Characterizing cardiac contractile motion for noninvasive radioablation of ventricular tachycardia

Background Respiratory motion management strategies are used to minimize the effects of breathing on the precision of stereotactic ablative radiotherapy for ventricular tachycardia, but the extent of cardiac contractile motion of the human heart has not been systematically explored. Objective We aim to assess the magnitude of cardiac contractile motion between different directions and locations in the heart. Methods Patients with intracardiac leads or valves who underwent 4D cardiac computed tomography (4DCT) prior to a catheter ablation procedure for atrial or ventricular arrhythmias at 2 medical centers were studied retrospectively. The displacement of transvenous right atrial appendage (RA), right ventricle (RV) ICD, coronary sinus (CS) lead tips and prosthetic cardiac devices across the cardiac cycle were measured in orthogonal 3D views on a maximal-intensity projection CT reconstruction. Results A total of 31 pre-ablation cardiac 4DCTs were analyzed. The LV lead tip had significantly greater motion compared to the RV lead in the anterior-posterior direction (6.0±2.2mm vs 3.8±1.7mm; p=0.01) and superior-inferior direction (4.4±2.9mm vs 3.5±2.0mm; p=0.049). The prosthetic aortic valves had the least movement of all fiducials, specifically compared to the RV lead tip in the left-right direction (3.2±1.2mm vs 6.1±3.8mm, p=0.04) and the LV lead tip in the antero-posterior direction (3.8±1.7mm vs 6.0±2.2mm, p=0.03). Conclusion The degree of cardiac contractile motion varies significantly (1mm to 15.2 mm) across different locations in the heart. The effect of contractile motion on the precision of radiotherapy should be assessed on a patient-specific basis.