Abstract
OBJECTIVES
The purpose of this study was to compare the effectiveness of moderate-intensity stationary cycling and walking exercise programmes in the early postoperative period after first-time coronary artery bypass graft surgery.
METHODS
In this prospective trial, 64 patients (57 men, 7 women, mean age = 66 ± 9 years) performed twice daily, moderate-intensity exercise sessions, of 10-min duration, from postoperative day 3 until discharge from hospital. Patients were randomly assigned to stationary cycling or walking exercise intervention groups. Preoperative and discharge functional exercise capacity and health-related quality of life were assessed using 6-min walk and cycle assessments and the SF-36 version 2.0 questionnaire. Compliance with exercise was calculated as the proportion of scheduled exercise sessions completed.
RESULTS
There were no significant differences between intervention groups at hospital discharge for 6-min walk distance (cyclists: 402 ± 93 m vs walkers: 417 ± 86 m, P = 0.803), 6-min cycle work (cyclists: 15.0 ± 6.4 kJ vs walkers: 14.0 ± 6.3 kJ, P = 0.798) or health-related quality of life. There was no significant difference between intervention groups for postoperative length of hospital stay (P = 0.335). Compliance rates for intervention groups were cyclists: 185/246 (75%) scheduled exercise sessions completed vs walkers: 199/242 (82%) scheduled exercise sessions completed (P = 0.162).
CONCLUSIONS
Stationary cycling provides a well-tolerated and clinically effective alternative to walking in the early postoperative period after coronary artery bypass graft surgery. The optimal frequency, intensity and duration of exercise in the early postoperative period require further investigation. (Clinical trials register: Australian New Zealand Clinical Trials Registry; identification number: ACTRN12608000359336; http://www.anzctr.org.au/trial_view.aspx?ID=82978).
Keywords: Coronary artery surgery, Exercise, Physical therapy modalities, Postoperative care
INTRODUCTION
The aims of an exercise-based cardiac rehabilitation programme in the early postoperative (inpatient) period after coronary artery bypass graft surgery (CABG) are to restore the physical functional capacity of the patient and establish appropriate levels of physical activity after hospital discharge [1]. The American College of Sports Medicine has published guidelines for exercise prescription in the early postoperative period after CABG [1]. These guidelines make recommendations on the intensity, duration, frequency and pertinently, mode of exercise.
Despite early reports of the safe use of stationary cycling after CABG [2, 3], stationary cycling is neither recommended in the guidelines, nor customarily selected as a mode of exercise in the early postoperative period. Walking exercise is, however, explicitly recommended in the guidelines and commonly prescribed by surgeons and allied health practitioners after CABG [1, 4–6]. Patients prescribed postoperative walking exercise programmes have significantly better functional capacity at hospital discharge after CABG than ‘no exercise’ controls [7], and a significantly reduced postoperative length of hospital stay [8].
Contrary to what is known about the benefits of walking exercise in the early postoperative period after CABG, there are few, if any, studies that support the inclusion of appropriately prescribed stationary cycling exercise for patients after CABG. Indeed, a review of Cochrane Central, Medline, CINAHL, Web of Science and PEDro databases found no studies comparing stationary cycling and walking exercise programmes in the early postoperative period after CABG. Therefore the aims of the present study were to determine: (i) whether moderate-intensity, stationary cycling improves functional capacity and health-related quality of life (HR-QoL) at hospital discharge when compared with moderate-intensity walking exercise after CABG? and (ii) what the compliance is of patients with moderate-intensity stationary cycling and walking exercise in the early postoperative period after CABG?
MATERIALS AND METHODS
The present study was conducted at Westmead Private Hospital, Sydney, Australia. Ethical approval for the study was obtained from Sydney West Area Health Service and Griffith University Human Research Ethics Committees, and written consent was obtained from patients prior to their participation.
Participants
Between August 2008 and July 2009, consecutive patients awaiting first-time CABG were assessed for study eligibility. A priori exclusion criteria were planned concomitant surgery and a clinical status that required emergency CABG. Additional exclusion criteria were musculoskeletal, neurological or peripheral vascular impairment that precluded the planned exercise testing and training and a non-English speaking background.
