Functional Capacity in Men and Women Following Cardiac Rehabilitation Michael A. Gee, MD, MPH; Anthony J. Viera, MD, MPH; Paula F. Miller, MD; Sue Tolleson-Rinehart, PhD
■ PURPOSE: Cardiac rehabilitation (CR) has been shown to generally increase functional capacity and lower cardiovascular morbidity in patients with ischemic heart disease. The effectiveness of CR in female participants, however, is unclear. We thus examined whether improvement in functional capacity after CR differs between men and women with ischemic heart disease. ■ METHODS: Our study was a retrospective cohort study that included 1104 participants (346 women and 758 men) enrolled in CR from 2002 through 2011. We measured change in metabolic equivalents (METs) after CR to assess improvement in functional capacity in male and female participants. We considered various potential confounders, including baseline METs, CR referral indication, age, race, body mass index, baseline cholesterol, and home zip code average prosperity. ■ RESULTS: Men experienced a greater improvement in METs following CR in all models, including the unadjusted model (2.16 METs in men, 1.65 METs in women; P = .0001), the model adjusting for CR indication only (2.15 METs in men, 1.67 METs in women; P = .0003), and the model adjusting for age, body mass index, and CR indication (2.12 METs in men, 1.66 METs in women; P = .0004). ■ CONCLUSIONS: We show that men obtain greater benefit from current CR programs than do women. This implies that tailoring CR programs to women may yield further improvement in functional capacity for female CR participants.
Nearly 1 in 3 Americans suffers from cardiovascular disease (CVD), which is responsible for more than 850 000 American deaths each year.1 Although CVD is often considered a disease of men, more than half of CVD patients in the United States are women, and more than half of CVD-related deaths in the United States occur in women.2 Cardiac rehabilitation (CR) is an important component of treatment for many patients with CVD.3 Cardiac rehabilitation has been endorsed by several medical organizations, including the American College of Cardiology Foundation, the American Association of Cardiovascular and Pulmonary Rehabilitation, and the American Heart Association.4 Still, fewer than 30% of eligible patients participate in www.jcrpjournal.com
K E Y
W O R D S
exercise therapy females males metabolic equivalent myocardial ischemia
Author Affiliation: School of Public Health, University of North Carolina, Chapel Hill. The authors declare no conflicts of interest. Correspondence: Michael A. Gee, MD, 1201 East West Hwy, Apt 401, Silver Spring, MD 20910 (mgee1230@gmail .com). DOI: 10.1097/HCR.0000000000000066
CR after a CVD event.5 The rate of referral for female patients is particularly low.5 Despite the general effectiveness of CR and the high prevalence of CVD in women, surprisingly few studies examine the effectiveness of CR in women. We are aware of only 5 studies published on the effectiveness of CR in women over the last 20 years. These studies showed that CR does provide a benefit to women; however, it is unclear whether women benefit as much from CR as do men.6-10 Of these 5 studies, 3 did not assess intergroup P values between men and women, so it is impossible to determine whether differences between men and women are statistically significant in these studies.6-8 Only 2 studies examined intergroup Functional Capacity, Gender, CR / 255
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
JCRP-D-13-00135_LR 255
24/06/14 1:11 AM
P values,9,10 and these 2 studies reached very different conclusions. One found no statistically significant difference between men and women in functional capacity gains following CR,9 while the other found that there was a statistically significant difference.10 Given the lack of clarity on this point, our research seeks to address the important question of whether CR is, in fact, more effective in men than in women.
METHODS Our research used University of North Carolina (UNC) Health Care System Cardiac Rehabilitation Program participant data collected from 2002 through 2011. The UNC Cardiac Rehabilitation Program receives referrals both from unaffiliated private physicians and UNC-affiliated physicians. Program participants come from 5 different counties, with most participants from Orange County, where the university and the program are located. Given our research question, we only included CR participants referred for an ischemic diagnosis, such as stable angina, myocardial infarction, percutaneous coronary intervention (PCI), or coronary artery bypass graft (CABG). This yielded 1104 CR participants and excluded 268 CR participants. We thereafter separated CR participants into 2 main groups: those 781 participants completing CR and those 323 participants not completing CR.
