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Unlabelled: Controversy exists as to whether patients with single segmental mismatch (SSM) on a ventilation/perfusion (VQ) lung scan should be given a low or an intermediate probability of pulmonary embolism (PE)., Methods: Pulmonary angiography was used to evaluate the incidence of PE in SSM at the authors' institution. From January 1991 to January 1993, 1449 VQ scans were performed., Results: With modified Biello criteria, 283 were high probability; 628, low probability; 273, normal; and 273, intermediate probability. Of the intermediate probability scans, 61 had SSM. Forty of these patients underwent pulmonary angiography. Twelve patients had PE in the area of the SSM, giving an incidence of PE of 30%. The risk of PE in SSM in the different lung regions was also analyzed. Twenty-three SSM were in the bases of the lung with a 22% incidence of PE; 17 SSM were either in the midzone or apex with a 41% incidence of PE (p = not significant)., Conclusion: SSM carries a 30% risk of PE. Accordingly, SSM should be given an intermediate probability of PE and not a low probability of PE.

Purpose: To test the usefulness of lower limb Doppler venous compression ultrasound (US) and serum D-dimer measurements in diagnosis of pulmonary embolism in patients in whom ventilation-perfusion (V-P) scans indicate intermediate probability of pulmonary embolism., Materials and Methods: V-P scanning, pulmonary angiography, US, and D-dimer measurements were performed in 36 patients without known deep venous thrombosis but with intermediate probability of having a pulmonary embolism., Results: Pulmonary angiography demonstrated pulmonary embolism in 15 (41%) of 36 patients. US demonstrated deep venous thrombosis in only two patients, both with pulmonary embolism. Sensitivity of US was only 13%, but specificity was 100%. Five (14%) of the 36 patients had normal (< 220 micrograms/L) D-dimer levels; none of the five had pulmonary embolism. Sensitivity and specificity of D-dimer values were 100% and 16%, respectively, with a negative predictive value of 100%., Conclusion: Combined D-dimer measurement and US were helpful in correctly diagnosing pulmonary embolism in only seven (20%) of 36 patients. Pulmonary angiography is still required to diagnose pulmonary embolism in the majority of patients.

There remains no clear consensus as to the appropriate further investigation and management of the patient suspected of pulmonary embolism (PE) who has an intermediate lung scan. Clinical assessment is documented as unreliable, yet many of these patients are unlikely to be treated or to have further tests despite a 36% chance of having PE. Using Medical Decision Analysis, four management strategies for such patients have been examined in terms of mortality and morbidity up to 6 mo post-presentation. The strategies were: (1) treat all patients; (2) treat no patients; (3) perform pulmonary angiography; and (4) perform contrast venography. In the last two strategies, the patients with positive examinations are treated; those with negative examinations are not treated. An extensive literature review was performed to provide probability estimates of chance events and outcomes. If all patients are treated, there is 96.8% chance of survival, with an 85.8% chance of survival with no major complications. If no patients are treated, survival is 89.3% and complication-free survival is 89.3%. Angiography and venography results were 96.7%, 93.1% and 94.6% and 89.6%, respectively. We conclude that in patients suspected of PE who have intermediate lung scan results, the optimal strategy is pulmonary angiography since this results in the highest survival with the lowest complications.