Complex off-pump coronary artery bypass surgery can be safely taught to cardiothoracic trainees
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《血管的通路杂志》
Department of Cardiothoracic Surgery, St George's Hospital, Blackshaw Road, London SW17 0QT, UK
Presented at the 54th International Congress of the European Society for Cardiovascular Surgery, Athens, May 19–22, 2005.
Abstract
Objectives: Off-pump coronary revascularisation is demanding technically as the surgeon is faced with a beating heart and not a bloodless field. The potential clinical advantages of off-pump coronary revascularisation have made this procedure an essential part of a cardiothoracic training program. The aim of this study is to investigate the impact of teaching trainees complex off-pump coronary artery surgery (arterial grafting, ‘Y’ grafts, sequential grafting and minimally invasive direct coronary artery bypass) on clinical outcomes. Methods: All 323 off-pump coronary revascularisation cases performed by one service over a 24-month period were analysed. The 125 (39%) operations performed by two trainees with previous exposure in on-pump surgery were compared with the 198 (61%) performed by an experienced consultant surgeon. Patient and disease characteristics, intra- and post-operative data, morbidity and mortality were analysed using uni- and multivariate analysis. Results: The trainees performed 51% of the MIDCABs, 36% of the ‘Y’ grafts and 27.5% of the sequential grafts. The internal thoracic artery was used in 96% of the cases, radial artery in 49% and bilateral internal thoracic arteries in 11% equally distributed between trainees and consultant. The average number of grafts per case was 3.7 for the consultant and 3.3 for the trainees. Patients operated by the consultants were more likely to have unstable angina (P=0.008), ejection fraction <30% (P=0.01) previous cardiac surgery (P=0.027) and more likely to receive over 4 grafts (P=0.01). Operative mortality was 1.5% for the consultant and 0 for the trainees (P=0.17). Post-operative morbidity, such as re-operation for bleeding (consultant 1% vs. trainee 0.8%), stroke (0.5% vs. 0.8%), haemofiltration (3.5% vs. 0.8%) was similar between the two groups. Hospital stay was also similar. Conclusions: The results of this study suggest that trainees under supervision perform complex off-pump coronary artery surgery safely with low rate of mortality and complications. These findings are in agreement with previous literature reports. Trainees should be allowed to operate on sufficient number of patients undergoing off-pump surgery according to their skills and abilities. Patients should be reassured that safety is not compromised by the presence of a trainee as a primary surgeon.
Key Words: Off-pump coronary artery surgery; Training; Outcomes
1. Introduction
Coronary artery bypass grafting (CABG) without cardiopulmonary bypass (CPB) in the last few years has gained a wide popularity as an alternative to conventional myocardial revascularisation in the treatment of coronary artery disease [1] and is currently being performed by many surgeons world wide [2]. The use of CPB and cardioplegic arrest allows the optimisation of the surgical field and consistent placement of grafts. However, it is associated with significant dysfunction of major organs (lungs, kidneys, brain) and coagulation abnormalities as well [3]. Studies have shown that off-pump coronary artery bypass (OPCAB) surgery is effective, safe and exhibits excellent short- and mid-term results and minimal morbidity [4].
The potential clinical advantages of OPCAB and the advances made in surgical technology have made this procedure an essential part of a cardiothoracic training program. However, several questions and concerns may arise as to whether and to which extent, coronary artery grafting without the use of CPB should be considered an integral part of the education in cardiothoracic surgery for the current trainees [5].
The aim of this study is to compare the clinical outcomes of patients undergoing more complex OPCAB like Minimally Invasive Direct Coronary Artery Bypass (MIDCAB), sequential and ‘Y’ grafting after procedures performed by a consultant surgeon or a trainee as the primary operator over a 24-month period. This study follows our previously reported study in the STS meeting, January 2005, Tampa, USA, which assessed the safety of training residents to perform off-pump coronary artery bypass surgery [6].
2. Material and methods
2.1. Patients and collection of data
A standard set of perioperative data were collected retrospectively for all patients undergoing consecutive isolated CABG in this study under the care of one consultant surgeon (V.C.) at one institution, between July 2002 and July 2004. Four hundred and three patients underwent CABG during the study period, of which 323 patients underwent OPCAB. The remaining 80 patients underwent on-pump coronary artery bypass (on-CAB) as a part of a randomised trial and were therefore excluded from this analysis. There were no intra-operative conversions from OPCAB to on-CAB during the study period.
