Because of the lack of activity and obesity, cardiovascular disease is a leading health care issue in the United States. Fortunately, exercise is an important and effective part of the solution to the problems we have seen above and can have profound public health benefits. As an illustration, hospital discharges for people over the age of 65 show an incidence of 767.9/10,000 for heart disease, 175.6/10,000 for cerebrovascular disease, while all cancers combined account for 172.2/10,000 population (1). The savings from even a small reduction in these numbers would be astounding, not to mention that the individual patients would be saved from illness and pain. Reviewing these numbers should provide a serious motivation to individuals to improve their own health status with a program of vigorous exercise as part of a cardiovascularly healthy lifestyle.

Despite the attention given to many other medical conditions, cardiovascular disease is still the most common cause of death and disability in the United States. Some startling statistics regarding cardiovascular health in the United States can be gleaned from the CDC reports on health behaviors of adults. The picture on leisure time physical activity is very alarming and is an area that most people can make a significant impact on their health. Despite this fact, little has been done on a national basis to engage this issue, and compliance with exercise regime remains a national concern. In the 2002 to 2004 time period, 38% of adults never engaged in any light, moderate, or vigorous physical activity, with only one in eight adults engaging in any vigorous activity at least five times a week (2). Additionally, women and older people performed less activity, and people with lower educational status and socioeconomic status were less likely to engage in physical activity. In the area of body weight, the nation has had a progressive increase in weight over the last 50 years, and in the most recent data, this trend continues (3). Overall, nearly six out of ten adults were overweight or obese in the 2002 to 2004 survey, and 23% of adults were obese. Overweight status was most common in adults between the ages of 45 and 74, being much lower for adults over 75 and under less than 45. Again, higher education was associated with a better health status, with less obesity being associated with greater education. With regard to smoking, just over a fifth of all American adults were currently smokers (4). Cigarette smoking also was associated with the onset of the disease at a younger age—four in five smokers started smoking before the age of 21. Fortunately, there is increased motivation on the part of many individuals to stop smoking, and this can help to improve the success rate.

As a rehabilitation specialist, the opportunity to intervene with your patients is especially strong, since most patients have just undergone a life-altering disability, or are seeking advice for exercise related to injuries, and may be more receptive to appropriate counseling.

It is essential for a practicing physiatrist to be familiar with the many types of heart disease that might be encountered. For practitioners of cardiac rehabilitation, post-myocardial infarction (MI) patients are most common; however, improved survival and increased availability of advanced treatments have increased the frequency of post-coronary artery bypass graft (CABG) surgery, posttransplant, heart failure, arrhythmia, and postvalvular surgery patients. The details of cardiac rehabilitation for these different populations will be discussed later in this chapter.

As noted above, the incidence of cardiac disease has been lowered due to the recognition of cardiac risk factors and interventions to prevent ischemic cardiac disease. Specifically, decreased cigarette smoking, lower red meat consumption, and increased exercise have all contributed to a decrease in coronary artery disease.

Diabetes is one of the most potent risk factors for the development or reoccurrence of ischemic cardiac disease. Close control of blood sugars has been shown to decrease the risk of cardiac disease through the slowing of the development of atherosclerosis and lowering the incidence of secondary conditions such as nephrogenic hypertension (28, 29). In addition to oral hypoglycemic medications and the use of insulin, a combination of exercise training, weight loss, and dietary modification can assist in improving diabetic control (30). The appropriate selection of treatments for an individual patient can be helped with following the American Diabetes Association guidelines, and early intervention can be an essential component of the prevention of later cardiac disease. The exact benefits of exercise training in combination with good glucose control are still being elucidated, but they are present. Essentially, prevention of development of a combination of diabetes, hypertension, dyslipidemia, and obesity is essential as the combination, called the multiple metabolic syndrome, can lead to increased incidence of heart disease.

Establishing adequate control of blood pressure is an important part of the management of individuals with cardiac disease. Although control of hypertension has been shown to be clearly beneficial in the prevention of stroke, the data for heart disease have been more mixed. Still, it is important to control hypertension in postinfarct patients and in patients with risk for cardiac disease. Historically, blood pressure control has been shown to be most useful for patients with normal electrocardiograms (31, 32).

