Detection and significance of subclinical mitral regurgitation by colour Doppler techniques.

Two papers in this issue demonstrate clinical consequences from the presence of clinically silent mitral regurgitation in paediatric and adolescent populations. Both are potentially important as the development of progressive doxorubicin cardiomyopathy 1 and the presence of rheumatic carditis 2 have long term implications. A parallel example, which highlights some of the problems inherent in attempting to derive clinical conclusions from the presence of mild regurgitation in an adult population, exists in the recent " phen/fen " controversy. 3 Attempting to extract useful prognostic information from the presence of clinically silent, Doppler detected, mitral regurgitation through morphologically normal valves is not new—its negative impact on the prognosis of acute infarction has been recognised for over a decade. 4 However, a fundamental prerequisite in attempting to utilise this type of information is an appreciation of the factors which underlie the presence of the colour flow signal. The appearance of mitral regurgitation is dependent upon the mechanical substrate for regurgitation itself, the fluid dynamics of the resultant flow disturbance, and lastly, processing using a colour flow mapping algorithm to produce an image. In particular, we need to question the reproducibility of findings obtained by diVerent examiners and between diVerent echo system implementations of colour flow mapping before we can feel comfortable about extrapolating these findings into clinical practice. Mechanical substrates for regurgitation In some very mild cases of rheumatic carditis and subtle forms of the " phen/fen " eVect, leaflet damage not apparent on two dimensional echo is the intuitive mechanism of subclinical regurgitation. However, in the majority of cases, the valve is merely responding to changes in ventricular geometry, pressure loading, or both. In a series of elegant studies, 5 Levine's group has demonstrated that functional mitral regurgitation is a dynamic entity, with maximal flow occurring in early and late systole accompanied by a characteristic mid-systolic dip, 6 suggesting a role for the trans-mitral systolic pressure gradient in determining the severity of regurgitation. 7 In contrast to the study of Allen and colleagues, 1 three dimensional studies in animal models 8 and two dimensional clinical observations, 6 suggest that depressed systolic function in isolation does not result in mitral regurgitation in the absence of ventricular dilatation. The principal requirements for functional mitral regurgita-tion include outward papillary muscle displacement, annu-lar dilatation, and possibly a reduction in leaflet closing forces. 5 Physical properties of regurgitant jet sprays Despite the presence of ambient counterflows …