All the clinical data were collected in line with the appended Minimum Dataset (MDS) defined by the Society of Cardiothoracic Surgeons. The current MDS, and its associated definitions, is compatible with all existing initiatives in the UK such as the UK Heart Valve Registry, the Central Cardiac Audit Database and the British Cardiac Intervention Society database. The definitions and data fields are also compatible with evolving European initiatives, the Society of Thoracic Surgeons, the American College of Cardiology and the Healthcare Financing Administration in the United States [7]. Local validation of the collected data is performed regularly and external validation is being performed by the Society on a 3 to 5 yearly cycle.
2.1.1. Anaesthetic and operative techniques
The anaesthetic and operative techniques used for OPCAB at our institution have been described in a separate study report [8]. These include anaesthetic pre-medication with morphine (10 mg) and hyoscine (0.3 mg) administered intramuscularly 2 h before the operation. Anaesthesia was introduced with midazolam (100–200 μg/kg), fentanyl (150–200 μg) and pancuronium (50–100 μg/kg), and sustained with propofol (5–10 mg/kg/h). Heparin in a dose of 150 U/kg was used to achieve anticoagulation during the procedure maintaining an activated clotting time over 300 s. Heparin was reversed completely with protamine sulphate at the end of the procedure. The operation was performed through median sternotomy using the GUIDANT AcrobatTM SUV Vacuum Stabiliser System (OM-9000) (Santa-Clara, CA, USA). The target vessel was exposed by the use of swabs in the transverse sinus (deep pericardial stay sutures were not used), and by allowing the right side of the pericardium down. Interruption of the blood flow from the proximal vessel was achieved by occlusion with a soft bulldog clamp. All distal anastomoses were constructed with 8/0 prolene. The proximal end was implanted onto the aorta with 6/0 prolene. Care was given to the mean arterial blood pressure which was maintained between 50 and 70 mmHg during the procedure by manipulating the preload, repositioning the heart and selective use of vasoconstrictors, such as metaraminol and norepinephrin.
2.2. Training method
The two trainees participating in this study had previously received training in on-pump CABG involving over 100 cases each. In our institution approximately 31% of coronary surgery is done off-pump. During the period between 2002 and 2004 the training surgeon and his team, including the trainees, performed 477 OPCABs (85.5%) and 81 on-CABs. The trainees during the study period performed mostly off-pump CABG because the training surgeon prefers to do his CABGs off-pump. The patients operated upon by the trainees were selected by assessing their suitability for training taking into account the urgency of the operation, their co-morbidities, the quality of the coronary arteries and the number of grafts required. Patients with poor left ventricular (LV) function and unstable haemodynamics were not used for training purposes. Training in OPCAB focused, therefore, on teaching the technique of handling the heart, positioning the stabiliser and performing the anastomoses at the front of the heart initially. Furthermore, the training progressed to gradually increasing levels of complexity and responsibility according to the surgical abilities of the trainee. More specifically the trainees were taught how to perform ‘Y’ grafts, sequential grafts, MIDCABs, usage of bilateral internal mammary arteries (IMA) and total arterial revascularisation. The sequence of grafting consisted of the left anterior artery grafted first, if it was critically diseased, followed by the vessels of the left side of the heart and/or the vessels of the posterior wall. All the training took place under the supervision of the same consultant surgeon, who assisted in the majority of cases and allowed the trainees to perform the operations on their own at the final stages of the training period with the trainer being in the vicinity of the operating room.
2.3. Statistical methods
Contingency tables for categorical data were compared between the two groups using Pearson's Chi-square test or Fisher's exact test. Distributions of continuous data were observed and t-tests or Mann–Whitney tests were performed accordingly for comparisons of groups. When no normal distribution of data was detected, variables were presented as median with 25th and 75th percentiles (inter-quartile range). The European System for Cardiac Operative Risk Evaluation (EuroSCORE) was used to analyse patients according to predicted risk for operative mortality [9]. Odds ratios with 95% confidence intervals were calculated for all compared variables. Logistic regression was used to correlate pre-operative patient and disease characteristics with post-operative outcomes. P-values less than 0.05 indicate a statistically significant difference between patient groups. All analyses were carried out using the statistical software SPSS 11.0 (SPSS Inc., USA).
