Myocardial infarction and risk region relationships: evaluation by direct and noninvasive methods

Optimal quantitation of myocardial infarction requires resolution of the three-dimensional geometry of the ischemic region at a time that progression of tissue necrosis has been completed and can be sharply delineated from noninfarcted myocardium but before significant remodeling of the ventricular chamber. Although this can be achieved at two to three days after coronary occlusion by histologic techniques, a variety of technologies including two-dimensional echo, CTT, SPECT, PET, and NMR have demonstrated potential for providing noninvasive quantitative measurements of the extent of myocardial infarction. Additional studies are needed to clarify the utility of these technologies for resolving the highly variable transmural distribution of infarction that is present in the clinical setting. Assessment of the region at risk for infarction, the ischemic zone, requires quantitative measurements of the degree of ischemia as well as the size of the ischemic region. Although the above technologies may provide quantitative measurements of the dimensions of the ischemic zone, the utility for resolving the highly variable transmural distribution of regional myocardial blood flow using clinically applicable methodologies has not been convincingly established at present. It is possible that cine CT, new generation PET, and NMR technologies may eventually provide noninvasive quantitative measurements of regional myocardial blood flow.