Assessment of carotid artery stenosis before coronary artery bypass surgery. Is it always necessary?

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JC Cornily, D Le Saux, U Vinsonneau... - Archives of ..., 2011 - Elsevier BACKGROUND: Extracranial internal carotid artery stenosis is a risk factor for perioperative stroke in patients undergoing coronary artery bypass surgery (CAB). Although selective and non-selective methods of preoperative carotid screening have been advocated, it remains ...

Perioperative stroke is one of the major complications of coronary artery bypass surgery (CAB), with a reported incidence of 2.1 5.2% [1] and [2] and a related mortality of 0 38% [3] and [4]. Significant extracranial internal carotid artery stenosis (i.e. ≥70% luminal narrowing) is a well-established risk factor for perioperative stroke in patients undergoing CAB [5], [6] and [7]. To prevent this serious complication, carotid endarterectomy (CEA) has been recommended in patients undergoing CAB in a staged or concomitant approach; CEA/CAB studies have been conducted since the 1970s [8] and [9]. Although the benefits of CEA/CAB remain uncertain, some of these studies reported reductions in stroke rates, prompting the notion that preoperative screening for carotid stenosis in all CAB patients is necessary to reduce perioperative and long-term stroke rates [10] and [11]. Such systematic, non-selective carotid screening does, however, add considerable time and expense to preoperative workups.

Alternatively, some investigators have identified risk factors for carotid disease that could be used for more selective screening. These risk factors include older age [12] and [13], carotid bruit [14] and [15], previous neurological event [14] and [15], previous carotid surgery [15], peripheral vascular disease (PVD) [15], hypertension, diabetes, dyslipidaemia and smoking [12]. Unfortunately, there are neither consensus criteria to provide guidelines for centres looking to optimize their carotid screening practices nor prospective management outcome studies.

In the present study, we sought to report the results of our single-centre routine experience in non-selective preoperative carotid screening of CAB patients over a 5-year period. Our hypothesis was that selective carotid screening is as effective as non-selective screening in detecting significant carotid stenosis and does not result in higher perioperative stroke rates. We also studied whether selective screening would result in significant changes in surgical management.

We retrospectively reviewed the files of all consecutive patients undergoing isolated de novo CAB from January 2003 to December 2008, who fulfilled the necessary criteria. Inclusion criteria were: patients undergoing CAB with no other concomitant cardiac procedure (such as valve replacement/repair, aneurysmectomy, atrial septal defect closure); carotid screening by ultrasonography performed exclusively in our centre; and assessment of carotid bruit by at least one of the senior physicians in our department. Exclusion criteria were: aortic stenosis even if not significant (bruit of aortic stenosis can hide a carotid bruit); need for emergency surgery; and carotid evaluation performed in another centre.

Prespecified preoperative, operative and postoperative clinical data were extracted independently by two investigators (D.L.S., J.-C.C.) from all patients charts using a standardized form. Information discrepancies were resolved by consensus or by retrieving further information from additional medical records. Preoperative variables included demographic data, smoking status, diabetes mellitus diagnosed as a documented history of diabetes or use of any antidiabetic medication, hypertension, history of previous stroke, carotid bruit, cerebrovascular disease (CVD) and PVD. Patients were considered as having PVD if they had intermittent claudication, a history of peripheral revascularization or duplex ultrasound showing significant arterial stenosis.

Evaluation of internal carotid stenosis was performed with duplex ultrasound. The degree of stenosis was expressed as the percentage of luminal narrowing estimated by ipsilateral internal common carotid artery flow velocity ratios (duplex ultrasound). Carotid artery stenosis was considered significant when there was ≥70% luminal narrowing of the affected internal carotid artery, which was determined by duplex ultrasonography in accordance with widely accepted clinical guidelines. In our institution, CEA is considered if carotid stenosis is >70% in asymptomatic patients; surgery is decided on a case-by-case basis [5], [6] and [16].

Postoperative data were extracted from a neurological assessment/outcome database initiated at our centre to prospectively monitor the neurological progress and clinical outcomes of all patients after cardiac surgery. These data were collected on a daily basis and included death and stroke ratios. A cerebral vascular accident or stroke was defined as an acute neurological event resulting from cerebral circulatory impairment and lasting >24 hours. The outcome of postoperative stroke was defined as the clinical diagnosis of stroke and confirmed by brain imaging (head computed tomography, magnetic resonance imaging or both). A transient ischaemic attack was defined as a temporary neurological deficit attributable to circulatory impairment and lasting 70 years. Patients without any of these risk factors were included in the low-risk group. We determined the prevalence of significant carotid stenosis, the number of CE As performed and the number of perioperative strokes in the high-risk and low-risk groups. We retrospectively applied the screening algorithm (high-risk and low-risk groups) to our cohort of CAB patients who underwent routine carotid screening and then determined the prevalence of carotid stenosis in each group. Finally, the predictive value of the selective screening strategy based upon these risk factors was estimated.

Preoperative, operative and postoperative outcome data were reviewed. Continuous and dichotomous variables were compared using Student's t test and the Chi2 test, respectively. Fisher's exact test was used for comparisons in which at least one cell value was 70 years. There are, of course, many other risk factors for carotid stenosis but we selected these because they appeared to be prominent, clinically relevant and, therefore, easy to recognise in the preoperative stage in candidates for CAD. Patients with symptomatic CVD are not only more likely to have ≥70% carotid stenosis, but those with carotid stenosis benefit more from CEA than their asymptomatic counterparts in terms of 5-year stroke reduction [5] and [20]. Carotid bruit is a marker of turbulent flow secondary to carotid stenosis; in our cohort, 25% of CAB patients with a bruit also had ≥70% carotid stenosis. Finally, advanced age has been reported to increase the association between carotid disease and perioperative stroke in CAB. Faggioli et al. found that CAB patients aged >60 years with >75% carotid stenosis had a stroke rate of 15% [13].

Of the 205 patients who underwent carotid screening, five (2.4%) patients had perioperative strokes. Of these five, two had significant carotid stenosis, confirming that significant carotid stenosis is a risk factor for stroke (16.7% vs 1.6%; p = 0.03) (Table 2) but three patients had no significant carotid artery stenosis, confirming that degree of stenosis is not the only predictive stroke factor.

We applied our screening algorithm retrospectively to our cohort of CAB patients who underwent routine carotid screening, stratifying them into high-risk and low-risk groups. A selective approach towards screening only high-risk patients would have allowed us to screen only 59% of our cohort with very good outcome. None of the low-risk patients underwent CEA and none had a perioperative stroke. These data support the first component of our hypothesis: selective carotid screening is similar to non-selective screening in terms of detecting significant and high-risk carotid stenosis. Moreover, carotid stenosis is not the only risk factor for stroke (others being atrial fibrillation, etc.) [7].

We performed an analysis of the impact that selective screening would have had on patient outcome by retrospectively examining the surgical management and perioperative stroke rates of the high-risk versus low-risk groups among the 205 patients who underwent carotid screening (Fig. 1). Our selective screening approach would have identified, as high risk, all five patients who ultimately had perioperative strokes. These data suggest that patients classified as low risk derived negligible benefit from routine carotid screening, in terms of affecting surgical management or neurological outcomes. Furthermore, the fact that routine carotid screening of all low-risk patients over 5 years in a busy clinical cardiac surgery department revealed only one patient with significant carotid stenosis, suggests that this practice is relatively unproductive.

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Ann Thorac Surg, 72 (2001), pp. 1195 1201 [discussion 201 2]

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