CR Program The UNC Health Care Cardiac Rehabilitation Program is an outpatient-based CR program. In line with CR standards,11 the program includes supervised exercise, dietary education, and counseling.12 Cardiac rehabilitation participants are encouraged to attend 3 CR sessions per week for a period of 3 months for a total of 36 sessions. This is consistent with the number of sessions in most CR programs, which typically ranges from 24 to 36 total sessions.10,12 Recommendation for exercise at the CR center are based on the American Association of Cardiovascular and Pulmonary Rehabilitation guidelines, both in terms of duration of exercise and degree of exertion (guided by target heart rate). These recommendations are the same for male and female participants. Recommendation for exercise outside of the CR center is, of necessity, individualized on the basis of the participant progress during the program and input from the referring physician. Approximately 1 week before entering the program, participants engaged in symptom-limited exercise testing; the vast majority of participants (more than 88%) underwent exercise testing with a ramped
Bruce protocol. Most of the remaining participants completed a modified Bruce, a standard Naughton, or a modified Naughton protocol. One week before completing the CR program, participants again engaged in a graded exercise tolerance test, with similar percentages undergoing each type of testing protocol.
Statistical Analysis We assessed the change in maximal metabolic equivalents (METs) achieved during exercise testing as our outcome of interest. Metabolic equivalents is a continuous variable expressed in the units of mLO2·kg−1·min−1.13 Metabolic equivalents achieved “is considered the best measure of cardiovascular fitness and exercise capacity,” according to the American Heart Association.14 Standard methods were used to estimate METs.15 Change in METs was calculated by subtracting participant METs at baseline from the METs upon program completion. Metabolic equivalent change is currently the favored measurement to assess effectiveness of CR.16-18 Our main independent variable was participant sex. Covariates included age, race, body mass index (BMI), total cholesterol at baseline, resting blood pressure at baseline, primary referral diagnosis, and zip code prosperity. Resting blood pressure measurements do not account for current blood pressure medications, as this data is not available. “Zip code prosperity” is a proxy measure of respondent relative affluence; we first identified each participant residential zip code and then calculated each zip code average income by dividing the zip code total adjusted gross income by its total number of returns, based on 2008 United States Internal Revenue Service data.19 We determined that all covariates except home zip code prosperity were normally distributed. We thus used a Wilcoxon ranked sum test to evaluate the association between sex and zip code prosperity. For all other covariates, we used either t test or χ2 test, as appropriate. All statistical analyses were performed using STATA 12.0 (StataCorp, College Station, TX). Reported P values are 2-sided; a P value of
■ PURPOSE: Cardiac rehabilitation (CR) has been shown to generally increase functional capacity and lower cardiovascular morbidity in patients with ischemic heart disease. The effectiveness of CR in female participants, however, is unclear. We thus examined whether improvement in functional capacity after CR differs between men and women with ischemic heart disease. ■ METHODS: Our study was a retrospective cohort study that included 1104 participants (346 women and 758 men) enrolled in CR from 2002 through 2011. We measured change in metabolic equivalents (METs) after CR to assess improvement in functional capacity in male and female participants. We considered various potential confounders, including baseline METs, CR referral indication, age, race, body mass index, baseline cholesterol, and home zip code average prosperity. ■ RESULTS: Men experienced a greater improvement in METs following CR in all models, including the unadjusted model (2.16 METs in men, 1.65 METs in women; P = .0001), the model adjusting for CR indication only (2.15 METs in men, 1.67 METs in women; P = .0003), and the model adjusting for age, body mass index, and CR indication (2.12 METs in men, 1.66 METs in women; P = .0004). ■ CONCLUSIONS: We show that men obtain greater benefit from current CR programs than do women. This implies that tailoring CR programs to women may yield further improvement in functional capacity for female CR participants.