3. Results
Of the 323 patients included in this study, 198 (61.3%) underwent OPCAB by the consultant and 125 (38.7%) by a trainee as the primary surgeon. There were no intra-operative conversions from OPCAB to on-CAB during the study period. The conversion rate from OPCAB to on-CAB for the training surgeon is generally low and between the years 2002 and 2004 out of a total of 477 OPCABs there were 4 conversions to on-CAB.
The demographic and pre-operative clinical characteristics of the two patient groups are presented in Table 1. The characteristics of the two groups were similar with the exception of unstable angina (more patients in the consultant group P=0.008), previous PCI (more patients in the consultant group, P=0.002), left ventricular ejection fraction (lower in the consultant group, P<0.013) and the urgency of the operation (more emergencies in the consultant group, P=0.038). Most of the re-operations included in the study were performed by the consultant (P=0.027). The predicted mortality risk, as calculated by EuroSCORE, was identical in the two patient groups. These small demographic differences in the two groups reflect the fact that cases with low ejection fraction, second time operation, or emergencies are not used traditionally for training purposes. Therefore an absolute match of the two groups is not practical and maybe not ethical as well.
Table 2 shows intra- and post-operative characteristics of the patients. Trainees operated on significantly less patients requiring five or more grafts (P=0.046), but the mean number of grafts per patient was 3.7 for the consultant group and 3.3 for the trainee group which is not statistically significantly different. This is explained by the fact that the consultant operated on a higher number of patients requiring more than 4 grafts because these patients were not used for training purposes. Furthermore, the trainees performed 51% of the MIDCABs (18 out of 35 in total), 36% of the ‘Y’ grafts (42 out of a total of 117) and 27.5% of the sequential grafts (22 out of 80 in total). The trainees performed less ‘Y’ and less sequential grafts because these complex procedures were employed at a later stage of their training and also the coronary anatomy and coronary artery disease should be suitable for the purposes of training. The use of IMA was employed in 96% of the cases, of the radial artery in 49% and of bilateral IMAs in 11%, equally distributed between the consultant surgeon and the trainees. The use of total arterial revascularisation was equally distributed between the two groups; 41% of the patients in the consultant group underwent total arterial revascularisation, whereas the ratio for the trainee group was 43%. The patients operated by the trainees stayed significantly less hours in the ICU (P=0.007), whereas the median total hospital stay was similar between the two groups. Rates of serious complications remained low in both groups. There were three 30-day deaths in the consultant patient group (1.5%), while no patients died in the trainee group. All three deaths were emergencies involving patients transferred from the catheterisation laboratory after failed PCI with extensive myocardial necrosis and haemodynamic instability. The total mortality of the firm for CABG in the study period was therefore 0.9% (3/323).
4. Discussion
A lot of professional bodies have shown interest in surgical training and especially in the training of cardiothoracic residents recently. In order to improve the clinical outcomes of training, specific curricula, examinations and close scrutiny of surgical performances have been introduced [10]. Providing the best possible clinical outcomes and the best possible training in cardiac surgery at the same time can be a very complex dilemma to reconcile [11], especially with respect to teaching trainees to perform OPCAB surgery. This study does not aim to compare the outcomes of the trainees to the outcomes of the trainers but to show that complex OPCAB surgery can be taught with low rate of complications and equally good outcomes.
In an earlier study of ours, we demonstrated that OPCAB surgery can be performed safely by supervised cardiac surgical trainees [6] and our findings were in accordance with the findings of most of the studies published by others on the same subject. This article demonstrates that complex OPCAB surgery (i.e. MIDCABs, ‘Y’ and sequential grafting) is a safe and reproducible surgical technique that can be taught successfully to cardiothoracic trainees. The trainees performed 51% of the MIDCABs, 36% of the ‘Y’ grafts and 27.5% of the sequential grafts and 43% of the patients operated upon by the trainees received a total arterial revascularisation procedure. The relatively low percentage of ‘Y’ and sequential grafts performed by the trainees can be explained by the fact that these more complex techniques of grafting coronary arteries were taught at a later stage of the training, because as it is expected in the beginning of the training the trainees ought to master the principles of simple OPCAB surgery.
