Quantifying Relative Importance of Coronary Risk Factors on Patient Survival Following Coronary Artery Bypass Grafting: A Maximum Likelihood Analysis

Abstract

Background: Coronary artery bypass grafting (CABG) is a major surgical intervention to relieve symptoms and promote survival for individuals with coronary heart disease (CHD). The benefits of the intervention are thought to be improved when underlying risk factors of CHD are ameliorated. However in current health care systems the long-term follow-up of patients following CABG is not centralized to allow for the determination of survival trends and their optimization. The survival of study participants who underwent CABG is compared with age and gender matched individuals from the general population. Differences in rates of survival are interpreted in terms of lifestyle choices and the impact of risk factors of CHD.Method: Survival data were obtained from government records to 18 years post intervention on a cohort of patients who underwent CABG and participated in a long-term follow-up program. Cardiac symptoms and risk factors of CHD were collected from consenting participants (44 women and 164 men) prior to CABG and at clinical assessments at one and eight-year follow-ups. Important clinical and lifestyle factors were identified and their impact on post-operative survival was quantified using a maximum likelihood technique. Male and female patients were investigated separately and a good fit between observed and simulated survival experiences was confirmed by Monte Carlo simulation.Results: Cardiac symptoms were exhibited by 75.8% of women and 68.3% of men (χ 2 =0.712, p=0.3988) one-year post operation, and by 84.2% of women and 70.2% of men eight-years post operation (χ 2 =1.556, p=0.212). Male longterm survival at 54.3% after 18 years was significantly better than 36.4% for females (χ 2 =4.449, p=0.035), but both were worse than 73.0% and 71.5% (p=0.6114) respectively for gender and age-matched cohorts from the general population.Important risk factors for women were post-operative smoking and postoperative hypertension reducing annual post-operative survival by 3.9% and 2.7% respectively and by 6.6% when both are present. Equivalent important risk factors for men are post-operative smoking and unrelieved/recurring cardiac symptoms reducing annual survival rates by 2.4% and 1.2% respectively and by 3.6% when both are present. Conclusion:Eighteen year survival post CABG was significantly better for men than women, but both were worse than that for the general population. Post-operative smoking was the most significant risk factor associated with decreased rates of survival followed by unrelieved/recurring cardiac symptoms for men and persisting hypertension for women.