[Cardiac effects of isoproterenol in the complex echocardiographic evaluation (author's transl)]

The cardiac response to isoproterenol was examined in 10 normal subjects by echocardiography. The complete qualitative and computer-assisted quantitative analysis of one-dimensional recordings of the left ventricle is combined with two-dimensional echograms. The results - including the well-known facts that cardiac output and the velocity of contraction are increased while the end-diastolic dimensions are partly decreased - indicate that the stroke volume is not significantly diminished in the supine position. In two cases it is even enlarged. Moreover, a "pseudo-Sam" and the changes of the systolic time intervals demonstrate the strong positive inotropic effect of the drug. The amplitude of the descent of the base movement is also enlarged. The velocity of relaxation is not as increased as the velocity of contraction in that part of the posterior wall which is hit by the echobeam. There is a remarkable dissociation between the Ecg and the actual cardiac movements. E.g., with isoproterenol the mitral valve opens during the ascending T-wave, while normally relaxation only starts after complete electrical repolarisation. The shortening fractions of the phases of the cardiac cycle induced by the drug as compared to the control state are determined. It is shown that shortening of the whole cardiac cycle causes the systolic phase to shorten to a nearly adequate ratio. The slow filling phase mostly shortens to the smallest while the rapid filling phase always shortens to the greatest ratio. We discuss all echocardiographic parameters that are used for this study and we demonstrate some limitations to the interpretation of time-dimension curves derived from M-mode echocardiograms. These are especially evident after a strong beta-sympathomimetic stimulation, because after the injection of isoproterenol the appearance of the septal echo-lines changes from one subjects to the other in a striking way.