Noninvasive cardiac arrhythmia ablation with particle beams

Reconstruction of excitation waves from mechanical deformation using physics-informed neural networks

Non-invasive assessment of the electrical activation pattern can significantly contribute to the diagnosis and treatment of cardiac arrhythmias, due to faster and safer diagnosis, improved surgical planning and easier follow-up. One promising path is to measure the mechanical contraction via echocardiography and utilize this as an indirect way of measuring the original activation pattern. To solve this demanding inversion task, we make use of physics-informed neural networks, an upcoming methodology to solve forward and inverse physical problems governed by partial differential equations. In this study, synthetic data sets were created, consisting of 2D excitation waves coupled to an isotropic and linearly deforming elastic medium. We show that for both focal and spiral patterns, the underlying excitation waves can be reconstructed accurately. We test the robustness of the method against Gaussian noise, reduced spatial resolution and projected tri-planar data. In situations where the data quality is heavily reduced, we show how to improve the reconstruction by additional regularization on the wave speed. Our findings suggest that physics-informed neural networks hold the potential to solve sparse and noisy bio-mechanical inversion problems and may offer a pathway to non-invasive assessment of certain cardiac arrhythmias.

Quantifying dose uncertainties resulting from cardiorespiratory motion in intensity-modulated proton therapy for cardiac stereotactic body radiotherapy

Background

Cardiac stereotactic body radiotherapy (CSBRT) with photons efficaciously and safely treats cardiovascular arrhythmias. Proton therapy, with its unique physical and radiobiological properties, can offer advantages over traditional photon-based therapies in certain clinical scenarios, particularly pediatric tumors and those in anatomically challenging areas. However, dose uncertainties induced by cardiorespiratory motion are unknown.

Objective

This study investigated the effect of cardiorespiratory motion on intensity-modulated proton therapy (IMPT) and the effectiveness of motion-encompassing methods.

Methods

We retrospectively included 12 patients with refractory arrhythmia who underwent CSBRT with four-dimensional computed tomography (4DCT) and 4D cardiac CT (4DcCT). Proton plans were simulated using an IBA accelerator based on the 4D average CT. The prescription was 25 Gy in a single fraction, with all plans normalized to ensure that 95% of the target volume received the prescribed dose. 4D dose reconstruction was performed to generate 4D accumulated and dynamic doses. Furthermore, dose uncertainties due to the interplay effect of the substrate target and organs at risk (OARs) were assessed. The differences between internal organs at risk volume (IRV) and OARreal (manually contoured on average CT) were compared. In 4D dynamic dose, meeting prescription requirements entails V25 and D95 reaching 95% and 25 Gy, respectively.

Results

The 4D dynamic dose significantly differed from the 3D static dose. The mean V25 and D95 were 89.23% and 24.69 Gy, respectively, in 4DCT and 94.35% and 24.99 Gy, respectively, in 4DcCT. Eleven patients in 4DCT and six in 4DcCT failed to meet the prescription requirements. Critical organs showed varying dose increases. All metrics, except for Dmean and D50, significantly changed in 4DCT; in 4DcCT, only D50 remained unchanged with regards to the target dose uncertainties induced by the interplay effect. The interplay effect was only significant for the Dmax values of several OARs. Generally, respiratory motion caused a more pronounced interplay effect than cardiac pulsation. Neither IRV nor OARreal effectively evaluated the dose discrepancies of the OARs.

Conclusions

Complex cardiorespiratory motion can introduce dose uncertainties during IMPT. Motion-encompassing techniques may mitigate but cannot entirely compensate for the dose discrepancies. Individualized 4D dose assessments are recommended to verify the effectiveness and safety of CSBRT.

