The association between the embolic load and atrial size in acute pulmonary embolism

Background: Early identification by computed tomography pulmonary angiography (CTPA) of patients with acute pulmonary embolism (PE) who have signs associated with a high embolic burden would be highly desirable. Objectives: To investigate whether an increased obstruction of the pulmonary vasculature is associated with reduced left atrial (LA) and increased right atrial (RA) areas. Methods: We retrospectively analyzed a consecutive series of CTPA studies of 137 patients with acute PE and 38 controls without PE between October 2004 and March 2006. Left and right atrial areas and longitudinal and short axis diameters were measured and correlated with the pulmonary arterial obstruction index (PAOI) divided into tertiles (obstruction of <12.5%, 12.5%-42.5% and ≥42.5%). Results: There was a significant negative age- and gender-adjusted correlation between the PAOI and LA measurements, particularly the LA area (r=-0.259) and the LA short axis diameter (r=-0.331). All RA measurements had positive correlations (RA area, r=0.279; RA short axis diameter, r=0.313). The LA/RA area ratio correlated negatively with the PAOI (r=-0.447). All above-mentioned correlations had P<0.002. All the LA measurements were the largest in the controls and gradually decreased with higher PAOIs. A receiver operating characteristic curve analysis demonstrated that the RV/LV diameter, LA/RA area and LA/RA short axis diameter ratios had comparable discriminative ability for higher PAOI tertiles. Conclusions: The higher the clot load in the pulmonary arteries, the smaller the LA area and the larger the RA area. Atrial area measurements by CTPA may serve as a real-time parameter in assessing the severity of PE upon diagnosis.