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Patients
Data were analysed of a cohort of all consecutive patients (≥ 18 years) scheduled for elective open heart surgery, including coronary artery bypass graft surgery, valve surgery, aortic surgery, or combinations of these surgeries in the University Medical Center Groningen (UMCG), the Netherlands, between March 2015 and August 2016 and who were invited to participate in the Heart-ROCQ-pilot program. Patients from regional hospitals are referred to the Heart Center of Groningen for Heart Team consultation immediately after diagnosis. This process normally takes 2–3 days. After the Heart Team makes a decision about the treatment, the referring cardiologist is notified the same day and the patient is placed on the waiting list within one week for surgery at the UMCG and concomitantly for inclusion in the Heart-ROCQ-pilot program. Patients were excluded if they had comorbidities that prevented participation in one of the program elements (e.g., disorders to the nervous or musculoskeletal system that limit exercise capacity, severe COPD with GOLD classification ≥ 3, non-coping behaviour, addiction, serious psychological illness) or if exercise was deemed undesirable (i.e., hypertrophic cardiomyopathy, unstable angina, advice from a cardiologist). Furthermore, patients were excluded if they were unable to understand or read Dutch instructions. Patients who did not give permission to use data or who followed an adapted program (i.e., not able to follow bicycle training) were also excluded from the analysis. Data were collected from existing databases and medical records. All collected data were anonymised in according with the Dutch Privacy Law. Ethical approval and consent for the study were waived by the Medical Ethics Board of the UMCG. Since this was a feasibility study, no sample size calculation was done.
Heart-ROCQ-pilot program
The Heart-ROCQ-pilot program consists of three phases: preoperative outpatient (PRE phase: minimum of 4 weeks until surgery, 3x/wk.), early postoperative inpatient (POST-in phase: 3 weeks, 5x/wk. during a working week), and postoperative outpatient (POST-out phase: 4 weeks, 2x/wk.) rehabilitation (Fig. 1). Key elements of the program were bicycle and strength training (Fig. 1). In order to estimate the individual, initial intensity of bicycle and strength training, different physical tests were performed [12]. Preoperatively, a submaximal bicycle test and six to ten repetition maximum (RM) of six strength exercises (triceps dips, rowing, chest press, seated leg press, seated leg curl, leg extension) were conducted (Fig. 1). The submaximal bicycle test used a 5–25 W/min ramp protocol and was ended when 70% of expected heart rate or expected workload was reached, or standard indications to terminate a test occurred [12]. Postoperatively, at the end of the POST-in phase, a symptom limited ergometer test with a 5–25 W/min ramp protocol and cardiopulmonary measurements was performed (Fig. 1). Expected workload was calculated based on gender, age, and height. The value of the expected workload defined the height of the steps of the ramp protocol. After establishing the initial intensity during the first bicycle training session, training sessions were based on the rate of perceived exertion (RPE; Fig. 1). All bicycle and strength sessions were conducted under the supervision of two physical therapists specialized in cardiac rehabilitation. During bicycle training patients were monitored with continuous 3-wire lead ECG. Additional elements of this multidisciplinary program were swimming, sports and games, inspiratory muscle training, and guidance from a dietician, a psychologist, an occupational health consultant, and a stop-smoking consultant. These elements were not evaluated in the current study.
Overview of the physical elements of the Heart-ROCQ-pilot program. ↑: An increase; LE: lower extremities; Max-IP: Maximum inspiratory pressure; rep: repetitions; RM: repetition maximum; RPE: rate of perceived exertion (Borg scale 0–10); UE: upper extremities; VO2: oxygen uptake
Feasibility
Compliance
Compliance (%) was defined as the number of actual bicycle and strength training sessions completed by the patients relative to the number of offered sessions. The offered sessions were those planned and presented to the patients. The sessions according to the protocol were as prespecified in the protocol (Fig. 1). It was assumed that patients completed a session when data of the training equipment was available. When malfunctioning of the equipment occurred (i.e., no absence was recorded in the patient rehabilitation planning systems, but no data was available for any of the scheduled patients for that session), the patient was assumed to be present during that session. The reasons for not offering a session according to the protocol and a patient’s absence were also evaluated.
Training characteristics
The training characteristics for bicycle training were duration (min), external workload (W), heart rate (bpm), workload to heart rate ratio (W/HR-ratio [W/beat]), and a subjective evaluation (Fig. 1). Subjective evaluation was assessed on the Borg scale 0–10, with higher scores indicating a higher level of the three components: RPE of fatigue and shortness of breath, and perceived discomfort [24]. The isopower ergometers with ECG (Corival IV Rehab and Lode ECG streamer, Lode) monitored (5 Hz) the external workload and the heart rate. For strength training, the absolute volume load (Kg) of leg (VL-leg, i.e., seated leg press, seated leg curl, and leg extension), arm (VL-arm, i.e., triceps dips, rowing, and chest press), and total of all exercises (VL-total) were evaluated (Fig. 1). Equipment for strength training (Enraf-Nonius) monitored the training characteristics in sets, repetitions, and intensity.
Data analyses
Data of bicycle training was exported using the LCRM software (v2.15.0, Lode). MATLAB (vR2018a, Mathworks) was used to interpolate and filter (8th order low-pass Butterworth, cut-off frequency: 0.1 Hz) the heart rate data. Subsequently, the mean values of external workload and heart rate of the training phase (excluding warm-up and cooling down) over each session were calculated. W/HR-ratio was calculated by dividing the mean external workload by the mean heart rate of the training phase over each session. Data of strength training was exported from the En-Track software (v6.29.4, Enraf-Nonius EN-track). Per session, the VL-arm, VL-leg, and VL-total (Formula 1) were calculated using STATA statistical software (v15.0, StataCorp).
Formula 1:
$${\sum\nolimits_{iExercise}^{nExercise} {(\sum\nolimits_{iSet}^{nSet} {Repetitions} } _{iSet}} \times \,Intensity_{_{iSet}}^{}{)_{iExercise}}$$
With iExercise is the number of the exercise and iSet is the number of sets of the exercise [25].
Statistical analyses
Statistical analyses were performed using IBM SPSS statistics software (v23). Descriptive statistics were used to present patient characteristics, compliance, RPE, and perceived discomfort. Repeated measures analyses were performed to analyse differences in training characteristics for each rehabilitation phase separately, using external workload, heart rate, W/HR-ratio, VL-leg, VL-arm, and VL-total as dependent variables. The within subject factor was the first and last session of each phase. The analyses were repeated with the last session in the POST-out phase and the first and last sessions in the PRE phase as the within subject factor. Patients were excluded from the analysis of a phase due to missing data when data from only one session in a phase was available or when there were only two sessions available either at the beginning or at the end of a phase. When the data consisted of different sample sizes, separate repeated measures analyses (or paired samples t-tests) were performed. Non-parametric equivalents were performed when the assumption of normal distribution was not met. All statistical tests were two-sided and P-values < 0.05 were considered statistically significant.
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