From passage to inhibition: Uncovering the structural and physiological inhibitory mechanisms of MCUb in mitochondrial calcium regulation

Mitochondrial calcium (Ca²⁺ ) regulation is critically implicated in the regulation of bioenergetics and cell fate. Ca²⁺ , a universal signaling ion, passively diffuses into the mitochondrial intermembrane space (IMS) through voltage-dependent anion channels (VDAC), where uptake into the matrix is tightly regulated across the inner mitochondrial membrane (IMM) by the mitochondrial Ca²⁺ uniporter complex (mtCU). In recent years, immense progress has been made in identifying and characterizing distinct structural and physiological mechanisms of mtCU component function. One of the main regulatory components of the Ca²⁺ selective mtCU channel is the mitochondrial Ca²⁺ uniporter dominant-negative beta subunit (MCUb). The structural mechanisms underlying the inhibitory effect(s) exerted by MCUb are poorly understood, despite high homology to the main mitochondrial Ca²⁺ uniporter (MCU) channel-forming subunits. In this review, we provide an overview of the structural differences between MCUb and MCU, believed to contribute to the inhibition of mitochondrial Ca²⁺ uptake. We highlight the possible structural rationale for the absent interaction between MCUb and the mitochondrial Ca²⁺ uptake 1 (MICU1) gatekeeping subunit and a potential widening of the pore upon integration of MCUb into the channel. We discuss physiological and pathophysiological information known about MCUb, underscoring implications in cardiac function and arrhythmia as a basis for future therapeutic discovery. Finally, we discuss potential post-translational modifications on MCUb as another layer of important regulation.

Stereotactic body radioablation therapy as an immediate and early term antiarrhythmic palliative therapeutic choice in patients with refractory ventricular tachycardia

BACKGROUND

Stereotactic body radioablation therapy (SBRT) has recently been introduced with the ability to provide ablative energy noninvasively to arrhythmogenic substrate while reducing damage to normal cardiac tissue nearby and minimizing patients' procedural risk. There is still debate regarding whether SBRT has a predominant effect in the early or late period after the procedure. We sought to assess the time course of SBRT's efficacy as well as the value of using a blanking period following a SBRT session.

METHODS

Eight patients (mean age 58 ± 14 years) underwent eight SBRT sessions for refractory ventricular tachycardia (VT). SBRT was given using a linear accelerator device with a total dose of 25 Gy to the targeted area.

RESULTS

During a median follow-up of 8 months, all patients demonstrated VT recurrences; however, implantable cardioverter-defibrillator (ICD) and anti-tachycardia pacing therapies were significantly reduced with SBRT (8.46 to 0.83/per month, p = 0.047; 18.50 to 3.29/per month, p = 0.036, respectively). While analyzing the temporal SBRT outcomes, the 2 weeks to 3 months period demonstrated the most favorable outcomes. After 6 months, one patient was ICD therapy-free and the remaining patients demonstrated VT episodes.

CONCLUSIONS

Our findings showed that the SBRT was associated with a marked reduction in the burden of VT and ICD interventions especially during first 3 months. Although SBRT does not seem to succeed complete termination of VT in long-term period, our findings support the strategy that SBRT can be utilized for immediate antiarrhythmic palliation in critically ill patients with otherwise untreatable refractory VT and electrical storm.

Case Report: Treatment Planning Study to Demonstrate Feasibility of Transthoracic Ultrasound Guidance to Facilitate Ventricular Tachycardia Ablation With Protons

Background

Cardiac arrhythmias, such as ventricular tachycardia, are disruptions in the normal cardiac function that originate from problems in the electrical conduction of signals inside the heart. Recently, a non-invasive treatment option based on external photon or proton beam irradiation has been used to ablate the arrhythmogenic structures. Especially in proton therapy, based on its steep dose gradient, it is crucial to monitor the motion of the heart in order to ensure that the radiation dose is delivered to the correct location. Transthoracic ultrasound imaging has the potential to provide guidance during this treatment delivery. However, it has to be noted that the presence of an ultrasound probe on the chest of the patient introduces constraints on usable beam angles for both protons and photon treatments. This case report investigates the possibility to generate a clinically acceptable proton treatment plan while the ultrasound probe is present on the chest of the patient.