Lifestyle modification can provide two of the most important factors in the control of hypertension: (a) reduction of salt in the diet and (b) increasing exercise to improve conditioning. Although there are many classes of pharmacological agents available for the control of hypertension, there has not been a clear benefit shown with the use of one type of agent over another except in some special situations (32). The major groups of medications for the control of hypertension are divided into beta blockers, alpha blockers, diuretics, calcium channel blockers, and ACE inhibitors. The agents that used to be believed to be most beneficial of these were the beta blockers. This is still the case in individuals with CHF, arrhythmia, hypertrophic obstructive cardiomyopathy, and prior MI. In this group of patients, these agents provide cardiac protection by decreasing the maximum cardiac oxygen consumption and through decreasing inotropy and limiting heart rate (HR) response. However, in individuals with only hypertension and no other cardiac disease, the most recent evidence indicates that there is an increased risk of stroke and no clear benefit over other agents in the prevention of cardiac disease. The current recommendations are for beta blockers not to be used as monotherapy or as a first-line agent for uncomplicated hypertension (33, 34). Diuretics have been shown in large trials to have beneficial effects on decreasing mortality, especially in isolated or uncomplicated hypertension (33). Consideration needs to be made for special populations in the treatment of hypertension. For example, hypertension is more prevalent, and severe, and occurs at a younger age in African Americans (35). The issue of which agent is most effective is often not a pertinent discussion, since combination therapy is usually required to adequately control blood pressure (36). The standards for the management of hypertension are evolving rapidly, and the latest European guidelines issued in 2007 by the European Society of Hypertension and the European Society of Cardiology (ESH-ESC) (37) are likely to be incorporated in the next revision of American guidelines that are issued periodically by the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (36). The current guidelines are from 2003 and are due for revision. Since there is so much change in the management guidelines, it is recommended that rehabilitation physicians seek the advice of the treating cardiologist or internist for assistance in the optimal management of each individual patient.

Elevated levels of serum cholesterol are a modifiable risk factor that has received a great deal of attention. In the popular press and among patients, this is the most commonly discussed risk factor. A combination of dietary modification, exercise, and medications can be very effective at controlling hypercholesterolemia. Decreased cholesterol levels and increased high density lipoprotein (HDL) have been known for a long time to be associated with decreased risk of cardiac disease (38, 39, 40). The initial approach to mild elevation of serum cholesterol is through a decrease in dietary intake of saturated fats and cholesterol, with the goal of lowering serum lipid levels, and thereby decrease cardiac risk. Even a moderate risk factor modification program can help.

Patients can decrease lipid levels by adhering to a low-cholesterol, low-fat diet along with weight reduction, even without the addition of exercise (41). Current recommendations are that the total amount of calories from fat in the diet should not exceed 30%. Control of cholesterol can be achieved through a three-step program, as outlined in the NCEP guidelines (35). Phase I is an adoption of nutritional guidelines, lifestyle changes, and general improvement in health habits. Phase II involves the addition of fiber supplements and possibly nicotinic acid. Phase III includes lipid-lowering drugs. Lipid-lowering programs have been shown to retard the progression of coronary artery disease. With the addition of physical activity, HDL cholesterol concentration can rise 5% to 16%, but the data on the lowering of low density lipoprotein (LDL) cholesterol are still controversial.

Any current discussions of risk factor modification must involve the metabolic syndrome, which is defined by a combination of a constellation of risk factors. These risks include hypertension, abdominal obesity, dyslipidemia, and insulin resistance. The definition of metabolic syndrome was formalized by the National Cholesterol Education Program in 2001 with the requirement of the presence of three or more risk factors out of five (41) (Table 41-2). The prevalence of the syndrome from the NHANES III survey was 23.7% in 47 million individuals (42). This incidence has likely only increased since
the population has continued to have increased the incidence of obesity. Presence of the metabolic syndrome is associated with a fourfold increase in fatal CHD and a twofold increase in CVD and all-cause mortality, even after adjustment for age, LDL, smoking, and family history of CHD (43); in women, it is associated with a fivefold to ninefold increase in diabetes (44, 45). The major issue in the prevention of the metabolic syndrome is the control of weight gain and requires changes in a variety of behaviors, including increasing activity, decreasing sedentary activities, and reducing caloric intake. Reduction of salt intake is also essential for these individuals (46).

The importance of weight management has become clearer recently with the clarification of the role of central obesity in the metabolic syndrome. Weight management is an integral part of any cardiac rehabilitation program for individuals who are overweight, and there are many outside programs that can be used to help with weight management. Dietary counseling is also important, and specific counseling is based on lipoprotein levels, blood pressure, presence of diabetes or heart disease, and other risk factors. As little as a 5 lb weight loss can be associated with a 40% reduction in cardiovascular risk, according to the Framingham Heart Study (47). A 10% weight reduction can lead to a significant reduction in a number of cardiac risk factors (48). As a rehabilitation specialist, it is important to emphasize the importance of exercise and activity on the loss of weight and maintenance of target weight. The benefits of improved lipid profile and exercise have already been discussed above.

