Should Perfusion Scintigraphy Be Performed to Follow Patients with Acute Pulmonary Embolism? If So, When?

This investigation evaluated the changes of pulmonary perfusion at 4 different points of follow-up within 1 y in patients with pulmonary embolism (PE) and the factors predictive of complete or incomplete recovery of pulmonary perfusion. Patients with symptomatic PE underwent perfusion lung scintigraphy and blood gas analysis within 48 h from clinical presentation, after 1 wk, and after 1, 6, and 12 mo; echocardiography was performed at baseline and after 6 and 12 mo. All perfusion lung scintigraphy scans were examined by 2 expert nuclear medicine physicians with a scoring method that attributed a score of 0, 0.5, or 1 for extension (maximum score, 18) to the presence of perfusion defects (PD), both at baseline and on each follow-up scan. Among 183 patients who completed 1 y of follow-up, the median baseline PD score was 8.2; it decreased significantly at each follow-up time point until 6 mo ( < 0.001). Median baseline alveolar-arterial difference in oxygen partial pressure (PA-aO) was 50.9 and decreased significantly up to 1 mo ( < 0.001); median pulmonary artery systolic pressure (PAsP) was 45.9 mm Hg and decreased significantly until 12 mo ( < 0.001). A correlation was found between PD and both PA-aO ( < 0.05) and PAsP ( < 0.05). We found a correlation between PD ≠ 0 and PAsP ≥ 40 mm Hg at 12 mo ( < 0.05); in 6 (3.3%) of these patients such a correlation was still present after 24 mo, suggesting they could develop chronic thromboembolic pulmonary hypertension. Low baseline PD (odds ratio, 0.80; < 0.0001) and high 1-wk percent recovery (odds ratio, 1.04; < 0.0001) were predictive factors of complete 6-mo recovery. Perfusion scintigraphy may be useful to follow patients with PE. The follow-up should consist of 3 steps: the baseline examination, which reflects the severity of PE; the scan at 1 wk, which indicates the early amount of reperfusion; and the scan at 6 mo, which demonstrates the maximum attainable recovery. Patients with incomplete recovery and persistence of pulmonary hypertension on the 24-mo control should be further studied for possible development of chronic thromboembolic pulmonary hypertension.