Heart failure is a global, chronic health problem affecting at least 26 million people worldwide and is increasing in prevalence, owing to advances in treatment modalities along with an aging population.1 In the United States, an estimated 6.2 million adults have chronic heart failure (CHF). Among adults 65 years and older, the incidence of heart failure is estimated to affect 21 in 1000 older adults. By the year 2030, CHF prevalence is expected to increase to 8 million adults, with direct costs expected to reach $69.8 billion in the United States.2 Adults with CHF frequently experience low exercise tolerance, poor quality of life (QOL), depression, and recurrent hospitalizations and are at greater risk for morbidity and mortality.3,4
Exercise-based cardiac rehabilitation is safe and effective for patients with CHF, with improved exercise tolerance, better QOL, and fewer CHF-related hospitalizations reported.4,5 Among older adults with CHF, reported benefits of cardiac rehabilitation include better physical function (eg, balance and gait speed) and improved exercise capacity and QOL, with less depression and social isolation.4 A recent systematic review and meta-analysis among adults with CHF having either reduced (<45%) ejection fraction or those with preserved (≥45%) ejection fraction found that exercise-based cardiac rehabilitation was effective in reducing overall hospitalizations (risk ratio, 0.70; 95% confidence interval [CI], 0.60–0.83) and improving QOL (standard mean difference, −0.60; 95% CI, −0.82 to −0.39; I2 = 87%), despite different types of exercise, doses, or delivery methods (eg, home vs clinic).3 However, cardiac rehabilitation services are greatly underused among adults with CHF, with only 10% (heart failure with reduced ejection fraction = 12.2%, heart failure with preserved ejection fraction = 8.8%) receiving a referral to cardiac rehabilitation upon discharge from hospital.6,7
Tai chi is a promising adjunct to exercise-based cardiac rehabilitation for adults with CHF.8–10 As a low-impact, low- to moderate-intensity exercise originating in China, tai chi is suitable for older adults to perform, including those with chronic health conditions or poor exercise tolerance.11,12 According to a systematic review examining adverse events reported in tai chi intervention studies,13 tai chi is a safe form of exercise. Reported adverse events were typically minor and primarily musculoskeletal related (eg, knee or back pain), whereas no intervention-related serious adverse events as a result of participation in tai chi were reported.13 Reported benefits of tai chi exercise include improved physical function such as reduced blood pressure among hypertensive adults,14,15 better balance, strength and flexibility,16,17 fewer falls,18,19 and improved aerobic endurance.20,21 Other reported benefits include improved cognitive function,22 less stress, anxiety, depression, and better QOL.10,23 Qualitative research conducted among adults with CHF confirms these findings, relating better physical and mental health, such as walking ability, energy, social support, and empowerment, after participation in a tai chi intervention.24,25 Given the reported benefits, there has been increasing interest in using tai chi exercise for adults with CHF.
To date, a total of 4 meta-analyses focused on CHF have been conducted, examining the effectiveness of tai chi.12,26–28 However, these meta-analyses were limited in scope (eg, search limited to 2 or 4 databases),12,27 included data from the same study twice (second article was a secondary analysis reporting outcome data on the same participants),26,28 or included studies with a high risk of bias (lack of allocation concealment and blinding of outcome assessors absent).26,28 Thus, the aim of this systematic review and meta-analysis was to address these issues, examining clinical trials published during the past 15 years, to assess the potential benefits of tai chi exercise among persons with CHF.
This systematic review and meta-analysis is reported in accordance with the Preferred Reporting Items of Systematic Reviews and Meta-analysis guidelines29 and conforms with the principles outlined in the Declaration of Helsinki.
