Abstract
A number of institutions routinely perform carotid artery ultrasound screening before coronary artery bypass grafting (CABG) to identify carotid artery disease requiring revascularization before or during CABG, with the expectation of reducing perioperative neurologic events. The assumptions are that carotid disease is causally related to perioperative stroke and that prophylactic carotid revascularization decreases the risk of post-CABG neurologic events. Although carotid artery stenosis is a known risk factor for perioperative stroke in patients undergoing CABG, it might be a surrogate marker for diffuse atherosclerotic disease rather than a direct etiologic factor. Moreover, the benefit of prophylactic carotid revascularization in patients with asymptomatic unilateral carotid disease is uncertain. Therefore, we have reviewed the literature for evidence that preoperative carotid artery screening, by identifying patients with significant carotid artery stenosis and altering their management, reduces perioperative neurologic events in those undergoing CABG.
Abbreviation and Acronym:
CABG (coronary artery bypass grafting)Key Words
CTSNet classification
Carotid artery duplex ultrasound.
Central Message
A number of institutions routinely perform carotid artery ultrasound screening before coronary artery bypass grafting, with the expectation of decreasing perioperative neurologic events. However, carotid artery stenosis might simply be a surrogate marker for diffuse atherosclerotic disease, and the benefit of prophylactic carotid revascularization in asymptomatic patients with unilateral carotid disease is uncertain.
Author's Perspective
A number of institutions routinely perform carotid artery ultrasound screening before coronary artery bypass grafting (CABG) to identify carotid artery disease that necessitates revascularization before or during CABG, with the expectation of reducing perioperative neurologic events. However, among patients undergoing CABG, clinical variables alone can identify those who have significant carotid artery disease, with as high a degree of sensitivity as ultrasound. Moreover, carotid duplex ultrasound screening, whether selective or nonselective, identifies only a minority of patients who will develop perioperative stroke, and intervening for those with carotid disease might not decrease the risk of these neurologic events.
Stroke is a devastating complication of coronary artery bypass grafting (CABG).
1
For this reason, a number of institutions routinely screen patients undergoing CABG (Table 1)2
, 3
, 4
, 5
, 6
, 7
for severe carotid artery stenosis and potential carotid revascularization, with the expectation of reducing the risk of post-CABG stroke. This practice is contrary to guidelines recommending screening in selected patients only.8
, - Hillis L.D.
- Smith P.K.
- Anderson J.L.
- Bittl J.A.
- Bridges C.R.
- Byrne J.G.
- et al.
2011 ACCF/AHA Guideline for Coronary Artery Bypass Graft Surgery. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, Society of Cardiovascular Anesthesiologists, and Society of Thoracic Surgeons. Executive summary.
J Am Coll Cardiol. 2011; 58: 2584-2614
9
The underlying assumptions are that carotid disease is causally related to perioperative stroke and that prophylactic carotid revascularization decreases its risk. However, if carotid artery stenosis is not a direct etiologic risk factor for perioperative stroke, routine nonselective screening may not be cost effective.The Society of Thoracic Surgeons. Five things physicians and patients should question. Choosing wisely. An initiative of the ABIM Foundation. Available at: http://www.choosingwisely.org/doctor-patient-lists/the-society-of-thoracic-surgeons/ Accessed September 4, 2013.
