Heart failure (HF) affects more than 5 million people, representing 2 % of the population.1,2 At 40 years of age, the lifetime risk of developing HF, regardless of gender, is one in five, with an incidence of 10 per 1,000 population after the age of 65 years.1,3 Despite efforts focused toward primary prevention of HF in the areas of hypertension (HTN), diabetes, obesity, use of cardiotoxic chemotherapies, and ischemic coronary artery disease (CAD), there continues to be an increasing incidence. Seventy-five percent of HF patients have antecedent HTN, and a sedentary lifestyle furthermore places them at high risk of developing HF.1 This disease is of major economic significance, with an estimated cost of $34.8 billion in direct and indirect health-related care in the US in 2008.4 The majority of this economic burden is related to hospitalizations and readmissions: a third of patients are readmitted within 90 days and the number of hospitalizations has tripled from 1,274,000 in 1979 to 3,860,000 in 2004.1,3 From a patient’s perspective, HF remains fairly unrecognized as a deadly disease, although it has a mortality rate that prevails over that of many cancers, reaching 50 % within five years from the time of first diagnosis.1,5
Regardless of the etiology of HF, congestive features, dyspnea and fatigue are the leading limiting symptoms that determine prognosis, quality of life, and use of tailored therapies.6 These symptoms limit exercise and may progress to pulmonary congestion and peripheral edema, creating a continual cycle of decompensation and hospitalization. If these symptoms could be quantified and placed in context, patients would not need to seek as much inpatient medical care and would be able to enjoy an overall better quality of life. Exercise capacity is one parameter with potential to be used in diagnosis, prognosis, and therapeutic measurements of chronic HF, and also as a therapy with the intent of improving symptoms.
Exercise Capacity in Diagnosis and Prognosis
In routine clinical care, physicians address blood pressure and lipid targets, nutrition, exercise, and obesity with patients as part of the primary prevention of cardiovascular (CV) disease. However, more emphasis needs to be placed on physicians identifying those at risk of HF who require intensified primary prevention practices and advanced therapies to prevent progression. In addition, this would need to include an assessment of exercise capacity, with each patient given a specific exercise prescription.7
This could range from a conversation during an office visit to more advanced screening for high-risk individuals, with the selection of an exercise test to further assess functional capacity and the need for therapy. Physicians also need to be aware of the patient’s current level of conditioning, factors that predict safety in exercising, and proven methods to increase exercise adherence among patients.
In the evaluation of HF, clinical assessment of dyspnea, fatigue, and exertional symptoms have been used for diagnosis and staging.2 Exercise capacity has also been used to determine prognosis because it can be quantified objectively with a six-minute walk test, treadmill or cycle stress test, and cardiopulmonary exercise testing (CPET).8–13 The limiting component in exercise capacity for those with HF is impaired cardiac output (CO). Patients with HF achieve <50 % of the maximal CO attained by healthy individuals at peak exercise.14 This occurs because there is a reduced ability to augment left ventricular ejection fraction (LVEF) due to a combination of impaired contractility, reduced β-adrenergic responsiveness, elevated systemic vascular resistance, and a blunted peripheral arterial vasodilator response to exercise.14 This response can be detected clinically by symptoms and further validated by the assessment of exercise capacity. In patients with HF, there is a poor correlation between measures of cardiac performance and symptoms, although one could logically assume a good correlation.2 One additional valuable finding is that patients at high risk of early arrhythmic death can be identified through electrocardiographic monitoring during testing, potentially altering clinical management.9,15,16
There are subjective and objective criteria of the improvement in exercise capacity with training that need to be measured during assessments. Subjectively, examples of patients’ perceived exertion rating include the Borg number or omnibus (OMNI)-picture scale.17–20 This can be correlated to direct measurements of exercise capacity using the six-minute walk test, CPET, or a treadmill or cycle stress test; however, these have not shown reproducibility or reliability.21 Clinically, physicians have used questions such as ‘How far can you walk?’, ‘How many flights of stairs can you go up before stopping?’, and ‘What limits you the most when exercising?’ to detect and monitor exercise capacity.
Exercise capacity can be measured objectively in terms of peak oxygen uptake (VO2) or VO2 at anaerobic threshold, duration of exercise and metabolic equivalents (METs). The modality of exercise testing—for instance, walk, cycle, or arm ergometer and treadmill—as well as the design of the stress protocol can have an impact on the assessment of exercise capacity.11–13,22–27 Exercise testing has been used objectively to measure exercise capacity; however, this is not a true representation of the day-to-day physical exertion or exertion during exercise sessions routinely performed by those with HF. Congestion, dyspnea, and motivation limit the reproducibility of these measurements for comparisons and assessment of overall improvement.27–29 Overall, formal exercise testing in patients with HF has not been defined beyond the evaluation for consideration of heart transplantation.2
Exercise as Treatment for Chronic Heart Failure
Historically, there have been concerns that exercise could potentially cause an exacerbation of heart failure, angina requiring hospitalization, arrhythmias including sudden cardiac death, myocardial infarctions, transient ischemic events, and even strokes.14,16,30 The most common events associated with exercise in HF patients include post-exercise hypotension, atrial and ventricular arrhythmias, and worsening of HF symptoms.14 Although adverse events rarely occur, the three most important factors that predict a higher risk include age, presence of heart disease, and intensity of exercise.14 The risk of myocardial infarction during physical exercise is higher than that of sudden cardiac arrest—particularly with exercise above six METS—and is 100-fold higher in those who do not regularly participate in physical activity compared with habitual exercisers.14,31 Therefore, patient selection for exercise therapy should be performed by a physician. The approach should be individualized, with the extent of initial monitoring based on heart failure class, recent myocardial events, and baseline level of conditioning.14,32
An initial exercise test establishes the baseline exercise capacity level for an individual and provides information regarding symptoms, patient comfort, arrhythmias, and hemodynamic response. After the exercise test is reviewed, a tailored exercise prescription can be developed ensuring that there is appropriate warm-up, ramped intensity, and cool-down. Exercise therapy should include sessions of 20–30 minutes performed three to five times a week.