Randomization
Patients were randomized to intervention group (stationary cycling or walking) through means of selection of cards within sequentially numbered, sealed, opaque envelopes. Randomization was stratified by sex and by presence or absence of acute myocardial infarction (AMI) within the 4 weeks prior to surgery.
Sample size calculations
Preliminary sample size calculations indicated that recruitment of 64 patients would provide 80% power to detect a clinically important difference (54 m) [9] in discharge 6-min walk distance (6MWD) at a significance level of 0.05, assuming a standard deviation of 75 m. Recent investigations of the 6-min walk test (6MWT), published subsequent to the present study, report a smaller clinically important difference of 25–35 m for the 6MWT in patients with chronic obstructive pulmonary disease [10, 11].
Interventions
The four cardiothoracic surgeons operating at Westmead Private Hospital during the present study used a common clinical pathway for the perioperative care of patients undergoing CABG. The interventions received by stationary cycling and walking exercise groups are listed in Table 1. Interventions were administered by members of the hospital's physiotherapy department. For the first 2 days postoperatively, all patients received identical interventions. Study interventions, i.e. twice daily, 10-min stationary cycling and walking exercise sessions, commenced from postoperative day (POD) 3.
Table 1:
Interventions for stationary cycling and walking groups
| Stationary cycling | Walking | |
|---|---|---|
| Preoperative | Respiratory assessment | As per stationary cycling group |
| Education regarding the effects of surgery on respiratory function and postoperative respiratory techniques | ||
| Education regarding the use of the Borg CR-10 Scale® in relation to postoperative exercise | ||
| POD 1 | Morning | As per stationary cycling group |
| Patient assisted to sit upright in bed | ||
| Respiratory assessment and techniques | ||
| Shoulder and thoracic spine ROM movements | ||
| Afternoon | ||
| Patient assisted to walk on spot (3 repetitions of 1 min) and to sit out of bed | ||
| Respiratory assessment and techniques | ||
| Shoulder and thoracic spine ROM movements | ||
| POD 2 | Morning | As per stationary cycling group |
| Patient assisted to walk ∼100 m and to sit out of bed | ||
| Respiratory assessment and techniques | ||
| Shoulder and thoracic spine ROM movements | ||
| Afternoon | ||
| Patient assisted to walk ∼5 min and to sit out of bed | ||
| Respiratory assessment and techniques | ||
| Shoulder and thoracic spine ROM movements | ||
| POD 3 onwards | First a.m. | First a.m. |
| Respiratory assessment and techniques | Respiratory assessment and techniques | |
| Shoulder and thoracic spine ROM movements | Shoulder and thoracic spine ROM movements | |
| Morning | Morning | |
| 10-min physiotherapy-supervised stationary cycling exercise session | 10-min physiotherapy-supervised walking exercise session | |
| Patient instructed to exercise at an RPE of 3–4 of 10 | Patient instructed to exercise at an RPE of 3–4 of 10 | |
| Afternoon | Afternoon | |
| 10-min physiotherapy-supervised stationary cycling exercise session | 10-min physiotherapy-supervised walking exercise session | |
| Patient instructed to exercise at an RPE of 3–4 of 10 | Patient instructed to exercise at an RPE of 3–4 of 10 | |
| Prior to hospital discharge | Patient supervised in ascent/descent of stairs (performed on one occasion prior to hospital discharge) | As per stationary cycling group |
| Education regarding the progression of exercise following hospital discharge | ||
| Referral to outpatient CR |
POD: postoperative day; ROM: range-of-motion; RPE: rating of perceived exertion; CR: cardiac rehabilitation.
Stationary cycling exercise sessions were undertaken on an electronically braked cycle ergometer (Lode Excalibur, Quinton Instruments, Seattle). The cycle ergometer was programmed such that the power was proportional to the square of the cycling speed. Walking exercise sessions took place in an indoor, air-conditioned corridor.