4
, 10
In addition, the benefit of prophylactic carotid revascularization in patients with asymptomatic unilateral carotid disease is controversial.11
, 12
, 13
, 14
, 15
Therefore, we have reviewed the literature for evidence that preoperative carotid artery screening, by identifying patients with substantial carotid stenosis and altering their management, decreases perioperative neurologic events in patients undergoing CABG.Table 1Carotid artery screening in patients undergoing coronary artery bypass grafting
| First author and year | No. of screened patients | Population | Routine screening | Screening method | Degree of internal carotid artery stenosis considered significant (%) | Prevalence (%) |
|---|---|---|---|---|---|---|
| Wanamaker 104 2012 | 559 | CABG | No | DUS | >50 | 36 |
| Ansari 81 2011 | 116 | CABG with/without valve surgery | No | DUS | >70 | 6.6 |
| Drohomirecka 80 2010 | 682 | CABG | No | DUS | ≥50 | 18 |
| Cornily 82 2010 | 205 | CABG | No | DUS | ≥70 | 5.8 |
| Anastasiadis 4 2009 | 307 | Cardiac surgery | Yes | DUS | >70 | 6.5 |
| Kiernan 79 2009 | 643 | CABG | No | DUS | >70 | 7.7 |
| Sheiman 77 2007 | 295 | CABG | Yes | DUS | ≥50 | 24 |
| Shirani 6 2006 | 1045 | CABG with/without valve surgery | Yes | DUS | >60 | 6.9 |
| Durand 5 2004 | 1138 | CABG | Yes | DUS and/or angiography | ≥70 | 13.4 |
| Fukuda 3 2000 | 308 | CABG | Yes | DUS | >50 | 14.3 |
| Salasidis 78 1995 | 387 | CABG | No | DUS | >80 | 8.5 |
CABG, Coronary artery bypass grafting; DUS, duplex ultrasonography.
Perioperative Stroke in Patients Undergoing CABG
Stroke is a serious complication of CABG that occurs in 1.3% to 2.0% of patients
1
, 16
, 17
, 18
and results in acute mortality of up to 38%.19
, 20
The cause of post-CABG stroke is multifactorial, but because most strokes occur ≥24 hours after surgery, embolic events are the most likely culprits.15
, 21
, 22
, 23
, 24
Macroembolization of atherothrombotic debris from the severely atherosclerotic aorta is strongly associated with postoperative stroke.16
, 25
, 26
, 27
Shedding of emboli to the brain might be caused by manipulation of the ascending aorta during aortic clamping, cannulation, and proximal graft anastomosis.23
, 28
, 29
Dislodging of emboli from the heart due to manipulation by the surgeon or atrial fibrillation are other possible causes.30
Intraoperative hemodynamic abnormalities, such as hypotension during cardiopulmonary bypass, and pulmonary diastolic hypertension after cardiopulmonary bypass, are also associated with increased risk of post-CABG stroke.31
Microembolization of platelet aggregates and turbulent blood flow during cardiopulmonary bypass are other possible causes.28
, 32
In addition, atherosclerotic disease of the cerebral arteries is an important mechanism of stroke in patients undergoing CABG.7
Risk factors for perioperative stroke include older age, prior stroke or transient ischemic attack, peripheral artery disease, hypertension, left ventricular dysfunction, preoperative atrial fibrillation,
1
, 25
, 28
, 33
, 34
, 35
, 36
and carotid artery stenosis.11
, 24
, 28
, 34
, 37
A carotid bruit has been found to be a preoperative predictor of severe aortic arch atheroma.38
Therefore, some consider carotid artery disease to be an epiphenomenon, serving as a marker for diffuse systemic atherosclerotic disease, rather than being a causal factor.10
, 12
, 39
, 40
Data from Cleveland Clinic patients undergoing noncardiac surgery demonstrated no association between carotid artery stenosis and stroke (odds ratio 1.0, with a 95% confidence interval of 0.99-1.02) for a 10-unit increase in internal carotid artery peak systolic velocity, the variable used to quantify carotid artery stenosis.41
Possible Mechanisms by Which Carotid Artery Stenosis Could Lead to Perioperative Stroke
It is thought that carotid intraplaque hemorrhage can result in plaque destabilization
42
, 43
, 44
, 45
, 46
and intimal ulceration, creating a nidus for thromboembolism.47
, 48
, 49
, 50
, 51
, 52
Intraplaque hemorrhage detected by magnetic resonance imaging is associated with increased risk of ipsilateral stroke in symptomatic and asymptomatic nonsurgical patients53
, 54
and is strongly related to onset of symptoms.55
We hypothesize that anticoagulating patients during CABG might be responsible for increased intraoperative risk of intraplaque hemorrhage. Mechanical causes can trigger intraplaque hemorrhage as well, such as turbulent blood flow and hypertension, both of which can occur during cardiac surgery.55
Impaired cerebral hemodynamic function distal to carotid artery stenosis is another determinant of postoperative stroke.