Mortality and morbidity can be very low. The 30-day mortality among the 125 patients in the trainee group was zero while the only major complications involved one re-sternotomy for bleeding, one mediastinal infection requiring sternal rewiring and one stroke. In the consultant group mortality and morbidity were slightly but not significantly higher (mortality 1.5%). This can be explained by the fact that emergent cases and patients with severely impaired left ventricular function (EF<30%), which are expected to have higher mortality and morbidity, are not normally used for training purposes and therefore are operated upon by the consultant surgeon. The median time for hospital stay following OPCAB was the same in both groups.
It is commonly believed that operations allocated to trainees involve patients with low predicted operative risk. In our study, patients in the trainee group had, overall, less unstable angina and higher left ventricular ejection fraction. Operative risk scoring, as assessed by the EuroSCORE, demonstrated median scores of four in both groups, with a 75th percentile of four in the trainee group versus six in the consultant group. Our study suggests that overall average predicted risk does not differ between patients performed by trainees as compared with consultants, although particularly high risk operations are performed by a consultant surgeon.
Small sample size is the main limitation of our study. Low rates of outcome measures, such as mortality and morbidity, precluded our regression analysis from detecting correlation between patient characteristics and outcome and differences in outcomes between subgroups of patients as well. Low complication rates were, nevertheless, encouraging. A non-significant trend for cases performed by trainees to develop less post-operative complication reinforces the notion that trainees can be taught to operate safely off-CPB. The study was necessarily observational in nature both for logistical and ethical reasons. It is very difficult to assess the criteria used by the trainer in the allocation of the cases to the trainees. Consultant surgeons are likely to use more subtle clinical signs to select cases for trainees than can be readily documented by formal data collection. A second issue that may have influenced the results of this study is how often the trainer intervened during the operation, either by taking over in a planned manner to perform one or more anastomoses, or to position the heart for the trainee, who performed the anastomosis subsequently. By reviewing the operation notes of all the cases involved in this study and by questioning the trainees as well, we conclude that changes in designation in the main operator were extremely rare. Analysis of higher numbers of OPCAB cases performed by a variety of trainees should be performed in future studies to reconfirm the main findings of this trial. Long term follow-up of patients will also be of interest.
Many surgeons believe that complex cardiothoracic procedures are too difficult for trainees to perform under supervision. It has been asserted that this practice is not a matter of safety but one of philosophy [12]. A learning curve clearly exists over the course of a surgeon's career [13]. No matter how well trained residents are, their results will improve over the course of their careers. The more experience the trainees can gain while under the supervision of a consultant, especially with the more complex cases, the less they will need to improve as consultant surgeons and the less impact this will have on patient outcomes.
Baskett et al. showed that it is safe to train junior surgeons in the performance of complex cardiac procedures, such as mitral valve repair. They found that mortality and morbidity were not statistically significantly different between the patients operated by the trainees and the consultants and that it was possible for the trainees to perform an adequate number of cases in order for them to obtain the required experience [14]. Similarly, propensity score-matched cases showed no significantly different complication rates in the two patient groups. The concept and outcome of training in OPCAB in a single UK cardiac surgical centre has been presented comprehensively in a series of publications, all largely concerning the same patient population [15–18]. The last report of the series summarises outcome on 990 CABG cases performed by trainees of which 474 were OPCABs. These operations were compared with those performed by an experienced consultant surgeon. Predicted and observed risk of death or serious complications was similar for trainee and consultant operations. The authors conclude that it is safe to teach OPCAB to trainee surgeons and that continuous performance monitoring for trainees is possible and desirable.
There is clearly a need currently to teach trainees to perform OPCAB surgery. Consultants have the responsibility to learn new techniques themselves and to teach them to the trainees if they want to offer high standards of care to their patients. A recent survey from cardiothoracic training centres in the United States showed that only a very small number of residents achieved competent levels in performing OPCAB surgery [19]. Our study therefore may have important implications for the training of the future cardiothoracic surgeons in beating heart surgery. We have previously demonstrated that trainees under supervision perform OPCAB safely with low rate of complications including patients with triple vessel disease and grafting to the posterior wall of the heart. With this study we have demonstrated that complex OPCAB surgery (MIDCAB, ‘Y’ and sequential grafting and total arterial revascularisation) can be taught to cardiothoracic trainees with low mortality and morbidity. Therefore, we believe that a modern surgical training program in cardiothoracic surgery should expose trainees to complex surgical cardiothoracic procedures, possibly at the more advanced stages during their training, under the supervision of senior surgeons proficient in the technique.
