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J Thorac Cardiovasc Surg 2007;133:169-173
© 2007 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease

Postoperative stroke after off-pump versus on-pump coronary artery bypass surgery

Fausto Biancari, MD, PhD*, Martti Mosorin, MD, Elsi Rasinaho, MS, Jarmo Lahtinen, MD, Jouni Heikkinen, MD, Eija Niemelä, MS, Vesa Anttila, MD, PhD, Martti Lepojärvi, MD, PhD, Tatu Juvonen, MD, PhD

Division of Cardio-thoracic and Vascular Surgery, Department of Surgery, Oulu University Hospital, Oulu, Finland.

Received for publication March 30, 2006; revisions received May 25, 2006; accepted for publication June 28, 2006.

* Address for reprints: Fausto Biancari, MD, PhD, Division of Cardio-thoracic and Vascular Surgery, Department of Surgery, Oulu University Hospital, PO Box 21, 90029 Oulu, Finland. (Email: faustobiancari{at}yahoo.it; fausto.biancari{at}ppshp.fi).


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
OBJECTIVE: The value of off-pump over conventional coronary artery bypass surgery in reducing the risk of postoperative stroke is controversial. This issue has been evaluated in light of our recent clinical experience.

METHODS: Off-pump coronary artery bypass surgery was performed in 557 patients, and conventional coronary artery bypass surgery was performed in 445 patients. Preoperative stroke risk was calculated according to the Northern New England Cardiovascular Disease Study Group stroke risk-scoring method.

RESULTS: Off-pump coronary artery bypass surgery was associated with a lower but not significant rate of postoperative stroke in the overall series (1.8% vs 2.5%, P = .45), a difference that slightly increased in the highest tertile of the Northern New England Cardiovascular Disease Study Group score (2.8% vs 4.2%, P = .75). The postoperative stroke rate was significantly lower when the operation was performed by off-pump coronary artery bypass surgeons using routinely epiaortic ultrasonographic scanning compared with conventional coronary artery bypass surgeons not using epiaortic ultrasonographic scanning (0.4% vs 3.9%, P = .015). The Northern New England Cardiovascular Disease Study Group score (mean, 4.6 ± 2.1 vs 4.9 ± 2.2; P = .189) was similar in these groups. Logistic regression showed that when adjusted for Northern New England Cardiovascular Disease Study Group stroke risk score and critical preoperative status, the treatment approach (off-pump coronary artery bypass surgery and routine epiaortic ultrasonographic scanning) was an independent predictor of postoperative stroke (P = .012; odds ratio, 34.1; 95% confidence interval, 2.2-533.7).

CONCLUSIONS: The neuroprotective efficacy of off-pump coronary artery bypass surgery is marginal compared with that of conventional coronary artery bypass surgery. A decreased risk of postoperative stroke after off-pump coronary artery bypass surgery is expected, mostly in high-risk patients and when epiaortic ultrasonographic examination is routinely used for better planning of operative strategy, aiming to minimize the risk of intraoperative embolism.

Abbreviations and Acronyms CCAB = conventional coronary artery bypass surgery; CI = confidence interval; NNECVDSG = Northern New England Cardiovascular Disease Study Group; OPCAB = off-pump coronary artery bypass surgery; OR = odds ratio; ROC = receiver operating characteristic; TIA = transient ischemic attack


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Two recent meta-analyses1,2Go have shown that the benefit of off-pump coronary artery bypass surgery (OPCAB) over conventional coronary artery bypass surgery (CCAB) in reducing the risk of postoperative stroke is marginal. Indeed, a significant reduction in terms of postoperative stroke can be expected only in patients at high risk of stroke and with a surgical strategy aiming to reduce the risk of intraoperative embolism. This issue has been evaluated in our recent experience when the preoperative risk of stroke was stratified according to the Northern New England Cardiovascular Disease Study Group (NNECVDSG) stroke risk score.3,4Go


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
From April 2004 through December 2005, 1016 consecutive patients underwent isolated coronary artery bypass surgery at our institution. All patients who underwent any other associated procedure were not included in the present analysis. OPCAB was performed in 539 (53.1%) patients, CCAB was performed in 468 (46.1%) patients, and beating heart coronary surgery with cardiopulmonary bypass support was performed in 9 (0.9%) patients.

