Physiological Implications of Myocardial Scar Structure

Abstract

Once myocardium dies during a heart attack, it is replaced by scar tissue over the course of several weeks. The size, location, composition, structure and mechanical properties of the healing scar are all critical determinants of the fate of patients who survive the initial infarction. While the central importance of scar structure in determining pump function and remodeling has long been recognized, it has proven remarkably difficult to design therapies that improve heart function or limit remodeling by modifying scar structure. Many exciting new therapies are under development, but predicting their long-term effects requires a detailed understanding of how infarct scar forms, how its properties impact left ventricular function and remodeling, and how changes in scar structure and properties feed back to affect not only heart mechanics but also electrical conduction, reflex hemodynamic compensations, and the ongoing process of scar formation itself. In this article, we outline the scar formation process following an MI, discuss interpretation of standard measures of heart function in the setting of a healing infarct, then present implications of infarct scar geometry and structure for both mechanical and electrical function of the heart and summarize experiences to date with therapeutic interventions that aim to modify scar geometry and structure. One important conclusion that emerges from the studies reviewed here is that computational modeling is an essential tool for integrating the wealth of information required to understand this complex system and predict the impact of novel therapies on scar healing, heart function, and remodeling following myocardial infarction.

Optimal site selection and image fusion guidance technology to facilitate cardiac resynchronization therapy

“…The non-viability and reduced plasticity of infarcted scar tissue is associated with a reduction in efficient and effective mechanical function during systole. Nearly all of the determinants of systolic function are negatively impacted by the presence of scar including cardiac shape and dimensions, preload, afterload and contractility [39]. During systole, the scared region stretches and bulges outward while the remaining myocardium contracts, causing a reduction in the mechanical efficiency of the heart as a pump.…”

Microscopic Isthmuses and Fibrosis Within the Border Zone of Infarcted Hearts Promote Calcium-Mediated Ectopy and Conduction Block

“…Absence of PVCs in the BiV model is likely due to the geometry of the BZ used here. The 3D infarct morphology reflects tissue damage resulting from coronary artery occlusion, which can vary size and structure depending on individual variability in coronary anatomy and the extent of collaterals [38]. Different scar anatomy models with thinner isthmuses (<1 mm) could potentially result in PVCs.…”

Cardiac Magnetic Resonance and Myocardial Viability: Why Is It so Important?

“…Myocardial viability is defined as a regional wall motion abnormality (hypokinesia, dyskinesia, or akinesia) without the presence of necrotic myocardial tissue. 4,6,12 After an acute event, the ischemic cascade is triggered, and myocardial viability, especially the reversibility of this process, can be influenced. A series of pathophysiological modifications appear in the damaged myocardium with the intent to replace the dead tissue with fibrotic scar tissue, as the viable myocardium tries to compensate the dysfunctional myocardium in order to maintain a competent cardiac output.…”

“…Left ventricular remodeling is defined as a structural, geometrical, and functional change in the infarct patch and remote viable myocardium. [4][5][6] Thus, new treatment options cannot limit ventricular remodeling. It was demonstrated that a coronary intervention improves left ventricular fraction with only 3% to 4%.…”