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Ann Thorac Surg 2002;74:1058-1065
© 2002 The Society of Thoracic Surgeons
a Department of Cardiothoracic and Vascular Surgery, The University of Texas at Houston Medical School, Memorial Hermann Hospital, Houston, Texas, USA
* Address reprint requests to Dr. Safi, Department of Cardiothoracic and Vascular Surgery, The University of Texas at Houston Medical School, UTH Medical Center, 6410 Fannin St, Suite 450, Houston, TX 77030 USA
e-mail: hazim.j.safi{at}uth.tmc.edu
Presented at the Forty-eighth Annual Meeting of the Southern Thoracic Surgical Association, San Antonio, TX, Nov 810, 2001.
| Abstract |
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Methods. Between January 1991 and May 2001, we repaired 423 aneurysms of the ascending aorta or aortic arch using profound hypothermic circulatory arrest. Median age was 65 years. Retrograde cerebral perfusion (RCP) was used in 357 cases. Mean pump and RCP times were 139 and 33.9 minutes, respectively. Survival was ascertained by direct patient contact or by searching the social security death index. Survival was analyzed by Kaplan-Meier stratified analysis and by multivariate Cox regression.
Results. Overall actuarial survival was 72% at 5 years and 71% at 10 years after surgery. Univariate analysis identified increasing age (p < 0.0001), chronic obstructive pulmonary disease (p < 0.014), concurrent unoperated aneurysm (p < 0.005), arch involvement (p < 0.042), pump time (p < 0.0004), concurrent aortic valve replacement (p < 0.009), and postoperative renal failure (p < 0.0002) as factors that negatively influenced survival. Multivariate analysis identified increasing age (p < 0.0001) and pump time (p < 0.0001). RCP did not have a significant independent effect on the long-term survival.
Conclusions. Our experience indicates that repair of the ascending aorta and aortic arch can be accomplished with good long-term survival.
| Introduction |
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Because perioperative neurologic complications often lead to early mortality, cerebral protection is of paramount importance. By 1975, profound hypothermic circulatory arrest (PHCA) had become the mainstay for repairs of the aortic arch in adult patients [1]. Techniques to augment cerebral protection soon included the use of retrograde cerebral perfusion (RCP) and selective antegrade cerebral perfusion (ACP) [25]. Other important operative techniques that played a role in improved patient outcome included open distal anastomosis, root reconstruction, reattachment of the coronary arteries during root reconstruction, valve preservation, and the elephant trunk technique for extensive aortic aneurysms [610]. Long-term survival since the implementation of modern techniques has been favorable [1114]. The purpose of this study was to examine our contemporary experience of repairs involving the ascending and transverse aortic arch utilizing PHCA and RCP in order to determine the factors that influence long-term survival.
| Material and methods |
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Outcome variables
Preoperative factors analyzed included age, gender, history of chronic obstructive pulmonary disease, history of cerebrovascular disease, hypertension, rupture, and renal insufficiency. Operative factors analyzed were PHCA, RCP, associated aortic valve replacement, transverse arch involvement, aortic cross-clamp time, and cardiopulmonary bypass time. Postoperative factors analyzed included renal failure, reoperation for bleeding, stroke, myocardial infarction, and pulmonary failure requiring tracheostomy (Table 2).
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Indications for operation included aneurysmal dilatation of greater than 5.0 cm for non-Marfan patients, aneurysmal dilatation of greater than 4.5 cm for patients with Marfan syndrome, or the presence of acute type A dissection. Other indications included infection/fistula formation (three cases) and symptomatic atheromatous ascending aorta/transverse arch (five cases).
Operative mortality refers to deaths that occurred within 30 days of surgery. Actuarial survival was determined at 5 and 10 years for each of the factors analyzed. Chronic obstructive pulmonary disease was defined by a history of chronic bronchitis and emphysema, or <60% of predicted forced expired volume in one second (FEV1). A serum creatinine level of greater than 2.0 mg/dL or the need for dialysis defined renal dysfunction. Rupture included both free and contained rupture. Definitions of other aneurysm, previous aneurysm, and reoperation are noted in Table 2. Repairs involving dissection were considered acute if surgery was performed in less than 14 days from the onset of pain, and chronic if after 14 days. Cerebrovascular disease was defined by history of cerebrovascular accident or intervention for carotid artery disease. Cerebrovascular accidents were identified by a thorough neurologic examination and confirmed by computed tomographic (CT) scan or magnetic resonance imaging of the head.
