A 72-year-old man with prior tobacco use, hypertension, and type 2 diabetes presented to the emergency department with prolonged chest pain (4 hours in duration). An electrocardiogram (ECG) showed evidence of ST-segment elevation in leads V1 to V4 (Figure 9-1).
A 12-lead electrocardiogram showing ST-segment elevation in leads V1-V4, indicating anteroseptal ST-segment elevation myocardial infarction.
EPIDEMIOLOGY AND DIAGNOSIS
ST-segment elevation myocardial infarction (STEMI) patients present with ischemic symptoms, ST-segment elevation on ECG, and subsequent release of biomarkers of myocardial necrosis. Most of these patients will progress to Q-wave myocardial infarction (MI), representing transmural infarction.1,2 The incidence of STEMI is approximately 80 cases per 100,000 people-years, and it composes 25% to 40% of MIs. Of note, the incidence of STEMI appears to be declining, whereas the incidence of non-STEMI is increasing. In-hospital mortality for STEMI ranges between 6% and 14%.
It is incredibly important to make the diagnosis of STEMI at the time of first medical contact (FMC). When suspected, guidelines advocate for a time from FMC to ECG of ≤10 minutes. A history of chest pain lasting more than 20 minutes and not responsive to nitroglycerine is frequent, with possible radiation to the left arm, jaws, and neck. However, up to 30% of patients have atypical symptoms such as nausea/vomiting, shortness of breath, fatigue, and palpitations. These patients, more commonly women and elderly, tend to present later and are less likely to receive reperfusion therapy. An early ECG is of paramount importance.1,2 ST-segment elevation (1 mm, >0.1 mV) should be apparent in 2 contiguous leads, although elevation of 2 mm (>0.2 mV) in V2-V3 is the standard for anterior MI.3 In the setting of suspected inferior wall MI, V3R and V4R should be assessed to determine potential right ventricular involvement. In addition, it should be realized that ST-segment depression in V1-V3 may be representative of posterior STEMI, in which case V7-V9 should be placed to corroborate. Left ventricular hypertrophy, left bundle branch block, and paced rhythms may obscure the interpretation of the ECG. If STEMI is identified on the ECG, biomarkers should not delay access to reperfusion therapy. Diagnosis is confirmed by angiography, which often displays a totally occluded vessel (Figure 9-2).
Angiography in right anterior oblique cranial view showing occlusion (white arrow) of the left anterior descending coronary artery just after the origin of first diagonal and septal branches.
STEMI is caused by an abrupt thrombotic occlusion of a coronary artery. Two mechanisms tend to precede this: ...