Gated Versus First-Pass Radioangiography in the Evaluation of Left-to-Right Shunts

Excluding regurgitant ventricles and multiple shunting, left-to-right shunts of the central circulation can be evaluated from the difference between the right ventricular stroke counts (SCRV) and the left ventricular stroke counts (SCLV), which are obtained from gated radioangiography. The pulmonary-to-systemic flow ratio (Qp/Qs) is equated to SCRV/SCLV in atrial shunts and to SCLV/SCRV in ventricular and ductal shunts. In this paper, the potentials of the stroke count method have been compared to the gamma fit first-pass technique, incorporating the recent refinements in ductal shunts and deconvolution of the pulmonary curve. In 17 patients with left-to-right shunt, the stroke count method and the gamma fit method correlated moderately with oximetry (r = .71 and .87), respectively. The gamma variate method appeared superior in the detection and estimation of small shunts, whereas when Qp/Q8 was two or larger, the stroke count method yielded closer agreement with oximetry data.