Stereotactic cardiac radioablation for refractory ventricular tachycardia - electrical properties and conduction velocity analysis
T Jadczyk, S Williams, V Markides, E Pruvot, J Solana Muno, P Peichl, J Cvek, P G Postema, W Hoeksema, V Vigneswaran, A Gharaviri, A Von Kietzell, K Malaczynska-Rajpold, O Blanck, J WhitakerAbstract
Background
Stereotactic cardiac radioablation (cRA) has emerged as a novel non-invasive therapy for refractory ventricular tachycardia (VT). Although cRA markedly decreases VT burden, the mechanism underlying its rapid antiarrhythmic effect remains uncertain. Experimental studies suggest that ionising radiation can modify myocardial electrophysiology and conduction velocity, but human data are scarce.
Purpose
To evaluate the effect of cRA on myocardial voltage and conduction velocity using quantitative electroanatomical mapping (EAM) before and after cRA treatment.
Methods
Electroanatomical maps acquired in sinus rhythm from patients before and after cRA were selected from European centres participating in the STOPSTORM consortium. Voltage analysis was performed using both low- and high-density maps. Conduction velocity analysis using high-density EAM data was performed. Pre- and post-cRA EAM maps were exported from EAM systems and processed offline. Anatomic alignment between radiotherapy planning CT and EAM data was performed using 3D slicer. Dose distribution maps were coregistered with EAM data to delineate myocardial regions receiving ≥20 Gy. Electrophysiologic data was assessed in EP Workbench (v.1.0.0.beta-1) using the OpenEP framework. Local bipolar and unipolar voltage amplitudes, and conduction velocity (CV) were computed within the ≥20 Gy isodose volume. Conduction velocity analysis was performed by fitting a multiquadratic radial basis function to interpolated local activation time data and computing local conduction vectors as the spatial gradient of the interpolation surface. The magnitude of these vectors represented local CV. For each patient, paired datasets were extracted as Pre-cRA and Post-cRA according to anatomically matched regions, Figure 1a-b.
Results
Data were collected from fifteen patients (see Table 1), but CV analysis was feasible in only eight due to availability of high-density EAM data, resulting in sixteen maps (8 Pre-cRA, 8 Post-cRA). After cRA, median bipolar voltage amplitude within ≥20 Gy isodose volume decreased from 1.94 mV (IQR 0.74-2.05) to 0.51 mV (IQR 0.29-1.02) (Δ=-1.43 mV, p<0.001). Median unipolar voltage amplitude decreased from 4.87 mV (IQR 3.10-8.21) to 2.74 mV (IQR 1.89-4.86) (Δ=-2.13 mV, p<0.001). Median CV decreased from 0.41 m/s (IQR 0.32-0.58) to 0.22 m/s (IQR 0.18-0.41) (Δ=-0.19 m/s, p<0.001). Of note, in 1 patient CV increased after cRA from 0.30 m/s (IQR 0.18-0.45) to 0.56 m/s (IQR 0.35-0.94) (Δ=0.26 m/s, p<0.001. Pooled Pre-cRA and Post-cRA data are presented in Figure 1c-e.
Conclusion
Based on the observational data, stereotactic cardiac radioablation is associated with a reduction in myocardial voltage and alters CV, with the predominant effect being a decrease in conduction speed. Further studies are needed to confirm these preliminary results.