Asian Cardiovasc Thorac Ann 2007;15:118-122
© 2007 Asia Publishing EXchange Ltd
Subclavian Cannulation Improves Outcome of Surgery for Type A Aortic Dissection
Seyed M Nouraei, FRCS,
SA Reza Nouraei, MBBChir1,
Anand K Sadashiva, MBBS,
Thasee Pillay, FRCS
Regional Cardiothoracic Centre, Freeman Hospital, Newcastle upon Tyne
1 Department of Otolaryngology, Charing Cross Hospital, London, United Kingdom
For reprint information contact: Seyed M Nouraei, FRCS Tel: 44 191 284 7081 Fax: 44 870 458 0775 Email: SMNouraei{at}yahoo.co.uk, 6 Finstock Court, Newcastle upon Tyne, NE3 1TR, United Kingdom.
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ABSTRACT
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Acute type A aortic dissection is a major emergency that continues to cause significant morbidity and mortality. Given the anatomy of the lesion, different circulatory configurations achieved during cardiopulmonary bypass using different arterial inflow sites can influence outcome. Patients who had subclavian artery cannulation were compared with those who had femoral artery cannulation. Forty-nine consecutive patients (mean age, 60 ± 14 years) undergoing emergency surgery for acute type A aortic dissection between 1999 and 2004 were reviewed. Data on presentation, preoperative characteristics, operative details, hospital mortality, and neurological outcome were analyzed. Twenty-nine patients had femoral artery cannulation, and 20 had subclavian artery cannulation. The groups were comparable in terms of preoperative characteristics. The mean follow-up was 29 months. Subclavian artery cannulation conferred significant advantages in respect of hospital death (10% vs. 44%) and neurological impairment. Significantly fewer patients required re-operation following subclavian artery cannulation.
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INTRODUCTION
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Acute type A dissection of the thoracic aorta is a challenging surgical emergency, which, despite major advances in diagnosis, surgical technique, and postoperative care, continues to be associated with significant morbidity and mortality.1 The femoral artery has been a common cannulation site for instituting cardiopulmonary bypass (CPB) in this setting, but the resulting circulatory configuration with retrograde perfusion through the diseased aorta can potentially elevate a flail intimal flap resulting in hypoperfusion, or cause particulate embolization leading to visceral or neurological injury. The vascular configuration achieved by cannulating the right subclavian artery on the other hand theoretically avoids these problems, and evidence is accumulating to suggest that its selection can improve the surgical outcome.2–6 In this study, we reviewed our experience with the surgical management of acute type A aortic dissection, particularly in respect of our increasing use of subclavian artery cannulation to establish CPB.
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PATIENTS AND METHODS
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Records of all 49 patients undergoing surgery for acute type A dissection of the thoracic aorta between 1999 and 2004 at our institution were reviewed. Information about patient referral, clinical presentation, diagnostic work-up, diagnosis-to-treatment times, details of surgery, postoperative morbidity, and outcome were obtained from clinical and operating records. There were 37 males and 12 females, and details of their demographics and preoperative characteristics are provided in Table 1
. All patients had a preoperative chest radiograph, just over half had a chest computed tomogram, 20 had an echocardiogram, and 7 had preoperative angiography. The diagnosis-to-operation time was 1.3 days (range, 0–4 days), and all patients were operated on within 6 hr of transfer to our institution. Thirty eight operations were performed as emergency procedures, whereas 11 were classed as salvage procedures on patients with significant hemodynamic instability, including during cardiopulmonary resuscitation.