References
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Presented at the 54th International Congress of the European Society for Cardiovascular Surgery, Athens, May 19–22, 2005.
Abstract
Objectives: Off-pump coronary revascularisation is demanding technically as the surgeon is faced with a beating heart and not a bloodless field. The potential clinical advantages of off-pump coronary revascularisation have made this procedure an essential part of a cardiothoracic training program. The aim of this study is to investigate the impact of teaching trainees complex off-pump coronary artery surgery (arterial grafting, ‘Y’ grafts, sequential grafting and minimally invasive direct coronary artery bypass) on clinical outcomes. Methods: All 323 off-pump coronary revascularisation cases performed by one service over a 24-month period were analysed. The 125 (39%) operations performed by two trainees with previous exposure in on-pump surgery were compared with the 198 (61%) performed by an experienced consultant surgeon. Patient and disease characteristics, intra- and post-operative data, morbidity and mortality were analysed using uni- and multivariate analysis. Results: The trainees performed 51% of the MIDCABs, 36% of the ‘Y’ grafts and 27.5% of the sequential grafts. The internal thoracic artery was used in 96% of the cases, radial artery in 49% and bilateral internal thoracic arteries in 11% equally distributed between trainees and consultant. The average number of grafts per case was 3.7 for the consultant and 3.3 for the trainees. Patients operated by the consultants were more likely to have unstable angina (P=0.008), ejection fraction <30% (P=0.01) previous cardiac surgery (P=0.027) and more likely to receive over 4 grafts (P=0.01). Operative mortality was 1.5% for the consultant and 0 for the trainees (P=0.17). Post-operative morbidity, such as re-operation for bleeding (consultant 1% vs. trainee 0.8%), stroke (0.5% vs. 0.8%), haemofiltration (3.5% vs. 0.8%) was similar between the two groups. Hospital stay was also similar. Conclusions: The results of this study suggest that trainees under supervision perform complex off-pump coronary artery surgery safely with low rate of mortality and complications. These findings are in agreement with previous literature reports. Trainees should be allowed to operate on sufficient number of patients undergoing off-pump surgery according to their skills and abilities. Patients should be reassured that safety is not compromised by the presence of a trainee as a primary surgeon.
Key Words: Off-pump coronary artery surgery; Training; Outcomes
1. Introduction
Coronary artery bypass grafting (CABG) without cardiopulmonary bypass (CPB) in the last few years has gained a wide popularity as an alternative to conventional myocardial revascularisation in the treatment of coronary artery disease [1] and is currently being performed by many surgeons world wide [2]. The use of CPB and cardioplegic arrest allows the optimisation of the surgical field and consistent placement of grafts. However, it is associated with significant dysfunction of major organs (lungs, kidneys, brain) and coagulation abnormalities as well [3]. Studies have shown that off-pump coronary artery bypass (OPCAB) surgery is effective, safe and exhibits excellent short- and mid-term results and minimal morbidity [4].
The potential clinical advantages of OPCAB and the advances made in surgical technology have made this procedure an essential part of a cardiothoracic training program. However, several questions and concerns may arise as to whether and to which extent, coronary artery grafting without the use of CPB should be considered an integral part of the education in cardiothoracic surgery for the current trainees [5].
The aim of this study is to compare the clinical outcomes of patients undergoing more complex OPCAB like Minimally Invasive Direct Coronary Artery Bypass (MIDCAB), sequential and ‘Y’ grafting after procedures performed by a consultant surgeon or a trainee as the primary operator over a 24-month period. This study follows our previously reported study in the STS meeting, January 2005, Tampa, USA, which assessed the safety of training residents to perform off-pump coronary artery bypass surgery [6].
2. Material and methods
2.1. Patients and collection of data
A standard set of perioperative data were collected retrospectively for all patients undergoing consecutive isolated CABG in this study under the care of one consultant surgeon (V.C.) at one institution, between July 2002 and July 2004. Four hundred and three patients underwent CABG during the study period, of which 323 patients underwent OPCAB. The remaining 80 patients underwent on-pump coronary artery bypass (on-CAB) as a part of a randomised trial and were therefore excluded from this analysis. There were no intra-operative conversions from OPCAB to on-CAB during the study period.
