Biomarkers of Cardiac Ischemia

Cardiac ischemia occurs when there is a supply versus demand mismatch in coronary blood flow. In patients who present with unstable angina, ischemia occurs due to partial or total occlusion of a coronary artery due to plaque rupture. In stable angina however, there is progressive vascular occlusion resulting ultimately in a luminal stenosis of greater than 70%, impeding blood flow to the distal tissue. If the ischemia is reversible, no permanent myocardial damage occurs.If however the ischemic episode is prolonged; there will be cellular necrosis which will lead to acute myocardial infarction (AMI).The immediate clinical challenge is to be able to identify acutely impaired myocardial perfusion before the necrotic process starts. Currently, the only strategy for this is to detect ST-segment changes on the electrocardiogram (ECG), however the ECG is non-diagnostic in many cases. The sensitivity of the admission ECG for the diagnosis of AMI is typically around 50%. Reperfusion, be it pharmacological or surgical, is the essential life-saving intervention with the aim of salvaging myocardial tissue localised at the affected site. Many patients however who present with chest pain to the emergency department (ED) do not have a final diagnosis of AMI. There is therefore a need for a strategy which could detect cardiac ischemia before necrosis occurs and result in prompt revascularisation. Blood borne biomarkers for ischemia may be of diagnostic and prognostic value.