Ans. b (Cardiac Troponin I and II) (Ref. Harrison's medicine 17th ed., Ch. 238-239)CARDIAC BIOMARKERS# Patients with Unstable Angina who have elevated biomarkers of necrosis, such as CK-MB and troponin (a much more specific and sensitive marker of myocardial necrosis), are atrisk for death or recurrent MI.# Elevated levels of these markers distinguish patients with NSTEMI from those with UA. There is a direct relationship between the degree of troponin elevation and mortality.# However, minor troponin elevations have been reported and can be caused by congestive heart failure, myocarditis, or pulmonary embolism, or they may be false-positive readings. Thus, in patients with an unclear history, small troponin elevations may not be diagnostic of an ACS.In the first 6 hours, ECG is the gold standard. Cardiac troponin I rises after 4 hours and is*for 7-10 days; more specific than other protein markers. CK-MB is predominantly found in myocardium but can also be released from skeletal muscle.Useful in diagnosing reinfarction following acute Ml because levels return to normal after 48 hours. ECG changes can include ST elevation (STEMl, acute transmural infarct), ST depression (subendocardial infarct), and pathologic Q waves (evolving or old transmural infarct).Appearance of infarcted myocardiumCardiac enzymes TimeGrossHistologicTroponin 1 peaks first (4 h): remains elevated CK-MB peaks within 24 h: remains elevated1 hourNo gross changesIntracellular edema evidentLDH peaks later (about 2 days): remains elevated AST also rises and falls predictably in myocardial infarction, but, may indicate6-12 hours Wavy myocardial fibres,liver damage instead.12-24 hoursPale, cyanotic, edematousvacuolar degeneration, contraction band necrosisDefinition of abbreviations: AST, asparate aminotransferase; CK-MB, creatine kinase MB fraction; LDH, lactate24-48 hoursWell-demarcated, soft, paleMeutrophlic infiltrate, increased cytoplasmic eosinphilia, and coagulation necrosis become evidentdehydrogenase3-10 daysInfarct becomes soft, yellow, surrounded by hyperemic rimMonocytic infiltrate predominates at 72 hrs 2 weeksInfarct area is surrounded by granulation tissue that is gradually replaced by scar tissue. Creatine phosphokinase (CK) rises within 4-8 h and generally returns to normal by 48-72 h.# drawback :lack of specificity for STEMI, as CK may be elevated with muscle disease/trauma/ IM injection.# The MB isoenzyme of CK has the advantage over total CK that it is not present in significant concentrations in extracardiac tissue and therefore is considerably more specific. However, cardiac surgery, myocarditis, and electrical cardioversion often result in elevated serum levels of the MB isoenzyme.# A ratio (relative index) of CKMB mass:CK activity >2.5 suggests but is not diagnostic of a myocardial source.