Early recognition and immediate treatment of acute ST-segment elevation myocardial infarction (STEMI) are essential; diagnosis is based on characteristic history, ECG, and serum cardiac biomarkers.
Chest pain similar to angina (Chap. 33) but more intense and persistent; not fully relieved by rest or nitroglycerin, often accompanied by nausea, sweating, apprehension. However, 20−25% of MIs are clinically silent.
Pallor, diaphoresis, tachycardia, S4, dyskinetic cardiac impulse may be present. If heart failure exists, pulmonary crackles and S3 may be present. Jugular venous distention is common in right ventricular infarction.
ST elevation in at least two contiguous leads (≥2 mm in men, or ≥ 1.5 mm in women, in leads V2−V3, or ≥1 mm in other leads), followed (if acute reperfusion is not achieved) by T-wave inversion then Q-wave development over several hours.
Cardiac-specific troponins T and I are highly specific for myocardial injury and are the preferred biochemical markers for diagnosis of acute MI. Serum levels remain elevated for 7–10 days. Creatine kinase (CK), another biomarker (which is not necessary to measure if cardiac troponin is assessed) rises within 4–8 h, peaks at 24 h, and returns to normal by 48–72 h. CK-MB isoenzyme is more specific for MI than total CK (which may be elevated in skeletal muscle injury). The decision to proceed with reperfusion therapies in acute STEMI should be made urgently from the pt’s history and ECG, and not await the results of biomarker assays.
NONINVASIVE IMAGING TECHNIQUES
May be useful when diagnosis of MI is not clear. Echocardiography detects infarct-associated regional wall motion abnormalities (but cannot distinguish acute MI from a previous myocardial scar). Echo is also useful in detecting RV infarction, LV aneurysm, and LV thrombus. MRI with delayed gadolinium enhancement accurately indicates regions of infarction, but is technically difficult to perform in acutely ill pts.
TREATMENT STEMI INITIAL THERAPY
Initial goals are to (1) quickly identify if pt is candidate for reperfusion therapy, (2) relieve pain, and (3) prevent/treat arrhythmias and mechanical complications.
Aspirin should be administered immediately (162–325 mg chewed at presentation, then 75–162 mg PO qd), unless pt is aspirin-intolerant.
Perform targeted history, examination, and ECG to identify STEMI (>1 mm ST elevation in two contiguous limb leads, ≥2 mm ST elevation in two contiguous precordial leads, or new LBBB) and appropriateness of reperfusion therapy (percutaneous coronary intervention [PCI] or IV fibrinolytic agent), which reduces infarct size, LV dysfunction, and mortality.
Primary PCI is more effective than fibrinolysis and is preferred at experienced centers capable of performing the procedure rapidly (Fig. 121-1), especially when diagnosis is in doubt, cardiogenic shock is present, bleeding ...