Matched ventilation, perfusion and chest radiographic abnormalities in acute pulmonary embolism.

Abstract

This investigation assessed the positive predictive value of matched ventilation/perfusion (V/Q) and chest radiographic defects (triple-matched defects) for the detection of acute pulmonary embolism (PE). Data are from the Prospective investigation of Pulmonary Embolism Diagnosis (PIOPED). Only patients randomized for obligatory pulmonary angiography were included. Lungs were excluded if they showed any mismatched V/Q defect or any pleural effusion. Positive predictive values of triple-matched defects in the upper plus middle zones, 1 of 27 (4%), were less frequent than in the lower zones, 13 of 57 (23%) (p < 0.05). Triple-matched defects that involved 25-50% of a zone showed PE in 12 of 38 (32%) which was a higher positive predictive value than with smaller or larger triple-matched defects, 2 of 46 (4%) (p < 0.001). Refinement of the PIOPED data by elimination of nonrandomized patients, elimination of lungs with mismatched perfusion defects and elimination of lungs with a pleural effusion indicate that triple matches with PE (radiographic pulmonary infarcts) are infrequent in the upper and middle lung zones. When a triple match with PE occurs, it is most likely to be 25-50% of a zone.