The presence of obesity in patients with heart failure (HF) is associated with improved survival when compared with their nonobese counterparts. This apparent obesity paradox is well studied; yet, the underlying mechanisms remain incompletely understood. Cardiorespiratory fitness (CRF) influences the obesity paradox. Past studies demonstrate that obesity is protective predominantly in HF patients with low CRF, but this protective effect is not present at higher levels of CRF.1-4 The impact of phase 2 cardiac rehabilitation (CR) on obese patients with HF is unknown. This study compares outcomes between obese and nonobese patients with HF with reduced ejection fraction (HFrEF) who completed CR.
METHODS
Between 2012 and 2017, 504 individuals completed CR, consisting of aerobic and strength training, with additional focus on behavior modification. The study sample included 108 participants with a diagnosis of HFrEF. Cardiorespiratory fitness (CRF), defined as peak metabolic equivalents (METs), was determined at entry and exit from the CR program via symptom-limited exercise testing.5 Participants were stratified as obese or nonobese based on a body mass index (BMI) >=30 kg/m2 or <30 kg/m2, respectively. Participants with BMI >45 kg/m2 were excluded.
The electronic medical record was reviewed for all-cause mortality in the 5 yr following CR completion and hospitalizations or emergency department visits for 2 yr following CR completion. Completion of CR was defined as participation in the number of prescribed sessions, which in >95% of cases was 36 sessions.
Continuous data are presented as means +/- SD and categorical data as n (%). Baseline variables between the nonobese and obese groups were compared using Student's t test for continuous variables and chi-square testing for categorical variables. Multivariable regression testing was performed to correct for factors found to be associated with outcomes of interest on univariate analysis with a P < .20. Variables considered for the logistic models included age, race, sex, ischemic cardiomyopathy, atrial fibrillation, diabetes mellitus, hyperlipidemia, chronic kidney disease, and peripheral arterial disease. Statistical significance was defined as P < .05. The present study was approved by the institutional review board of the Cleveland Clinic.
RESULTS
Baseline characteristics are summarized in the Table. Thirty-one percent of CR participants with HFrEF were obese. Obese participants were more likely to have comorbid hypertension and diabetes mellitus. There were no significant differences between the obese and nonobese participants with respect to left ventricular ejection fraction, sex, or age. Upon entry to CR, CRF was greater among nonobese than among obese participants with HFrEF (5.5 +/- 2.0 vs 4.5 +/- 2.3 METs; P = .02).
Upon adjusted multivariable analysis, obese participants experienced significantly less percentage increases in CRF after participating in CR (21 +/- 32% increase in METs vs 39 +/- 28%; OR = 0.84; P < .05). There was no significant difference regarding the rate of hospitalization or emergency department visit in the 2 yr following CR (62% [obese] vs 57% [nonobese]; OR = 1.02; 95% CI 0.40-2.62). In addition, there was no difference in mortality in the 5 yr following CR (18% [obese] vs 10% [non-obese]; OR = 2.78; 95% CI 0.62-12.5).
DISCUSSION
This study evaluated the effect of CR participation on clinical outcomes of obese versus nonobese patients with HFrEF. Among CR participants with HFrEF, obesity is not a feature leading to improved survival or decreased risk of hospitalization. Thus, these findings do not support the presence of an obesity paradox in CR participants with HFrEF.
Outcomes of this cohort are consistent with prior data. A 2019 Cochrane review assessed all-cause mortality from trials of CR in participants with HFrEF with >1 yr follow-up and demonstrated 17% mortality.6 Comparatively, mortality in the 5 yr following CR was 15% in our cohort. The same review assessed hospital admissions in CR participants with HFrEF in trials with >1 yr of follow-up and found an incidence of 57%. The overall incidence of hospitalization or emergency department visit in the 2 yr following CR was 58% in our cohort.
A key factor in negating the obesity paradox is that nonobese CR participants with HFrEF have better CRF than their obese counterparts. Although both groups demonstrate an improvement in absolute CRF via CR participation, nonobese participants showed a greater percentage improvement than their obese counterparts. The percentage increase in METs seen in obese and nonobese CR participants with HFrEF in our cohort is similar to past investigations. A 1996 study of obese CR participants with coronary artery disease demonstrated a 24% increase in METs upon completion of CR and nonobese participants saw a 36% increase.7 This is similar to the 21% and 39% increases seen in our study, suggesting that more directed interventions to improve CRF specifically in obese CR participants are needed.
Strengths of the current study include the proportion of women included (27%). The majority of studies exploring the obesity paradox in HF include a very limited number of women. For example, in a study that evaluated the impact of CRF on outcomes of obese patients with HFrEF, women accounted for only 15% of obese participants.3 Inclusion of women is vital to improve generalizability because previous studies demonstrate sex differences in CRF and mortality, as well as response to CR.8,9
A study limitation is that the results are only applicable in HFrEF and cannot be generalized to HF with preserved ejection fraction (HFpEF). The obesity paradox is not as consistently reported for HFpEF as it is for HFrEF.10 This may be, in part, due to a lack of reimbursement by Medicaid and Medicare for exercise-based CR in patients with HFpEF, leading to an absence of data. Despite this, studies demonstrate that exercise training improves cardiac function in patients with HFpEF. In addition, dietary caloric restriction and exercise training improve CRF and peak oxygen uptake in obese patients with HFpEF.11,12
Overall, the present observations do not support the presence of an obesity paradox in obese CR participants with HFrEF. Both obese and nonobese individuals demonstrate a similar risk of hospitalization or death. Although obese and nonobese patients with HFrEF improve CRF by participating in CR, nonobese patients experience a greater improvement.
Asad Khan, MD
Department of Internal Medicine,
Cleveland Clinic Foundation, Cleveland, Ohio
Erik H. Van Iterson, PhD
Luke J. Laffin, MD
Section of Preventive Cardiology and Rehabilitation,
Department of Cardiovascular Medicine,
Cleveland Clinic Foundation, Cleveland, Ohio
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