Information on exercise capacity and training in patients who underwent valvular surgery is scarce. The aim of this study is to evaluate postoperative exercise capacity and functional improvement after exercise training according to the preoperative risk and type of surgery. In this prospective study, 145 patients who underwent aortic valve surgery (AVS) or mitral valve surgery (MVS) and who were referred for cardiac rehabilitation were stratified according to the preoperative risk (European System for Cardiac Operative Risk Evaluation [EuroSCORE]) and type of surgery (sternotomy vs ministernotomy or port access). Exercise capacity was evaluated at the start and end of cardiac rehabilitation. Postoperative exercise capacity and the benefit from exercise training were compared between the groups. Patients with a higher preoperative risk had a worse postoperative exercise capacity, with a lower load, peak VO 2 , anaerobic threshold and 6-minute walking distance (all p <0.001), and a higher VE/VCO 2 slope (p = 0.01). In MVS, port access patients performed significantly better at baseline (all p <0.05), but in AVS, ministernotomy patients performed better than sternotomy patients with a concomitant coronary artery bypass graft (p <0.05). Training resulted in an improvement in exercise capacity in each risk group and each type of surgery (all p <0.05). This gain in exercise capacity was comparable for the EuroSCORE risk groups and for the types of surgery, for patients after AVS or MVS. In conclusion, exercise capacity after cardiac surgery is related to the preoperative risk and the type of surgery. Despite these differences in postoperative exercise capacity, a similar benefit from exercise training is obtained, regardless of their preoperative risk or type of surgery.
Information on exercise capacity and exercise training in patients who underwent valvular surgery is scarce. Current literature suggests that exercise capacity does not recover spontaneously after aortic valve surgery (AVS) or mitral valve surgery (MVS). This argues in favor of the need for cardiac rehabilitation. The primary aim of this study was to evaluate the difference in exercise capacity early after valvular surgery between patients with a low or high preoperative risk profile, assessed using the European System for Cardiac Operative Risk Evaluation (EuroSCORE). Similarly, the difference in postoperative exercise capacity was evaluated between patients after invasive versus minimal invasive surgery. The secondary aim was to assess whether the functional improvement after exercise training was affected by this preoperative risk profile or type of surgery.
Methods
One hundred and forty-five patients who underwent AVS (n = 72) or MVS (n = 73) for valvular regurgitation or stenosis and who were referred for cardiac rehabilitation between October 2007 and March 2012 were prospectively included. Patients with multivalvular disease were not eligible for inclusion, and neither were patients with transcatheter aortic valve implantation or mitraclip because of the fewer number of these procedures. Only patients with classic sternotomy, ministernotomy, or port access were considered for analysis. Combined coronary artery bypass graft (CABG) and valvular surgery was performed in 52 patients (36%). This study protocol was approved by the ethical committee of the 2 participating hospitals (AZ Maria Middelares Ghent and Onze-Lieve-Vrouw Hospital Aalst), and all patients gave informed consent. The clinical investigations were conducted according to the principles of the Declaration of Helsinki.
The EuroSCORE was used to assess the mortality risk in cardiac surgery. EuroSCORE I calculation consists of patient, cardiac, and operation-related factors and results in an additive and a logistic risk score. According to the additive EuroSCORE, patients were divided into 3 risk groups. A score of 0 to 2 was classified as a low-risk (n = 20), 3 to 5 as a medium-risk (n = 64), and >5 as a high-risk profile (n = 60). EuroSCORE was not calculated for 1 patient because of missing data on the left ventricular function. The decision regarding the type of surgery (classic sternotomy vs ministernotomy or port access) was made by the cardiac surgeon on the basis of preoperative clinical data and anatomic status.
