The recently revised American College of Cardiology/American Heart Association guidelines for valvular heart disease emphasise that surgery is now indicated for severe mitral regurgitation (MR), even in asymptomatic patients, provided that the valve anatomy is suitable for repair, and that surgery is performed in an experienced centre with at least a 90% chance of successful repair.1 A corollary to this recommendation is that it is important to determine accurately the severity of MR, since surgery is only indicated for severe MR. In 2003, the American Society of Echocardiography and the European Society of Echocardiography published recommendations for quantification of valvular regurgitation.2 This paper summarises those recommendations, as they pertain to MR. First, a theoretical framework for understanding the determinants of MR severity and how they relate to echocardiography will be presented. Then, the practical application of various echocardiographic techniques for assessing MR severity will be discussed. In accordance with the above guidelines, an emphasis will be made on integrating multiple parameters into the final determination of MR severity.2

HAEMODYNAMIC DETERMINANTS OF MITRAL REGURGITATION

The Gorlin hydraulic orifice equation, commonly used to evaluate aortic stenosis, can also be used to derive the haemodynamic determinants of regurgitant volume in MR.3 Thus, regurgitant volume in MR is determined by the regurgitant orifice area (ROA), a constant known as the discharge coefficient (C_d), the mean systolic pressure gradient (MPG) between the left ventricle (LV) and left atrium (LA), and the duration of MR during systole (T).

When assessing severity of MR, one should give careful consideration to each aspect of this equation. First, the ROA in MR is often dynamic and load dependent.4 In rheumatic MR, the valve is generally fibrotic, calcified and immobile, and therefore the ROA is fixed. However, in patients with dilated cardiomyopathy or myxomatous degeneration, ROA can vary during …