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Ann Thorac Surg 2003;76:2000-2006
© 2003 The Society of Thoracic Surgeons

Original article: cardiovascular

Early and medium-term results after on-pump and off-pump coronary artery surgery: a propensity score analysis

Andreas Boening, MDa*, Christine Friedrich, PhD, Juergen Hedderich, MSb, Jan Schoettler, MDa, Sandra Fraund, MDa, Jochen T. Cremer, MDa

a Department of Cardiovascular Surgery, University Hospital, Kiel, Germany,
b Institute for Biometry and Medical Statistics, University Hospital, Kiel, Germany

Accepted for publication June 19, 2003.

* Address reprint requests to Dr Boening, Department of Cardiovascular Surgery, University Hospital Schleswig-Holstein, Arnold-Heller-Str. 7, 24105 Kiel, Germany.
e-mail: aboening{at}kielheart.uni-kiel.de


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Comment
 References
 
BACKGROUND: Comparative publications on beating-heart off-pump coronary artery bypass grafting (OPCAB) surgery versus conventional coronary artery bypass grafting (CCAB) surgery frequently do not offer conclusive information because of investigator bias.

METHODS: Trying to eliminate this problem, a propensity score analysis of the data of all CCAB patients (n = 517) and OPCAB patients (n = 133) operated on by the same surgeons during the same time period (1998 to 2001) was applied. After matching patients with similar propensity score values, 97 CCAB patients and 72 OPCAB patients entered the final analysis.

RESULTS: Early results were similar in both groups: the 30-day mortality reached 1.4% in the CCAB group and 2.8% in the OPCAB group; strokes did not happen. Perioperative myocardial infarctions occurred in 4.1% of the CCAB patients and 4.3% of the OPCAB patients. Drainage blood loss in the first 24 hours after surgery (830 ± 687 mL, CCAB group; and 909 ± 678 mL, OPCAB group) was similar (p = 0.06) in both groups. Medium term results (freedom from percutaneous transluminal coronary angioplasty or reoperation, freedom from myocardial infarction, freedom from stroke, and the quality of life) also were not significantly different between the off-pump and on-pump groups after a mean follow-up of 27 ± 11 months.

CONCLUSIONS: Our results suggest that elective-surgery patients with coronary artery disease can be operated on either on-pump or off-pump with the same early and late mortality and morbidity.


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Comment
 References
 
Off-pump coronary artery bypass grafting (OPCAB) surgery as an alternative method for surgical coronary artery revascularisation is still discussed controversially regarding its benefits compared with conventional coronary artery bypass grafting (CCAB) surgery. There are only few prospective randomized [1–5] or matched studies [6–8] available. The majority of the published studies have inherent methodical limitations: comparisons between surgery from different periods of time [9], retrospective analyses with noncomparable patient groups [10, 11], and studies of patient subgroups such as elderly patients [12, 13] or patients with poor left ventricular function [14]. Moreover most frequently it is not evident whether OPCAB and CCAB patients have been operated on by the same surgeon or by different surgeons. Mack and associates [15] showed in a retrospective analysis how important the influence of the surgeon can be in reporting improved outcomes after OPCAB versus CCAB surgery. This has been nicely pointed out in the accompanying editorial too [16].

We have analyzed our data of a 4-year OPCAB practice of two surgeons (A.B., J.C.) from 1998 to 2001 including the full learning curve and have compared these data with the data of the same surgeons' CCAB patients from the same period. To overcome the shortcomings of a retrospective, nonrandomized analysis we employed the propensity score statistical technique recommended by Blackstone [17]. In brief this technique assigns a scoring value to every patient after a multiple regression analysis attributing the patient into one or the other comparison group. Only patients with similar scores were compared in the final analysis.

Thus this paper describes the results of our comparison between OPCAB and CCAB patients using a statistical method that is coming very close to a prospective randomized analysis.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Comment
 References
 
Patients
From January 1998 to December 2001, 133 patients have been revascularized without and 517 patients with the use of the extracorporeal circulation through a median sternotomy by two surgeons. No other surgeon in our department was practicing OPCAB surgery. Not included were 237 patients with left internal mammary–left anterior descending artery bypass through an anterior minithoracotomy. There were two main patient groups for OPCAB surgery: either one-vessel or two-vessel disease or a suitable coronary anatomy, or patients with a high risk for neurologic problems or a heavily calcified aorta. Basic OPCAB patient data before surgery are compared with the CCAB patient data in Table 1.