Cardiopulmonary exercise testing was performed 1 month (31 ± 16 days) after surgery on a cyclo-ergometer using a ramp protocol adapted to the patient’s physical status. Ventilatory and respiratory gas measurements were obtained on a breath-by-breath basis using an Oxycon Pro spirometer (Jaeger–Viasys Healthcare, Germany). Heart rate was continuously registered by a 12-lead electrocardiogram, and blood pressure was noninvasively measured using a manual sphygmomanometer every 2 minutes during the exercise test. Patients exercised to the limits of their functional capacities established by a respiratory exchange ratio >1.15 or until the physician stopped the test because of adverse signs and/or symptoms, such as chest pain, dizziness, potentially life-threatening arrhythmias, significant ST segment displacement (≥1 mm), and marked systolic hypotension or hypertension. The maximal achieved load during incremental exercise was recorded. Peak oxygen consumption (peak VO 2 ) was defined as the mean of the last 30 seconds of peak exercise and was expressed as milliliter per minute per kilogram. The slope of the linear relation between VE (y axis) and VCO 2 (x axis), the VE/VCO 2 slope, was calculated by including all data points to the end of the exercise. The anaerobic threshold (AT) was defined as the exercise level at which ventilation starts to increase exponentially, relative to the increase in VO 2 . At the beginning of the exercise training program, a 6-minute walk test was performed in a 30-m hallway. The distance a patient could quickly walk in a period of 6 minutes (i.e., 6-minute walking distance [6MWD]) was measured. This protocol was repeated at the end of the rehabilitation program. The gain in exercise capacity was expressed as a percentage of improvement and calculated for the previously mentioned exercise parameters: (exercise parameter end − exercise parameter start )/(exercise parameter start ) × 100.
Rehabilitation was initiated at the hospital on the first day after surgery and focused on respiration in combination with low-intensity aerobic exercises. After discharge, patients were encouraged to continue low-intensity aerobic exercises at home until they were referred for outpatient cardiac rehabilitation (43 ± 22 days after surgery). Outpatient rehabilitation was started not earlier than 4 weeks after surgery to ensure optimal healing. Patients trained 2 or 3 times a week for 60 minutes during a period of 3 to 5 months with a maximum of 45 sessions. The exercise training program consisted of a combination of aerobic and strengthening exercises. Aerobic training mainly included cycling (15 minutes), treadmill walking (15 minutes), and stepping (5 minutes) and was performed at an intensity of the heart rate at AT combined with an evaluation of the rating of perceived exertion. Strengthening exercises (15 minutes) primarily targeted lower body muscles with leg press and leg curl exercises at 60% of 1 repetition maximum for 2 sets of 15 to 20 repetitions. In a later phase, after the sternum had healed, upper body strength training for biceps, triceps, and trunk was added. Every training session was initiated and terminated with 5 minutes warm-up and cool-down period.
Statistical analysis was performed with IBM SPSS Statistics for Windows, Version 21.0 (Armonk, New York, USA: IBM Corp). Differences in clinical characteristics between patients who had AVS or MVS were assessed with chi square and independent samples t or Mann-Whitney U test, as appropriate. Because of an unequal number of patients and an unequal spread in variances, nonparametric tests were chosen for analyzing exercise capacity according to the preoperative risk profile. Differences in baseline exercise capacity and differences in functional improvement after the exercise training program were evaluated with a Kruskal-Wallis or Mann-Whitney U test, depending on the number of groups. A Wilcoxon matched-pairs signed-ranks test was used to evaluate the improvement after the exercise training program within each group separately. Same statistical tests were used to evaluate the differences between invasive versus minimal invasive surgery. A p value <0.05 was considered to be statistically significant.
Results
Clinical characteristics of the 145 study patients are listed in Table 1 . Age, gender, and body mass index were comparable between AVS and MVS. MVS patients had a slightly lower preoperative left ventricular function as compared with AVS patients (60% vs 67%, p <0.01). MVS was mainly performed for mitral regurgitation (97%), whereas AVS patients were mainly referred for aortic stenosis (75%). Mitral valve repair was performed in 85% of those who were referred for MVS. The large majority of patients who were referred for AVS underwent aortic valve replacement. In mitral valve disease, sternotomy was performed in 40 patients (55%), of whom 28 patients also underwent CABG and 33 patients (45%) underwent minimal invasive surgery through port access. Sternotomy was performed in 45 patients with aortic valve disease (63%), of whom 23 patients had a concomitant CABG and 27 patients (37%) underwent a ministernotomy. Patients attended 38 training sessions on an average; this number was comparable for AVS and MVS. At the end of the exercise training program, an overall increase in exercise capacity was seen in the total patient group with an increase of 31% in load, 23% in peak VO 2 , 10% in AT, and 26% in 6MWD. A decrease of 5% was recorded for the VE/VCO 2 slope.
