Cardiac rehabilitation: Effective yet underutilized in patients with cardiovascular disease

Abstract Cardiac rehabilitation is a comprehensive program that treats patients with multiple cardiac conditions including post‐myocardial infarction, stable angina, post‐coronary artery bypass surgery, chronic heart failure, and peripheral vascular disease with structured exercise, and nutrition and risk factor counseling. It is an effective tool that has been shown to improve not only quality of life but also reduce adverse cardiac events, including death. While the value of cardiac rehabilitation is supported by a large body of evidence and its recommendation by the American Heart Association/American College of Cardiology it is significantly underutilized due to both patient and systemic factors. Continued efforts should be made to remove the obstacles to make cardiac rehabilitation available to all those who qualify.

included progressively more physical activity and in the 1970s a structured and supervised rehabilitation program was established. 10 This program contained three phases. Phase I was initiated while the patient was still in the hospital after a cardiovascular event as lowlevel supervised activity. This was followed by Phase II, which was supervised exercise on an outpatient basis with ECG monitoring.
Next was Phase III, a community-based or gymnasium rehabilitation plan where patients may or may not have had medical monitoring. 11 The American Heart Association published a statement in 1995 that delineated the required components of any cardiac rehabilitation program: (1) training in exercise with prescribed activity, (2) modification of risk factors, and (3) psychosocial assessment and counseling. 12 In 1982, Medicare began to provide insurance coverage for cardiac rehabilitation in patients who were enrolled within one year of an acute MI, status postcoronary artery bypass graft (CABG) surgery, or had been experiencing chronic stable angina. 13 In 2014 Medicare expanded its coverage for cardiac rehabilitation to patients with chronic, stable heart failure who had not had a recent (within 6 weeks) hospitalization. 14 Cardiac rehabilitation structure and indications have evolved over the years and there continues to be important and significant change. (Figure 1).

| Coronary artery disease
The first group of patients in whom cardiac rehabilitation was intended was those who had sustained an acute MI, were post-CABG or had stable angina. 12 In the 2021 Cochrane Review, "Exercisebased cardiac rehabilitation for coronary heart disease," investigators analyzed 85 trials enrolling a total of 23 430 patients with coronary artery disease. They found significantly lower rates of MI and allcause hospitalization at 6−12 months. Moreover, at medium-term follow-up (>12−36 months), and long-term follow-up (>36 months) there were lower rates of MI and cardiovascular mortality in patients who had undergone cardiac rehabilitation. Lastly, at 1 year follow-up, patients who participated in cardiac rehabilitation reported a significant improvement in health-related quality of life. 15 A randomized controlled trial of 101 men with single vessel coronary artery disease with stenosis ≥75% and Class 1−3 angina symptoms (using the Canadian Cardiovascular Society [CCS] classification system) with ischemia present on treadmill or nuclear stress test were randomized to percutaneous coronary intervention (PCI) or exercise training and followed for 1 year. 16  16.3% vs. 24.6%, all p < .001). Of the patients who attended cardiac rehabilitation, "high-users" (those who attended ≥25 sessions), had significantly lower 1 year mortality (1.1% vs. 2.6%, p < .011) and 5 year mortality (14% vs. 17.2%, p < .011) compared to "low-users" (those who attended ≤24 or less sessions). 2  Living with Heart Failure Questionnaire was used to measure the health-related quality of life and showed a significant improvement in the patients who had undergone cardiac rehabilitation (mean improvement 5.9, p = .018). In addition, assessment using the 6-min walk test showed a significant improvement in patients who also had participated in cardiac rehabilitation (mean difference 21.0 m, p = .034). 18

| Peripheral arterial disease
Cardiac rehabilitation not only helps with secondary risk reduction in subjects with peripheral arterial disease, many of whom also have coronary artery disease, but also improves physical mobility. A study by Perkins and colleagues evaluated 56 patients with stable claudication symptoms who were randomized to treatment with percutaneous revascularization versus exercise training. 19 The patients were followed at 6, 9, 12, and 15 months. The distance to claudication symptoms was significantly lower in patients who were randomized to the exercise training compared to percutaneous revascularization at 6 months (p = .005) up to 15 months (p = .0001).
Interestingly, there were significant improvements in the arterial brachial pressure indices (ABPI) levels in those who were randomized to percutaneous revascularization compared to those who were randomized to exercise training (p ≤ .04). This lack of ABPI change despite increased walking distance in the structured exercise training group is likely due to changes at the cellular level that improve oxygen utilization by tissues. 19 A Cochrane review including 21 trials (1400 subjects) compared three different modalities of exercise for patients with peripheral arterial disease: supervised exercise therapy, home-based exercise therapy, and walking. 20 Investigators found that there was increased pain-free walking distance of 120 meters after 3 months in patients who had undergone the supervised exercise therapy (standard median difference 0.51, p = .0009). They also found an increased maximal walking distance of 210 meters in patients who had undergone supervised exercise therapy versus walking advice at 3 months (standard mean difference 0.8, p = .00001). There was also a longer pain-free walking distance and improved quality of life in the structured exercise therapy group compared to the home-based exercise therapy group and walking group. 20 Structured exercise benefits patients with symptomatic peripheral arterial disease through improvement in walking distance without symptoms in addition to providing guidance on diet and smoking cessation counseling.

