Vena Contracta

It is characterized by high velocity, laminar flow.

It is slightly smaller than the anatomic regurgitant orifice due to boundary effects.

The cross-sectional area of the vena contracta represents a measure of the effective regurgitant orifice area, which is the narrowest area of actual flow.

The size is independent of flow rate and driving pressure for a fixed orifice.

If the regurgitant orifice is dynamic, the vena contracta may change with hemodynamics, or during the cardiac cycle.

In contrast to the to the jet in the receiving chamber, the vena contracta is less sensitive to technical factors such as pulse repetition frequency.

Because of the small values of the width of the vena contracta (usually < 1 cm), small errors in its measurement may lead to a large percent error and misclassification of the severity of regurgitation.

Technical tips:
It may be necessary to angulate the transducer out of the normal echocardiographic imaging planes to separate out the area of proximal flow acceleration, the vena contracta, and the downstream expansion of the jet.
The color flow sector should be as narrow as possible, with the least depth, to maximize lateral and temporal resolution.

Full text article on assessment of mitral regurgitation severity.

1. Grayburn PA, Fehske W, Omran H, Brickner ME, Luderitz B. Multiplane transesophageal echocardiographic assessment of mitral regurgitation by Doppler color flow mapping of the vena contracta. American Journal of Cardiology 1994 Nov 1;74(9):912-7
   Assessment of the severity of mitral regurgitation (MR) by Doppler color flow mapping is limited by dependence of jet area on hemodynamic and technical variables. The width of the MR jet at its origin may be less dependent on hemodynamic variables, and thus should more accurately reflect the severity of MR. Doppler color flow mapping was performed in 80 subjects by transesophageal echocardiography (TEE) within 48 hours of catheterization. Width of the MR jet at its vena contracta was measured by both single plane and multiplane TEE and compared with the angiographic grade of MR and regurgitant volume. The width of the MR jet correlated closely with angiographic grade by both methods. A jet width > or = 6 mm identified angiographically severe MR with a sensitivity and specificity of 100% and 83% by single-plane TEE, and 95% and 98% by multiplane TEE. The sensitivity and specificity for detecting a regurgitant volume > or = 80 ml was 93% and 76% for single-plane TEE, and 86% and 95% for multiplane TEE. Thus, the width of the MR jet at its vena contracta by Doppler color flow mapping is an accurate marker of the severity of MR. By virtue of its ability to obtain orthogonal views specifically oriented to mitral leaflet coaptation, multiplane TEE is superior to single-plane TEE in assessing MR jet width.

2. Fehske W, Omran H, Manz M, Kohler J, Hagendorff A, Luderitz B. Color-coded Doppler imaging of the vena contracta as a basis for quantification of pure mitral regurgitation. American Journal of Cardiology 1994 Feb 1;73(4):268-74
   The narrowest central flow region of a jet is defined as the vena contracta. This term is applied also to the contracted zone of the Doppler color flow image of a jet at its passage through an incompetent mitral valve. The clinical applicability of measuring the size of the vena contracta by transthoracic color-coded Doppler echocardiography for estimating the severity of mitral regurgitation (MR) was evaluated. In 78 of 82 patients with angiographically proved MR, a coherent flow image across the valve was visualized. The maximal diameter in the apical long-axis view was considered as a representative value for the size of the vena contracta. In comparison with the maximal left atrial velocity pixel area, this parameter revealed higher correlations to the angiographic degree of MR and to the regurgitant volume (r = 0.94 vs 0.72, and 0.83 vs 0.71, respectively). The highest positive and negative predictive accuracies for differentiating mild-to-moderate from severe MR were determined for a diameter of 6.5 mm (88 and 96%, respectively). Because the vena contracta is directly related to the severity of MR, it is concluded that it is helpful to use this parameter instead of the maximal velocity pixel area for semiquantitative grading.

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