Treatment of carotid stenosis before coronary surgery

Background

Atherosclerosis is a systemic disease and typically affects multiple arterial beds within the same patient. The incidence of coexisting coronary and carotid artery disease varies between 2 - 14% and 8% of patients undergoing CABG have a significant stenosis in an extracranial carotid artery. These individuals may be at an increased risk for stroke [1]. Conversely, significant coronary artery disease occurs in nearly one third of patients with high-grade carotid stenosis who are being considered for carotid endarterectomy [2].
It has been shown that coexistent carotid artery stenosis greater than 75% is an independent predictor of stroke risk during cardiac operation [3]. The incidence of perioperative stroke in patients with carotid atherosclerosis ranges from 2.8 – 22% in various studies [4]. The stroke risk is highest among patients with previous stroke or ischemic attack. The risk also correlates with the severity of the underlying carotid atherosclerosis. Naylor and co-workers showed that the odds ratio of occurrence of stroke after cardiac surgery is at 4.3 in case of = 50% stenosis compared to = 50% stenosis. Review of literature shows the stroke rate of 3% in asymptomatic CABG patients with unilateral 50–99% carotid stenosis, 5% in those with bilateral 50% to 99% stenosis, and 7 to 11% in individuals with carotid occlusion [5].  Therefore, the coexistence of severe carotid artery stenosis and symptomatic coronary artery disease represent a serious treatment dilemma. Namely, the operative repair of one arterial bed is related to a substantial risk for complication from the other. In patients with a coexistence of severe carotid and coronary artery disease, the sequence for the treatment of coronary and carotid revascularisation procedures also remains controversial.

1) Causes of stroke during cardiac surgery

There are no relevant clinical trials that have specifically addressed the question of which patients with carotid occlusive disease are at highest risk for stroke during CABG, in whom perioperative stroke is caused by carotid atherosclerosis, and in whom CABG without carotid endarterectomy represents a higher risk for stroke than previous carotid surgery. Stroke during cardiac surgery has several mechanisms and carotid stenosis is only one of them. The presence of carotid stenotic disease causes ischemic stroke in patients undergoing CABG by acting as an embolic source and/or causing hypoperfusion of the ipsilateral cerebral hemisphere.
There is evidence that the stroke risk during CABG related to carotid atherosclerosis may have been over-estimated. Even in individuals with carotid atherosclerosis, stroke during CABG is more likely to result from other sources than from carotid stenosis such as cardiac emboli or significant atheroma in the ascending aortic arch [6]. The North American Symptomatic Carotid Endarterectomy Trial has shown that in patients who had stroke around the CABG, stroke was attributed to emboli in 62.1% of patients and to hypoperfusion in only 8.8%. Furthermore, two-thirds of strokes occurred after an uneventful initial recovery from surgery, suggesting that hemodynamic failure during the operation is of minimal causal role [7]. Radiological and post-mortem studies show that 70% of perioperative strokes are bilateral or multiple, implicating proximal embolic sources [8]. A study of Wolman and co-workers has identified that all major predictors of perioperative stroke are related to the presence of intracardiac thrombus or aortic atheromatous plaque [9]. This finding is important, as nearly half of all patients with carotid atherosclerosis have severe aortic disease as well. These data indicate that in surgical patients with asymptomatic carotid atherosclerosis other risk factors are often responsible for perioperative stroke and not carotid stenosis.

The risk for stoke in CABG patients is also related to operative duration and postoperative atrial fibrillation [7]. Therefore, revascularisation of asymptomatic carotid stenosis is unlikely to completely abolish the risk for perioperative stroke, particularly in patients with advanced cardiac and aortic atherosclerotic disease. A meta-analysis estimated that prophylactic carotid revascularisation would prevent 40 to 50% of perioperative stroke in these patients [5].

2) Risk of operative procedures

In patients with co-existent carotid and coronary artery disease, there are different surgical options, including a separate operation of carotid and coronary arteries, the actual timing and sequencing of the procedures is controversial. One of the options is also combined carotid endarterectomy and CABG; however this type of treatment is related to high stroke and death rates of 7.4% to 9.4% [10] which is nearly twice the risk of each operation alone. In a multicenter review, the risk of stroke and/or death was even higher, and accounts for 18.6% in patients who have carotid endarterectomy performed in conjunction with CABG [11]. Patients who have undergone carotid endarterectomy before CABG are also at higher risk for complications. The carotid endarterectomy guidelines report that the incidence of stroke, myocardial infarction and death is 16.44 % for combined carotid endarterectomy and CABG, 26.15% for carotid endarterectomy, followed by CABG and 16.35% for CABG followed by carotid endarterectomy [12]. In spite of that, recent meta-analysis concluded that there is no significant difference in outcome for staged or synchronous procedures [13]. The European Society of Vascular Surgery (ESVS) Guidelines recommend as appropriate management of patients with concomitant severe coronary and carotid artery disease an individualised surgical approach [14]. 
Therefore, because of high operative complication rate, benefit from carotid surgery (separate or in combination with CABG) is expected only in high risk groups and these high complication rates would clearly offset the long-term benefit from secondary stroke prevention.

3) Carotid angioplasty in high risk coronary patients

Carotid angioplasty and stenting are evolving as a valid alternative to carotid endarterectomy. A few small studies have shown that the complication rate in patients who have undergone carotid angioplasty and stenting followed by CABG is significantly lower than in patients who have undergone combined carotid endarterectomy and open heat surgery [15]. Similarly, a meta-analysis of 30-day outcome following staged carotid artery stenting before coronary bypass surgery showed that carotid artery stenting plus CABG is an attractive and less invasive alternative to carotid endarterectomy plus CABG [16]. Although the number of reported studies and included patients are so far small, the data support validity of stenting particularly in high-risk surgical patients.

Conclusion:

Patients with carotid occlusive disease who undergo CABG are at high risk for perioperative stroke. The risk is related to the severity of stenosis and is highest among patients with previous stroke or ischemic attack. However, besides carotid atherosclerosis, other risk factors, particularly advanced cardiac and aortic atherosclerotic disease, are responsible for perioperative stroke. Therefore, treatment of carotid stenosis before coronary surgery is indicated only in patients at high risk for perioperative stroke and in whom it is expected that the risk is predominantly related to carotid atherosclerosis: asymptomatic patients with high grade carotid stenosis (>80%) [17] and patients with previous stroke or ischemic attack. In patients with severe carotid atherosclerosis, surgical treatment is indicated. In patients with severe coronary and carotid artery disease, an individualised surgical approach is recommended as the most appropriate management. Stenting of carotid arteries represents a less invasive alternative in high risk surgical patients.