A supine resting 12-lead ECG was performed before all exercise sessions, and patients were monitored with wireless 12-lead ECG (Mortara X12+, Mortara Instrument, Milwaukee) throughout each exercise session and for 5 min post exercise. Systolic and diastolic blood pressure (SBP, DBP) measurements were taken at rest before all exercise sessions (supine and seated), at the end of each exercise session (seated) and again 5 min post exercise (seated). Individual exercise sessions were not commenced if any of the following criteria were met: resting heart rate (HR) <40 beats min−1 or > 125 beats min−1; resting SBP > 200 mmHg or resting DBP > 110 mmHg; atrial fibrillation (AF) with signs of haemodynamic compromise; if the patient required inotropic support or invasive haemodynamic monitoring; if the patient declined to exercise, e.g. for reasons of fatigue or pain; or if the treating physiotherapist had other concerns for the patient's safety.
Exercise sessions were terminated if the patient's HR consistently exceeded 90% of their age-predicted maximum HR (calculated as 220 − age), or fell below 40 beats min−1; if the patient showed signs of ataxia, cyanosis, pallor, diaphoresis, severe dyspnoea or angina; or if the treating physiotherapist had other concerns for the patient's safety.
Patients were familiarized with the Borg CR-10 Scale® prior to each exercise session [12], and were instructed to exercise at an RPE of 3–4 (‘moderate’ to ‘somewhat strong’). Patients were allowed to rest as required within the exercise sessions, however sessions were not extended beyond 10 min. Supplemental oxygen was used during exercise sessions if the resting oxygen saturation (SpO2) was <92% breathing room air.
In addition to the study interventions, patients performed physiotherapy-supervised respiratory techniques and musculoskeletal movements per standard clinical protocols [7].
Primary outcomes
The primary outcome measures for the study were (i) 6MWA distance; (ii) 6-min cycle assessment (6MCA) work and (iii) HR-QoL, as measured by the SF-36 version 2.0 questionnaire (SF-36v2) [13]. Testing took place on the day prior to surgery (preoperative) and on the day of hospital discharge (discharge) as determined by the operating surgeon who was blinded to the intervention group. Tests were administered by one of two physiotherapists, including the primary researcher, who were also blinded to the intervention group.
The 6-min walk assessment (6MWA)
The 6MWA was conducted as previously described [7]. Patients were instructed to walk lengths of a 43.5 m corridor for 6 min, walking as far as possible while maintaining an RPE of 3–4. Monitoring, commencement and termination criteria for the 6MWA were as per exercise sessions. The preoperative 6MWA was also omitted if patients had current resting angina, presented with recent AMI, required intravenous anticoagulant medication, or if the surgeon or cardiologist anticipated a possibility of AMI with testing. Walk distance was measured to the nearest 0.5 m.
The 6-min cycle assessment
Cycling capacity was assessed using a 6MCA, similar to that described and validated by Verrill et al. [14]. The 6MCA was performed 1 h following completion of the 6MWA. Monitoring, commencement and termination criteria for the 6MCA were again as per exercise sessions. In the 6MCA, patients were instructed to cycle on an electronically braked cycle ergometer for 6 min, producing as much work as possible while maintaining an RPE of 3–4 of 10. As with stationary cycling exercise sessions, the cycle ergometer was programmed such that power was proportional to the square of the cycling speed. Work for the 6MCA was measured to the nearest 0.1 kJ.
The SF-36 version 2.0
Patients completed preoperative and discharge SF-36v2 questionnaires while resting between the 6MWA and the 6MCA. The SF-36v2 is a generic, HR-QoL questionnaire that yields an eight sub-scale profile of scores reflecting differing health concepts (physical function, role-physical, bodily pain, general health, vitality, social function, role-emotional, mental health) [13]. The ‘acute’ version of the questionnaire with a 1-week recall period was used. Raw sub-scale scores were transformed to ‘norm-based’ scores using published algorithms [13]. Norm-based physical and mental component summary (PCS, MCS) scores were also calculated from raw sub-scale scores.
Secondary outcomes
Compliance
Exercise sessions were numbered sequentially from the morning of POD 3 onwards. Compliance with stationary cycling and walking exercise programmes was calculated for individual exercise sessions as the proportion of patients completing that number session with their prescribed mode of exercise. Patients were deemed to have completed an exercise session if the exercise session was commenced and was not terminated by patient or physiotherapist.
