CAD Risk Factors After CABG Vs Medical Management
How do we explain an intervention the randomized studies show doesn't help and possibly harms survival of patients with early disease (ie, 1 or 2 vessels involved) while it increases the chances of survival in more advanced disease groups (ie, left main and 3-vessel stenosis) for up to about 12 years?
Let us consider the possibility that the temporary improvement in survival outcome in high-risk groups is not due to the surgical revascularization but rather to a temporarily increased motivation to reduce CAD risk factors among patients surviving surgery compared with patients treated medically.
CABG is much more than a surgical intervention for CAD in which blood is rerouted around obstructed arteries. The patient risks his/her life by going under the knife, realizing that about 3% of these surgeries result in death within the first month. Additionally, the physical and emotional trauma in the postoperative period leave potentially life-transforming impressions on people. Therefore, the standard CAD risk reduction recommendations given to all patients (ie, exercise, stop smoking, reduce dietary fat and cholesterol, reduce stress) may make a greater impression on the CABG-treated patients than people treated merely with pills. Given the profound relationship of risk factors on the incidence of CAD, possible differences in the lifestyle-related reduction of CAD risk between the CABG and medically treated groups must be considered. Exercise, diet, and tobacco use are the most significant modifiable risk factors.
A sedentary lifestyle has been shown to significantly increase the risk of CAD, myocardial infarction, and death. Exercise training programs, especially high-intensity ones, have improved cardiac performance.[78,79] Studies have shown that the lower the initial myocardial capacity, the greater the benefits.[80,81] Coats demonstrated that exercise capacity predicted survival and that exercise capacity can be improved. Exercise enhanced survival most in patients with advanced disease manifested by low ejection fractions and congestive heart failure.[82,83,84,85]
In a multivariate analysis of clinical, anatomic, and functional risk factors in medically treated patients with CAD, exercise capacity (ie, cardiac output at the highest work load or COmax) correlated best by far with CAD 5-year survival. Data from meta-analyses of randomized studies revealed that regular aerobic exercise reduced CAD mortality by about 20%.[87,88]
Despite these encouraging data, less than 10% of heart attack patients in the early 1990s participated in exercise programs. None of the randomized studies comparing CABG with medical therapy reported the numbers of patients participating in exercise programs. So the CABG experience could have motivated more patients to participate in exercise programs than those patients randomized to medical therapy.
Countless studies have demonstrated that smoking is a major risk factor for death with CAD. On average, CABG patients who quit smoking lived longer than those who did not quit. When smokers have quit cigarettes, their risk of CAD mortality has declined within a year and nearly reached baseline in 2 to 3 years. Of the major randomized studies of CABG vs medical treatment, only the European Coronary Surgery Study (ECSS) kept data on the number of smokers in the 2 groups at various intervals after study initiation. Both groups had 43% of smokers before randomization. At 6 months, 20% of CABG patients still smoked vs 30% of medically treated patients (P < .01). At 1 year, the CABG patients still had significantly fewer smokers than the medically treated group (P < .05).
Given that smokers with CAD have a relative risk of dying that is 1.73 times that of nonsmokers with CAD, a significant part of the mortality difference in the early years of the randomized CABG studies could have been accounted for by the difference in smoking. The fact that data from the ECSS showed declining differences between CABG and medical groups in the prevalence of smoking after the first year may have reflected the higher death rates in smokers and the diminution of motivation of the CABG patients to reduce CAD risks as the experience of their heart surgery faded from memory.
For each 1% reduction in serum cholesterol, a 2% decline in cardiovascular mortality has been demonstrated. Reducing dietary salt, fat, and cholesterol decreased the risk of hypertension and hypercholesterolemia, which are major CAD risk factors.[94,95] The American Heart Association has recommended that all Americans eat less than 2.4 g of sodium per day and consume 30% or less of calories from fat.[96,97] However, studies showing that compliance with these fairly timid guidelines halts or reverses the progression of CAD have not been published.
Indeed, it has been recently shown that slightly more aggressive reduction of dietary fat to below 27% of calories decreased blood pressure on average by 11 points systolic and 5 points diastolic within 2 weeks. In numerous studies, fat and cholesterol intake after CABG correlated with survival, and the lower the blood lipids after CABG, the more likely the grafts were to remain patent, and the slower the progression of CAD.[99,100,101,102,103,104]
Due to the motivating effect of major heart surgery, patients randomized to CABG may well have reduced their dietary fat, cholesterol, and salt significantly more than medically treated patients, especially in the early years of the studies. A significant dietary difference between the CABG and medically treated CAD patients may have altered the survival statistics in the first decade of the study. None of the randomized CABG studies considered this possibility or kept data to analyze it.
© 2002 Medscape
Cite this: Coronary Artery Bypass Grafting (CABG): Reassessing Efficacy, Safety, and Cost - Medscape - Jun 19, 2002.