Radionuclide Phase Imaging of Ventricular Tachycardia

Abstract

The emptying sequence of ventricular blood pool was studied by scintigraphic regional phase mapping in 10 patients with monomorphic and sustained ventricular tachycardia (VT) and compared to an electrophysiological study in order to assess the scintigraphic accuracy for the noninvasive localization of abnormal site of activation. All patients underwent both phase imaging and electrical mapping studies. There were 6 coronary artery disease patients, 3 patients with arrhythmogenic right ventricular disease and 1 patient with dilatative cardiomyopathy. Phase image studies were performed by first harmonic Fourier analysis of radionuclide angiography either during sinus rhythm or during spontaneous or catheter-induced VT. Eleven morphologically distinct VTs with a heart rate ranging from 145 to 260 beats min^-1 (mean 173 ± 32 beats min^-1) were imaged. Endocardial catheter mapping was accomplished in 9 different VT morphologies. Three patients also had epicardial intraoperative mapping. The site of origin of VT by a scintigraphic method was defined as the area of earliest regional contraction on the biventricular scintigram. By separating the right ventricle into 5 segments and the left ventricle into 7 segments, with multiple view cardiac imaging, a close correspondence between the site of origin determined by electrophysiological study and the region of earliest emptying of radioactivity was observed in 7 of 9 (77%) VTs. In 2 patients the extension of regional akinesia during VT prevented us from an accurate mapping of the regional time sequence of contraction. Scintigraphic phase mapping has inherent limitations due to wall motion dependency and relatively low resolution power but it is feasible in selected patients with monomorphic, inducible and long-sustained VT in whom adequate time for data collection is provided. In this subset of patients the site of origin of VT could be localized on a 'segmental' basis with close correspondence to electrophysiological mapping studies.