The Relative Atrial Index (RAI)-A Novel, Simple, Reliable, and Robust Transthoracic Echocardiographic Indicator of Atrial Defects

Background: The detection of atrial septal defects (ASDs) and other shunts is sometimes difficult on transthoracic echocardiography. In addition, the quantitative assessment of right-heart volume loading as an indicator of significant shunting can be difficult, with subjective estimation commonly used. Thus, the initial aim of this study was to test the accuracy of a simple, noninvasive index using atrial area dimensions to detect the presence of an ASD. Subsequently, the index was used to assess the degree of normalization and remodeling of atrial size following percutaneous ASD device closure. Methods: The relative atrial index (RAI) was derived from standard apical 4-chamber views as right atrial area divided by left atrial area. RAI was calculated in patients with previously diagnosed secundum atrial defects (n = 219) with no concomitant lesions and then compared with those calculated in age-matched controls (n = 219). 101 of the 219 patients with secundum atrial defects underwent percutaneous device closure. Measurements were obtained before and 1 day after percutaneous closure as well as in the early (mean, 124 days) and late (mean, 390 days) stages of follow-up. Results: The mean RAI in patients with ASDs (1.23 +/- 0.23) was significantly higher than that in the age-matched normal control group (0.78 +/- 0.1) (P < .0001). The mean RAI in patients with ASD was also significantly higher than that in the general population (0.81 +/- 0.15) (P < .0001). Receiver operating characteristic curve analysis suggested that a nominal RAI cutoff value of > 0.92 predicted patients with ASDs versus matched controls with 99.1% sensitivity and 90.5% specificity. After percutaneous closure, significant atrial remodeling occurred immediately, with a reduction in the mean RAI at day 1 to 0.93 +/- 0.16 (P < .0001) and complete normalization at early follow-up to 0.81 +/- 0.12. Conclusion: The RAI, a novel and simple transthoracic parameter, reliably identifies patients with possible atrial shunting. The resolution of right atrial enlargement occurs remarkably early after percutaneous ASD closure, as demonstrated by this novel parameter. (J Am Soc Echocardiogr 2010;23:275-81.)