Asian Cardiovasc Thorac Ann 1999;7:168-172
© 1999 Asia Publishing EXchange Pte Ltd
Epiaortic Ultrasound: Aortic Screening in Coronary Revascularization
Mehmet Ali Özatik, MD,
Kerem M Vural, MD,
Erol Sener, MD,
O
uz Ta
demir, MD
Department of Cardiovascular Surgery
Türkiye Yüksek  htisas Hospital
Ankara, Turkey
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For reprint information contact: Kerem M Vural, MD Tel: 90 312 426 7574 Fax: 90 312 426 6181 email: kvural{at}tr-net.net.tr N Tandogan cad. 5/6 Kavaklidere, Ankara 06540, Turkey.
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Abstract
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Two hundred and fourteen consecutive patients (174 males and 40 females; mean age, 61 years) undergoing coronary artery bypass grafting were screened by intraoperative epiaortic B-mode ultrasonography. The operative strategy was modified under ultrasonographic guidance in 26 patients to reduce the risk of stroke. Aortic cannulation, clamping, and vein graft attachment sites were changed in 15 patients (7%), the operation was performed on a beating heart in 7 (3.3%), cardiopulmonary bypass was established via femoral cannulation and coronary artery bypass grafting was performed on a fibrillating heart in 4 (1.9%). The incidence of stroke in our coronary artery bypass patients decreased from 2.8% to 0.9%. Sensitivity of detection of ascending aortic atherosclerosis was calculated as 35.48% for palpation and 96.8% for epiaortic ultrasonography. Risk factors for significant ascending aortic atherosclerosis were age over 70 years (p = 0.004), hypertension (p = 0.03), and associated peripheral arterial disease (p = 0.02). The most frequently affected segments were the anterior (41%) and upper left (32%) aspects of the aorta. Intraoperative epiaortic B-mode ultrasonography was found to be a reliable method of detecting ascending aortic atherosclerosis, allowing the surgeon to determine operative strategy to reduce the risk of perioperative stroke.
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Introduction
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In the current era of cardiac surgery, increasing numbers of older and high-risk patients are undergoing coronary artery bypass grafting.1 However, the incidence of neurological complications in cardiac surgery is also increasing and the current rate is between 2% and 5%.2 A major cause of stroke following coronary artery bypass grafting is atherosclerotic debris embolism during cannulation or clamping of the ascending aorta.2–4 Among the methods for screening ascending aortic disease, intraoperative epiaortic B-mode ultrasonography (IEU) appears to be a reliable, fast, cost-effective, and practical tool. The aim of this study was to determine the value of IEU in the early diagnosis of ascending aortic disease as a means of dictating appropriate safety measures against potential perioperative stoke.
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Patients and Methods
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Between December 1996 and February 1997, 214 patients undergoing coronary artery bypass grafting (CABG) were screened by intraoperative epiaortic B-mode ultrasound for ascending aortic atherosclerotic disease and appropriate operative strategy was adopted when necessary to reduce the risk of stroke. There were 174 males (81%) and 40 females (19%). The mean age was 61 ± 9 years. Risk factors for atherosclerosis were: diabetes mellitus in 51 (24%); hypertension in 92 (43%); hyperlipidemia in 142 (66%); and a history of smoking in 74 (35%) patients. Fourteen patients (6.5%) had left main coronary artery disease, 102 (47.66%) had triple-vessel disease, 67 (31%) had double-vessel disease, and 31 (15%) had single-vessel (proximal left anterior descending coronary artery) disease. Two patients also had an abdominal aortic aneurysm and 10 had symptomatic peripheral arterial disease. All patients underwent a carotid Doppler ultrasound evaluation preoperatively. Significant carotid stenosis was further evaluated by carotid digital subtraction angiography. Patients with angiographically significant carotid artery stenosis underwent carotid endarterectomy 2 weeks prior to CABG. Patients who had recently suffered such neurological events were referred to a neurological clinic for further evaluation and stabilization.
Following routine anesthetic induction, median sterno-tomy, graft harvesting, and placement of stay sutures on the pericardial edges, the ascending aorta was inspected and palpated for evidence of atherosclerotic disease. Any visual or palpation abnormality implying atherosclerotic involvement was noted. Then, an epiaortic 5-MHz probe wrapped in a sterile nylon sheath filled with sonolucent gel was placed on the ascending aortic wall. Two-dimensional images were obtained with a Hewlett Packard Sonos 1000 device (Hewlett Packard, Andover, MA, USA). Imaging of the ascending aorta was performed sequentially for the upper (cannulation site), middle (clamping and proximal anastomosis site), and lower (aortic needle site) segments and the front, back, left, and right aspects. All of these segments were assessed in transverse and longitudinal frames and the images were recorded on video tape. This procedure took approximately 5 minutes and the images were compared with the information obtained by inspection and palpation. The algorithm in Figure 1
was then applied as the operative strategy.