All operations were carried out via the median sternotomy approach. Cardiopulmonary bypass was achieved using femoral artery cannulation in 29 patients and subclavian artery cannulation in 20. For subclavian artery cannulation, a transverse incision was made 2 cm below the right clavicle. Pectoralis major fibers were split and the muscle was retracted along with the pectoralis minor to expose the neurovascular bundle. The artery was dissected with no manipulation of the brachial plexus. A 10-mm Dacron graft was anastomosed end-to-side to the subclavian artery with a continuous 6/0 Prolene suture, and the graft was cannulated. A 2-stage venous cannula was inserted into the right atrium, and CPB was instituted at a flow rate of 2.2–2.5 L·min–1·m–2. The left ventricle was vented via the right superior pulmonary vein. Anticoagulation was achieved with intravenous heparin. Systemic cooling was started and body temperature was monitored with an esophageal temperature probe. The ascending aorta was cross clamped, opened longitudinally, and blood cardioplegic solution was introduced directly into the coronary ostia (10–15 mL·kg–1), and supplemented every 20 min. Additional myocardial protection was achieved using topical cold saline around the heart. The ascending aorta was transected and the coronary ostia and the aortic valve were examined. If these were intact, a supracoronary interposition graft was constructed using a collagen pretreated graft. If the coronary ostia were involved, aortic root replacement with coronary re-implantation, with or without replacement of the aortic valve, was undertaken. When the proximal repair was completed, deep hypothermic circulatory arrest at 18°C was instituted, and the aortic clamp was released. Further cerebral protection was achieved with local ice-pack cooling around the head and retrograde cerebral perfusion via the superior vena cava. Cerebral temperature was monitored using a nasal temperature probe. The distal aorta was assessed and reinforced with Teflon and fibrin glue, and an open anastomosis to the distal aortic stump was fashioned. The aortic cannula was repositioned in the ascending aortic graft and after de-airing, CPB with patient rewarming was commenced. After rewarming and de-airing of the heart, the cross clamp was released and the cannulas were removed. Heparin was reversed with protamine. Hemostasis was secured and the chest was closed in the routine manner over mediastinal and pericardial drains.
The aortic arch vessels were involved in 6 patients; in these cases, the distal anastomosis was performed beyond the arch under deep hypothermic circulatory arrest, and the neck vessels were excised from the superior surface of the dissected aorta as a unit, reinforced with Teflon felt and fibrin glue, and then anastomosed to the graft using continuous 4/0 Prolene suture. Cerebral cooling and selective antegrade cerebral perfusion were used for neuroprotection during this period. Cardiopulmonary bypass was re-instituted through the graft and the proximal repair was then performed using a separate graft in the manner described above. The two grafts were anastomosed. Patients in the subclavian and femoral cannulation groups were comparable in terms of the nature and extent of surgery performed. Further details of surgical treatment are provided in Table 2.
Data are presented either as means with standard deviations or as percentages when appropriate. The impact of different pre- and perioperative variables on hospital death or development of a neurological deficit was assessed using the chi-squared test. Stepwise logistic regression analysis was used to identify independent predictors of hospital death or neurological deficit. Data were analyzed using SPSS release 12 for Windows (SPSS, Inc., Chicago, IL, USA)
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RESULTS
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There were no significant differences in the preoperative characteristics of the patients in the two groups. In particular, the proportion of patients undergoing urgent or salvage surgery was not significantly different between the groups ( p = 0.16). There was no significant difference in the number of patients requiring aortic arch reconstruction in each group ( p > 0.9). The postoperative ventilation time was 159 ± 351 hr (range, 0–1,320 hr) and 17 patients required a tracheostomy. Intensive care unit stay was 9 ± 14 days (range, 1–63 days) and the mean length of hospitalization was 20 ± 20 days (range, 0–72 days). There were no significant differences between the subclavian and femoral artery groups in respect of these times. Eighteen patients required re-operation, mainly to control bleeding, and 7 developed renal failure in the postoperative period. There were no cases of brachial plexus injury, subclavian artery dissection or thrombosis, and no wound infections at the subclavian artery cannulation sites. The incidence of re-operation following subclavian artery cannulation was significantly lower compared with the femoral group (odds ratio 1.7; 95% confidence interval 1.08–2.8; p < 0.05).
Fifteen patients (31%) developed a neurological deficit in the postoperative period. Univariate analysis revealed significant associations between operative urgency (emergency vs. salvage), preoperative New York Heart Association class III or IV, the need for re-operation, and selection of the femoral artery as the cannulation site as significant predictors of a neurological deficit. Femoral cannulation was however the only factor remaining statistically significant on multivariate stepwise logistic regression analysis (Table 3).
