Can ventilation-perfusion scans accurately diagnose acute pulmonary embolism?

To examine the accuracy of ventilation-perfusion (V/Q) scanning, we retrospectively reviewed pulmonary angiograms and V/Q scans from 150 patients clinically suspected of having pulmonary embolism. Pulmonary emboli were documented by angiography in 56 patients (37%). In seven patients V/Q scans were interpreted as being normal and these seven patients were angiographically negative for emboli. The remainder of the scans were classified as showing a low, moderate, or high probability of emboli, or as indeterminate scans. Among these four abnormal classifications, pulmonary angiography demonstrated emboli in 13.6%, 62.5%, 85.7%, and 18.4% of these patients, respectively. An analysis of these data demonstrates that an unacceptably high error rate would result if V/Q scans alone were relied upon to establish the presence or absence of pulmonary emboli. In view of the high mortality that results when pulmonary emboli are untreated and the relatively low mortality and morbidity of pulmonary angiography, angiography remains an essential diagnostic procedure in patients suspected of having pulmonary embolism.