Evidence for Exercise Training
Fifty years ago, the most common advice given to patients who had experienced an MI was to take several weeks of complete bed rest (3). Today, however, exercise training is an ordinary part of treatment for people with CHD. Cardiac rehabilitation programs use a multidisciplinary approach of education and exercise to help clients with heart disease return to normal function within the limits of their disease (14).
There is no question that patients with CHD have improved cardiovascular function as a result of exercising. This is evidenced by higher V.O2max values, higher work rates achieved without ischemia (as shown by angina pectoris or ST segment changes), and an increased capacity for prolonged submaximal work (7, 19, 21). Moderate reductions in body fat, BP, total cholesterol, serum triglycerides, and LDL-C have been shown to occur with regular exercise, along with increases in HDL-C. The improved lipid profile is a function of more than the exercise alone, given that weight loss and the saturated-fat content of the diet can modify these variables.
A major focus of cardiac rehabilitation programs is to reduce the occurrence of subsequent MIs (3). This is referred to as secondary prevention of CHD. The Framingham Heart Study has shown that people who have experienced one heart attack are at increased risk of a second heart attack. Further, the likelihood of recurrence clearly is associated with many of the same risk factors that caused atherosclerosis in the first place. Thus, cardiac rehabilitation personnel must monitor BP, blood cholesterol levels, and smoking in their patients. In general, research has shown that a cardiac rehabilitation program involving exercise results in a 20% to 25% reduction in all-cause and cardiovascular mortality after an MI. This is good news, because it indicates that such patients derive a substantial benefit from participating in cardiac rehabilitation. In addition, patients gain an improved sense of well-being (14).
One of the most exciting developments in cardiac rehabilitation in recent years is the demonstration that lifestyle modification can reverse CAD. Ornish and colleagues (18) conducted a series of studies in which they showed that a program consisting of a strict vegetarian diet, yoga, meditation, smoking cessation, and physical activity reversed the atherosclerotic process. Patients in this study showed actual reversal of blockages in their coronary arteries, lending credibility to the idea that this condition can, in some cases, be treated with nonsurgical interventions. The lifestyle intervention group had more regression of CHD after 5 yr than after 1 yr, while the control group (which made more modest changes in lifestyle) showed continued progression of atherosclerosis and more than twice as many cardiac events.
Special Diagnostic Tests to Detect Coronary Heart Disease
Testing a patient with CHD is much more involved than testing the apparently healthy person. There are some classes of patients with CHD for whom exercise or exercise testing is inappropriate and dangerous (2). (See chapter 7 for absolute and relative contraindications to exercise.) In others, however, the benefits of a graded exercise test (GXT) outweigh the risks. Diagnostic exercise testing is nearly always performed in a hospital environment with a physician present. A 12-lead ECG is monitored at discrete intervals during the GXT, and three leads are displayed continuously on an oscilloscope. BP, RPE, and various signs and symptoms also are noted. Emergency equipment includes a defibrillator, supplemental oxygen, and emergency medications. Personnel trained and certified in advanced cardiac life support (ACLS) are on hand to provide assistance if needed.
Treadmill tests commonly used in diagnostic exercise testing are the Naughton, Balke, Bruce, and Ellestad protocols, named after their developers (2). These protocols are all GXTs that increase speed or grade at regular intervals to increase the exercise intensity. For those who are unable to perform treadmill exercise, a cycle test or arm ergometer test may be used. The criteria for terminating the GXT focus on various pathological signs (e.g., ST segment depression on the ECG) or symptoms (e.g., angina pectoris) rather than on achieving some percentage of age-adjusted maximal HR (2). A subjective angina scale may be used to assess the severity of the symptoms (see table 18.1).
Other tests of heart function include radionuclide procedures, typically administered in conjunction with either exercise or pharmacological (nonexercise) stress tests (5, 6, 16). In the latter case, the pharmacologic agents provoke myocardial ischemia through either increased myocardial oxygen demand or coronary vasodilation. For instance, thallium-201 (a radioactive substance) can be injected intravenously to assess myocardial perfusion. Thallium is taken up by well-perfused myocardium similarly to the way potassium is taken up. Ischemic myocardium tends not to take up the thallium, thus identifying areas of the heart with poor blood flow. Another technique involves a radioisotope that binds to the red blood cells (technetium-99m), which is useful for cardiac blood pool imaging. This allows the end-systolic volume (ESV) and end-diastolic volume (EDV) to be measured, and the ejection fraction then can be computed as follows: Ejection fraction = (EDV − ESV) ÷ EDV. A normal ejection fraction is 55% to 70%, but a person with a severely damaged myocardium may have an ejection fraction of only 30%. Ventricular wall motion abnormalities also can be identified (6).
