Part One: For the Motion Carotid Disease is Rarely Responsible for Stroke after Coronary Bypass Surgery

Abstract

Significant carotid stenoses (SCS, ≥ 50% stenosis in diameter) are associated with an increased risk of post-operative stroke following coronary artery bypass grafting (CABG) surgery.1Schwartz L.B. Bridgman A.H. Kieffer R.W. Wilcox R.A. McCann R.L. Tawil M.P. et al.Asymptomatic carotid artery stenosis and stroke in patients undergoing cardiopulmonary bypass.J Vasc Surg. 1995; 21: 146-153Google Scholar, 2Engelman D.T. Cohn L.H. Rizzo R.J. Incidence and predictors of TIA’s and strokes following coronary artery bypass grafting: report and collective review.Heart Surg Forum. 1999; 2: 242-245Google Scholar, 3Naylor A.R. Mehta Z. Rothwell P.M. Bell P.R. Carotid artery disease and stroke during coronary artery bypass: a critical review of the literature.Eur J Vasc Endovasc Surg. 2002; 23: 283-294Google Scholar Evidence in support of this statement is robust and compelling. The data implicating SCS as the primary cause of the increased stroke risk are neither, even though there seems to be a trend of higher incidence of stroke with more severe carotid stenosis.1Schwartz L.B. Bridgman A.H. Kieffer R.W. Wilcox R.A. McCann R.L. Tawil M.P. et al.Asymptomatic carotid artery stenosis and stroke in patients undergoing cardiopulmonary bypass.J Vasc Surg. 1995; 21: 146-153Google Scholar, 3Naylor A.R. Mehta Z. Rothwell P.M. Bell P.R. Carotid artery disease and stroke during coronary artery bypass: a critical review of the literature.Eur J Vasc Endovasc Surg. 2002; 23: 283-294Google Scholar, 4Salasidis G.C. Latter D.A. Steinmetz O.K. Blair J.F. Graham A.M. Carotid artery duplex scanning in preoperative assessment for coronary artery revascularization: the association between peripheral vascular disease, carotid artery stenosis, and stroke.J Vasc Surg. 1995; 21 ([discussion 161–2]): 154-160Google Scholar, 5Mickleborough L.L. Walker P.M. Takagi Y. Ohashi M. Ivanov J. Tamariz M. Risk factors for stroke in patients undergoing coronary artery bypass grafting.J Thorac Cardiovasc Surg. 1996; 112: 1250-1258Google Scholar In our opinion, the impression of a causal relationship between stroke risk and asymptomatic SCS in cardiac surgery has been largely based on a few false assumptions. To bring these to light, we frame our discussion around these areas to test their validity. Assumption one: The incidence of SCS is high and most perioperative stroke during CABG occurs in the subgroup of patients with SCS. Data gleaned from preoperative carotid ultrasonography would suggest the contrary. The incidence of SCS is fairly low, ranging from 2% to 22% with an average of 8 to 9% in patients undergoing CABG.3Naylor A.R. Mehta Z. Rothwell P.M. Bell P.R. Carotid artery disease and stroke during coronary artery bypass: a critical review of the literature.Eur J Vasc Endovasc Surg. 2002; 23: 283-294Google Scholar, 6Lazar H.L. Menzoian J.O. Coronary artery bypass grafting in patients with cerebrovascular disease.Ann Thorac Surg. 1998; 66: 968-974Google Scholar Therefore, in the overwhelming majority of operative patients SCS is not implicated in the mechanism of perioperative stroke. Analysis of the status of the carotid arteries in patients with perioperative stroke also bears this out. For example, Wijdicks et al reported that among the 13 patients with post-operative stroke who also had carotid evaluation, only one patient had an ipsilateral SCS.7Wijdicks E.F. Jack C.R. Coronary artery bypass grafting-associated ischemic stroke. a clinical and neuroradiological study.J Neuroimaging. 1996; 6: 20-22Google Scholar In one prospective study, 34 of the 38 perioperative strokes (89%) occurred in patients with less than 80% carotid stenosis.8Bilfinger T.V. Reda H. Giron F. Seifert F.C. Ricotta J.J. Coronary and carotid operations under prospective standardized conditions: incidence and outcome.Ann Thorac Surg. 2000; 69: 1792-1798Google Scholar Our recent retrospective analysis indicated that 58 of the 76 perioperative strokes (76%) occurred in patients without SCS.9Li Y. Walicki D. Mathiesen C. Jenny D. Li Q. Isayev Y. et al.Strokes after cardiac surgery and relationship to carotid stenosis.Arch Neurol. 