The search strategy initially yielded 4544 articles and duplicate articles were discarded. A total of 19 articles were subjected to a full-text review, from which we excluded 15 studies comprising 2 case reports, 1 animal study, 1 nonrandomized control trial study, 8 studies that included non-DCM patients, and 3 studies based on the same patient group (Figure).
BASELINE NYHA CLASSIFICATION
The New York Heart Association (NYHA) classification is commonly used as a method for functional classification in patients with cardiac disease. The functional status is categorized by 4 classifications with high numbers indicating more severe limitation of physical function. The NYHA classification of study patients was I and II in 2 studies, while the other 2 studies by Mehani12 and Holloway et al2 included 9 and 4 patients with NYHA classification III, respectively. Only the study by Stolen et al13 described the change of NYHA classification after intervention with an improvement from 1.6 ± 0.5 to 1.2 ± 0.4.
MAXIMAL OXYGEN UPTAKE
In 3 of the studies, symptom-limited exercise testing was performed using an electrically-braked cycle ergometer. The specific testing protocol was not described in any of the included articles. In the study by Holloway et al,2 a 6-min walk test (6MWT) was used as the testing mode for estimating exercise capacity. Exercise capacity improved in all studies in patients who received exercise training. Although the training periods varied, improvement of maximal oxygen uptake (
O2max) ranged between 8% and 27% in patients receiving exercise training compared with patients not receiving exercise training. In the study by Stolen et al,13 symptom-limited, incremental cycle ergometer testing with continuous respiratory gas exchange analysis was used and reported the highest improvement in exercise capacity (27%; mean ± SD
O2max = 19.4 ± 4.1 mL/kg/min; 6.7 metabolic equivalents [METs]) pre-training versus 24.6 ± 5.2 mL/kg/min (8.5 METs) post-training. The increase in 6MWT distance increased from 469 ± 21 m before exercise training to 508 ± 25 m (8% increase) after exercise training was reported by Holloway et al.2 The remaining 2 studies12,14 both used an electrically braked cycle ergometer for exercise testing; 1 used an individualized ramp protocol and the other used the Wasserman protocol. These studies reported improvements in exercise capacity resulting from exercise training from 16.1 ± 3.65 mL/kg/min (5.6 METs) to 21.08 ± 5.47 mL/kg/min (7.6 METs) (26%)12 and from 21.7 ± 3.8 mL/kg/min (7.3 METs) to 25.3 ± 5.2 mL/kg/min (8.7 METs) (17%).14 The average exercise capacity in the included studies was 6.5 METs before intervention and 8.3 METs after intervention. These values are lower values compared with average values for 50 age-matched healthy adults.16
An exercise prescription consists of exercise frequency, intensity, time, type, and a recommendation on whether supervision is needed. Exercise frequency ranged from 3 to 5 times/wk in the 4 studies we evaluated. The initial exercise intensity was 50% to 55% of the functional capacity determined in each study and was progressively increased over the intervention period of 2 to 7 mo to achieve a goal of 80% of peak exercise intensity in 3 studies, and 70% in 1 study,13 which used an initial exercise intensity of 50% of peak
O2 and progressively increased during the 5-mo period. Three of the studies utilized aerobic exercise as the main exercise type, while Stolen et al13 also prescribed resistance training twice/week beginning after 4 wk of aerobic exercise. A study by Mehani12 used interval aerobic circuit training using a treadmill, cycle ergometer and a Stairmaster (Life Fitness) with initial exercise intensity of 55% of heart rate reserve (HRR) and increasing to 80% at the end of the seventh month. The maximum exercise time was 45 min in 3 studies and 20 min in 1 study2 that prescribed exercise intensity to achieve a training heart rate between 70% and 80% of the initial exercise test maximum heart rate. The study duration ranged from 2 to 7 mo, but 1 study14 used a 2-mo training period and determined clinical outcomes after 2 and 8 mo from baseline. The exercise intervention was conducted with supervision in 3 studies, while patients in the Holloway et al2 study were prescribed a home-based exercise program without direct supervision.
