A systematic review of yoga for heart disease

Abstract

Background

This systematic review of randomized controlled trials (RCTs) aimed to evaluate the quality of evidence and the strength of recommendation for yoga as an ancillary intervention for heart disease.

Methods

Medline/PubMed, Scopus, the Cochrane Library, and IndMED were searched up to October 2013. Main outcome measures were mortality, nonfatal cardiac events, exercise capacity, health-related quality of life, and modifiable cardiac risk factors. Risk of bias, quality of evidence, and the strength of the recommendation for or against yoga were assessed according to the Cochrane Collaboration and GRADE recommendations.

Results

Seven RCTs with 624 patients comparing yoga to usual care were included. For coronary heart disease (four RCTs), there was very low evidence for no effect on mortality, for a reduced number of angina episodes, and for increased exercise capacity, and low evidence for reduced modifiable cardiac risk factors. For heart failure (two RCTs), there was very low evidence for no effect on mortality, and low evidence for increased exercise capacity, and for no effect on health-related quality of life. For cardiac dysrhythmias treated with implantable cardioverter-defibrillator (one RCT), there was very low evidence for no effect on mortality, and for improved quality, and low evidence for effects on nonfatal device-treated ventricular events. Three RCTs reported safety data and reported that no adverse events occurred.

Conclusions

Based on the results of this review, weak recommendations can be made for the ancillary use of yoga for patients with coronary heart disease, heart failure, and cardiac dysrhythmia at this point.

Cardiac dysrhythmia, cardiology, complementary therapies, coronary heart disease, heart failure, review, yoga

Background

Heart disease is the most common cause of death worldwide.^1–3 In 2008, an estimated 7.3 million people died from coronary heart disease alone.² Men and women were almost equally affected.⁴ Being one of the major noncommunicable diseases, coronary heart disease constitutes a substantial socioeconomic burden in all countries worldwide.^1,5 Other heart diseases including cardiomyopathy, heart failure, cardiac dysrhythmia, and valvular heart disease also have emerged as major health challenges with increasing prevalence.^1,2,6–8 Modifiable risk factors are the main cause of the majority of heart diseases:^4,9 the most important risks include hypertension, hyperlipidaemia, hyperglycemia, and abdominal obesity. Besides biological risk factors, psychosocial variables, mainly depression and psychosocial stress, account for a considerable risk of heart disease.⁹ Medical guidelines recommend medication, surgical interventions as well as lifestyle modification such as regular exercise, dietary advice, and stress management.¹⁰

Yoga is a mind/body medical intervention that includes all those lifestyle aspects. Traditionally rooted in Indian philosophy and spiritual practice,¹¹ yoga has been adapted for use in complementary and alternative medicine in North America and Europe.¹² In Western societies, it is most often associated with physical postures (‘Asana’), breath control (‘Pranayama’), and meditation (‘Dhyana’); traditional yoga on the other hand often also includes lifestyle and dietary advice.^11,12 Yoga is thought to improve physical health, calm the mind, and provide relaxation.¹³ Yoga is now increasingly used as a therapeutic intervention. More than 13 million American adults (about half of American yoga practitioners) reported that they had started to practice yoga explicitly to improve their health,^14,15 and about 14 million reported that yoga had been recommended to them by a physician or therapist.¹⁶

It has been demonstrated that yoga has the potential to improve psychosocial cardiovascular disease risk factors such as stress^17,18 and depression.¹⁹ Moreover, positive effects have also been found for biological risk factors such as hypertension,²⁰ hyperlipidaemia,²¹ and insulin resistance.²² However, the evidence of yoga for patients with diagnosed heart disease remains unclear.²³ The aim of this review was to systematically assess the effects of yoga on mortality, nonfatal cardiac events, exercise capacity, health-related quality of life, and modifiable cardiac risk factors in patients with coronary artery disease, cardiomyopathy, heart failure, cardiac dysrhythmia, and valvular heart disease.

Methods

The review was planned and conducted in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines²⁴ and the recommendations of the Cochrane Collaboration.²⁵

Eligibility criteria

Studies that were randomized controlled trials (RCTs), cluster-randomized trials or randomized cross-over studies were eligible. No language restrictions were applied.