2009; 66: 1091-1096Google Scholar The low incidence of SCS in patients undergoing CABG suggests it is unlikely to be a major contributor to the perioperative stroke risk. Assumption two: The perioperative stroke in patients undergoing CABG occurs primarily in the territory of carotid artery. To the contrary, analysis of the laterality and regional distribution of perioperative strokes on brain imaging indicates that the majority of such strokes occur in the territory of multiple vessels, the hemisphere contralateral to existing carotid stenosis or the distribution of vertebrobasilar arteries. For example, Hise et al reported that 8 of 15 patients (53%) with an evidence of acute infarction on CT scan demonstrated a stroke in the posterior cerebral artery distribution or the cerebellum.10Hise J.H. Nipper M.L. Schnitker J.C. Stroke associated with coronary artery bypass surgery.Am J Neuroradiol. 1991; 12: 811-814Google Scholar Barbut et al examined 19 patients with infarction on CT scan. Fifteen patients (79%) and 14 patients (74%) had stroke in the cerebellum and posterior cerebral artery territories, respectively.11Barbut D. Grassineau D. Lis E. Heier L. Hartman G.S. Isom O.W. Posterior distribution of infarcts in strokes related to cardiac operations.Ann Thorac Surg. 1998; 65: 1656-1659Google Scholar Wityk et al used MRI to examine a group of 14 patients. Nine of 10 patients (90%) with acute lesions on diffusion weighted imaging (DWI) showed multiple strokes in bilateral hemispheres.12Wityk R.J. Goldsborough M.A. Hillis A. Beauchamp N. Barker P.B. Borowicz Jr., L.M. et al.Diffusion- and perfusion-weighted brain magnetic resonance imaging in patients with neurologic complications after cardiac surgery.Arch Neurol. 2001 Apr; 58: 571-576Google Scholar In one of the most comprehensive reviews to date, Naylor and colleagues concluded that primary carotid thrombo-embolic disease alone is not responsible for up to nearly 60% of strokes based on CT scan or autopsy studies.3Naylor A.R. Mehta Z. Rothwell P.M. Bell P.R. Carotid artery disease and stroke during coronary artery bypass: a critical review of the literature.Eur J Vasc Endovasc Surg. 2002; 23: 283-294Google Scholar Such a distribution pattern of perioperative stroke also holds true for patients with SCS.9Li Y. Walicki D. Mathiesen C. Jenny D. Li Q. Isayev Y. et al.Strokes after cardiac surgery and relationship to carotid stenosis.Arch Neurol. 2009; 66: 1091-1096Google Scholar, 13D’Agostino R.S. Svensson L.G. Neumann D.J. Balkhy H.H. Williamson W.A. Shahian D.M. Screening carotid ultrasonography and risk factors for stroke in coronary artery surgery patients.Ann Thorac Surg. 1996; 62: 1714-1723Google Scholar, 14Dashe J.F. Pessin M.S. Murphy R.E. Payne D.D. Carotid occlusive disease and stroke risk in coronary artery bypass graft surgery.Neurology. 1997; 49: 678-686Google Scholar Therefore the majority of perioperative strokes occur outside a single carotid territory. Since less than 3% of patients undergoing CABG have bilateral SCS,3Naylor A.R. Mehta Z. Rothwell P.M. Bell P.R. Carotid artery disease and stroke during coronary artery bypass: a critical review of the literature.Eur J Vasc Endovasc Surg. 2002; 23: 283-294Google Scholar neither unilateral nor bilateral carotid stenosis is likely responsible for the majority of perioperative stroke based on the infarction territory. Assumption three: Although SCS could be a small contributor to perioperative stroke risk, preoperative carotid revascularization would eliminate stroke in some of these patients and hence should be offered. Data from the NASCET trial suggested that in patients with SCS, stroke could still be due to small vessel lacunae, thrombotic infarction due to intracranial diseases or even cardioembolic infarction but carotid endarterectomy should not help to prevent such strokes.15Inzitari D. Eliasziw M. Gates P. Sharpe B.L. Chan R.K. Meldrum H.E. et al.The causes and risk of stroke in patients with asymptomatic internal-carotid-artery stenosis. North American symptomatic carotid endarterectomy trial collaborators.N Engl J Med. 2000; 342: 1693-1700Google Scholar The incidence of lacunar infarction and intracranial atherosclerosis may not be trivial in patients undergoing cardiac surgery. For example, Libman et al reported that 16% of the post-operative stroke following cardiac surgery can be lacunar syndromes secondary to small vessel disease.16Libman R.B. Wirkowski E. Neystat M. Barr W. Gelb S. Graver M. Stroke associated with cardiac surgery. determinants, timing, and stroke subtypes.Arch Neurol. 