Pathophysiological vs biochemical ischaemia: a key to transition from reversible to irreversible damage

‘Myocardial ischaemia’ is defined as an imbalance between fractional uptake of oxygen and the rate of cellular oxidation in the heart. This condition may have several potential outcomes: (1) when ischaemia is brief, a transient post-ischaemic ventricular dysfunction occurs on reperfusion, a condition named ‘stunned myocardium’; (2) when it is prolonged and severe, irreversible damage occurs, with no recovery in contractile function upon reperfusion; (3) when ischaemia is less severe, but still prolonged, the myocytes may remain viable but exhibit depressed contractile function. Under this condition, named ‘hibernating myocardium’, the reperfusion is able to restore contractility. During these different ischaemic conditions, many biochemical changes occur: initially they represent a defensive and protective reaction against ischaemia such as cellular acidosis and increase of inorganic phosphate levels that rapidly abolish the contractile activity. But with the prolongation of ischaemia and restoration of the coronary flow, alterations in ions and overall Ca2+ homeostasis occur, together with an oxidative stress mediated by oxygen free radicals, not adequately counteracted by the cellular antioxidant defences. The mitochondria are likely to play a central role in these events which leads to membrane damage and irreversible deterioration of contractile function. The issue of reperfusion injury, however, is not unanimously accepted. Many, but not all, cardiologists are of the opinion that some components of reperfusion may be detrimental and able to inflict injury over and above that attributable to ischaemia. This article defines the sequence of events occurring during the transition from angina to infarction.