[The viable myocardium: metabolic, diagnostic and therapeutic aspects].
The term stunned myocardium is used to indicate a reversible post-ischemic dysfunction of the ventricular mechanism which may persist for hours, days or weeks after the restoration of coronary flow following spontaneous or pharmacological thrombolysis, transluminal coronary angioplasty, aorto-coronary bypass and ischemic attacks. Hibernating myocardium is used to describe a depression of ventricular contractility in the presence of chronic hypoperfusion which may be reversed following revascularization as a result of aorto-coronary by-pass surgery. Three biochemical and physiopathological hypotheses are currently acknowledged to explain the phenomenon of stunning: the hypothesis of free oxygen radicals, the hypothesis related to an energy deficit and that involving a calcium overload. It is possible that oxydizing stress induced by free radicals may modify the activity of one or more sarcolemmic proteins which regulate the flow of calcium or other ions. Alterations in the transport and accumulation of calcium ions due to a Na+/Ca++ pump deficit and calcium-ATPase of the sarcoplasmatic reticle appear to be responsible for contractile dysfunction. The hypothesis concerning an energy deficit appears to be least probable since even if ATP levels are low the intracellular energy status does not appear to be a factor which limits mechanical function which may be stimulated in the absence of further variations in the content of highly energetic phosphates. There is also reduced myofibrillar creatinkinase activity. In hibernating myocardium the mechanical dysfunction is due to a metabolic and therefore contractile "down-regulation' with low myocardial energy and oxygen consumption to ensure the survival of chronically hypoperfused areas.(ABSTRACT TRUNCATED AT 250 WORDS)
Strozzi
C
C
Istituto di Medicina Interna, Università degli Studi di Ferrara.
Spisani
P
P
D005260:Female; D006321:Heart / Q000503:physiopathology; D006801:Humans; D008297:Male; D015428:Myocardial Reperfusion Injury; D017682:Myocardial Stunning / Q000175:diagnosis / Q000209:etiology / Q000628:therapy; D009206:Myocardium / Q000378:metabolism*
Il miocardio vitale: aspetti metabolici, diagnostici e terapeutici.