertension

Catheter-based pulmonary artery denervation (PADN) has achieved promising outcomes to treat pulmonary hypertension (PH). We herein present stereotactic body radiotherapy (SBRT) as a novel noninvasive approach for PADN. A single fraction of 15 Gy, 20 Gy or 25 Gy was delivered for PADN in a thromboxane A2 (TxA2) - induced acute PH swine model. We demonstrated that PADN by 20-Gy SBRT reduced mean pulmonary artery (PA) pressure during the TxA2 challenge. All SBRT dosages led to a deeper denervation area compared with radiofrequency ablation (RFA) and reduced sympathetic neural norepinephrine synthesis in the ablation zone. Probable radiation related side effects were mostly found in animals treated with 25-Gy. In subsequent monocrotaline-induced chronic PH animals, PADN by 20-Gy SBRT resulted in more significant improvement in pulmonary hemodynamics and PA remodeling in comparison to RFA. In summary, our findings suggest that appropriate SBRT scheme could balance the efficacy and safety for PADN, potentiating to be a novel strategy to treat PH.

Refining Treatment Planning in STereotactic Arrhythmia Radioablation: Benchmark Results and Consensus Statement From the STOPSTORM.eu Consortium

PURPOSE

STereotactic Arrhythmia Radioablation (STAR) showed promising results in patients with refractory ventricular tachycardia. However, clinical data are scarce and heterogeneous. The STOPSTORM.eu consortium was established to investigate and harmonize STAR in Europe. The primary goal of this benchmark study was to investigate current treatment planning practice within the STOPSTORM project as a baseline for future harmonization.

METHODS AND MATERIALS

Planning target volumes (PTVs) overlapping extracardiac organs-at-risk and/or cardiac substructures were generated for 3 STAR cases. Participating centers were asked to create single-fraction treatment plans with 25 Gy dose prescriptions based on in-house clinical practice. All treatment plans were reviewed by an expert panel and quantitative crowd knowledge-based analysis was performed with independent software using descriptive statistics for International Commission on Radiation Units and Measurements report 91 relevant parameters and crowd dose-volume histograms. Thereafter, treatment planning consensus statements were established using a dual-stage voting process.

RESULTS

Twenty centers submitted 67 treatment plans for this study. In most plans (75%) intensity modulated arc therapy with 6 MV flattening filter free beams was used. Dose prescription was mainly based on PTV D95% (49%) or D96%-100% (19%). Many participants preferred to spare close extracardiac organs-at-risk (75%) and cardiac substructures (50%) by PTV coverage reduction. PTV D0.035cm3 ranged from 25.5 to 34.6 Gy, demonstrating a large variety of dose inhomogeneity. Estimated treatment times without motion compensation or setup ranged from 2 to 80 minutes. For the consensus statements, a strong agreement was reached for beam technique planning, dose calculation, prescription methods, and trade-offs between target and extracardiac critical structures. No agreement was reached on cardiac substructure dose limitations and on desired dose inhomogeneity in the target.

CONCLUSIONS

This STOPSTORM multicenter treatment planning benchmark study not only showed strong agreement on several aspects of STAR treatment planning, but also revealed disagreement on others. To standardize and harmonize STAR in the future, consensus statements were established; however, clinical data are urgently needed for actionable guidelines for treatment planning.

Ablation options for sub-epicardially located ventricular substrates responsible for ventricular tachycardia: where is it all headed?

PURPOSE OF REVIEW

Patients with nonischemic and ischemic cardiomyopathy (NICM and ICM) exhibit re-entrant tachycardias related to scar tissue in subepicardial, in addition to typical subendocardial locations. Control of ventricular arrhythmias related to these targets has remained elusive despite advances in mapping and ablation technology.

RECENT FINDINGS

Percutaneous epicardial ablation is the standard after failed endocardial ventricular ablation, but recurrence rates are disappointing. Pulsed-field energy has been associated with coronary artery spasm and therefore may be less suitable for epicardial ablation. Commercially available energy sources, including pulsed-field, have limited depths of myocardial penetration when applied epicardially. Lateral volumetric thermal spreading of ablation injury is associated with decreasing depth of ablation and is difficult to control. A new cryoablation technology based on liquid helium and developed specifically for epicardial work may be able to overcome these limitations.

SUMMARY

Ablation strategies that can improve lesion formation in subepicardial ventricular myocardium may improve outcomes of ablation in nonsubendocardial NICM and ICM targets.

Mechanistic Insights and Knowledge Gaps in the Effects of Radiation Therapy on Cardiac Arrhythmias

Stereotactic body radiation therapy (SBRT) is an innovative modality for the treatment of refractory ventricular arrhythmias (VAs). Phase 1/2 clinical trials have demonstrated the remarkable efficacy of SBRT at reducing VA burden (by >85%) in patients with good short-term safety. SBRT as an option for VA treatment delivered in an ambulatory nonsedated patient in a single fraction during an outpatient session of 15 to 30 minutes, without added risks of anesthetic or surgery, is clinically relevant. However, the underlying mechanism remains unclear. Currently, the clinical dosing of SBRT has been derived from preclinical studies aimed at inducing transmural fibrosis in the atria. The propitious clinical effects of SBRT appear earlier than the time course for fibrosis. This review addresses the plausible mechanisms by which radiation alters the electrophysiological properties of myocytes and myocardial conduction to impart an antiarrhythmic effect, elucidate clinical observations, and point the direction for further research in this promising area.