The decision of whether to perform OPCAB or CCAB was based on the surgeon’s individual choice. Although in some institutions enthusiasm for OPCAB has driven toward a complete shift from CCAB to OPCAB, this did not happen in many others. In our institution as well, there are surgeons entirely committed to OPCAB opposed to surgeons entirely committed to CCAB, with a few others using both techniques according to the patient’s comorbidities and coronary anatomy.

Surgeons dedicated to epiaortic ultrasonography used it on a routine basis to identify any atherosclerotic lesions of the ascending aorta. In patients with a diseased ascending aorta, the decision of whether to avoid aortic manipulation was based on the location and characteristics of the atherosclerotic lesion. Side-bite clamping was believed safe in case of flat atherosclerotic lesions located in the posterior wall of the ascending aorta or at the level of the origin of the brachiocephalic trunk far enough from the site of aortic clamping. Exophytic atherosclerotic lesions were considered an absolute contraindication to aortic manipulation. Heartstring anastomotic devices (Guidant, Indianapolis, Ind) were used in 19 patients with diseased ascending aortas. Proximal aortic connectors were used also in a few patients without diseased ascending aortas because they were included in a study evaluating the efficacy of these devices.

Stroke was defined as prolonged or permanent deficit occurring during the in-hospital stay, and it was considered the main postoperative outcome end point of this study. The overall mortality and stroke rates during the stay in our hospital were 1.5% and 2.3%, respectively. The postoperative stroke rates after OPCAB, CCAB, and beating-heart coronary surgery with cardiopulmonary bypass support were 1.9%, 2.6%, and 11.1%, respectively (P = .151).

We were able to calculate the NNECVDSG stroke risk score in 952 of 1016 patients because preoperative estimation of left ventricular ejection fraction was missing in 64 patients. They form the basis of the present study, and their characteristics, as well as operative data, are summarized in Table 1.


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  		TABLE 1. Clinical and operative data
 
Heparin (3.0 mg/kg) was administered intravenously after sternotomy to maintain an activated clotting time of more than 400 seconds, and it was neutralized at the end of the procedure by using protamine sulfate (3.0 mg/kg). Intermittent antegrade and retrograde cold blood cardioplegia was used during CCAB. Proximal anastomoses were sutured to the aorta during crossclamping, and aortic side clamping was never used during CCAB. Side-bite clamping was used in 437 (86.2%) patients who underwent OPCAB. Proximal aortic anastomotic devices were used in 9 patients, and Heartstring anastomotic devices were used in 19 patients. The aorta was left untouched in 42 patients who underwent OPCAB. In 21 (50%) of these patients, both internal thoracic artery grafts were used. Intracoronary shunts were routinely used in patients who underwent OPCAB.

Neither heparin nor warfarin was administered postoperatively in these patients unless they had atrial fibrillation. Since the policy of using anticoagulants since the first episode of atrial fibrillation was introduced in our practice at the beginning of 2004, only patients treated after that were included in this study. Acetylsalicylic acid, but not clopidogrel, was given to all patients postoperatively.

Statistical analysis was performed with SPSS statistical software (SPSS version 12.0.1; SPSS Inc, Chicago, Ill). Continuous variables are reported as the mean ± standard deviation. The {chi}2 and Fisher exact tests were used for univariate analysis of categoric data. The Mann–Whitney test was used to assess the distribution of continuous variables in different subgroups. The receiver operating characteristic (ROC) analysis was used to assess the validity of the NNECVDSG stroke risk score. Only variables with P values of less than .2 were entered into the logistic regression model.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
OPCAB was performed in 507 (53.3%) patients, and conversion to CCAB was required in 3 patients because of hemodynamic instability. The outcome of these patients is summarized in Table 2. A significantly lower incidence of postoperative cardiac low output syndrome was observed in the OPCAB group. Otherwise, no significant difference in the other outcome end points was observed.


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  		Table 2. Postoperative complications
 
NNECVDSG stroke risk scores were similar in the study groups and were significantly associated with the postoperative risk of stroke (Mann–Whitney test, P = .004; area under the ROC curve, 0.690; 95% confidence interval [CI], 0.590-0.789), stroke/transient ischemic attack (TIA; Mann–Whitney test, P = .004; area under the ROC curve, 0.667; 95% CI, 0.577-0.757), neuropsychological complications (Mann–Whitney test, P < .0001; area under the ROC curve: 0.629; 95% CI, 0.574-0.683), and stroke/TIA/neuropsychological complications (Mann–Whitney test, P < .0001; area under the ROC curve, 0.638; 95% CI, 0.589-0.688). OPCAB was associated with a slightly lower rate of postoperative stroke in the overall series (1.8% vs 2.5%, P = .454), a difference that increased in the highest tertile of the NNECVDSG score (2.8% vs 4.2%, P = .749, Figure 1) but failed to reach statistical significance.


