Comment on: “exercise training and cardiac autonomic function following coronary artery bypass grafting: a systematic review and meta-analysis”
The Egyptian Heart Journal volume 75, Article number: 19 (2023)
Low cardiorespiratory fitness is associated with poor prognosis in individuals with coronary artery disease and after coronary artery bypass grafting surgery. Thus, we comment about a meta-analysis that adds important information about the effect of exercise training on cardiac autonomic function in individuals following coronary artery bypass grafting surgery.
The study by Kushwaha et al. showed positive effects for heart rate variability and heart rate recovery in subjects after coronary artery bypass grafting surgery in response to acute physical training. These data are relevant, since heart rate variability is an independent predictor of for all-cause and cardiovascular mortality for individuals with cardiovascular disorders. Additionally, attenuated heart rate recovery is associated with increased risk for the same outcomes. Moreover, we summarize the quantitative data from studies that compared the effect of physical training in comparison with control group in cardiorespiratory fitness in adults following coronary artery bypass grafting.
Our findings suggest that improvements in peak oxygen consumption result in an additional benefit in adults following coronary artery bypass grafting. Considered that, the increased cardiorespiratory fitness is an independent predictor of longer survival in coronary artery disease.
We read with great interest the systematic review by Kushwaha et al.  that adds important information on the effects of exercise training on cardiac autonomic function in individuals after coronary artery bypass grafting (CABG) surgery. The study shows positive effects for heart rate variability (HRV) and heart rate recovery (HRR) in subjects after CABG surgery in response to acute physical training .
In their results, the authors reported that, for HRV in the time domain, there was an increase in the standard deviation of RR intervals (SDNN) (SMD 0.44 [0.17–0.71], P = 0.002, I2 0%) and increase in square root of the mean squared differences between successive RR intervals (RMSSD) (SMD 0.68 [0.28–1.08], P = 0.0008, I2 7%). Furthermore, results showed an increase in high frequency (HF) domain (SMD 0.58 [0.18–0.98], P = 0.0005, I2 35%), which may reflect additional positive changes in parasympathetic tone. In addition, suggesting an overall balance of sympathetic and parasympathetic function, there was a reduction in the low frequency-to-high frequency ratio (LF/HF) (SMD − 0.34 [ − 0.65 to 0.02], P = 0.03, I2 0%). Moreover, for HRR in the first minute after exercise, significant improvement was demonstrated (SMD 0.71 [0.39–1.02], P < 0.001, I2 0%), corresponding to a larger decrease HRR, that is, a greater reactivation of the parasympathetic nervous system [1, 2]. These data are relevant, since regulation of the cardiac autonomic nervous system is an important outcome of physical training .
Conceptually, HRV and HRR are indirect, noninvasive, reliable and safe measures for monitoring and assessing cardiac autonomic control. HRV is an independent predictor of all-cause and cardiovascular mortality for individuals with atrial fibrillation . In addition, low HRV is associated with a higher risk of heart failure with preserved ejection fraction and with a higher incidence of hospitalization for heart failure in postmenopausal women . Attenuated HRR is associated with increased risk of cardiovascular events and all-cause mortality  (Table 1).
Physical training is a Class I recommendation and one of the main elements in the cardiac rehabilitation program by the American Heart Association College of Cardiology and the European Society of Cardiology. Physical training increases cardiorespiratory fitness, reduces the risk of cardiovascular mortality, acute myocardial infarction and hospitalization . In addition, a meta-analysis showed that resistance training resulted in improvement of all HRV parameters in the time and frequency domains, in contrast to resistance training and aerobic high-intensity interval combined. A meta-regression also showed that after the physical training program, improvement in LF/HF domains was significantly associated with improvement in peak oxygen consumption (VO2 peak) [coefficient: − 0.05 ( − 0.081 to 0.019), P = 0.005, I2 0.0%] . In conclusion, studies show that physical training alone or a combination of aerobic and resistance training leads to adaptations in cardiac autonomic control (Table 2).
