LEFT-VENTRICULAR RELAXATION AND DIASTOLIC FILLING

The cardiac cycle, as revisited by modern authors, consists of 3 fundamental phases : contraction, which includes isovolumic contraction and first part of ejection; relaxation which begins with left ventricular peak pressure, continues with second part of ejection and isovolumic relaxation, and ends together with ventricular rapid filling (i.e. as filling rate has decreased by 50 p. cent); finally compliance or slow filling which lasts until atrial systole. The LV diastolic dysfunction refers to filling abnormalities which are related to either relaxation abnormalities or compliance troubles or both. The mechanisms of these abnormalities are biochemical (deficiency in cyclic AMP resulting in calcium handling dysregulation) and mechanical: right ventricular filling, pericardial restraint, coronary arteries perfusion, myocardial inertial forces, myocardial visco-elastic properties, ventricular wall elasticity (depending itself on its thickness and its collagen content). The methods of analysis of LV filling are: left ventriculography, gamma angiography, digitized M-Mode echography and, mainly, Doppler echocardiography. This technique allows 2 types of mitral flow abnormalities to be distinguished: 1) the abnormal relaxation which combines an increased isovolumic relaxation time, an increased deceleration time and a diminished E/A ratio, but this pattern may be << normalized >> by an increase in filling pressure; 2) the restriction to filling which results in an increased E/A ratio, a diminished deceleration time and, sometimes, a diastolic mitral regurgitation. The effets of drugs on LV diastolic function are difficult to assess : a beneficial result may be due either to a direct effect on the myocardium or to an improvement in load conditions, heart rate or contractility.