Figure 1
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  		Figure 1. Risk of in-hospital stroke after off-pump coronary artery bypass surgery (OPCAB) versus conventional coronary artery bypass surgery (CCAB) according to the Northern New England Cardiovascular Disease Study Group (NNECVDSG) stroke risk score tertiles.

 
Logistic regression, including critical preoperative status, recent myocardial infarction, left ventricular ejection fraction of less than 40%, hypertension, history of stroke, extracardiac arteriopathy, urgent operation, and emergency operation, showed that critical preoperative status was the only independent predictor of postoperative stroke (P = .001; odds ratio [OR], 6.246; 95% CI, 2.145-18.194; Hosmer–Lemeshow test, P = .588). When the NNECVDSG stroke risk score was included in the regression model, critical preoperative status maintained its significance (P < .0001; OR, 6.607; 95% CI, 2.303-18.961), and NNECVDSG score was also an independent predictor of postoperative stroke (P = .024; OR, 1.285; 95% CI, 1.034-1.598).

We compared the results of 3 surgeons with a prevalent (>80% of cases) OPCAB approach using routinely epiaortic ultrasonographic scanning (228 patients) with those of 3 surgeons with a prevalent (>79% of cases) CCAB approach not using epiaortic ultrasonographic scanning (204 patients). The other surgeons were not considered in this subanalysis because they do not routinely use epiaortic ultrasonography, they perform CCAB and OPCAB with a similar prevalence, or both. The NNECVDSG score was similar in these groups (mean, 4.6 ± 2.1 vs 4.9 ± 2.2; median, 4.8 vs 5.0; P = .189). The postoperative stroke rate in the OPCAB group was 0.4%, and it was 3.9% in the CCAB group (P = .015), whereas the postoperative stroke/TIA rates were 1.3% versus 3.9% (P = .125). Logistic regression showed that even when adjusted for NNECVDSG stroke risk score and critical preoperative status (both maintained their independent prognostic value), the treatment approach was an independent predictor of postoperative stroke (P = .012; OR, 34.135; 95% CI, 2.183-533.746; Hosmer–Lemeshow test, P = .507). The number of distal anastomoses (3.6 ± 0.9 vs 3.7 ± 0.9, P = .73) was similar in these study groups, whereas the number of proximal anastomoses to the aorta (1.7 ± 0.7 vs 1.9 ± 0.6, P = .009) was lower in the OPCAB group. The ascending aorta was left untouched in 18 (7.9%) patients operated on by these 3 OPCAB surgeons. In 5 (2.5%) patients who underwent CCAB, no proximal anastomoses were carried out. Surgeons committed to OPCAB have used Heartstring proximal aortic anastomotic devices in 13 patients. These devices have never been used by surgeons committed to CCAB in this series.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The results of this relatively small study suggest that patients at high risk of postoperative stroke, as identified by using the NNECVDSG scoring method, would most benefit from undergoing OPCAB. However, such a difference is not likely to become significant without an appropriate strategy aiming to reduce intraoperative embolism to the brain. In fact, the benefits of this minimally invasive treatment must be optimized by means of routine intraoperative ultrasonographic examination of the ascending aorta and, when indicated, avoidance of aortic manipulation to avoid dangerous side clamping of a diseased aorta.5Go

However, the risk of postoperative stroke does not completely vanish, even after a carefully planned and performed operation. In fact, even if the exact day of occurrence of stroke is not always clear because some patients are intubated and sedated for several days after surgical intervention, preoperative stroke might suddenly occur a few days after the operation, complicating an apparently normal postoperative recovery (Figure 2). 6-8Go This suggests that other causes of stroke occurring after the first postoperative day must be advocated. Embolism from the left atrium and ventricle, as well as extracranial and intracranial vascular disease, might be causes of such late strokes. In this study postoperative atrial fibrillation was not associated with the occurrence of postoperative stroke (P = .226), likely because of our current policy to administer anticoagulants since the first episode of atrial fibrillation. Because the benefits of concurrent carotid endarterectomy are still to be demonstrated,9Go probably embolism from the left cavities of the heart is the main causative mechanism of such late stroke. We also suspect that in a few patients paradoxical embolism through a patent foramen ovale defect might occur because asymptomatic pulmonary embolism after coronary artery surgery is not uncommon.10Go This means that to further reduce the risk of stroke, anticoagulation during the in-hospital period should be considered in high-risk patients.


