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Perioperative Myocardial Ischemia and Infarction


Case Synopsis

A 62-year-old man is scheduled for cystectomy. He has a history of coronary artery disease (CAD) and underwent coronary artery bypass grafting 8 years ago. He has diabetes mellitus, hypertension, and hyperlipidemia. He takes aspirin, atenolol, pravastatin, and losartan. He is able to walk up a flight of stairs without symptoms. His intraoperative course is uneventful except for tachycardia during extubation. In recovery, he is tachycardic to 110 beats per minute but denies chest pain. Troponin levels are ordered and are elevated.

Problem Analysis

Definition

Myocardial ischemia results from an imbalance between myocardial oxygen supply and demand. Myocardial oxygen demand depends on preload, afterload, contractility, and heart rate. Myocardial oxygen supply depends on the capacity of the coronary arterial bed. Atherosclerosis of the coronary arteries limits coronary artery blood flow and consequently myocardial oxygen supply. A mismatch of supply and demand can lead to ischemia ( Box 160.1 ). Ischemia that persists for an extensive period of time can lead to myocardial infarction (MI).

BOX 160.1
Factors That Contribute to Myocardial Ischemia

Increased Myocardial Oxygen Demand

  • Increased heart rate

  • Increased contractility

  • Increased left ventricular end-diastolic volume

  • Increased wall tension (afterload)

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