Ann Thorac Surg 2006;82:579-585
© 2006 The Society of Thoracic Surgeons
Original article: Cardiovascular
Short-Term and Intermediate-Term Outcomes of Aortic Root Replacement with St. Jude Mechanical Conduits and Aortic Allografts
Brian Lima, MD,
G. Chad Hughes, MD,
Anthony Lemaire, MD,
James Jaggers, MD,
Donald D. Glower, MD,
Walter G. Wolfe, MD*
Division of Cardiovascular and Thoracic Surgery, Department of Surgery, Duke University Medical Center, Durham, North Carolina
Accepted for publication March 21, 2006.
* Address correspondence to Dr Wolfe, Division of Cardiovascular and Thoracic Surgery, Department of Surgery, Duke University Medical Center, DUMC Box 3507, Durham, NC 27710 (Email: wolfe001{at}mc.duke.edu).
Presented at the Fifty-second Annual Meeting of the Southern Thoracic Surgical Association, Orlando, FL, Nov 10–12, 2005.
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Abstract
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BACKGROUND: Few studies have directly evaluated outcomes in patients undergoing aortic root replacement with St. Jude mechanical conduits or aortic allografts (ALLO), yet both approaches have been advocated. The purpose of this study was to provide a detailed description of outcomes in a large series of aortic root replacements performed with either St. Jude mechanical conduits or aortic allografts.
METHODS: A retrospective analysis was performed on 172 consecutive adult patients undergoing aortic root replacement with either St. Jude mechanical conduits (n = 73) or aortic allografts (n = 99) from January 1990 to December 2002. Maximal follow-up was 15 years, and median follow-up was 5 years.
RESULTS: Both groups were similar with regard to median age, preoperative ejection fraction, and New York Heart Association class. The aortic allograft patient group had a higher proportion (p < 0.05) of women (43% versus 18%), prior sternotomies (52% versus 26%), preoperative renal failure (9% versus 1%), and cerebrovascular disease (16% versus 4%). Operative indications for the aortic allograft group were more frequently endocarditis (29% versus 3%; p < 0.0001) and prosthetic valve dysfunction (13% versus 1%; p < 0.01), and less frequently annuloaortic ectasia (34% versus 60%; p < 0.001) or aortic dissection (3% versus 26%; p < 0.0001). Concomitant coronary artery bypass grafting or other valve surgery was performed in 30% of patients in both groups. Incidence of early postoperative complications, including bleeding, stroke, renal failure, and respiratory failure, was similar in both groups. Thirty-day mortality was 5.5% in the St. Jude mechanical conduit group and 8.1% in the aortic allograft group (p = 0.4). Unadjusted actuarial survival at 1, 5, and 10 years was 90%, 81%, 67%, and 86%, 70%, 67%, for the St. Jude mechanical conduit and aortic allograft groups, respectively (p = 0.09). Event-free survival at 1 and 5 years was similar for both groups (p = 0.4). By multivariate analysis, New York Heart Association class III or IV, emergently performed aortic root replacement, and postoperative respiratory failure, but not valve conduit type (p = 0.3), were independent predictors of mortality.
CONCLUSIONS: Aortic root replacement can be safely performed with either allograft or mechanical conduits, even in the setting of acute dissection, redo sternotomy, or endocarditis.
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Introduction
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Aortic root replacement is the preferred management strategy for the treatment of complex aortic root pathologic disease, owing to annuloaortic ectasia, native and prosthetic valve endocarditis, or dissection [1]. Some even advocate aortic root replacement for aortic valve replacement in the presence of a normal aortic root [2, 3]. Since the introduction of the original Bentall procedure in 1968 [4], aortic root replacement has undergone several modifications and adaptations, including the introduction of various mechanical valve conduit prototypes, aortic allografts [5, 6], aortic valve-sparing approaches [7, 8], and more recently, stentless porcine bioprostheses [9–11]. Selection of the most suitable prosthesis or surgical approach for aortic root replacement in any given patient is not straightforward and remains controversial, requiring careful consideration of patient comorbidities, life expectancy, surgeon preference, device availability, and nature of the aortic root disease itself. To date, no randomized controlled trials comparing biologic versus mechanical aortic root replacement have been performed, with only a select few retrospective reviews of institutional outcomes contrasting these approaches [12]. These latter studies also frequently include heterogeneous groupings of aortic allografts and stentless porcine bioprostheses in the biologic category and various prosthetic types in the mechanical category.