22
, 56
Maximally dilated vessels distal to carotid artery stenosis can no longer vasodilate in response to hemodynamic compromise. Therefore, perioperative reduction in blood pressure or cardiac output in this group of patients is hypothesized to lead to cerebral ischemia.40
, 56
Moreover, reduced cerebral blood flow might result in decreased washout of microemboli in patients undergoing CABG.57
Detecting Carotid Artery Disease
Carotid artery duplex ultrasound, which is used to visualize plaque and measure flow velocity to quantify stenosis, is the screening test usually used to identify patients with carotid artery stenosis (see Central Image).
58
The sensitivity of carotid ultrasound to detect carotid artery stenosis, of >70% is 86% to 90%, with a specificity of 87% to 94%.59
Although ultrasound screening is currently used to determine the degree of carotid artery stenosis, other duplex-determined plaque characteristics are also associated with cerebrovascular symptoms, including hypoechoic lesions (low grayscale median, larger juxtaluminal black area), plaque heterogeneity (presence of noncalcified, discrete white areas without acoustic shadowing), plaque ulceration, and larger plaque area.60
, 61
, 62
, 63
, 64
, 65
, 66
, 67
, 68
, 69
, 70
, 71
, 72
, 73
, 74
, 75
Therefore, both carotid artery flow velocity and plaque characterization could be used to identify patients who are at higher risk of developing perioperative neurologic events when undergoing CABG.57
Regardless of whether carotid artery stenosis is an etiologic factor for perioperative stroke, carotid artery ultrasound screening detects only a minority of patients who experience perioperative neurologic events. For example, by screening every patient undergoing CABG, Durand and colleagues
5
found that 13.4% had carotid artery stenosis of ≥70%. Among those who developed postoperative stroke after undergoing CABG, only 19% had carotid artery stenosis of ≥70% ipsilateral to the side of the stroke.An alternative to routine ultrasound screening is risk profiling. Several groups have identified risk factors associated with significant carotid artery stenosis in patients undergoing CABG (Table 2). Peripheral artery disease, cerebrovascular disease (prior stroke or transient ischemic attack), and old age were the risk factors most consistently identified in these studies.
2
, 3
, 4
, 6
, 37
, 76
, 77
, 78
, 79
, 80
, 81
Applying carotid disease–screening algorithms to cohorts of ultrasound-screened patients undergoing CABG showed that most who had significant carotid artery stenosis could be detected.5
, 77
, 82
Thus, Durand and colleagues5
found that a risk-profiling algorithm based on a prior stroke or transient ischemic attack, carotid bruit on exam, or age >65 years would have missed significant carotid disease in only 2.3% of patients undergoing CABG (26 of 1138), although this represented 17% of 152 patients with significant carotid disease, and 582 had a false-positive result.5
Thus, their selective screening algorithm had a sensitivity and specificity of 83% and 41%, respectively.Table 2Risk factors for significant carotid artery stenosis
| First author and year | Older age (y) | Female | Bruit | Smoking | DM | Htn | LMCA | History of CVD | PAD | Others |
|---|---|---|---|---|---|---|---|---|---|---|
| Wanamaker 104 2012 | Yes | Yes | NS | No | No | Yes | Yes | Yes | Yes | Renal failure (dialysis) |
| Ansari 81 2011 | Yes | NS | NS | No | No | No | NS | Yes | Yes | Hypercholesterolemia/abnormal renal function |
| Cornily 82 2010 | NS | No | Yes | No | Yes | No | NS | No | Yes | |
| Drohomirecka 80 2010 | Yes | No | NS | NS | No | No | No | Yes | Yes | Unstable angina |
| Anastasiadis 4 2009 | No | No | Yes | No | No | No | No | Yes | NS | |
| Kiernan 79 2009 | NS | NS | Yes | NS | NS | NS | Yes | Yes | Yes | |
| Sheiman 77 2007 | NS | No | NS | Yes | Yes | Yes | Yes | Yes | Yes | History of carotid disease |
| Shirani 6 2006 | >50 | Yes | NS | No | Yes | NS | NS | NS | NS | Cholesterol >240 Triglycerides >240 |
| Durand 5 2004 | >65 | Yes | Yes | NS | No | Yes | Yes | Yes | Yes | |
| Fukuda 3 2000 | No | NS | NS | No | No | No | No | Yes | Yes | Atherosclerosis of ascending aorta |
| D'Agostino 37 1996 | Yes | Yes | NS | Yes | Yes | NS | Yes | Yes | Yes | Prior vascular operation |
| Salasidis 78 1995 | Yes | NS | NS | No | No | No | NS | Yes | Yes | Prior carotid endarterectomy |
| Berens 76 1992 | NS | Yes | NS | Yes | NS | No | Yes | Yes | Yes |
Bruit, Carotid bruit; DM, diabetes mellitus; Htn, hypertension; LMCA, left main coronary artery; CVD, cerebrovascular disease; PAD, peripheral artery disease; NS, not studied.