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  		Table 1. Preoperative Data of All Isolated Coronary Artery Bypass Procedures Off-Pump (OPCAB) and Conventional On-Pump (CCAB)

 
The data of the 72 OPCAB patients (80.6% male, 19.4% female) and the 97 CCAB patients (84.5% male, 15.5% female) included in the definite analysis after employing the propensity score statistics are given in Table 2. It becomes obvious that the propensity score has established two comparable patient groups (Table 2) whereas the whole cohort of OPCAB and CCAB patients showed some differences (Table 1).


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  		Table 2. Preoperative Data

 
One-vessel disease was present in 1 CCAB patient, two-vessel disease in 43.1% of the OPCAB patients and 28.9% of the CCAB patients, and three-vessel disease in 56.9% of the OPCAB and 70.1% of the CCAB patients. This distribution was not significantly different.

To be able to state a similar severity of the coronary artery disease in both groups coronary artery diameters were measured intraoperatively and a mean value for every vessel was calculated (Table 3).


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  		Table 3. Completeness of Revascularization and Diameter of Bypassed Vessels

 
Methods
For the OPCAB procedures stabilization of the target vessel was achieved using suction devices and exposure of the coronary vessels was facilitated by using deep pericardial sutures or an apical suction device. During the anastomoses the vessels were temporarily occluded by a proximal and sometimes also distal 4-0 Prolene (Ethicon, Somerville, NJ) suture and a soft tourniquet as described earlier [18]. Shunts were only used in case of excessive bleeding or hemodynamic or rhythm instability. Heparin was administered in a dosage of 150 (only arterial grafts) or 300 IU/kg (venous and arterial grafts) and was fully antagonized by protamine.

For the CCAB procedures, after cannulation of the aorta and the right atrium the patient was cooled to 28°C to 34°C, the aorta was cross-clamped, and 10 mL/kg cold (4°C) antegrade crystalloid (St. Thomas') cardioplegia was given. Distal anastomoses were done first and proximal anastomoses thereafter with a partially clamped aorta. Heparin was administered in a dosage 300 IU/kg and was fully antagonized by protamine. Aprotinin (low dose 2 KIU) was used for every CCAB patient but not for OPCAB patients.

Definitions and thresholds
Perioperative myocardial infarction was defined as creatine kinase CK-MB more than 10% of CK and new Q waves in the discharge electrocardiogram.

Extubation was carried out when the patient was hemodynamically stable without bleeding, warm (>36°C), conscious, able to breathe spontaneously with an FiO2 less than 0.40 and a pO2 more than 80 mm Hg, and a pCO2 less than 50 mm Hg.

The thresholds for blood transfusion were hemoglobin values less than 8.0 mg/dL in a stable situation and less than 9.0 mg/dL in an unstable situation. Fresh frozen plasma was given when bleeding (>300 mL/h) occurred thromboplastin time, factor V and VIII were subnormal. Thrombocytes were transfused in case of bleeding and thrombocyte counts were less than 80,000/µL.

An emergency case was defined as need for surgery within 24 hours after coronary angiography or a patient being given inotropic agents or having an intraaortic ballon pump before surgery.

The index for completeness of revascularization (Table 3) was calculated using the following formula: the number of intended anastomoses divided by the number of realized anastomoses [5].

Follow-up
All patients were contacted by a letter containing a quality of life [19] form and a questionnaire about cardiovascular endpoints (death, reoperation, percutaneous transluminal coronary angioplasty, myocardial infarction, stroke) between April 2002 and October 2002. Approximatley 75% of patients in both groups sent back written informations about their postprocedural quality of life. Patients who did not respond were contacted by telephone. Follow-up completeness reached 91% in the OPCAB group (mean follow-up, 27.5 ± 10.8 months) and 92% in the CABG group (mean follow-up, 27.1 ± 11.8 months).