QUALITY OF LIFE
Several of the included studies used a questionnaire to evaluate QOL after an exercise intervention. Specifically, Mehani12 used the Kansas City Cardiomyopathy Questionnaire (KCCQ), a disease-specific instrument for evaluating QOL in patients with chronic heart failure, and reported a statistically significant difference between both groups in the functional score (75.0%) and clinical summary scores (129.3%). Holloway et al2 used the Minnesota Living With Heart Failure Questionnaire (MLHFQ), which was designed to measure physical and emotional dimensions of QOL for heart failure. A decreased score after an intervention means an improvement in physical or emotional state, and this reported an improvement of 28% compared with baseline in patients who received exercise training, with an average post-intervention score of 17 ± 3 versus a pre-intervention score of 26 ± 5. Stolen et al13 used the RAND 36-item health survey (SF-36), which measures generic health-related QOL and a higher score denotes improvement in QOL, and the results demonstrated an improvement in general health, pain, and vitality compared with baseline in patients who received exercise training.
Proper exercise intensity is important to ensure both the safety and effectiveness of an exercise intervention. Exercise training can improve exercise capacity and QOL while reducing cardiac mortality in several different types of cardiac patients.6–8 To help provide insight into the role of exercise therapy for exercise professionals in patients with DCM, we systematically reviewed 4 published articles in which exercise therapy was conducted specifically for patients with DCM.
The NYHA classification scheme is commonly used to define the level of function in patients with cardiac disease and is based on symptoms during physical activity.17 Importantly, aerobic exercise in patients with heart failure can lead to a 0.5 improvement in NYHA functional class.18 Among the articles included in our systematic review, the highest NYHA classification prior to intervention was III. In 1 of the reviewed studies, the NYHA class improved from 1.6 ± 0.5 to 1.2 ± 0.5 (change: −18.5%) after an exercise intervention, while there was a minimal change in the control group from 1.2 ± 0.4 to 1.1 ± 0.4 (change: −4.8%).13 Although the correlation between the improvement in NYHA functional class and exercise capacity in that study was not very high, the exercise capacity in the training group was significantly improved from 19.4 ± 4.1 to 24.6 ± 5.2 mL/kg/min (change: +27.2%) compared with the control group (change: +4.2%). A previous study19 reported that NYHA functional class correlated inversely with 6-min walk distance, and thus we speculated the possibility that an improvement in exercise capacity was the main factor behind the change in NYHA class in the study groups. Further studies will be needed to verify these results.
Most patients with DCM in the reviewed studies were NYHA classes II and III. In these patients, exercise intervention was conducted safely without adverse events during the intervention period, supporting the idea that exercise intervention in this patient population is relatively safe. However, extra care should be taken when prescribing exercise training to NYHA class IV patients to prevent any complications because the studies reviewed did not provide recommendations for these patients.
