Evaluation of myocardial function by invasive methods.

The evaluation of myocardial performance requires an understanding of the contributions of loading conditions (preload and afterload), heart rate, and contractility. Although the measurement of these parameters often requires specialized techniques, more easily performed invasive evaluation can take place applying the principles derived from an understanding of the factors affecting cardiac performance. The construction of ventricular function curves permits the evaluation of the influence of preload on the work of the heart. Changes in afterload and/or myocardial contractility can produce a series of such function curves. Construction of pressure-volume loops and the examination of end-systolic pressure-volume relationships offer insights into the status of myocardial contractility apart from loading conditions, as well as into the response of the heart to acute and chronic alteration in loading conditions. Ventricular function curves can be obtained during exercise, pacing, and pharmacologic intervention in order to detect subtle cardiac dysfunction, to assess the severity of dysfunction, and to gauge the response to therapy.