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Ann Thorac Surg 1998;66:396-401
© 1998 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Replacing the atherosclerotic ascending aorta is a high-risk procedure

^a Division of Thoracic and Cardiovascular Surgery, Department of Surgery, University of Virginia Health Sciences Center, Charlottesville, Virginia, USA

Address reprint requests to Dr Kron, Division of Thoracic and Cardiovascular Surgery, Department of Surgery, Box 310, University of Virginia Health Sciences Center, Charlottesville, VA 22908

Presented at the Forty-fourth Annual Meeting of the Southern Thoracic Surgical Association, Naples, FL, Nov 6–9, 1997.

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. Improved techniques in cerebral and myocardial protection have made replacement of the chronically aneurysmal ascending thoracic aorta a safe and effective procedure. We hypothesized that patients with severe ascending or aortic arch atherosclerosis were at greater risk for operative complications during ascending aortic replacement because of the diffuse nature of their atherosclerotic process.

Methods. We retrospectively analyzed the records of 17 patients who received ascending aortic replacement during elective coronary artery bypass grafting (CABG) because of the intraoperative finding of severe atherosclerosis. All 17 patients underwent tube graft replacement of the ascending aorta under hypothermic circulatory arrest and retrograde cerebral perfusion before coronary artery bypass grafting. The outcomes for these patients were compared with those of a control group of 89 consecutive patients who underwent replacement for ascending thoracic aortic aneurysm.

Results. The hospital mortality rate for replacement of the ascending thoracic aorta for severe atherosclerosis was 23.5% (4/17) versus 2.25% (2 of 89) for the control group (p = 0.006). The incidence of cerebrovascular accident in the atherosclerotic group was 17.6% (3/17) and 3.37% (3/89) for the control group (p = 0.051). Nine of 17 atherosclerotic patients (52.9%) had operative morbidity. Only 20.2% (18 of 89) of the control patients had nonfatal postoperative complications.

Conclusions. The severely atherosclerotic ascending aorta is a marker of diffuse atherosclerosis. Despite improved techniques of myocardial and cerebral protection, we have been unable to duplicate our success with ascending thoracic aneurysm repair. Preoperative screening of the ascending aorta by chest computed tomography may be appropriate in select high-risk patients to determine operability.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Replacement of the ascending thoracic aorta has been demonstrated to be a safe and effective procedure for the treatment of chronic aneurysmal disease of the ascending thoracic aorta. Recent improvements in operative technique have resulted in improved outcomes. Collagen-impregnated Dacron grafts, valved conduits, improved circulatory support, and the implementation of new techniques for both myocardial and cerebral preservation have reduced operative mortality rates to a range of 2% to 5% in the most successful series [1–3].

Atherosclerosis of the ascending aorta and aortic arch has been described as an independent risk factor for systemic embolic disease. Large, complicated, or mobile arch lesions may contribute to the rate of arterial embolization by as much as 33%, and to the rate of stroke by as much as 12% [4]. The sclerotic ascending aorta also is a specific marker for diffuse cardiovascular disease involving the coronary, carotid, and peripheral arteries [5, 6]. The Framingham study concluded that patients with radiographic evidence of calcific aortic plaques were nearly twofold more likely to suffer sudden coronary death younger than age 65, and were nearly 3.5 times more likely to suffer a stroke after age 65 years [7]. In a second study, patients older than 60 years with evidence of severe ascending or aortic arch atherosclerotic plaques (at least 4.0 mm) on transesophageal echocardiography were 9.1 times more likely to suffer an ischemic cerebrovascular accident [8]. This same study also documented that nearly two thirds of patients with plaques between 1.0 and 3.9 mm thick had ultrasonographic evidence of severe carotid arterial stenosis (at least 70% occluded).

Embolization of atheroma from the ascending aorta has been the principal cause of stroke after cardiac operations. As the age of the patient population for cardiac procedures has increased, so has the rate for ischemic cerebrovascular accidents. In 1985, Gardner and associates [9] reported an increased stroke rate of 2.4% for patients undergoing coronary artery bypass grafting (CABG). Gardner and associates’ case-control study demonstrated that older patient age, preexisting carotid stenosis, and severe atherosclerosis of the ascending aorta all significantly increased the risk of perioperative stroke. Blauth and associates [10] documented an increased number of atheroembolic events (37.4%) in patients with severely diseased ascending aortas who had cardiac operations. The mechanism for these neurologic events was related to the dislodgement of atheroemboli during clamping and manipulation of the atherosclerotic aorta [11].