All the clinical data were collected in line with the appended Minimum Dataset (MDS) defined by the Society of Cardiothoracic Surgeons. The current MDS, and its associated definitions, is compatible with all existing initiatives in the UK such as the UK Heart Valve Registry, the Central Cardiac Audit Database and the British Cardiac Intervention Society database. The definitions and data fields are also compatible with evolving European initiatives, the Society of Thoracic Surgeons, the American College of Cardiology and the Healthcare Financing Administration in the United States [7]. Local validation of the collected data is performed regularly and external validation is being performed by the Society on a 3 to 5 yearly cycle.
2.1.1. Anaesthetic and operative techniques
The anaesthetic and operative techniques used for OPCAB at our institution have been described in a separate study report [8]. These include anaesthetic pre-medication with morphine (10 mg) and hyoscine (0.3 mg) administered intramuscularly 2 h before the operation. Anaesthesia was introduced with midazolam (100–200 μg/kg), fentanyl (150–200 μg) and pancuronium (50–100 μg/kg), and sustained with propofol (5–10 mg/kg/h). Heparin in a dose of 150 U/kg was used to achieve anticoagulation during the procedure maintaining an activated clotting time over 300 s. Heparin was reversed completely with protamine sulphate at the end of the procedure. The operation was performed through median sternotomy using the GUIDANT AcrobatTM SUV Vacuum Stabiliser System (OM-9000) (Santa-Clara, CA, USA). The target vessel was exposed by the use of swabs in the transverse sinus (deep pericardial stay sutures were not used), and by allowing the right side of the pericardium down. Interruption of the blood flow from the proximal vessel was achieved by occlusion with a soft bulldog clamp. All distal anastomoses were constructed with 8/0 prolene. The proximal end was implanted onto the aorta with 6/0 prolene. Care was given to the mean arterial blood pressure which was maintained between 50 and 70 mmHg during the procedure by manipulating the preload, repositioning the heart and selective use of vasoconstrictors, such as metaraminol and norepinephrin.
2.2. Training method
The two trainees participating in this study had previously received training in on-pump CABG involving over 100 cases each. In our institution approximately 31% of coronary surgery is done off-pump. During the period between 2002 and 2004 the training surgeon and his team, including the trainees, performed 477 OPCABs (85.5%) and 81 on-CABs. The trainees during the study period performed mostly off-pump CABG because the training surgeon prefers to do his CABGs off-pump. The patients operated upon by the trainees were selected by assessing their suitability for training taking into account the urgency of the operation, their co-morbidities, the quality of the coronary arteries and the number of grafts required. Patients with poor left ventricular (LV) function and unstable haemodynamics were not used for training purposes. Training in OPCAB focused, therefore, on teaching the technique of handling the heart, positioning the stabiliser and performing the anastomoses at the front of the heart initially. Furthermore, the training progressed to gradually increasing levels of complexity and responsibility according to the surgical abilities of the trainee. More specifically the trainees were taught how to perform ‘Y’ grafts, sequential grafts, MIDCABs, usage of bilateral internal mammary arteries (IMA) and total arterial revascularisation. The sequence of grafting consisted of the left anterior artery grafted first, if it was critically diseased, followed by the vessels of the left side of the heart and/or the vessels of the posterior wall. All the training took place under the supervision of the same consultant surgeon, who assisted in the majority of cases and allowed the trainees to perform the operations on their own at the final stages of the training period with the trainer being in the vicinity of the operating room.
2.3. Statistical methods
Contingency tables for categorical data were compared between the two groups using Pearson's Chi-square test or Fisher's exact test. Distributions of continuous data were observed and t-tests or Mann–Whitney tests were performed accordingly for comparisons of groups. When no normal distribution of data was detected, variables were presented as median with 25th and 75th percentiles (inter-quartile range). The European System for Cardiac Operative Risk Evaluation (EuroSCORE) was used to analyse patients according to predicted risk for operative mortality [9]. Odds ratios with 95% confidence intervals were calculated for all compared variables. Logistic regression was used to correlate pre-operative patient and disease characteristics with post-operative outcomes. P-values less than 0.05 indicate a statistically significant difference between patient groups. All analyses were carried out using the statistical software SPSS 11.0 (SPSS Inc., USA).