Case

A treatment plan study was performed based on a 4D cardiac-gated computed tomography scan of a 55 year-old male patient suffering from refractory ventricular tachycardia who underwent cardiac radioablation. A proton therapy treatment plan was generated for the actual treatment target in presence of an ultrasound probe on the chest of this patient. The clinical acceptability of the generated plan was confirmed by evaluating standard target dose-volume metrics, dose to organs-at-risk and target dose conformity and homogeneity.

Conclusion

The generation of a clinically acceptable proton therapy treatment plan for cardiac radioablation of ventricular tachycardia could be performed in the presence of an ultrasound probe on the chest of the patient. These results establish a basis and justification for continued research and product development for ultrasound-guided cardiac radioablation.

Stereotactic Radiotherapy Ablation and Atrial Fibrillation: Technical Issues and Clinical Expectations Derived From a Systematic Review

Aim

The purpose of this study is to collect available evidence on the feasibility and efficacy of stereotactic arrhythmia radio ablation (STAR), including both photon radiotherapy (XRT) and particle beam therapy (PBT), in the treatment of atrial fibrillation (AF), and to provide cardiologists and radiation oncologists with a practical overview on this topic.

Methods

Three hundred and thirty-five articles were identified up to November 2021 according to preferred reporting items for systematic reviews and meta-analyses criteria; preclinical and clinical studies were included without data restrictions or language limitations. Selected works were analyzed for comparing target selection, treatment plan details, and the accelerator employed, addressing workup modalities, acute and long-term side-effects, and efficacy, defined either by the presence of scar or by the absence of AF recurrence.

Results

Twenty-one works published between 2010 and 2021 were included. Seventeen studies concerned XRT, three PBT, and one involved both. Nine studies (1 in silico and 8 in vivo; doses ranging from 15 to 40 Gy) comprised a total of 59 animals, 12 (8 in silico, 4 in vivo; doses ranging from 16 to 50 Gy) focused on humans, with 9 patients undergoing STAR: average follow-up duration was 5 and 6 months, respectively. Data analysis supported efficacy of the treatment in the preclinical setting, whereas in the context of clinical studies the main favorable finding consisted in the detection of electrical scar in 4/4 patients undergoing specific evaluation; the minimum dose for efficacy was 25 Gy in both humans and animals. No acute complication was recorded; severe side-effects related to the long-term were observed only for very high STAR doses in 2 animals. Significant variability was evidenced among studies in the definition of target volume and doses, and in the management of respiratory and cardiac target motion.

Conclusion

STAR is an innovative non-invasive procedure already applied for experimental treatment of ventricular arrhythmias. Particular attention must be paid to safety, rather than efficacy of STAR, given the benign nature of AF. Uncertainties persist, mainly regarding the definition of the treatment plan and the role of the target motion. In this setting, more information about the toxicity profile of this new approach is compulsory before applying STAR to AF in clinical practice.

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.

A proof of concept treatment planning study of gated proton radiotherapy for cardiac soft tissue sarcoma

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Challenges of a cardiac target due to the respiration, the heart motion and the interplay effect.

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Cardiac respiratory double gating with additional ECG signals for proton radiotherapy.

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Proton planning study with a cardiac-gated CT scan obtained at the end-expiration.

Background and Purpose

Few studies on radiotherapy of cardiac targets exist, and none using a gating method according to cardiac movement. This study aimed to evaluate the dose-volume advantage of using cardiac-respiratory double gating (CRDG) in terms of target location with additional ECG signals in comparison to respiratory single gating (RSG) for proton radiotherapy of targets in the heart.