MAXIMAL OXYGEN UPTAKE
Exercise capacity can be precisely measured by
O2max during exercise, which represents the limit of cardiopulmonary function for transporting oxygen to the exercising muscles.20 Exercise capacity can also be expressed in METs, with 1 MET representing energy expenditure with a person in the sitting position, and is equal to 3.5 mL/kg/min. METs can be used to describe the intensity of a variety of physical activities.21 The intensity of physical activity can be categorized into 3 levels, with light physical activity classified as activity requiring <3 METs, moderate activity classified as 3 to 6 METs, and vigorous activity classified as >6 METs.21 Peak METs are 1 of the strongest predictors of all-cause mortality,22,23 and the increase of a 1 MET for exercise capacity was associated with 13% and 15% reduction of risk in all-cause and cardiovascular mortality, respectively. Additionally, patients with a maximal aerobic capacity of ≥7.9 METs had a lower risk of all-cause and cardiovascular mortality compared with those with an aerobic capacity of <7.9 METs.24
In this systematic review, the baseline exercise capacity of participants was much lower than that of an age-matched general healthy population. For example, the lowest exercise capacity among participants in the study by Mehani12 was 3.6 METs. Although the correlation between NYHA functional class and exercise capacity was not significant, several studies have demonstrated a significant difference in exercise capacity between NYHA functional classes II and III/IV.19,25,26 In the studies evaluated in this review, exercise capacity improved between 8% and 27% from baseline in patients who received an exercise intervention. The greatest improvement in exercise capacity was reported by Mehani12 (26%; mean 4.5-5.4 METs). Previous studies on the effects of exercise in patients with heart failure have reported a similar range (0%-27%) in the improvement of exercise capacity.27 Based on a previous meta-analysis,28 the difference in the improvement in exercise capacity is dependent on the intensity of exercise intervention, age of the patient, gender, and baseline
Many studies24,29 have reported that physical inactivity and low exercise capacity are associated with the development of cardiovascular disease. Likewise, exercise therapy has been shown to improve exercise capacity and QOL in patients with cardiac disease.6,7,9 Individualization of the exercise prescription for patients with DCM is essential for obtaining the maximal benefit. Such individualization can be achieved by considering a patient's current exercise habits, exercise capacity, and other individual factors.9 The principle of an exercise prescription is based on the FITT principle: frequency (F), intensity (I), time (T), and type (T) of exercise.30,31 In the studies we reviewed, the frequency of exercise ranged from 3 to 5 times/wk, consistent with the general exercise recommendations for healthy adults,32 which also suggest combining moderate and vigorous intensity exercise.
Based on the reviewed studies, the appropriate intensity of aerobic exercise for patients with DCM was like that recommended in previous studies33–36 conducted with patients with other forms of heart failure. Aerobic exercise intensity can be determined using 1 of several commonly used equations based on %HRR, %
O2R, or %maximal heart rate. A graded exercise test is recommended for evaluating exercise capacity before and after exercise intervention. Most of the studies we reviewed determined exercise intensity based on the %
O2R and %HRmax data. Specifically, the initial exercise intensity prescribed was generally as low as 50% of
O2peak, representing an optimal moderate-intensity regimen (40%-60%
O2R),21 and increased up to 80%
O2R, representing vigorous exercise intensity used in 1 study.29
Current guidelines recommend prescribing a progressive increase in exercise intensity to achieve a safe and effective intervention.37 In general, %HRR and %
O2R parameters are used to determine exercise intensity; however, the rating of perceived exertion (RPE) is recommended for patients being treated with β-blockers or who have undergone heart transplantation. The RPE scale ranges from 6 to 20, and an RPE of 12 to 13 is consistent with moderate intensity, while an RPE of 14 to 17 is associated with vigorous intensity.31 Among the studies we reviewed, 2 mentioned the use of the RPE scale for prescribing exercise intensity using 12 to 14 and 13 to 15 ranges, respectively.2,14
Three of the studies evaluated in this review prescribed aerobic exercise for a total of 45 min/session, while Holloway et al2 prescribed 20 min of cycling-based exercise/day. The prescription for the duration of exercise in patients with chronic heart failure is usually 20 to 30 min at the desired intensity,36 while the duration of target aerobic exercise is generally 20 to 60 min/session for cardiac patients.37 Ultimately, the prescription for the initial duration of exercise should vary according to the individual current state of health of the patient and should also consider previous levels of physical activity and baseline exercise capacity. The exercise protocols of the reviewed studies included both continuous and intermittent exercise, for which the minimum duration of intermittent exercise should be at least 10 min.21 Lastly, the total duration of an exercise intervention in the reviewed articles was 2 to 7 mo; however, health professionals should adjust the initial prescription for exercise duration according to the health status of the patients, exercise tolerance, and exercise program goals.