Statistical methods
According to Blackstone [17], we have used the propensity score method for the statistical analysis of this comparison between two operative techniques. The first step included 517 CCAB patients and 133 OPCAB patients (Table 1) to form a propensity score calculated by logistic regression analysis. For this regression analyis preoperative demographic data (age, sex, diabetes, pulmonary disease, peripheral vascular disease, arterial hypertension, dialysis, neurologic diseases, Canadian Cardiovascular Society angina classification, left ventricular ejection fraction, one-, two-, or three-vessel disease, and the EURO-Score [18]) were taken into consideration. After having obtained a score value for every single patient, patients with similar scores were chosen for the final comparison. Using this technique comparable patient groups could be identified (Tables 1 and 2).

The propensity score is only an estimate of the propensity toward belonging to one group versus another [17]; it does not say anything about the risk profile of a specific patient. A propensity score value close to zero means a higher probability of belonging to the OPCAB group and a value of close to 1 means a higher probability of belonging to the CCAB group. In our study we have matched at least 1 CCAB patient with a similar propensity score value to 1 OPCAB patient, leading to more CCAB patients (n = 97) than OPCAB patients (n = 72) in our analysis. We would like to show by the following example why the propensity score in the CCAB group in our study must be higher than in the OPCAB group: after matching 1 patient from each group with a propensity score of 0.3 and then 1 patient in the OPCAB group with 2 patients in the CCAB group with a propensity score of 0.85, the mean propensity score value in the OPCAB group is 0.58 ± 0.39 and in the CCAB group it is 0.67 ± 0.32. We have addressed this statistical problem by repeating the analysis with 62 patients in each group and seen that also with this population the preoperative demographic data (Table 2) were not significantly different.

Ordinal and nominal data were compared in a 2 x 2 table using the {chi}2 test or Fisher's exact test, if one of the expected values in the 2 x 2 table was less than 5. After having tested interval or ratio data for normal distribution (one-sample Kolmogorov-Smirnov test) normally distributed values were compared using the t test. Not normally distributed values were compared using the Mann-Whitney U test. Statistical significant differences were assumed when p values were lower than 0.05.


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Comment
 References
 
Short-term results
The number of peripheral anastomoses were significantly higher in the CCAB group (3.4 ± 0.9) than in the OPCAB group (2.4 ± 0.7). However incomplete revascularization in the OPCAB group can be excluded by an index for completeness of revascularization of 0.98 (Table 3). Two patients from the OPCAB group (2.8%) were converted to an extracorporeal circulation procedure because of unstable intraoperative hemodynamics.

The outcome was similar in both groups (Table 4). The 30-day mortality reached 1.4% in the CCAB group and 2.8% in the OPCAB group. One CCAB patient died on postoperative day 8 because of fulminant pulmonary embolism; 1 OPCAB patient died on postoperative day 9 from pulmonary embolism and closure of the bypass segment to a posterior descending artery in a sequential graft to the obtuse marginal branch and posterior descending artery. For these lethal complications, both reasons for death were confirmed by autopsy. The other OPCAB patient died on postoperative day 9 from a massive ulcus ventriculi bleeding in another hospital.


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  		Table 4. Outcome Data of Patients After OPCAB Versus CCAB Surgery

 
Clinically assumed neurologic deficits occurred in 1 CCAB patient and in 1 OPCAB patient but could not be confirmed when magnetic resonance imaging scans were carried out and deficits had resolved at the day of discharge. Postoperative delirium was found in 6 CCAB patients (6.2%) and in 3 OPCAB patients (4.3%), mostly in patients with preoperative risk factors (carotid artery disease, history of stroke, advanced age, or calcified aorta).

Perioperative myocardial infarctions occurred in 4.1% of the CCAB patients and 4.3% of the OPCAB patients (p = 0.62). Only 1 patient in the CCAB group required an intraaortic balloon pump preoperatively as well as postoperatively. The number of patients with a CK-MB more than 80 U/L was not significantly different (p = 0.465) in the OPCAB group (n = 4, 6.1%) and the CABG- group (n = 3, 3.4%). However postoperative CK values (p = 0.023) as well as CK-MB values (p < 0.0001) were significantly lower in the OPCAB group. There were 3 rethoracotomies for bleeding in the CCAB group and 1 in the OPCAB group. In each group one reopening had to be done for a bypass reintervention. Mediastinitis or deep sternal wound infection did not occur in any of the study patients.

Although ventilation time was significantly shorter in the OPCAB group (Table 5), the length of stay in the intensive care unit (median, 1 day in both groups) and the length of stay in the hospital (median: CCAB, 12 days; OPCAB, 13 days) were similar.