Cigarette smoking is one of the greatest single modifiable risk factors for cardiac disease (49, 50). There are significant benefits to smoking cessation, even as secondary prevention. Ten year mortality in individuals with angiographically demonstrated coronary artery disease or MI who stopped smoking is decreased by over 30%. Part of the mechanism of smoking induced risk is through accelerated atherosclerosis, and as a contributor to hypertension. In evaluating techniques to help with smoking cessation, exercise alone does not contribute to decreased smoking (50), and smokers tend to be less compliant in cardiac rehabilitation programs (50). However, in a program of cardiac rehabilitation coupled with counseling for smoking cessation, with appropriate medication use, a decrease in smoking has been demonstrated (50). Since smoking cessation is so critical for survival, it is essential to include cessation or enrolment in a cessation program counseling as part of a complete cardiac rehabilitation program.

Of particular importance is a familiarity with the normal distribution of the major arteries of the heart, cardiac valvular anatomy, and the structures at risk from ischemia or infarction in these distributions. Comfort with cardiac anatomy also facilitates an informed dialogue with the referring cardiac specialists and gives the rehabilitation specialist an ability to anticipate complications and problems associated with the specific design of an exercise program specific to the patient’s cardiac disease.

Overall, the heart consists of paired atria and ventricles, with deoxygenated venous blood entering the right atrium. Blood then flows into the right ventricle via the tricuspid valve and is then pumped out through the pulmonic valve into the pulmonary artery. After oxygenation in the lungs, the blood reenters the left atrium and passes through the mitral valve into the left ventricle. The left ventricle then ejects the blood through the aortic valve into the aorta and the systemic circulation. The heart valves ensure unidirectional flow of the blood, and the atria act in coordination with the ventricles to augment cardiac output (CO). Atrial contraction assists in diastolic filling of the ventricles, and can add up to 15% to 20% to the total CO. The benefits of atrial function are greater with increased HR and in conditions with decreased ventricular compliance (51). The loss of the contribution of atrial “kick” is especially important to consider in disease conditions where atrial dysfunction is seen, such as atrial fibrillation.

The cardiac conduction system is a specialized system of muscle cells (myocytes) adapted to facilitate the appropriate sequencing of the contraction of the atria and ventricles at the physiologically appropriate rate (52) (Fig. 41-1). It is a unique feature of all cardiac muscle cells that they have the intrinsic ability to contract. Additionally, myocytes are able to conduct electrical activity in order to synchronize their contractions with other cells. The usual pacemakers of the heart, with cells with the most rapid intrinsic conduction rate, are the cells of the sinoatrial (SA) node. The SA node is located in the right atrium. The electrical signal, or pulse, then travels through three atrial internodal pathways to the atrioventricular (AV) node. The AV node has a special quality of delayed conduction allowing for the sequential contraction of the atria, followed, after a short delay created by the AV node, by the contraction of the ventricles. The signal, after passing through the AV node, passes into the bundle of His, located in the intraventricular septum, which then divides further into left and right bundles. The left bundle has a final division into anterior and posterior fascicles. Terminal branches of both the right and left conduction systems carry the pulse signals that excite the myocytes, causing contraction. MI, aging, and other conditions can alter the conduction system, leading to a variety of conditions such
as heart block and sick sinus syndrome. Congenital defects and accessory tracts can lead to life-threatening arrhythmias such as the Wolff-Parkinson-White syndrome (WPW). When prescribing or supervising a program of cardiac rehabilitation, it is important for the clinician to have a good understanding of the conduction system. This knowledge is helpful in evaluating arrhythmias and assessing the risks faced by patients prior to the initiation of cardiac conditioning programs.

Cardiac myocytes are among the most metabolically active tissues in the body. In order to allow for this extremely high level of metabolic activity, oxygen extraction is nearly 65% at all levels of activity (compared to 36% for brain and 26% for the rest of the body) (54). The heart is most efficient at aerobic metabolism, but is able to perform both anaerobic and aerobic metabolism, using a variety of substrates. Carbohydrates are usually 40% of the metabolism, with fatty acids making up most of the remaining 60% metabolism (55). This high oxygen extraction and metabolism presents a relatively high risk for ischemic injury to cardiac myocytes, since coronary blood flow is only present during diastole. This is especially important for
the endocardium, where increased wall tension and myocardial hypertrophy may place these myocytes at greater risk. Given the near maximum extraction of oxygen, there are only limited ways to increase oxygen supply in a situation of decreased cardiac perfusion. Under normal conditions, the coronary arteries can dilate to meet the demands of exercise. There are a number of substances secreted by the body that can increase the coronary blood flow, with nitric oxide as the final agent of many pathways (56). However, in disease vessels or situations of myocardial hypertrophy or excessive wall tension, this mechanism may not be able to allow for sufficient perfusion, and ischemia can result. Since it is so critical to restore or preserve myocardial perfusion, most medical and surgical therapies aim to restore the normal blood flow to the myocardium, either through vasodilatation or through bypass or endovascular procedures. It is also important to include exercise in the treatment regimen since regular exercise can increase cardiac collateral circulation and improve arteriolar vasodilation. These improvements are routinely seen as a result of the exercises that are a part of a cardiac rehabilitation program.