| Variable | Total Group (n = 145) | Mitral Valve Surgery (n = 73) | Aortic Valve Surgery (n = 72) | p Value |
|---|---|---|---|---|
| Age (yrs) | 64 ± 10 | 64 ± 9 | 65 ± 12 | 0.696 |
| Men | 74 | 71 | 76 | 0.480 |
| BMI (kg/m²) | 26 ± 4 | 25 ± 3 | 26 ± 4 | 0.128 |
| LVEF (%) | 64 ± 13 | 60 ± 15 | 67 ± 11 | 0.004 |
| EuroSCORE risk profile | 0.296 | |||
| Low risk | 14 | 18 | 10 | |
| Medium risk | 44 | 45 | 43 | |
| High risk | 42 | 37 | 47 | |
| Type of valve disease | <0.001 | |||
| Regurgitation | 61 | 97 | 25 | |
| Stenosis | 39 | 3 | 75 | |
| AVS/MVS | <0.001 | |||
| Mechanical Prosthetic valve | 17 | 4 | 30 | |
| Bioprosthetic Valve | 40 | 11 | 69 | |
| Repair | 43 | 85 | 1 | |
| CABG | 36 | 38 | 33 | 0.528 |
| Type of surgery | <0.001 | |||
| Sternotomy | 58 | 55 | 63 | |
| Ministernotomy | 19 | — | 37 | |
| Port access | 23 | 45 | — | |
| NYHA classification | 0.990 | |||
| I | 69 | 70 | 68 | |
| II | 26 | 25 | 27 | |
| III | 5 | 5 | 5 | |
| NT-proBNP (pg/ml) | 565 (309–1,149) | 686 (357–1,508) | 476 (297–919) | 0.225 |
| Hypertension | 50 | 45 | 54 | 0.281 |
| Hyperlipidemia | 40 | 44 | 36 | 0.342 |
| Diabetes | 12 | 4 | 19 | 0.004 |
| Smoking | 9 | 6 | 12 | 0.271 |
| COPD | 1 | 2 | 0 | 0.489 |
| PAD | 3 | 3 | 4 | 0.681 |
| AF at start cardiac rehabilitation | 13 | 12 | 14 | 0.781 |
| Pacemaker | 6 | 4 | 7 | 0.494 |
| Medication | ||||
| β Blocker | 88 | 82 | 94 | 0.022 |
| ACE-I/ARB | 37 | 34 | 39 | 0.562 |
| Diuretics | 26 | 29 | 22 | 0.366 |
| Statins | 49 | 44 | 54 | 0.213 |
Exercise capacity early after surgery and functional improvement after attending cardiac rehabilitation was assessed for all patients according to the EuroSCORE risk profile ( Figure 1 ). Patients with a higher preoperative risk had a worse postoperative exercise capacity as expressed by a lower load, peak VO 2 , AT, and 6MWD (all p <0.001) and a higher VE/VCO 2 slope (p = 0.01). Load, peak VO 2 , and 6MWD at baseline were significantly different between the 3 risk groups (all p <0.01). AT was significantly decreased, and VE/VCO 2 slope was significantly increased in the high-risk group as compared with the low- and medium-risk groups (all p <0.05). Exercise training resulted in a significant improvement in load, peak VO 2 , AT, and 6MWD in each risk group separately (all p <0.01). A small but significant decrease in the VE/VCO 2 slope was present only in the medium- and high-risk patient groups (p <0.05). The percentage of improvement in exercise capacity was comparable in low-, medium-, and high-risk groups. Table 2 lists the training effects according to the preoperative risk profile, stratified by aortic and mitral valve disease. In patients with MVS, postoperative exercise capacity was significantly worse in high-risk as compared with low-/medium-risk patients (all p <0.01). In contrast, load, peak VO 2 , AT, and 6MWD were lower but not significantly different in high-risk as compared with low-/medium-risk AVS patients. Only in AVS, VE/VCO 2 slope was significantly higher in high-risk patients (p <0.05). After exercise training, distinct improvements in the load, peak VO 2 , and 6MWD were seen in all groups (all p <0.01). An increase in the AT was present in MVS (all p <0.05). The VE/VCO 2 slope was significantly decreased in the high-risk group of AVS (p <0.05). The functional improvement in exercise capacity was generally comparable in low-/medium-risk and high-risk patients, for AVS and MVS.