3. Results
Of the 323 patients included in this study, 198 (61.3%) underwent OPCAB by the consultant and 125 (38.7%) by a trainee as the primary surgeon. There were no intra-operative conversions from OPCAB to on-CAB during the study period. The conversion rate from OPCAB to on-CAB for the training surgeon is generally low and between the years 2002 and 2004 out of a total of 477 OPCABs there were 4 conversions to on-CAB.
The demographic and pre-operative clinical characteristics of the two patient groups are presented in Table 1. The characteristics of the two groups were similar with the exception of unstable angina (more patients in the consultant group P=0.008), previous PCI (more patients in the consultant group, P=0.002), left ventricular ejection fraction (lower in the consultant group, P<0.013) and the urgency of the operation (more emergencies in the consultant group, P=0.038). Most of the re-operations included in the study were performed by the consultant (P=0.027). The predicted mortality risk, as calculated by EuroSCORE, was identical in the two patient groups. These small demographic differences in the two groups reflect the fact that cases with low ejection fraction, second time operation, or emergencies are not used traditionally for training purposes. Therefore an absolute match of the two groups is not practical and maybe not ethical as well.
Table 2 shows intra- and post-operative characteristics of the patients. Trainees operated on significantly less patients requiring five or more grafts (P=0.046), but the mean number of grafts per patient was 3.7 for the consultant group and 3.3 for the trainee group which is not statistically significantly different. This is explained by the fact that the consultant operated on a higher number of patients requiring more than 4 grafts because these patients were not used for training purposes. Furthermore, the trainees performed 51% of the MIDCABs (18 out of 35 in total), 36% of the ‘Y’ grafts (42 out of a total of 117) and 27.5% of the sequential grafts (22 out of 80 in total). The trainees performed less ‘Y’ and less sequential grafts because these complex procedures were employed at a later stage of their training and also the coronary anatomy and coronary artery disease should be suitable for the purposes of training. The use of IMA was employed in 96% of the cases, of the radial artery in 49% and of bilateral IMAs in 11%, equally distributed between the consultant surgeon and the trainees. The use of total arterial revascularisation was equally distributed between the two groups; 41% of the patients in the consultant group underwent total arterial revascularisation, whereas the ratio for the trainee group was 43%. The patients operated by the trainees stayed significantly less hours in the ICU (P=0.007), whereas the median total hospital stay was similar between the two groups. Rates of serious complications remained low in both groups. There were three 30-day deaths in the consultant patient group (1.5%), while no patients died in the trainee group. All three deaths were emergencies involving patients transferred from the catheterisation laboratory after failed PCI with extensive myocardial necrosis and haemodynamic instability. The total mortality of the firm for CABG in the study period was therefore 0.9% (3/323).
4. Discussion
A lot of professional bodies have shown interest in surgical training and especially in the training of cardiothoracic residents recently. In order to improve the clinical outcomes of training, specific curricula, examinations and close scrutiny of surgical performances have been introduced [10]. Providing the best possible clinical outcomes and the best possible training in cardiac surgery at the same time can be a very complex dilemma to reconcile [11], especially with respect to teaching trainees to perform OPCAB surgery. This study does not aim to compare the outcomes of the trainees to the outcomes of the trainers but to show that complex OPCAB surgery can be taught with low rate of complications and equally good outcomes.
In an earlier study of ours, we demonstrated that OPCAB surgery can be performed safely by supervised cardiac surgical trainees [6] and our findings were in accordance with the findings of most of the studies published by others on the same subject. This article demonstrates that complex OPCAB surgery (i.e. MIDCABs, ‘Y’ and sequential grafting) is a safe and reproducible surgical technique that can be taught successfully to cardiothoracic trainees. The trainees performed 51% of the MIDCABs, 36% of the ‘Y’ grafts and 27.5% of the sequential grafts and 43% of the patients operated upon by the trainees received a total arterial revascularisation procedure. The relatively low percentage of ‘Y’ and sequential grafts performed by the trainees can be explained by the fact that these more complex techniques of grafting coronary arteries were taught at a later stage of the training, because as it is expected in the beginning of the training the trainees ought to master the principles of simple OPCAB surgery.
