BASICS OF MYOCARDIAL PUMP FUNCTION

Myocardial pump function and the performance of the entire cardiovascu lar system are determined by preload, afterload and contractility. The best clinical measure of preload is the end-diastolic volume of the h eart, which can be assessed by ventriculography, echocardiography or b y indicator dilution techniques. Afterload is basically the wall tensi on during the ejection phase. For clinical purposes afterload can be r easonably monitored by arterial blood pressure. The most difficult par ameter to assess under clinical conditions is contractility, since exa ct measurement of contractility requires instantaneous measurements of left-ventricular pressure-volume loops and an artificial afterload or preload challenge. However, most recent theoretical analysis of ventr icular-arterial coupling by various models revealed that the ejection fraction seems to be an appropriate parameter to evaluate, whether the prevailing contractility matches preload and afterload conditions. An ejection fraction of approximately 60% under almost any clinical circ umstances is associated with an optimal performance of the heart in te rms of myocardial oxygen utilisation.