New operative techniques were developed to minimize the risk of stroke for patients with significant atherosclerotic disease of the ascending and arch aorta. Perioperative identification of patients at risk for an atheroembolic episode secondary to manipulation of the thoracic aorta during cardiac operation became possible with the use of transesophageal echocardiography and epiaortic ultrasound. A strong correlation between the severity of atherosclerotic disease as determined by intraoperative transesophageal echocardiography or epiaortic ultrasound and the incidence of perioperative stroke was demonstrated. Patients with moderate to severe disease experienced stroke rates as high as 36% to 45% [12, 13].

Both of these sonographic modalities proved superior to clinical inspection alone and became useful in screening high-risk patients before aortic manipulation to identify which patients may benefit from operative techniques aimed at reducing the incidence of atheroembolic events [12, 14]. Reported successful operative modifications have included alterations in the site of aortic cannulation and clamping, "no-touch" coronary bypass with composite or bilateral mammary grafts, hypothermic arrest, retrograde cerebral perfusion, ascending aortic replacement, and arch debridement [15–17]. We hypothesized that the routine replacement of the severely atherosclerotic ascending thoracic aorta at the time of CABG using hypothermic arrest and appropriate retrograde cerebral perfusion would significantly reduce the atheroembolic morbidity and mortality rates associated with this patient population. Theoretically, we anticipated that the outcome of this operation would be similar to that for replacement of the ascending thoracic aorta in patients with chronic aneurysmal disease.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
We retrospectively analyzed the charts of 17 patients who underwent ascending thoracic aortic replacement between January 1994 and June 1997, secondary to the intraoperative finding of severe atherosclerosis before elective CABG. All patients had either intraoperative transesophageal echocardiography or epiaortic ultrasound scanning to confirm severe calcification of the ascending thoracic aorta. Severe atherosclerosis of the ascending aorta was defined as multiple or circumferential sclerotic plaques greater than 3 mm thick involving all 3 segments of the ascending aorta. Two of these patients received femoral artery cannulation. A soft spot, confirmed by ultrasound, in the proximal aortic arch was cannulated in 11 patients. The remaining 4 patients were cannulated very distally in the aortic arch. We attempted to cannulate the axillary artery in 2 patients, but were unable to do so because of severe atherosclerosis in both patients. Both of these patients were cannulated in a soft spot in the proximal arch. All 17 patients received tube graft replacement at the time of CABG under hypothermic circulatory arrest and retrograde cerebral perfusion. Myocardial protection was achieved with cold retrograde blood cardioplegia. No clamps were placed on the diseased aorta. All clamp times represented graft occlusion after completion of the distal aortic anastomosis. Four patients underwent aortic valve replacement. One patient received an additional graft from the replaced aorta to the right subclavian artery.

The operative outcomes for patients with severe aortic atherosclerosis were compared with those of a control group of 89 consecutive patients who underwent replacement of the ascending thoracic aorta for an ascending thoracic aortic aneurysm (ATAA) between 1986 and 1997. Twenty-three ATAA patients underwent tube graft reconstruction; 66 received ascending aorta and aortic valve replacement with or without a composite graft, 5 required arch reconstruction, and 22 received CABG. Demographic data and operative specifications for each group are given in Table 1.

	Results

Top Abstract Introduction Patients and methods Results Comment References

Other complications
Other morbidity was defined as a nonfatal, perioperative complication that resulted in reoperation, long-term disability, or increased length of stay resulting from additional medical therapies. The operative morbidity rate of the atherosclerotic patients was 52.9% (9 of 17). These complications included 6 episodes of postoperative bleeding, 2 episodes of acute renal failure, 1 perioperative myocardial infarction, 1 episode of sustained ventricular tachycardia, and 2 episodes of prolonged ventilation or sepsis. Only 20.2% (18 of 89) of the ATAA patients had nonfatal postoperative complications.

Reoperations
Two patients (11.8%) in the atherosclerosis group required reoperation. Both of these operations were for significant postoperative mediastinal bleeding. Six (6.7%) of the ATAA patients required reoperation for bleeding. Six other reoperations included 2 pericardial drainages, 1 pacemaker insertion, and 1 sternal debridement.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
Kouchoukos and associates [18] have advocated replacement of the severely atherosclerotic ascending aorta when encountered during cardiac operations. Their success has been due in large part to the use of hypothermic circulatory arrest and retrograde cerebral perfusion. This approach was used in 47 patients more than 50 years of age with only 2 deaths (4.3%) and no episodes of perioperative stroke [18]. Our experience with 17 patients over age 60 (mean, 71.5 years) has not been as encouraging. There were 4 deaths (23.5%) and 3 strokes (17.6%) in this population of debilitated patients.

