Load dependence of mammalian heart relaxation during cardiac hypertrophy and heart failure

Mechanical properties of relaxation were studied in left ventricular rat papillary muscle during cardiac hypertrophy induced by chronic pressure and/or volume overload. Maximum velocity of isotonic lengthening was linearly related to total extent of isotonic shortening and to maximum velocity of isotonic contraction and depended on the type of chronic overloading without correlation with the degree of cardiac hypertrophy. Time to peak shortening was significantly increased in each group of hypertrophied heart muscles as compared to controls. The sensitivity of cardiac relaxation to the loading conditions was determined by the time course of relaxation. To quantify the degree of load sensitivity, we measured the ratio of isotonic area to isometric area, which was the area limited by the afterloaded force vs. time at 50% of the isometric peak tension divided by the area of the force vs. time trace in the isometric twitch below the same level of load. The value of this ratio was about 0.81 in normal rat and did not show any significant differences in hypertrophied heart muscles even at the terminal stage of congestive heart failure. During acute hypoxia the load sensitivity of relaxation disappeared both in normal and in hypertrophied hearts. Thus inadequacy in oxygen supply has more drastic effects, as compared with those induced by chronic overload, probably by affecting the sarcoplasmic reticulum uptake of activating calcium.

Post-extrasystolic left ventricular peak pressure with and without left ventricular failure

18 patients without valvular pathology, coronary artery disease, or idiopathic hypertrophic subaortic stenosis were haemodynamically and angiographically investigated in order to analyse the effects of a ventricular extrasystolic beat upon the post-extrasystolic left ventricular peak pressure. In eight normal patients (group I), the post-extrasystolic peak pressure (P.ES.P.P.) was lower than that of the pre-extrasystolic beat; in 10 patients with symptoms of left ventricular failure (group II) the P.ES.P.P. significantly increased. The reasons are: 1) cardiac origin: stroke volume increased more in group II; 2) arterial origin. a) aortic compliance was lower in group II (this is probably related to the older age of patients in group II), and by decrease in end-diastolic aortic pressure was smaller in group II. Part of this arterial effect (2b) may probably be explained from the fact that post-extrasystolic compensatory pauses are equal in both groups, but the decay time of arterial pressure during diastole (assuming an exponential decay) is larger in group II. At the same age and with the identical aortic compliance only the two factors 1 and 2b play a part in the changes in P.ES.P.P.

[The relationship between left ventricular end-systolic pressure and volume. Comparative study of changes in load and inotropism]

This work consists of a comparison of the indices of left ventricular performance measured during the isovolumic nad/or ejection period under changes in load and inotropism, and of the findings on measuring the pressure/volume ratio of the left ventricle. The indices of performance of the left ventricle. The indices of performance of the left ventricle during the ejection phase (ejection fraction, mean speed of fibre shortening, mean standardised speed of systolic ejection) and the ratio pressure/volume were listed for 36 patients, 21 of them before and after perfusion with nitroprussiate, in 6 before and after perfusion of angiotensine, and in 9 from the group before and after post-extra-systolic potentialisation. The indices of left ventricular performance during the isovolumic (formula see text) were measured in 24 of these patients, 15 of them before and after nitroprussiate, and 9 before and after post-extra-systolic potentialisation. These results show that the level of the pressure/volume ratio at the moment of end-systole is independent of the conditions of load--to a greater extent than any other index measured during the isovolumic period or ejectional period--and appears to be thoroughly related to the changes of inotropism.

[Value of myocardial mass measurements in the hemodynamic and angiographic evaluation of aortic stenosis: 70 cases]

The prognosis of aortic stenosis is often evaluated according to clinical criteria; but it is well known that the myocardial mass is one of the important determinants of prognosis. Starting from the fact that the ratio systolic work/myocardial mass (WS/VM) is a stable one in normal subjects (0.81 +/- 0.03), we were able to divide up the 70 patients with congenital and acquired aortic stenosis into three groups as follows:--Group I. WS/VM greater than 0.87; this group is called hyperfunctional, and characterised by an increase in WS, and a myocardial mass which is ostensibly normal.--Group II: 0.87 larger than or equal to WS/VM larger than or equal to 0.75; this isofunctional group is characterised by parallel increases in mass and systolic work.--Group III: WS/VM less than 0.75; this group is called hypofunctional, and is characterised by an increase in mass unrelated to an increase in work. A comparison of the sensitivity of other parameters with that of WS/VM gives rise to optimism that the precision of determination of the prognosis will increase, as will that of the choice of the time to operative, but only those patients in groups I and II can expect a return to normal function and ventricular mass.