Studies that included adult participants with coronary heart disease or angina pectoris, cardiomyopathy, heart failure or cor pulmonale, cardiac dysrhythmia, or valvular heart disease were eligible. Studies that compared the intervention yoga with usual care or nonpharmalogical interventions were eligible. No restrictions were made regarding yoga tradition, length, frequency, or duration of the programme. Cointerventions were allowed. Head-to-head comparisons of different types of yoga without a nonyoga control group were excluded.

To be eligible, studies had to assess at least one of the following main outcome measures: (1) mortality: all-cause mortality or cardiac mortality (myocardial infarction, sudden cardiac death, death from cerebrovascular disease); (2) nonfatal cardiac events (nonfatal myocardial infarction, angina episodes, severe arrhythmias, nonfatal cerebrovascular accident); (3) exercise capacity; (4) health-related quality of life (physical wellbeing, mental wellbeing, psychosocial distress); and (5) modifiable cardiac risk factors (blood pressure, blood lipid levels). Secondary outcome measures referred to safety (adverse events, serious adverse events).

Search methods

Medline/PubMed, Scopus, the Cochrane Central Register of Controlled Trials (Central), and IndMED were searched from their inception to 28 October 2013. Embase was not searched separately since it is included in Scopus. The literature search was constructed around search terms for ‘yoga’ and search terms for ‘heart disease’. The complete search strategy for Pubmed/Medline is shown in Table 1. The search strategy was adapted for each database as necessary.

Table 1.

Complete search strategy for Medline/Pubmed.

1	“Cardiovascular Diseases”[Mesh] OR “Cardiovascular Disease”[Title/Abstract] OR “Coronary Artery Disease“[Mesh] OR “Coronary artery disease”[Title/Abstract] OR “Coronary heart disease”[Title/Abstract] OR “Coronary Atherosclerosis”[Title/Abstract]
2	“Cardiomyopathies”[Mesh] OR “Cardiomyopathy”[Title/Abstract] OR “Myocardial disease”[Title/Abstract]
3	“Heart Failure”[Mesh] OR “Heart Failure”[Title/Abstract] OR “Cardiac Failure”[Title/Abstract] OR “Heart Decompensation”[Title/Abstract] OR “Pulmonary Heart Disease”[Mesh] OR “Pulmonary Heart Disease”[Title/Abstract] OR “Cor Pulmonale”[Title/Abstract]
4	“Arrhythmias, Cardiac”[Mesh] OR “Cardiac Arrhythmias”[Title/Abstract] OR “Cardiac Dysrhythmias”[Title/Abstract]
5	“Heart Valve Diseases”[Mesh] OR “Heart Valve Disease”[Title/Abstract] OR “Valvular Heart Disease”[Title/Abstract]
6	1 OR 2 OR 3 OR 4 OR 5
7	"Yoga"[Mesh] OR “Yoga”[Title/Abstract] OR “Yogic”[Title/Abstract] OR “Asana”[Title/Abstract] OR “Pranayama”[Title/Abstract] OR “Dhyana”[Title/Abstract]
8	6 AND 7

In addition, reference lists of identified original articles or reviews and the tables of contents of the International Journal of Yoga Therapy and the Journal of Yoga and Physical Therapy were searched manually.

Abstracts identified during literature search were screened and potentially eligible articles were read in full independently by three review authors (HC, RL, HH) to determine whether they met the eligibility criteria.

Data extraction and management

Data on participants (e.g. diagnosis, age, gender, race), interventions (e.g. yoga type, components, duration), control interventions (e.g. type, duration), outcomes (e.g. outcome measures, assessment time points), and results were extracted independently by two review authors (RL and HH) using an a-priori-developed data extraction form. Discrepancies were discussed with a third review author (HC) until consensus was reached.

As only few RCTs were expected to be eligible for the review and due to the broad research question that covered a number of different diseases, no meta-analysis was planned or performed.

Risk of bias in individual studies

Risk of bias was independently assessed by two review authors (RL and HH) using the Cochrane risk of bias tool.²⁵ Risk of bias was assessed on the following domains: selection bias (random sequence generation, allocation concealment), performance bias (blinding of participants and personnel), detection bias (blinding of outcome assessment), attrition bias (incomplete outcome data), reporting bias (selective reporting), and other bias as: (1) low risk of bias, (2) unclear, or (3) high. Discrepancies were discussed with a third review author (HC) until consensus was reached.