Stereotactic arrhythmia radioablation (STAR)-A systematic review and meta-analysis of prospective trials on behalf of the STOPSTORM.eu consortium

Stereotactic arrhythmia radioablation (STAR) is a noninvasive treatment of refractory ventricular tachycardia (VT). In this study, we aimed to systematically review prospective trials on STAR and pool harmonized outcome measures in a meta-analysis. After registration in the International Prospective Register of Systematic Reviews (PROSPERO: CRD42023439666), we searched OVID Medline, OVID Embase, Web of Science Core Collection, the Cochrane Central Register of Controlled Trials, and Google Scholar on November 9, 2023, to identify reports describing results of prospective trials evaluating STAR for VT. Risk of bias was assessed using the Risk Of Bias In Non-randomized Studies of Interventions tool. Meta-analysis was performed using generalized linear mixed models. We identified 10 prospective trials in which 82 patients were treated with STAR between 2016 and 2022. The 90-day rate of treatment-related grade ≥3 adverse events was 0.10 (95% confidence interval [CI] 0.04-0.2). The proportions of patients achieving given VT burden reductions were 0.61 (95% CI 0.45-0.74) for ≥95%, 0.80 (95% CI 0.62-0.91) for ≥75%, and 0.9 (95% CI 0.77-0.96) for ≥50% in 63 evaluable patients. The 1-year overall survival rate was 0.73 (95% CI 0.61-0.83) in 81 patients, 1-year freedom from recurrence was 0.30 (95% CI 0.16-0.49) in 61 patients, and 1-year recurrence-free survival was 0.21 in 60 patients (95% CI 0.08-0.46). Limitations include methodological heterogeneity across studies and moderate to significant risk of bias. In conclusion, STAR is a promising treatment method, characterized by moderate toxicity. We observed 1-year mortality of ≈27% in this population of critically ill patients suffering from refractory VT. Most patients experience a significant reduction in VT burden; however, 1-year recurrence rates are high. STAR should still be considered an investigational approach and recommended to patients primarily within the context of prospective trials.

Evaluation of the impact of cardiac implantable electronic devices on cine MRI for real-time adaptive cardiac radioablation on a 1.5 T MR-linac

BACKGROUND

Stereotactic arrhythmia radioablation (STAR) is a novel treatment approach for refractory ventricular tachycardia (VT). The risk of treatment-induced toxicity and geographic miss can be reduced with online MRI-guidance on an MR-linac. However, most VT patients carry cardiac implantable electronic devices (CIED), which compromise MR images.

PURPOSE

Robust MR-linac imaging sequences are required for cardiac visualization and accurate motion monitoring in presence of a CIED during MRI-guided STAR. We optimized two clinically available cine sequences for cardiorespiratory motion estimation in presence of a CIED on a 1.5 T MR-linac. The image quality, motion estimation accuracy, and geometric fidelity using these cine sequences were evaluated.

METHODS

Clinically available 2D balanced steady-state free precession (bSSFP, voxel size = 3.0 × $\times$ 3.0 × $\times$ 10 mm3, Tscan = 96 ms, bandwidth (BW) = 1884 Hz/px) andT 1 ${\rm T}_{1}$ -spoiled gradient echo (T 1 ${\rm T}_{1}$ -GRE, voxel size = 4.0 × $ \times$ 4.0 × $ \times$ 10 mm3, Tscan = 97 ms, BW = 500 Hz/px) sequences were adjusted for real-time cardiac visualization and cardiorespiratory motion estimation on a 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden), while complying with safety guidelines for MRI in presence of CIEDs (specific absorption rate < $ <$ 2 W/kg andd B d t < $\frac{dB}{dt}<$ 80 mT/s). Cine acquisitions were performed in five healthy volunteers, with and without an implantable cardioverter- defibrillator (ICD) placed on the clavicle, and a VT patient. Generalized divergence-curl (GDC) deformable image registration (DIR) was used for automated landmark motion estimation in the left ventricle (LV). Gaussian processes (GP), a machine-learning technique, was trained using GDC landmarks and deployed for real-time cardiorespiratory motion prediction.B 0 $B_{0}$ -mapping was performed to assess geometric image fidelity in the presence of CIEDs.

RESULTS

CIEDs introduced banding artifacts partially obscuring cardiac structures in bSSFP acquisitions. In contrast, theT 1 ${\rm T}_{1}$ -GRE was more robust to CIED-induced artifacts at the expense of a lower signal-to-noise ratio. In presence of an ICD, image-based cardiorespiratory motion estimation was possible for 85% (100%) of the volunteers using the bSSFP (T 1 ${\rm T}_{1}$ -GRE) sequence. The in-plane 2D root-mean-squared deviation (RMSD) range between GDC-derived landmarks and manual annotations using the bSSFP (T1-GRE) sequence was 3.1-3.3 (3.3-4.1) mm without ICD and 4.6-4.6 (3.2-3.3) mm with ICD. Without ICD, the RMSD between the GP-predictions and GDC-derived landmarks ranged between 0.9 and 2.2 mm (1.3-3.0 mm) for the bSSFP (T1-GRE) sequence. With ICD, the RMSD between the GP-predictions and GDC-derived landmarks ranged between 1.3 and 2.2 mm (1.2-3.2 mm) using the bSSFP (T1-GRE) sequence resulting in an RMSD-increase of 42%-143% (bSSFP) and -61%-142% (T1-GRE). Lead-induced spatial distortions ranged between -0.2 and 0.2 mm (-0.7-1.2 mm) using the bSSFP (T 1 ${\rm T}_{1}$ -GRE) sequence. The 98th percentile range of the spatial distortions in the gross target volume of the patient was between 0.0 and 0.4 mm (0.0-1.8 mm) when using bSSFP (T 1 ${\rm T}_{1}$ -GRE).

CONCLUSIONS

Tailored bSSFP andT 1 ${\rm T}_{1}$ -GRE sequences can facilitate real-time cardiorespiratory estimation using GP trained with GDC-derived landmarks in the majority of landmark locations in the LV despite the presence of CIEDs. The need for high temporal resolution noticeably reduced achievable spatial resolution of the cine MRIs. However, the effect of the CIED-induced artifacts is device, patient and sequence dependent and requires specific assessment per case.

Stereotactic cardiac radiotherapy for refractory ventricular tachycardia in structural heart disease patients: a systematic review

AIMS

Among patients with structural heart disease with ventricular tachycardia (VT) refractory to medical therapy and catheter ablation, cardiac stereotactic body radiotherapy (SBRT) is a paradigm-changing treatment option. This study aims to assess the efficacy of cardiac SBRT in refractory VT by comparing the rates of VT episodes, anti-tachycardia pacing (ATP) therapies, and implantable cardioverter-defibrillator (ICD) shocks post-SBRT with pre-SBRT.