Postoperative complications and mortality
The incidence of postoperative AF was determined through review of the medical record at the time of hospital discharge. Patients were contacted by telephone at 6 months postoperatively regarding outpatient cardiac rehabilitation attendance (not reported here), enabling the determination of 6-month mortality.
Statistical methods
Repeated measures analysis of variance was used to compare intervention groups for 6MWA distance, 6MCA work, SF-36v2 norm-based sub-scale scores, PCS and MCS. Mean between-group differences and 95% confidence intervals (CIs) for 6MWA distance and 6MCA work at hospital discharge were calculated using independent samples t-tests, with preoperative scores used as a covariate. Kruskal–Wallis non-parametric analysis of variance was used to test for group differences in postoperative length of hospital stay.
Generalized linear mixed effects models were used to assess the impact of intervention group, exercise session number and their interaction, on the odds of patients completing an exercise session. Pearson chi-square and Fisher's exact test were used to compare intervention groups for the incidence of AF and 6-month mortality.
The statistical software packages S-PLUS version 8.0, SPSS for Windows version 12.0 and SPSS Statistics 17.0 for Mac were used to analyse the data. Two-tailed tests with a 5% significance level were used throughout.
RESULTS
A flowchart indicating the progression of patients through the study is shown in Fig. 1. Thirty-four patients were initially allocated to the stationary cycling group and 32 to the walking group. Two patients, both randomized to the stationary cycling group, were excluded prior to the completion of the preoperative assessment. Excluded patients had a similar male:female ratio to included patients (22:6 vs 57:7, P = 0.184). Baseline anthropometric data, preoperative clinical characteristics and perioperative data for the 64 patients attending preoperative assessment are shown in Table 2. All 64 patients had CABG with the use of cardiopulmonary bypass.
Figure 1:
Flowchart of patients through the study period. *Excluded from subsequent analysis; **analyzed on an ‘intention-to-treat’ basis.
Table 2:
Baseline anthropometric data, clinical characteristics and selected perioperative parameters for intervention groups and for all patients (mean ± SD)
| Stationary cycling (n = 32) | Walking (n = 32) | All patients (n = 64) | |
|---|---|---|---|
| Age (years) | 65.3 ± 9.8 | 65.9 ± 8.7 | 65.6 ± 9.2 |
| Height (m) | 1.70 ± 0.09 | 1.69 ± 0.07 | 1.69 ± 0.08 |
| Weight (kg) | 87.3 ± 19.3 | 79.5 ± 13.9 | 83.4 ± 17.2 |
| BMI (kg m−2) | 30.1 ± 4.9 | 27.9 ± 3.9 | 29.0 ± 4.5 |
| Male, AMI | 3 | 4 | 7 |
| Male, no AMI | 24 | 26 | 50 |
| Female, AMI | 2 | 1 | 3 |
| Female, no AMI | 3 | 1 | 4 |
| Chronic obstructive pulmonary disease | 2 | 2 | 4 |
| Smoking history (current smoker:past smoker:non-smoker) | 2:19:11 | 3:15:14 | 5:34:25 |
| Diabetes (insulin dependent:oral agent treatment:diet-controlled:non-diabetic) | 1:3:2:26 | 2:8:2:20 | 3:11:4:46 |
| Hypertension | 26 | 30 | 56 |
| Cerebrovascular disease | 2 | 2 | 4 |
| Peripheral arterial vascular disease | 2 | 0 | 2 |
| Previous cardiac intervention | 7 | 4 | 11 |
| NYHA I | 10 | 7 | 17 |
| NYHA II | 13 | 20 | 33 |
| NYHA III | 4 | 2 | 6 |
| NYHA IV | 5 | 3 | 8 |
| Elective:urgent | 21:11 | 24:8 | 45:19 |
| Number of distal anastamoses | 3.5 ± 1.1 | 3.5 ± 1.2 | 3.5 ± 1.1 |
| Number of arterial anastamoses | 1.3 ± 0.8 | 1.4 ± 1.1 | 1.4 ± 1.0 |
| Number of venous anastamoses | 2.2 ± 1.3 | 2.1 ± 1.3 | 2.1 ± 1.3 |
| Operation duration (min) | 189 ± 59 | 180 ± 54 | 184 ± 56 |
| Cardiopulmonary bypass time (min) | 73 ± 29 | 67 ± 30 | 70 ± 29 |
| Aortic cross-clamp time (min) | 46 ± 18 | 46 ± 21 | 46 ± 19 |
| Postoperative ventilation time (h) | 9.3 ± 3.2 | 9.8 ± 3.8 | 9.5 ± 3.5 |
BMI: body mass index; AMI: acute myocardial infarction; NYHA: New York Heart Association (Class).