Exercise is an intervention that is relatively low-cost, easily accessible, and easy to perform. Studies have shown that most benefits are derived from interval training at various intensities, including 50 %, 60 %, and 70 % of maximal capacity, with advancement in intensity as the patient becomes more conditioned.14,25 The setting for exercise recommendation will vary from self-monitored home exercise to supervised telemetry monitoring with scheduled evaluations to alter and advance therapy.32–34
Furthermore, other factors such as age, race, pharmacologic therapy, depression, sex, income, and comorbidities need to be studied to determine alternative methods to the assessment and prescription of exercise capacity in heart failure.14,26,35–39 In addition, the transition from monitored exercise training to home exercise training may also contribute to poor adherence.40–43 In most cases, there is improved adherence when support and encouragement is provided by family, friends, and co-workers in concert with physician follow-up and feedback.41,44,45
The Exercise Training Program to Improve Clinical Outcomes in Individuals with Congestive Heart Failure (HF-ACTION) was a National Institutes of Health-sponsored study completed in 2008. Results note that, regardless of the etiology of HF and New York Heart Association (NYHA) class, exercise training was safe and had a modest clinical benefit.31,36 Exercise has direct benefits for multiple organ systems that may be compounding the disease burden of HF and may even prevent improvement. Specifically in the HF subset, exercise can improve left ventricular diastolic compliance, aortic distensibility, blood pressure, and skeletal muscle function in both those with systolic and diastolic heart failure.8 Exercise training has been shown to improve exercise capacity and quality of life.33,36,46,47
To date, the evidence shows that the intensity of training does not directly relate to improvements in exercise capacity; therefore, after discussion with the physician, patients should be encouraged to initiate a low-intensity exercise program that can be maintained.14 Furthermore, increases in congestion and dyspnea raise mental and physical barriers to performing exercise consistently, even at lower intensities. HF is intimately associated with exercise intolerance; therefore, it is challenging to improve it with a therapy that magnifies this discomfort. The inability to exercise can have a domino effect, causing anxiety and further avoidance for fear of an oncoming exacerbation.
Exercise attenuates the abnormal physiology that develops with HF, which can create a break in the vicious cycle if one can overcome the initial discomfort.48 Initially, and at intervals throughout training, working with a comprehensive care team should help patients become more efficient with their time investment and improve their perceptions of quality of life with HF. After the establishment of routine exercise regimens and comfort in exercising, home-based programs and community exercise programs have enabled individuals to extend their exercise training to become a routine part of their lives.34,39,40,49
When asked how improved exercise capacity affects quality of life, rated using the Minnesota Living with Heart Failure Questionnaire, the Kansas City Cardiomyopathy Questionnaire, or the EuroQol Visual Analog Scale, patients have reported significant short- and long-term improvements.21,54,55 This was demonstrated in the HF-ACTION trial: patients reported significant improvements in health status that occurred early and persisted.56 Objectively, this has also been shown because those who have undergone exercise training have higher VO2, increased cardiac outputs, improved skeletal muscle conditioning, improved peripheral hemodynamics, increased ability to exercise longer at higher workloads, improved symptoms, improved tolerance to exercise, and improved quality of life.48,51,53,57,58 To date, evidence suggests that patients who are in NYHA class II–III, have stable symptoms for three months and LVEF <40 %, and are in sinus rhythm benefit most from exercise training.52 More studies are being performed to identify the factors in patients who respond to exercise training, in order to predict who may benefit from exercice so that these patients can be targeted.51,59
The optimal prescription of exercise training—including intensity, duration, and amount to lessen HF-related symptoms and provide maximum clinical benefit—has not yet been determined. However, exercise training has been demonstrated to be cost-effective for longer duration training periods, with $1,773 per life-year saved and improvement in survival by 1.82 years.50 It is apparent that exercise training should be a component of comprehensive care for those with HF. It is ideally initiated under supervision, with an exercise prescription for further training in group exercise programs or at home.
Exercise capacity is an important variable to consider in the diagnosis and prognosis of patients with chronic heart failure, but the specific use of exercise training remains undetermined. Although there is acceptance that exercise is safe and may have a positive impact on morbidity and quality of life, improved mortality has yet to be clearly demonstrated. Exercise regimens have been altered to be more cost-effective and to integrate seamlessly into a patient’s daily life with the goal of improving adherence. Specific prescriptions for exercise training have not been developed because many variables and confounding factors have prevented research trials from demonstrating an ideal regimen. Furthermore, combination therapy of exercise training and pharmacologic therapy is being investigated. The knowledge obtained from research investigations into exercise is expanding and advancing care for those suffering from HF. Perhaps the most benefit from exercise training would be derived from an exercise prescription as part of a strategy that would prevent HF in high-risk patients, such as those with HTN, diabetes, obesity, exposure to cardiotoxins, and CAD.60,61 In future, specific population subsets could be identified to better target the patients who would receive the most benefits from a dedicated exercise program.