METHODS AND RESULTS

We performed a comprehensive literature search and included all clinical studies reporting outcomes on cardiac SBRT for VT. Treatment efficacy was evaluated as random-effects pooled rate-ratios of VT episodes, ATP therapies and ICD shocks post-SBRT (after 6-week blanking) and pre-SBRT, with patients serving as their own controls. Post-SBRT overall survival was assessed using Kaplan-Meier method. We included 23 studies published 2017-24 reporting on 225 patients who received cardiac SBRT, with median follow-up 5.8-28 months. There was significant heterogeneity among the studies for all three efficacy endpoints (P < 0.00001). The random-effects pooled rate-ratios of VT episodes, ATP therapies and ICD shocks post- vs. pre-SBRT were 0.10 (95% CI 0.06, 0.16), 0.09 (0.05, 0.15), and 0.09 (0.05, 0.17), respectively (all P < 0.00001). The most common reported complications included pericardial (8.0%, including 0.9% late oesophagogastro-pericardial fistula) and pulmonary (5.8%). There was no change in left ventricular ejection fraction post-SBRT (P = 0.3) but some studies reported an increase in mitral regurgitation. The combined 3-, 12-, and 24-month overall patient survival was 0.86 (0.80, 0.90), 0.72 (0.65, 0.78), and 0.57 (0.47, 0.67), respectively.

CONCLUSION

Among patients with refractory VT in context of structural heart disease, VT burden and ICD shocks are dramatically reduced following cardiac SBRT. The overall mortality in this population with heart failure and refractory VT receiving palliative cardiac SBRT remains high.

Optimal electrode placements for localizing premature ventricular contractions using a single dipole cardiac source model

INTRODUCTION

The inverse problem of electrocardiography describes non-invasively the electrical activity of the heart using potential recordings from tens to hundreds of torso electrodes. Regrettably, the use of numerous electrodes poses a challenge to its integration into routine clinical practice.

METHODS

Optimal electrode placements, ranging from 8 to 112 electrodes, were derived from the singular values of the transfer matrices computed for all feasible positions of a single dipole cardiac source across 12 patients with unique geometrical characteristics from the Bratislava dataset. The transfer matrices were computed using the boundary element method. Subsequently, these optimal electrode placements were used to compute the inverse solution for localizing the origin of premature ventricular contraction (PVC) with a single dipole cardiac source. The localization error (LE) was computed as the Euclidean distance between the true PVC origin, obtained through an invasive radiofrequency ablation, and the inverse solution. This enabled a direct comparison of LE computed for each optimal electrode placement with that from the full 128-electrode set.

RESULTS

Results showed that subsets of electrodes, particularly 32 to 112, provided comparable localization accuracy (LE of 30.5 ± 15.0 mm and 26.8 ± 12.6 mm) to the full 128-electrode set (LE of 27.2 ± 11.5 mm). High errors were observed with 8 and 16-electrode placements (LE of 48.6 ± 21.3 mm and 41.0 ± 18.3 mm).

CONCLUSION

Precise PVC localization can be achieved using strategically positioned subsets of electrodes, offering advantages in reduced preparation time, enhanced patient comfort, and improved cost-effectiveness of body surface potential mapping.

Radiation therapy for ventricular arrhythmias

Ventricular arrhythmias (VA) can be life-threatening arrhythmias that result in significant morbidity and mortality. Catheter ablation (CA) is an invasive treatment modality that can be effective in the treatment of VA where medications fail. Recurrence occurs commonly following CA due to an inability to deliver lesions of adequate depth to cauterise the electrical circuits that drive VA or reach areas of scar responsible for VA. Stereotactic body radiotherapy is a non-invasive treatment modality that allows volumetric delivery of energy to treat circuits that cannot be reached by CA. It overcomes the weaknesses of CA and has been successfully utilised in small clinical trials to treat refractory VA. This article summarises the current evidence for this novel treatment modality and the steps that will be required to bring it to the forefront of VA treatment.

Impact of Imaging and Pharmacological Treatment Strategies in Refractory Ventricular Tachycardia in Critically Ill Patients: A Systematic Review

Ventricular tachycardia (VT) is a life-threatening arrhythmia often leading to sudden cardiac death, particularly in critically ill patients. Refractory VT, characterized by recurrent episodes requiring intervention, poses unique challenges for management, necessitating advanced diagnostic and therapeutic strategies. This systematic review evaluates the impact of imaging and pharmacological treatments in managing refractory VT in critically ill patients. A systematic literature search was conducted using keywords such as "refractory ventricular tachycardia", "critical illness", "imaging techniques", "pharmacological treatments", "antiarrhythmic drugs", "ICD interventions", and "non-invasive therapy". Databases searched included PubMed, Google Scholar, and Cochrane Library, identifying 1590 publications. After screening, 11 studies meeting the inclusion criteria were included in this review. Oral procainamide significantly reduced VT episodes but caused severe side effects in certain patients. Noninvasive interventions such as transcutaneous magnetic stimulation (TcMS) and noninvasive electrophysiology-guided radioablation reduced VT burden and antiarrhythmic drug (AAD) use, with TcMS decreasing VT episodes in the sham group (P < 0.001). Stereotactic body radiation therapy (SBRT) and stereotactic arrhythmia radiotherapy (STAR) reduced VT episodes. Ultrasound-guided stellate ganglion blockade decreased VT episodes (P < 0.001) within 24 hours. Catheter ablation improved composite outcomes, including ICD shocks and heart failure hospitalizations, compared to AAD therapy. Quality of life significantly improved with noninvasive therapies, though SBRT presented rare complications like pneumonitis. Imaging and pharmacological interventions effectively reduce VT burden and ICD interventions while showing varying safety profiles. However, the limited sample sizes, short follow-up durations, and heterogeneity across studies highlight the need for further high-quality research to establish long-term efficacy and safety.

Pre-ablation and Post-ablation Factors Influencing the Prognosis of Patients with Electrical Storm Treated by Radiofrequency Catheter Ablation: An Update

Catheter ablation-based management strategies for the drug-refractory electrical storm (ES) have been proven to abolish acute ventricular arrhythmic episodes and improve long-term outcomes. However, this effect is highly influenced by multiple independently acting factors, which, if identified and addressed, may allow a more tailored management to each particular case to improve results. This review synthesizes existing evidence concerning ES outcome predictors of patients undergoing ablation and introduces the role of novel scoring algorithms to refine risk stratification. The presence of these factors should be assessed during two distinct phases in relation to the ablation procedure: before (based on preprocedural multimodal evaluation of the patient's structural heart disease and comorbidities) and after the ablation procedure (in terms of information derived from the invasive substrate characterization, procedural results, postprocedural recurrences (spontaneous or during non-invasive testing), and complications).

