Chapter 25

• 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 categorized by presentation with or without ST elevation, in accordance with treatment strategies. Patients with ST elevation benefit from immediate reperfusion with thrombolytic agents or direct angioplasty.
• All patients with suspected myocardial ischemia should be given aspirin at presentation.
• Myocardial infarction is diagnosed by a compatible clinical history, evolution of characteristic electrocardiographic changes, and an increase and subsequent decrease in cardiac enzymes.
• Acute reperfusion of the occluded coronary artery is the key to achieving a good outcome. The promptness of reperfusion is more important than the mode by which it is accomplished.
• 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, use of low-molecular-weight heparin, glycoprotein IIb/IIIa inhibition, and an early invasive approach is preferred.
• Aspirin, β blockers, angiotensin-converting enzyme inhibitors, and statins have been shown to decrease mortality rate after myocardial infarction.
• Echocardiography is extremely useful for the diagnosis of complications after myocardial infarction.
• Patients with cardiogenic shock should be stabilized with an intra-aortic balloon pump and promptly revascularized, if possible, by angioplasty or bypass surgery.

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

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 history of or multiple risk factors for coronary artery disease (CAD).

Myocardial ischemia results from an imbalance of oxygen supply and oxygen demand. The heart is an aerobic organ with only a limited capacity for anaerobic glycolysis, and 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, increases in demand must be met by commensurate increases in coronary blood flow.

Classically, myocardial ischemia has been divided into categories such as stable angina, unstable angina, and myocardial infarction (MI). 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 is unchanged over the previous 6 months. Acute coronary syndromes comprise unstable angina and MI. Unstable angina consists of ischemic symptoms that ...

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