| Geriatric and frail population
The geriatric and frail population is one that may have been determined as too high-risk to undergo cardiac rehabilitation. Clinical improvements in elderly patients with heart failure who undergo cardiac rehabilitation have also been reported. The REHAB-HF (Rehabilitation Therapy in Older Acute Heart Failure Patients) study was a prospective, multicenter randomized controlled trial that evaluated patients ≥60 years old who had been hospitalized with acute decompensated heart failure and were then randomized to either cardiac rehabilitation or usual care. 21 The primary outcome was the Short Physical Performance Battery which consists of gait speed, strength (through a sit-to-stand test) and a standing balance test. While baseline scores were similar, patients who participated in cardiac rehabilitation had significant improvement in the Short Physical Performance Battery at 3 months compared to those who had usual care (8.3 vs. 6.9, p < .001). 21 Frailty, however, is a factor that may dissuade providers from referring patients to cardiac rehabilitation. This issue was studied by At UF we continue to promote the cardiac rehabilitation program that was started by Dr. C. Richard Conti nearly 7 years ago. For example, as part of a quality improvement project, we significantly increased the proportion of ACS patients referred to our cardiac rehabilitation program from 10% to 43% (p < .001) by instituting a combination of an automated referral order in the electronic medical record, participation of the cardiac rehabilitation staff on discharge rounds, and housestaff and patient education regarding the benefits of cardiac rehabilitation. 22,23 In addition, the cardiac rehabilitation gym was relocated to a more centrally-located area adjacent to the hospital making access easier for patients.

| The future of cardiac rehabilitation
Modifying the structure of cardiac rehabilitation, for example, using telehealth to allow participation to be done, 26,27 and using technology for metric tracking, 28  were no deaths or cardiovascular events related to the exercise in either the HIIT or MICT groups. 30 This study supports both moderate and high intensity exercise as being beneficial in cardiac rehabilitation patients.
Advancements in technology can be used to enhance the cardiac rehabilitation experience and improve outcomes for patients. In a randomized controlled trial, ACS patients treated with PCI were randomized to standard cardiac rehabilitation or cardiac rehabilitation plus digital health intervention (DHI). 28 The DHI curriculum included a smartphone-or web-based application that required patients to There was no significant difference between the two groups with respect to blood pressure, laboratory values, depression or rehabilitation attendance. 28 With respect to mobile technology, a study by Imran 29  Another aspect of cardiac rehabilitation that continues to be evaluated is home-based cardiac rehabilitation. There are many benefits to home-based programs, especially as transportation and distance from rehabilitation centers can be limiting factors in patients' participation, in addition to concerns of infection throughout the COVID pandemic. In one randomized, controlled trial heart failure patients with an ejection fraction < 50% were randomized to a homebased cardiac rehabilitation group versus a control group with usual medical care. 26 The cardiac rehabilitation group participated in 1 week of outpatient rehabilitation then transitioned to home-based rehabilitation for three, 30-min sessions per week. At 90 day followup, patients who had undergone home-based cardiac rehabilitation had significant improvement in their peak VO 2 (18.2 ml/kg/min before and 20.9 ml/kg/min at follow-up, p = .02) and anaerobic threshold (5.5 ml/kg/min before and 6.0 ml/kg/min at follow-up, p = .005). In addition, home-based cardiac rehabilitation program subjects had improvement in their Minnesota Living with Heart Failure Questionnaire scores (from 32.1 to 20.2, p < .01). 26 On the other hand, patients randomized to usual care had a significant reduction in their peak VO 2 at follow-up (from 18.7 to 16.5 ml/kg/ min, p < .01). 26 In a randomized control trial by Bravo-Esocbar et al. home-based cardiac rehabilitation was compared to hospital-based cardiac rehabilitation for 28 patients with stable coronary artery disease. 27 The home-based cardiac rehabilitation group had one session of supervised exercise per week in the outpatient center and two sessions with remote electrocardiographic monitoring using a device.  27 These studies suggest that homebased cardiac rehabilitation may be as effective in improving patient's exercise capacities and, from a practical standpoint, are safe alternatives with respect to COVID infection.

| CONCLUSION
Cardiac rehabilitation has been shown to effectively reduce mortality, modify risk factors and enhance quality of life, and therefore is a Class 1 indication for multiple cardiac dignoses. [5][6][7][8][9] Despite its proven benefits, cardiac rehabilitation continues to be an underutilized resource, which is secondary to multiple patient and institutional factors. Initiatives to educate patients and physicians about the short-and long-term health benefits of cardiac rehabilitation, increase referrals of patients to cardiac rehabilitation programs, augment availability of programs across the country, expand homebased programs for underserved areas, and improve insurance coverage are crucial to make this valuable resource to the wide population of patients who could benefit from the program.

DATA AVAILABILITY STATEMENT
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