Valve Regurgitation: In the Eye of the Beholder

I recently had the opportunity to attend two meetings on consecutive days. One was the Structural Heart Disease Summit, and the other was the Annual Scientific Sessions of the American Society of Echocardiography (ASE). Although dealing broadly with structural heart disease, the Summit was largely devoted to interventional procedures, both surgical and transcatheter. The ASE meeting, of course, was primarily devoted to non-invasive imaging. Both meetings dealt in-depth with valve regurgitation from both a diagnostic and therapeutic perspective. However, the approach to the quantitation of the regurgitation that was taken in the two meetings was strikingly different.

The Structural Summit presented a number of cases of mitral, aortic, and tricuspid regurgitation consisting only of the color Doppler flow images. The ultrasound videos were shown and it was commented that it could be clearly seen that the patient had mild, moderate, or severe regurgitation, according to the case. In the ASE meeting, cases of valve regurgitation were accompanied by a vast array of specific measurements, that were used to determine severity, often to the decimal point. While it is certain that much of the presentations was governed by the agenda of the session and the time allotted for the lecture, there nevertheless appeared to be a dichotomy between the two groups in the approach to determining the degree of regurgitation. On occasion this dichotomy seemed striking.

At both meetings the assessment of valve regurgitation began with color-Doppler recordings which were the basis of the diagnosis and the first approach to quantitation, The presence of a flow disturbance in the retrograde chamber established the presence of regurgitation, while the size of the turbulent flow provided some measure of its severity. However, while the description of the lesion at the Summit often ended there, at the ASE meeting this typically was followed by a number of specific measurements that combined to yield an assessment of severity. The echocardiographers indicated that the size of the regurgitant jet had multiple determinants, and was not fully representative of regurgitant volume, while colleagues from the Summit suggested that, especially for severe lesions, evaluation of the color Doppler was all that was often done clinically, and that a focus on measurements of uncertain precision could lead to neglect of the overall clinical picture and ventricular function.

It is clear that the size of the flow disturbance has multiple determinants, and while it bears a general relationship to angiographic grade of regurgitation, it does not correlate closely with regurgitant volume.¹ In fact, the turbulent jet actually represents a spray, and the pressure gradient across the valve is the predominant determinant of the spray area. My favorite analogy to demonstrate the relationship of flow disturbance size to pressure is the syringe. If one has a 10cc syringe and pushes the plunger slowly, the spray is confined to a small area distal to the syringe. However, if the plunger is pushed forcefully, the resultant spray encompasses a large area. In both cases the total flow volume is 10cc, but the resultant size of the spray is very different. Increasing the spray from a garden hose by partial occlusion of the tip is a similar analogy. As jet size is related to momentum, the product of regurgitant area and jet velocity, the regurgitant orifice area influences jet size. The acuity of regurgitation, entrainment of flow by the jet, and constraint of the receiving chamber (best exemplified by the reduction of spray area by contact with a wall known as the Coanda Effect) are additional factors that determine the size of a regurgitant flow disturbance. Numerous instrument and technical factors involved in recording the turbulence also exist and can modify the results. Thus, the size of a regurgitant jet by echo is, at best, only a very general, and sometimes misleading, criteria for the severity and volume of valve regurgitation.

Given the quantitative limitations of jet size, a number of other criteria have emerged to assess the magnitude of valve regurgitation. As stated earlier, cardiac chamber size is a good reflection of regurgitant volume, but can also be due to other causes of remodeling. Regurgitant flow into the pulmonary veins, descending aorta, or inferior vena cava/hepatic veins is a usually specific if insensitive finding for severe regurgitation of mitral, aortic, and tricuspid valves respectively. Measurements derived from the vena contacta area at or just below the regurgitant orifice, and two quantitative methods to estimate regurgitant volume from either the area of jet acceleration just proximal to the leaflets (PISA) or from the difference of measures of ventricular inflow and outflow, provide alternate criteria for severity. These metrics may present challenges to precision and reproducibility of measurement, and require a number of assumptions. Therefore, application of these measurements to quantify regurgitation require care and experience, are best done routinely rather than waiting until quantitation is crucial to decision making, and must be interpreted in the context of their limitations, especially with suboptimal echo recordings.

In view of the above, it seems reasonable that, in a heart failure patient with no other etiology and in whom dilated ventricles and atria and a large regurgitant jet are present on echo, one can conclude that there is severe regurgitation. However, even here it would be of value to provide some additional evidence that the regurgitation is indeed severe. In anything less than such a case, it would seem imperative to perform and provide a more detailed quantitative analysis employing the additional echo measurements and calculations. Regardless of the specific circumstances, in my opinion the best approach to assessing and presenting the severity of valve regurgitation would be to examine and present the color Doppler jet images and, at the least, comment that they were supported by quantitative calculations. It would, of course, be even better to present the actual echo measurements. No matter what approach to presentation is taken, it should be obvious that quantitation of valve regurgitation should not be left to the eye of the beholder.