Previous studies have shown that there are differences in the magnitude of changes in HRV induced by physical training according to training protocol . In the study by Kushwaha et al. , an interesting point was the inclusion of studies that analyzed patients with and without beta-blocker therapy (5 [16,17,18,19,20] and 3 [21,22,23] studies respectively). Nevertheless, the study reported improvements in HRV and HHR. Beta-blockers are the first-line therapy to control symptoms in stable coronary artery disease and to reduce exercise-induced angina [24, 25]. Beta-blockers modify heart rate  and, thus, can affect HRV and HRR . Therefore, as a contribution to the present study, we suggest that further clinical trials and systematic reviews should consider this type of analysis to see how it affects the magnitude of the effect and heterogeneity.
In addition to these findings, other issues regarding to the cardiorespiratory fitness of individuals after CABG surgery need to be considered. In 2016, a scientific statement from the American Heart Association considered the importance of assessing cardiorespiratory fitness in clinical practice considering it as a clinical vital sign . Moreover, it is already well described in the scientific literature that low cardiorespiratory fitness is associated with poor prognosis in individuals with coronary artery disease and after CABG surgery [24, 27]. Despite the excellent systematic review with meta-analysis performed by Kushwaha et al. , no meta-analysis has been performed for VO2 peak. When pooling the available studies for the meta-analysis comparing physical training (different types of exercise training including aerobic, resistance, interval and combined aerobic and resistance training either alone or combined) with controls (no exercise), we observed significant effect for the VO2 peak in the physical training group (MD = 1.59 mL O2 Kg−1 min−1, (95% CI 1.04–2.14, I2 = 61%, 5 [16, 17, 19, 23, 28] studies, N = 300, P < 0.00001), (Fig. 1). Considering the results presented by Kushwaha et al.  and confirmed by our meta-analysis, the improvement in HRR can also be associated with improvement in cardiorespiratory fitness [1, 27]. Improvements in cardiorespiratory fitness play a role as an independent predictor for survival in coronary artery disease. In addition, increments in VO2 peak have been associated with a 14–17% reduction in the risk of cardiovascular disease and death from all causes . Therefore, it is reasonable for healthcare professionals to assess the cardiorespiratory fitness of individuals after CABG.
In conclusion, we congratulate Kushwaha et al.  in this important research. Additionally, we provide information about cardiorespiratory fitness of the included studies that showed a difference of 1.59 mL O2 Kg−1 min−1 in VO2 peak between physical training and control after CABG surgery. Finally, it is important to address the need for further studies to investigate if there is any association between improvements in cardiorespiratory fitness and improvement cardiac autonomic function (HRV and HRR), as well as additional benefits from physical/exercise training in adults after CABG surgery.
Availability of data and materials
Coronary artery bypass grafting
Heart rate variability
Heart rate recovery
Deviation of RR intervals
Squared differences between successive RR intervals
Low frequency-to-high frequency ratio
- VO2 peak:
Peak oxygen consumption
Very low frequency
Standard deviations of RR intervals of all 5 min segments
Standard deviations of RR intervals of all 5 min segments
High frequency normalize units
Kushwaha P, Moiz JA, Mujaddadi A (2022) Exercise training and cardiac autonomic function following coronary artery bypass grafting: a systematic review and meta-analysis. Egypt Heart J 74:67. https://doi.org/10.1186/s43044-022-00306-5
