Components of cardiac rehabilitation and exercise prescription

Orlando Rodriguez, MD Lynne T Braun, PhD, RN Robert S Rosenson, MD Geoffrey S Ginsburg, MD, PhD

Mar 19, 1999

Multifactorial cardiac rehabilitation can significantly reduce both total and cardiovascular mortality following myocardial infarction; in comparison, a beneficial effect of exercise rehabilitation alone on morbidity and mortality has not been shown. (See "Efficacy of cardiac rehabilitation after myocardial infarction").

Cardiac rehabilitation following a cardiac event is divided into three phases [1].

  •  Phase I or inpatient phase was introduced in the 1960s and consists of the early graded mobilization of the stable cardiac patient to the level of activity required to perform simple household tasks.

  •  Phase II consists of outpatient monitored exercise and risk factor reduction. This multidimensional approach gained popularity in the 1970s and became well structured in the 1980s [2,3].

  •  Phase III or maintenance phase consists of home- or gymnasium-based exercise with the goal of continuing the risk factor modification and exercise program learned during phase II.

A multifactorial rehabilitation program consists of three main components: exercise; coronary risk factor reduction; and psychosocial intervention.

This card will review the components of phase II or outpatient cardiac rehabilitation and exercise programs. Most such programs consist of weekly ECG-monitored exercise sessions for 8 to 12 weeks. The goals of these sessions are to develop and teach an individualized exercise prescription that is both safe and effective, to initiate interventions aimed at reducing coronary risk factors, and to identify and manage the psychosocial problems that commonly affect the cardiac patient [1,4,5]. Testing procedures to assess exercise capacity are discussed separately. (See "Exercise assessment and measurement of exercise capacity in patients with coronary heart disease").

RISK STRATIFICATION FOR EXERCISE — The risk of cardiovascular complications from exercise training should be evaluated before starting an exercise program. The risk stratification guidelines published by the American Heart Association use four categories of risk according to clinical characteristics [4]. Similar guidelines have been published by the Health and Public Policy Committee of the American College of Physicians.

  •  Class A are individuals who are apparently healthy and in whom there is no clinical evidence of increased cardiovascular risk of exercise.

  •  Class B individuals have established CHD that is clinically stable. These individuals are at low risk of cardiovascular complications of vigorous exercise.

  •  Class C individuals are at moderate or high risk of cardiac complications during exercise by virtue of a history of multiple myocardial infarctions or cardiac arrest, NYHA class III or IV (show table 1), exercise capacity of less than six METs, and significant ischemia on the exercise test. (See "Exercise assessment and measurement of exercise capacity in patients with coronary heart disease" for discussion of measurement of exercise capacity and significance of METs).

  •  Class D patients are those with unstable disease who require restriction of activity and for whom exercise is contraindicated.

Patients referred for outpatient cardiac rehabilitation typically belong to class B or C. They require different degrees of monitoring during exercise (see Supervision below).

EXERCISE PRESCRIPTION — The components of an exercise prescription include the mode, frequency, duration, and intensity of exercise. Exercise progression and provision of appropriate supervision are also important elements of the program.

Mode — The mode of exercise should be one that requires the use of large muscle groups and aerobic exercise such as walking, jogging, cycling, rowing, machine stair climbing, and other endurance activities [5,6]. Low impact activities are recommended because of a lesser risk of physical injury. The mode or modes of exercise chosen should be enjoyable for the individual and simple to carry out in order to maximize compliance.

Frequency — The recommended frequency of exercise is three to five times a week, which is necessary to achieve a significant improvement in functional capacity [4,6].

Content and duration — Each exercise session includes three phases:

  •  Warm-up for 5 to 10 minutes. Warm-up exercises consist of stretching, flexibility movements, and aerobic activity that gradually increases the heart rate into the target range. This gradual increment in blood flow minimizes the risk of exercise-related cardiovascular complications.

  •  Conditioning phase, which consists of at least 20 minutes and preferably 30 to 45 minutes of continuous or discontinuous aerobic activity.

  •  Cool-down for 5 to 10 minutes. The cool-down period involves low-intensity exercise and permits a gradual recovery from the conditioning phase. Omission of cool-down can result in a transient decrease in venous return, reducing coronary blood flow when heart rate and myocardial oxygen consumption are still high. Adverse consequences can include hypotension, angina, ischemic ST-T changes, and ventricular arrhythmias [7].

Intensity — Intensity of exercise may range from 40 to 85 percent of functional capacity (VO2max), which corresponds to 55 to 90 percent of maximal heart rate (estimated as 220 minus the age in years, or more accurately measured at the highest exercise intensity on the maximal exercise test). (See "Exercise physiology").

The target heart rate range may be determined by several methods:

  •  Selection of a fixed percentage of maximal heart rate, which is the method most commonly used to guide exercise intensity. A percentage range is calculated from the maximal heart rate (percent HRmax) reached at peak exercise during a symptom limited exercise tolerance test [6]. Exercise intensity has been categorized using the percent HRmax as light (<60 percent), moderate (60 to 79 percent), and heavy (80 percent).

