01 сентября 2001 00:00
Management of porcelain aorta during coronary artery bypass grafting
Background . Patients with porcelain aorta carry a high risk of systemic embolism during coronary artery bypass grafting. No currently proposed surgical approach avoids manipulation of the heavily calcified ascending aorta. A novel surgical approach avoiding manipulation of the porcelain aorta was evaluated with regard to its efficacy in prevention of atheroemboli.
Methods . The following surgical protocol was performed in 23 patients with porcelain aorta: (1) arterial cannulation of the axillary artery, (2) hypothermic fibrillatory arrest for performance of the distal anastomosis, and (3) construction of the proximal anastomosis to the inominate artery or to a disease-free area of the ascending aorta during hypothermic circulatory arrest.
Results . The postoperative course was uneventful in all patients. No patient experienced a cerebrovascular accident or visceral organ injury as a result of atheroemboli.
Conclusions . The proposed surgical approach is safe and reliable in patients with porcelain aorta and has the potential to reduce the prevalence of stroke and systemic embolization associated with coronary artery bypass grafting in patients with porcelain aorta.
Severe atherosclerosis of the ascending aorta is associated with increased morbidity and mortality during coronary artery bypass grafting because of the increased risk of perioperative atheroembolism [1] [2] [3] . The incidence of significant atheromatous disease of the ascending aorta in patients undergoing cardiac operation varies between 14% and 29% in recent series [4] [5] . At autopsy Blauth and coworkers [6] identified a strong correlation between atheroembolism and ascending aortic atherosclerosis in 221 patients who died after cardiac operation. Most of these patients (46 [96%] of 48) with evidence of atheroemboli had severe atherosclerosis of the ascending aorta [6] .
At least three different maneuvers during coronary artery bypass grafting can cause atheromatous embolism from the diseased ascending aorta: (1) cannulation of the aorta, (2) cross-clamping, and (3) partial clamping for construction of the proximal anastomosis. Different techniques have been proposed to reduce the risk of atheroembolism in patients with a diseased ascending aorta: single-clamp technique [7] , placement of proximal saphenous vein (SV) grafts to the internal mammary artery (IMA) or the inominate artery [8] [9] , complete arterial revascularization with pedicled arterial grafts, hypothermic fibrillatory arrest avoiding clamping of the ascending aorta [10] , replacement of the ascending aorta [4] , aortic endarterectomy [11] , patch aortoplasty [12] , and arterial cannulation of the axillary artery [13] . In all proposed techniques the diseased ascending aorta or the aortic arch is either cannulated or clamped, which increases the risk of debris dislocation.
A surgical protocol avoiding manipulation of a heavily calcified ascending aorta and aortic arch (porcelain aorta) was evaluated with regard to its efficacy in preventing atheroembolism. The protocol consisted of a combination of three techniques: (1) arterial cannulation of the axillary artery; (2) hypothermic fibrillatory arrest for performing the distal anastomosis; and (3) construction of the proximal anastomosis to the inominate artery before the start of cardiopulmonary bypass or to a disease-free area of the ascending aorta during hypothermic circulatory arrest in patients with concomittant severe atherosclerosis of the inominate artery.
Patients and methods
Analysis of 1,861 consecutive patients undergoing first-time coronary artery bypass grafting from January 1995 to June 1997 revealed 23 patients (1.2%) with porcelain aorta in its most severe form, with circumferential calcification of the entire ascending aorta and proximal aortic arch. The patients' demographic data are depicted in . [Table 1] The diagnosis was made before operation either by chest x-ray film or during cineangiography in 12 patients and after median sternotomy by palpation in the remaining 11. In none of the patients was ultrasound scanning of the ascending aorta and aortic arch performed.
Cardiopulmonary bypass
Cardiopulmonary bypass was conducted either at moderate hypothermia with a core temperature of 28°C or at deep hypothermia with circulatory arrest at 20°C when needed. A nonpulsatile pump flow was maintained at 2.4 L · min -1 · m -2 with a perfusion pressure sustained at 80 mm Hg.
Surgical technique
The axillary artery was exposed through an incision below and parallel to the right clavicle after one or both IMAs were harvested. A transverse incision was made, and the axillary artery was cannulated with a 21Ch or 24Ch right-angled cannula (THI aortic perfusion cannula; Sherwood Medical, Petit-Rechain, Belgium). Before cardiopulmonary bypass the inominate artery was inspected for atherosclerotic plaques. If no atherosclerotic plaques were seen, the artery was partially clamped, and one proximal anastomosis with a short venous segment was established by using a continuous 5.0 polypropylene suture (Ethicon, Norderstedt, Germany) before cardiopulmonary bypass. Severe atherosclerosis of the inominate artery precluded partial clamping. After hypothermic induced ventricular fibrillation, the distal SV and IMA anastomoses were performed. The left ventricle was decompressed through the right superior pulmonary vein. The SV grafts were sutured end-to-end or end-to-side to the previously created SV graft at the inominate artery. When severe atherosclerosis of the inominate artery was present, one or two SV grafts were placed to the ascending aorta during deep hypothermic circulatory arrest in a nondiseased area of the ascending aorta and sutured with continuous 5.0 polypropylene, and the subsequent SV grafts were placed end-to-side to these SV grafts by means of 7.0 polypropylene sutures. After termination of cardiopulmonary bypass, the transverse incision in the axillary artery was closed with interrupted 5.0 polypropylene sutures.
