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Variation in mortality risk factors with time after coronary artery bypass graft operation
Dexiang Gao1, Gary K Grunwald, John S Rumsfeld
1Department of Veterans Affairs Medical Center, Denver, Colorado 80220, USA.
Insights
Mortality risk factors after coronary artery bypass grafting (CABG) change over time. Cardiac risks are highest initially, while non-cardiac risks increase in the months following surgery.
Area of Science:
- Cardiovascular Surgery
- Health Services Research
- Biostatistics
Background:
- Mortality risk factors after coronary artery bypass grafting (CABG) vary by time period.
- Limited understanding exists regarding the dynamic nature of these risk factors post-CABG.
Purpose of the Study:
- To investigate the time-varying effects of mortality risk factors within 210 days after CABG.
Main Methods:
- Analysis of 11,815 veteran patients undergoing CABG (1997-1999).
- Utilized Cox B-spline regression to assess time-varying effects of 14 mortality risk factors.
- Estimated daily risk for each variable post-operation.
Main Results:
- Eight risk factors exhibited significant time-varying effects.
- Cardiac factors (prior heart operation, myocardial infarction, balloon pump, anginal class) peaked immediately post-CABG, then declined.
- Non-cardiac factors (age, functional status, COPD, renal dysfunction) showed increasing risk over several months.
Conclusions:
- A significant number of mortality risk factors demonstrate time-dependent changes after CABG.
- Cardiac risks diminish post-operation, while non-cardiac risks escalate over time.
- Findings aid in tailoring patient management strategies in the 7 months following CABG.
Background:
Differences in mortality risk factor sets during different time periods (eg, short-term versus intermediate-term) after coronary artery bypass grafting have been reported. However, little is known about the time-varying effects of mortality risk factors after the operation.
Methods:
We analyzed 11,815 veterans who had coronary artery bypass grafting at any of the 43 Veterans Affairs cardiac surgery centers from October 1997 to September 1999. Time-varying effects of 14 mortality risk factors during the 210 days after coronary artery bypass grafting were evaluated using Cox B-spline regression, which provides an estimate of risk for each variable for each day after operation.
Results:
Eight variables showed significant time-varying effects after operation. The effect of prior heart operation was very high immediately after operation, but disappeared within 1 week. Three other cardiac variables (prior myocardial infarction, preoperative intraaortic balloon pump, and Canadian Cardiovascular Society anginal class III or IV) also conferred the highest risk on the day of operation and decreased thereafter. In contrast, the four time-varying noncardiac risk variables (age, impaired functional status, chronic obstructive pulmonary disease, and renal dysfunction) showed little or no association with mortality immediately after operation, but had increasing impact during the several months after operation.
Conclusions:
A sizable number of mortality risk factors have time-varying effects after coronary artery bypass grafting. Several cardiac risk factors have peak impact immediately after operation but dissipate thereafter. Several noncardiac risk factors confer little risk immediately after operation, but these risks increase during several months. This information may help clinicians focus management strategies for patients during the 7 months after operation.