In this issue, an article by Turner and colleagues examines patient characteristics that are predictive of compliance with a cardiac rehabilitation (CR) program. This article reports on a prospective evaluation of more than 1900 patients treated in a hospital-affiliated, community-based program at the Alton and Basingstoke Cardiac Rehabilitation Unit. As with most CR programs, the centerpiece of the Alton and Basingstoke program is a graduated course of physical exercise. In this case, the prescribed program for each individual patient may extend from 6 weeks to 6 months, depending on the patient's age, medical history, and current physical and medical condition. Turner and coauthors examine the causes underlying patient noncompliance with CR. Understanding and effectively addressing noncompliance are important because compliance with CR is a strong predictor of future outcomes. 1

Individuals who participate in cardiac rehabilitation (CR) have a greatly reduced likelihood of subsequent morbidity and mortality. A major step toward improving the nation's health status and reducing the alarmingly high rates of mortality from heart disease will require a substantial increase in the rate at which eligible patients are treated in CR. 2 Significant improvements in the percentage of patients who receive treatment will require efforts on at least three fronts: enhanced physician education and training to improve referral rates, improved patient education to increase the likelihood that patients will follow through with recommended treatment, and advanced understanding of the causes behind patient attrition and noncompliance.

Comprehensive CR includes medical evaluation, exercise prescription, cardiac risk factor modification, education, and counseling. Cardiac rehabilitation produces significant improvements in exercise tolerance, symptom reduction, blood lipid levels, psychological well-being, and reduced smoking, which substantially reduce the risk of further morbidity and mortality. However, despite the substantial benefits provided by CR, only a minority of eligible patients are ever referred for comprehensive CR services. Physician education and training to increase referral and awareness of the benefits from CR services are greatly needed.

Even after successful referral, approximately one fourth to one third of patients will not adhere to treatment. 1 Perceptions of patients and their social environment affect decision making about whether to follow through with recommended treatment. Adherence to prescribed treatment is strongly predictive of both short- and long-term outcomes. Those who adhere have a substantially reduced risk of future morbidity and mortality compared with those who do not complete treatment. 3

The benefits of CR are experienced most by those who fully participate. A dose-response pattern of efficacy has been demonstrated in numerous outcome studies. 4 Those who comply with treatment benefit the most, whereas those who only partially comply obtain fewer benefits. The results of numerous studies demonstrate that patients who comply with treatment experience improved exercise tolerance, decreased disease symptoms, improved blood lipid levels, improved psychological well-being, and reduced morbidity and mortality. However, knowledge concerning the underlying causes of noncompliance with CR is muddied by a lack of consistent language use between studies. The terms "compliance" and "adherence" have been used at various times and across studies to mean: program attendance, achievement of program goals, achievement of desired outcomes, and maintenance of prescribed behaviors after the end of formal treatment. This mixing of terminology makes it difficult to compare across studies and hinders the development of a more specific understanding of noncompliance causes. If the research field can reach a consensus on standard meanings and usages of these terms, it will enable more meaningful comparisons across studies and advance understanding of the specific factors that place an individual patient at high risk for program dropout or failure to comply with prescribed behavior changes.

Moreover, even when the meaning of noncompliance is clear, researchers often do not distinguish between voluntary noncompliance (eg, lack of interest in continuing the program) and involuntary reasons for noncompliance (eg, moving away, rehospitalization). Making this distinction is crucial in helping clinicians understand clearly the predictors of voluntary noncompliance that are high-priority targets for intervention. In their examination of the differences in patient characteristics between the patients who completed their prescribed course of treatment and those who dropped out of treatment, Turner and her coauthors take the extra step of controlling for nonvoluntary attrition such as rehospitalization and mortality incidence.

The results in the article by Turner and coauthors show that depressed patients are twice as likely to drop out of CR voluntarily, as compared with nondepressed patients. The importance of understanding and treating depression in cardiac patients cannot be overstated. Numerous studies have shown a link between initial development of heart disease and depression. 5 Furthermore, up to 25% of patients will have an episode of major depression after myocardial infarction. Depressed individuals also have poorer outcomes after treatment. A fourfold increase in mortality during the first 6 months after myocardial infarction and an eightfold increase in the 18 months afterward.

In contrast, CR treatment reduces depression and subsequent mortality by more than 25%. However, evidence shows that depression also is a predictor of program noncompliance (dropout). Therefore, research is needed that distinguishes the degree to which depression is improved by participation in CR from the tendency of depressed individuals to drop out of treatment. Further work also is needed to examine the extent to which exercise and cognitive-behavioral therapy may improve depressive symptoms among those who adhere to treatment.

Physical exercise is a cornerstone of CR programs. Physical activity itself has a long history of association with lower incidence of depression and depressed mood. 6 Cross-sectional data from observational studies have consistently demonstrated a link between participation in physical exercise and lower incidence of depression. Prospective intervention studies have demonstrated that individuals who begin even moderate participation in physical activity show significant decreases in depressive symptoms. These results seem especially true for studies among women and older populations. Relief from depression and depressive symptoms have been demonstrated in studies using experimental designs with both aerobic and resistance training. The benefits of exercise training specifically, and CR in general, for the relief of depression have been well established. Given the association between depression and negative outcomes for cardiovascular disease, it is a special concern that depression was a significant predictor of program dropout in the study of Turner and her coauthors. Although the efficacy of cognitive-behavioral therapy for improving mood disorders has been well demonstrated, it remains unclear whether such therapy changes the cardiac prognosis in patients with affective disorders and coronary artery disease.

Additional large-scale studies, such as the Turner study, that examine patient characteristics associated with dropping out of therapy are greatly needed. In particular, work is needed that carefully distinguishes program attrition from failure to enroll and achieve program goals. Researchers should be careful to identify differences between involuntary and voluntary program attrition. Most importantly, studies are needed that focus on modifiable factors for which interventions can be developed to improve compliance.

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