**2.6.3 Vena contracta**

It is one of the preferred echocardiographic indexes for its efficacy and its simplicity. The vena contracta is the narrowest portion of a jet that occurs at or just downstream from the orifice (Baumgartner, 1991). It is characterized by high velocity, laminar flow and is slightly smaller than the anatomic regurgitation orifice due to boundary effects.

The cross-sectional area of the vena contracta represents a measure of the effective regurgitant orifice area (EROA), which is the narrowest area of the actual flow. The size of the vena contracta is independent of the flow rate and driving pressure for a fixed orifice. However, if the regurgitant orifice is dynamic, the vena contracta may change with hemodynamics or during the cardiac cycle. Comprised of high velocities, the vena contracta is considerably less sensitive to technical factors such as PRF compared to the jet in the receiving chamber. To specifically image the vena contracta, it is often necessary to angulate the transducer out of the normal echocardiographic imaging planes, such that the area of proximal flow acceleration, the vena contracta, and the downstream expansion of the jet can be distinguished. It is preferable to use a zoom mode to optimize visualization of the vena contracta and facilitate its measurement. The Colour flow sector should also be as narrow as possible, with the minimal depth, so as to maximize lateral and temporal resolution.

The Degenerative Mitral Valve Regurgitation:

surgeon decide the length of the neochordae (14C).

account when the surgical strategy is discussed with the surgeon.

of mitral regurgitation is done by transthoracic exam.

From Geometrical Echocardiographic Concepts to Successful Surgical Repair 17

Fig. 14. (A,B,C). Intraoperative echocardiographic measurements showing prolapsed with flail of the posterior mitral leaflet (14A). The red line indicates the prolapsing plane; the green indicates the targeted coaptation plane (14B). Measuring the distance between the targeted position of the P2 scallop plane and the tip of the papillary muscle helps the

The preoperative echocardiographic examination must be performed under normal or near normal loading conditions. If hypovolemia were present, not only the severity of mitral regurgitation might be underestimated, as stated before, but also a false prolapse of various segments might erroneously be described. Often, a false prolapse may be encountered at the level of the anterior mitral leaflet (scallops A2 and A3) when, in fact, the lesion, usually flail, eversion or extreme prolapse, is typically located on the posterior leaflet. In order to avoid this risk, the echocardiographer should bear in mind the diagnosis of the preoperative transthoracic examination and carefully compare it to his own findings. One should not forget that most of the times the transesophageal examination confirms most of the elements from the transthoracic exam. By using the new harmonics echocardiographic machines, approximately 2/3 of the lesions found in transthoracic examination will be confirmed by TEE exam. The mitral annulus might also be underestimated when hypovolemia is present. This is the case in the operating room when the prepump exam is performed. In our experience the transthoracic measurement of the mitral annulus should always be taken into

It is important to remember that mitral regurgitation is dynamic and is affected by loading conditions. Reduction of afterload or intravascular volume at the time of the operation may reduce the true severity of the regurgitation. When mitral regurgitation is less significant than expected, the intravascular blood volume should be expanded and systemic vascular resistance should transiently be increased, by using repeated boluses of IV phenylephrine. The velocity of mitral regurgitation, and therefore display of its jet by Colour Doppler, depends on the pressure difference between the left atrium and left ventricle, which is higher in the presence of hypertension. The size of the jet in the left atrium is also very sensitive to changes in colour gain (directly proportional) and pulse repetition frequency (PRF) (inversely proportional). In any case, remember that the true assessment of the degree

Because of the small values of the width of the vena contracta (usually <1cm), small errors in its measurement may lead to a large percentage error and misclassification of the severity of regurgitation. Therefore, it is very important to acquire accurate primary data and measurement (Zoghbi, 2003).

The vena contracta method for assessing mitral regurgitation by colour Doppler echocardiography overestimates true mitral regurgitant orifice, it is markedly influenced by flow rate and the ultrasound system that is used. However, a diameter of a vena contracta over 8mm has a very good sensitivity and specificity for discriminating severe from non-severe mitral regurgitation (Zoghbi, 2003). The estimation of the diameter of the vena contracta is considered to have a good reproducibility of 10-15% (Margulescu, Brickner).