A cycle ergometer is commonly used to assess aerobic exercise capacity and was the main exercise modality used in the reviewed studies. The type of exercise prescribed should be determined according to the goal of exercise. In general, both aerobic and strength exercises are recommended for cardiac patients. However, of the included studies, only Stolen et al13 combined both resistance training and aerobic exercise intervention. Different types of exercise training included aerobic training, resistance training, and combined training, all of which are safe and effective methods for maximizing improvement of exercise capacity.38 Furthermore, resistance training for cardiac patients is recommended as a way to complement aerobic training, and provides additional benefits with respect to muscular strength and endurance.39,40 In the study by Stolen et al,13 the training prescription consisted of a high number of repetitions (10-15) in 2 to 3 sets at a low frequency (2-3 sessions/wk). This recommendation is consistent with the general guidelines published by the American College of Sports Medicine (ACSM).41 Likewise, according to the ACSM guidelines for cardiac patients, it is recommended that patients start resistance exercise a minimum of 5 wk following myocardial infarction and cardiac surgery and a minimum of 2 to 3 wk following transcatheter procedures.42 Although the evidence supporting the effectiveness of resistance training for patients with DCM is scarce, combining resistance training along with aerobic training may be beneficial considering general exercise training guidelines for cardiac patients.
QUALITY OF LIFE
Quality of life in patients with DCM is considered an important parameter for both clinical and hard outcomes such as mortality, and should be included in any determination of the effect of exercise intervention. Selection of a relevant questionnaire is very important for properly evaluating the effects of exercise therapy.43,44 Questionnaires for QOL can be divided primarily into generic and disease-specific types.45 In this systematic review, 3 questionnaires were used, namely, the KCCQ, MLHFQ, and SF-36, for which the overall results showed that exercise led to an improvement in QOL compared with baseline results. The study conducted by Mehani12 showed a significant association between peak
O2 and KCCQ score, suggesting that exercise capacity may have a positive impact on QOL in patients with DCM.
This systematic review has some limitations. First, although we searched 4 large databases (PubMed, CENTRAL, EMBASE, and EBSCO), there is still the possibility that some relevant articles were not identified. There are other large databases such as CLINICAL and OVID that might include additional studies. Second, the present study identified only 4 articles using our review protocol and they all used relatively small samples. This makes generalization of the study findings to all patients with DCM difficult. Future research is needed to make general recommendations for exercise prescription.
In this systematic review, we evaluated the evidence for optimal exercise therapy in patients with DCM. Overall, exercise therapy appeared to be a safe and effective intervention for improving exercise capacity and QOL in patients with DCM. An exercise prescription for patients with DCM consisted of exercise frequency, intensity, time, and type according to recommendation by ACSM guidelines. The different results in reviewed articles resulted from application of different exercise intensity and times for each article. Therefore, these parameters should be considered an important factor in prescribing suitable exercise. Lastly, with respect to developing an exercise prescription for patients with DCM, it is important for exercise professionals to consider the baseline exercise capacity of the patients, previous exercise habits, and daily condition when prescribing initial exercise intensity and adjusting day-to-day training. Furthermore, large trials are needed to define optimal exercise intervention for patients with DCM considering the insufficiency of data from 4 reviewed studies.
1. Andersson B, Caidahl K, Waagstein F. An echocardiographic evaluation of patients with idiopathic heart failure. Chest. 1995;107(3):680–687.
2. Holloway CJ, Dass S, Suttie JJ, et al Exercise training in dilated cardiomyopathy
improves rest and stress cardiac function without changes in cardiac high energy phosphate metabolism. Heart. 2012;98(14):1083–1090.
3. Escobedo LG, Zack MM. Comparison of sudden and nonsudden coronary deaths in the United States. Circulation. 1996;93(11):2033–2036.