Two patients allocated to the stationary cycling group switched to the walking exercise programme, due to: (i) debilitation precluding mounting the ergometer and (ii) anxiety regarding cycling. One patient allocated to the walking group switched to the stationary cycling exercise programme, as he refused to exercise outside his room. One patient allocated to the walking group failed to attend any exercise sessions due to severe postoperative debilitation. Data for all patients were analysed on an intention-to-treat basis.
Primary outcome data
6MWA, 6MCA and norm-based SF-36v2 data are presented in Tables 3 and 4. Sixteen patients did not commence a preoperative 6MWA for the following reasons: recent AMI (n = 10); intravenous anticoagulant (n = 2); surgeon or cardiologist's recommendation (n = 2); groin haematoma (n = 1) and resting angina (n = 1). Four patients did not complete the preoperative 6MWA, for reasons of angina during testing (n = 3) and uncontrolled tachycardia (n = 1). An additional 3 patients did not commence a preoperative 6MCA, 2 of whom had demonstrated persistent T-wave inversion on ECG for >5 min after the 6MWA (which had resolved by 15 min after completion of the 6MWA), and 1 because of failure of the ECG monitoring. Two patients did not complete the preoperative 6MCA due to uncontrolled tachycardia (n = 1) and frequent multifocal ventricular ectopic beats (n = 1).
Table 3:
Six-minute walk assessment (6MWA) distance and 6-min cycle assessment (6MCA) work preoperatively and at hospital discharge for intervention groups and for all patients (mean ± SD)
| Preoperative | Discharge | P value (vs preoperative) | Mean difference (95% CI) | P value for between-group differences at dischargea | Mean (95% CI) for between-group differences at dischargea | |
|---|---|---|---|---|---|---|
| 6MWA (m) | ||||||
| Stationary cycling | 450 ± 76 (n = 24) | 401 ± 93 (n = 32) | ||||
| Walking | 484 ± 86 (n = 20) | 417 ± 86 (n = 31) | ||||
| All patients | 465 ± 82 (n = 44) | 408 ± 89 (n = 63) | <0.001 | −56 (−77 to −34) | 0.803 | −5 (−50 to 39) |
| 6MCA (kJ) | ||||||
| Stationary cycling | 19.1 ± 10.6 (n = 22) | 15.0 ± 6.4 (n = 30) | ||||
| Walking | 19.0 ± 9.9 (n = 17) | 14.0 ± 6.3 (n = 30) | ||||
| All patients | 19.0 ± 10.2 (n = 39) | 14.5 ± 6.3 (n = 60) | 0.001 | −3.6 (−5.7 to −1.6) | 0.798 | −0.4 (−3.2 to 2.5) |
As there were no interaction between group and time effects, within-group differences in means are reported only for ‘all patients’.
aUsing preoperative scores as covariate.
