Detailed analysis of patients with matched ventilation-perfusion defects and chest radiographic opacities

We performed a retrospective evaluation of the data obtained from the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study to determine the prevalence and distribution of pulmonary embolism (PE) in patients with matching ventilation-perfusion (V/Q) defects and chest radiographic opacities (triple matches). From the 1,487 patients in whom diagnostic V/Q scans were obtained, 247 (17%) patients were recorded as having matching V/Q defects and chest radiograph opacities in at least one lung zone. Diagnostic angiograms were available for 275 lung zones (233 patients) which demonstrated matching V/Q defects and chest radiograph opacities. The overall prevalence of PE in all lung zones with triple matches was 26%. The prevalences of PE in the upper, middle and lower lung zones were 11%, 12% and 33%, respectively. Pulmonary embolism was significantly more common in lower lung zone triple matches compared with the upper and middle lung zone triple matches (p < 0.005). There was no correlation between the size of the V/Q and chest radiographic abnormalities and the prevalence of PE. We conclude that in patients with matching V/Q defects and chest radiographic opacities isolated to the upper and middle zones the V/Q scan can be interpreted as representing a low probability of PE. Similar findings in the lower lung zones represent an intermediate probability of PE. The application of this modification to V/Q scan interpretation criteria will aid in reducing the number of intermediate V/Q lung scan interpretations.