An electronic literature search was conducted using the following databases: Allied and Complementary Medicine Database, Cumulative Index to Nursing and Allied Health Literature, Embase, OpenGrey, PsycARTICLES, PsycINFO, PubMed, Scopus, SPORTDiscus, and Web of Science. The following terms were utilized in the search: tai ji OR tai chi OR tai chi chuan AND heart failure OR cardiac failure OR chronic heart failure OR congestive heart failure. The search was limited to humans, clinical trials, full-text articles, and published in English or German languages between January 1, 2004, and August 1, 2019. The search was limited to the past 15 years, given the advances in diagnostic modalities and treatment of heart failure, as newly developed medications and devices for heart failure have been widely adopted in clinical practice, unlike in years before 2004.30 An example of the search in PubMed can be found in Appendix A.
Full-text articles using a clinical trial study design (ie, randomized clinical trial [RCT] or quasi-experimental study with a comparison group), incorporating a tai chi exercise intervention, among individuals with heart failure (all types) were included. There were no limits according to age, gender/sex, outcome, the type of control/comparison groups, or the tai chi intervention frequency, intensity, time, or type.
After removing duplicates of articles retrieved, 2 reviewers (RTP and BF) independently screened the titles and abstracts of potentially eligible articles to determine whether the articles satisfied the eligibility criteria. After initial screening, full-text manuscripts of potential articles were retrieved and reviewed in detail according to eligibility criteria.
Two reviewers (RTP and BF) extracted data independently in a standardized manner. Data pertinent to location, study design, participant population, intervention and control/comparison groups, outcomes measured, and challenges to scientific rigor were recorded. Inclusion and exclusion of studies were conducted in accordance with the Preferred Reporting Items of Systematic Reviews and Meta-analysis guidelines.29
Comprehensive Meta-Analysis Version 2.0 software (Biostat, Inc, Englewood, New Jersey) was used to calculate effect sizes (ie, Hedges g) and 95% CIs using random-effects models, to estimate the mean of the distribution of effects that could have been observed (eg, different participants or intervention protocols). Hedges g was used to calculate the standardized mean difference and is similar to Cohen d, but with an adjustment to correct bias inherent when using Cohen d with small sample sizes.31 Using the random effects model, the individual study weights are more balanced; thus, the summary effect is more conservative. In addition, the ratio of true heterogeneity to total observed variation was also calculated using the I2 statistic, as the number of studies in the analysis does not directly affect I2. I2 is not scale dependent but is expressed as a ratio ranging from 0% to 100% (25% = low, 50% = moderate, 75% = high heterogeneity). Meta-analyses were conducted when at least 3 studies reported the same outcome.
Study Quality of Individual Studies
Study quality was assessed using a modified version32 of the Downs and Black Quality Index checklist.33 The Quality Index checklist is widely used with established psychometric properties for determining the methodological quality of both RCTs and nonrandomized studies.34–36 The Quality Index checklist contains 27 items to evaluate reporting (10 items), external validity (3 items), bias (7 items), confounding (6 items), and power (1 item) of published studies. In 2005, the Agency for Healthcare Research and Quality used a modified version of Downs and Black Quality Index checklist for an evidence report on perinatal depression.32 The modified Quality Index checklist simplified the 1-item power question. All of the items are scored either as a 1 (yes) or 0 (no or unable to determine), except for 1 item reporting the distribution of potential confounders (yes = 2, partial = 1, no = 0) and the single item on power, which is scored from 0 to 2 (ie, power analysis conducted: yes, ≥2 outcomes = 2; yes, 1 outcome = 1; no = 0). Possible scores range from 0 to 29, with the higher score representing a higher quality study (low quality = score ≤14, moderate quality = score 15–23, high quality = score ≥24). Two reviewers (RTP and BF) independently assessed the studies using the modified Downs and Black Quality Index checklist.32 Any discrepancy in scoring was reviewed until a consensus was reached.
Figure 1 summarizes the literature search and study selection process. The search identified a total of 127 potential articles. After removing 45 duplicates, 82 articles were screened for inclusion based on the title and abstract. After screening, a total of 72 articles were excluded. The main reasons for exclusions were the study design (eg, qualitative, descriptive, review papers, protocols, commentaries), not using a tai chi intervention, inappropriate study sample (ie, no heart failure diagnosis), or no full-text article available (eg, abstract only).
