Clinical aspects of left ventricular diastolic function assessed by Doppler echocardiography following acute myocardial infarction

S H Poulsen
Danish Medical Bulletin 2001, 48 (4): 199-210
LV systolic function and dilation after Ml have been extensively studied and have been related to heart failure and cardiac mortality. In recent years, it has been increasingly apparent that LV diastolic dysfunction contributes to signs and symptoms of heart failure and LV diastolic dysfunction is associated with increased mortality rates in patients chronic heart failure independent of systolic function. LV diastolic dysfunction is difficult to assess on basis of clinical examination including chest radiography and electrocardiography. LV diastolic filling has traditionally been evaluated by cardiac catherization with direct measurement of filling pressures and relaxation. However, the invasive approach describing LV compliance and relaxation as the major determinants of LV diastolic function, is not feasible and suitable for routine investigations of diastolic function. Two-dimensional and Doppler echocardiography has become a well accented practical and safe non-invasive method for diagnosis of LV diastolic dysfunction. Combined invasive and echocardiographic studies have shown that analysis of mitral and pulmonary venous flow velocities relate to invasively measured filling pressures and relaxation rate in cardiac diseases. Based on Doppler analysis of mitral and pulmonary venous flow three abnormal LV filling patterns are identified: impaired relaxation, "pseudonormalization" and restrictive. These LV filling patterns have been related to symptoms, relaxation rate, filling pressure and prognosis in patients with restrictive and dilated cardiomyopathy. The Doppler flow profiles are influenced by several factors including age, heart rate, load conditions and valve heart diseases which must be taken into consideration during evaluation. During the last decade information about LV diastolic function assessed non-invasively by Doppler echocardiography has gained in patients with CAD. Myocardial ischemia induced by brief coronary artery occlusion or pacing leads to abnormal myocardial relaxation which can be reversed to normal by restoring normal myocardial blood flow. The diastolic abnormality is present within seconds and a characteristic impaired relaxation filling pattern are identified by mitral and pulmonary venous flow analysis. Diastolic dysfunction has been recognized during the early as well during the post-MI phase with or without LV systolic dysfunction. In the acute phase both an abnormal relaxation pattern and restrictive LV filling pattern are present which has been related to in-hospital heart failure. The identification of a pseudonormal or restrictive LV filling pattern are associated with later readmission to hospital with heart failure and cardiac death. Abnormal relaxation filling is the most pronounced filling pattern after one year which might be related to the remodeling process including compensatory hypertrophy, scarring of the infarct zone leading to a non-uniform relaxation of the LV. Remodeling of the LV following a MI is subject to several factors which might involve diastolic function. This is supported by the presence of an impaired relaxation and restrictive filling pattern are associated with progressive LV dilatation following Ml. Furthermore, the LV remodeling process following the very early phase includes the scarring process with collagen deposition in the infarcted and non-infarcted myocardium. The extent and quality of the repair process involving collagen deposition are believed to influence the remodeling process. Increased collagen deposition in the subacute phase of Ml indicated by elevated values of the collagen marker PIIINP is found to be related to LV dilation, depressed systolic function and restrictive LV filling. Development of a restrictive filling in patients with increased collagen deposition might be due to increasing LV volume but also to increased myocardial stiffness. Regarding prognosis diastolic dysfunction seems to be an important marker of outcome as abnormal diastolic properties are related to progressive LV dilatation, development of heart failure and cardiac death following MI. The beneficial effects of BB on morbidity and mortality in post-MI patients are well established. Recently, it has been demonstrated that BB has beneficial effects on progressive CHF and cardiac mortality in patients with chronic heart failure and moderate to severe systolic dysfunction. The mechanisms behind these effects are not fully understood. However, improvement of both systolic and diastolic function during BB therapy are demonstrated in patients with CHF. A few studies in patients with MI indicates that long-term BB therapy improves LV diastolic function which seems to be followed by improvement in systolic function. BB has the potential to lengthening diastole, improving subendocardial myocardial perfusion and affecting symptomatic amd neurohumoral activation following MI which might affect LV systolic and diastolic function and thereby improving outcome. Functional capacity following Ml is a well known predictor for outcome in MI patients. LV diastolic function a closely related to exercise capacity in contrast to measures of systolic function. BB therapy in patients with mild to moderate systolic dysfunction seems to improve exercise capacity which is related to improvement in LV diastolic function. Thus, BB improves exercise capacity and diastolic function by increasing LV compliance which might have prognostic implications. Even though LV systolic and diastolic dysfunction coexist, few two-dimensional and Doppler echocardiographic variables combine measurements of both phases of the cardiac cycle. Recently, the MPI has been suggested as a measure of combined systolic and diastolic myocardial performance which is based on Doppler time intervals of the systolic and diastolic phases. The MPI is easily obtained, reproducible, non-geometric and seems less dependent on heart rate and load conditions compared to traditional Doppler measurements. In patients with MI is has shown to reflect disease severity and contain prognostic information. The assessment of MPI seems therefore to be a relevant attractive alternative to established measurements of LV function following MI.

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