Sheiman and colleagues
77
used 7 risk factors (history of carotid artery disease, prior cerebrovascular event, hypertension, diabetes, peripheral artery disease, smoking, left main coronary disease, and female gender) to predict which patients have carotid artery disease. The presence of any 1 of these factors was 100% sensitive, but only 30% specific, in detecting patients with ≥50% carotid stenosis. Similarly, Cornily and colleagues82
found that risk factors including age >70 years, history of cerebrovascular disease, diabetes mellitus, peripheral artery disease, or carotid bruit on physical examination could have detected 11 of 12 patients with significant carotid artery stenosis. These studies suggest that clinical factors are sensitive in identifying patients with carotid disease, but that specificity is low, requiring more specific screening modalities, such as ultrasound, in more than half of patients.Role of Carotid Revascularization in Decreasing the Risk of Neurologic Events
Carotid revascularization by staged or synchronous carotid endarterectomy or carotid artery stenting is considered acceptable in patients with symptomatic carotid disease, bilateral 70% to 99% carotid stenosis, or a unilateral 70% to 99% carotid stenosis with a contralateral occlusion.
10
, 83
, 84
, 85
However, most carotid revascularization procedures are performed prophylactically in patients with asymptomatic unilateral carotid artery stenosis,11
, 19
, 20
, 24
, 37
and the value of such interventions is uncertain.The assumed benefit of treating asymptomatic patients is extrapolated from the Asymptomatic Carotid Atherosclerosis Study and Asymptomatic Carotid Surgery Trial, which concluded that carotid endarterectomy decreases the 5-year risk of ipsilateral stroke in patients with asymptomatic isolated carotid disease.
86
, 87
However, the purpose of prophylactic carotid revascularization in patients undergoing CABG is to reduce perioperative neurologic events. Thus, long-term risk reduction of stroke should not be used as a justification to perform carotid revascularization in these patients, especially if operative morbidity from the combined procedures is higher than the added risks of the procedures performed separately.12
Results of the ongoing Coronary Artery Bypass graft surgery in patients with Asymptomatic Carotid Stenosis (CABACS) randomized clinical trial comparing the safety and efficacy of isolated CABG versus synchronous CABG and carotid endarterectomy in patients with asymptomatic high-grade carotid artery stenosis will elucidate whether surgical carotid revascularization helps to reduce the risk of perioperative stroke in patients undergoing CABG.88
However, the trial does not have a staged carotid artery stenting arm, so the best approach to managing these patients might remain unclear.89
Currently, several findings argue against the usefulness of carotid revascularization in patients undergoing CABG. First, no direct causal relationship has been found between carotid artery stenosis and postoperative ipsilateral stroke,
12
and most strokes occur outside the territory supplied by the carotid artery.90
Second, the risk of perioperative stroke in patients with carotid disease is low.12
, 13
, 91
, 92
, 93
In a meta-analysis by Naylor and Bown,94
the risk of ipsilateral stroke in patients with a unilateral, asymptomatic 50% to 99% stenosis was found to be only 2%.Third, if carotid disease is truly an important risk factor for post-CABG stroke, then patients with bilateral, severe carotid disease undergoing unilateral carotid revascularization should have a high rate of stroke ipsilateral to the “nonrevascularized” artery. However, studies show that the risk of perioperative neurologic events ipsilateral to the nonrevascularized artery is low.