A total of 6 clinical trials (5 RCTs37–41 and 1 quasi-experimental study with a comparison group42) met the inclusion criteria (Table 1). These studies were conducted in North America (67%, n = 4) or Europe (33%, n = 2), and all were published in English. A total of 299 participants with CHF enrolled in these studies. These participants were on average 68 years old and most were men (72%). Participants had on average a New York Heart Association functional class II, although it ranged from I to IV, with left ventricular ejection fraction ranging from 23% to 63.5%.
Tai Chi Intervention
The Yang style of tai chi was most commonly practiced in these studies (n = 5, 83%), whereas 1 study used the Wu style of tai chi.37 The study intervention length for most studies (n = 5, 83%) was 12 weeks with 2 sessions provided each week (total = 24 sessions), whereas 1 study had a 16-week intervention with 2 sessions each week (total = 32 sessions).37 Intervention adherence was only reported by 67% of these studies (n = 4). Among the studies reporting intervention adherence rates, the average was approximately 84% (range, 75%–89%; Table 1).
Usual care (n = 3 studies) was the most common control condition, followed by other aerobic exercise (n = 2 studies) or a health education-control (n = 1 study). Adherence rates to these control conditions were reported by only 33% of these studies (n = 2), with adherence rates of 67% or 88% reported (Table 1).
These studies mainly assessed exercise capacity (n = 5 studies), QOL (n = 5 studies), depression (n = 4 studies), and B-type natriuretic peptide (n = 4 studies). Other reported outcomes were echocardiograms,41 physical activity,39,41 exercise self-efficacy,39,41 fatigue,42 lower body strength,38 fall risk,39 plasma norepinephrine,40 and 24-hour electrocardiograms.40
Meta-analyses were conducted when there were at least 3 studies reporting the same outcome. Exercise capacity was assessed using a variety of measures including cycle ergometers, a 6-minute walk test, or an incremental shuttle walk test. The 6-minute walk test or the incremental shuttle walk test data were used to quantify exercise capacity in the meta-analysis. Quality of life was assessed using either the Minnesota Living With Heart Failure Questionnaire, a visual analog scale, or the MacNew Quality of Life After Myocardial Infarction questionnaire. The Minnesota Living With Heart Failure Questionnaire or the visual analog scale was used to quantify QOL in the meta-analysis. Depression was assessed using the Profile of Mood States depression scale, the Beck Depression Inventory, or the Symptom Checklist-90-Revised depression scale. B-type natriuretic peptide was assessed using a commercially available fluorescence immunoassay, whereas N-terminal pro-B type natriuretic peptide was assessed using an electrochemiluminescence immunoassay (Table 1).
Methodological Quality of the Individual Studies
The average study quality of the clinical trials using the modified Downs and Black Quality Index checklist32 was moderate (mean score, 23; range, 18–27; Table 2). Among the studies included in this meta-analysis, potential internal and external validity weaknesses identified challenges to scientific rigor. Internal validity weaknesses comprised unknown intervention adherence rates with potentially inadequate tai chi doses, differential dropout rates among groups, potential testing bias as outcomes were assessed multiple times, and small samples with insufficient power to detect significant differences between groups. External validity weakness encompassed the limited representativeness of the study samples, study replication difficulties as some interventions were not well described, along with possible interaction effects as treatment variation was possible because of different instructors (Table 1).
Synthesis of Results
Meta-analyses were conducted for exercise capacity, QOL, depression, and B-type natriuretic peptide, as at least 3 studies assessed these outcomes. When tai chi was compared with controls, a significant small effect for better exercise capacity (Hedges g = 0.353; P = .026, I2 = 32.72%; Figure 2A), a significant moderate effect for better QOL (g = 0.617; P = .000, I2 = 0%; Figure 2B), a significant moderate effect for less depression (g = 0.627; P = .000, I2 = 0%; Figure 2C), and a significant small effect for lower B-type natriuretic peptide expression (g = 0.333; P = .016, I2 = 0%; Figure 2D) were found.