Understanding the Utility of Endocardial Electrocardiographic Imaging in Epi-Endocardial Mapping of 3D Reentrant Circuits

Background

Studies of VT mechanisms are largely based on a 2D portrait of reentrant circuits on one surface of the heart. This oversimplifies the 3D circuit that involves the depth of the myocardium. Simultaneous epicardial and endocardial (epi-endo) mapping was shown to facilitate a 3D delineation of VT circuits, which is however difficult via invasive mapping.

Objective

This study investigates the capability of noninvasive epicardial-endocardial electrocardiographic imaging (ECGI) to elucidate the 3D construct of VT circuits, emphasizing the differentiation of epicardial, endocardial, and intramural circuits and to determine the proximity of mid-wall exits to the epicardial or endocardial surfaces.

Methods

120-lead ECGs of VT in combination with subject-specific heart-torso geometry are used to compute unipolar electrograms (CEGM) on ventricular epicardium and endocardia. Activation isochrones are constructed, and the percentage of activation within VT cycle length is calculated on each surface. This classifies VT circuits into 2D (surface only), uniform transmural, nonuniform transmural, and mid-myocardial (focal on surfaces). Furthermore, the endocardial breakthrough time was accurately measured using Laplacian eigenmaps, and by correlating the delay time of the epi-endo breakthroughs, the relative distance of a mid-wall exit to the epicardium or the endocardium surfaces was identified.

Results

We analyzed 23 simulated and in-vivo VT circuits on post-infarction porcine hearts. In simulated circuits, ECGI classified 21% as 2D and 78% as 3D: 82.6% of these were correctly classified. The relative timing between epicardial and endocardial breakthroughs was correctly captured across all cases. In in-vivo circuits, ECGI classified 25% as 2D and 75% as 3D: in all cases, circuit exits and entrances were consistent with potential critical isthmus delineated from combined LGE-MRI and catheter mapping data.

Conclusions

ECGI epi-endo mapping has the potential for fast delineation of 3D VT circuits, which may augment detailed catheter mapping for VT ablation.

3D-targeted, electrocardiographic imaging-aided stereotactic radioablation for ventricular tachycardia storm: a case report

Background

Stereotactic arrhythmia radioablation (STAR) is a promising non-invasive therapy for patients with ventricular tachycardia (VT). Accurate identification of the arrhythmogenic volume, or clinical target volume (CTV), on the radiotherapy (RT) 4D planning computed tomography (CT) scan is key for STAR efficacy and safety. This case report illustrates our workflow of electro-structural image integration for CTV delineation.

Case summary

A 72-year-old man with ischaemic cardiomyopathy and VT storm, despite two (endocardial and epicardial) catheter-based ablations, was consented for STAR. A 3D electro-structural arrhythmia model was generated from co-registered electroanatomical voltage and activation maps, electrocardiographic (ECG) imaging, and the cardiac CT angiography scan (in ADAS 3D), pinpointing the VT isthmus and inferoapical VT exit. At this location, an area with short recovery times was found with ECG imaging. A multidisciplinary team delineated the CTV on the transmural ventricular myocardium, which was fused with the 4D planning CT scan using a digital images and communication in medicine (DICOM) radiotherapy file. The CTV was 63% smaller compared with using the conventional American Heart Association 17-segment approach (11 vs. 24 cm3). A single fraction of 25 Gy was delivered to the internal target volume. After an 8-week blanking period, no VT recurrences or radiation-related side-effects were noted. Eight months later, the patient died from end-stage heart failure.

Discussion

We report a novel workflow for 3D-targeted and ECG imaging-aided CTV delineation for STAR, resulting in a smaller irradiated volume compared with segmental approaches. Acute and intermediate outcome and safety were favourable. Non-invasive ECG imaging at baseline and during induced VT holds promise for STAR guidance.

Cardiac SABR: Image matching techniques for accurate treatment delivery

BACKGROUND

Ventricular tachycardia is an irregular heartbeat conventionally treated using invasive cardiac catheter ablation and medication. However, when standard treatments have been exhausted, cardiac SABR provides a final treatment option to this high-mortality condition. Complex diagnostic mapping and planning scans enable multi-disciplinary target delineation for a 25Gy single fraction. However, organs at risk (OAR) near the target make this treatment challenging to plan and deliver. Publications from cardiologists report the efficacy of cardiac SABR, however there is limited data on the treatment delivery and image matching of this complex procedure.

METHODS

Four specialist therapeutic radiographers experienced in cardiac SABR reviewed 40 CBCTs from 10 patients treated in the UK. Each therapeutic radiographer conducted five image matches: a manual match (manual), an automatic match to the heart structure (auto) and the auto match followed by manual adjustment to the PTV (PTV), all using three degrees of freedom (DoF) only. The auto and PTV matches were also repeated using 6DoF. Inter-observer variability was quantified using 95% limits of agreement from a modified Bland-Altman analysis.

RESULTS

The limits of agreement were smallest in the automatic matches suggesting the algorithm is reliable. A manual adjustment from the auto match to the PTV is clinically appropriate to optimise target coverage. The limits of agreement were smaller in the 6DoF PTV match 1.06 mm, 1.24 mm, 1.68 mm than the 3DoF PTV match 1.57 mm, 2.06 mm, 2.11 mm (lateral, vertical, longitudinal).

CONCLUSION

The 6DoF CBCT image match has less variability and therefore suggest using a 6DoF couch for treatment delivery.

IMPLICATIONS FOR PRACTICE

Cardiac SABR CBCT image matching at treatment delivery is complex, optimisation of CBCT acquisition parameters and therapeutic radiographer training is essential prior to implementation.

Management of Ventricular Arrhythmias in Heart Failure: Can Less Be More?

PURPOSE OF REVIEW

Ventricular arrhythmias (VAs) affect many patients with heart failure and underlying structural heart disease and are associated with significant morbidity and mortality. Antiarrhythmic drugs are often the initial treatment, but medication alone often fails to sufficiently suppress VAs. While catheter ablation (CA) remains the gold standard for treatment of VAs, CA is an invasive procedure and can be associated with periprocedural complications including acute clinical decompensation. Thus, there is an important need for alternative therapies.