The most definitive tests for CHD are coronary angiography and positron emission tomography (PET) scans. In angiography, a cardiac catheter is inserted into the femoral artery and pushed all the way up the aorta until it reaches the entrance to a coronary artery, where the curved tip of the catheter guide allows it to be inserted into the artery. A contrast dye is injected through the catheter into the coronary artery. By viewing an image of the coronary arteries on a screen, the cardiologist can measure the degree of occlusion (narrowing) that exists (see figure 18.4). PET scans use [18F]deoxyglucose or [13N]ammonia. These substances allow the level of myocardial cell metabolism to be assessed. Metabolically active areas, indicative of good perfusion, can be distinguished from underperfused areas by color.
Special types of diagnostic tests can determine whether a patient has CHD. Using GXTs on the treadmill (with close monitoring of the ECG and BP) is a common method of detecting signs and symptoms of heart disease. Radionuclide tests can more definitively confirm the presence or absence of heart disease.
Typical Exercise Prescription
Fitness professionals who work in health clubs and YMCAs often encounter clients who have gone through a cardiac rehabilitation program. Thus, it is important to have an understanding and appreciation of what these clients have experienced during their recovery process. In addition, many individuals with a master’s degree in exercise physiology can, with the proper training, find jobs in cardiac rehabilitation. As part of a team of medical professionals that includes physicians, nurses, dieticians, physical therapists, and clinical psychologists, the fitness professional can play an important role in helping patients to resume a healthy life after a heart event (20). A fitness professional working in cardiac rehabilitation must be vigilant about monitoring the signs and symptoms of heart disease. This involves knowing how to read an ECG, take BP readings, and administer the angina rating scale (refer back to table 18.1). Fitness professionals should be trained in emergency procedures and preferably should achieve certification in ACLS.
The details of how to design and implement cardiac rehabilitation programs, from the first steps taken after patients are confined to bed to the time that they return to work and beyond, are provided in the AACVPR guidelines (3). This section briefly introduces these programs.
Cardiac rehabilitation programs are organized in progressive phases of programming to meet the needs of clients and their families. Phase I (the acute phase) begins when a patient arrives in the hospital step-down unit after leaving the intensive or coronary care unit (14). Within 1 to 3 days of the MI or revascularization procedure, the patient has already been taught the risk factors for atherosclerotic disease and begun the rehabilitation process. Patients are exposed to orthostatic or gravitation stress by intermittently sitting and standing. Later, bedside activities and slow ambulation (i.e., walking) in the hallways are recommended (3).
Phases II and III refer to outpatient exercise programs conducted in a hospital environment. Rhythmic activities using large muscle groups are recommended for physical conditioning; these activities include treadmill exercise, cycle ergometry, combined arm and leg exercise, rowing, and stair-climbing. Light to moderate resistance training is accomplished with free weights (dumbbells) and elastic tubing. Special care must be taken when prescribing upper-body exercises to clients who have undergone CABG procedures because of limitations related to the chest incision. See chapter 13 for more details on resistance training in cardiac populations.
Recommendations for aerobic exercise programming in outpatient cardiac rehabilitation (phases II and III) are as follows, with patients progressing on an individual basis (9-11):
- Frequency: 3 to 4 days ? wk−1
- Intensity: 40% to 75% of V.O2max or HRR
- Duration: 20 to 40 min ? day−1
- 5 to 10 min of warm-up and cool-down exercises
Fitness professionals who work in cardiac rehabilitation must have knowledge of cardiovascular medications (for a description of these, see chapter 25). Patients who are on beta-blockers require special consideration, because the Karvonen formula for computing THR range is invalid if the client was not on beta-blockers at the time of testing. For these patients, a THR is sometimes computed by adding 20 to 30 beats · min−1 to the client’s standing, resting HR. However, in view of the wide differences in physiological responses to beta-blockade, another approach is to use RPE ratings around somewhat hard, which correspond to 11 to 14 on the original Borg RPE scale (3).
In phase II, clients are monitored carefully for vital signs (HR, BP, ventilation), and the ECG is monitored at a central observation station via telemetry (radio signals). A single-channel recording of 6 to 10 patients can be monitored simultaneously on a computer screen, and in the event of arrhythmias or ST segment changes, a rhythm strip is printed out. The rate–pressure product (SBP ? HR) is sometimes used as an indicator of myocardial oxygen demand. After training, the rate–pressure product at a fixed work rate is reduced, allowing the cardiac patient to exercise at higher work rates before the onset of angina (20). In addition to exercise classes, patient education classes are offered, and they cover topics such as healthy eating, stress management, cardiovascular medications, and principles of behavior modification. Phase II programs typically last about 12 wk and are covered by health insurance.