1997; 54: 83-87Google Scholar Yoon et al reported that 30% of patients undergoing CABG had stenosis in the intracranial arteries. In multivariate analysis, the presence of intracranial disease was also found to have an independent association with the development of perioperative strokes.17Yoon B.W. Bae H.J. Kang D.W. Lee S.H. Hong K.S. Kim K.B. et al.Intracranial cerebral artery disease as a risk factor for central nervous system complications of coronary artery bypass graft surgery.Stroke. 2001; 32: 94-99Google Scholar Furthermore, existing data strongly suggest that most of the perioperative strokes are cardioembolic mainly due to the presence of aortic atherosclerosis and/or atrial fibrillation. Using intra-operative echocardiography, Katz et al identified protruding atheroma in the aortic arch in 23 of 130 patients undergoing cardiac surgery. Five of the 23 patients (22%) developed a perioperative stroke while the stroke risk was only 2% in patients without such atheroma.18Katz E.S. Tunick P.A. Rusinek H. Ribakove G. Spencer F.C. Kronzon I. Protruding aortic atheromas predict stroke in elderly patients undergoing cardiopulmonary bypass: experience with intraoperative transesophageal echocardiography.J Am Coll Cardiol. 1992; 20: 70-77Google Scholar Gardner and colleagues reported that in patients with intra-operative evidence of severe aortic atherosclerosis, the perioperative stroke risk jumped approximately four fold higher to 14%.19Gardner T.J. Horneffer P.J. Manolio T.A. Pearson T.A. Gott V.L. Baumgartner W.A. et al.Stroke following coronary artery bypass grafting: a ten-year study.Ann Thorac Surg. 1985; 40: 574-581Google Scholar A multivariable logistic regression analysis on a multicenter database of 19,224 CABG patients suggested that calcified aorta was the single most significant variable associated with perioperative stroke with an odds ratio (OR) of 3.01, whereas the presence of carotid disease was also associated with an OR of 1.59.20John R. Choudhri A.F. Weinberg A.D. Ting W. Rose E.A. Smith C.R. et al.Multicenter review of preoperative risk factors for stroke after coronary artery bypass grafting.Ann Thorac Surg. 2000; 69: 30-35Google Scholar In another multivariate analysis, calcified aorta was an independent predictor of perioperative stroke but SCS was not.8Bilfinger T.V. Reda H. Giron F. Seifert F.C. Ricotta J.J. Coronary and carotid operations under prospective standardized conditions: incidence and outcome.Ann Thorac Surg. 2000; 69: 1792-1798Google Scholar Microembolism from the aorta or heart to the brain has been well documented by multiple studies using Transcranial Doppler, correlating with the onset and releasing of aorta clamping.21Barbut D. Hinton R.B. Szatrowski T.P. Hartman G.S. Bruefach M. Williams-Russo P. et al.Cerebral emboli detected during bypass surgery are associated with clamp removal.Stroke. 1994; 25: 2398-2402Google Scholar, 22Baker A.J. Naser B. Benaroia M. Mazer C.D. Cerebral microemboli during coronary artery bypass using different cardioplegia techniques.Ann Thorac Surg. 1995; 59: 1187-1191Google Scholar, 23Clark R.E. Brillman J. Davis D.A. Lovell M.R. Price T.R. Magovern G.J. Microemboli during coronary artery bypass grafting. Genesis and effect on outcome.J Thorac Cardiovasc Surg. 1995; 109: 249-257Google Scholar Furthermore, D’Agostino and colleagues reported that atrial fibrillation occurred in approximately 30% of post-operative patients, and perioperative stroke occurred in 4.6% of patients with atrial fibrillation compared with 1.5% patients without.13D’Agostino R.S. Svensson L.G. Neumann D.J. Balkhy H.H. Williamson W.A. Shahian D.M. Screening carotid ultrasonography and risk factors for stroke in coronary artery surgery patients.Ann Thorac Surg. 1996; 62: 1714-1723Google Scholar Lahtinen et al discussed that recurrent atrial fibrillation preceded symptoms of cerebral ischemia in 36.5% of patients with perioperative stroke by a mean of 21.3 h.24Lahtinen 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: 1241-1244Google Scholar In the subgroup of high-risk patients with new post-operative DWI lesions, 75% also had post-operative atrial fibrillation.25McKhann G.M. Grega M.A. Borowicz Jr., L.M. Baumgartner W.A. Selnes O.A. Stroke and encephalopathy after cardiac surgery: an update.Stroke. 