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To conduct a systematic review of the literature evaluating tai chi exercise as an intervention for patients with cardiovascular disease (CVD) or with cardiovascular risk factors (CVRF).
We searched: 1) Medline, CAB Alt Health Watch, BIOSIS previews, Science Citation Index, EMBASE, and Social Science Citation Index from inception through October 2007; 2) Chinese Medical Database, China Hospital Knowledge, China National Knowledge Infrastructure, and China Traditional Chinese Medicine Database from inception through June 2005; and 3) performed hand searches at the medical libraries of Beijing and Nanjing Universities. Clinical studies published in English and Chinese including participants with established CVD or CVRF were included. Data were extracted in a standardized manner; 2 independent investigators assessed methodological quality, including the Jadad score for randomized controlled trials (RCT).
Twenty-nine studies met inclusion criteria: 9 RCT, 14 non-randomized studies (NRS), and 6 observational trials (OBS). Three studies examined subjects with coronary heart disease, 5 in heart failure, and 10 in heterogeneous populations that included those with CVD. Eleven studies examined subjects with CVRF (hypertension, dyslipidemia, impaired glucose metabolism). Study duration ranged from 8 weeks to 3 years. Most studies included <100 subjects (range 5–207). Six of nine RCTs were of adequate quality (Jadad ≥3). Most studies report improvements with tai chi, including blood pressure reductions and increases in exercise capacity. No adverse effects were reported.
Preliminary evidence suggests that tai chi exercise may be a beneficial adjunctive therapy for some patients with CVD and CVRF. Further research is needed.
Cardiovascular disease is clearly an important public health problem, with 1 in 3 American adults affected.1 Mortality due to underlying cardiovascular disease accounts for more than one-third of all deaths. The evidence from long-term prospective studies consistently suggests that the majority of cardiovascular disease is preventable with healthy lifestyles and modification of known risk factors.2 While pharmacological therapy is often emphasized, the critical importance of non-pharmacological approaches and lifestyle modifications, including physical activity and exercise, continues to be recognized for both primary and secondary prevention of cardiovascular disease.
In recent years, with the popularity and prevalence of mind-body therapies, there has been a growing interest in tai chi exercise for patients with cardiovascular disease.3–5 Tai chi (t’ai chi or taiji) has origins in ancient Chinese martial arts and combines gentle physical activity, with elements of meditation, body awareness, imagery, and attention to breathing. The scientific literature describing tai chi is varied, with studies reporting benefits in a number of health conditions, from balance and reduction of falls in frail adults, to improvements in quality of life and symptoms in rheumatoid arthritis, human immunodeficiency virus, cancer, and heart failure.6,7 A substantial amount of research examines the cardiovascular effects of tai chi, including cardiorespiratory fitness and exercise capacity, although most data are available for blood pressure.4,8–10
To date, there have been no comprehensive systematic reviews examining the use of tai chi specifically in patients with cardiovascular conditions, and very little is known about what is published in the Chinese language. Our objective was to conduct a systematic review of the Chinese and English language literature on tai chi exercise as an intervention for patients with cardiovascular disease and cardiovascular risk factors, and to offer recommendations for future research.
We conducted electronic literature searches of Medline (from 1966), CAB (from 1973), Alt Health Watch , BIOSIS previews (from 1969), Science Citation Index (from 1945), EMBASE (from 1991) and the Social Science Citation Index (from 1956) through October 2007 using search terms “tai chi,” “tai chi chuan”, “ta’i chi,” “tai ji,” and “taijiquan." In addition, we performed searches of the Chinese Medical Database, China Hospital Knowledge, China National Knowledge Infrastructure, and China Traditional Chinese Medicine Database from inception to June 2005, and performed hand searches at the medical libraries of Beijing and Nanjing Universities in China. We also performed hand searches of retrieved articles for additional references.
Available human clinical studies published in English and Chinese which specified a target study population of subjects with a known cardiovascular condition or with cardiovascular risk factors (including hypertension, dyslipidemia, and diabetes) were included. Studies that specifically examined subjects with stroke were not included. Studies that examined cardiovascular outcomes in healthy individuals were not included (eg, blood pressure or cholesterol in subjects with normal baseline blood pressure or lipid profiles).
