The mitral valve in hypertrophic cardiomyopathy--an echocardiographic approach.

In the recent past, the mitral valve was referred to as the cornerstone of any echocardiographic examination. Changes in its echocardiographic pattern were considered, in many cases, to be specific for the diseases in which they were described. Among such diseases was hypertrophic cardiomyopathy. Three abnormalities were successively described in the M-mode echocardiograms of patients with the obstructive form of hypertrophic cardiomyopathy. The first was a prolonged mitral valve-septum contact, with a slow diastolic closing slope the E-F slope, whether measured along the first (E-FO) or the second (FO-F) components (Edler, 1967). The second abnormality was a systolic anterior movement attributed to the anterior leaflet. The third was a thickening of the septum, out ofproportion compared with the opposite posterior wall asymmetric septal hypertrophy. Both the echocardiographic mitral valve abnormalities and asymmetric septal hypertrophy were initially considered to be specific for the disease but later this was questioned. In fact the diagnostic value ofechocardiographic mitral valve abnormalities in the spectrum ofhypertrophic cardiomyopathy was greatly reduced when it was recognized that even in their absence the study of left ventricular walls allowed identification of many cases of hypertrophic cardiomyopathy, generally with asymmetrical septal hypertrophy, but occasionally with concentric hypertrophy. Furthermore, systolic anterior motion was described, though rarely, in conditions other than hypertrophic cardiomyopathy (Maron & Epstein, 1980). On the other hand, it was also recognized that asymmetric septal hypertrophy could occur in other entities and that mitral valve abnormalities could be present in the absence of asymmetric septal hypertrophy or even left ventricular hypertrophy detectable by M-mode echocardiography (Mintz et al., 1978). When examining 1009 consecutive adult patients, we found that among 84 (8.3%) having asymmetric septal hypertrophy, only 30 (2.9%) had hypertrophic cardiomyopathy; 2 patients, in whom the only echocardiographic abnormalities present were mitral valve abnormalities, had familial hypertrophic cardiomyopathy (Madeira et al., 1978). Despite obvious limitations, changes in the mitral valve echocardiographic pattern, namely systolic anterior motion, are highly specific. The prevalence of true systolic anterior motion is very low in the general population and among cardiac patients without hypertrophic cardiomyopathy (Maron et al., 1981). Therefore it retains an important diagnostic value, though only for the obstructive form of the disease. Apart from its usefulness in diagnosing hypertrophic (obstructive) cardiomyopathy, the study of echocardiographic mitral valve abnormalities both systolic and diastolic permits the prediction of a gradient and to a certain extent the type ofdistribution and degree of septal hypertrophy. There is now substantial data supporting the concept that narrowing of the left ventricular outflow tract, caused by septal thickening and by the anteriorly displaced mitral valve, is the basis for the dynamic obstruction leading to systolic anterior motion, due to the Venturi effect (Gilbert et al., 1980). Our data, presented in Figure 1, from a study of38 patients with hypertrophic cardiomyopathy12 with resting obstruction, 13 with latent obstruction and 13 with no obstruction shows that patients with resting obstruction are those who have a thicker septum, in whom the mitral valve is significantly more anteriorly placed and who have a larger atrium, possibly indicating the presence of mitral regurgitation. Further indirect evidence that narrowing of the outflow tract by the septum interferes with the normal dynamics of the mitral valve can also be found from the analysis of its echocardiographic diastolic pattern (Figure 2). Whereas in non-obstructive hypertrophic cardiomyopathy the diastolic closing slope (E-F) is an almost uniphasic line (see Figure 2, top left), in the obstructive form there is a prolongation ofE-FO time (see Figure 2, top right and bottom). The E-FO time is a substantial part of the rapid diastolic filling period (Kalmanson et al., 1975; Vignola et al., 1977), and echocardiographically it represents the ring movement (Zaky et al., 1968), after which the valve semi-closes due to vortices formed between the anterior leaflet and