Reports of Safety and Adverse Events
A total of 3 clinical trials reported serious adverse events that occurred during the study period, although none were attributable to the tai chi intervention or study protocol. Two studies reported that no serious adverse events occurred during the study, whereas 1 study failed to report if there were any adverse events (Table 1).
This systematic review and meta-analysis of clinical trials published during the past 15 years was conducted to assess the benefits of tai chi exercise interventions among adults with CHF. Overall, the meta-analysis results indicate that tai chi led to significantly better exercise capacity, improved QOL, less depression, and lower B-type natriuretic peptide level, compared with controls. Our findings extend previously published systematic reviews and meta-analyses12,26–28 by using a comprehensive search of relevant articles from 10 electronic databases and only including studies with moderate or higher study quality. Consistent with previous meta-analyses, we found statistically significant improvements in exercise capacity12,26–28 and QOL,26–28 although previous meta-analyses included data from the same study twice,26,28 which may have overestimated the effects reported. In previous meta-analyses, depression was not assessed,26–28 and B-type natriuretic peptide expression was either not assessed,12 had nonsignificant findings,27 or included data from the same study twice.26,28 Furthermore, our findings support recommendations from the European Society of Cardiology that adults with heart failure participate in regular exercise to improve aerobic capacity and QOL.43 However, the most recent heart failure guidelines from the American College of Cardiology/American Heart Association Task Force focus on management of patients with heart failure, specifically pharmacological treatment for heart failure with reduced ejection fraction or heart failure with preserved ejection fraction, and management of important comorbidities.44 While these heart failure guidelines recommend assessment of B-type natriuretic peptide or N-terminal pro-B type natriuretic peptide to establish severity of heart failure, exercise recommendations or guidelines for heart failure were not included,44 with the most recent heart failure exercise guidelines published in 2003.45
Tai chi exercise is considered a low- to moderate-intensity exercise, similar to other types of exercise used among adults with CHF, with the 6-minute walk test frequently used as an indicator of exercise capacity. Our results are similar to findings of other meta-analyses, that exercise capacity among adults with CHF significantly improved after combined aerobic and resistance training,46 resistance training only,47 or exercise-based cardiac rehabilitation,48 when compared with usual care. Two recent studies support these findings with significant improvements in exercise capacity (6-minute walk test, P < .001) among adults with CHF (eg, heart failure with reduced ejection fraction or heart failure with preserved ejection fraction) reported after either a 12-week walking program49 or supervised exercise training (cycle ergometer at 60%–70% max effort),50 compared with usual care controls.
Quality of life is another important indicator of health and well-being, with the Minnesota Living With Heart Failure Questionnaire commonly used among adults with HF. Our results examining the effect of tai chi on QOL are similar to other meta-analyses reporting significantly better QOL after combined aerobic and resistance training,46 resistance training only,47 or exercise-based cardiac rehabilitation,48 compared with usual care. Moreover, the meta-analysis conducted by Palmer and colleagues48 reported that exercise-based cardiac rehabilitation led to a clinically significant improvement in QOL (−8.5 points on the Minnesota Living With Heart Failure Questionnaire). Two recent RCTs support these findings, with significantly better QOL among persons with CHF participating in either a low-intensity (walking, P = .02)49 or moderate-intensity (cycle ergometer, P < .001) exercise.50 As a low- to moderate-intensity exercise, tai chi is a viable exercise option among persons with CHF to foster improved QOL. However, our findings are in contrast to an RCT among persons with heart failure with preserved ejection fraction in a supervised endurance plus resistance training program, reporting no significant difference in QOL postintervention (P = .07), compared with usual care.51
In this meta-analysis, tai chi led to significantly less depression postintervention, compared with controls. Our results are similar to a recent study among persons with CHF reporting mild to moderate depression, participating in 12 weeks of supervised moderate-intensity exercise (treadmill at 60%–70% max effort) and reporting less depression (P = .001) postintervention, compared with usual care.52 However, these findings are in contrast to reported results from a combined aerobic and resistance training meta-analysis (P > .05),46 a 12-week walking program (P = .06),49 and a 12-week supervised endurance plus resistance training program (P = .735) among adults with CHF,51 that no improvements in depression were found when compared with usual care. Nevertheless, tai chi is considered a mind-body exercise and less depression is frequently reported among persons with chronic health conditions10,53; thus, tai chi likely offers mental health benefits beyond traditional western exercise.
