Myocardial blood flow and contractile function are closely linked, but an ischemic insult can result in myocardial dysfunction (despite restoration of blood flow) in viable """"""""stunned"""""""" tissue that seems identical to nonviable infarcted tissue. Thus, myocardial dysfunction alone is insufficient to determine viability. In addition, conventional imaging techniques, which cannot resolve blood flow or function across the heart wall, often yield inaccurate viability classification due to volume averaging. Moreover, the lack of techniques to measure perfusion and function simultaneously has severely hindered the ability to determine the prevalence of stunned myocardium in patients. Cardiac magnetic resonance imaging (MRI), because of its high spatial resolution, is ideally suited to assess noninvasively both transmural myocardial function (using tagged MRI) and myocardial perfusion (using contrast- enhanced MRI). However, the potential to integrate MR parameters of myocardial function and perfusion to enhance the detection of stunned, ischemic, and infarcted tissue has not been exploited. Thus, the goal of this research is to determine the relationship between compromised myocardial perfusion and mechanical dysfunction through simultaneous measurement of perfusion and function using novel MRI techniques applied to canine ischemic models. More specifically, can these combined MRI measurements of perfusion and function be used to distinguish infarcted, ischemic, and stunned myocardium? Based on preliminary data we have obtained, combined MR indices of myocardial function and perfusion can enhance the identification of stunned myocardium. Thus, we will test whether: 1) Myocardial perfusion determined by contrast-enhanced MRI and myocardial function determined by tagged MRI, both individually and combined,, will enable the distinction of viable and nonviable tissue after ischemic insult that can be directly correlated to postmortem assessment and microsphere measurements of viability and blood flow, respectively; 2) Transmural differences in myocardial function and perfusion using MRI can be used to accurately classify tissue viability in clinical practice using conventional contrast agents and peripheral injections of contrast. The feasibility of this integrated MRI exam will be tested in animal models and in stable patients after myocardial infarction. Because the MRI techniques developed in these studies will be readily adaptable to clinical studies, the proposed research could have a significant impact on patient care in ischemic heart disease.
