Myocardial reperfusion may not benefit all patients and may actually be harmful to some. Components of reperfusion injury may occur not only in isolation but also in combination--when more profound consequences might be expected. The exact mechanisms of reperfusion injury are uncertain, but they probably include cellular overload of calcium, osmotic cell swelling, and myocyte or microvascular damage from cytotoxic free radicals derived from oxygenhttp://www.bmj.com/cgi/content/full/310/6978/477
Although reperfusion is essential for salvage of the ischemic heart, reperfusion beyond a certain period of ischemia may cause injury to the myocardium. Dramatic changes in contractile function, arrhythmias, and ultrastructure occur in the ischemic-reperfused heart as a consequence of the generation of oxyradicals, loss of cation homeostasis, depletion of energy stores, and changes in subcellular activities. These acute effects of reperfusion appear to be the result of the occurrence of oxidative stress and intracellular Calcium overload in the heart. Alterations in cardiac gene expression may account for delayed recovery of subcellular organelles in the ischemic myocardium.http://www.heartandmetabolism.org/pdf/37/8.pdf
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