RECENT FINDINGS

Recent advances in risk stratification and the development of new ablation technologies may reduce some of the periprocedural complications and limitations of CA. In addition, less invasive therapies for VAs may provide an alternative treatment strategy for patients in both the acute and chronic setting. For patients acutely admitted with ventricular tachycardia electrical storm (VT-ES) or recurrent VT and cardiogenic shock, risk stratification tools have been developed to identify patients at high risk of acute hemodynamic decompensation during CA. These patients require a multidisciplinary approach and might need mechanical circulatory support (MCS) if CA is selected as the treatment strategy. Alternatively, less invasive therapies targeting the autonomic nervous system may be reasonable. In the chronic setting, developments in medical therapy have reduced the risk of sudden cardiac death in heart failure patients and stereotactic whole-body radiation (SBRT) has evolved as a potential, non-invasive therapy. Further research is needed to personalize VA therapy for individual patients.

One-year mortality and causes of death after stereotactic radiation therapy for refractory ventricular arrhythmias: A systematic review and pooled analysis

Patients treated with cardiac stereotactic body radiation therapy (radioablation) for refractory ventricular arrhythmias are patients with advanced structural heart disease and significant comorbidities. However, data regarding 1-year mortality after the procedure are scarce. This systematic review and pooled analysis aimed at determining 1-year mortality after cardiac radioablation for refractory ventricular arrhythmias and investigating leading causes of death in this population. MEDLINE/EMBASE databases were searched up to January 2023 for studies including patients undergoing cardiac radioablation for the treatment of refractory ventricular arrhythmias. Quality of included trials was assessed using the NIH Tool for Case Series Studies (PROSPERO CRD42022379713). A total of 1,151 references were retrieved and evaluated for relevance. Data were extracted from 16 studies, with a total of 157 patients undergoing cardiac radioablation for refractory ventricular arrhythmias. Pooled 1-year mortality was 32 % (95 %CI: 23-41), with almost half of the deaths occurring within three months after treatment. Among the 157 patients, 46 died within the year following cardiac radioablation. Worsening heart failure appeared to be the leading cause of death (52 %), although non-cardiac mortality remained substantial (41 %) in this population. Age≥70yo was associated with a significantly higher 12-month all-cause mortality (p<0.022). Neither target volume size nor radiotherapy device appeared to be associated with 1-year mortality (p = 0.465 and p = 0.199, respectively). About one-third of patients undergoing cardiac stereotactic body radiation therapy for refractory ventricular arrhythmias die within the first year after the procedure. Worsening heart failure appears to be the leading cause of death in this population.

Stereotactic arrhythmia radioablation (STAR) opens a new era in the treatment of arrhythmias?

Tachyarrhythmias are common cardiovascular emergencies encountered in clinical practice. Among these, atrial fibrillation (AF) and ventricular tachycardia (VT) pose significant hazards due to their prevalence and severity. Initially, non-invasive pharmacological antiarrhythmic interventions were the primary treatment modality; however, due to their limited control rates and side effects, invasive therapies have been introduced in recent years. These include catheter ablation, alcohol ablation, cardiac implantable electronic devices, and heart transplantation. Nonetheless, for some patients, invasive treatments do not offer a definitive cure for arrhythmias and carry the risk of recurrence, especially with AF and VT, where the relapse rates are high and the treatment for VT is correlated with the type of tachycardia present. Currently, novel non-invasive treatment methods are emerging, with stereotactic radioablation therapy becoming an effective alternative for the management of refractory tachyarrhythmias. This review provides an overview of the application background of Stereotactic Arrhythmia Radioablation (STAR) therapy and promising results from its use in animal models and clinical applications.

Small metal artifact detection and inpainting in cardiac CT images

Background

Quantification of cardiac motion on pre-treatment CT imaging for stereotactic arrhythmia radiotherapy patients is difficult due to the presence of image artifacts caused by metal leads of implantable cardioverter-defibrillators (ICDs). The CT scanners' onboard metal artifact reduction tool does not sufficiently reduce these artifacts. More advanced artifact reduction techniques require the raw CT projection data and thus are not applicable to already reconstructed CT images. New methods are needed to accurately reduce the metal artifacts in already reconstructed CTs to recover the otherwise lost anatomical information.

Purpose

To develop a methodology to automatically detect metal artifacts in cardiac CT scans and inpaint the affected volume with anatomically consistent structures and values.

Methods

Breath-hold ECG-gated 4DCT scans of 12 patients who underwent cardiac radiation therapy for treating ventricular tachycardia were collected. The metal artifacts in the images caused by the ICD leads were manually contoured. A 2D U-Net deep learning (DL) model was developed to segment the metal artifacts automatically using eight patients for training, two for validation, and two for testing. A dataset of 592 synthetic CTs was prepared by adding segmented metal artifacts from the patient 4DCT images to artifact-free cardiac CTs of 148 patients. A 3D image inpainting DL model was trained to refill the metal artifact portion in the synthetic images with realistic image contents that approached the ground truth artifact-free images. The trained inpainting model was evaluated by analyzing the automated segmentation results of the four heart chambers with and without artifacts on the synthetic dataset. Additionally, the raw cardiac patient images with metal artifacts were processed using the inpainting model and the results of metal artifact reduction were qualitatively inspected.

Results

The artifact detection model worked well and produced a Dice score of 0.958 ± 0.008. The inpainting model for synthesized cases was able to recreate images that were nearly identical to the ground truth with a structural similarity index of 0.988 ± 0.012. With the chamber segmentations on the artifact-free images as the reference, the average surface Dice scores improved from 0.684 ± 0.247 to 0.964 ± 0.067 and the Hausdorff distance reduced from 3.4 ± 3.9 mm to 0.7 ± 0.7 mm. The inpainting model's use on cardiac patient CTs was visually inspected and the artifact-inpainted images were visually plausible.

Conclusion

We successfully developed two deep models to detect and inpaint metal artifacts in cardiac CT images. These deep models are useful to improve the heart chamber segmentation and cardiac motion analysis in CT images corrupted by mental artifacts. The trained models and example data are available to the public through GitHub.

