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Chapter 8: Acute Myocardial Infarction

Andrew J. Boyle

Introduction

ESSENTIALS OF DIAGNOSIS

  • Chest discomfort, usually described as “pressure,” “dull,” “squeezing,” or “aching.”

  • Characteristic electrocardiographic changes.

  • Elevated biomarkers, such as troponin.

  • Imaging may show new regional wall motion abnormality with preserved wall thickness.

  • The elderly, women, and diabetics may have atypical presentation.

General Considerations

Acute myocardial infarction (MI) is a clinical syndrome that results from occlusion of a coronary artery, with resultant death of cardiac myocytes in the region supplied by that artery. Depending on the distribution of the affected coronary artery, acute MI can produce a wide range of clinical sequelae, varying from a small, clinically silent region of necrosis to a large overwhelming area of infarcted tissue resulting in cardiogenic shock and death. About 1.2 million people experience MI in the United States each year; every minute, one American will die of coronary artery disease.

The risk of having an acute MI increases with age, male gender, smoking, dyslipidemia, diabetes, hypertension, abdominal obesity, a lack of physical activity, low daily fruit and vegetable consumption, alcohol overconsumption, and psychosocial index. As much as 90% of the risk of acute MI has been attributed to the modifiable risk factors. The diagnostic criteria for acute MI are listed in Table 8–1.

Table 8–1.ESC/ACC Definition of Myocardial Infarction
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Table 8–1. ESC/ACC Definition of Myocardial Infarction

Criteria for acute MI

The term acute myocardial infarction (MI) should be used when there is evidence of myocardial necrosis in a clinical setting consistent with acute myocardial ischemia. Under these conditions, any one of the following criteria meets the diagnosis for MI:

  1. Typical rise and fall of biochemical markers of myocardial necrosis (preferably cardiac troponin) with at least one of the following:

    1. Ischemic symptoms

    2. Development of pathologic Q waves on the ECG

    3. ECG changes indicative of ischemia (ST-segment/T-wave changes)

    4. Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality.

    5. Identification of an intracoronary thrombus by angiography or autopsy

  2. Cardiac death with symptoms suggestive of myocardial ischemia and presumed new ischemic ECG changes or new LBBB.

  3. Percutaneous coronary intervention (PCI)–related MI is arbitrarily defined by elevation of cTn in patients with normal baseline values or a rise of cTn values > 20% if the baseline values are elevated and are stable or falling. In addition, either (i) symptoms suggestive of myocardial ischemia or (ii) new ischemic ECG changes or (iii) angiographic findings consistent with a procedural complication or (iv) imaging demonstrating new loss of viable myocardium or new regional wall motion abnormality are required.

  4. Stent thrombosis associated with MI when detected by coronary angiography or autopsy in the setting of myocardial ischemia and with a rise and/or fall of cardiac biomarkers.

  5. Coronary artery bypass grafting (CABG)–related MI is arbitrarily defined by elevation of cardiac biomarkers in patients with normal baseline values. In addition, either (i) new pathologic Q waves ...

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