Interaction of age and preoperative risk factors in predicting operative mortality for coronary bypass surgery.
BACKGROUND
Models for predicting operative mortality for coronary bypass surgery assume that preoperative risk factors affect mortality to the same extent in all patients groups.


RESULTS
To determine whether certain preoperative risk factors disproportionately increase operative mortality in the elderly, 663 consecutive elderly patients (age 75 years or older) and 1,464 younger patients (age 65 or younger) undergoing isolated coronary bypass surgery between 1982 and 1990 were studied. Hospital mortality was significantly greater in the elderly patients than in younger patients (7.5% versus 1.8%; relative risk, 4.5). Univariate analysis identified age, prior coronary artery bypass grafting, congestive heart failure, left main disease, New York Heart Association functional class, hypertension, prior myocardial infarction (MI), and preoperative atrial fibrillation as associated with mortality. Multivariate analysis was then used to construct a model to describe the risk of operative mortality in terms of selected risk factors. However, comparison of observed mortality rates with those predicted by the model revealed problems with the model's goodness of fit. Further testing revealed that young patients without prior MI had a mortality rate lower by an order of magnitude than either younger patients with prior MI or elderly patient groups with and without MI. Two separate models were therefore constructed stratifying by the presence of prior MI. This resulted in a significant improvement in the fit of the models to the observed data.


CONCLUSIONS
These results suggest that the impact of risk factors on the elderly may be significantly different from the effect of these risk factors on younger patients. Models for predicting outcome after bypass surgery should be tested for potential interactions between age and risk factors.
Khan
S S
SS
Division of Cardiac-Thoracic Surgery, Cedars-Sinai Medical Center, Los Angeles, CA 90048.
Kupfer
J M
JM
Matloff
J M
JM
Tsai
T P
TP
Nessim
S
S
D000328:Adult; D000367:Age Factors; D000368:Aged; D015331:Cohort Studies; D001026:Coronary Artery Bypass / Q000401:mortality*; D005260:Female; D006746:Hospital Bed Capacity, 500 and over; D017052:Hospital Mortality; D006801:Humans; D015141:Los Angeles; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data*; D012307:Risk Factors; D016896:Treatment Outcome