Cardiac radioablation in the treatment of ventricular tachycardia

Abstract

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

Keywords: Cardiac arrhythmias; Cardiac mapping; Cardiac radioablation; SBRT; Ventricular tachycardia.

Fig. 1

Comparison of necrosis stained autopsy slides (left) and magnetic resonance (right). Adapted from Kim et al. Circulation. 1999 Nov 9;100 :1992–2002.

Fig. 2

CRT Substrate Mapping. (A) Right Anterior-Oblique Projection. (B) Left Anterior-Oblique Projection:. (C) Posterior-Anterior Projection: Left ventricular endocardial bipolar voltage mapping in a patient with prior myocardial infarction (MI). Three maps in different projections (RAO = right anterior oblique (A), LAO = left anterior oblique (B), and posterior-anterior projection (C)) are displayed with color coding based on local voltage measurements. Areas with voltage less than 0.5 mV (dense scar) are color coded as red whereas the healthy tissues (>1.5 mV) are displayed as purple. This patient demonstrated extensive basal anterior, basal lateral, and basal inferior scar segments, consistent with prior MI due to the large left circumflex artery occlusion. Surviving tissues within the dense scar were identified and extensive ablation was carried out to “homogenize” the scar zone (scar mapping and ablation). Pink and red circles indicate ablation points. The rainbow color bar in the top right corner in each figure (yellow arrow) indicates the color coding scheme used in this map and cut-off values for dense scar (less than0.5 mV) and healthy tissues (>1.5 mV). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

CRT Substrate Mapping. (A) Right Anterior-Oblique Projection. (B) Left Anterior-Oblique Projection:. (C) Posterior-Anterior Projection: Left ventricular endocardial bipolar voltage mapping in a patient with prior myocardial infarction (MI). Three maps in different projections (RAO = right anterior oblique (A), LAO = left anterior oblique (B), and posterior-anterior projection (C)) are displayed with color coding based on local voltage measurements. Areas with voltage less than 0.5 mV (dense scar) are color coded as red whereas the healthy tissues (>1.5 mV) are displayed as purple. This patient demonstrated extensive basal anterior, basal lateral, and basal inferior scar segments, consistent with prior MI due to the large left circumflex artery occlusion. Surviving tissues within the dense scar were identified and extensive ablation was carried out to “homogenize” the scar zone (scar mapping and ablation). Pink and red circles indicate ablation points. The rainbow color bar in the top right corner in each figure (yellow arrow) indicates the color coding scheme used in this map and cut-off values for dense scar (less than0.5 mV) and healthy tissues (>1.5 mV). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

CRT Substrate Mapping. (A) Right Anterior-Oblique Projection. (B) Left Anterior-Oblique Projection:. (C) Posterior-Anterior Projection: Left ventricular endocardial bipolar voltage mapping in a patient with prior myocardial infarction (MI). Three maps in different projections (RAO = right anterior oblique (A), LAO = left anterior oblique (B), and posterior-anterior projection (C)) are displayed with color coding based on local voltage measurements. Areas with voltage less than 0.5 mV (dense scar) are color coded as red whereas the healthy tissues (>1.5 mV) are displayed as purple. This patient demonstrated extensive basal anterior, basal lateral, and basal inferior scar segments, consistent with prior MI due to the large left circumflex artery occlusion. Surviving tissues within the dense scar were identified and extensive ablation was carried out to “homogenize” the scar zone (scar mapping and ablation). Pink and red circles indicate ablation points. The rainbow color bar in the top right corner in each figure (yellow arrow) indicates the color coding scheme used in this map and cut-off values for dense scar (less than0.5 mV) and healthy tissues (>1.5 mV). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Cardiac Radioablation Treatment Workflow. Blue Panel: Identifying and Mapping the CRA Target. In clockwise order, non-invasive EKG, SPECT, Cardiac CT w/ contrast, and endocardial catheter-based voltage map used to localize the ventricular scar prior to radiation planning. Orange Panel: Target Delineation. Top panel shows 17-segment left ventricular model targeting 4 segments identified during mapping. Bottom panel with radiation therapy planning software showing PTV (red) contoured within the left and right ventricle. Yellow Panel: Developing a Radiation Plan. External beam planning software showing dose color wash of PTV (red) from 80 to 110% of prescription dose. Green Panel: Treating the Patient. Aligning PTV using cone beam CT on the day of treatment. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)