Radiation-associated cardiovascular disease in patients with cancer: current insights from a cardio-oncologist

Radiation-associated cardiovascular disease (RACD), a complex disease characterized with pericarditis, myocardial damage, valvular heart diseases, heart failure, vasculopathy and ischemic heart disease, has a generally poor prognosis. While RACD may be acute, it often manifests in the late years or even decades following radiation exposure to the chest. With an increasing number of cancer survivors, RACD is likely to become an important issue in cardio-oncology. This review discusses pre-radiation therapy (RT) preparation, peri-RT patient management and long follow-up planning post-RT from a cardiology perspective. Additionally, a novel technique of stereotactic radiotherapy, which has been applied for the treatment of intractable cardiac arrhythmias, is presented. Appropriate patient examination and management during and after RT are essential to support patients undergoing cancer treatment to improve long life expectancy. A multidisciplinary team is needed to determine how to manage patients who receive RT to reduce RACD, to detect early phases of RACD and to provide the best treatment for RACD. Recent studies increasingly report advances in diagnosis using new equipment that has the potential to detect early phases of RACD, along with growing evidence for the optimal treatment for RACD. This review provides an overview of recent studies and guidelines to report on the latest findings, and to identify unresolved issues surrounding RACD that require validation in future studies.

Utility of CT and MRI in Cardiac Electrophysiology

Cardiac electrophysiology involves the diagnosis and management of arrhythmias. CT and MRI play an increasingly important role in cardiac electrophysiology, primarily in preprocedural planning of ablation procedures but also in procedural guidance and postprocedural follow-up. The most common applications include ablation for atrial fibrillation (AF), ablation for ventricular tachycardia (VT), and for planning cardiac resynchronization therapy (CRT). For AF ablation, preprocedural evaluation includes anatomic evaluation and planning using CT or MRI as well as evaluation for left atrial fibrosis using MRI, a marker of poor outcomes following ablation. Procedural guidance during AF ablation is achieved by fusing anatomic data from CT or MRI with electroanatomic mapping to guide the procedure. Postprocedural imaging with CT following AF ablation is commonly used to evaluate for complications such as pulmonary vein stenosis and atrioesophageal fistula. For VT ablation, both MRI and CT are used to identify scar, representing the arrhythmogenic substrate targeted for ablation, and to plan the optimal approach for ablation. CT or MR images may be fused with electroanatomic maps for intraprocedural guidance during VT ablation and may also be used to assess for complications following ablation. Finally, functional information from MRI may be used to identify patients who may benefit from CRT, and cardiac vein mapping with CT or MRI may assist in planning access. ©RSNA, 2024 Supplemental material is available for this article.

Hypertrophic obstructive cardiomyopathy with recurrent ventricular tachycardias: from catheter ablation and stereotactic radiotherapy to heart transplant-a case report

Background

Management of hypertrophic obstructive cardiomyopathy (HOCM) is often challenging, depending on clinical manifestation. This case report illustrates the complex treatment of HOCM with associated recurrent ventricular arrhythmias.

Case summary

A 54-year-old female with HOCM diagnosed in 2012 underwent a failed attempt for alcohol septal ablation, implantation of an implantable cardioverter-defibrillator, and repeated radiofrequency ablations (including ablation of the septal bulge to reduce LV obstruction). For ventricular tachycardia (VT) recurrences, she had stereotactic arrhythmia radioablation with subsequent epicardial cryoablation from mini-thoracotomy, and endocardial ablation with pulsed field energy. The situation was finally solved by mechanical support and heart transplantation.

Discussion

A few important lessons can be learned from the case. First, radiofrequency ablation was used successfully to decrease left outflow tract obstruction. Second, stereotactic radiotherapy has been used after four previous endo/epicardial catheter ablations to decrease the recurrences of VT. Third, mini-thoracotomy was used after previous epicardial ablation with subsequent adhesions to modify the epicardial substrate with cryoenergy. Fourth, pulsed field ablation of atrial fibrillation resulted in an excellent therapeutic effect. Fifth, pulsed field ablation was also used to modify the substrate for VT, and was complicated by transient AV block with haemodynamic deterioration requiring mechanical support. Finally, a heart transplant was the ultimate solution in the management of recurrent VT.

The Current Landscape of Ventricular Tachycardia Trials: A Systematic Review of Registered Studies

BACKGROUND

Although there are evolving techniques and technologies for treating ventricular tachycardia (VT), the current landscape of clinical trials for managing VT remains understudied.

OBJECTIVE

The objective of this study was to provide a systematic characterisation of the interventional management of VT through an analysis of the ClinicalTrials.gov, clinicaltrialsregister.eu, anzctr.org.au and chictr.org.cn databases.

METHODS

We queried all phase II to IV interventional trials registered up to November 2023 that enrolled patients with VT. Published, completed but unpublished, terminated, or ongoing trials were included for final analysis.

RESULTS

Of the 698 registered studies, 135 were related to VT, with 123 trials included in the final analysis. Among these trials, 25 (20%) have been published, enrolling a median of 35 patients (interquartile range [IQR] 20-132) over a median of 43 months (IQR 19-62). Out of the published trials, 14 (56%) were randomised, and 12 (48%) focused on catheter ablation. Twenty-two (18%) have been completed but remain unpublished, even after a median of 36 months (IQR 15-60). Furthermore, 27 (22%) trials were terminated or withdrawn, with the most common cause being poor enrolment. Currently, 49 (40%) trials are ongoing and novel non-ablative technologies, such as radioablation and autonomic modulation, account for 35% and 8% of ongoing trials, respectively.

CONCLUSIONS

Our analysis revealed that many registered trials remain unpublished or incomplete, and randomised controlled trial evidence is limited to only a few studies. Furthermore, many ongoing trials are focused on non-catheter ablation-based strategies. Therefore, larger pragmatic trials are needed to create stronger evidence in the future.