Operative procedure
Operations varied depending on the etiology of disease, but the basic features of our current technique for acute dissection or aneurysm of the distal ascending or transverse aortic arch include cardiopulmonary bypass, profound hypothermia, circulatory arrest, and retrograde cerebral perfusion.
Cardiopulmonary bypass is established after exposure of the right common femoral artery and vein. The chest is entered by median sternotomy. The superior vena cava is cannulated via the right atrium and snares are applied to both the inferior and superior vena cava. Systemic cooling is initiated and the patients temperature is monitored using both a nasopharyngeal and rectal temperature probe. Myocardial protection is achieved using continuous retrograde cold blood cardioplegia through the coronary sinus, supplemented with direct antegrade coronary ostia infusion once the aorta is opened. A left ventricular sump is inserted through the right superior pulmonary vein. If coronary artery bypass is required, it is performed during the cooling period once the heart is arrested.
A 10-lead electroencephalogram (EEG) monitors cerebral function, and a near-infrared spectroscopy unit continuously monitors cerebral oxygenation. Once the EEG is isoelectric, which coincides with a nasopharyngeal temperature of 15°C to 20°C, cardiopulmonary bypass is discontinued and circulation is arrested. Retrograde cerebral perfusion is begun through the superior vena cava cannula. In the past, we used a conventional flow rate of 500 mL/min in the RCP circuit and kept superior vena cava line pressure below 25 mm Hg. We now utilize transcranial Doppler (TCD) to directly monitor cerebral flow in both middle cerebral arteries. TCD identifies any reversal of flow during RCP and provides a guide for optimal RCP flow.
Circulatory arrest is utilized for aneurysms that originate in the mid-to-distal ascending aorta and for all dissections. This permits complete resection of the diseased aorta and an open distal anastomosis. For the ascending and arch portions of extensive aortic aneurysms, we perform the first stage of the elephant trunk technique [15] (Fig 1A, 1B). In the case of a severely atheromatous descending thoracic aorta, we often modify the elephant trunk procedure by placing a separate Dacron tube graft into the proximal descending thoracic aorta and reconstructing a beveled transverse arch. In the case of total arch replacement, the great vessels (innominate, left common carotid, and subclavian arteries) are reattached as an island to the graft. If the great vessels are aneurysmal, they are replaced by separate bypass grafts.
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Data analysis
Data were collected from chart reviews done by a trained nurse abstractor, and were entered into a dedicated Microsoft Access database. Data were exported to SAS for analysis, and all computations were performed using SAS version 6.12 running under Windows 2000. Patients were followed until death or until follow-up reached the study end date (August 31, 2001). Surviving patients were right-censored from the denominator when their maximum follow-up time was reached or on the date they were lost to follow-up. Univariate risk factor effects on survival were evaluated using the product-limit method of Kaplan and Meier. Continuous variables were stratified by quartile. Hypothesis tests of homogeneity over strata were computed using the log-rank test. Adjusted effects of risk factors on survival were evaluated using Cox proportional-hazards regression analysis, using stepwise and best-subsets model selection techniques. Continuous variables were left continuous for the Cox analyses. The null hypothesis was rejected at p < 0.05.
| Results |
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Multivariable analysis demonstrated that the independent predictors of decreased long-term survival were older age (p = 0.0001), cardiopulmonary bypass time (p < 0.0001), and concurrent aortic valve replacement (p > 0.008) (Table 3). Figures 3, 4, and 5 illustrate the Kaplan-Meier curves for long-term survival with regard to age, pump time, and concurrent aortic valve replacement, respectively.
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| Comment |
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Crawford and associates observed that factors independently associated with decreased long-term outcome included aneurysm symptoms, angina, the extent of proximal replacement, concurrent unoperated aneurysm, cardiac dysfunction, stroke, and renal dysfunction [11]. Other studies have also included age, Marfan syndrome, and acute or chronic dissection as factors that negatively influence long-term survival [14, 18, 19].
In this study, consistent with previous findings, univariate analysis revealed that age, chronic obstructive pulmonary disease, renal dysfunction, concurrent aneurysm, and transverse arch involvement were associated with decreased long-term survival [11]. Also similar to previous reports, concurrent unoperated aneurysms and transverse arch involvement were associated with decreased long-term survival [11]. The influence of increasing age as a risk factor for early and late mortality has been examined previously and corroborates the findings in this study [5, 20]. Decreased survival was observed at 65 years, with the most significant decrease after 73 years. Although the effect of prolonged cardiopulmonary bypass time has been associated with increased early mortality [20], in this study, the cause for an association with decreased long-term survival was unclear.
