[Time constant of the left ventricular pressure fall, and onset and rate of expansion of the left ventricular segment in hypertrophic cardiomyopathy].

The left ventricular diastolic properties of patients with hypertrophic cardiomyopathy are impaired. Since there is degeneration or disarray of myocardial fibers in patients with hypertrophic cardiomyopathy (HCM), the rate of expansion in diastole may become asynchronous. Biplane coronary cineangiograms were performed in eight normal subjects and nine patients with HCM. The coordinates (x,y,z) of the ramifying points of the left coronary artery were measured, and the distance between any two of the points of the coronary artery was calculated (segment length). Fifteen segment lengths were calculated for each subject. Since the onsets of expansion of these 15 segment lengths were not simultaneous, they expanded at different times and the onsets of expansion occurred within a very short period of time, nearly at end-diastole. The variance (standard deviation) of the timing of expansions of these 15 segments and the rate of expansion within the late 40 msec of the isovolumic relaxation period (% delta L) were calculated. The time constant of the left ventricular pressure fall (T) in normal subjects was 41.3 +/- 7.7 (SD) msec, T in HCM was prolonged to 52.7 +/- 11.1 msec. The variance was 47 +/- 17 msec in normal subjects, but it increased to 99 +/- 26 msec in HCM. The rate of expansion again decreased in HCM (Normal 2.24 +/- 0.60 vs HCM 1.40 +/- 0.96%). The conspicuous diastolic asynchrony in the onset of expansion and the reduced rate of diastolic expansion in HCM may be the mechanism of impairing the diastolic properties of the left ventricle.