Data were extracted in a standardized manner by 2 independent reviewers. Data were extracted from Chinese language articles with direct translation to English. To assess methodological quality of studies, we developed an A,B,C summary quality grading system adapted from methods used in Evidence Reports of the AHRQ Evidence-Based Practice Centers (www.ahrq.gov/clinic/epcindex.htm). Two independent investigators assessed methodological quality, evaluating each study according to specific criteria for each study design type (randomized controlled trial [RCT], prospective non-randomized controlled and non-controlled studies [NRS], and observational controlled and non-controlled studies [OBS]) and assigning an A, B, or C grade based on the potential for bias in the study. Summary quality grading criteria for each of the 3 design strata are listed in Table 1. This system evaluates and rates studies within each of the study design strata. By design, it does not attempt to assess the comparative validity of studies across different design strata. Thus, in interpreting the methodological quality of a study, one should note the quality grade and the study design. Grade A was given to studies where there appeared to be the least amount of bias and results were likely valid. Grade B was given to studies that appeared susceptible to some bias, but not sufficient to invalidate the results. Grade C was given to studies with evidence of significant bias that may invalidate the results. For RCTs, in addition to the summary quality grade, we also indicate a modified Jadad score. Because in most cases, double-blinding is impractical in tai chi studies, our modification gives one point for proper single blinding of the outcome assessors. Grading discrepancies between the independent reviewers occurred rarely and were resolved via discussion.
We screened 841 English-language and 859 Chinese-language abstracts and full text articles for potentially relevant data. A total of 31 studies (14 in English, 17 in Chinese) met the inclusion criteria. Two Chinese studies were excluded: one due to poor quality and insufficient information for data extraction, and one that reported on children with cardiac murmurs and congenital heart disease.11,12 The remaining 29 studies were analyzed, including 9 RCTs, 14 NRS, and 6 OBS.13–41 Studies were conducted in 1) homogeneous populations of subjects with reported coronary heart disease or heart failure (Table 2), in 2) heterogeneous populations with a proportion of subjects having a cardiovascular condition (eg, coronary disease, arrhythmia, “cardiovascular condition” not otherwise specified) (Table 3), and in 3) both homogeneous and heterogeneous populations of subjects with cardiovascular risk factors (ie, hypertension, dyslipidemia, impaired glucose metabolism or diabetes mellitus) (Table 4). Within these trials, reported outcomes included blood pressure, heart rate, exercise capacity, heart rate variability, lipids, fasting glucose, pulmonary function, cardiac hemodynamic indices, functional measures, flexibility, mood and quality-of-life. Study duration ranged from 8 weeks to 3 years. Most studies included <100 subjects (range 5–207). Study heterogeneity precluded formal meta-analysis. No adverse events associated with tai chi were reported. Of the 9 RCT’s, 5 received an A rating and 2 received a B rating. Of the 14 NRS, 10 received a B rating. Of 6 OBS, 1 received an A rating and 5 received a B rating.
