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Ann Thorac Surg 2005;80:1679-1687
© 2005 The Society of Thoracic Surgeons
Division of Cardiac Surgery, Brigham and Women's Hospital, Boston, Massachusetts
Accepted for publication March 18, 2005.
* Address correspondence to Dr Aranki, Division of Cardiac Surgery, Brigham and Women's Hospital, 75 Francis St, Boston, MA 02115 (Email: saranki{at}partners.org).
Presented at the Forty-first Annual Meeting of The Society of Thoracic Surgeons, Tampa, FL, Jan 2426, 2005.
| Abstract |
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METHODS: From1998 to 2004, 70 patients who underwent aortic valve replacement had an aorta that was unclampable. Median age was 76 years; 33 (47%) were women; 46 (66%) had concomitant coronary artery bypass grafting; 9 (13%) had concomitant mitral valve surgery; and 4 (6%) were reoperations. Hypothermic circulatory arrest was used to replace the aortic valve alone, to do an aortic endarterectomy, or replace the ascending aorta with a tube graft.
RESULTS: Operative mortality was 4%. There were 8 (11%) strokes and 1 (1.4%) transient ischemic attack. Statistical analysis showed no association between circulatory arrest period and occurrence of adverse cerebral events. There was no significant difference among the three groups when operative mortality and cerebral events were compared.
CONCLUSIONS: Hypothermic circulatory arrest is an important adjunct that allows aortic valve replacement to be performed with an acceptable mortality but with an increased risk of cerebral event in this high-risk and elderly group of patients.
| Introduction |
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The challenges encountered in such situations are related to accurate diagnosis and optimal management, aimed at reducing adverse events related to atheroembolism. The availability of epiaortic ultrasound scanning can accurately map the diseased portion of the aorta and identify safe zones for cannulation and placement of proximal anastomoses. In addition, a surgical strategy can evolve for managing the diseased ascending aorta. These strategies include AVR under hypothermic circulatory arrest (HCA), local endarterectomy, or total replacement of the ascending aorta under HCA to allow for safe placement of a cross-clamp followed by AVR. The purpose of these three different strategies is to avoid any manipulation of the ascending aorta and thus avoid atheroembolism. Other options include cross-clamping the diseased ascending aorta with unknown and unpredictable consequences. A final option would be closing the sternum and not replacing the aortic valve with known natural history outcome in these symptomatic patients [49].
The purpose of this retrospective study is to analyze the results of different strategies of AVR and deep HCA in patients with an unclampable ascending aorta.
| Patients and Methods |
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Diagnosis of Atherosclerotic Disease
The presence of atherosclerotic disease of the ascending aorta is usually suspected on preoperative plain chest radiographs or noncontrast chest computed tomographic scan. Intraoperative transesophageal echocardiography may strongly suggest the presence of severe disease by detecting disease in the descending aorta and root of the aorta. Digital palpation may also be used intraoperatively. Most patients had epiaortic ultrasound scans. Clear cross-sectional and longitudinal views identified the location and extent of atherosclerotic disease. A disease-free site for cannulation was marked along with a suitable site for placement of a proximal anastomosis if a combined AVR and coronary artery bypass graft (CABG) operation was planned. The extent of the disease in the ascending aorta served as an accurate guide to the subsequent surgical strategy as follows:
If the disease was isolated to the distal ascending aorta with less disease in the proximal aorta, then AVR was performed under HCA (AVR group).
If the disease was confined to the site of the aortic cross-clamp, debridement or endarterectomy of this area under HCA was performed followed by cross-clamping and AVR during rewarming (aortic endarterectomy [AE] group).
If the disease extensively involved the proximal and distal ascending aorta above the sinotubular junction, the ascending aorta was replaced with a tube graft (TG) under HCA. The graft was clamped, and AVR was performed during rewarming (TG group). The remnant of the ascending aorta above the sinotubular junction often required debridement or endarterectomy to facilitate end-to-end anastomosis.
Cardiopulmonary Bypass
Aortic cannulation was the preferred site if a disease-free area was identified. Alternatively, the femoral or axillary arteries were used. The right atrium was cannulated directly. In reoperations or minimally invasive procedures (lower hemisternotomy or minithoracotomy), a common femoral percutaneous venous cannulation of the right atrium under transesophageal echocardiography guidance was used.