Energy expenditure is related to both intensity and duration. In general, lower intensity exercise should be performed for a longer duration. Symptom-limited patients may begin with discontinuous exercise and progress to 20 to 30 minutes of continuous exercise. The duration is increased before increasing the intensity. It is common for cardiac rehabilitation patients to rotate among a variety of dynamic exercise modalities: treadmill, bicycle, Schwinn Aerodyne, arm ergometer, rowing machine, etc. Energy expenditure and heart rate response are related to the intensity of the activity and the amount of muscle mass used to perform the activity.

Beta blockers, which are administered to many patients after myocardial infarction, reduce the cardiac output response to exercise by limiting heart rate and stroke volume. As a result, patients may experience fatigue and reduce the intensity of training or compliance with exercise. Although resting heart rate, submaximal and maximal exercise heart rates are reduced by beta blockers, traditional heart rate methods may be used to prescribe exercise intensity as long as the patient's maximal heart rate was measured during an exercise test performed on medication.

Symptom-limited exercise refers to a submaximal testing modality in which a patient's test is terminated at the onset of symptoms related to CAD, usually chest pain and extreme shortness of breath (leg fatigue if it is severe and occurs well before the patient is near his age-predicted functional capacity. This heart rate level becomes the maximal heart rate, and the exercise training heart rate is a given.

  •  Use of the heart rate maximum reserve (a percent of the difference between the maximal and resting heart rates). Table 1 shows an example of an exercise prescription using the HRmax reserve method in a 40 year old individual (HRmax of 180), with a resting heart rate of 60 and a desired exercise intensity of 60 to 80 percent capacity (show table 2).

  •  Observation of the relationship between exercise heart rate and VO2 or metabolic equivalents (METs) (show figure 1).

These methods require the monitoring of heart rate or pulse-taking. Exercise intensity can also be prescribed using the rating of perceived exertion (RPE) (show table 3). This is a validated method that most patients can learn and apply easily [8]. On the category scale (6 to 20), an RPE of 12 to 13 (somewhat hard) corresponds to 60 percent VO2max and an RPE of 16 (hard-very hard) corresponds to 85 percent VO2max. An individual's subjective response during graded exercise testing is employed in specifying the RPE level for exercise training.

The exercise intensity for healthy adults is usually 60 to 70 percent of functional capacity (using VO2max, maximal METs, or heart rate maximum reserve) or a 12 to 13 level of the RPE (Borg) scale. The incremental benefit of very high intensity exercise (>90 percent of HRmax) is small and is not recommended because it leads to lactate accumulation and fatigue, and increases the risk of physical injury and cardiovascular complications [4,6]. Individuals with a low baseline fitness level may begin at a lower percentage of capacity. Patients with stable angina may have an exercise prescription based upon 60 to 70 percent of the heart rate at which ischemic ST segment changes appear.

Exercise progression — Another important element of the exercise prescription is the progression of exercise through stages [6]:

  •  Exercise programs should begin at the light intensity level, then gradually progress over a four to six week period to a moderate intensity level. This period is referred to as the conditioning stage.

  •  During the subsequent four to five months or improvement stage, exercise intensity can be further increased to the upper range of moderate intensity as training effects occur. These include a reduction in resting or submaximal exercise heart rate and increased ease with which a submaximal work load is performed

  •  Finally, during the long-term maintenance stage, the objective is to maintain compliance with the exercise regimen without any further significant changes.

Supervision — The last important consideration when prescribing an exercise regimen in a cardiac rehabilitation program is the level of supervision required.

  •  Patients who fall in the category of moderate or high risk of cardiac complications from exercise (Class C) should participate in a medically supervised program with ECG monitoring and personnel and equipment suitable for advanced cardiac life support. This level of medical supervision should be continued for 8 to 12 weeks until the safety of the prescribed exercise regimen has been established [4].

  •  Low risk patients (class B) initially benefit from medically supervised ECG monitored programs (6 to 12 sessions) which help to reassure the patient about the safety of the program. Self-monitored, home-based exercise programs have been shown to be effective and safe in these patients, and result in better rates of adherence when compared to group-based programs [9,10]. Patients may exercise without supervision when they understand how to monitor activity levels. They are taught to guide exercise intensity by heart rate and/or RPE. Low level isometric activities may be prescribed for low-risk patients to increase muscular strength; however, it is safest to monitor the ECG and blood pressure response to this type of exercise in a supervised setting.

Heart failure — Exercise training in compensated congestive heart failure does not improve cardiac function, as estimated from left ventricular ejection fraction, baseline cardiac output, or patient survival [11]. It can, however, enhance VO2 and peak cardiac output, improve muscle energetics and the efficiency of oxygen utilization, and restore autonomic tone towards normal. (See "Cardiac rehabilitation in patients with congestive heart failure").