Another consideration in maximizing cardiac function is maintaining adequate venous pressures to the right side of the heart, without overloading the ventricle. The CO is in part related to increase in venous return, which increases the length of the myocardial fibers in diastole prior to the initiation of cardiac contraction. Clinicians who work with patients with cardiac disease will often refer to maintaining this filling pressure as “preload.” The benefit of myofibril stretch is to increase the overlap of the actin and myosin fibers in order to maximize the strength of contraction. However, excessive dilation of the ventricle, with further stretching in a weakened myocardium can cause the overlap of myosin and actin to decrease, yielding a decline in the strength of ventricular contraction. The relationship between the length of the fibers and the filling of the ventricle, which leads to increased contractility, is described by the Frank-Starling curve (Fig. 41-2). The clinical effects of this overlap of myosin and actin and the resultant decreases in cardiac function are seen in both constrictive heart disease (which limits the ability to move to the right on the Frank-Starling curve) and in patients with dilated cardiomyopathies, where there is a decrease in CO due to ventricular dilation moving too far out to the right on the curve. In cases of constriction, surgery can be done to allow greater dilation of the ventricle and restoration of CO, and in dilated heart failure, therapies are directed to decrease the size of the ventricles in order to increase CO (57).

In order for clinicians practicing cardiac rehabilitation to be able to discuss the basic principles of aerobic training and cardiac conditioning there is a need to have a basic understanding of the terminology and the principles of exercise physiology. These will be presented here.

HR is a useful measure to guide exercise as it has a linear increase in relation to VO₂ or other measures of work. Maximum HR is determined by age and can be roughly estimated by subtracting the age of the individual in years from 220. The Karvonen equation is another equation to estimate peak HR and target HRs that takes resting HR into account. The slope of the line between HR and VO₂ is determined by physical conditioning and the maximum HR continues to decline with age even with ongoing exercise. The physiologic regulation of HR is mediated by the interaction of vagal and sympathetic tone and circulating catecholamines (Fig. 41-4).

Stroke volume (SV) is the quantity of blood pumped with each heartbeat. Since the heart is a muscle and strengthens with exercise, in a patient with normal myocardial function, SV can increase with exercise. During incremental exercise, SV increases the most during early exercise, with the major determinant of SV being diastolic filling time. SV is sensitive to postural changes, changing little in supine as it is near maximum at rest, while in erect position it increases in a curvilinear fashion until it reaches maximum at approximately 40% of VO_2max (Fig. 41-5). There is also a decreased response of SV seen with advancing age and in cardiac conditions which result in decreased compliance, such as left ventricular hypertrophy.

CO is the product of the HR and SV. CO increases linearly with work, and in early exercise the principal increase is via
the Frank-Starling mechanism (SV increase), while in late exercise it is predominantly increased by HR. In general, the relationship between CO and VO₂ is linear with a break in the slope at the anaerobic threshold. The anaerobic threshold is the level of exercise at which the ability to deliver oxygen to the exercising muscles is below the demand for oxygen, marking the transition from aerobic to anaerobic metabolism. The maximum CO is the primary determinant of VO_2max and declines with age without any change in linearity or slope. The CO seen in submaximal work is parallel but lower in upright work compared to supine work, with VO_2max and maximal CO less in supine than erect positions (Fig. 41-6).

Myocardial oxygen consumption (MVO₂) is the oxygen consumption of the heart. MVO₂ rises in a linear fashion with workload. The anginal threshold is the point where MVO₂ exceeds the maximum coronary artery oxygen delivery. Although MVO₂ can be determined directly with cardiac catheterization, this is not practical. MVO₂ is usually estimated using the rate pressure product (RPP), calculated as the product of the HR and the systolic blood pressure (SBP) divided by 100. The increase in RPP with some activities versus others explains some of the seemingly paradoxical findings in patient symptoms. For example, activities with the upper extremities and exercises with isometric components to them have a higher MVO₂ for a given VO₂ due to higher SBP for a given level of work. Activities performed in supine also demonstrate a higher MVO₂ at low intensity and a lower MVO₂ at high intensity when compared to activities performed in the erect position. Finally, the MVO₂ increases for any activity when performed in the cold, after smoking, or after eating (Fig. 41-7).