Our approach to replacing the ascending thoracic aorta includes intraoperative transesophageal echocardiography or epiaortic ultrasound to confirm the severity of disease and to identify a soft spot for aortic cannulation. Once access for cardiopulmonary bypass has been achieved, replacement of the ascending aorta can be carried out with either a simple Dacron tube graft or a valved conduit, if necessary. Hypothermic arrest with or without retrograde cerebral perfusion is instituted if disease precludes cross-clamping of the ascending aorta.

We have successfully treated chronic aneurysmal disease of the ascending aorta in the preceding manner. We have repaired 18 ascending thoracic aortic aneurysms using hypothermic circulatory arrest and retrograde cerebral perfusion without a single incidence of intraoperative death or neurologic deficit. We have not been able to duplicate these results in patients receiving ascending aortic replacement at the time of CABG for severe atherosclerosis. The increased morbidity and mortality rates seen in this patient population can be attributed to the severity of their atherosclerotic disease and comorbidities associated with advanced age.

Independent risk factors for increased mortality rate or poor neurologic outcome after CABG include age, concomitant cerebrovascular disease, peripheral vascular disease, and proximal aortic atherosclerosis [10, 19–21]. The significant comorbidities for the 17 patients in this series included age greater than 65 years (94.1%), evidence of cerebrovascular disease (29.4%), evidence of peripheral vascular disease (35.3%), hypertension (47.1%), previous myocardial infarction (23.5%), and decreased left ventricular function (23.5%). Two of the deaths in this study occurred in patients with left ventricular ejection fractions less than 25%. The other 2 deaths occurred in patients who had previously undergone carotid endarterectomy and had clinical evidence of diffuse atherosclerosis with subsequent end organ damage.

A suitable site for arterial cannulation becomes an issue in patients with severe systemic atherosclerosis. Femoral artery cannulation may decrease the incidence of systemic atheroembolization and subsequent stroke. However, in some patients, femoral artery access may be impossible secondary to a previous vascular operation or severe concomitant lower extremity atherosclerosis. Lesser degrees of femoral artery atherosclerosis also may be associated with a significant risk of arterial dissection or retrograde embolization. Both patients cannulated through the femoral artery did not have operative complications. However, 2 of 3 patients (Table 3, patients 9 and 14) who had cerebrovascular accidents were unable to undergo femoral artery cannulation secondary to severe atherosclerosis of the lower extremity arteries. Of the 4 patients who died, 2 were unable to undergo either axillary, subclavian, or femoral artery cannulation secondary to severe atherosclerosis at those sites (Table 3, patients 2 and 9).

These 17 patients, although at increased risk, would not have been excluded from CABG alone. Their predicted mortality rate of 1.9% to 7% and predicted neurologic complication rate of 3.6% to 8.9% would have been considered acceptable when compared with the United States population matched for age and sex [22–24]. However, when older age and significant comorbidities are combined with the presence of a severely atherosclerotic ascending aorta, the operative risk may increase regardless of technique. Preoperative aortic screening may be indicated in patients greater than 65 years of age with compelling evidence of diffuse atherosclerosis in the setting of decreased left ventricular function or a prior neurologic event. Screening may be particularly necessary in patients whose comorbidities make them marginal operative candidates. Two of the 4 patients in the atherosclerotic group (Table 3, patients 2 and 9) who suffered hospital death would not have been offered an operation if the extent of their aortic disease was known beforehand.

Transesophageal echocardiography and epiaortic ultrasound have been useful in determining the severity of atherosclerosis in the thoracic aorta intraoperatively [12, 13]. These modalities are now commonly used to direct operative technique when the atherosclerotic aorta is encountered [14, 15]. The disadvantages of these techniques include inadequate visualization of the aortic arch with transesophageal echocardiography and the need for an open chest to perform epiaortic ultrasound. The ability to study the proximal aorta before an operation could aid in identifying high-risk patients for coronary revascularization in light of severe ascending aortic atherosclerosis.

Transesophageal echocardiography could serve as a preoperative aortic screening tool. However, transesophageal echocardiography is not without procedural risk and is limited in its ability to image the aortic arch. A better alternative for imaging the potentially atherosclerotic thoracic aorta could be the helical computed tomographic scan. A recent study from the University of Michigan demonstrated a 92% predictive value of helical computed tomography with multiplanar reconstruction in identifying correctly thoracic aortic abnormality before operation [25]. Helical computed tomography also helped to predict accurately the need for hypothermic arrest during operation in 94% of the patients studied.

In summary, CABG is a safe and effective procedure for the treatment of coronary artery disease in appropriately selected elderly patients. Replacement of the severely atherosclerotic ascending aorta before CABG may be a high-risk procedure in elderly patients with diffuse, severe, vascular disease. Preoperative radiologic assessment of the thoracic aorta may help delineate the severity of atherosclerosis and define a subset of patients who are at an unacceptable risk for surgical intervention.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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