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  		Table 5. Perioperative Data of OPCAB and CCAB Patients Entering Final Analysis

 
Drainage blood loss in the first 24 hours after surgery as well as the rate of blood transfusion during the entire hospital stay were similar (Table 5).

Medium-term results
At a medium follow-up of more than 2 years cardiovascular endpoints of the study occurred in a similar number percentage of patients in both groups: freedom from death was 98.4% in the OPCAB and 95.5% in the CCAB group (p = 0.937), freedom from PTCA and reoperation was 94.9% in the OPCAB group and 97.6% in the CCAB group (p = 1.0), freedom from myocardial infarction was 97.6% in the OPCAB group and 95% in the CCAB group (p = 0.649), and freedom from stroke was 96.5% in the OPCAB and 100% in the CCAB group (p = 0.190).

Quality of life was similar in both groups and not different from a healthy population sample (Fig 1).



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  		Fig 1. Quality of life after a medium follow-up of 27 ± 11 months, comparing off-pump coronary artery bypass grafting surgery and on-pump coronary artery surgery with a normal population sample. Diamonds = on-pump conventional coronary artery surgery; squares = off-pump coronary artery bypass graft surgery; triangles = control.

 

   Comment
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
References
 
Our data show that in elective, low-risk patients off-pump and on-pump coronary surgery are equivalent procedures for myocardial revascularization. The short-term results, for example mortality, myocardial infarction, stroke, and reoperation rates, did not differ significantly between the OPCAB and the CCAB group. The medium-term results after a follow-up period of more than 2 years do not show significant differences regarding major cardiac adverse events and quality of life between those groups.

These data are obtained using statistical methods that exclude investigational bias factors for retrospective studies effectively. Retrospective studies operate in normal clinical practice without any interventions implemented by randomized assignment rules and represent the spectrum of medical practice better than the setting of randomized experiments [20]. Bias factors in retrospective studies [17] exist if such studies comparing CCAB and OPCAB results include patients from different time periods [9] or with different demographic data [7, 11, 22, 23]. Moreover it is usually not evident whether the same surgeons have done both on-pump and off-pump procedures and whether the same thresholds for extubation, discharge from hospital, and blood transfusion were valid for both groups.

Even though this study is retrospective the difference from most reports is obvious: two surgeons have operated on patients in both groups during the same time period, the use of the propensity score has resulted in comparable basic data for both groups, and the thresholds are equal for both groups.

The published prospective randomized studies [1, 3, 5] do not report major outcome differences between on- and off-pump surgery but only minor advantages regarding cost, transfusion requirement, and length of stay in the hospital.

If the results of off-pump and on pump surgery in elective patients with low operative risk are similar, why should we not continue to use extracorporeal circulation for routine patients? Of course there is no scientific proof for it but the extracorporeal circulation provides a "protected environment" for cardiac surgeons: hemodynamic stability is maintained, the operative field is quiet and blood free, communication with other disciplines is limited to a minimum, questions about quality of the anesthesiologist or the assistant are not important, and everything can be done in an absolutely standardized way.

Moreover there are still uncertainties regarding the long-term patency of vein grafts after OPCAB surgery: The results reported by Kim and associates [24] (67.9% patency after 1 year) and Ömeroglu and associates [25] (47.1% patency after 3 years) are disappointing. As our data show in agreement with other publications there is a tendency to do more anastomoses on pump than off pump: there is a significantly higher index for completeness of revascularization in the CCAB group in our series compared with the already high index for completeness of revascularization in the OPCAB group. Small coronary arteries (diameter below 1.5 mm) have been regarded as a contraindication to off-pump surgery [26] and complex arterial revascularizations to vessels sometimes in the 1 mm range can be done easier on pump. Minor advantages of off-pump surgery such as cost reduction mainly induced by a shorter length of stay of off-pump patients [5, 8], a lower postoperative CK-MB level [27], or a lower transfusion rate [5, 7] do not convince OPCAB opponents to change their way of myocardial revascularization.

Admittedly the data are quite different for high risk patients: There are reports demonstrating a better outcome for patients with neurologic comorbidities or a high risk for perioperative stroke, for olderly patients or patients with poor left ventricular function [28] but neither are these data from prospective, randomized studies nor is it clear whether the patients are operated on by the same surgeons.