Liu W-L, Lin Y-Y, Mündel T, Chou C-C, Liao Y-H (2022) Effects of acute interval exercise on arterial stiffness and cardiovascular autonomic regulatory responses: a narrative review of potential impacts of aging. Front Cardiovasc Med 9:864173. https://doi.org/10.3389/fcvm.2022.864173
Hammerle P et al (2020) Heart rate variability triangular index as a predictor of cardiovascular mortality in patients with atrial fibrillation. J Am Heart Assoc 9:016075. https://doi.org/10.1161/JAHA.120.016075
Baig M, Moafi-Madani M, Qureshi R, Roberts MB, Allison M, Manson JE, LaMonte MJ, Liu S, Eaton CB (2022) Heart rate variability and the risk of heart failure and its subtypes in post-menopausal women: The Women’s Health Initiative study. PLoS ONE 17:e0276585. https://doi.org/10.1371/journal.pone.0276585
Qiu S, Cai X, Sun Z, Li L, Zuegel M, Steinacker JM, Schumann U (2017) Heart rate recovery and risk of cardiovascular events and all-cause mortality: a meta-analysis of prospective cohort studies. J Am Heart Assoc 6:e005505. https://doi.org/10.1161/JAHA.117.005505
Yang L, Zhao Y, Qiao B, Wang Y, Zhang L, Cui T, Fu P (2021) Heart rate variability and prognosis in hemodialysis patients: a meta-analysis. Blood Purif 50:298–308. https://doi.org/10.1159/000511723
Zhou X, Ma Z, Zhang L, Zhou S, Wang J, Wang B, Fu W (2016) Heart rate variability in the prediction of survival in patients with cancer: a systematic review and meta-analysis. J Psychosom Res 89:20–25. https://doi.org/10.1016/j.jpsychores.2016.08.004
Lanza GA et al (2006) Prognostic value of ventricular arrhythmias and heart rate variability in patients with unstable angina. Heart 92:1055–1063. https://doi.org/10.1136/hrt.2005.070714
Hadase M, Azuma A, Zen K, Asada S, Kawasaki T, Kamitani T, Kawasaki S, Sugihara H, Matsubara H (2004) Very low frequency power of heart rate variability is a powerful predictor of clinical prognosis in patients with congestive heart failure. Circ J 68:343–347. https://doi.org/10.1253/circj.68.343
de Castilho FM, Ribeiro ALP, da Silva JLP, Nobre V, de Sousa MR (2017) Heart rate variability as predictor of mortality in sepsis: A prospective cohort study. PLoS ONE 12:e0180060. https://doi.org/10.1371/journal.pone.0180060
Johansson JK, Niiranen TJ, Puukka PJ, Jula AM (2012) Prognostic value of the variability in home-measured blood pressure and heart rate. Hypertension 59:212–218. https://doi.org/10.1161/HYPERTENSIONAHA.111.178657
Anderson L, Oldridge N, Thompson DR, Zwisler A-D, Rees K, Martin N, Taylor RS (2016) Exercise-based cardiac rehabilitation for coronary heart disease: cochrane systematic review and meta-analysis. J Am Coll Cardiol 67:1–12. https://doi.org/10.1016/j.jacc.2015.10.044
Picard M, Tauveron I, Magdasy S, Benichou T, Bagheri R, Ugbolue UC, Navel V, Dutheil F (2021) Effect of exercise training on heart rate variability in type 2 diabetes mellitus patients: a systematic review and meta-analysis. PLoS ONE 16:e0251863. https://doi.org/10.1371/journal.pone.0251863
Raffin J, Barthélémy J-C, Dupré C, Pichot V, Berger M, Féasson L, Busso T, Da Costa A, Colvez A, Montuy-Coquard C, Bouvier R, Bongue B, Roche F, Hupin D (2019) Exercise frequency determines heart rate variability gains in older people: a meta-analysis and meta-regression. Sports Med 49:719–729. https://doi.org/10.1007/s40279-019-01097-7
Masroor S, Bhati P, Verma S, Khan M, Hussain ME (2018) Heart rate variability following combined aerobic and resistance training in sedentary hypertensive women: a randomised control trial. Indian Heart J 70:S28–S35. https://doi.org/10.1016/j.ihj.2018.03.005
Wu S-K, Lin Y-W, Chen C-L, Tsai S-W (2006) Cardiac rehabilitation vs. home exercise after coronary artery bypass graft surgery: a comparison of heart rate recovery. Am J Phys Med Rehabil 85:711–717. https://doi.org/10.1097/01.phm.0000228597.64057.66