Cardiac transplants — The cardiovascular response to exercise is influenced by the loss of autonomic control of heart rate after cardiac transplantation. Therefore, RPE must be used to regulate intensity which is initially set at 60 to 70 percent of VO2max. A longer warm-up and cool-down period is important because the physiologic responses to exercise and recovery take longer than in patients with intact cardiac innervation. Intensity and duration are increased as tolerated.

Lifestyle exercise in healthy individuals — A changing paradigm exists in the prescription of exercise for apparently healthy individuals or those at increased risk for CHD. The goal is to assist these individuals in achieving significant health benefits from regular exercise which are related to the degree of both exercise and fitness (show figure 2). (See "Preventive cardiology: Role of exercise").

Studies have shown that only moderate-intensity exercise is required for cardiovascular health benefits, not the higher intensities that might be necessary for substantial gains in aerobic fitness [12,13,14,15]. Exercise may also be performed for short periods several times a day and integrated into the course of one's daily life. When lifestyle activity was compared with structured exercise in a randomized trial of 235 healthy, but sedentary, men and women, both groups had a similar increase in energy expenditure over baseline at six months (1.53 versus 1.34 kcal/kg/day) [16]. Although both groups had an increase in fitness compared to baseline, the increase was greater in the structured group (3.64 versus 1.58 ml/kg/min in the lifestyle group, p<0.001). A significant reduction in total cholesterol, total cholesterol/HDL cholesterol ratio, diastolic blood pressure, and percentage of body fat occurred in both groups; however, there were no significant differences in outcome [17]. These results were maintained for up to 24 months [18].

Since lifestyle activity is as effective as a structured exercise program for increasing energy expenditure and reducing cardiovascular risk, patients may be advised to accumulate at least 30 minutes of moderately intense physical activity on most, preferably all, days of the week. Examples of lifestyle activity are brisk walking at a speed of 3 to 4 miles (4.8 to 6.4 km) per hour (equivalent to 3 to 6 METs), active yard work, walking up stairs, dancing, and active play with children [19].

CORONARY RISK FACTOR MODIFICATION — The components of risk factor modification efforts in a cardiac rehabilitation program include the following features, in addition to regular exercise training [5].

Nutritional counseling — Nutritional counseling is aimed at achieving weight loss and an improved lipid profile. It is best offered by a registered dietitian who can spend enough time with the patient to discuss dietary habits, food choices and how to implement an individualized dietary plan. The American Heart Association recommends a two step approach to diet. Step I restricts total dietary fat to 30 percent and saturated fat to 10 percent of the total caloric intake and total cholesterol to 300 mg per day. If the patient fails to achieve the desired cholesterol and weight reduction on this diet after a three to six month period, the Step II approach should be instituted, in which saturated fat is restricted to seven percent of the caloric intake and total cholesterol to 200 mg/day [20].

Patients with persistent hypercholesterolemia may benefit from addition of a lipid-lowering drug.

Cessation of smoking — Effective smoking cessation is difficult to achieve because of the strong psychologic and physiologic dependence that occurs. Some approaches that may be helpful for the smoker to quit and avoid relapse include patient education about the risks of continued smoking, referral to smoking cessation group programs, nicotine patch therapy or Nicorette gum, self-help literature, and encouragement by the primary care providers [5,21].

Therapy of hypertension and hyperlipidemia — The pharmacologic management of hypertension and dyslipidemias are usually instituted in parallel by the physician. (See "Treatment guidelines for hypercholesterolemia").

The long-term success of any of the risk factor reducing interventions depend largely upon patient compliance. Thus, compliance with exercise, diet, and smoking cessation should be assessed regularly by the rehabilitation nurses and physical therapists. When poor compliance is suspected, the cause should be identified and alternatives should be provided.

PSYCHOSOCIAL INTERVENTION — The third major component of a cardiac rehabilitation program is the identification and management of the variety of psychosocial and vocational problems that arise as a consequence of a cardiac event [21]. Depression, anxiety, and denial are common in patients following myocardial infarction, occurring in up to 20 percent of patients [22]. Depression is associated with lower exercise capacity, reduced levels of HDL-cholesterol, less energy, more fatigue, and a reduced quality of life and sense of well being.

These symptoms often translate into problems within the family, marriage, and the workplace and may lead to low rates of return to work, job loss, or disability. Individual or group psychotherapy and sometimes pharmacotherapy can be beneficial. Trained personnel including psychologists, psychiatrists and social workers should be available within the rehabilitation program or on a referral basis to best manage these issues.

The rate of reemployment after myocardial infarction or coronary artery bypass graft remains low and is influenced by several factors such as age, prior employment status and socioeconomic status. To date, no studies have shown a significant impact of cardiac rehabilitation programs on reemployment rate [9]. These results may be due to the multiple factors that affect reemployment rates and conclusive evidence on this question awaits further studies.