It was not surprising that the aortic valve replacement was associated with decreased long-term survival. It has been reported that isolated aortic valve replacement and aortic valve replacement in conjunction with ascending repairs are associated with decreased long-term survival [17, 21].
Interestingly, neither Marfan syndrome nor the presence of dissection (acute or chronic) affected long-term outcome. This may be attributed to close follow-up for patients with these conditions. Any abnormalities identified during the follow-up period are then addressed immediately.
As demonstrated in this study, the use of RCP during PHCA was associated with a significant decrease in the incidence of cerebrovascular accidents (1.1% with RCP vs 7.6% without RCP, p < 0.008). Based on our experience, we prefer RCP to antegrade perfusion due to the simplicity of setup and the reduction of clutter in the operative field. We also believe that RCP provides uniform cerebral cooling, prevents embolic injury by flushing of atheromatous debris in a retrograde fashion, and may provide nutrient flow.
Whereas some authors argue that RCP provides minimal to no cerebral perfusion and thus affords only minimal cerebral protection [2225], we have recently begun to use TCD to identify and monitor RCP. One advantage of TCD is the detection of adequate RCP flow, by identification of flow reversal in the middle cerebral arteries [26, 27]. Previously, cerebral venous pressure during RCP was monitored by measuring internal jugular venous pressure and kept below 25 mm Hg to prevent cerebral edema, independent of the patient characteristics or pump flow [3]. With TCD monitoring, we have observed that a pressure of 25 mm Hg may not always provide sufficient RCP, and that higher flow rates may be required. Researchers using TCD have noted that a higher starting pressure may be required to achieve adequate flow in antegrade perfusion [26]. Similarly, we have observed that a higher starting pressure is sometimes required to reach optimal retrograde cerebral flow. The clinical significance of TCD for RCP monitoring is under current investigation.
Limitations of this study include its retrospective nature. Gross neurologic dysfunction is easily identified as the occurrence of stroke, but the incidence of temporary neurologic dysfunction (TND) or transient neurocognitive deficits was not evaluated. Temporary neurologic dysfunction may be accountable for significant long-term disability and thus may influence survival [20, 24]. Although we currently use RCP and support its use in conjunction with profound hypothermic circulatory arrest during arch repair, a prospective, randomized, controlled investigation will be necessary to identify the ideal adjunct for cerebral protection in relation to stroke and TND.
This report presents the results of a contemporary series of patients who underwent repair of the ascending and transverse aortic arch, using a consistent operative strategy. Repairs of the ascending and transverse aortic arch for aneurysm or dissection that include profound hypothermic circulatory arrest and retrograde cerebral perfusion for transverse aortic arch involvement provide good intermediate and long-term survival. Ongoing follow-up is necessary for all patients who undergo repair. Although repair of the ascending aorta and transverse aortic arch can be performed on older patients, careful selection should be assumed.
| Acknowledgments |
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| Discussion |
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My second question relates to acute dissections. Dr Moon and I have been interested in the impact of hemiarch replacement on the need for reoperations on the arch. I wonder if you have looked at the subgroup of your patients who had acute DeBakey Type I dissections, and compared the event-free survival of those who had a hemiarch replacement with those who did not.
Once again, a remarkable series. Thank you for presenting it to us at the Southern Thoracic Association.
DR ESTRERA: Thank you for the comments and questions. In terms of pseudoaneurysm formation, we do follow all our patients with serial CT scans; the frequency of how often we obtain CT scans depends on the etiology of the disease. For example, patients with aortic dissection will initially be monitored on a quarterly basis for the first year after diagnosis, and after the first year, if the aorta is stable, this can be extended to an annual exam. In regards to our incidence of pseudoaneurysm formation, I do not know its exact incidence, but we do not see it often.
In regards to acute type A aortic dissection, we are currently analyzing these data, and it has been our observation that replacement of the hemiarch does not increase morbidity or mortality. In this report, we did observe that patients who had total transverse aortic arch replacement, in general, had decreased long-term survival. This is consistent with Dr Safis philosophy about replacing the entire transverse arch after acute type A aortic dissection. If at all possible, we avoid replacing the entire transverse aortic arch since we feel it does decrease both immediate and long-term survival. Our aim with type A aortic dissection is to ultimately convert it to a type B aortic dissection by replacing the ascending aorta and/or hemiarch only. We will replace the transverse arch, however, if there is a large hematoma, extensive intimal disruption of the arch, or free rupture in the arch. Again, we are currently analyzing our experience over the past 10 years with type A aortic dissection.
| References |
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