The Determinants of Vena Contracta and Its Value in Evaluating Severity of Aortic Regurgitation

Recent studies evaluating the severity of valvular insufficiencies have focus on effective orifice area (EOA). This area corresponds hydrodynamically to the cross-sectional area of the vena contracta (VC), the smallest cross-sectional area of the regurgitant flow stream. The aim of the present study was to quantify the aortic regurgitation (AR) by using the color Doppler imaged VC.
METHODS
The fifty five patients with chronic AR were enrolled in the study. VC was visualized by transthoracic echocardiography from the apical echocardiographic window. Quantitative Doppler (QD) method depending on mitral (SVm) and aortic stroke volumes (SVao) was taken as reference method. EOA, regurgitant volume (RV) and regurgitant fraction (RF) were calculated by using both VC and QD simultaneously in all patients. By using VC; EOA, RV and RF were calculated as follows: EOAVC= (VC)2 x ?/4, RVVC= EOAVC x VTIAR and RFVC= RVVC/SVao. The same parameters were obtained by QD method as: RVQD= (SVao)-(SVm), RFQD= (RVQD/SVao) x 100 and EOAQD= RVQD/VTIAR. The relationships between VC and patients parameters were evaluated by using simple linear regression analysis. To find the determinants of VC, multivariate analysis was performed with the parameters having significant correlations. Parameters obtained by both methods were compared with each other using simple regression analysis and the method of Bland-Altman for agreement.
RESULTS
EOAQD (r=0.96), RFQD (r=0.84), RVQD (r=0.82), angiographically III/IV degree AR (r=0.74), patient age (r=-0.67), and left ventricle end-diastolic diameter (r=0.47) had statistically significant correlations with VC (0.48±0.12 cm). As the result of the multivariate analysis with these parameters, VC was found to be related with only EOAQD. The EOA (r=0.96, p<0.001; mean difference 0±0.03 cm2, SEE=0.004 and p>0.05), RV (r=0.97, p<0.001; mean difference =1.3±4.8 cm3, SEE=0.65 cm3 and p>0.05) and RF (r=0.93, p<0.001; mean difference =1.46±4.9%, SEE=0.66% and p>0.05) obtained by both methods agreed well with each other. VC had a sensitivity of 80%, specificity of 86% and accuracy of 84% in determining severe AR when the lower limit was taken as 0.54 cm.
CONCLUSION
VC obtained by color Doppler is a simple and reliable noninvasive parameter for evaluating severity of AR.