A 60-year-old man develops acute shortness of breath, tachypnea, and tachycardia while hospitalized for congestive heart failure. On physical examination the patient is tachypneic and anxious; there is no jugular venous distention and the lungs are clear to auscultation and percussion. There is a loud P2 sound. Examination of the lower extremities shows no edema or tenderness. Which of the following is the most important diagnostic step?
A. Catheter pulmonary angiogramFor suspected pulmonary embolism, CT with intravenous contrast has surpassed the ventilation-perfusion scan as the diagnostic method of choice. New multislice scanners can detect peripheral as well as central clots. Lung scanning may be useful in selected circumstances. PE is very unlikely in patients with normal or near-normal scans, and is highly likely in patients with high-probability scans. In patients with a high clinical index of suspicion for pulmonary embolus but low-probability scan, the diagnosis becomes more difficult. Catheter-based contrast pulmonary angiography (the “gold standard”) may occasionally be necessary but is not the first step. About two-thirds of patients with pulmonary embolus have evidence of deep venous disease on venous ultrasound. Therefore, pulmonary embolus cannot be excluded by a normal study. The quantitative D-dimer enzyme-linked immunosorbent assay is positive in 90% of patients with pulmonary embolus. It has been used to rule out PE in patients with a low-probability scan. A contrast CT study is needed, however, in patients with intermediate or high pretest probability of pulmonary embolism. High-resolution CT scan of the chest is useful in the diagnosis of interstitial disease but does not adequately assess pulmonary vasculature; IV contrast is necessary to diagnose PE.