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[Exercise is Medicine]

Exercise for Coronary Artery Disease: A Cornerstone of Comprehensive Treatment

Michael H. Cox, PhD

Series Editor: Nicholas A. DiNubile, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 25 - NO. 12 - DECEMBER 97


In Brief: Exercise is effective in both preventing and treating coronary artery disease (CAD). Exercise improves cardiovascular efficiency and, in combination with other measures such as medication use, diet changes, and smoking cessation, may arrest or reverse atherosclerosis. Exercise prescriptions will vary according to disease level or risk, but the basic principle—physiologic evaluation followed by moderate exercise as tolerated—is the same for treatment or prevention. Most patients should work toward at least 20 to 30 minutes of moderate aerobic exercise three or more times a week.

The burden of cardiovascular disease rests most heavily on the least active." These strong words about the health burden of a sedentary lifestyle on the US population come from the National Institutes of Health's recent consensus conference statement on physical activity and cardiovascular health (1). They underscore the importance of exercise as both prevention and treatment for coronary artery disease (CAD).

Cardiovascular disease is the leading cause of morbidity and mortality in the United States. It accounts for 50% of deaths each year (2,3) and affects 13.5 million Americans (4). Though the number of deaths in the United States from CAD has decreased steadily over the past 25 years, the prevalence of CAD has increased for both men and women (5). Thus, the impact of the disease remains staggering. About 1.5 million people have heart attacks each year, and 500,000 die (6). Forty-five percent of those who have heart attacks are under age 65 and in the most productive phase of their lives (7).

Most of these premature deaths are preventable, and exercise is a cornerstone of a multifaceted plan for preventing and reversing CAD.

Contributors and Consequences

CAD is a disease of lifestyle; contributors include a high-fat diet, habitual inactivity, cigarette smoking, obesity, and high stress. These factors contribute to the formation of subintimal arterial deposits of cholesterol and triglycerides that are invaded over time by fibrous tissue and, frequently, calcify to atherosclerotic deposits in the lumen. The most common site for this process is the first few centimeters of coronary artery.

Consequences of atherosclerotic deposits in the coronary arteries can include chronically decreased arterial lumen size and/or acute atherosclerotic plaque rupture and thrombosis, leading to angina. With acute plaque rupture and thrombosis, myocardial infarction or sudden death may occur. Acute interventions, including drug therapy, coronary artery bypass graft surgery, and angioplasty, do not attack the underlying causes of the disease. Only a lifestyle change can do that.

The Changing Role of Exercise

Exercise has been shown in multiple studies to be effective in primary prevention of CAD (8-11). Increasingly, it has also proved effective in treatment for a broad spectrum of cardiovascular patients—from people who haven't had symptoms of a cardiac event but have multiple cardiac risk factors, to those who have had an event or have undergone bypass surgery or angioplasty.

The role of exercise in treating CAD has evolved dramatically over the last three decades. Before the mid-1960s, the standard treatment for heart attack survivors was several weeks to 6 months of bed rest. By the late 1960s, Kavanaugh et al (12) and Shephard (13) began demonstrating the benefits of early ambulation and exercise training. They found that exercise improved oxygen uptake, lowered myocardial oxygen demand, decreased blood pressure at a given workload, and increased the exercise threshold for the onset of cardiac symptoms. Later studies (14-18) showed that regular exercise increased serum high-density lipoproteins, decreased triglyceride levels, and reduced total body fat.

On the other hand, by the mid-1980s researchers found that exercise alone was not enough to slow the progression of atherosclerosis or reduce the number of myocardial infarctions (19). Patients needed effective, intensive efforts to modify the four major coronary risk factors: elevated lipids, smoking, hypertension, and sedentary lifestyle. The Stanford Coronary Risk Intervention Project (SCRIP) (20), the Lifestyle Heart Trial (21,22), and a study by Schuler et al (23) incorporated multiple interventions such as low-fat and low-cholesterol diets, exercise, weight loss, smoking cessation, stress management, and medications to favorably alter lipoprotein profiles. These studies proved the benefits of multiple lifestyle modifications and laid the groundwork for current CAD management.

The current view is that exercise is only one part of a sophisticated, multifaceted approach to treating CAD—an approach that also includes medication, behavior modification, and diet. State-of-the-art cardiac rehabilitation programs incorporate risk modification and motivational strategies tailored to the individual patient to enhance interest and adherence, assess readiness for change, and overcome barriers to participation in the program.

Benefits and Limits of Exercise

Unless patients make important lifestyle changes, coronary artery bypass graft surgery and angioplasty are simply palliative measures for treating CAD. Generally, exercise alone cannot reverse atherosclerotic build-up, but the combination of regular exercise and intensive dietary therapy with or without lipid-lowering drugs can reverse or limit the progression of angiographically documented atherosclerosis. Among patients in a case-control study (24) who underwent a 12-month exercise and diet intervention, 90% (26) had either no change or regression of CAD, as compared with 55% (18) of the control group.

