Exercise in the tertiary prevention of ischemic heart disease: experimental proof

Factors hampering experimental demonstration of the value of physical activity in decreasing the cardiac mortality rate after myocardial infarction are shown to include (1) inter-individual differences in disease severity, (2) secular changes in 'standard' therapy, (3) variations in the prescribed exercise with respect to time of initiation, frequency, intensity and duration of effort, level and duration of supervised programming, (4) incidental influences of group therapy, (5) poor compliance of test subjects and a contamination of control subjects, (6) selective referral of a low-risk sample of patients, and (7) an insufficient sample size. Because of practical difficulties in organizing a controlled trial, many early reports were based on non-randomized comparisons between programs. While such studies appeared to suggest a substantial advantage to those who were exercised, factors of patient selection cannot be ruled out. Randomized controlled trials using samples of up to 750 patients have generally shown a small (around 20%) and statistically insignificant decrease of mortality in exercised populations relative to controls. When available information from the 10-12 major trials has been combined, using various techniques of meta-analysis, the benefit from exercise has become statistically significant. The implication seems that if a patient begins and continues a program of endurance exercise, the lifespan may be increased by an average of some two years, at the cost of a considerable involvement in exercise classes. While this is a useful gain of longevity, an improved quality of life seem more important reason for advocating exercise to the post-coronary patient.