Basics of myocardial pump function.

Myocardial pump function and the performance of the entire cardiovascular system are determined by preload, afterload and contractility. The best clinical measure of preload is the end-diastolic volume of the heart, which can be assessed by ventriculography, echocardiography or by indicator dilution techniques. Afterload is basically the wall tension during the ejection phase. For clinical purposes afterload can be reasonably monitored by arterial blood pressure. The most difficult parameter to assess under clinical conditions is contractility, since exact 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 ventricular-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 circumstances is associated with an optimal performance of the heart in terms of myocardial oxygen utilisation.