Major pulmonary embolism, part 2: Diagnostic confirmation

Given that two thirds of patients who die of pulmonary embolism (PE) do so within 1 hour of presentation, the evaluation must be rapid. Duplex ultrasonography has a high sensitivity and specificity for symptomatic deep venous thrombosis, but it cannot rule out PE and thus has limited value in the initial evaluation. Transthoracic echocardiography is valuable because it recognizes the cardiovascular characteristics of major PE and defines alternative diagnoses. The combination of ventilation-perfusion (V̇/Ȯ) lung scan findings and clinical probability can confirm or rule out PE. However, most V̇/Q̇ scans are nondiagnostic, and spiral CT is evolving toward replacing the V̇/Q̇ scan and angiography as the confirmatory study of choice in major PE. Real-time MRI can quickly provide artifact-free images during normal breathing, but technical improvements and clinical evaluation are needed before it can be used as an alternative to already-established diagnostic modalities.