Of 22 randomized trials of rehabilitation with exercise after myocardial infarction (MI), one trial had results that achieved conventional statistical significance. To (OR= 1.09 [0.88, 1.341) of follow-up. The observed 20% reduction in overall mortality reflects a decreased risk of cardiovascular mortality and fatal reinfarction throughout at least 3 years and a reduction in sudden death during the 1st year after infarction and possibly for 2-3 years. With respect to the independent effects of the physical exercise component of cardiac rehabilitation, the relatively small number of "exercise only" trials, combined with the possibility that they may have had a formal or informal nonexercise component precludes the possibility of reaching any definitive conclusion. To do so would require a randomized trial of sufficient size to distinguish between no effect and the most plausible effect based on the results of this overview. (Circulation 1989;80:234-244) T he potential value of rehabilitation with exercise in individuals with coronary heart disease was recognized nearly as early as the clinical description of the disease itself. In 1772, Heberdent noted that one of his patients with CHD was "nearly cured" after 6 months of sawing wood for half an hour a day. In the United States, each year over one million individuals experience myocardial infarction and 670,000 survive.2 Ambulation See p 416 early after myocardial infarction, the use of exercisebased cardiac rehabilitation, and the modification of cardiovascular risk factors are widely practiced.

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The design of PDSA quality improvement research should follow from the purpose and context of the project. Improving the rigor of the quality improvement literature will build a stronger foundation and more convincing justification for the study and practice of quality improvement in health care.