39 How does recent myocardial infarction affect
the perioperative risks of coronary artery bypass
grafting?
Jonathan Unsworth-White
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 cardio-
pulmonary 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 al^1 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^2 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^3 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^4 found ejection fraction less than 30%, cardio-
genic shock and age greater than 70 years to be significant deter-
minants 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.
RReeffeerreenncceess
1 Herlitz J, Brandrup G, Haglid M et al. Death, mode of death, morbidity,
and rehospitalization after coronary artery bypass grafting in relation