Mortality and morbidity can be very low. The 30-day mortality among the 125 patients in the trainee group was zero while the only major complications involved one re-sternotomy for bleeding, one mediastinal infection requiring sternal rewiring and one stroke. In the consultant group mortality and morbidity were slightly but not significantly higher (mortality 1.5%). This can be explained by the fact that emergent cases and patients with severely impaired left ventricular function (EF<30%), which are expected to have higher mortality and morbidity, are not normally used for training purposes and therefore are operated upon by the consultant surgeon. The median time for hospital stay following OPCAB was the same in both groups.
It is commonly believed that operations allocated to trainees involve patients with low predicted operative risk. In our study, patients in the trainee group had, overall, less unstable angina and higher left ventricular ejection fraction. Operative risk scoring, as assessed by the EuroSCORE, demonstrated median scores of four in both groups, with a 75th percentile of four in the trainee group versus six in the consultant group. Our study suggests that overall average predicted risk does not differ between patients performed by trainees as compared with consultants, although particularly high risk operations are performed by a consultant surgeon.
Small sample size is the main limitation of our study. Low rates of outcome measures, such as mortality and morbidity, precluded our regression analysis from detecting correlation between patient characteristics and outcome and differences in outcomes between subgroups of patients as well. Low complication rates were, nevertheless, encouraging. A non-significant trend for cases performed by trainees to develop less post-operative complication reinforces the notion that trainees can be taught to operate safely off-CPB. The study was necessarily observational in nature both for logistical and ethical reasons. It is very difficult to assess the criteria used by the trainer in the allocation of the cases to the trainees. Consultant surgeons are likely to use more subtle clinical signs to select cases for trainees than can be readily documented by formal data collection. A second issue that may have influenced the results of this study is how often the trainer intervened during the operation, either by taking over in a planned manner to perform one or more anastomoses, or to position the heart for the trainee, who performed the anastomosis subsequently. By reviewing the operation notes of all the cases involved in this study and by questioning the trainees as well, we conclude that changes in designation in the main operator were extremely rare. Analysis of higher numbers of OPCAB cases performed by a variety of trainees should be performed in future studies to reconfirm the main findings of this trial. Long term follow-up of patients will also be of interest.
Many surgeons believe that complex cardiothoracic procedures are too difficult for trainees to perform under supervision. It has been asserted that this practice is not a matter of safety but one of philosophy [12]. A learning curve clearly exists over the course of a surgeon's career [13]. No matter how well trained residents are, their results will improve over the course of their careers. The more experience the trainees can gain while under the supervision of a consultant, especially with the more complex cases, the less they will need to improve as consultant surgeons and the less impact this will have on patient outcomes.
Baskett et al. showed that it is safe to train junior surgeons in the performance of complex cardiac procedures, such as mitral valve repair. They found that mortality and morbidity were not statistically significantly different between the patients operated by the trainees and the consultants and that it was possible for the trainees to perform an adequate number of cases in order for them to obtain the required experience [14]. Similarly, propensity score-matched cases showed no significantly different complication rates in the two patient groups. The concept and outcome of training in OPCAB in a single UK cardiac surgical centre has been presented comprehensively in a series of publications, all largely concerning the same patient population [15–18]. The last report of the series summarises outcome on 990 CABG cases performed by trainees of which 474 were OPCABs. These operations were compared with those performed by an experienced consultant surgeon. Predicted and observed risk of death or serious complications was similar for trainee and consultant operations. The authors conclude that it is safe to teach OPCAB to trainee surgeons and that continuous performance monitoring for trainees is possible and desirable.
There is clearly a need currently to teach trainees to perform OPCAB surgery. Consultants have the responsibility to learn new techniques themselves and to teach them to the trainees if they want to offer high standards of care to their patients. A recent survey from cardiothoracic training centres in the United States showed that only a very small number of residents achieved competent levels in performing OPCAB surgery [19]. Our study therefore may have important implications for the training of the future cardiothoracic surgeons in beating heart surgery. We have previously demonstrated that trainees under supervision perform OPCAB safely with low rate of complications including patients with triple vessel disease and grafting to the posterior wall of the heart. With this study we have demonstrated that complex OPCAB surgery (MIDCAB, ‘Y’ and sequential grafting and total arterial revascularisation) can be taught to cardiothoracic trainees with low mortality and morbidity. Therefore, we believe that a modern surgical training program in cardiothoracic surgery should expose trainees to complex surgical cardiothoracic procedures, possibly at the more advanced stages during their training, under the supervision of senior surgeons proficient in the technique.
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