Materials and Methods

Cardiac motion was modeled using a cardiac-gated four-dimensional computed tomography scan obtained at the end-expiration. Plans with the prescription dose of 50 Gy (RSG and CRDG plans at diastole and systole phases) were compared in terms of clinically relevant dose-volume criteria for various target sizes and seven cardiac subsites. Potential dose sparing by utilizing CRDG over RSG was quantified in terms of surrounding organ at risk (OAR) doses while the dose coverage to the targets was fully ensured.

Results

The average mean dose reductions were 28 ± 10% when gated at diastole and 21 ± 12% at systole in heart and 30 ± 17% at diastole and 8 ± 9% at systole in left ventricle compared to respiratory single gating. The diastole phase was optimal for gated treatments for all target locations except right ventricle and interventricular septum. The right ventricle target was best treated at the systole phase. However, an optimal gating phase for the interventricular septum target could not be determined.

Conclusions

We have studied the dose-volume benefits of CRDG for each cardiac subsite, and demonstrated that CRDG may spare organs at risk better than RSG.

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

BACKGROUND AND PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSION

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

Inhibition of voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells by the class Ic antiarrhythmic agent lorcainide

Voltage-dependent K⁺ (Kv) channels play the role of returning the membrane potential to the resting state, thereby maintaining the vascular tone. Here, we used native smooth-muscle cells from rabbit coronary arteries to investigate the inhibitory effect of lorcainide, a class Ic antiarrhythmic agent, on Kv channels. Lorcainide inhibited Kv channels in a concentration-dependent manner with an IC₅₀ of 4.46 ± 0.15 μM and a Hill coefficient of 0.95 ± 0.01. Although application of lorcainide did not change the activation curve, it shifted the inactivation curve toward a more negative potential, implying that lorcainide inhibits Kv channels by changing the channels' voltage sensors. The recovery time constant from channel inactivation increased in the presence of lorcainide. Furthermore, application of train steps (of 1 or 2 Hz) in the presence of lorcainide progressively augmented the inhibition of Kv currents, implying that lorcainide-induced inhibition of Kv channels is use (state)-dependent. Pretreatment with Kv1.5 or Kv2.1/2.2 inhibitors effectively reduced the amplitude of the Kv current but did not affect the inhibitory effect of lorcainide. Based on these results, we conclude that lorcainide inhibits vascular Kv channels in a concentration and use (state)-dependent manner by changing their inactivation gating properties. Considering the clinical efficacy of lorcainide, and the pathophysiological significance of vascular Kv channels, our findings should be considered when prescribing lorcainide to patients with arrhythmia and vascular disease.

Proton or photon radiosurgery for cardiac ablation of ventricular tachycardia? Breath and ECG gated robust optimization

PURPOSE

Ventricular tachycardia (VT) is a life-threatening heart disorder. The aim of this preliminary study is to assess the feasibility of stereotactic body radiation therapy (SBRT) photon and proton therapy (PT) plans for the treatment of VT, adopting robust optimization technique for both irradiation techniques.

METHODS

ECG gated CT images (in breath hold) were acquired for one patient. Conventional planning target volume (PTV) and robust optimized plans (25GyE in single fraction) were simulated for both photon (IMRT, 5 and 9 beams) and proton (SFO, 2 beams) plans. Robust optimized plans were obtained both for protons and photons considering in the optimization setup errors (5 mm in the three orthogonal directions), range (±3.5%) and the clinical target volume (CTV) motion due to heartbeat and breath-hold variability.

RESULTS

The photon robust optimization method, compared to PTV-based plans, showed a reduction in the average dose to the heart by about 25%; robust optimization allowed also reducing the mean dose to the left lung from 3.4. to 2.8 Gy for 9-beams configuration and from 4.1 to 2.9 Gy for 5-beams configuration. Robust optimization with protons, allowed further reducing the OAR doses: average dose to the heart and to the left lung decreased from 7.3 Gy to 5.2 GyE and from 2.9 Gy to 2.2 GyE, respectively.