4. Leung WH, Lau CP, Wong CK, Cheng CH, Tai YT, Lim SP. Improvement in exercise performance and hemodynamics by labetalol in patients with idiopathic dilated cardiomyopathy
. Am Heart J. 1990;119(4):884–890.
5. Pina IL, Apstein CS, Balady GJ, et al Exercise and heart failure. Circulation. 2003;107(8):1210–1225.
6. Fleg JL, Cooper LS, Borlaug BA, et al Exercise training as therapy for heart failure. Circ Heart Fail. 2015;8(1):209–220.
7. Pollmann AGE, Frederiksen M, Prescott E. Cardiac rehabilitation
after heart valve surgery: improvement in exercise capacity and morbidity. J Cardiopulm Rehabil Prev. 2017;37(3):191–198.
8. Sagar VA, Davies EJ, Briscoe S, et al Exercise-based rehabilitation for heart failure: systematic review and mata-analysis. Open Heart. 2015;2(1):e000163.
9. O'Connor CM, Whellan DJ, Lee KL, et al HF-ACTION Investigators. Efficacy and safety of exercise training in patients with chronic heart failure: HF-ACTION randomized controlled trial. JAMA. 2009;301(14):1439–1450.
10. Bushman BA. Determining the I (intensity) for a FITT-VP aerobic exercise prescription
. ACSMs Health Fit J. 2014;18(3):4–7.
11. Kirin PC, Das S, Zinen P, et al The exercise response in idiopathic dilated cardiomyopathy
. Clin Cardiol. 1984;7(4):205–210.
12. Mehani S. Correlation between changes in diastolic dysfunction and health-related quality of life after cardiac rehabilitation
programs in dilated cardiomyopathy
. J Adv Res. 2013;4(2):189–200.
13. Stolen KQ, Kemppainen J, Ukkonen H, et al Exercise training improves biventricular oxidative metabolism and left ventricular efficiency in patients with dilated cardiomyopathy
. J Am Coll Cardiol. 2003;41(3):460–467.
14. Beer M, Wagner D, Myers J, et al Effects of exercise training on myocardial energy metabolism and ventricular function assessed by quantitative phosphorus-31 magnetic resonance spectroscopy and magnetic resonance imaging in dilated cardiomyopathy
. J Am Coll Cardiol. 2008;51(19):1883–1891.
15. Burns PB, Rohrich RJ, Chung KC. The levels of evidence and their role in evidence-based medicine. Plast Reconstr Surg. 2011;128:305–310.
16. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 8th ed. Philadelphia, PA: Lippincott Williams and Wilkins; 2010:84–89.
17. Hurst JW, Morris DC, Alexander RW. The use of the New York Heart Association's classification of cardiovascular disease as part of the patent's complete problem list. Clin Cardiol. 1999;22(6):385–390.
18. European Heart Failure Training Group. Experience from controlled trials of physical training in chronic heart failure. Protocol and patient factors in effectiveness in the improvement in exercise tolerance. Eur Heart J. 1998;19(3):466–475.
19. Yap J, Lim FY, Gao F, Teo LL, Lam CS, Yeo KK. Correlation of the New York Heart Association Classification and the 6-minute walk distance: a systematic review. Clin Cardiol. 2015;38(10):621–628.
20. Hawkins MN, Raven PB, Snell PG, et al Maximal oxygen uptake as a parametric measure of cardiorespiratory capacity. Med Sci Sports Exerc. 2007;39(1):103–107.
21. Haskell WL, Lee IM, Pate RR, et al Physical activity and public health: updated recommendation from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc. 2007:39(8):1423–1434.
22. Kokkinos P, Myers J, Faselis C, et al Exercise capacity and mortality in older men: a 20-year follow-up study. Circulation. 2010;122(8):790–797.
23. Kokkinos P, Manolis A, Pittaras A, et al Exercise capacity and mortality in hypertensive men with and without additional risk factors. Hypertension. 2009;53(3):494–499.