On cardiopulmonary bypass, the patient was cooled to the desired temperature depending on the anticipated period of total circulatory arrest. Because the aorta was not clamped during this period of cooling, no cardioplegia was given.
In the presence of significant aortic incompetence, cooling was conducted at a slower pace to allow the heart to continue beating for a much longer time and thus preventing premature onset of ventricular fibrillation and distention of the left ventricle. If distention occurred, a left ventricular vent and, if necessary, a pulmonary artery vent were used additionally to prevent potentially damaging distention during ventricular fibrillation. Usually a bolus of potassium or retrograde blood cardioplegia was given after the onset of ventricular fibrillation to achieve asystolic arrest and lower any risk of potential damage to the heart. Antegrade cardioplegia was given after the ascending aorta was opened during circulatory arrest and was delivered directly to the left and right coronary arteries and supplemented by means of the retrograde route as necessary.
If the axillary artery was cannulated, selective antegrade cerebral perfusion with systemic circulatory arrest was conducted if occlusion of the arch vessels appeared to be safe. Occasionally, retrograde cerebral perfusion was used before resuming circulation, to flush out any air or debris that may have embolized into the cerebral circulation.
Operative Procedure
For isolated AVR, the aorta was opened or transected on circulatory arrest with the patient in Trendelenburg position. The ascending aorta was opened obliquely, the aortic valve was exposed, the leaflets were resected, and the annulus and adjacent aortic wall were thoroughly debrided. The left ventricular cavity was washed with copious amounts of cold saline solution to flush out (by suction) any remaining calcific debris. The aortic valve was then replaced in a routine fashion. An endarterectomy of the edges of the aortotomy was often needed to facilitate closure of the aorta. While the patient was still in Trendelenburg position, circulation was restarted slowly, to expel air from the aorta. The aorta was then closed, and rewarming was initiated.
In cases with localized atheromatous disease of the cross-clamp site, the ascending aorta was transected or opened obliquely. The ascending aorta was inspected, and the site of the subsequent cross-clamp was carefully cleared by a combination of debridement and endarterectomy. Circulation was restarted slowly, expelling air from the ascending aorta. The endarterectomized aorta was cross-clamped. Full flow was resumed, rewarming started, and the aortic valve was replaced.
In cases with extensive disease, the ascending aorta was transected above the level of the sinotubular junction and just below the level of the innominate artery. Distal anastomosis between the appropriately sized Hemashield (Boston Scientific, Boston, MA) graft and the ascending aorta was performed in an end-to-end fashion. Localized endarterectomy of the distal anastomosis site was often required. Circulation was restarted slowly, expelling all air from the aortic arch and the TG. Aortic cross-clamp was applied to the graft. Full flow was resumed, and rewarming was started. The aortic valve was replaced, and the proximal anastomosis between the graft and the remnant of the ascending aorta was performed in an end-to-end fashion.
In combined CABG and AVR procedures, distal anastomoses were performed during the period of cooling. Right coronary and left anterior descending anastomoses were performed first to minimize lifting and distending the heart while the patient was relatively warm. Circumflex branch anastomoses were performed last when the temperature was much cooler, when cardiopulmonary flow could be safely reduced to minimize distention during lifting of the heart. Proximal anastomoses were performed after AVR and closure of the aorta while the clamp was still on. In cases of TG replacement, the proximal anastomoses were applied directly onto the TG.
In combined mitral valve surgery and AVR, mitral valve repair or replacement was done during the cooling phase. The field was often obscured with blood in the presence of aortic incompetence. Lowering the cardiopulmonary flow, which can be safely done at lower temperatures, reduced this. Alternatively, mitral valve surgery was performed after applying the cross-clamp in cases of AE or TG replacement, before replacing the aortic valve.
