Myocardial mechanics in aortic and mitral valvular regurgitation: the concept of instantaneous impedance as a determinant of the performance of the intact heart

Abstract

A B STR A C T The effects on myocardial mechanics of acute, artificial aortic and mitral regurgitation were studied in the dog to determine the manner in which the changes in load induced by valvular regurgitation alter ventricular performance. With mitral and aortic regurgitant volumes of approximately the same magnitude as the forward stroke volume, immediate increases occurred in total stroke volume, left ventricular enddiastolic pressure, and peak ejection velocity, whereas contractility remained unchanged. Although calculated myocardial fiber tension rose, the rate of decline of tension during ejection was accelerated with regurgitation due to the more rapid decrease in ventricular size. Average tension therefore decreased relative to average pressure. As a consequence of the increased fiber length and this unloading, contractile element velocity, work, and power were increased. Despite unchanged contractility of the myocardium, the ejection fraction rose with both aortic and mitral regurgitation.When regurgitant beats were compared with control beats at a constant end-diastolic volume, ventricular stroke volume, work, power, and ejection fraction, as well as contractile element velocity, work, and power consistently increased. Thus, reduction of instantaneous impedance to ejection allowed the ventricle to empty further, reducing ventricular wall tension with a resultant Received for publication 5 June 1967 and in revised form 14 November 1967. increase in the velocity of shortening. External energy output was increased despite unchanged contractility and diastolic fiber length. It is concluded that the impedance to ejection and myocardial fiber tension during ejection govern the velocity and extent of contractile element shortening, and hence affect stroke volume, peak aortic flow rate, and ejection fraction. The alterations of ventricular function accompanying valvular regurgitation can be explained by an evaluation of the effects of these lesions on the instantaneous impedance to left ventricular ejection.

Quantitative echocardiography of the mitral complex in dilated cardiomyopathy: the mechanism of functional mitral regurgitation.

“…However, the LVSs and LVDs, and EFs so obtained were presumably satisfactory for intergroup comparisons. Although never reaching statistical significance, the MR group tended to have slightly greater ventricular motion compared with the no MR group, perhaps reflecting the unloading effect of MR. 37 The conclusion drawn from this study contrasts with that from a previous autopsy study. 4 Postmortem changes conceivably may occur, but echocardiographic and autopsy measurements of the mitral annular circumference in normal patients are similar.…”

The Contractility and Performance of the Preterm Left Ventricle before and after Early Patent Ductus Arteriosus Occlusion in Surfactant- Treated Lambs

“…In this study neither peak dP/dt nor peak dP/dt normalized to end-diastolic volume changed upon ductal occlusion (33). Thus, it appears that the LV was unable to augment contractility as expected in the presence of the left-to-right shunt and increasing volume load (31). It has been demonstrated that sympathetic innervation of the heart is incomplete at term and the ncwborn LV may be more dependent on and sensitive to circulating catecholamines (14,34).…”

Echocardiographic prediction of survival after surgical correction of organic mitral regurgitation.

“…(1) The potential beneficial impact of valve repair on survival is controversial26'49 and has been analyzed separately.61 (2) The current study demonstrates that left ventricular dysfunction is associated with excess late mortality even in patients who have a valve repair. (3) Preoperative variables remained independent predictors of survival in a combined model incorporating the type of correction performed.…”