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 preload, afterload and inotropic state of the left ventricle on the first derivative of apex cardiogram (dA/dt) was studied in the anesthetized dogs, in an attempt to clarify some of the determinants of the negative peak of dA/dt and isovolumetric relaxation time. First derivative of apex cardiogram was recorded simultaneously with left ventricular pressure, conventional left apex cardiogram, first derivative of left ventricular pressure, electrocardiogram and phonocardiogram. Both dA/dt and dP/dt curves represent similarity in contour and were found to occur nearly simultaneously. This close relationship was preserved during various acutely hemodynamic changes. Maximum negative dA/dt and isovolumic relaxation period was closely related to the level of afterload. Large rapid augmentation of mean aortic pressure did results in statistically significant increase of negative dA/dt and shortening of isovolumic relaxation time, where reduction of after load had an opposite effect. Another interventions, which acutely augment min dA/dt was nitroprusside and isoprenalin. It is concluded, that negative peak dA/dt under some conditions provides a reliable noninvasive index for assessing myocardial relaxation.