High Density Body Surface Potential Mapping with Conducting Polymer-Eutectogel Electrode Arrays for ECG imaging

Electrocardiography imaging (ECGi) is a non-invasive inverse reconstruction procedure which employs body surface potential maps (BSPM) obtained from surface electrode array measurements to improve the spatial resolution and interpretability of conventional electrocardiography (ECG) for the diagnosis of cardiac dysfunction. ECGi currently lacks precision, which has prevented its adoption in clinical setups. The introduction of high-density electrode arrays could increase ECGi reconstruction accuracy but is not attempted before due to manufacturing and processing limitations. Advances in multiple fields have now enabled the implementation of such arrays which poses questions on optimal array design parameters for ECGi. In this work, a novel conducting polymer electrode manufacturing process on flexible substrates is proposed to achieve high-density, mm-sized, conformable, long-term, and easily attachable electrode arrays for BSPM with parameters optimally selected for ECGi applications. Temporal, spectral, and correlation analysis are performed on a prototype array demonstrating the validity of the chosen parameters and the feasibility of high-density BSPM, paving the way for ECGi devices fit for clinical application.

Impact of abdominal compression on heart and stomach motion for stereotactic arrhythmia radioablation

PURPOSE

To evaluate the effectiveness of abdominal compression (AC) as a respiratory motion management method for the heart and stomach during stereotactic arrhythmia radioablation (STAR).

METHODS

4D computed tomography (4DCT) scans of patients imaged with AC or without AC (free-breathing: FB) were obtained from ventricular-tachycardia (VT) (n = 3), lung cancer (n = 18), and liver cancer (n = 18) patients. Patients treated for VT were imaged both FB and with AC. Lung and liver patients were imaged once with FB or with AC, respectively. The heart, left ventricle (LV), LV components (LVCs), and stomach were contoured on each phase of the 4DCTs. Centre of mass (COM) translations in the left/right (LR), ant/post (AP), and sup/inf (SI) directions were measured for each structure. Minimum distances between LVCs and the stomach over the respiratory cycle were also measured on each 4DCT phase. Mann-Whitney U-tests were performed between AC and FB datasets with a significance of α = 0.05.

RESULTS

No statistical difference (all p values were >0.05) was found in COM translations between FB and AC patient datasets for all contoured cardiac structures. A reduction in COM translation with AC relative to FB was patient, direction, and structure specific for the three VT patients. A significant decrease in the AP range of motion of the stomach was observed under AC compared to FB. No statistical difference was found between minimum distances to the stomach and LVCs between FB and AC.

CONCLUSIONS

AC was not a consistent motion management method for STAR, nor does not uniformly affect the separation distance between LVCs and the stomach. If AC is employed in future STAR protocols, the motion of the target volume and its relative distance to the stomach should be compared on two 4DCTs: one while the patient is FB and one under AC.

Dosimetric Impact of Delineation and Motion Uncertainties on the Heart and Substructures in Lung Cancer Radiotherapy

AIMS

Delineation variations and organ motion produce difficult-to-quantify uncertainties in planned radiation doses to targets and organs at risk. Similar to manual contouring, most automatic segmentation tools generate single delineations per structure; however, this does not indicate the range of clinically acceptable delineations. This study develops a method to generate a range of automatic cardiac structure segmentations, incorporating motion and delineation uncertainty, and evaluates the dosimetric impact in lung cancer.

MATERIALS AND METHODS

Eighteen cardiac structures were delineated using a locally developed auto-segmentation tool. It was applied to lung cancer planning CTs for 27 curative (planned dose ≥50 Gy) cases, and delineation variations were estimated by using ten mapping-atlases to provide separate substructure segmentations. Motion-related cardiac segmentation variations were estimated by auto-contouring structures on ten respiratory phases for 9/27 cases that had 4D-planning CTs. Dose volume histograms (DVHs) incorporating these variations were generated for comparison.

RESULTS

Variations in mean doses (Dmean), defined as the range in values across ten feasible auto-segmentations, were calculated for each cardiac substructure. Over the study cohort the median variations for delineation uncertainty and motion were 2.20-11.09 Gy and 0.72-4.06 Gy, respectively. As relative values, variations in Dmean were between 18.7%-65.3% and 7.8%-32.5% for delineation uncertainty and motion, respectively. Doses vary depending on the individual planned dose distribution, not simply on segmentation differences, with larger dose variations to cardiac structures lying within areas of steep dose gradient.

CONCLUSION

Radiotherapy dose uncertainties from delineation variations and respiratory-related heart motion were quantified using a cardiac substructure automatic segmentation tool. This predicts the 'dose range' where doses to structures are most likely to fall, rather than single DVH curves. This enables consideration of these uncertainties in cardiotoxicity research and for future plan optimisation. The tool was designed for cardiac structures, but similar methods are potentially applicable to other OARs.

Ventricular arrhythmia inducibility in porcine infarct model after stereotactic body radiation therapy

BACKGROUND

Ventricular arrhythmia (VA) is the primary mechanism of sudden death in patients with structural heart disease. Cardiac stereotactic body radiation therapy (SBRT) delivered to the scar in the left ventricle significantly reduces the burden of VA.

OBJECTIVE

The goal of this study was to investigate the impact of SBRT on scar morphology and VA inducibility in a porcine infarct model.

METHODS

Myocardial infarction (MI) was created in 10 Yorkshire pigs involving the left anterior descending artery territory. Cardiac positron emission tomography and computed tomography were performed for targeted SBRT. Alternative pigs received SBRT at 25 Gy in a single fraction. The terminal experiment included endocardial mapping, programmed ventricular stimulation, and tissue harvesting.

RESULTS

Of the 10 pigs infarcted, 2 died prematurely after MI and 8 (4 MI and 4 MI+SBRT) survived. Mean time from MI to SBRT was 48 ± 12 days, and mean time from SBRT to harvest was 32 ± 12 days. Scar was localized on intracardiac mapping in all pigs, and the scar was denser in the MI+SBRT compared with the MI-only group (33% ± 20% vs 14% ± 11%; P = .07). All 4 MI pigs had inducible VA during programmed stimulation, whereas only 1 of 4 pigs had inducible VA in the MI+SBRT arm (100% vs 25%; P = .07). No myocardial fibrosis was seen in the remote areas in either group.

CONCLUSION

SBRT reduced VA inducibility in pigs with scarring after MI. Endocardial mapping revealed denser scar in pigs receiving SBRT compared with those that did not, suggesting that SBRT suppresses VA inducibility through better scar homogenization.