Phase III programs are hospital-based programs in which outpatients are encouraged to continue their exercise regimens and are provided access to continuing health care and patient education. In these cases, the client’s ECG usually is not monitored by telemetry, but clients continue to follow an individualized exercise prescription and attend patient education classes. Eventually, clients may enter the maintenance phase and move to a phase IV program in a nonhospital setting (e.g., sports medicine clinic).
For heart patients who are unable to attend a traditional cardiac rehabilitation outpatient program due to geography or finances, there are other options. Many hospitals offer rehabilitation programs following a distance-education model and can even monitor a client’s ECG over the Internet. In addition, a group called Mended Hearts (mendedhearts.org/) offers support-group meetings and online resources to help clients with heart disease and their families deal with the physical and emotional effects of heart disease.
Cardiac rehabilitation programs are divided into four phases. Phase I is the acute phase, performed while the patient is still in the hospital. Phases II and III are conducted on an outpatient basis, and phase IV is the maintenance phase. Cardiac patients can benefit from aerobic and resistance training, but working with this population requires special knowledge of their medical conditions.
1. Define atherosclerosis, and list three alterable cardiovascular risk factors that promote the atherosclerotic process.
2. Describe what will happen if an atherosclerotic plaque leads to a blockage in blood flow to a carotid artery, coronary artery, or femoral artery.
3. Where does CVD rank among causes of death in the United States today? What are four subcategories of CVD?
4. Describe the effects of aerobic exercise on people with hypertension. What are some other recommended treatments for hypertension?
5. List four specific patient populations who are commonly referred to cardiac rehabilitation programs.
6. What evidence is there that exercise training can be beneficial for individuals with CHD?
7. One of the goals of any cardiac rehabilitation program is secondary prevention of CHD. Explain what this means.
8. Identify diagnostic tests that can be used to detect the presence of CHD.
9. Outline the recommendations for aerobic exercise programming in phase II and phase III cardiac rehabilitation in terms of frequency, intensity, duration, and mode. Is weight training recommended?
10. Why is the Karvonen formula often not very useful in establishing a THR for a cardiac patient?
You can check your answers by referring to appendix A.
1. John is a 46-yr-old male. He is an insurance executive who is married with two children. John is active in his church and plays golf on the weekends. He went to see his cardiologist because he experienced recent fatigue with chest pain on exertion. He has never smoked but he consumes 1 to 2 alcoholic drinks a day. His medical history reveals a blood cholesterol level of 263 mg · dl−1, a triglyceride level of 195 mg · dl−1, and an HDL-C value of 45 mg · dl−1. Considering his sex, age, symptoms, and risk factors, what do you think is the likelihood he has CHD? What would be a reasonable next step to diagnose the presence or absence of CHD?
2. Jane is a 61-yr-old retired female. She recently underwent a left heart catheterization, which revealed significant occlusion in the left anterior descending artery and the circumflex artery. Therefore, a balloon angioplasty procedure was performed. Approximately 2 wk later, she performed a GXT with the following results:
Protocol: Balke (3.3 mi · hr−1, or 5.3 km · hr−1)
Resting: HR = 72 beats · min−1, BP = 130/72 mmHg
End point: stage 3 for 1 min (approximately 7 METs)
HR = 126 beats · min−1, BP = 160/90 mmHg
Reason for termination: Fatigue
No ST segment depression, no reported symptoms
Jane was taking atenolol (a beta-blocker) at the time of her test, and her physician instructed her to continue taking this medication. She was referred to the cardiac rehabilitation center for supervised exercise and risk-factor modification. List some types of exercise that would be appropriate for her. In addition to the mode, be sure to recommend an appropriate frequency, intensity, and duration of exercise.
3. Ralph is a 65-yr-old male who had CABGs on two coronary arteries (left anterior descending and circumflex). Both arteries were 75% occluded at the time of his surgery, which involved a sternectomy. His sternum was cut and separated, and the saphenous vein in his leg was harvested to obtain the grafting material; the sternum was then closed and fastened with stainless steel wires that are still in his chest. Ralph has completed phase I cardiac rehabilitation and has now been referred to an outpatient cardiac rehabilitation program 3 wk postoperative. He has inquired about a weight training program as part of his 12 wk phase II cardiac rehabilitation. What type of resistance training program would you design for this cardiac patient?