Bilińska M, Kosydar-Piechna M, Mikulski T, Piotrowicz E, Gąsiorowska A, Piotrowski W, Nazar K, Piotrowicz R (2013) Influence of aerobic training on neurohormonal and hemodynamic responses to head-up tilt test and on autonomic nervous activity at rest and after exercise in patients after bypass surgery. Cardiol J 20:17–24. https://doi.org/10.5603/CJ.2013.0004
Ghardashi-Afousi A, Holisaz MT, Shirvani H, Pishgoo B (2018) The effects of low-volume high-intensity interval versus moderate intensity continuous training on heart rate variability, and hemodynamic and echocardiography indices in men after coronary artery bypass grafting: A randomized clinical trial study. ARYA 14:260–271
Iellamo F, Legramante JM, Massaro M, Raimondi G, Galante A (2000) Effects of a residential exercise training on baroreflex sensitivity and heart rate variability in patients with coronary artery disease: a randomized, controlled study. Circulation 102:2588–2592. https://doi.org/10.1161/01.cir.102.21.2588
Ribeiro BC, da Poça JJG, Rocha AMC, da Cunha CNS, da Cunha K et al (2021) Different physiotherapy protocols after coronary artery bypass graft surgery: a randomized controlled trial. Physiother Res Int 26:e1882. https://doi.org/10.1002/pri.1882
Tsai S-W, Lin Y-W, Wu S-K (2005) The effect of cardiac rehabilitation on recovery of heart rate over one minute after exercise in patients with coronary artery bypass graft surgery. Clin Rehabil 19:843–849. https://doi.org/10.1191/0269215505cr915oa
Shao H, Liang J, Zhong P, Xu J, Li Y (2013) Influence of exercise on heart rate variability in patients undergoing coronary artery bypass grafting. Chin J Cardiovasc Rehabil Med 22:10–14
Takeyama J, Itoh H, Kato M, Koike A, Aoki K, Fu LT, Watanabe H, Nagayama M, Katagiri T (2000) Effects of physical training on the recovery of the autonomic nervous activity during exercise after coronary artery bypass grafting: effects of physical training after CABG. Jpn Circ J 64:809–813. https://doi.org/10.1253/jcj.64.809
Knuuti J et al (2020) 2019 ESC guidelines for the diagnosis and management of chronic coronary syndromes. Eur Heart J 41:407–477. https://doi.org/10.1093/eurheartj/ehz425
Van Thanh N, Hien NS, Son PN, Son PT (2022) Pattern changes in the heart rate variability of patients undergoing coronary artery bypass grafting surgery. Cardiol Res Pract 2022:1455025. https://doi.org/10.1155/2022/1455025
Bertrand ME, Ferrari R, Remme WJ, Simoons ML, Fox KM (2015) Perindopril and β-blocker for the prevention of cardiac events and mortality in stable coronary artery disease patients: a EUropean trial on Reduction Of cardiac events with Perindopril in stable coronary Artery disease (EUROPA) subanalysis. Am Heart J 170:1092–1098. https://doi.org/10.1016/j.ahj.2015.08.018
Ross R et al (2016) Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign: a scientific statement from the American Heart Association. Circulation 134:e653–e699. https://doi.org/10.1161/CIR.0000000000000461
Mehani SHM (2012) Autonomic adaptation and functional capacity outcomes after hospital-based cardiac rehabilitation post coronary artery by pass graft. Indian J Physiother Occupat Ther Int J 6:257–261
This report has supported with a scholarship holder by CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior).
Ethics approval and consent to participate
Consent for publication
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Gois, C.O., Conceição, L.S.R., de Andrade Guimarães, A.L. et al. Comment on: “exercise training and cardiac autonomic function following coronary artery bypass grafting: a systematic review and meta-analysis”. Egypt Heart J 75, 19 (2023). https://doi.org/10.1186/s43044-023-00344-7