Epidemiologic data also support the role of exercise in slowing or reversing CAD. Mortality studies (25,26) show that exercise reduces deaths from CAD by 20% to 25%.

The physiologic rationale for using exercise as a treatment for CAD is that it increases cardiovascular functional capacity with no adverse effects on left ventricular function, and it decreases myocardial oxygen demand at a given submaximal workload. The functional outcome is that the cardiovascular system is more efficient, responding to a higher workload with less effort. Exercise is important as an angina and postmyocardial infarction therapy because it is thought to decrease myocardial ischemia by increasing the interior diameter of the coronary arteries, resulting in increased coronary blood flow (27-29). These findings, however, have been limited to animal studies. The reduction in ischemia has also been confirmed in electrocardiographic (ECG) studies (30).

Most adaptations to exercise in patients who have CAD take place at the peripheral level. However, there are central changes as well in some patients, including improved cardiac contractility and stroke volume (31,32). Exercise seems to have slight or inconsistent effects on regional wall motion abnormalities, ventricular ejection fraction, left ventricular function, and ventricular arrhythmias.

Exercise also reduces CAD risk by raising high-density lipoproteins (33), increasing insulin sensitivity, and reducing body fat (34) and hypertension (35). Endurance exercise enhances the breakdown of blood clots and decreases the adhesiveness and aggregation of platelets. These factors in turn reduce thrombosis (11).

Another important benefit of exercise is that it helps patients feel better by improving exercise tolerance (4), symptoms (4), and sense of well-being (36). Psychologically, exercise gives patients self confidence, reduces depression, and provides a foundation for approaching other behavioral changes such as smoking cessation and weight loss efforts.

Barriers to Compliance

With such a convincing case for exercise, it is unfortunate that more patients don't enjoy its benefits. Fewer than 20% of patients who have CAD participate in cardiac rehabilitation (37,38), which suggests a vast underutilization, particularly among older adults, women, and minorities. The barriers to participation may include lack of physician referral, patient resistance, reimbursement problems, and lack of access (4).

The Exercise Prescription

The goal of exercise—whether in a home regimen or a cardiac rehabilitation program—is to improve patients' functional capacity and exercise tolerance, which improves their quality of life. The key to success is setting short-term, attainable goals for patients, such as small improvements in exercise tolerance, reduced angina, weight loss, smoking cessation, lower blood lipids, reduced hypertension, improved psychological well-being and social adjustment, and return to work (39). Clinically, improvements in exercise tolerance can be objectively measured, and reduced myocardial ischemia is evidenced by ECG changes.

Home exercise. Patients who have mild CAD—those who have documented mild, stable occlusion but who haven't had a coronary event—and those who have two or more cardiac risk factors should be advised to work gradually toward the exercise goal suggested for all Americans: 30 minutes of moderate activity on most days of the week (see "Exercise for Mild Coronary Artery Disease"). Patients who have cardiac risk factors should have a medical evaluation before undertaking a regular exercise program. Patients with two or more CAD risk factors and/or a functional capacity of less than 8 metabolic equivalents (METs) should be in a supervised exercise program, according to the exercise guidelines established by the American College of Sports Medicine (40).

Cardiac rehabilitation. Patients who have had coronary artery bypass surgery, angioplasty, or myocardial infarction are better treated with a formal cardiac rehabilitation program. In general, the type and duration of supervision a patient needs is determined by his or her risk status. The American Association of Cardiovascular and Pulmonary Rehabilitation (41) and the American College of Cardiology (42) have published criteria regarding supervised and unsupervised programs, as well as guidelines for ECG monitoring. High-risk patients can be identified by applying these guidelines (table 1: not shown).

Though each patient's treatment plan will be individualized, the rehabilitation phases and the types of exercise are generally the same regardless of disease severity. Based on the patient's risk factors, the amount of time for each phase may differ. Major alterations in dosage and type of exercise are made for patients who have heart failure or arrhythmias or who have had heart transplantation. Elderly patients may require supervised exercise; some may never have exercised before.

Dose. Research regarding the exercise dose-response relationship in patients who have CAD has been inconclusive, and the topic remains controversial. More research is needed to determine the optimum exercise prescription to maximize cardiac benefits. Until this is clarified, the goal is for patients to exercise regularly without exceeding their maximal work capacity or triggering symptoms.

Unless future studies show that the added benefits of high-intensity exercise outweigh the risks, it appears prudent to recommend moderate exercise for CAD patients (43). Physiologically, "moderate" means equal to or less than 60% of VO2 max or, using the Borg scale of perceived exertion, at a rating less than 13 (somewhat hard). This moderate level of exercise is a realistic goal for most patients. Examples of moderate exercise are activities that work the large muscle groups such as walking, cycling, swimming, and gardening, done at an appropriate pace. These activities are easy for patients to perform and measure. Three reports (43-45) on fitness level and mortality suggest that heart disease mortality can be reduced with 30 to 70 minutes of brisk daily walking.

