Noninvasive assessment of myocardial mechanics—a review of analysis of stress-shortening and stress-velocity

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Abstract
The development of newer, load-independent indices of contractility has not substantially reduced general clinical reliance on ejection fraction and shortening fraction to detect abnormalities of contractility, in spite of common understanding of the preload and afterload dependence of percent fiber shortening. The more widespread application of sensitive indices of contractility has been impeded in part by complex methods of acquisition and analysis of data as well as uncertainty concerning the clinical importance of the additional derived information. Substantial recent experience with analysis of stress-shortening and stress-velocity, nonetheless, demonstrates that physiologically meaningful indices of afterload, preload, and contractility can be obtained noninvasively without hemodynamic interventions. There is extensive theoretical and experimental basis for these methods, and the limitations are similar to other global indices of myocardial mechanics. The superiority of methods which allow distinction between contractile abnormalities and abnormal load are particularly important when altered ventricular loading conditions are a prominent feature of the disease state. Several clinical situations have been identified for which analysis of stress-shortening and stress-velocity demonstrates that assessment by fiber shortening alone has resulted in misrepresentation of myocardial status. The clinical utility of assessment of ventricular function is considerably enhanced when the relative contribution of load and contractile performance is determined.