Overview In the first 6 hours, ECG is the gold standard ECG changes can include ST elevation (transmural infarct) ST depression (subendocardial infarct) pathologic Q waves (transmural infarct) Cardiac troponin I rises after 4 hours and is elevated 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 AST is nonspecific and can be found in cardiac, liver, and skeletal muscle cells