2006; 37: 562-571Google Scholar Therefore, in patients undergoing CABG, cardioembolism and probably intracranial arterial stenosis or small vessel disease are the primary mechanisms of stroke. Preoperative cervical carotid revascularization would not prevent these events. Assumption four: SCS reduces distal internal carotid blood flow and hence puts the ipsilateral cerebral hemisphere at risk of ischemia during cardiopulmonary bypass. The carotid plaque at the bifurcation may either cause a regional hypoperfusion or act as an embolic source in causing a stroke. So far there are no data to suggest that carotid plaque becomes a more active source of embolism during CABG. Although often asserted as facts, there is very little evidence to suggest that unilateral asymptomatic SCS reduces ipsilateral hemisphere blood flow significantly. Perioperative strokes include both border zone (watershed) and territorial infarctions on brain imaging. Watershed infarctions are now more readily identified on MRI studies.26Floyd T.F. Shah P.N. Price C.C. Harris F. Ratcliffe S.J. Acker M.A. et al.Clinically silent cerebral ischemic events after cardiac surgery: their incidence, regional vascular occurrence, and procedural dependence.Ann Thorac Surg. 2006; 81: 2160-2166Google Scholar, 27Gottesman R.F. Sherman P.M. Grega M.A. Yousem D.M. Borowicz Jr., L.M. Selnes O.A. et al.Watershed strokes after cardiac surgery: diagnosis, etiology, and outcome.Stroke. 2006; 37: 2306-2311Google Scholar While the development of watershed infarction is frequently attributed to low cerebral flow, this has been challenged repeatedly by autopsy studies. Such watershed infarction may occur without SCS or documented intra-operative hypotension.28Graeber M.C. Jordan J.E. Mishra S.K. Nadeau S.E. Watershed infarction on computed tomographic scan. an unreliable sign of hemodynamic stroke.Arch Neurol. 1992; 49: 311-313Google Scholar Embolic calcified material or cholesterol crystals were detected in vessels adjacent to watershed infarction in patients after cardiac surgery.29Gilman S. Cerebral disorders after open-heart operations.N Engl J Med. 1965; 272: 489-498Google Scholar, 30Price D.L. Harris J. Cholesterol emboli in cerebral arteries as a complication of retrograde aortic perfusion during cardiac surgery.Neurology. 1970; 20: 1209-1214Google Scholar Watershed infarctions can be caused by microemboli consisting of atheromatous material or tumor masses lodged preferentially in the brain border zone.31Torvik A. Skullerud K. Watershed infarcts in the brain caused by microemboli.Clin Neuropathol. 1982; 1: 99-105Google Scholar Angiography in three patients with watershed infarction did not show SCS in two patients and revealed an embolic occlusion of the arterial branch corresponding to the site of the infarct in another patient.28Graeber M.C. Jordan J.E. Mishra S.K. Nadeau S.E. Watershed infarction on computed tomographic scan. an unreliable sign of hemodynamic stroke.Arch Neurol. 1992; 49: 311-313Google Scholar These brain border zones appear to be favored destinations for microemboli. On the other hand, there is no compelling evidence that cerebral blood flow is significantly reduced distal to SCS in association with cardiopulmonary bypass. Lundar and colleagues described that blood flow in the middle cerebral and internal carotid arteries actually increased rather than decrease during cardiopulmonary bypass as a result of hemodilution.32Lundar T. Frøysaker T. Lindegaard K.F. Wiberg J. Lindberg H. Rostad H. et al.Some observations on cerebral perfusion during cardiopulmonary bypass.Ann Thorac Surg. 1985; 39: 318-323Google Scholar, 33Lundar T. Lindegaard K.F. Frøysaker T. Aaslid R. Wiberg J. Nornes H. Perfusion during nonpulsatile cardiopulmonary bypass.Ann Thorac Surg. 1985; 40: 144-150Google Scholar In a study using positron emission tomography in patients with asymptomatic unilateral SCS, most patients had normal cerebral flow.34Powers W.J. Press G.A. Grubb Jr., R.L. Gado M. Raichle M.E. The effect of hemodynamically significant carotid artery disease on the hemodynamic status of the cerebral circulation.Ann Intern Med. 1987; 106: 27-34Google Scholar Hupperts et al reported 10 of 37 patients with perioperative strokes had infarction in the vascular border zones. Registered periods of hypotension, lowest mean arterial pressure and lowest hematocrit were similar among the subgroups of patients with border zone, territorial infarction or no infarction.35Hupperts R. Wetzelaer W. Heuts-van Raak L. Lodder J. Is haemodynamical compromise a specific cause of border zone brain infarcts following cardiac surgery?.Eur Neurol. 