Table 4:
Norm-based SF-36v2 sub-scale and component summary scores preoperatively and at hospital discharge for intervention groups and for all patients (mean ± SD)
| Preoperative (n = 64) | Discharge (n = 63) | P value (vs preoperative) | Mean difference (95% CI) | P value for between-group differences | |
|---|---|---|---|---|---|
| Physical function | |||||
| Stationary cycling | 42 + 11 | 37 ± 10 | |||
| Walking | 43 ± 9 | 36 ± 8 | |||
| All patients | 42 ± 10 | 37 ± 9 | <0.001 | −6 (−8 to −3) | 0.848 |
| Role-physical | |||||
| Stationary cycling | 38 ± 12 | 28 ± 9 | |||
| Walking | 37 ± 13 | 30 ± 10 | |||
| All patients | 37 ± 12 | 29 ± 10 | <0.001 | −8 (−12 to −4) | 0.863 |
| Bodily pain | |||||
| Stationary cycling | 49 ± 11 | 37 ± 9 | |||
| Walking | 49 ± 11 | 34 ± 10 | |||
| All patients | 49 ± 11 | 36 ± 9 | <0.001 | −13 (−17 to −10) | 0.723 |
| General health | |||||
| Stationary cycling | 49 ± 9 | 52 ± 8 | |||
| Walking | 47 ± 8 | 49 ± 8 | |||
| All patients | 48 ± 9 | 50 ± 8 | 0.011 | 2 (1 to 4) | 0.203 |
| Vitality | |||||
| Stationary cycling | 47 ± 10 | 44 ± 9 | |||
| Walking | 46 ± 10 | 44 ± 10 | |||
| All patients | 47 ± 10 | 44 ± 9 | 0.048 | −3 (−6 to 0) | 0.858 |
| Social function | |||||
| Stationary cycling | 44 ± 15 | 30 ± 16 | |||
| Walking | 41 ± 15 | 29 ± 13 | |||
| All patients | 43 ± 15 | 30 ± 14 | <0.001 | −13 (−17 to −8) | 0.541 |
| Role-emotional | |||||
| Stationary cycling | 43 ± 12 | 39 ± 17 | |||
| Walking | 43 ± 14 | 39 ± 15 | |||
| All patients | 43 ± 13 | 39 ± 16 | 0.124 | −4 (−9 to 1) | 0.804 |
| Mental health | |||||
| Stationary cycling | 46 ± 12 | 47 ± 9 | |||
| Walking | 49 ± 10 | 48 ± 10 | |||
| All patients | 48 ± 11 | 48 ± 10 | 1.000 | 0 (−3 to 3) | 0.359 |
| PCS | |||||
| Stationary cycling | 44 ± 10 | 36 ± 7 | |||
| Walking | 43 ± 8 | 34 ± 7 | |||
| All patients | 43 ± 9 | 35 ± 7 | <0.001 | −8 (−11 to −6) | 0.482 |
| MCS | |||||
| Stationary cycling | 46 ± 11 | 44 ± 10 | |||
| Walking | 47 ± 11 | 44 ± 12 | |||
| All patients | 47 ± 11 | 44 ± 11 | 0.170 | −2 (−5 to 1) | 0.897 |
As there were no interactions between group and time effects, within-group differences in means are reported only for ‘all patients’.
PCS: Physical Component Summary (score); MCS: Mental Component Summary (score).
One patient in the walking group remained too unwell at the time of discharge to perform a discharge 6MWA and 6MCA. Outcome data for the 6MCA for one patient in the walking group was electronically lost. Two further patients, both from the stationary cycling group, did not attend a discharge 6MCA due to coccygeal pain and unspecified reasons respectively. One patient from the stationary cycling group did not complete a discharge SF-36v2.
There were no significant differences between intervention groups for either 6MWA distance or 6MCA work. There was a significant decrease in both 6MWA distance and 6MCA work from preoperative to discharge for ‘all patients’. There were no significant differences between intervention groups for any aspect of HR-QoL, i.e. sub-scale and component summary scores of the SF-36v2. PCS score decreased significantly from preoperative to discharge, but there was no significant change in MCS score.
There was no significant difference in postoperative length of hospital stay between intervention groups (stationary cycling: mean: 7.9 ± 1.7 days, median: 7 days, inter-quartile range (IQR): 7.0–8.5 days vs walking: mean: 7.7 ± 2.7 days, median: 7.0 days, IQR: 7.0–8.0 days, P = 0.335).
Secondary outcome data
Completion rates for stationary cycling and walking exercise sessions from POD 3 to POD 6 are shown in Table 5. One hundred and eighty-five of 246 (75%) of scheduled stationary cycling exercise sessions, and 199 of 242 (82%) of scheduled walking exercise sessions were completed. There was no significant difference in completion rates between intervention groups (P = 0.162), nor were there significant differences in completion rates across exercise sessions for either intervention group (stationary cycling: P = 0.972, walking: P = 0.211).
