Quest for Diastolic Prognostic Indicators of Clinical Outcome After Acute Myocardial Infarction

Abstract

Immediately after acute infarction, the region of the myocardium ceases to contract, and over the next 72 hours, the infarct zone stretches and thins, a process known as infarct expansion. This regional left ventricular wall thinning and failure to contract perturb the normally uniform distribution of the stress/strain relationship that preserves cardiac architecture and function. Simultaneous with these early biomechanical changes, myocyte necrosis releases a number of cytokines that, together with the local increase in the regional myocardial deformation, cause stretch activation of a portfolio of matrix metalloproteinases that initiate myocardial repair. Article p 2591 The stability of myocardial repair after acute myocardial infarction is determined by the balance between the distending forces from ventricular dilatation resulting from infarct expansion and the restraining forces from deposition of a viscoelastic collagen scaffold by the extracellular matrix that increases the tensile strength of the scar. The dynamic equilibrium between collagen degradation and collagen deposition is modulated by a number of activated cytokines and neurohormones that normally result in buttressing the infarct and adjacent border zones, preventing progressive remodeling to heart failure. Changes in the composition of the myocardium in terms of increased collagen content during and after repair of the infarct zone in forming a fibrous tissue scar alter the material properties of the myocardium after myocardial infarction and confer on the heart increased myocardial and chamber stiffness. These alterations in left ventricular composition, architecture, and chamber/myocardial stiffness affect left ventricular filling dynamics, the rate of detachment of cross-linking, and sequestration of cytosolic calcium by the sarcoplasmic reticulum, all of which affect diastolic function as much as systolic function. However, most studies of the predictors of clinical outcome after myocardial infarction have focused almost exclusively on ejection-phase indexes of systolic contraction. Factors shown to be powerful predictors of clinical outcome after myocardial …