Results
Surgical data of the 23 patients are presented in . [Table 2] Axillary artery cannulation was uncomplicated in all patients, and cardiopulmonary bypass flow with 2.4 L · min -1 · m -2 could be easily obtained. Deep hypothermia with circulatory arrest was used to construct one or two proximal ascending aortic anastomoses in 15 patients.
One patient had transient mild weakness and numbness of the right arm caused by brachial plexus alteration. No new major adverse cerebral complications, defined as stroke, transient ischemic attack, stupor, or coma, at time of hospital discharge were observed. Two patients had short episodes of confusion that were fully resolved at the time of discharge. No patient had evidence of visceral organ injury as a result of an atheroembolic event detected by clinical and laboratory findings. Furthermore, no evidence of atheroembolism of the extremities could be detected. An 84−year-old male patient with severe cerebrovascular disease, a history of two preoperative insults, and normal neurologic function developed seizures postoperatively that were easily controlled by phenytoin. Repetitive cerebral computer tomographic scans revealed no new cerebral ischemic areas in this patient, and his further postoperative course was uneventful, with no neurologic sequelae.
Comment
The significance of atheroemboli from severe atherosclerosis of the ascending aorta was highlighted by Mills and Everson [9] , who described an extraordinarily high incidence of stroke after cannulation and clamping of a severe atherosclerotic ascending aorta, with nine (45% [9 of 20]) cerebrovascular accidents and four fatal strokes in a series of 20 patients [9] .
On the basis of these findings, modifications of standard surgical techniques are mandatory in patients with severe atherosclerosis of the ascending aorta to avoid atheroemblism. In most proposed surgical modifications of the standard technique, the cannulation side is either the aortic arch or the femoral arteries [4] [7] [8] [9] [10] [11] [12] . However, coexisting aortic arch atherosclerosis is a problem, and cannulation of the aortic arch may result in atheroembolism [11] [14] . Culliford and coworkers [11] reported liberation of debris in 2 of 12 patients with severe atherosclerosis of the ascending aorta after cannulation of the distal ascending aorta or the aortic arch in an area thought to be free of atherosclerotic changes by palpation and observation. Therefore we believe that neither the ascending aorta nor the aortic arch should be touched if at all possible in patients with atherosclerosis of the ascending aorta. The high incidence of abdominal aortic and iliofemoral artery disease in patients with coronary artery disease can result in inability to cannulate the femoral arteries [6] [9] . Furthermore, retrograde blood flow through a diseased aorta carries a high risk of retrograde atheroemboli [15] [16] . An alternative site for arterial cannulation that avoids manipulation of the ascending aorta or aortic arch and provides antegrade blood flow is the axillary artery. Sabik and colleagues [13] demonstrated that axillary artery cannulation is an effective and safe technique of arterial cannulation for cardiopulmonary bypass in patients with severe atherosclerosis of the ascending aorta (n = 16).
In addition to arterial cannulation, clamping and declamping of a diseased aorta invites the risk of atheroemboli. Hypothermic circulatory arrest with endarterectomy, patch aortoplasty, or graft replacement of the ascending aorta may be an acceptable practice [4] [11] [17] . However, these demanding surgical modifications expose the patient to an extended surgical procedure with an overall increased perioperative risk. Proximal SV anastomoses end-to-side to the IMA graft [9] or sequential arterial anastomoses may be an option. Arterial revascularization with pedicled arterial grafts is an acceptable technique in some patients. Nevertheless, these techniques can result in incomplete revascularization or leaving the IMA as the sole source of blood supply with the potential risk of IMA hypoperfusion. Anastomosis of proximal SV grafts to the inominate artery has been discribed [8] . Involvement of the inominate artery in the atherosclerotic process of the ascending aorta is a common finding, with the potential risk of clamp injury and distal embolization. The prevalence of atherosclerotic plaques in the inominate artery varies between 21% and 30% in patients with severe atherosclerosis of the ascending aorta [5] [18] . In the present study, severe atherosclerosis of the inominate artery precluded partial clamping in 15 (65%) of 23 patients, and proximal SV anastomoses were performed during a short period of deep hypothermic circulatory arrest (7.3 ± 1.7 minutes) in a disease-free area of the ascending aorta. During circulatory arrest, the ascending aorta is gently palpated to identify possible noncalcified areas between heavy calcification for construction of proximal SV graft anastomoses [9] .
The present study focused on the severely calcified ascending aorta, which is easily diagnosed by palpation or chest x-ray film or during cineangiography. However palpation underestimates the incidence of severe ascending aortic atherosclerosis [4] . Significant atherosclerotic disease of the ascending aorta was detected by ultrasound scanning in 14% to 29% of patients undergoing cardiac operation [4] [5] . In such patients, the proposed technique may also be applied, with the potential to reduce the prevalence of perioperative atheroemboli associated with bypass grafting.
Although patients with porcelain aorta carry a high risk for atheroemboli, none of our patients had any clinical evidence of major adverse cerebral complications or visceral organ injury. We believe this result to be due to the modification in surgical management, which avoids manipulation of the ascending aorta. The simplicity and applicability of the technique presented, as well as the clinical results, are encouraging and justify this combined approach and should be added to the surgeon's armamentarium. However, prospective, randomized studies will be necessary to determine the best way to manage the diseased aorta during coronary artery bypass grafting.
References
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