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Abstract
New clinical requirements for triaging chest pain patients challenge the abilities of the current cardiac markers. Serial measurements of myoglobin, creatine kinase (CK) isoenzyme MB (CKMB) mass, or CK isoforms in emergency rooms help to rapidly rule out acute myocardial infarction (AMI). However, within the first 3 to 4 h from chest pain onset, their sensitivities are too low to contribute significantly to AMI diagnosis during this period. CKMB and lactate dehydrogenase (LDH) isoenzyme 1 are not heart-specific, which hampers reliable diagnosis in patients with concomitant skeletal muscle damage. By contrast, the regulatory proteins troponin I and troponin T are expressed in three different isoforms: one for slow-twitch skeletal muscle fibers, one for fast-twitch skeletal muscle fibers, and one for cardiac muscle (cTnI, cTnT); cardiac-specific cTnI and cTnT assays are already available for routine use. cTnT and cTnI are the most promising markers for risk stratification in patients with unstable angina pectoris. Recent reports on increased cTnT in patients with renal failure or myopathy without evidence of myocardial injury and undetectable cTnI suggest that cTnT could be reexpressed similar to CKMB and LDH-1 in chronically damaged human skeletal muscle. Therefore, cTnI is probably the most heart-specific marker. Among the recently proposed new markers for early AMI diagnosis: glycogen phosphorylase isoenzyme BB (GPBB), fatty acid binding protein, phosphoglyceric acid mutase isoenzyme MB, enolase isoenzyme αβ S100a0, and annexin V, GPBB is the most promising because it increases as early as 1 to 4 h from chest pain onset and its early release appears to be essentially dependent on ischemic myocardial injury.