"High-quality follow-up data" for the results of off-pump versus on-pump coronary artery surgery, as demanded by Ascione and associates [28] in a recent review, are now available. In agreement with the medium-term outcome data published by Calafiore and associates [8], by Angelini and associates [1], and by Nathoe and associates [3], our data also show no significant differences between off-pump and on-pump patients 1 to 5 years after surgery.

Limitations
Because there were no clear indications for on- and off-pump surgery at the beginning of this study (and there are still no differential indications), an institutional bias—taking patients with more severe coronary artery disease or with smaller coronary vessels on extracorporeal circulation and leaving the "good coronaries" for OPCAB—would be possible. However the coronary artery diameter was similar in both groups (Table 3), and the percentage of female patients was similar in both groups.

As this study is retrospective its design can not be regarded as good as that of a prospective, randomized study. However applying the propensity score [17, 21] we were able to overcome most of the bias sources of nonmatched studies. Moreover we have compared CCAB and OPCAB patients of two surgeons with off-pump experience during the same time frame using the same definitions for adverse events and thresholds for treatment decisions in each group. Therefore it reflects the clinical reality in our department even when the use of the propensity score caused a reduction of the number of patients from 656 to 169 in the final analysis. This patient number is not sufficient to find out differences in outcome determinants with an incidence of less than 3% and a difference between the groups of less than 50% in each outcome determinant. But even a prospective, randomized study would have to include thousands of patients to show differences between on- and off-pump surgery when outcome determinants are distributed this way.

Our results suggest that elective patients with coronary artery disease can be operated on either on pump or off pump with the same mortality and perioperative morbidity. Moreover the medium-term results show that a similar freedom from cardiovascular events can be achieved with both surgical methods. From studies with a high level of evidence there is no proof for a general improvement in postoperative outcome by a radical change from on-pump to off-pump coronary artery surgery.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 