Quality of evidence

Based on the methodological quality and the confidence in the results across studies, the quality of evidence for each outcome in each disease group was assessed according to the GRADE recommendations.²⁶ After consideration of study limitations, inconsistency between studies, indirectness, imprecision, publication bias, and other bias, the quality of evidence was judged as: (1) high quality: further research is very unlikely to change the confidence in the estimate of effect; (2) moderate quality: further research is likely to have an important impact on the confidence in the estimate of effect and may change the estimate; (3) low quality: further research is very likely to have an important impact on the confidence in the estimate of effect and is likely to change the estimate; (4) very low quality: any estimate of effect is very uncertain.

Strength of recommendation

Based on the direction and quality of evidence and the risk of undesirable effects of the intervention, the strength of recommendation for or against yoga as a therapeutic option in a specific heart disease group was judged according to the GRADE recommendations as either strong or weak. Possible recommendations include: (1) strong recommendation against the use of yoga; (2) weak recommendation against the use of yoga; (3) strong recommendation for the use of yoga; and (4) weak recommendation for the use of yoga.²⁶

Results

Literature search

A total of 312 nonduplicate records were revealed by literature search, 291 of which were excluded because they were not RCTs, did not include patients with heart disease, and/or did not include yoga as an intervention. Twenty-one full texts were assessed for eligibility, and 13 articles were excluded because they were either duplicate publications of the same RCT,²⁷ were not randomized,^28–36 or included yoga only as a part of a multimodal intervention.^37–39 Seven RCTs on coronary heart disease (four RCTs), heart failure (two RCTs), and cardiac dysrhythmia (one RCT) with a total of 624 patients were finally included in the analysis^40–46 (Figure 1). The characteristics of the included studies and risk of bias in individual studies are shown in Tables 2 and 3, respectively.

Figure 1.

Flowchart of the results of the literature search.

Table 2.

Characteristics of the included studies.

