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KEY POINTS

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  • Myocardial ischemia results from an imbalance between myocardial oxygen demand and supply. The major determinants of myocardial oxygen requirements are heart rate, contractility, and wall stress (afterload).

  • Patients with myocardial ischemia are divided by presentation into those with or without ST elevation, in accordance with treatment strategies. Patients with ST elevation benefit from immediate reperfusion with percutaneous coronary intervention or fibrinolytic agents.

  • Myocardial infarction is diagnosed by a compatible clinical history, evolution of characteristic ECG changes, and an increase and decrease in cardiac enzymes.

  • All patients with suspected myocardial ischemia should be given aspirin upon presentation.

  • Prognosis after myocardial infarction is most closely related to the degree of left ventricular impairment.

  • Risk stratification is the key to initial management of patients with non-ST elevation acute coronary syndromes.

  • In patients with high-risk non-ST elevation acute coronary syndromes, an early invasive approach is preferred.

  • Aspirin, clopidogrel, β-blockers, angiotensin converting enzyme inhibitors, and statins have been shown to decrease mortality after myocardial infarction.

  • Echocardiography is extremely useful for the diagnosis of complications after myocardial infarction. Invasive hemodynamic monitoring may be necessary in some cases as well.

  • Patients with cardiogenic shock should be stabilized with an intra-aortic balloon pump and revascularized promptly with percutaneous coronary intervention or bypass surgery.

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INTRODUCTION

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Myocardial ischemia can go unrecognized in an ICU setting. Signs of myocardial ischemia may be obscured by other illnesses present in the critically ill patient. Physical examination in these patients often is limited, or its results altered, by the presence of other disease processes.

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Myocardial ischemia and attendant left ventricular dysfunction may complicate the course and treatment of a particular illness. Conversely, multisystem illness may set the conditions for increased oxygen demand, often accompanied by diminished delivery of oxygen to the heart. For these reasons, the critical care physician must maintain a high index of suspicion for myocardial ischemia in the ICU setting, especially in the patient with a prior history of or multiple risk factors for coronary artery disease.

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TERMINOLOGY
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Myocardial ischemia results from an imbalance of oxygen supply and oxygen demand. The heart is an aerobic organ whose capacity for anaerobic glycolysis is limited; it makes use of oxygen avidly and efficiently, extracting 70% to 80% of the oxygen from coronary arterial blood.1 Because the heart extracts oxygen nearly maximally independent of demand, any increases in demand must be met by commensurate increases in coronary blood flow.

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Classically, myocardial ischemia has been divided into categories including stable angina, unstable angina, and myocardial infarction. Typical angina is exertional, and is relieved promptly by rest or nitroglycerin. Stable angina occurs reproducibly with a similar level of exertion, in a pattern that has not changed over the past 6 months. Acute coronary syndromes comprise unstable angina and myocardial infarction. Unstable angina consists of ischemic symptoms which are more frequent, severe, or prolonged than the patient’s ...

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