Influence of acute hemodynamic changes on the negative peak of the first derivative of apex cardiogram during ventricular relaxation in dogs.

The effect of various alterations in the preload, the afterload and the inotropic state of the left ventricle on the first derivative of apex cardiogram (dA/dt) was studied in 9 anesthetized dogs to clarify some of the determinants of the negative peak of dA/dt and isovolumic relaxation time. The first derivative of the apex cardiogram was recorded simultaneously with the left (ventricular pressure, conventional left apex cardiogram, first derivative of left ventricular pressure (dP/dt), electrocardiogram and phonocardiogram. Both dA/dt and dP/dt curves were similar in contour and occurred nearly simultaneously. This close relationship was preserved during various acute haemodynamic changes. The maximum negative dA/dt and the isovolumic relaxation period was closely related to the level of afterload. Large rapid augmentation of mean aortic pressure resulted in a significant increase in the negative dA/dt and shortening of the isovolumetric relaxation time, where reduction of afterload had an opposite effect. Isoprenaline acutely augmented minimum dA/dt. It is concluded that measurement of negative peak dA/dt under some conditions is a reliable noninvasive technique for assessing myocardial relaxation.