CONCLUSIONS

Our study demonstrates the importance of the optimization technique adopted in the treatment planning system for VT treatment. It has been shown that robust optimization can significantly reduce the dose to healthy cardiac tissues and that PT further increases this gain.

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

Ventricular tachycardia (VT) caused by myocardial scaring bears a significant risk of mortality and morbidity. Antiarrhythmic drug therapy (AAD) and catheter ablation remain the cornerstone of VT management, but both treatments have limited efficacy and potential adverse effects. Stereotactic body radiotherapy (SBRT) is routinely used in oncology to treat non-invasively solid tumors with high precision and efficacy. Recently, this technology has been evaluated for the treatment of VT. This review presents the basic underlying principles, proof of concept, and main results of trials and case series that used SBRT for the treatment of VT refractory to AAD and catheter ablation.

Stereotactic Ablative radiation therapy (SABR) for cardiac arrhythmia: A new therapeutic option?

AIM

Stereotactic ablative radiation therapy (SABR) is used in non-oncologic indications, recently even for cardiac arrhythmias. Thus, aim of this analysis is to review preclinical, early clinical evidences and future direction of the latter new treatment approach.

METHOD

A collection of available data regarding SABR and cardiac arrhythmias was made, by Pubmed research and 2 independent researchers, including preclinical and clinical data. A review of ongoing trials was conducted on ClinicalTrials.gov.

RESULTS

Preclinical research conducted in animal models showed that a safe and effective noninvasive treatment approach for cardiac arrhythmias could be represented by SABR with a median time of response around 2-3 months. The treatment dose plays a crucial role: the atrioventricular node would seem more radiosensitive than the other cardiac electric zones. Clinical data, such as published case series, case reports and early prospective studies, have already suggested the feasibility, efficacy and safety of SABR (25 Gy in one session) for refractory ventricular arrhythmias.

CONCLUSION

Considering the ongoing trials of SABR and new technological improvements in radiotherapy (e.g. hybrid magnetic resonance) and in arrhythmias noninvasive mapping systems, the future analyses will improve the reliability of those preliminary results.

Radiosurgery for ventricular tachycardia: preclinical and clinical evidence and study design for a German multi-center multi-platform feasibility trial (RAVENTA)

Background

Single-session high-dose stereotactic radiotherapy (radiosurgery) is a new treatment option for otherwise untreatable patients suffering from refractory ventricular tachycardia (VT). In the initial single-center case studies and feasibility trials, cardiac radiosurgery has led to significant reductions of VT burden with limited toxicities. However, the full safety profile remains largely unknown.

Methods/design

In this multi-center, multi-platform clinical feasibility trial which we plan is to assess the initial safety profile of radiosurgery for ventricular tachycardia (RAVENTA). High-precision image-guided single-session radiosurgery with 25 Gy will be delivered to the VT substrate determined by high-definition endocardial electrophysiological mapping. The primary endpoint is safety in terms of successful dose delivery without severe treatment-related side effects in the first 30 days after radiosurgery. Secondary endpoints are the assessment of VT burden, reduction of implantable cardioverter defibrillator (ICD) interventions [shock, anti-tachycardia pacing (ATP)], mid-term side effects and quality-of-life (QoL) in the first year after radiosurgery. The planned sample size is 20 patients with the goal of demonstrating safety and feasibility of cardiac radiosurgery in ≥ 70% of the patients. Quality assurance is provided by initial contouring and planning benchmark studies, joint multi-center treatment decisions, sequential patient safety evaluations, interim analyses, independent monitoring, and a dedicated data and safety monitoring board.

Discussion

RAVENTA will be the first study to provide the initial robust multi-center multi-platform prospective data on the therapeutic value of cardiac radiosurgery for ventricular tachycardia.

Trial registration number

NCT03867747 (clinicaltrials.gov). Registered March 8, 2019. The study was initiated on November 18th, 2019, and is currently recruiting patients.

Graphic abstract