The assessment of cardiac dysfunction in patients with CHF typically includes either B-type natriuretic peptide or N-terminal pro-B type natriuretic peptide blood tests, as an increase in these peptides reflects a diminished capacity of the heart to deliver oxygenated blood to the body. According to the European Society of Cardiology heart failure guidelines, blood test values for B-type natriuretic peptide levels greater than 100 pg/mL or N-terminal pro-B type natriuretic peptide levels greater than 300 pg/mL indicate symptomatic heart failure, warranting further diagnostic investigation.43 In this meta-analysis, we found that tai chi led to significantly less B-type natriuretic peptide expression postintervention, compared with controls. Our results are similar to a recent RCT among adults with CHF (average left ventricular ejection fraction, 48%), reporting significantly lower (P < .001) B-type natriuretic peptide, after 12 weeks of supervised exercise training (cycle ergometer at 60%–70% max effort), compared with usual care.50 The decrease in B-type natriuretic peptide levels suggests a more stable heart failure condition after the exercise intervention.
There are several limitations to this study. First, both RCTs and quasi-experimental studies with a comparison group were included. However, comprehensive quality assessments of all included studies were conducted using an established checklist32,33 and were found to be either moderate37,38,42 or high39–41 quality. Second, moderate (32.72%) heterogeneity was observed for the exercise capacity meta-analytic outcome; however, no (0%) heterogeneity was observed for the other meta-analytic outcomes: QOL, depression, and B-type natriuretic peptide expression. Finally, our analyses were limited to full-text articles written in English, which may have omitted relevant literature published in other languages. However, this systematic review and meta-analysis was reported following established Preferred Reporting Items of Systematic Reviews and Meta-analysis guidelines, with 2 independent reviewers conducting the literature search, extracting the data, and assessing study quality.
Suggestions for Future Research
Considering the paucity of studies conducted to date, it is imperative that further research using tai chi among persons with CHF be conducted. Future research is suggested to examine biological, psychological, and social factors underpinning tai chi that may lead to improved health and well-being among adults with CHF. Further investigation of tai chi as a nonpharmacological intervention for reducing depressive symptoms among patients with CHF is warranted. Going forward, it is important that future studies report tai chi instructor training, tai chi style, number of postures, and intervention adherence rates.
Among adults with CHF, tai chi was effective in improving exercise capacity and QOL, with less depression and B-type natriuretic peptide levels observed, when compared with controls. Tai chi is a safe form of exercise and can be easily integrated into existing cardiac rehabilitation programs using either classes in person or remotely via online video instruction at home. Across the studies reviewed, small to moderate improvements within physical health (ie, exercise capacity, B-type natriuretic peptide levels) and mental health (ie, QOL and depression) domains were detected. However, few studies in the past 15 years have examined the benefits of tai chi among adults with CHF. Further research is needed with rigorous study designs, diverse samples inclusive of women, and adequate descriptions of important tai chi exercise intervention features.
What’s New and Important
- Tai chi is suitable for older adults to perform, including those with chronic health conditions (eg, CHF) or poor exercise tolerance.
- Meta-analytic evidence indicates tai chi improves exercise capacity and QOL, decreases depression, and lowers B-type natriuretic peptide levels among adults with CHF, when compared with usual care controls.
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