Table 5:
Completion rates for exercise sessions 1–8 (from postoperative day 3 to postoperative day 6) for intervention groups
| POD 3 |
POD 4 |
POD 5 |
POD 6 |
|||||
|---|---|---|---|---|---|---|---|---|
| Morning | Afternoon | Morning | Afternoon | Morning | Afternoon | Morning | Afternoon | |
| Exercise session number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Stationary cycling | 26/32 (81%) | 23/32 (72%) | 24/32 (75%)a | 26/32 (81%)a | 24/31 (77%)a | 23/31 (74%)a | 21/28 (75%)a | 18/28 (64%)a |
| Walking | 25/32 (78%) | 24/32 (75%)b | 25/32 (78%)b | 26/32 (81%)b | 27/32 (84%) | 30/32 (94%)b | 20/25 (80%)b | 22/25 (88%)b |
POD: postoperative day.
aAdditional one patient allocated to the stationary cycling group completed a walking exercise session.
badditional one patient allocated to the walking group completed a stationary cycling exercise session.
Reasons for not commencing exercise sessions were inotropic support required (n = 5); cardiac rate/rhythm disturbance (n = 33); non-cardiac medical reason (n = 31); patient performed sessions, but with the alternative mode of exercise (n = 12) and patient declined to perform sessions (n = 18). Five exercise sessions were terminated due to: cardiac rate/rhythm disturbance (n = 1) and patient request secondary to fatigue (n = 4).
Twenty-two patients (34%) experienced AF before hospital discharge. There was no significant difference between intervention groups for the incidence of AF (stationary cycling: 13/32 patients (41%) vs walking: 9/32 patients (28%), P = 0.292). No patient experienced sternal wound healing disturbance before hospital discharge, nor was any patient re-admitted to Westmead Private Hospital within 6 months of hospital discharge for sternal wound management. There was no difference in 6-month mortality between intervention groups (stationary cycling: 0/32 patients (0%) vs walking: 1/31 patients (3%), P = 0.492 (1 patient uncontactable).
Discussion
This study is the first to have compared stationary cycling and walking exercise programmes in the early postoperative (inpatient) period after CABG. Moderate-intensity stationary cycling was found to be as effective as moderate-intensity walking exercise in the restoration of postoperative functional exercise capacity, independent of the mode of exercise testing. Mode of exercise did not affect HR-QoL at the time of hospital discharge, or postoperative length of hospital stay. Finally, there was no significant difference in compliance to stationary cycling and walking exercise programmes. As such, stationary cycling presents a practical alternative to walking exercise in Phase I CR after CABG.
Mean 6MWA distances at hospital discharge for both stationary cycling and walking exercise groups (stationary cycling: 401 ± 93 m, walking: 417 ± 86 m) were similar to those previously reported for patients receiving postoperative exercise interventions after CABG (431 ± 98 to 444 ± 84 m) [7]. Five other studies have reported the use of a non-RPE regulated 6MWT performed ∼7 days after CABG (with varying postoperative exercise regimens) [8, 15–18]; of these five studies only one reported considerably higher 6MWDs (466 ± 82 m to 560 ± 73 m) than the present study [15]. In that study, patients were younger (mean age 60 ± 8 years) and almost exclusively male (15/16 patients), and two postoperative 6MWTs were performed at hospital discharge with the higher distance being recorded.
The 6MCA was novel to this study, precluding comparison with previous research. Verrill et al. described the use of a ‘North Carolina 6-Minute Cycle Test’ (6MCT) at entry to a Phase II CR programme after CABG [14]; outcome for this 6MCT, however, was reported as the distance cycled, rather than work produced. As the 6MCT necessitates the use of a specific cycle ergometer (the Schwinn Airdyne, Nautilus, Inc., WA, USA), the ability to generalize 6MCT data beyond institutions using this equipment is limited. The only available data pertaining to cycling power/work within Phase I CR after CABG are those reported by Kirkeby-Garstad et al. who imposed supine cycling workloads of 10 and 30 W on POD 1, primarily with a view to assessment of physiological responses [19].