The data are limited with only 3 studies that specifically studied patients with coronary disease.13–15 In the only RCT, Channer et al13 randomized patients recovering from an acute myocardial infarction to a mixed tai chi/qigong intervention or to conventional aerobic exercise or to a cardiac support group. After 8 weeks, both aerobic exercise and tai chi were associated with significant reductions in systolic blood pressure (SBP) (−4 ± 7.5 and −3 ± 3.3) mmHg, respectively, both P<.05). Diastolic blood pressure (DBP) was improved in the tai chi group only (−2 ± 2.7 mmHg, P<.01). No between-group comparisons were made. This study also reported decreases in resting heart rate and greater compliance with tai chi class.13
Similarly, there were only 5 studies examining patients with heart failure. Two of 3 RCTs were of adequate quality.16,20 Yeh et al16 randomized patients to a tai chi intervention or to usual care. After 12 weeks, patients who practiced tai chi showed an increase in exercise capacity (+84 ± 45 vs. −51 ±88 meters on a 6-minute walk, P<.01), improved B-type natriuretic peptide(−48 ± 105 vs. +89 ±210 pg/ml, P=.03) and improved disease-specific quality of life using the Minnesota Living with Heart Failure Questionnaire, compared with the control group.16 Barrow et al20 found similar results in quality of life using a 16-week tai chi intervention compared to usual care. No difference was seen, however, between groups in exercise tolerance using the incremental shuttle walk test. A correlation was reported between home practice time and improvement in walk distance.20 Other small, prospective, non-randomized studies provide limited evidence for improvements in physiological parameters and functional capacity.18,21 Of note, both Chinese language studies report improvements in left ventricular ejection fraction.19,21
Ten studies (5 NRS, 5 OBS) examined tai chi in heterogeneous populations that included some proportion of subjects with cardiovascular disease (eg, coronary heart disease). These studies vary in quality and report improvements in blood pressure, resting heart rate (HR) HR, HR recovery after exercise, and cardiac hemodynamics such as stroke volume and cardiac output. Two studies included patients with chronic obstructive pulmonary disease and reported improvements in pulmonary function tests (increased vital capacity, total lung capacity, and forced vital capacity) after tai chi (within group analysis) and compared with usual care.23,25 Three observational studies with heterogeneous cardiovascular populations were designed to examine tai chi’s acute physiological effects and to measure tai chi exercise intensity. These studies report conflicting results with respect to direction of change acutely in heart rate and blood pressure. No adverse effects were reported.
Four RCT’s were available that report on blood pressure changes in patients with hypertension.30–33 All 4 studies report a reduction in blood pressure with tai chi (usually a 12 week intervention). In the highest quality of these, Young et al compared a light intensity tai chi program that “emphasized physical movements rather that meditational aspects” to moderate intensity walking and low-impact aerobic dance.30 They reported comparable blood pressure changes (±SD) in both groups (−7.0 ± 8.8 vs. −8.4 ± 8.8) mmHg SBP; −2.4 ±5.5 vs. −3.2 ±5.5 mmHg DBP, respectively), however, no difference between groups. Of note, they did report higher compliance with home exercise in the tai chi group.
Two RCTs are available that examined changes in lipid profile. While Tsai et al31 reported reductions in total cholesterol (−15.2 md/dL), LDL (−20 md/dL), TG (−23.8 mg/dL) and increases in HDL (+4.7 mg/dL) after 12 weeks of tai chi in patients with hypertension compared to usual care, Thomas et al32 reported no change in these same parameters in a mixed population that included more than half of patients with dyslipidemia. One larger observational trial conducted in China did suggest improvements in lipid parameters.41
Two RCTs are available that examined changes in glucose metabolism, suggesting no effect with tai chi.32,34–35 Tsang et al34 reported no change in insulin resistance or sensitivity (0 vs. −0.1 Homeostasis Model Assessment Index 2 (HOMA2)-insulin resistance and −0.8 vs. 5 for HOMA2%-insulin sensitivity), hemoglobin A1c (HgbA1C) (−0.07% vs. 0.12%), or body composition (−0.39 vs. −0.07 kg/m2, body-mass index) after 16 weeks of tai chi compared to calisthenics and gentle stretching in patients with type 2 diabetes. There was a reduction in body fat in both groups, although no difference between groups. Thomas et al32 compared 12 weeks of tai chi to strength and resistance training and to usual care in elder participants with cardiovascular risk factors. Fasting glucose and HgbA1C were reduced in each of the groups (−0.5 vs. −0.5 vs. −0.3 mmol/L and −0.3% vs. −0.3% vs. −0.3% in tai chi, resistance training, control groups, respectively), yet there were no differences between groups. Only 14% of this study population had impaired glucose metabolism at baseline. One NRS did suggest modest reductions in HgbA1C and reductions in fasting glucose.40
The available studies suggest that tai chi exercise may have beneficial effects for patients with cardiovascular conditions and some cardiovascular risk factors, although the literature to date is limited. Very few studies specifically examine patients with coronary artery disease or heart failure, although the available studies report positive results in both functional and physiological parameters. In investigations of patients with cardiovascular risk factors, most information is available on blood pressure effects and hypertension. The data on tai chi’s effect on lipids and glucose metabolism are unclear. More than half of the studies in this review were published in Chinese and offer data that have historically been excluded from other reviews.
