TABLE 33-1 Electrical Complications of Acute MI | ||||||||||||||||||||||||||||||||||||||||||||||
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TABLE 33-2 Mechanical Complications of Acute MI | |||||||||||||||||||||||||||||||||||
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ST-Segment Elevation Myocardial Infarction
ST-Segment Elevation Myocardial Infarction
Ian J. Neeland
James A. de Lemos
I. GENERAL PRINCIPLES
A. Rapid reperfusion of the infarct-related artery (IRA), with either primary percutaneous coronary intervention (PCI) or fibrinolytic therapy, is the cornerstone of management for patients with ST-segment elevation myocardial infarction (STEMI).
B. Adjunctive therapy with aspirin, P2Y12 receptor inhibitors, β-blockers, angiotensin-converting enzyme inhibitors, and statins further reduces the risk of death and major cardiovascular events after reperfusion.
II. PATHOPHYSIOLOGY
A. Rupture of lipid-rich, inflammatory atherosclerotic plaque causes collagen exposure leading to platelet adhesion, activation, and aggregation.
B. Fibrin-platelet clot develops as thrombin converts fibrinogen to fibrin and completely occludes the IRA causing transmural myocardial injury, manifested by ST-segment elevation on the electrocardiogram (ECG).
III. DIAGNOSIS
A. Differential diagnosis: Rapidly consider/rule out pneumothorax, aortic dissection, pericarditis, tamponade, pulmonary embolism, stress cardiomyopathy with apical ballooning (takotsubo syndrome), and severe hyperkalemia.
B. History.
1. Severe, pressure-type midsternal pain, often with radiation to the left neck, arm, or jaw, occurring at rest.
2. Associated symptoms: dyspnea, nausea, vomiting, diaphoresis, or weakness.
3. Silent infarction in 25% of cases, especially in elderly and diabetic patients.
C. Physical examination.
1. Not helpful in confirming the diagnosis of STEMI.
2. Should focus on eliminating other potential diagnoses and assessing for complications of STEMI (Tables 33-1 and 33-2).
D. ECG.
1. ST elevations in regional vascular distribution with concurrent ST depression in reciprocal leads.
2. ECG mimics: pericarditis (global ST elevation with PR depression), early repolarization, old left ventricular (LV) aneurysm, and Prinzmetal angina.
3. New left bundle branch block (LBBB) may represent large anterior infarction, but has a high false-positive rate; primary PCI strongly preferred over fibrinolytic therapy for LBBB.
E. Cardiac biomarkers.
1. Biomarkers of limited use for emergency diagnosis of STEMI.
2. Cardiac troponins are the preferred biomarkers for confirmation of myocardial infarction (MI).
F. Additional evaluation.
1. Echocardiography useful when ECG is indeterminate to evaluate for focal wall motion abnormalities.
2. Risk assessment scores predict early mortality and recurrent infarction. TIMI (http://www.mdcalc.com/timi-risk-score-for-stemi). GRACE (http://www.outcomes-umassmed.org/grace/acs_risk/acs_risk_content.html).