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Figure 1. Operative strategy based on intraoperative epiaortic ultrasound (IEU) findings. CABG = coronary artery bypass grafting, CPB = cardiopulmonary bypass, IMA = internal mammary artery, LAD = left anterior descending coronary artery, LIMA = left internal mammary arteries, OM = obtuse marginal branch of the circumflex coronary artery, RCA = right coronary artery, RIMA = right internal mammary arteries.
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Operative Strategy
In patients with minimal intimal thickening in the ascending aorta, a standard operation was performed without modification. In 15 (7%) cases of mild to moderate atherosclerotic changes in ascending aorta (defined as greater than 3 mm of intimal thickening or plaque formation in a limited area), cannulation and proximal anastomosis was performed with avoidance of such areas of high risk (Figure 2). In severe aortic disease (defined as multiple plaques or porcelain aorta), several measures were adopted (Figure 3). In patients with left anterior descending coronary artery disease with or without right coronary artery involvement, coronary revascularization was performed on a beating heart using pedicled left or right internal mammary arteries (7 patients, 3.3%). In 4 (1.9%) patients with more extensive atherosclerotic disease (left main coronary artery disease or triple-vessel disease), arterial cannulation was established via the femoral artery and revascularization was carried out on a fibrillating heart with moderately hypothermic cardiopulmonary bypass and without cardioplegia. The left ventricle was continuously vented during fibrillation. In one of these patients, the internal mammary artery was used for sequential grafting of the left anterior descending coronary artery and intermediate arteries and in another, proximal saphenous vein anastomoses were performed one over the other. In a third case, a bridging saphenous vein graft bypassing the stenosis was interposed between the proximal and distal right coronary artery.
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Figure 2. Intraoperative epiaortic ultrasound image indicating diffuse intimal thickening exceeding 3 mm (arrow).
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Figure 3. Intraoperative epiaortic ultrasound image indicating multiple calcified foci in a severely diseased ascending aorta (arrow).
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Patients were evaluated for neurological outcome in the early postoperative period by the intensive care unit staff. When a cerebrovascular event was suspected, an independent neurologist was called on to evaluate the patient. Diagnosis of a cerebral complication was confirmed when a neurological disturbance that did not exist preoperatively was confirmed by the neurologist on the basis of clinical evaluation and computed tomography or electroencephalographic findings.
Statistical analysis was performed using chi-squared and Fisher's exact tests for univariate analysis and logistic regression for multivariate analysis. A p value equal to or less than 0.05 was considered statistically significant.
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Results
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The incidence of stroke was 0.9% (2 patients) among the screened patients. One of these two patients had a history of a transient ischemic episode preoperatively. In his intraoperative epiaortic ultrasonographic evaluation, an atherosclerotic plaque was detected near the annulus in the lower segment of the aorta. Postoperative cerebral computed tomography revealed multiple old infarcts in the brain hemispheres. In the second patient, only minimal intimal and medial thickening had been detected and he had undergone a normal cannulation procedure. A postoperative computed tomography scan was normal. Neither of these patients awoke after the operation and they both remained in coma until they died in the early postoperative period. No other cerebrovascular events occurred following operations in which the surgical technique was modified according to the ultrasonographic findings. IEU revealed intimal or medial thickening in 31 patients (14.5%). In another 31 patients (14.5%), plaque formation was evident; the atherosclerotic presentation was irregular plaque in 24 patients (11.2%) and diffuse calcification in 7 patients (3.3%). Palpation detected atherosclerotic plaque in only 12 cases. Further, only 4 of the 7 diffusely-calcified aortic walls revealed a palpation abnormality. In one patient who appeared normal by both palpation and IEU, soft atheromatous material was found in the anterior aspect during proximal anastomosis. Sensitivity was calculated as 35.48% for palpation and 96.8% for IEU. Results of palpation and IEU assessments are shown in Table 1. The most frequently affected segments were the anterior and left-upper aspects of the aorta, which were involved in 41% and 32% respectively of the atherosclerotic aortas.
According to multivariate analysis, age over 70 years (p = 0.004), hypertension (p = 0.03), and associated peripheral arterial disease (p = 0.023) were associated with significant ascending aortic disease. Patients with a preoperative history of a cerebrovascular event were usually found to have either hypertension or carotid artery disease. Occasionally, IEU indicated aortic pathology in some of these patients but the correlation was not significant.