Given the existing evidence, tai chi exercise may be a reasonable adjunct to conventional care. It may be appropriate for those unable or unwilling to engage in other forms of physical activity, or as a bridge to more rigorous exercise programs in frail or de-conditioned patients. Patients with early detection of cardiovascular risk factors (eg, borderline hypertension) may be reluctant to begin drug therapy and non-pharmacological approaches are often welcomed. These lifestyle interventions have been recognized as important and effective strategies for primary prevention.42 In addition, patients with either pre-hypertension or established hypertension, who otherwise feel well, may be less motivated and find it difficult to engage in and maintain a regular exercise regimen. Finding an appropriate, non-threatening, easy-to-perform activity that patients will maintain is critical to therapeutic success. Clinical trials have reported excellent compliance with tai chi interventions, and suggest that tai chi may promote exercise self-efficacy.43,44 Likewise, exercise is a well-recognized and effective strategy for secondary prevention in patients with established cardiovascular disease. Unfortunately, studies have continued to show that conventional cardiac rehabilitation programs are underutilized.45 Therapies such as tai chi may offer patients additional options, whether as an adjunct to formal cardiac rehabilitation, as a part of maintenance therapy, or as an exercise alternative at any point along this continuum.
Collectively, these studies suggest that tai chi may be safe for patients with cardiovascular disease. The three studies with higher-risk coronary patients reported no adverse effects.13–15 In addition, exercise intensity of tai chi can be easily modified. Many studies have reported metabolic equivalents of 1.5–4.0 (approximately low-moderate intensity aerobic exercise), which may be a reasonable exercise level for even the more deconditioned cardiac patient.46–48
The quality of studies within this review varied significantly. Overall, quality was poorer in the Chinese language studies (6/15 vs. 0/14 earning a C rating) compared to English language studies. The majority of studies earned a B rating. Since most studies reported positive results, the possibility of publication bias exists. In addition, we were unable to perform meta-analyses due to study heterogeneity (with differences in design, selection of control, as well as intervention style, intensity, and dose/duration). There were also inherent limitations in our use of the Jadad scale, given the nature of tai chi trials and the difficulty and impracticality of double-blinding. Despite these limitations, this review provides the first comprehensive synthesis of both English and Chinese language literature describing the use of tai chi exercise in cardiovascular populations.
There is a clear need for more rigorous research of tai chi for cardiovascular health. However, as with many other mind-body interventions, tai chi is unlike a standardized pharmaceutical and inherently heterogeneous, posing significant challenges to the design and interpretation of studies. The current literature represents a mix of different styles, protocols, intervention dose and duration, emphases (eg, meditation vs. movement), combinations of other activities (eg, qigong warm-ups), and types or qualifications of instructors. On a further level, tai chi is heterogeneous because it integrates multiple therapeutic components (eg, musculoskeletal efficiency, breathing, mindfulness, psychosocial interaction, and rituals).49 For future studies, we will need to better address this heterogeneity and complexity. At the least, we will need larger sample sizes, clear reporting standards so that interventions are well-described and reproducible, and carefully chosen outcome measures that measure both mechanisms of effect and clinical efficacy.
Several trials are currently ongoing, including 2 independent investigator groups studying tai chi for patients with heart failure at Beth Israel Deaconess Medical Center/Harvard Medical School in Boston and the Veterans Research Medical Foundation in San Diego. A preliminary trial of tai chi in obese patients with cardiovascular risk factors is currently ongoing at Queen’s Medical Center in Honolulu. With these and future thoughtfully-designed investigations, we may better understand the benefits, mechanisms, and role of tai chi exercise in the prevention and management of cardiovascular disease.
Support: Dr. Yeh was supported by a career development award from NIH NCCAM (K23AT002624).