The overall hospital mortality rate was 31%. The mortality rate was 15% in patients who had undergone an urgent procedure, rising to over 80% in cases of salvage surgery. Subclavian artery cannulation conferred significant advantages in respect of hospital death (10% vs. 44%). Univariate analysis identified salvage surgery, the need for re-operation, development of a postoperative neurological deficit, and femoral cannulation as significant predictors of hospital death. Factors remaining significant on multivariate stepwise logistic regression analysis were salvage surgery and a postoperative neurological deficit (Table 3
). The mean patient follow-up was 29 months (range, 0–75 months). Most deaths occurred in the hospital, with 3 due to cardiovascular disease following discharge. Actuarial patient survival is shown in Figure 1.
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DISCUSSION
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Our study shows that in the setting of acute type A aortic dissection, cannulation of the subclavian artery improves the neurological outcome and reduces the re-operation rate and hospital mortality. An excellent account of the different approaches to subclavian artery cannulation has been provided by Pasic and colleagues.3 This technique, having been originally described but seldom used for the management of acute aortic dissection, was later popularized for elective cardiac surgery in patients with extensive atherosclerosis of the aorta and peripheral vasculature, and has recently gained popularity over femoral artery cannulation for the institution of CPB in patients with acute type A aortic dissection.3–7
The major appeal of this technique is the favorable circulatory configuration it achieves during CPB, because ensuring blood flow through the true lumen is of vital importance in managing patients with an acute type A aortic dissection.3 Femoral artery cannulation leads to retrograde blood flow over a dissected and potentially flail intimal flap. Blood may be directed into the false lumen, causing further intimal injury. Van Arsdell and colleagues8 showed in their study of over 50 autopsies following type A aortic dissection that retrograde perfusion was associated with a 24% incidence of a second intimal injury. Retrograde blood flow through the false lumen can also expand it, compressing the ostia of the major visceral and cranial vessels, leading to end-organ hypoperfusion. It can also encourage particulate embolization with embolic visceral and cranial injury.4,6 On the other hand, given that a type A aortic dissection seldom extends beyond the brachiocephalic artery, subclavian artery cannulation almost always leads to antegrade aortic perfusion and decompression of the false lumen, resulting in the resolution of distal hypoperfusion in over 90% of patients.9,10
Our data show that rates of hospital mortality, postoperative neurological deficit, and re-operation fell significantly with subclavian artery cannulation. These findings are consistent with the experiences of other institutions.1–4,6 We have found the technique to be simple and safe to apply even in the setting of a major emergency. This was made possible however because initial experience was gained with this technique in elective surgery. Subclavian artery cannulation is becoming more widely used for arterial cannulation in patients with calcified ascending aorta and aortic arch undergoing CPB, and there is little doubt that familiarity gained with the technique in elective settings can be gainfully applied to the management of this major emergency.5 We encountered no problems with brachial plexus injury or wound infections, the latter also being an advantage over a groin incision.
The main limitation of our study, and indeed other studies addressing this issue, is that it was observational, as many institutions have switched their practice from femoral to subclavian artery cannulation at some point in the past. Although we found no major differences in the pre- and perioperative characteristics of the patients in the two groups, potential selection bias arising from the non-randomized design of the study remains. To our knowledge however, no randomized controlled trials comparing subclavian with femoral cannulation in managing acute type A aortic dissection have been conducted. Such a study would be a major multicenter undertaking, and would be confounded by the fact that many surgeons now consider subclavian artery cannulation the standard of care in the management of acute type A aortic dissection and may object to their patients being randomized to receive femoral artery cannulation. It is therefore important for the experiences of different institutions to be shared to inform clinical practice, and to form a body of literature for a future meta-analysis.
In conclusion, we recommend subclavian artery cannulation as an effective method of improving the outcome of type A aortic dissection surgery.
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REFERENCES
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ABSTRACT
INTRODUCTION