| Variable | MVS (n = 73) | AVS (n = 71) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Low/Medium Risk (n = 46) | High Risk (n = 27) | Diff in Training Effects Between Risk Groups | Low/Medium Risk (n = 38) | High Risk (n = 33) | Diff in Training Effects Between Risk Groups | |||||
| Mean ± SD | p Value | Mean ± SD | p Value | p Value | Mean ± SD | p Value | Mean ± SD | p Value | p Value | |
| Load (W) | ||||||||||
| Start CR | 122 ± 36 | ] <0.001 | 78 ± 22*** | ] 0.001 | 102 ± 39 | ] <0.001 | 80 ± 26 | ] 0.004 | ||
| End CR | 157 ± 49 | 98 ± 30 | 136 ± 60 | 108 ± 35 | ||||||
| Δ Load (%) | 29 ± 16 | 26 ± 22 | 0.452 | 33 ± 20 | 39 ± 36 | 0.918 | ||||
| Peak VO 2 (ml·min −1 ·kg −1 ) | ||||||||||
| Start CR | 21 ± 6 | ] <0.001 | 15 ± 4*** | ] 0.006 | 19 ± 6 | ] 0.001 | 17 ± 3 | ] 0.003 | ||
| End CR | 26 ± 8 | 17 ± 5 | 25 ± 6 | 21 ± 5 | ||||||
| Δ peak VO 2 (%) | 23 ± 18 | 15 ± 17 | 0.135 | 29 ± 27 | 23 ± 21 | 0.603 | ||||
| HR at AT (per min) | ||||||||||
| Start CR | 99 ± 17 | ] 0.004 | 86 ± 12** | ] 0.028 | 102 ± 12 | ] 0.134 | 99 ± 24 | ] 0.209 | ||
| End CR | 110 ± 18 | 92 ± 11 | 109 ± 17 | 107 ± 21 | ||||||
| Δ HR at AT (%) | 12 ± 20 | 8 ± 11 | 0.577 | 8 ± 17 | 9 ± 20 | 0.930 | ||||
| VE/VCO 2 slope | ||||||||||
| Start CR | 31 ± 5 | ] 0.092 | 35 ± 7 | ] 0.422 | 30 ± 7 | ] 0.101 | 36 ± 5* | ] 0.012 | ||
| End CR | 30 ± 6 | 35 ± 8 | 28 ± 5 | 32 ± 4 | ||||||
| Δ VE/VCO 2 slope (%) | −4 ± 12 | −2 ± 12 | 0.553 | −5 ± 13 | −9 ± 8 | 0.186 | ||||
| 6MWD (m) | ||||||||||
| Start CR | 472 ± 62 | ] <0.001 | 359 ± 76*** | ] <0.001 | 430 ± 69 | ] <0.001 | 394 ± 92 | ] <0.001 | ||
| End CR | 582 ± 73 | 460 ± 93 | 551 ± 90 | 478 ± 108 | ||||||
| Δ 6MWD (%) | 24 ± 13 | 30 ± 24 | 0.501 | 29 ± 13 | 22 ± 13 | 0.021 | ||||
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