1995; 35: 276-280Google Scholar Therefore in patients with unilateral asymptomatic SCS undergoing CABG, the ipsilateral hemispheric blood flow is unlikely to be significantly altered in most patients if significant and prolonged hypotension can be avoided perioperatively. Furthermore, it is arguable whether carotid revascularization would significantly improve cerebral blood flow. Waaijer et al studied cerebral perfusion in a group of 36 patients with SCS and a mean degree of stenosis of 86%. On an average there was merely a 10% increase in cerebral blood flow following carotid stenting or endarterectomy.36Waaijer A. van Leeuwen M.S. van Osch M.J. van der Worp B.H. Moll F.L. Lo R.T. et al.Changes in cerebral perfusion after revascularization of symptomatic carotid artery stenosis: CT measurement.Radiology. 2007; 245: 541-548Google Scholar Assumption five: Preoperative carotid endarterectomy is necessary to avoid carotid territory stroke in patients undergoing CABG. To the contrary, studies suggest that a conservative management of SCS can be safe for patients undergoing cardiac surgery. Gerraty and colleagues reported 53 patients with SCS or occlusion (28 patients with 80% greater stenosis or occlusion) underwent vascular or cardiac surgeries. None suffered an ipsilateral perioperative stroke despite 22 patients experiencing a period of hypotension.37Gerraty R.P. Gates P.C. Doyle J.C. Carotid stenosis and perioperative stroke risk in symptomatic and asymptomatic patients undergoing vascular or coronary surgery.Stroke. 1993; 24: 1115-1118Google Scholar Safa et al reported that in a group of 94 patients with SCS undergoing cardiac surgery 71 patients had unilateral (80–99%), 17 patients had bilateral (80–99%), and six patients had unilateral SCS together with a contralateral carotid occlusion. Only one patient developed a perioperative stroke in the hemisphere contralateral to the carotid stenosis.38Safa T.K. Friedman S. Mehta M. Rahmani O. Scher L. Pogo G. et al.Management of coexisting coronary artery and asymptomatic carotid artery disease: report of a series of patients treated with coronary bypass alone.Eur J Vasc Endovasc Surg. 1999; 17: 249-252Google Scholar Ghosh et al reported 50 patients with asymptomatic SCS (20 patients with bilateral 80–99% disease, and five patients with unilateral occlusion and 70–79% contralateral stenosis) underwent CABG with optimal medical prevention. No stroke occurred within 30 days of surgery.39Ghosh J. Murray D. Khwaja N. Murphy M.O. Walker M.G. The influence of asymptomatic significant carotid disease on mortality and morbidity in patients undergoing coronary artery bypass surgery.Eur J Vasc Endovasc Surg. 2005; 29: 88-90Google Scholar Baiou et al reported a total of 61 cardiac procedures in patients with unilateral asymptomatic 70–99% stenosis (56% patients also had a contralateral 50–69% stenosis). No strokes occurred in the 30-day post-operative period.40Baiou D. Karageorge A. Spyt T. Naylor A.R. Patients undergoing cardiac surgery with asymptomatic unilateral carotid stenoses have a low risk of peri-operative stroke.Eur J Vasc Endovasc Surg. 2009; 38: 556-559Google Scholar Although larger confirmation studies are still needed, it appears safe and effective in most cases to conservatively manage CABG patients with SCS without the need for preoperative corrective carotid revascularization. In summary, there is compelling evidence to conclude that SCS is not the primary cause of most strokes following CABG surgery. This is consistent with the analysis by Stamou and colleagues who reported that only 6% of the perioperative 333 strokes were secondary to carotid disease.41Stamou S.C. Hill P.C. Dangas G. Pfister A.J. Boyce S.W. Dullum M.K. et al.Stroke after coronary artery bypass: incidence, predictors, and clinical outcome.Stroke. 2001; 32: 1508-1513Google Scholar This was also borne out in our own single center retrospective analysis of 4335 patients undergoing cardiac surgeries. Of the 76 patients with perioperative strokes, 72 (95%) were not related to SCS at the bifurcation.9Li Y. Walicki D. Mathiesen C. Jenny D. Li Q. Isayev Y. et al.Strokes after cardiac surgery and relationship to carotid stenosis.Arch Neurol. 