Reference	Patients (diagnosis, N randomized, N analysed, age, gender)	Cointerventions	Intervention groups		Follow up	Outcome measuresa	Resultsb
			Treatment	Control
Mahajan et al.40	Patients with stable CAD/history of angina pectoris, 40 randomized, 40 analysed, 56–59 years, male	No lipid-lowering drugs	4 days yoga residential camp +60 min daily home practice for 14 weeks (postures, breathing, relaxation, meditation, vegetarian diet)	Usual care (diet, moderate aerobic exertion)	14 weeks	(5) Lipid profile: TC, HDL, ratio TC/HDL, LDL, TG	(5) Significant group differences in favour of yoga for TC, TC/HDL, LDL, TG; no significant differences for HDL
Manchanda et al.41	Patients with chronic stable CAD, 42 randomized, 51 years (range 32–72 years), male	Continued angina medication/no lipid-lowering drugs	4 days yoga residential camp +90 min daily home practice for 12 months (postures, breathing, relaxation, meditation, vegetarian diet)	Usual care (diet)	12 months	(1) Mortality	(1) None
						(2) Nonfatal cardiac events: angina episodes/week	(2) Significant group differences in favour of yoga for angina episodes/week and mean lesion severity
						(3) Exercise capacity: exercise duration, double product achieved, ST-segment depression	(3) Significant group differences in favour of yoga for exercise duration and ST-segment depression; no significant differences for double product achieved
						(5) Lipid profile: TC, HDL, LDL, LDL/HDL, TG	(5) Significant group differences in favour of yoga for TC, LDL, LDL/HDL, TG; no significant differences for HDL
						(6) Safety	(6) No side effects in either group
Pal et al.42	CAD patients, 170 randomized, 154 analysed, 58.8 years, 15.3% female	Angina medication	35–40 min yoga lessons, 5 days/week for 6 months (postures, breathing, relaxation)	Usual care	6 months	(1) Mortality	(1) One death in yoga group
						(5) Lipid profile: TC, HDL, LDL, TG; Blood pressure: SBP, DBP, HR	(5) Significant group differences for TC, HDL, LDL, TG, SBP, DBP, HR
Pal et al.43	CAD patients, 258 randomized, 208 analysed, 57.8 years, 19.8% female	Angina medication	35–40 min yoga lessons, 5 days/week for 18 months (postures, breathing, relaxation)	Usual care	18 months	(1) Mortality	(1) Five deaths (two in yoga group, three in control group)
						(5) Blood pressure: SBP, DBP, HR	(5) Significant group differences in favour of yoga for SBP, DBP, HR
Pullen et al.44	Patients with chronic HF (NYHA class I to III), 19 randomized and analysed, 51.3 years, 58% female	HF medication	70 min yoga lessons, 2 days/week +1 or more days/week home practice for 8 weeks (postures, breathing, meditation, relaxation, education, home walk programme)	Standard medical care (education, home walk programme)	8 weeks	(1) Mortality	(1) None
						(3) Exercise capacity: treadmill time, VO2peak	(3) Significant group differences in favour of yoga for treadmill time and VO2peak
						(4) Health-related quality of life: MLHFQ	(4) No significant group differences for MLHFQ
						(6) Safety	(6) No AE in either group
Pullen et al.45	Patients with chronic HF (NYHA class I to III), 40 randomized and analysed, 54.2 years, 42.5% female	HF medication	60 min yoga lessons, 2 days/week +1 or more days/week home practice for 8–10 weeks (postures, breathing, meditation, relaxation, education, home walk programme)	Standard medical care (education, home walk programme)	8–10 weeks	(3) Exercise capacity: treadmill time, VO2peak	(3) Significant group differences in favour of yoga for treadmill time and VO2peak
						(4) Health-related quality of life: MLHFQ	(4) No significant group differences for MLHFQ
						(6) Safety	(6) No AE in either group
Toise et al.46	ICD patients, 55 randomized, 46 analysed, 66.3 years, 12.7% female	Continued medication	80 min yoga lessons, 1 day per week for 8 weeks +30 min home practice, 3 days peer week for 4 months (postures, breathing, meditation, relaxation)	Standard medical care (office visits, regularly calls from the nurses)	8 months	(1) Mortality	(1) None
						(2) Nonfatal cardiac events: DTV events	(2) 1 nonfatal cardiac-related drop-out in the control group; 32% lower risk in yoga group regarding DTV events (follow up)
						(4) Health-related quality of life: anxiety (FSAS), depression (CES-D)	(4) Significant group differences in favour of yoga for anxiety, but not for depression

a

1, Mortality; 2, nonfatal cardiac events; 3, exercise capacity; 4, health-related quality of life; 5, cardiac risk factors; 6, safety.

b

1, Mortality; 2, nonfatal cardiac events; 3, exercise capacity; 4, health-related quality of life; 5, cardiac risk factors; 6, safety.

AE, Adverse event; CAD, coronary artery disease; CES-D, Center for Epidemiological Studies Depression Scale; DBP, diastolic blood pressure; DTV, device-treated ventricular; FSAS, Florida Shock Anxiety Scale; HDL, high-density lipoprotein; HF, heart failure; HR, heart rate; ICD, implantable cardioverter defibrillator; LDL, low-density lipoprotein; MLHFQ, Minnesota Living with Heart Failure Questionnaire; NYHA, New York Heart Association; SBP, systolic blood pressure; TC, serum total cholesterol; TG, triglycerides.

Table 3.

Risk of bias assessment of the included studies using the Cochrane risk of bias tool.

Publication	Random sequence generation (selection bias)	Allocation concealment (selection bias)	Blinding of participants and personnel (performance bias)	Blinding of outcome assessment (detection bias)	Incomplete outcome data (attrition bias)	Selective reporting (reporting bias)	Other bias
Mahajan et al.40	Unclear	Unclear	Unclear	Unclear	Unclear	Low	Low
Manchanda et al.41	Unclear	Unclear	Unclear	Unclear	Unclear	Low	Low
Pal et al.42	Low	Unclear	Unclear	Unclear	High	Unclear	Low
Pal et al.43	Low	Unclear	Unclear	Unclear	High	Unclear	Low
Pullen et al.44	Unclear	Unclear	Unclear	Low	Low	Low	Low
Pullen et al.45	Unclear	Unclear	Unclear	Low	Low	Low	Low
Toise et al.46	Low	Low	High	High	Low	Low	Low

Coronary heart disease

Characteristics of the included studies

Four RCTs with a total of 510 coronary heart disease patients were included.^40–43 All RCTs originated from India. Coronary heart disease was assessed based on ‘clinical history’ without disclosing diagnostic criteria,^42,43 angiography,⁴¹ or echocardiography.⁴⁰ Between 0.0 and 15.3% of the included patients were female (median 7.7%) and mean age ranged from 51.5 to 58.75 years (median 57.75 years). No RCT reported ethnicity of the included patients.