Statistics
Descriptive statistics are expressed as mean ± standard deviation. The
2 and the Fisher's exact test were used to compare discrete variables. These tests were chosen as they are distribution-free and nonparametric.
| Results |
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There was one (1.4%) transient ischemic attack in the total group, and this occurred in the TG group (2.2%). There were a total of eight cerebrovascular accidents (11%). The AVR group had two strokes (15%), the AE group had one (7.6%), and the TG group had five (11.3%). There was no significant difference in the rate of cerebrovascular accidents in the three groups studied (p = 0.874). There were not enough events in each group for transient ischemic attack and mortality to test for statistical significance, although the trend indicated that there was no difference. These results are further outlined in Table 4. Of the group, 21 patients were discharged home and 46 were discharged to a rehabilitation facility. Seven of the 8 patients with cerebrovascular accident were discharged to a rehabilitation facility. Types, severity, and outcomes after stroke are outlined in Table 5.
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| Comment |
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Atherosclerotic disease of the ascending aorta is becoming an increasing problem in the practice of adult cardiac surgery. It is a complex and difficult problem that warrants further studies and analysis. It is therefore important to determine the prevalence of this disease entity. An accurate tool for diagnosis needs to be established, and consequently the optimal management or operative strategy needs to be developed and reported. The ultimate aim would be to reduce predictably bad outcomes by altering surgical techniques. Everyone understands that these adverse outcomes will never be eliminated completely but can certainly be significantly reduced.
Prevalence
Blauth and colleagues [1] in their autopsy study of 221 patients found embolic disease in 31.2% of patients. They noted that atheroembolic events occurred in 37.4% of patients with atherosclerosis compared with 2% in patients without significant atherosclerosis of the ascending aorta; 16.3% had atheroembolic disease in the brain. They also noted that 95.8% of patients with atheroemboli had severe atherosclerosis of the ascending aorta. Barbut and associates [2] using transcranial Doppler to monitor embolic signals during CABG noted that 34% of all embolic signals were detected at removal of aortic cross-clamp, 24% during removal of partial occlusion clamps, and only 5% at initiation of bypass. Boivie and coworkers [3] in a perfusion model of 10 human cadaveric aortas showed that initial aortic cross-clamping was associated with a substantial release of particulate matter that had embolic potential. Of note, 9 of the 10 aortas had calcification seen on simple visual inspection. Wareing and colleagues [10] in their series had the lowest (1.1%) stroke rate in patients with mild atherosclerosis of the ascending aorta. Van der Linden and associates [11] had an incidence of 1.8% stroke in patients with a normal aorta compared with 8.7% in patients who had atherosclerotic disease in the ascending aorta documented by epiaortic scanning.
Amarenco and colleagues [12] in a study of 500 consecutive autopsies found the prevalence of ulcerated plaque in the aortic arch was 57.8% among patients with no known cause of cerebral infarction compared with 20.2% in patients with a predisposing cause (p < 0.001). Amarenco and coworkers [13] in a prospective study used transesophageal echocardiography to evaluate the ascending aorta. They found that plaques 4 mm or greater were found in 14.4% of patients admitted with ischemic stroke compared with 2% in control patients, and the odds ratio for ischemic stroke in patients with such plaque was 9.1%. The national cardiac surgery database [14] predicts an overall mortality of 4.3% for isolated AVR, 8.0% for AVR and CABG, and 18.8% for multiple valve and CABG. Cerebral complications remain the leading cause of morbidity and disability after cardiac operations. Goto and associates [15], in a prospective study of 463 patients older than 60 years of age undergoing CABG by a single surgeon, reported a stroke rate of 10.5% in patients with severe atherosclerosis compared with 1.8% in normal or near-normal control patients (p < 0.001). Okita and coworkers [16] in their series of atherosclerotic arch aneurysms had an operative mortality of 20% and stroke rate of 11% with 50% mortality in the stroke group. Kronzon and Tunick [17] in their review found that protruding atherosclerotic lesions of the thoracic aorta were an important cause of embolic stroke. Lev-Ran and colleagues [18] were able to demonstrate a significant decrease in stroke rate using a clampless technique in off-pump coronary artery bypass grafting (0% versus 5.3%; p = 0.04) in patients with a diseased ascending aorta.