Figure 2
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  		Figure 2. Chronologic distribution of postoperative stroke according to type of operation. OPCAB, Off-pump coronary artery bypass surgery; CCAB, conventional coronary artery bypass surgery.

 
We believe that further comparative analyses on this issue cannot be appropriately performed if patients’ stroke risk is not stratified according to specific risk-scoring methods. In fact, this makes possible a more adequate comparison of the results between different surgical strategies and evaluation of any possible difference between different institutions. Indeed, the results of a series of patients with a median NNECVDSG score ranging from 1.1 to 1.55Go are not comparable with those of the present series, in which the overall median score was 5.0. Similarly, the characteristics and possibly the mechanisms leading to stroke in patients with a median NNECVDSG score of 2.87Go can be different from those of the ones herein reported, whose median score was 5.8.

In conclusion, the neuroprotective efficacy of OPCAB is marginal compared with that of CCAB. However, a decreased risk of postoperative stroke after OPCAB is expected, mostly in high-risk patients and when epiaortic ultrasonographic examination is routinely used for better planning of operative strategy, aiming to minimize the risk of intraoperative embolism.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Wijeysundera DN, Beattie S, Djaiani G, Rao V, Borger MA, Karkouti K, et al. Off-pump coronary artery surgery for reducing mortality and morbidity. Meta-analysis of randomized and observational studies. J Am Coll Cardiol 2005;46:872-882.[Abstract/Free Full Text]
  2. Cheng DC, Bainbridge D, Martin JET, Novick RJ, The Evidence-based Perioperative Clinical Outcomes Research Group Does off-pump coronary artery bypass reduce mortality, morbidity and resource utilization when compared with conventional coronary artery bypass?. A meta-analysis of randomized trials. Anesthesiology 2005;102:188-203.[Medline]
  3. Charlesworth DC, Likosky DS, Marrin CAS, Maloney CT, Quinton HB, Morton JR, et al. Development and validation of a prediction model for stroke after coronary artery bypass surgery. Ann Thorac Surg 2003;76:436-443.[Abstract/Free Full Text]
  4. Kangasniemi OP, Luukkonen J, Biancari F, Leo E, Vuorisalo S, Pokela R, et al. Risk scoring methods for prediction of postoperative stroke after coronary artery bypass surgery. J Thorac Cardiovasc Surg 2006;131:734-735.[Free Full Text]
  5. Kapetanakis EI, Stamou SC, Dullum MKC, Haile E, Boyce SW, Bafi AS, et al. The impact of aortic manipulation on neurologic outcomes after coronary artery bypass surgery: a risk-adjusted study. Ann Thorac Surg 2004;78:1564-1571.[Abstract/Free Full Text]
  6. Likosky DS, Marrin CAS, Caplan LR, Baribeau YR, Morton JR, Weintraub RM, et al. Determination of etiologic mechanisms of strokes secondary to coronary artery bypass graft surgery. Stroke 2003;34:2830-2834.[Abstract/Free Full Text]
  7. Peel GK, Stamou SC, Dullum MKC, Hill PC, Jablonski KA, Bafi AS, et al. Chronologic distribution of stroke after minimally invasive versus conventional coronary artery bypass. J Am Coll Cardiol 2004;43:752-756.[Abstract/Free Full Text]
  8. Lahtinen J, Biancari F, Salmela E, Mosorin M, Satta J, Rainio P, et al. Postoperative atrial fibrillation is a major cause of stroke after on-pump coronary artery bypass surgery. Ann Thorac Surg 2004;77:1241-1244.[Abstract/Free Full Text]
  9. Ricotta JJ, Wall LP, Blackstone E. The influence of concurrent carotid endarterectomy on coronary bypass: a case-controlled study. J Vasc Surg 2005;41:397-401.[Medline]
  10. Lahtinen J, Ahvenajärvi L, Biancari F, Ojala R, Mosorin M, Cresti R, et al. Pulmonary embolism after off-pump coronary artery bypass surgery as detected by computed tomography. Am J Surg 2006;192:396-398.[Medline]



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