Contemporary diagnostic approaches to acute pulmonary emboli.

Because of its availability and familiarity, the V/Q scan remains the most frequently used noninvasive screening study for the diagnosis of acute PE. Fast CT and MR imaging techniques probably will have more significant roles in the future in the diagnosis and management of PE, but limited availability and familiarity with these imaging modalities make it impractical to currently recommend them as primary screening tools for acute PE. Although the cost and time benefits appear to place fast CT ahead of MR imaging, more clinical experience and a greater understanding of the imaging nuances and pitfalls of interpretation for both fast CT and MR imaging are needed. Medicare reimbursements (both technical and professional fees) for a CT or MR scan are already competitive with a V/Q scan (Table 2), so that they may ultimately prove to be more cost-effective screening modalities for PE than a V/Q scan. Until the role for intraarterial DSA becomes further defined with clinical trials and outcome analyses, it cannot be recommended as a reference standard for the diagnosis of PE. Although conventional pulmonary angiography is associated with a 1% to 2% major nonfatal complication rate and a 0.1% to 0.5% mortality rate, chronic anticoagulation has reported major bleeding complication rates of 1.5% to 20% at 1 year, and inferior vena cava filters are associated with inferior vena cava thrombosis rates of 3% to 25%. Therefore, initiating or withholding therapy for the "presumed" presence or absence of PE based on a V/Q scan alone has the potential for generating excessive costs and morbidity in a large population of patients. Until the validity of fast CT and MR imaging have been proven, a pulmonary angiogram is required when there is any doubt about the diagnosis of PE. A negative pulmonary angiogram is often more useful in the management of a patient than an angiogram that demonstrates PE. By ruling out the presence of PE, an alternative and possibly more significant diagnosis will be pursued. Lastly, it is necessary for us to define more clearly the term clinically significant PE. This is important because fast CT, MR imaging and intraarterial DSA techniques can now reliably visualize third order pulmonary artery branches. Whether this degree of resolution allows for adequate detection of clinically significant PE will only be determined by extensive patient tracking and outcome analyses.