Pulmonary embolism among patients with a nearly normal ventilation/perfusion lung scan

Background: Among patients with nearly normal ventilation/perfusion (V over dot/Q over dot) lung scans in the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), pulmonary embolism (PE) was diagnosed more frequently in those who underwent pulmonary angiography than in those in whom PE was diagnosed on the basis of an adverse outcome while receiving no anticoagulant therapy. This may suggest that an adverse outcome is not apparent in patients with PE of such mild severity that the V over dot/Q over dot scan is nearly normal. If this were the case, patients with mild PE might not require treatment. Purpose: The purpose of this investigation was to evaluate patients in PIOPED with nearly normal V over dot/Q over dot lung scans. The V over dot/Q over dot scans and clinical characteristics of those in whom PE was diagnosed or excluded by pulmonary angiography (angiography group) were compared with those in whom PE was diagnosed or excluded by the presence or absence of an adverse outcome while not receiving anticoagulant therapy (outcome group). If the characteristics were the same, it would suggest that some patients with mild PE do well without treatment. If the characteristics were different, it would indicate that there is no evidence from these data that mild PE need not be treated. Methods: Data from PIOPED were evaluated from patients with suspected acute PE who had V over dot/Q over dot scans interpreted as nearly normal. There were 75 patients in the angiography group and 90 patients in the outcome group. Patients with entirely normal V over dot/Q over dot scans were excluded. Results: PE was more frequent in the angiography group. than in the outcome group, 8 of 75 (11%) vs 0 of 90 (0%) (p<0.01). In patients with nearly normal V over dot/Q over dot scans who were in the outcome group in comparison to the angiography group, the V over dot/Q over dot scan showed fewer mismatched segmental perfusion defects, a lower percentage of low-probability V over dot/Q over dot interpretations by one of the two V over dot/Q over dot readers (compared with very low or normal probability), and a generally lower clinical assessment. Conclusion: The observed lower frequency of PE in the outcome group in comparison to the angiography group can be attributed to a lower likelihood of PE in this group of patients with nearly normal V over dot/Q over dot scans in comparison to those who underwent pulmonary angiography. There is no evidence from these data that occasional patients with nearly normal V over dot/Q over dot scans who have PE do not require treatment.