Beta-blockers do not compromise exercise trainability. However, they do reduce exercise heart rate, and patients and physicians should be aware of this response. Nevertheless, the relationship between functional capacity and heart rate remains, thus allowing for the same exercise prescription calculations as in patients who are not taking these medications.

Phase 1. The goals of exercise in the first 2 weeks after myocardial infarction, bypass surgery, or angioplasty are to counter the effects of bed rest and/or previous inactivity, and to build patients' confidence that they can become physically active.

This phase is a 6- to 14-day inpatient program, and patients are closely monitored (40). A patient starts slowly and works up to 5 to 10 minutes of continuous movement. Range-of-motion exercises of the upper extremities are recommended unless the activity stresses the sternal incision in patients who have had bypass surgery. Symptoms, heart rate, blood pressure, and rating of perceived exertion are monitored during activity.

Phase 2. In phase 2, patients undergo graded exercise testing and receive a detailed exercise prescription (32). The outpatient exercise program can last 14 days to 12 weeks or longer and is implemented in a supervised setting, such as a hospital, YMCA, or university. It includes risk factor education and psychological and vocational counseling.

In this phase, large-muscle exercises should be performed at least 20 to 30 minutes at least three or four times a week. Warm-up and cool-down exercises should, respectively, begin and end each session. A supervised setting enhances patient education about the exercise program and provides ongoing supervision; however, home programs may be appropriate for patients at low risk who are highly motivated. Cardiac rehabilitation specialists are using new technologies to monitor patients at home, including fax machines, video recorders, Internet connections, and transtelephonic ECG monitoring devices. Traditional at-home monitoring consists of contact by phone and mail.

Phase 3. The extended, supervised outpatient phase of cardiac rehabilitation lasts 4 to 6 months. Patients are taught to monitor their exercise intensity, either by using a heart-rate counter or, if they're in a walking program, by monitoring their step rate (number of steps taken in a 15-second interval). Patients who have arrhythmias are monitored more closely.

Activities can progress in intensity and frequency as tolerance is demonstrated. Limited resistance exercises can be added at this time.

Phase 4. The maintenance phase of cardiac rehabilitation takes place in the home or in the community and is generally unsupervised. Yearly exercise testing is recommended, and additional risk factor modifications should be pursued aggressively (46).

What About Resistance Training?

Resistance training may benefit many patients who have CAD because it improves muscle tone and endurance. The current thinking is that patients who have had a cardiac event or have undergone invasive therapy can add light resistance training to their exercise routine after 4 to 6 weeks of a supervised aerobic program. Light resistance exercises are performed with elastic bands, light hand weights, or resistance training apparatus. Patients' blood pressure and ECG responses should be monitored when resistance training is started.

Patients who are hypertensive should not begin weight training exercises until their diastolic blood pressure is lower than 105 mm Hg (40), and sedentary patients should not begin resistance training until their exercise capacity is greater than 5 METs. Other contraindications to resistance training include unstable symptoms, arrhythmia, and uncontrolled hypertension.

The Role of Primary Care

The primary care physician can have a major role in treatment for patients who have CAD. All parts of a treatment plan are easy to implement and none of them is new. What is innovative is the simple logic that CAD treatment should be a total intervention that encompasses exercise, diet, medication, smoking cessation, and other lifestyle modifications.

Physicians are finding out how important the patient's significant others can be in fostering compliance with health interventions, including exercise. Because primary care physicians themselves have such an impact on behavior patterns, in this context they are among their patients' significant others. Primary care providers who steer their CAD patients toward home exercise or cardiac rehabilitation and support their exercise efforts will be instrumental in ensuring that more patients will benefit from the cardiac effects of exercise.

References

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This article was prepared by senior associate editor Lisa Schnirring.

Dr Cox is a corporate vice president for the Crozer-Keystone Health System in Media, Pennsylvania. He directs the Centers for Occupational Health, the Center for Preventive Medicine and Human Performance, and the health system's urgent care business. He is a member of the American College of Sports Medicine's National Executive Council on Certification and Education and an adjunct professor in the School of Allied Health at West Chester University in West Chester, Pennsylvania. Dr DiNubile is an orthopedic surgeon in private practice in Havertown, Pennsylvania, and director of sports medicine and wellness at the Crozer-Keystone Healthplex in Springfield, Pennsylvania. He is a clinical assistant professor in the department of orthopedic surgery at the University of Pennsylvania in Philadelphia and a member of the editorial board of The Physician and Sportsmedicine. Address correspondence to Michael H. Cox, PhD, Crozer-Keystone Health System, Healthplex Pavillion 2, 100 W Sproul Rd, Springfield, PA 19064; e-mail to [email protected].


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