Can pulmonary angiography be limited to the most suspicious side if the contralateral side appears normal on the ventilation/perfusion lung scan? Data from PIOPED

Purpose: The purpose of this investigation was to determine the frequency of pulmonary embolism (PE) in a single lung that showed a normal ventilation/perfusion (V over dot/Q over dot) lung scan when the V over dot/Q over dot scan on the contralateral side,vas interpreted as non-high-probability for PE. Methods: Data are from the national collaborative study Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). PE was diagnosed or excluded in all lungs by pulmonary angiography. Results: Single lungs with no V over dot/Q over dot abnormalities, when the V over dot/Q over dot scan on the contralateral side was interpreted as non-high-probability for PE, showed PE in 2 of 19 (11%) (95% confidence interval [CI], 1 to 33%), If PE was excluded by angiography on the side of the abnormal V over dot/Q over dot scan, then PE on the side of the normal V over dot/Q over dot scan was shown in only 1 of 19 (5%) (95% CI, 0 to 26%). Conclusion: A normal V over dot/Q over dot scan in a single lung, when the contralateral lung was interpreted as non-high-probability for PE, did not completely exclude PE on the apparently normal side, In such lungs, the probability of PE was in the range of low-probability interpretations. If the pulmonary angiogram showed no PE on the side of the abnormal V over dot/Q over dot scan, the probability of PE on the side of the normal V over dot/Q over dot scan satisfied the definition of very low probability for PE, This observation in patients undergoing pulmonary angiography may assist in determining whether the pulmonary angiogram should be bilateral.