All four RCTs simply labelled their intervention as ‘yoga’ without denoting a specific yoga style. Two RCTs used a 4-day residential programme with subsequent daily home practice for 60 min⁴⁰ or 90 min⁴¹ over a period of 14 weeks⁴⁰ or 12 months.⁴¹ The other two RCTs used five supervised yoga classes of 35–40 min duration per week for 6 months.^42,43 Median length of the intervention period across studies was 6 months, and median duration of daily yoga practice was 50 min. All four interventions included physical postures, breath control, and relaxation; two RCTs each also included meditation and dietary advice^40,41 or chanting and nasal cleansing.^42,43 Two RCTs did not report the qualification of the yoga teachers,^40,41 the interventions in the remaining two RCTs were conducted by experienced postgraduate yoga teachers.^42,43 Two RCTs compared yoga to conventional medical therapy, consisting of dietary control and moderate aerobic exercise;^40,41 the other two RCTs simply described their comparison group as ‘control’ without further description.^42,43

Risk of bias in individual studies generally was high: only two RCTs reported adequate randomization.^42,43 No trial reported on blinding, so risk of performance bias and detection bias remained unclear (Table 3). Two RCTs from the same research group were conducted as part of the same research project, had comparable designs, and were conducted during overlapping time periods.^42,43 When the authors were contacted to clarify whether the RCTs were conducted in distinct patient samples, no answer was retrieved; therefore, it remains unclear whether the respective RCTs included the same or distinct patient samples.

Outcomes and recommendation

Three RCTs reported mortality data.^41–43 In one RCT, no mortality in either group occurred during the 12-month study period:⁴¹ one RCT reported one death in the yoga group and no death in the control group during 6 months,⁴³ and one RCT reported two fatalities in the yoga group and three fatalities in the control group during 18 months.⁴² Overall, three out of 235 patients in the yoga groups and three patients out of 235 in the control groups died, resulting in very-low-quality evidence for no effect of yoga on mortality. One RCT assessed nonfatal cardiac events and reported a stronger reduction in number of episodes of angina per week in the yoga group than in the control group⁴¹ (very-low-quality evidence). One RCT assessed exercise capacity using a modified Bruce treadmill protocol⁴¹ and found a larger increase in exercise time in the yoga group than in the control group (very-low-quality evidence). All four RCTs assessed modifiable cardiac risk factors. Of those, two RCTs assessed blood pressure^42,43 and both found significant group differences favouring the yoga group for systolic and diastolic blood pressure. Three RCTs assessed blood lipid levels and all found significant group differences favouring the yoga group for total cholesterol, LDL, and triglycerides,^40,41,43 while only one found group differences for HDL.⁴³ Overall, the quality of evidence for effects of yoga on modifiable cardiac risk factors was judged low. Besides mortality and cardiac events, only one study reported safety data and stated that no side effects occurred in either group.

Overall, a weak recommendation can be made for the use of yoga in patients with coronary heart disease.

Heart failure

Characteristics of the included studies

Two RCTs from the same US research group assessed the effects of yoga on a total of 59 patients with chronic heart failure (New York Heart Association class I–III).^44,45 Between 42.5 and 52.6% of the included patients were female (median 47.6%), and mean age ranged from 51.3 to 54.2 years (median 52.8 years). One RCT reported ethnicity of the included patients: 95% were African Americans, 2.5% were Asians, and 2.5% were Caucasians.⁴⁵

Both RCTs used Hatha yoga interventions: twice weekly for 60 min⁴⁵ or 70 min each⁴⁴ (median 65 min) over 8 weeks⁴⁴ or 8–10 weeks⁴⁵ for a total of 16 sessions. Interventions were conducted by licensed yoga teachers and included physical postures, breath control, meditation, and relaxation. The control groups did not receive a specific intervention: both intervention and control groups received ‘standard medical care’ which was not further defined.