HR-QoL is increasingly being used as an objectively measurable, albeit patient-subjective, outcome of cardiac surgery. The SF-36v2 questionnaire used in the present study has been shown to correlate well with symptoms of coronary artery disease, and is sensitive to change over time in patients undergoing cardiac surgery [20]. SF-36v2 sub-scale and component summary scores in the present study are similar to those reported previously for patients undergoing CABG [7], however there was no significant change in MCS from preoperative to hospital discharge. A review of studies using generic HR-QoL instruments in patients undergoing CABG concluded that these instruments, including the SF-36v2, lacked sensitivity to detect differences between intervention groups [21].
Day-to-day compliance with Phase I CR exercise programmes after CABG has not been previously reported. Individual session compliance rates of ≥72% in the current study, regardless of mode of exercise, suggest that supervised, moderate-intensity exercise is both feasible and well-tolerated by POD 3. Notwithstanding the potential physiological benefits of this early postoperative exercise [22], promotion of moderate-intensity exercise to hospital-confined patients is also consistent with the physical activity counselling recommended in Phase II CR [23].
The finding that stationary cycling is as effective as walking exercise in Phase I CR has practical clinical implications. As the thorax and upper limbs are stationary throughout, stationary cycling facilitates the measurement and recording of haemodynamic parameters and pulse oximetry. Stationary cycling may thus be more promptly constrained or terminated should the patient have haemodynamic or respiratory compromise. Stationary cycling also allows for more precise measurement and manipulation of the imposed exercise load and total exercise dose than walking exercise [24]. Additionally, stationary cycling may provide an option for exercise training in those patients, albeit excluded from the present study, with orthopaedic or neurological conditions affecting gait, or who would normally require the use of gait aids. Potential limitations of stationary cycling as a mode of exercise relate primarily to the cycle ergometer, e.g. patient discomfort, ergometer purchase and maintenance costs, and transport implications. In comparison to walking, stationary cycling does require an increased knee flexion range of motion, which theoretically might have implications for saphenous vein graft site pain and/or bleeding. In the present study, no exercise session, stationary cycling or walking, was omitted or terminated for reasons of graft site pain or bleeding. It is noted, however, that in those patients requiring saphenous vein grafts (51/64 patients), endoscopic harvesting techniques were predominantly used.
Limitations of the study
The assessments of functional exercise capacity used in the current study were submaximal and RPE regulated. Relationships between performance on the 6MWA and 6MCA, and gold-standard measures of exercise capacity, e.g. maximal cardiopulmonary exercise testing, have yet to be established. Nonetheless, it is suggested that the 6MWA and 6MCA prima facie give an indication of exercise ‘ability’ at a level of exertion commonly prescribed in CR. Notwithstanding the use of RPE-regulated assessments in the current study, 25/64 participants (39%) remained unable to commence or complete both preoperative assessments, due to the possibly conservative commencement and termination criteria. Preoperative and discharge 6MWAs and 6MCAs were also performed at different times of the day due to hospital admission and discharge procedures; it is possible that time of day might have impacted, albeit minimally, on assessment performance.
Both men and women were included in the present study, so that results might be applicable to the broader population of patients undergoing CABG. It is noted however, that there are considerable data on sex-related differences in the acute cardiovascular response to exercise, and adaptive responses to exercise training [25]. Given that a minority of participants (7/64, 11%) in the present study were women, future research might look to confirm the findings in a larger cohort of women.
Conclusions
Moderate-intensity stationary cycling and walking exercise programmes are equally effective in the restoration of functional exercise capacity in the early postoperative period after CABG. Both modes of exercise are well tolerated. As such, surgeons and health practitioners prescribing and investigating aerobic exercise early after CABG should consider stationary cycling as a practical alternative mode of exercise to traditional walking. The optimal frequency, intensity and duration of exercise in the early postoperative period after CABG require further investigation.
Acknowledgements
The authors acknowledge the assistance of cardiothoracic surgeons Richard Chard, Robert Costa, Ian Nicholson and Hugh Paterson, and the clinical and administrative staff of Westmead Private Hospital, in facilitating the conduct of the study, and Karen Byth-Wilson, biostatistician, for advice with the statistical analysis.
Conflict of interest: none declared.
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