Assessing the utility of the ventilation phase in ventilation-perfusion imaging for acute pulmonary embolism

This study aims to identify patient characteristics that allow the exclusion of the ventilation phase in ventilation-perfusion imaging for the evaluation of acute pulmonary embolism (PE).

A total of 500 consecutive ventilation-perfusion reports with an indication for possible acute PE were retrospectively reviewed. Information on ventilation abnormalities, perfusion defects, PIOPED classification, age, sex, chest radiograph results, and presence of respiratory disease was recorded. Patients with moderate and large perfusion defects were analyzed to assess the utility of the ventilation phase on the final PIOPED classification.

Moderate (n=39) or large (n=26) perfusion defects were seen in 65 (13%) studies. Of these, 46 studies (70.8%) had defects unmatched on ventilation and three (4.6%) had triple-match defects, resulting in 49 reports (75.4%) classified as intermediate (n=28) or high (n=21) probability for PE. There was a statistically significant association between unmatched defects and a clear chest radiograph (P=0.03) and an association approaching statistical significance with younger age (P=0.05). There was a strong association with respiratory disease (P=0.12) and no association with patient sex (P=0.82). The percentage of studies with unmatched defects increased from 70.8 to 76.7% (33/43, P=0.39) if patients with respiratory disease were excluded, to 82.4% (28/34, P=0.14) if abnormal chest radiographs were excluded, and to 95.7% (22/23, P=0.01) if both were excluded.

There may be a subset of patients - younger patients with clear chest radiographs and no respiratory disease - for whom the ventilation phase can be excluded and the determination of a PE is based solely on perfusion abnormalities.