2009; 66: 1091-1096Google Scholar Does SCS play a significant role in causing stroke following CABG under any circumstance? Exceptions might exist in patients with symptomatic SCS, patients with bilateral critically severe carotid disease (> 80% diameter reduction), and patients with recent carotid occlusion. Overall 95% of the carotid stenosis in patients undergoing CABG is asymptomatic and less than 1.5% patients have such bilateral critically severe carotid disease.3Naylor A.R. Mehta Z. Rothwell P.M. Bell P.R. Carotid artery disease and stroke during coronary artery bypass: a critical review of the literature.Eur J Vasc Endovasc Surg. 2002; 23: 283-294Google Scholar Only a small fraction of patients would fit in this category. How then is the observed increased risk of post-operative stroke in patients with SCS explained? One likely explanation is that carotid stenosis is an epiphenomena serving as a marker of severe underlying systemic atherosclerotic disease. Patients with concomitant cerebrovascular and coronary artery disease represent a subset of patients with advanced arteriosclerosis, not only in the coronary and cerebrovascular vessels, but also other areas of arterial system. In patients with SCS, the incidence of other vascular complications such as coronary ischemic events is much higher than the stroke risk.42Redgrave J.N. Rothwell P.M. Asymptomatic carotid stenosis: what to do.Curr Opin Neurol. 2007; 20: 58-64Google Scholar Similar to SCS, there appears to be a positive correlation between the incidence of perioperative stroke and the severity of aortic atherosclerosis.43Hartman G.S. Yao F.S. Bruefach 3rd, M. Barbut D. Peterson J.C. Purcell M.H. et al.Severity of aortic atheromatous disease diagnosed by transesophageal echocardiography predicts stroke and other outcomes associated with coronary artery surgery: a prospective study.Anesth Analg. 1996; 83: 701-708Google Scholar Over the last twenty years, many prospective randomized trials were undertaken in carefully selected patients with symptomatic and asymptomatic SCS.44Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. North American symptomatic carotid endarterectomy trial collaborators.N Engl J Med. 1991; 325 (Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada): 445-453Google Scholar, 45Randomised trial of endarterectomy for recently symptomatic carotid stenosis: final results of the MRC European Carotid Surgery Trial (ECST).Lancet. 1998; 351: 1379-1387Google Scholar, 46Endarterectomy for asymptomatic carotid artery stenosis. Executive committee for the asymptomatic carotid atherosclerosis study.JAMA. 1995; 273: 1421-1428Google Scholar, 47Halliday A. Mansfield A. Marro J. Peto C. Peto R. Potter J. et al.Asymptomatic carotid surgery trial (ACST) collaborative GroupPrevention of disabling and fatal strokes by successful carotid endarterectomy in patients without recent neurological symptoms: randomised controlled trial.Lancet. 2004; 363: 1491-1502Google Scholar, 48Yadav J.S. Wholey M.H. Kuntz R.E. Fayad P. Katzen B.T. Mishkel G.J. et al.Stenting and angioplasty with protection in patients at high risk for endarterectomy investigators. protected carotid-artery stenting versus endarterectomy in high-risk patients.N Engl J Med. 2004; 351: 1493-1501Google Scholar All trials showed clear benefits of carotid revascularization in reducing subsequent stroke risk in patients with SCS but most excluded patients with symptomatic and severe coronary artery diseases. The results of these trials have undoubtedly had major influence on medical decision making but caution should be taken in extending their results to populations of patients with concomitant carotid and coronary artery diseases. More recently published data suggested that under intense medical therapy, the stroke risk for asymptomatic stenosis is exceedingly low, as low as less than 0.5% annually.49Marquardt L. Geraghty O.C. Mehta Z. Rothwell P.M. Low risk of ipsilateral stroke in patients with asymptomatic carotid stenosis on best medical treatment: a prospective, population-based study.Stroke. 2010; 41: e11-e17Google Scholar, 50Spence J.D. Coates V. Li H. Tamayo A. Muñoz C. Hackam D.G. et al.Effects of intensive medical therapy on microemboli and cardiovascular risk in asymptomatic carotid stenosis.Arch Neurol. 2010; 67: 180-186Google Scholar In the population of patients undergoing CABG, more effort should be geared towards reducing the overall risk of vascular complications with intense medical therapy, and preventing cardioembolism which remains to be the major source of stroke following cardiac surgery.