CHAPTER 14: ACUTE CORONARY SYNDROMES: NON-ST ELEVATED MYOCARDIAL INFARCTION
What laboratory test(s) help identify a patient with MI?
A. Elevated cTnT T (>0.4 ng/mL)
B. Elevated CK (>200 U/L)
C. Elevated CK-MB (>25 U/L)
Rationale: The three laboratory tests listed above are cardiac biomarkers, and elevations in these are used by clinicians to help diagnose acute coronary syndrome (ACS). Creatinine kinase (CK) is an enzyme released by nonspecific muscle cell necrosis or death. CK is first detectable about 4 to 6 hours after insult and remains detectable for about 2 to 3 days. CK-MB is a component of CK and is more specific to cardiomyocytes. When cardiomyocyte necrosis occurs, CK-MB is detectable in about 3 to 4 hours and remains elevated for about 1 to 2 days. Troponin is a protein found in heart (and skeletal) muscle. Troponin I and T are cardiospecific, and elevated levels indicate cardiomyocyte necrosis. Troponins become detectable about 3 to 4 hours after insult and can remain elevated for up to 14 days. Other laboratory tests that may be useful in diagnosis of ACS are myoglobin, BNP, NT-proBNP, alk phos, AST, and LDH.
Based on KT’s presentation, risk factors, EKG, and cardiac biomarkers, what is his probable diagnosis?
C. Non-ST-elevation myocardial infarction (NSTEMI)
D. ST-elevation myocardial infarction (STEMI)
Rationale: The patient presented with chest discomfort at rest and has several coronary artery disease (CAD) risk factors: age, sex, HTN, dyslipidemia, DM, overweight, sedentary job, family history. His atherosclerotic cardiovascular disease (ASCVD) risk score prior to the event was 34.3%. This indicates high risk. His EKG revealed t-wave inversions indicating myocardial ischemia, and his biomarkers are positive for myocyte necrosis (CK, CK-MB, and cTnT are all elevated). In combination, this points to NSTEMI. If his EKG had revealed ST-segment elevations, this would have indicated STEMI. If his biomarkers were negative, his likely diagnosis would have been unstable angina.
During cardiac catheterization, KT received a DES to treat a 90% occlusion of his LAD. In addition to the aspirin he received in the emergency department, which of the following is the most appropriate antiplatelet regimen for KT?
A. Ticagrelor 180 mg PO × 1; followed by ASA 162 mg PO daily and ticagrelor 90 mg PO bid × 12 months