94
, 95
Fourth, combined CABG and carotid revascularization is associated with higher risk than isolated CABG. Thus, Ghosh and colleagues13
found that occurrence of death, cerebrovascular events, and myocardial infarction within 30 days of CABG without prophylactic revascularization in asymptomatic patients with carotid artery stenosis of ≥70% was 4%, but Naylor10
reported that the composite risk of death, stroke, or myocardial infarction within 30 days of combined CABG and carotid revascularization was 9% to 11%.Surgeons can consider several other strategies to reduce the risk of perioperative neurologic events. First, monitoring of blood pressure throughout the procedure and postoperatively; avoiding extremes of blood pressure during surgery is important, because both hypertension, when it leads to carotid artery plaque rupture, and hypotension, when it leads to cerebral ischemia, can initiate neurologic damage. Second, postoperative antiplatelet therapy should be considered,
8
, - Hillis L.D.
- Smith P.K.
- Anderson J.L.
- Bittl J.A.
- Bridges C.R.
- Byrne J.G.
- et al.
2011 ACCF/AHA Guideline for Coronary Artery Bypass Graft Surgery. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, Society of Cardiovascular Anesthesiologists, and Society of Thoracic Surgeons. Executive summary.
J Am Coll Cardiol. 2011; 58: 2584-2614
96
because most strokes result from thromboembolic events.Third, because these patients are likely to have aortic arch atheroma as part of their diffuse atherosclerotic disease, intraoperative assessment of the aorta should be done before clamping, and strategies should be used to decrease the shedding of emboli from the aorta during surgery, such as off-pump CABG without a partial occlusion clamp, or on-pump CABG with continuous perfusion without aortic clamping. Monitoring brain oxygen saturation during CABG through cerebral oximetry, to avoid profound cerebral desaturation, is also associated with better outcomes.
97
Moreover, dynamic bubble trap and arterial line filters may be considered to reduce the occurrence of stroke in patients undergoing CABG.98
, 99
Value of Routine Carotid Screening
The Society of Thoracic Surgeons and the American College of Cardiology/American Heart Association recommend ultrasound screening for carotid artery stenosis in selected patients only (class IIa recommendation, level of evidence C).
8
, - Hillis L.D.
- Smith P.K.
- Anderson J.L.
- Bittl J.A.
- Bridges C.R.
- Byrne J.G.
- et al.
2011 ACCF/AHA Guideline for Coronary Artery Bypass Graft Surgery. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, Society of Cardiovascular Anesthesiologists, and Society of Thoracic Surgeons. Executive summary.
J Am Coll Cardiol. 2011; 58: 2584-2614
9
, The Society of Thoracic Surgeons. Five things physicians and patients should question. Choosing wisely. An initiative of the ABIM Foundation. Available at: http://www.choosingwisely.org/doctor-patient-lists/the-society-of-thoracic-surgeons/ Accessed September 4, 2013.
100
The guidelines document- Brott T.G.
- Halperin J.L.
- Abbara S.
- Bacharach J.M.
- Barr J.D.
- Bush R.L.
- et al.
2011 ASA/ACCF/AHA/AANN/AANS/ACR/ASNR/CNS/SAIP/SCAI/SIR/SNIS/SVM/SVS guideline on the management of patients with extracranial carotid and vertebral artery disease: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, and the American Stroke Association, American Association of Neuroscience Nurses, American Association of Neurological Surgeons, American College of Radiology, American Society of Neuroradiology, Congress of Neurological Surgeons, Society of Atherosclerosis Imaging and Prevention, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of NeuroInterventional Surgery, Society for Vascular Medicine, and Society for Vascular Surgery.
J Am Coll Cardiol. 2011; 57: 1002-1044
11
“2012 Appropriate Use Criteria for Peripheral Vascular Ultrasound and Physiological Testing” rated all clinical scenarios for cerebrovascular duplex scanning before cardiac surgery as uncertain (or “may be appropriate”).101
The Society of Vascular and Interventional Neurology recommends screening of selected patients undergoing CABG (grade B), but screening of all patients was considered a grade D recommendation.- Mohler III, E.R.
- Gornik H.L.
- Gerhard-Herman M.
- Misra S.
- Olin J.W.
- Zierler R.E.
