Volume 2 - Issue 8
P. Vijay Shekhar a , R. Sakthivel b
a Consultant, Cardiologist, Kauvery Hospital, Heartcity-Trichy, India
b Consultant, Cardiologist, Kauvery Hospital, Chennai, India
Commentary from Dr. P. Vijay Shekhar
Stereotactcic Body Radiotherapy (SBRT), which involves targeting a volume of tissue with radiotherapy was available for use for treatment of intracranial lesions.
SBRT as a treatment alternative to conventional ablation for ventricular arrhythmias was performed first in humans. The procedure involves identification and delineation of scar using noninvasive (ECHO, CT, MRI, Nuclear imaging) or invasive (3D electroanatomical mapping). An internal target volume (area of scar and arrhythmia zone) is created, and radiation therapy of 25 Gy is delivered to the target area as a single fraction ablative dose through a linear accelerator.
Multiple case series which used SBRT as a noninvasive ablation modality for ventricular arrhythmias treatment have reported promising results in terms of reduction in short term recurrences. But however, long term outcomes and effects due to collateral damage of radiation therapy remains a concern. With more studies and evolving strategies to determine the ideal dose of radiation, SBRT could be a potential alternative to conventional invasive ablation, which is the current standard of care. SBRT for VT treatment could serve as feasible option in patients whom the risk of conventional radiofrequency ablation carries high procedural risk due to patient co morbidities.
Commentary from Dr. R. Sakthivel
Unlike the ablation outcome of idiopathic focal ventricular tachycardia (VT) in a structurally normal heart, the outcomes of catheter based radiofrequency ablation of scar based VT is fraught with clinical recurrence and the likely possible reasons for the same are the presence of multiple circuits, intramural substrates, post-ablation neo-circuits formation and anatomical predilection for catheter instability etc. Not uncommonly, a patient with double valve replacement in aortic and mitral position who underwent extensive epicardial scar VT ablation will be left with no safe and efficacious redo option in the event of clinical recurrence accompanied with pericardial adhesions.
With the interdisciplinary collaboration between electrophysiologists and radiation oncologists, completely noninvasive electrophysiology (EP) guided cardiac radioablation was developed and studied for the treatment of VT with single dose of precision stereotactic body radiotherapy (SBRT), over an average of 15 minutes, when the patient is awake (no use of general anaesthesia). Unlike the catheter ablation, treatment here is delivered across the entire myocardial thickness without being restricted by anatomical access and is potentially seen as a daycare option. In a very sick patient with recurrent VT with limited longevity of life, SBRT could be a safe therapeutic strategy .
Multimodality imaging combining scar imaging (MRI and/or Nuclear imaging) and electrical mapping (ECG imaging or catheter derived map) is used offline to define a target for ablation. A plan is developed in the radiation therapy treatment planning system. On the day of treatment, the patient is immobilised to minimise patient motion, the treatment unit is aligned with the patient, and a highly focused dose of radiation is delivered with a linear accelerator .
Early clinical results on radioablation of ventricular arrhythmia were promising. ENCORE trial showed >99% reduction in total VT burden at 12 months after treatment in 5 patients with no adverse changes in left ventricular function and mild reversible inflammatory lung changes . Recently, Zhang et al. elucidated the molecular mechanisms underlying the rapid response of cardiac radiotherapy even before the onset of transmural fibrosis. Electrophysiologic assessment of irradiated murine hearts reveals a supra physiologic electrical phenotype mediated by upregulation of Nav1.5 (Notch signalling) and Cx43 .
Radiotherapy can have delayed effect on cardiac structures (eg, coronaries, conduction system, valves, myocardium, pericardium). Collateral damage can involve oesophagus, lungs and spinal cord. Continued improvement in strategies to compensate for cardiac and respiratory cycle motion in SBRT is needed to have targeted delivery . Multicenter studies are needed with randomized controlled trials comparing radioablation to repeated catheter ablation.
Cardiac Radiotherapy Reprograms Electrical Conduction of Heart Muscle Cells to Younger State
Cardiac radiotherapy induces electrical conduction reprogramming in the absence of transmural fibrosis
Dr. P. Vijay Shekhar
Dr. R. Sakthivel