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Discussion
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Stroke due to atherosclerotic debris embolism during manipulation of a diseased ascending aorta is an important cause of morbidity and mortality and may be the underlying or preceding factor in up to 25% of deaths following CABG.2,3 Other complications such as rupture, dissection, or visceral embolism may occur during clamping, cannulation, or proximal anastomosis. In view of this, the development of techniques to ensure early diagnosis of a severely diseased aorta and prevention of complications is mandatory.
Risk factors for postoperative stroke include advanced age, associated cerebrovascular disease, severe ascending aortic atherosclerosis, prolonged cardiopulmonary bypass, and severe perioperative hypotension.1 The incidence of ascending aortic atherosclerosis in the general population is approximately 2%.3 Gardner and colleagues1 reported a 14% incidence of stroke following cardiopulmonary bypass in patients with severe ascending aortic athero-sclerosis. Mills and Everson3 encountered a 25% incidence of fatal stroke following attempts to cannulate or clamp severely diseased ascending aortas. A number of risk factors for ascending aortic atherosclerosis have been determined in previous studies, such as diabetes mellitus, hypercholesterolemia, hypertriglyceridemia, hypertension, smoking, and peripheral arterial disease. Probably the most important risk factor is advanced age, especially in view of the increasing number of older patients undergoing CABG. Our results showed that age over 70 years was associated with ascending aortic atherosclerosis. The frequencies of stroke and hemiplegia tend to increase after this age and in one study, intraoperative ultrasound revealed severe atherosclerotic involvement in 32% of patients over 70 years.1,3,5,6 According to necropsy data, the incidence of ascending aortic atherosclerosis increases from 20% in the 5th decade to 80% at the age of 75, with a corresponding increase in the incidence of stroke from 1% to 7%.1,3 Disease is generally more prominent in the anterior wall of the aorta and less frequent in the posterior aspect and lower segment.7
Over a period of 8 years, Mills and Everson3 detected 152 cases of aortic atherosclerosis (8.8%; 4.5% mild, 2.3% moderate, and 2% severe) in a group of 1735 patients by angiography, palpation, and inspection. Using a no-touch technique, they avoided any mortality due to cerebral embolic events in 16 patients with severe atherosclerosis.3 In our study, palpation indicated aortic disease in only 12 of 62 patients. Only 4 of 7 patients with porcelain aorta were detected by palpation. The sensitivity of the palpation method was 35.48%, compared to 96.8% for IEU. Furthermore, palpation is reported to be among the causes of atheroembolism.8
Intraoperative epiaortic ultrasound has been reported to be a fast, reliable, and accurate method of predicting ascending aortic atherosclerosis. Hosoda and colleagues9 found 36 of 100 CABG candidates had moderate or severe ascending aortic atherosclerosis by intraoperative ultra-sonography. With no modification in their operative technique, a cerebral complication incidence of 8.3% was observed but no cerebral complication occurred in 64 ultrasonographically normal patients. Various strategies have been suggested to deal with ascending aortic atherosclerosis. These include Dacron graft replacement of the ascending aorta under hypothermic circulatory arrest that may itself cause permanent neurological injury.5,6 Culliford and colleagues8 reported bleeding and late aneurysmal formation after aortic endarterectomy with hypothermic circulatory arrest. Foley catheter occlusion to avoid clamping the aorta has also resulted in embolism.10 Other measures, including bypassing the lesion with a graft bridging the proximal and distal parts of the coronary vessel and the no-touch technique, seem more logical and were employed in our patients.11,12
It was concluded from this study that intraoperative epiaortic B-mode ultrasound was a reliable method of detecting ascending aortic atherosclerosis and may be useful in preventing neurological complications by either avoiding manipulation of high-risk areas or changing the operative strategy. In the era before we applied IEU, a similar patient population (our standard CABG population) was found to have a 2.8% incidence of postoperative cerebral complications during an identical time period. Using IEU as an early-detection tool to dictate operative strategy, our incidence of stroke after CABG decreased to 0.9%. At present, we routinely use IEU screening during CABG procedures. As this study is not a randomized case-matched comparative study, we merely state that IEU helped to decrease our postoperative complication rate. Certainly, randomized prospective trials would be required for definitive conclusions. However, such a study would raise ethical concerns as the control group would not be subjected to screening in spite of the evidence that strongly suggests its advantages in predicting and preventing postoperative neurological complications.
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References
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Hosoda Y, Watanabe M, Hirooka Y, Ohse Y, Tanaka A, Watanabe T. Significance of atherosclerotic changes of ascending aorta during coronary artery bypass surgery with intraoperative detection by echography. J Cardiovasc Surg (Torino) 1991;32:301–6.[Medline]
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Abstract
Introduction