- et al.
ACCF/ACR/AIUM/ASE/ASN/ICAVL/SCAI/SCCT/SIR/SVM/SVS/SVU [corrected] 2012 appropriate use criteria for peripheral vascular ultrasound and physiological testing part I: arterial ultrasound and physiological testing: a report of the American College of Cardiology Foundation appropriate use criteria task force, American College of Radiology, American Institute of Ultrasound in Medicine, American Society of Echocardiography, American Society of Nephrology, Intersocietal Commission for the Accreditation of Vascular Laboratories, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Interventional Radiology, Society for Vascular Medicine, Society for Vascular Surgery, [corrected] and Society for Vascular Ultrasound. [corrected].
J Am Coll Cardiol. 2012; 60: 242-276
102
- Qureshi A.I.
- Alexandrov A.V.
- Tegeler C.H.
- Hobson II, R.W.
- Dennis Baker J.
- Hopkins L.N.
Guidelines for screening of extracranial carotid artery disease: a statement for healthcare professionals from the multidisciplinary practice guidelines committee of the American Society of Neuroimaging; cosponsored by the Society of Vascular and Interventional Neurology.
J Neuroimaging. 2007; 17: 19-47
Because carotid artery stenosis is common in patients with coronary artery disease and is a marker of increased risk of cardiovascular events, detecting it is thought by some to be important for preoperative risk stratification.
103
However, the cost effectiveness of such nonselective screening in patients undergoing cardiac surgery is unknown. Indeed, the first research priority identified by the writing committee of the “2012 Appropriate Use Criteria for Peripheral Vascular Ultrasound and Physiologic Testing” document was to determine the clinical and cost effectiveness of carotid screening in patients undergoing cardiac surgery.101
- Mohler III, E.R.
- Gornik H.L.
- Gerhard-Herman M.
- Misra S.
- Olin J.W.
- Zierler R.E.
- et al.
ACCF/ACR/AIUM/ASE/ASN/ICAVL/SCAI/SCCT/SIR/SVM/SVS/SVU [corrected] 2012 appropriate use criteria for peripheral vascular ultrasound and physiological testing part I: arterial ultrasound and physiological testing: a report of the American College of Cardiology Foundation appropriate use criteria task force, American College of Radiology, American Institute of Ultrasound in Medicine, American Society of Echocardiography, American Society of Nephrology, Intersocietal Commission for the Accreditation of Vascular Laboratories, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Interventional Radiology, Society for Vascular Medicine, Society for Vascular Surgery, [corrected] and Society for Vascular Ultrasound. [corrected].
J Am Coll Cardiol. 2012; 60: 242-276
Conclusions
Among patients undergoing CABG, clinical variables alone can identify those who have significant carotid artery disease with as high a degree of sensitivity as ultrasound. However, low specificity would seem to dictate ultrasound screening, and possibly additional confirmatory testing
4
of a large proportion of these patients, to alleviate a false-positive diagnosis. On the other hand, carotid duplex ultrasound screening, whether selective or nonselective, identifies only a minority of patients who will develop perioperative stroke, and intervening for those with carotid disease might not decrease the risk of these neurologic events. Absence of a direct causal relationship between carotid artery stenosis and ipsilateral stroke, and the increased morbidity associated with carotid revascularization, support the argument that prophylactic carotid revascularization might be of no benefit in asymptomatic patients undergoing CABG. This area, then, is clearly in great need of further research.Conflict of Interest Statement
Authors have nothing to disclose with regard to commercial support.
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Article info
Publication history
Published online: February 09, 2015
Accepted:
February 3,
2015
Received in revised form:
January 29,
2015
Received:
September 18,
2014
Footnotes
This study was supported in part by the Sheikh Hamdan bin Rashid Al Maktoum Distinguished Chair in Thoracic and Cardiovascular Surgery, held by Dr Sabik, and the Kenneth Gee and Paula Shaw, PhD, Chair in Heart Research, held by Dr Blackstone. These individuals played no role in the collection of data or analysis and interpretation of the data, and had no right to approve or disapprove publication of the finished article.
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© 2015 The American Association for Thoracic Surgery. Published by Elsevier Inc.
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