Asymptomatic pulmonary embolism in patients with deep vein thrombosis. Is it useful to take a lung scan to rule out this condition?

One hundred and sixteen patients with proximal deep venous thrombosis (DVT) confirmed venographically had perfusion and ventilation lung scans performed 48 hours after admission to assess the incidence of asymptomatic pulmonary embolism (PE). Sixty-six patients had normal lung scans, 29 had high-probability defects suggestive of PE, and 21 had indeterminate-probability of PE. Chest X-ray, electrocardiogram and arterial blood gases were of no value in assessing the lung scan results. Six out of 29 patients with a baseline lung scan of high probability of PE experienced acute signs and/or symptoms suggestive of pulmonary embolism while on heparin therapy. A repeated scan this time did not disclose new perfusion defects in any patients. In the absence of a baseline study, these scans may be interpreted as demonstrating pulmonary embolism on treatment and lead to unnecessary caval interruption procedures for failed heparin therapy.