24. Kodama S, Saito K, Tanaka S, et al Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA. 2009;301(19):2024–2035.
25. van den Broek SA, van Veldhuisen DJ, de Graeff PA, Landsman ML, Hillege H, Lie KI. Comparison between New York Heart Association classification and peak oxygen consumption in the assessment of functional status and prognosis in patients with mild to moderate chronic congestive heart failure secondary to either ischemic or idiopathic dilated cardiomyopathy
. Am J Cardiol. 1992;70(3):359–363.
26. Russell SD, Saval MA, Robbins JL, et al New York Heart Association functional class predicts exercise parameters in the current era. Am Heart J. 2009;158(4):24–30.
27. Smart N, Marwick TH. Exercise training for patients with heart failure: a systematic review of factors that improve mortality and morbidity. Am J Med. 2004;116(10):693–706.
28. Uddin J, Zwisler AD, Lewinter C, et al Predictors of exercise capacity following exercise-based rehabilitation in patients with coronary heart disease and heart failure: a meta-regression analysis. Eur J Prev Cardiol. 2016;23(7):683–693.
29. Myers J. Principles of exercise prescription
for patients with chronic heart failure. Heart Fail Rev. 2007;13(1):61–68.
30. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 8th ed. Philadelphia, PA: Lippincott Williams and Wilkins; 2010:154.
31. American College of Sports Medicine. ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription. 7th ed. Philadelphia, PA: Lippincott Williams and Wilkins; 2014; 468–470.
32. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 8th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2010:153.
33. Roveda F, Middlekauff HR, Rondon MU, et al The effects of exercise training on sympathetic neural activation in advanced heart failure: a randomized controlled trial. J Am Coll Cardiol. 2003;42(5):854–860.
34. Demopoulos L, Bijou R, Fergus I, Jones M, Strom J, LeJemtel TH. Exercise training in patients with severe congestive heart failure: enhancing peak aerobic capacity while minimizing the increase in ventricular wall stress. J Am Coll Cardiol. 1997;29(3):597–603.
35. Dubach P, Myers J, Dziekan G, et al Effect of high intensity exercise training on central hemodynamic responses to exercise in men with reduced left ventricular function. J Am Coll Cardiol. 1997;29(7):1591–1598.
36. Belardinelli R, Georgiou D, Scocco V, Barstow TJ, Purcaro A. Low intensity exercise training in patients with chronic heart failure. J Am Coll Cardiol. 1995;26(4):975–982.
37. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 8th ed. Philadelphia, PA: Lippincott Williams and Wilkins; 2010:213.
38. Vona M, Codeluppi GM, Iannino T, Ferrari E, Bogousslavsky J, Segesser LK. Effects of different types of exercise training followed by detraining on endothelium-dependent dilation in patients with recent myocardial infarction. Circulation. 2009;119(12):1601–1608.
39. Piepoli MF, Conraads V, Corrà U, et al Exercise training in heart failure: from theory to practice. A consensus document of the Heart Failure Association and the European Association for Cardiovascular Prevention and Rehabilitation. Eur J Heart Fail. 2011;13(4):347–357.
40. Vanhees L, Rauch B, Piepoli M, et al Importance of characteristics and modalities of physical activity and exercise in the management of cardiovascular health in individuals with cardiovascular disease (part III). Eur J Prev Cardiol. 2012;19(6):1333–1356.
41. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 8th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2010:165–170.
42. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 8th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2010:219–220.
43. Mayou R, Bryant B: Quality of life in cardiovascular disease. Br Heart J. 1993;69(5):460–466.
44. Treasure T. The measurement of health related quality of life. Heart. 1999;81(4):331–332.
45. Thompson DR, Yu CM. Quality of life in patients with coronary heart disease-I: assessment tools. Health Qual Life Outcomes. 2003;1(1):42.
Keywords:Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
cardiac rehabilitation; dilated cardiomyopathy; exercise prescription