Both RCTs were incompletely reported. While risk of detection bias and attrition bias were low, there was high risk of reporting bias, and risk of selection bias and performance bias were unclear in both RCTs (Table 3).

Outcomes and recommendation

One RCT reported data on mortality:⁴⁴ no patient in either the intervention or the control group died during the 2-month study period (very-low-quality evidence). Exercise capacity was assessed by both RCTs using a graded exercise treadmill test. Both RCTs found significant group differences favouring the yoga group for exercise time and maximum oxygen consumption. Quality of evidence for effects on exercise capacity was graded low. Both RCTs assessed quality of life using the Minnesota Living with Heart Failure Questionnaire: no RCT found significant group differences in quality of life (low-quality evidence). Both RCTs reported safety data,^44,45 and reported that no adverse events occurred.

Based on these findings, a weak recommendation can be made for the use of yoga in heart failure patients.

Cardiac dysrhythmia

Characteristics of the included studies

One US RCT investigated the effects of yoga on 55 patients (12.7% female, mean age 66.3 years, 92.7% Caucasians) who were treated with an implantable cardioverter defibrillator for life-threatening arrhythmia.⁴⁶ The intervention consisted of weekly 80-min sessions over an 8-week period and included physical postures, breath control, meditation, and relaxation. The qualifications of the yoga teachers were not reported. The control group did not receive a specific intervention: both intervention and control groups received standard medical care (in-person office visits every 6–9 months).

Risk of bias was low for all domains except a high risk of bias for blinding (Table 3).

Outcomes and recommendation

No patient in either group died during the 8-month follow-up period (very-low-quality evidence). There was low-quality evidence for a lower number of nonfatal device-treated ventricular events in the yoga group than in the control group. Quality of life was assessed using the Florida Shock Anxiety Scale and the Center for Epidemiological Studies Depression Scale, and significant group differences were found for shock anxiety. Overall, the quality of evidence for effects of yoga on quality of life was graded very low. No safety data were reported.

Overall, a weak recommendation can be made for the use of yoga in arrhythmia patients treated with an implantable cardioverter defibrillator.

Discussion

Summary of evidence

This systematic review of seven RCTs found very low evidence for no effect on mortality, very low evidence for a reduced number of episodes of angina, very low evidence for increased exercise capacity, and low evidence for reduced modifiable cardiac risk factors in coronary heart disease. For heart failure, there was very low evidence for no effect on mortality, low evidence for increased exercise capacity, and low evidence for no effect on health-related quality of life. For cardiac dysrhythmia, there was very low evidence for no effect on mortality, low evidence for effects on cardiac events, and very low evidence for improved quality of life. It should be noted that while the quality of evidence was generally graded low or very low, this should not be misinterpreted as absence of evidence. Low and very low evidence simply mean that further research is likely to have an important impact on the confidence in the results.²⁶ Evidence that is based on few small-scale single-centre RCTs is always likely to be affected by further research.

Three RCTs assessed adverse events and reported that no adverse events occurred.^41,44,45

Agreements with prior systematic reviews

The results of this review are in line with an early systematic review on yoga for coronary heart disease that concluded that yoga practiced as a holistic discipline is beneficial for prevention and supportive of treatment for coronary heart disease.⁴⁷ However, this review included trials only up to 2002, and also included trials on multimodal interventions and those of healthy participants. Therefore, only two RCTs were included in both reviews.^40,41 Another systematic review on yoga for cardiac health found that little high-quality research on this topic had been published until 2003;⁴⁸ however, it concluded that yoga might have the potential to improve quality of life in postmyocardial infarction patient rehabilitation. A recent Cochrane review on secondary prevention of coronary heart disease found no eligible RCTs that met the inclusion criteria of the review.²³ This is a marked discrepancy to the present review that included four RCTs on coronary heart disease. However, this can be partly explained by differences in eligibility criteria, as the Cochrane review included only RCTs that assessed mortality, cardiovascular events, or quality of life and had a length of follow up of at least 6 months.²³ Two RCTs that were included in the present review were actually excluded from the Cochrane review.^41,43 One of these RCTs was judged to report on a combination of treatments.⁴¹ All components of the intervention (e.g. stress management, exercise, diet) were, however, described as being based on yoga that is multimodal by definition. The other RCT was judged not to include relevant outcome measures while it actually reported mortality data during a 6-month follow-up period.⁴³

