Should perfusion scintigraphy be done to follow patients with acute PE? If so, when?

Aims: This investigation evaluated the changes of pulmonary perfusion at four different points of follow-up within 1 year in patients with pulmonary embolism (PE) and the factors predictive of complete or incomplete recovery of pulmonary perfusion. Materials and Methods: Patients with symptomatic PE underwent perfusion lung scintigraphy (PLS) and blood gas analysis within 48 hours from clinical presentation, after 1 week, and after 1, 6 and 12 months; echocardiogram was made at baseline and after 6 and 12 months. All PLS were examined by two expert nuclear medicine physicians with a scoring method that attributed a score of 0, 0.5 or 1 for extension (maximum 18) to the presence of perfusion defects (PD), both at baseline and on each follow-up scan. Results: Among 183 patients who completed 1-year-follow-up, median baseline PD score was 8.2; it decreased significantly at each follow-up time point until 6 months (p<0.001). Median baseline alveolar-arterial difference of oxygen partial pressure (PA-aO2) was 50.9 and decreased significantly up to 1 month (p<0.001); median pulmonary artery systolic pressure (PAsP) was 45.9 mmHg, then decreased significantly until 12 months (p<0.001). A correlation was found between PD and both PA-aO2 (p<0.05) and PAsP (p<0.05). We found a correlation between PD ≠ 0 and PAsP≥ 40 mmHg at 12 months (p<0.05); in 6 (3.3%) of these patients such correlation was still present after 24 months, suggesting they could develop chronic thromboembolic pulmonary hypertension. Low baseline PD (odds ratio, OR,0.80, p< 0.0001) and high 1-week-percent recovery (OR 1.04, p< 0.0001) were predictive factors of complete 6 months-recovery. Conclusions: Perfusion scintigraphy may be useful to follow patients with PE. The follow-up should consist of three steps: the baseline examination since it reflects the severity of PE; the scan at 1-week that indicates the early amount of reperfusion; and the scan at 6-months that demonstrates the maximum attainable recovery. Patients with incomplete recovery and persistence of pulmonary hypertension on the 24-month control should be further studied for possible development of chronic thromboembolic pulmonary hypertension. Running title: Usefulness of follow-up in pulmonary embolism.