Diagnosis
Preoperatively, often chest roentgenographic (Fig 1) and cardiac catheterization (Fig 3) images demonstrate the presence of atherosclerosis. When atherosclerosis is suspected, computed tomographic scanning (Fig 2) often helps determine the severity and extent of disease [19]. Intraoperative assessment of the severity of atherosclerosis is best achieved by epiaortic scanning [20, 21] and is superior to palpation of the aorta or transesophageal echocardiography in determining safe sites for cannulation and cross-clamping [22]. Murkin and associates [23, 24] have shown that epiaortic scanning of diseased aorta has altered surgical technique significantly and also significantly decreases cerebral embolic load during aortic instrumentation. Wareing and coworkers [25] in a series of 500 consecutive epiaortic scans showed that 13.6% had significant ascending aortic disease and that palpation identified disease only in 26% of these patients. Wilson and colleagues [26] prospectively compared transesophageal echocardiography with epiaortic scanning and found epiaortic scanning to be superior. Hangler and associates [27] in their prospective study of 352 patients undergoing CABG were able to, by use of epiaortic scanning, modify their surgical technique based on the severity of atherosclerosis. For moderate disease they used a single-clamp technique, and for severe disease they used nontouch technique and reported stroke rates of 3.0% and 8.8%, respectively. Thus, epiaortic scanning (Fig 4) now appears to be the gold standard in diagnosis of severity and location of ascending aortic atherosclerosis.
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In our series we used one of three strategies: (1) HCA for replacement of ascending aorta with a TG followed by clamping of the tube graft and AVR under cardiopulmonary bypass, with a mortality of 6.8% and stroke rate of 11.3%; (2) HCA for endarterectomy of the aorta followed by clamping for AVR, with a mortality of 0% and stroke rate of 7.6%; or (3) HCA for AVR, with a mortality rate of 0% and stroke rate of 15%. Our overall mortality was 4.25%, and stroke rate was 11.4%.
Conclusions
Diffuse atherosclerotic disease of the aorta is becoming increasingly common as the population ages and the imaging modalities for its detection improves. Hypothermic circulatory arrest is an important adjunct that allows AVR to be performed with an acceptable mortality but with an increased risk of cerebral event in this high-risk and elderly group of patients. Routine use of epiaortic ultrasound scanning is, and should become, the standard of care. Aortic cannulation, when feasible, or axillary cannulation is the preferred route of cannulation, as most of these patients have diffuse disease of the descending aorta and are at high risk of retrograde embolization. Axillary artery cannulation is increasingly used as this further decreases the need for any aortic manipulation before circulatory arrest, and allows for selective antegrade cerebral perfusion during systemic circulatory arrest. The use of special filter devices to capture particulate matter is under investigation [36] and may further decrease cerebrovascular events.
| Discussion |
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DR NATHAN: Any presence of diffuse posterior plaque or a porcelain aorta or the presence of soft atheromatous plaque always made us choose the option of hypothermic circulatory arrest.
DR RANDALL B. GRIEPP (New York, NY): This is an impressive series with great results with regard to mortality, but there still is a significant incidence of stroke. Obviously the clamp is one thing to worry about, but the cannulation site is another. I assume most of these patients were cannulated somewhere other than the ascending aorta, and I rise to ask you about your experience with axillary cannulation, and, on the basis of our experience, to state that the use of axillary cannulation will itself have a significant beneficial effect on the incidence of stroke in these patients. Can you tell us how these patients were cannulated?
DR NATHAN: In our series, at least in the early group, the majority of patients did have cannulation at a soft spot in the aorta. In our later group of patients we have used axillary cannulation. The use of the epiaortic scan has helped us locate a site for safe cannulation of the aorta.
DR GREG RIBAKOVE (New York, NY): Congratulations on your series. I would just like to suggest one other alternative you didn't mention.
The calcified aorta and the atheroschlerotic aorta are two different disease processes that may occur together, but often do not. The calcified aorta can be handled in a different way. If your epiaortic echo does not show soft atheroma with mobile components, for example, I am wondering if in those cases you are still using hypothermic circulatory arrest? Our choice for the purely calcified aorta would be to go on cardiopulmonary bypass and then, rather than clamping the aorta externally, place a balloon as an internal clamp. The procedure can then be performed in the usual manner without the need for prolonged circulatory arrest.
DR NATHAN: In our institution we have not used the balloon for internal occlusion. In the cases of calcific aorta we have a choice of procedures, again, hypothermic circulatory arrest, depending on the extent of calcification, to either replace the ascending aorta or just do a limited endarterectomy or to replace the aortic valve.
| References |
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