Several further systematic reviews have shown that yoga can improve cardiovascular disease risk factors in healthy participants and in patients with hypertension, type 2 diabetes, and metabolic syndrome.^21,22,48,49 This was confirmed in a meta-analysis on yoga for hypertension that found evidence for effects of yoga on systolic and diastolic blood pressure when compared to no treatment or usual care but not when compared to other active treatments.²⁰

While only three RCTs in the present review reported safety data, prior systematic reviews^50–56 and cross-sectional studies^57,58 on yoga in other patient populations reported little evidence for yoga-associated adverse events.

Applicability of evidence

While the RCTs on coronary heart disease included mainly male Indian adults, those on chronic heart failure included mainly African American adults of both genders, and the RCT on cardiac dysrhythmia included mainly male Caucasians. The results of this review therefore seem to be of only limited applicability. As cardiovascular risk factors as well as controllability of heart disease differ between patients of different gender and ethnicity,^59–61 results that were found in patients of a specific gender and/or ethnic group cannot be directly applied to other patient groups.

Limitations

Only a limited number of RCTs especially for conditions other than coronary heart disease could be included. Regarding two RCTs,^42,43 it remains unclear whether they are really two distinct RCTs or dealt with the same patient sample. Moreover, the quality of evidence is clearly limited by the insufficient reporting of research methodology. Only a few RCTs reported data on mortality or cardiac events, and most did not officially include mortality as an outcome but reported mortality data in their CONSORT flowchart only. Applicability of the results is limited. As only three out of the seven RCT reported safety data,^41,44,45 the recommendations for yoga have to be regarded as preliminary until the safety of the intervention is clarified.

Implications for further research

Given the methodological drawbacks of the included studies, future RCTs should ensure rigorous methodology and reporting, mainly adequate sample size, randomization, allocation concealment, intention-to treat analysis, and blinding of at least outcome assessors.⁶² As yoga is an important part of traditional Indian philosophy and lifestyle¹¹ and might therefore unfold considerable unspecific effects in Indian patients, the results found on Indian coronary heart disease patients have to be replicated in European and North American patients. RCTs with longer follow-up periods are needed before potential effects of yoga on mortality and cardiac events can be conclusively judged. Only one RCT on patients with cardiac arrhythmias was located.⁴⁶ Recent uncontrolled trials have generated promising evidence that yoga can be a useful intervention in cardiac arrhythmias. In a small uncontrolled trial, a 12-week yoga breathing intervention markedly reduced indices of ventricular repolarization dispersion in patients with arrhythmias: this is a potential marker of risk of cardiac sudden death.⁶³ In another uncontrolled trial, 52 patients with paroxysmal atrial fibrillation participated in a 12-week yoga intervention consisting of physical postures, breath control, and relaxation.⁶⁴ After the yoga intervention, atrial fibrillation episodes and cardiovascular risk factors were reduced and quality of life and mental health were improved. While these findings are promising, future research should try to replicate them in more rigorous trials using a randomized study design. No RCTs on patients with cardiomyopathy or valvular heart disease could be included in the present review. While the evidence for yoga in coronary heart disease and heart failure is promising, more research is needed especially for other less common cardiovascular diseases. No RCT compared yoga to an active control intervention. To evaluate the specific effects of yoga in heart disease, it should be compared to guideline-endorsed active control interventions.^10,65 Since only single-centre trials have been conducted to date, there is a need for large multicentre trials to increase the generalizability of the results.

Conclusions

Based on the results of this review, weak recommendations can be made for the ancillary use of yoga in the management of coronary heart disease, chronic heart failure, and cardiac dysrhythmia. More rigorous RCTs are needed to underpin the available evidence.

Funding

This research was supported by the Corona-Foundation, Germany. The funding source had no influence on the design or conduct of the review; the collection, management, analysis, or interpretation of the data; or in the preparation, review, or approval of the manuscript.

Conflict of interest

The authors declare that there is no conflict of interest.