HIBERNATING MYOCARDIUM - AN INCOMPLETE ADAPTATION TO ISCHEMIA

Background We tested the hypothesis that hibernating myocardium repres ents an incomplete adaptation to a reduced myocardial oxygen supply, M ethods and Results In 38 patients, areas of hibernating myocardium wer e identified by angiography, multigated radionuclide ventriculography, thallium scintigraphy with reinjection, and low-dose dobutamine echoc ardiography. Biopsies removed at cardiac surgery showed structural deg eneration characterized by a reduced protein and mRNA expression and d isorganization of the contractile and cytoskeletal proteins myosin, ac tin, desmin, titin, alpha-actinin. and vinculin by electron microscopy , immunohistochemistry, and in situ hybridization. Additionally, an in creased amount of extracellular matrix proteins resulting in a signifi cant degree of reparative fibrosis was present. Dedifferentiation, ie, expression of fetal proteins, was absent. Apoptosis indicating suicid al cell death was found by the terminal deoxynucleotidyl transferase e nd-labeling method and electron microscopy. Radionuclide ventriculogra phy showed improvement of regional function at 3 months postoperativel y compared with preoperative values (mean values, 23.5% and 45%, respe ctively), and the echocardiographic wall-motion score index decreased from 3.4 to 1.8. The degree of severity of the morphological changes ( three stages) correlated well with the extent of postoperative functio nal recovery: more advanced clinical improvement was observed in patie nts with slight and moderate morphological degeneration (stages 1 and 2), but recovery was only partial in severe degeneration (stage 3). Co nclusions Cellular degeneration rather than adaptation is present in h ibernating myocardium. The consequence is progressive diminution of th e chance for complete structural and functional recovery after restora tion of blood flow. The practical consequence from this study should b e early revascularization in patients showing areas of hibernating myo cardium.