Revision of Gorlin constant for calculation of mitral valve area from left heart pressures.

Abstract

The constant (C= 3I) in the hydraulicformulafor calculation of mitral valve area was originally empirically determined by comparison of measured valve area at operation or necropsy with right heart catheterization data. This constant corrects, among other things, for overestimation of the diastolic filling and mitral valve gradient derived from a peripheral arterial tracing and pulmonary capillary wedge pressure, respectively. With left heart catheterization these measurements can be made directly and more accurately. In this study through simultaneous measurement of pulmonary capillary wedge, peripheral arterial, left atrial, and left ventricular pressures, a new constant (K= 40) was derived which should provide a more accurate estimation of mitral valve orifice area when left heart data are used.The hydraulic formula for the calculation of mitral valve area (MVA) developed by Gorlin and Gorlin (I95I) contains a constant (C) empirically calculated by comparison of mitral valve orifice area estimated at operation in ii patients with cardiac output (CO), pulmonary capillary wedge pressure (PC), and diastolic filling period measured peripherally from the brachial artery (pDFP). Left ventricular diastolic pressure was assumed to average 5 mmHg, yielding a mitral valve gradient of PC-5 and the following formula:where HR is heart rate. The constant, C, includes 5 factors: (i) conversion of pressure from mmHg to cm H20 (I-17), (2) deviation of the mitral valve from the 'perfect orifice' for which the formula is valid, (3) overestimation of the actual diastolic filling period (cDFP) because pDFP includes part of the isovolumic contraction and relaxation time, (4) With the development of techniques for retrograde and transseptal catheterization of the left side of the heart, the pressure gradient across the mitral valve (LA-LV) and cDFP are commonly measured directly from left atrial (LA) and left ventricular (LV) pressure tracings. The constant, C, originally estimated for use with indirect measurements will, when used with left heart data, result in an overestimation of mitral valve orifice area. It was the purpose of this study to arrive at a new value for this constant for use with left heart data. For clarity this new constant will be referred to as K, yielding the formula:Methods One way to arrive at a value for K would be to repeat the study of Gorlin and Gorlin (I95I) comparing mitral valve orifice area estimated at operation or measured at necropsy with calculated orifice area from left heart catheterization data obtained shortly before. However, due to the inaccuracies of measuring the mitral orifice at operation and the paucity of intact necropsy specimens, this method was deemed impractical. For the purposes of this study, it was assumed that the value for C of 3I for use with PC-s and pDFP was correct. Since, regardless of the technique of measurement, the mitral orifice is the same; then equation (i) equals equation (2) in a given patient. Solving for K, the following formula is derived:

Discrepancy between mitral valve areas measured by two-dimensional planimetry and three-dimensional transoesophageal echocardiography in patients with mitral stenosis

“…However, we assume that the MVA measured from 3D TOE is a gold standard, because we could confirm that the cross-sectional plane was correctly positioned at the tips of the MV using multiplanar reconstruction, and the image quality of 3D TOE appeared to be superior to that obtained using transthoracic 2D. Furthermore, the Gorlin method is invasive and has several pitfalls and technical limitations 23 24. Direct measurement of the MVA during surgery is not always successful either, especially in cases of severely distorted valves 25…”

Three-dimensional evaluation of the mitral valve area and commissural opening before and after percutaneous mitral commissurotomy in patients with mitral stenosis

“…Previous studies have shown promising results 3,4 and suggested that RT3DE may provide more accurate MVA measurements than 2DE. In addition to the fact that in these studies, the authors used the Gorlin's method, which cannot be considered as a gold standard, 6,7 such conclusions can be questioned for experienced observers because only 3D-guided 2D measurements were considered. Thus, with experience, accurate MVA measurements at the tips of the leaflet in a well-oriented plane are expected with 2DE and indeed, in the present study, similar results were observed using 2DE and RT3DE.…”

“…First, superiority of RT3DE against 2DE was demonstrated using haemodynamic measurements and the Gorlins' equation, which cannot be considered as a gold standard. 6,7 Secondly, only 3D-guided 2D measurements were considered and because RT3DE 'only' offers the opportunity to perform a well-oriented planimetry, its superiority for experienced operators can be questioned. In contrast, RT3DE may be particularly helpful for less experienced operators but this has not been clearly evaluated.…”

Real-time three-dimensional echocardiography for rheumatic mitral valve stenosis evaluation

“…Study limitations. Gorlin's method has multiple recognized limitations (16,17). Ideally, the desired gold standard should have been the measurement performed in the surgical specimen inspection.…”