Nearly 1 in 3 Americans suffers from cardiovascular disease (CVD), which is responsible for more than 850 000 American deaths each year.1 Although CVD is often considered a disease of men, more than half of CVD patients in the United States are women, and more than half of CVD-related deaths in the United States occur in women.2 Cardiac rehabilitation (CR) is an important component of treatment for many patients with CVD.3 Cardiac rehabilitation has been endorsed by several medical organizations, including the American College of Cardiology Foundation, the American Association of Cardiovascular and Pulmonary Rehabilitation, and the American Heart Association.4 Still, fewer than 30% of eligible patients participate in www.jcrpjournal.com
K E Y
W O R D S
exercise therapy females males metabolic equivalent myocardial ischemia
Author Affiliation: School of Public Health, University of North Carolina, Chapel Hill. The authors declare no conflicts of interest. Correspondence: Michael A. Gee, MD, 1201 East West Hwy, Apt 401, Silver Spring, MD 20910 (mgee1230@gmail .com). DOI: 10.1097/HCR.0000000000000066
CR after a CVD event.5 The rate of referral for female patients is particularly low.5 Despite the general effectiveness of CR and the high prevalence of CVD in women, surprisingly few studies examine the effectiveness of CR in women. We are aware of only 5 studies published on the effectiveness of CR in women over the last 20 years. These studies showed that CR does provide a benefit to women; however, it is unclear whether women benefit as much from CR as do men.6-10 Of these 5 studies, 3 did not assess intergroup P values between men and women, so it is impossible to determine whether differences between men and women are statistically significant in these studies.6-8 Only 2 studies examined intergroup Functional Capacity, Gender, CR / 255
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
JCRP-D-13-00135_LR 255
24/06/14 1:11 AM
P values,9,10 and these 2 studies reached very different conclusions. One found no statistically significant difference between men and women in functional capacity gains following CR,9 while the other found that there was a statistically significant difference.10 Given the lack of clarity on this point, our research seeks to address the important question of whether CR is, in fact, more effective in men than in women.
METHODS Our research used University of North Carolina (UNC) Health Care System Cardiac Rehabilitation Program participant data collected from 2002 through 2011. The UNC Cardiac Rehabilitation Program receives referrals both from unaffiliated private physicians and UNC-affiliated physicians. Program participants come from 5 different counties, with most participants from Orange County, where the university and the program are located. Given our research question, we only included CR participants referred for an ischemic diagnosis, such as stable angina, myocardial infarction, percutaneous coronary intervention (PCI), or coronary artery bypass graft (CABG). This yielded 1104 CR participants and excluded 268 CR participants. We thereafter separated CR participants into 2 main groups: those 781 participants completing CR and those 323 participants not completing CR.
CR Program The UNC Health Care Cardiac Rehabilitation Program is an outpatient-based CR program. In line with CR standards,11 the program includes supervised exercise, dietary education, and counseling.12 Cardiac rehabilitation participants are encouraged to attend 3 CR sessions per week for a period of 3 months for a total of 36 sessions. This is consistent with the number of sessions in most CR programs, which typically ranges from 24 to 36 total sessions.10,12 Recommendation for exercise at the CR center are based on the American Association of Cardiovascular and Pulmonary Rehabilitation guidelines, both in terms of duration of exercise and degree of exertion (guided by target heart rate). These recommendations are the same for male and female participants. Recommendation for exercise outside of the CR center is, of necessity, individualized on the basis of the participant progress during the program and input from the referring physician. Approximately 1 week before entering the program, participants engaged in symptom-limited exercise testing; the vast majority of participants (more than 88%) underwent exercise testing with a ramped
Bruce protocol. Most of the remaining participants completed a modified Bruce, a standard Naughton, or a modified Naughton protocol. One week before completing the CR program, participants again engaged in a graded exercise tolerance test, with similar percentages undergoing each type of testing protocol.
Statistical Analysis We assessed the change in maximal metabolic equivalents (METs) achieved during exercise testing as our outcome of interest. Metabolic equivalents is a continuous variable expressed in the units of mLO2·kg−1·min−1.13 Metabolic equivalents achieved “is considered the best measure of cardiovascular fitness and exercise capacity,” according to the American Heart Association.14 Standard methods were used to estimate METs.15 Change in METs was calculated by subtracting participant METs at baseline from the METs upon program completion. Metabolic equivalent change is currently the favored measurement to assess effectiveness of CR.16-18 Our main independent variable was participant sex. Covariates included age, race, body mass index (BMI), total cholesterol at baseline, resting blood pressure at baseline, primary referral diagnosis, and zip code prosperity. Resting blood pressure measurements do not account for current blood pressure medications, as this data is not available. “Zip code prosperity” is a proxy measure of respondent relative affluence; we first identified each participant residential zip code and then calculated each zip code average income by dividing the zip code total adjusted gross income by its total number of returns, based on 2008 United States Internal Revenue Service data.19 We determined that all covariates except home zip code prosperity were normally distributed. We thus used a Wilcoxon ranked sum test to evaluate the association between sex and zip code prosperity. For all other covariates, we used either t test or χ2 test, as appropriate. All statistical analyses were performed using STATA 12.0 (StataCorp, College Station, TX). Reported P values are 2-sided; a P value of
