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Competing risks after coronary bypass surgery: the influence of death on reintervention
1Department of Thoracic and Cardiovascular Surgery and the Department of Biostatistics and Epidemiology, The Cleveland Clinic Foundation, Cleveland, Ohio, USA. blackse@ccf.org
Insights
Bilateral internal thoracic artery grafting and older age reduce reinterventions. However, death significantly erodes the reintervention benefit in high-risk patients, highlighting the importance of competing risks analysis.
Area of Science:
- Cardiovascular Surgery
- Biostatistics
- Medical Statistics
Background:
- Competing risks analysis is crucial for understanding event probabilities in high-risk patient groups, especially when death can obscure nonfatal outcomes.
- Attrition by death significantly impacts the interpretation of event-free survival, necessitating advanced statistical methods.
Purpose of the Study:
- To quantify the difference in nonfatal event probabilities (e.g., reintervention) versus the potential probability without death using competing risks analysis.
- To evaluate the impact of bilateral versus single internal thoracic artery grafting on reintervention rates, considering competing risks.
Main Methods:
- Multivariable analyses were conducted on 2001 patients undergoing bilateral internal thoracic artery grafting and 8123 patients undergoing single internal thoracic artery grafting.
- Competing events analyzed included death before reintervention, reoperation, and percutaneous transluminal coronary angioplasty.
- Follow-up durations were approximately 9.7 years for bilateral and 10.8 years for single internal thoracic artery grafting groups.
Main Results:
- Single internal thoracic artery grafting was associated with shorter survival and increased reinterventions (P <.0001).
- Old age was a risk factor for death (P <.0001), while young age was a risk factor for reintervention (P <.0001).
- Death reduced the benefit of bilateral internal thoracic artery grafting on reintervention by angioplasty from 8.5% to 5.5% and by reoperation from 9.3% to 6.8% at 12 years, with greater erosion in older patients.
Conclusions:
- Bilateral internal thoracic artery grafting and older age are associated with fewer reinterventions, even after accounting for deaths.
- In high-risk patients, the benefit of bilateral internal thoracic artery grafting on freedom from reintervention is substantially diminished by mortality.
- Competing risks analysis clarifies that young age is a true risk factor for reintervention, not merely a consequence of passive attrition by death.
Objective:
For groups of patients at high risk of death, such as older patients, the actual probability of experiencing a nonfatal event, such as reintervention, must be far smaller than the potential probability were there no attrition by death. Competing risks analysis quantifies the difference.
Methods:
Multivariable analyses were performed for the competing events death before reintervention, reoperation, and percutaneous transluminal coronary angioplasty in 2001 patients after bilateral internal thoracic artery grafting and in 8123 after single internal thoracic artery grafting. Follow-up was 9.7 +/- 3.0 years and 10.8 +/- 5.2 years in bilateral and single internal thoracic artery groups, respectively.
Results:
Patients receiving single grafts experienced shorter survival and more reinterventions (P <.0001). However, other risk factors for death included old age (P <.0001), but risk factors for reintervention included young age (P <.0001). This difference confounds interpretation of event-free survival that is clarified by competing risks analysis. Death reduced the potential benefit of bilateral internal thoracic artery grafting on reintervention by angioplasty from a median of 8.5% to 5.5% at 12 years and by reoperation from 9.3% to 6.8%, with progressively greater erosion of benefit from attrition by death as age increased. Competing risks simulation confirmed that young age was a true risk factor for reintervention, excluding the explanation that it reflected simply passive attrition by death as patients age.
Conclusions:
Even after accounting for attrition by interim deaths, bilateral versus single internal thoracic artery grafting and older age are associated with fewer reinterventions. However, in high-risk patients, its benefit on freedom from reintervention is eroded considerably by death.