How does recent myocardial infarction affect the perioperative risks of coronary artery bypass grafting?

How does recent myocardial infarction affect the perioperative risks of coronary artery bypass grafting?

Common sense suggests that the more recent the infarction, the higher the operative risk. This is because the infarcted area is surrounded by a critically ischaemic zone. The ultimate survival of this zone depends on many factors, not least of which is the global function of the remaining myocardium. This function is temporarily further compromised by the process of cardiopulmonary bypass for coronary artery surgery. The likely outcome during this critical phase, therefore, is extension of the infarcted area, with obvious implications for survival of the patient.

It is the duration of this critical phase which is most in doubt. In a recent small retrospective analysis, Herlitz et al1 found that amongst patients with a history of myocardial infarction, infarction within 30 days of surgery was not an independent predictor of total mortality within 2 years of surgery. However, Braxton et al made a distinction between Q wave and non-Q wave infarctions in the perioperative period. Although both types rendered the use of balloon pumps and inotropes to wean from bypass more likely, only Q wave infarctions were associated with significantly increased surgical mortality and even then only if surgery was performed within 48 hours of the infarction.

An older but much larger series from Floten et al seems to support a high risk for the initial 24-48 hours or so, but more importantly emphasises the relationship between the number of diseased vessels and the risk of surgery after recent infarction. Applebaum et al found ejection fraction less than 30%, cardiogenic shock and age greater than 70 years to be significant determinants of death in patients operated upon within 30 days of infarction. These are not surprising factors, fitting as they do with the concept that it is the extent of the jeopardised myocardium which is the determinant of risk, especially within the first day or two after the myocardial infarction.

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