Mapping and Ablation of Premature Ventricular Complexes: State of the Art

Premature ventricular complexes (PVCs) are common arrhythmias in clinical practice. Although benign and asymptomatic in most cases, PVCs may result in disabling symptoms, left ventricular systolic dysfunction, or PVC-induced ventricular fibrillation. Catheter ablation has emerged as a first-line therapy in such cases, with high rates of efficacy and low risk of complications. Significant progress in mapping and ablation technology has been made in the past 2 decades, along with the development of a growing body of knowledge and accumulated experience regarding PVC sites of origin, anatomical relationships, electrocardiographic characterization, and mapping/ablation strategies. This paper provides an overview of the main indications for catheter ablation of PVCs, electrocardiographic features, PVC mapping techniques, and contemporary ablation approaches. The authors also review the most common sites of PVC origin and the main considerations and challenges with ablation in each location.

Stereotactic arrhythmia radioablation and its implications for modern cardiac electrophysiology: results of an EHRA survey

Stereotactic arrhythmia radioablation (STAR) is a treatment option for recurrent ventricular tachycardia/fibrillation (VT/VF) in patients with structural heart disease (SHD). The current and future role of STAR as viewed by cardiologists is unknown. The study aimed to assess the current role, barriers to application, and expected future role of STAR. An online survey consisting of 20 questions on baseline demographics, awareness/access, current use, and the future role of STAR was conducted. A total of 129 international participants completed the survey [mean age 43 ± 11 years, 25 (16.4%) female]. Ninety-one (59.9%) participants were electrophysiologists. Nine participants (7%) were unaware of STAR as a therapeutic option. Sixty-four (49.6%) had access to STAR, while 62 (48.1%) had treated/referred a patient for treatment. Common primary indications for STAR were recurrent VT/VF in SHD (45%), recurrent VT/VF without SHD (7.8%), or premature ventricular contraction (3.9%). Reported main advantages of STAR were efficacy in the treatment of arrhythmias not amenable to conventional treatment (49%) and non-invasive treatment approach with overall low expected acute and short-term procedural risk (23%). Most respondents have foreseen a future clinical role of STAR in the treatment of VT/VF with or without underlying SHD (72% and 75%, respectively), although only a minority expected a first-line indication for it (7% and 5%, respectively). Stereotactic arrhythmia radioablation as a novel treatment option of recurrent VT appears to gain acceptance within the cardiology community. Further trials are critical to further define efficacy, patient populations, as well as the appropriate clinical use for the treatment of VT.

Analysis of left ventricle regional myocardial motion for cardiac radioablation: Left ventricular motion analysis

PURPOSE

Left ventricle (LV) regional myocardial displacement due to cardiac motion was assessed using cardiovascular magnetic resonance (CMR) cine images to establish region-specific margins for cardiac radioablation treatments.

METHODS

CMR breath-hold cine images and LV myocardial tissue contour points were analyzed for 200 subjects, including controls (n = 50) and heart failure (HF) patients with preserved ejection fraction (HFpEF, n = 50), mid-range ejection fraction (HFmrEF, n = 50), and reduced ejection fraction (HFrEF, n = 50). Contour points were divided into segments according to the 17-segment model. For each patient, contour point displacements were determined for the long-axis (all 17 segments) and short-axis (segments 1-12) directions. Mean overall, tangential (longitudinal or circumferential), and normal (radial) displacements were calculated for the 17 segments and for each segment level.

RESULTS

The greatest overall motion was observed in the control group-long axis: 4.5 ± 1.2 mm (segment 13 [apical anterior] epicardium) to 13.8 ± 3.0 mm (segment 6 [basal anterolateral] endocardium), short axis: 4.3 ± 0.8 mm (segment 9 [mid inferoseptal] epicardium) to 11.5 ± 2.3 mm (segment 1 [basal anterior] endocardium). HF patients exhibited lesser motion, with the smallest overall displacements observed in the HFrEF group-long axis: 4.3 ± 1.7 mm (segment 13 [apical anterior] epicardium) to 10.6 ± 3.4 mm (segment 6 [basal anterolateral] endocardium), short axis: 3.9 ± 1.3 mm (segment 8 [mid anteroseptal] epicardium) to 7.4 ± 2.8 mm (segment 1 [basal anterior] endocardium).

CONCLUSIONS

This analysis provides an estimate of epicardial and endocardial displacement for the 17 segments of the LV for patients with normal and impaired LV function. This reference data can be used to establish treatment planning margin guidelines for cardiac radioablation. Smaller margins may be used for patients with higher degree of impaired heart function, depending on the LV segment.

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-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.

Efficacy and Safety of Stereotactic Radiotherapy in Patients With Recurrent Ventricular Tachycardias: The Czech Experience

BACKGROUND

Stereotactic arrhythmia radiotherapy (STAR) has been proposed recently in patients with refractory ventricular tachycardia (VT).

OBJECTIVES

The purpose of this study was to describe the efficacy and safety of STAR in the Czech Republic.

METHODS

VT patients were recruited in 2 expert centers after at least 1 previously failed catheter ablation (CA). A precise strategy of target volume determination and CA was used in 17 patients treated from December 2018 until June 2022 (EFFICACY cohort). This group, together with an earlier series of 19 patients with less-defined treatment strategies, composed the SAFETY cohort (n = 36). A dose of 25 Gy was delivered.

RESULTS

In the EFFICACY cohort, the burden of implantable cardioverter-defibrillator therapies decreased, and this drop reached significance for direct current shocks (1.9 ± 3.2 vs 0.1 ± 0.2 per month; P = 0.03). Eight patients (47%) underwent repeated CA for recurrences of VT during 13.7 ± 11.6 months. In the SAFETY cohort (32 procedures, follow-up >6 months), 8 patients (25%) presented with a progression of mitral valve regurgitation, and 3 (9%) required intervention (median follow-up of 33.5 months). Two cases of esophagitis (6%) were seen with 1 death caused by the esophago-pericardial fistula (3%). A total of 18 patients (50%) died during the median follow-up of 26.9 months.

CONCLUSIONS

Although STAR may not be very effective in preventing VT recurrences after failed CA in an expert center, it can still modify the arrhythmogenic substrate, and when used with additional CA, reduce the number of implantable cardioverter-defibrillator shocks. Potentially serious sides effects require close follow-up.