  1. Angelini G.D., Taylor F.C., Reeves B.C., Ascione R. Early and midterm outcome after off-pump and on-pump surgery in beating heart against cardioplegic arrest studies (BHACAS 1 and 2): a pooled analysis of two randomised controlled trials. Lancet 2002;359:1194-1199.[Medline]
  2. Van Dijk D., Nierich A.P., Jansen E.W., et al. Early outcome after off-pump versus on-pump coronary bypass surgery: results from a randomized study. Circulation 2001;104:1761-1766.[Abstract/Free Full Text]
  3. Nathoe H.M., Van Dijk D., Jansen E.W.L., et al. A comparison of on-pump and off-pump coronary bypass surgery in low-risk patients. N Engl J Med 2003;348:394-402.[Abstract/Free Full Text]
  4. Czerny M., Baumer H., Kilo J., et al. Complete revascularisation in coronary artery bypass grafting with and without cardiopulmonary bypass. Ann Thorac Surg 2001;71:165-169.[Abstract/Free Full Text]
  5. Puskas J.D., Williams W.H., Duke P.G., et al. Off-pump coronary artery bypass grafting provides complete revascularization with reduced myocardial injury, transfusion requirements, and length of stay. A prospective randomised comparison of two hundred unselected patients undergoing off-pump versus conventional coronary artery bypass grafting. J Thorac Cardiovasc Surg 2003;125:797-808.[Abstract/Free Full Text]
  6. Kilo J., Baumer H., Czerny M., et al. Target vessel revascularisation without cardiopulmonary bypass in elderly high-risk patients. Ann Thorac Surg 2001;71:537-542.[Abstract/Free Full Text]
  7. Sabik J.F., Giilinov A.M., Blackstone E.H., et al. Does off-pump surgery reduce mortality and morbidity?. J Thorac Cardiovasc Surg 2002;124:698-707.[Abstract/Free Full Text]
  8. Calafiore A.M., Di Mauro M., Canosa C., Di Giammarco G., Iaco A.L., Contini M. Early and late outcome of myocardial revascularization with and without cardiopulmonary bypass in high risk patients (EuroSCORE >= 6). Eur J Cardiothorac Surg 2003;23:360-367.[Abstract/Free Full Text]
  9. Patel N.C., Pullan D.M., Fabri B.M. Does off-pump total arterial revascularization without aortic manipulation influence neurological outcome? A study of 226 consecutive, unselected cases. Heart Surg Forum 2001;5:28-32.
  10. Chavanon O., Durand M., Hacini R., et al. Coronary artery bypass grafting with left internal mammary artery and right gastroepiploic artery, with and without bypass. Ann Thorac Surg 2002;73:499-504.[Abstract/Free Full Text]
  11. Hernandez F., Cohn W.E., Baribeau Y.R., et al. In-hospital outcomes of off-pump versus on-pump coronary artery bypass procedures: a multicenter experience. Ann Thorac Surg 2001;72:1528-1534.[Abstract/Free Full Text]
  12. Hirose H., Amano A., Takahashi A. Off-pump coronary artery grafting for elderly patients. Ann Thorac Surg 2001;72:2013-2019.[Abstract/Free Full Text]
  13. Al-Ruzzeh S, George S, Yacoub M, Amrani M. The clinical outcome of off-pump coronary artery bypass surgery in the elderly patients. Eur J Cardiothorac Surg 2001:1152–6
  14. Arom K.V., Flavin T.F., Emery R.W., Kshettry V.R., Petersen R.J., Janey P.A. Is low ejection fraction safe for off-pump coronary bypass operation?. Ann Thorac Surg 2000;70:1021-1025.[Abstract/Free Full Text]
  15. Mack M., Bachand D., Acuff T., et al. Improved outcomes in coronary artery bypass grafting with beating-heart techniques. J Thorac Cardiovasc Surg 2002;124:598-607.[Abstract/Free Full Text]
  16. Bonchek L.I. Off-pump coronary bypass. Is it for everyone?. J Thorac Cardiovasc Surg 2002;124:431-434.[Free Full Text]
  17. Blackstone E.H. Comparing apples and oranges. J Thorac Cardiovasc Surg 2002;123:8-15.[Free Full Text]
  18. Cremer J.T., Wittwer T., Böning A., et al. Minimally invasive coronary artery revascularization on the beating heart. Ann Thorac Surg 2000;69:1787-1791.[Abstract/Free Full Text]
  19. Ware J.E. Standards for validating health measures: definition and context. J Chron Dis 1987;40:473-480.[Medline]
  20. Nashef S.A., Roques F., Michel P., Gauducheau E., Lemeshow S., Salamon R. European system for cardiac operative risk evaluation (EuroSCORE). Eur J Cardiothorac Surg 1999;16:9-13.[Medline]
  21. Rubin D.B. Estimation from nonrandomized treatment comparisons using subclassification on propensity scores. Ann Intern Med 1997;127:757-763.[Abstract/Free Full Text]
  22. Kshettry V.R., Flavin T.F., Emery R.W., Nicoloff D.M., Arom K.V., Petersen R.J. Does multivessel, off-pump coronary artery bypass reduce postoperative morbidity?. Ann Thorac Surg 2000;69:1725-1731.[Abstract/Free Full Text]
  23. Cleveland J.C., Shroyer A.L.W., Chen A.Y., Peterson E., Grover F.L. Off-pump coronary artery bypass grafting decreases risk-adjusted mortality and morbidity. Ann Thorac Surg 2001;72:1282-1289.[Abstract/Free Full Text]
  24. Kim KB, Lim C, Lee C, et al. Off-pump coronary artery bypass may decrease the patency of saphenous vein grafts. Ann Thorac Surg 2001;72(Suppl):S1033–7
  25. Ömeroglu S.N., Kirali K., Güler M., et al. Midterm angiographic assessment of coronary artery bypass grafting without cardiopulmonary bypass. Ann Thorac Surg 2000;70:844-850.[Abstract/Free Full Text]
  26. Diegeler A, Matin M, Falk V, et al. Indication and patient selection in minimally invasive and off-pump coronary artery bypass grafting. Eur J Cardiothorac Surg 1999;16(Suppl 1):79–82
  27. Kilger E., Pichler B., Weis F., et al. Markers of myocardial ischemia after minimally invasive and conventional coronary operation. Ann Thorac Surg 2000;70:2023-2028.[Abstract/Free Full Text]
  28. Ascione R., Caputo M., Angelini G.D. Off-pump coronary artery bypass grafting: not a flash in the pan. Ann Thorac Surg 2003;75:306-313.[Abstract/Free Full Text]



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