The purpose of this retrospective review was to evaluate short-term and intermediate-term outcomes of aortic root replacement in a broad spectrum of diverse patients receiving St. Jude mechanical valve conduits (MECH) or aortic allografts (ALLO), representative of real-life surgical practice. This simplified analysis might determine whether aortic root replacement performed with either conduit type in the appropriate setting would yield equivalent overall and event-free survival. In addition, this study may also identify important patient or perioperative characteristics that may be predictive of survival.
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Patients and Methods
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This series consisted of 172 consecutive adult patients undergoing aortic root replacement from January 1, 1990, through December 31, 2002, at Duke University Medical Center using either a St. Jude mechanical valve conduit (MECH, n = 73) or aortic allograft (ALLO, n = 99). The study was reviewed and approved by the Institutional Review Board of Duke University on March 17, 2003. Individual patient consent was waived. Morbidity and mortality outcomes are based on data to February 2005. Survival data was obtained through the National Death Index. Deaths from all causes were included in the survival analyses. Morbidity follow-up was collected by means of direct telephone contact with patients. Maximal follow-up was 15 years, and median follow-up was 5 years.
The operative technique for MECH and ALLO aortic root replacement has been described extensively in previous studies [5, 12]. Briefly, the aortic root was replaced with a MECH or ALLO conduit, using either interrupted or running suture technique. Coronary artery buttons were subsequently implanted to the conduit. No valve-sparing procedures are included in this series. Myocardial protection was achieved with cardioplegia during standard hypothermic cardiopulmonary bypass. Patients undergoing concurrent procedures were not excluded. This series includes patients who underwent aortic root replacement on both elective and emergent operative conditions.
Preoperative patient characteristics were reported as percentages for discrete variables and compared using 
2 tests. Cumulative survival as a function of time after the date of surgery was generated by using the Kaplan–Meier method. Equivalence of long-term mortality between MECH and ALLO survival curves was evaluated by the log-rank (Peto) test. The Cox proportional hazards model was used to examine both univariate and multivariate relationships between baseline characteristics and mortality by using stepwise forward and backward selection of candidate variables at an 
value of 0.05. Adverse postoperative events were documented and analyzed according to the previously published guidelines for reporting morbidity and mortality after cardiac valvular operations [13]. Documentation of these adverse events was used to generate unadjusted event-free survival curves.
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Results
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Preoperative patient characteristics are summarized in Table 1. The mean age was similar between the MECH and ALLO groups. There was a significantly higher proportion of women in the ALLO (43%) versus the MECH group (25%). A higher proportion of patients in the ALLO group also had prior cardiac surgery. Both groups had similar preoperative ejection fraction and shared similar preoperative comorbidities or risk factors, including hypertension, smoking, chronic obstructive pulmonary disease, diabetes mellitus, peripheral vascular disease, and prior myocardial infarction. The ALLO group did, however, have a higher degree of preoperative renal failure, Marfan syndrome, and cerebrovascular disease. Operative indications for aortic root replacement differed significantly for each of the two groups, with MECH aortic root replacement having been performed more frequently for annuloaortic ectasia, aortic dissection, and ascending aortic aneurysm, and ALLO aortic root replacement performed more commonly for endocarditis and prosthetic valve dysfunction.
Aortic root replacement was performed emergently in a similar subset of MECH and ALLO patients (Table 2). Concurrent procedures, such as coronary artery bypass grafting, mitral valve repair or replacement, and tricuspid valve repair or replacement were carried out in 30% of both MECH and ALLO cases. Significantly longer aortic cross-clamp and cardiopulmonary bypass times were noted in the ALLO group. No differences were observed between groups with regard to the frequency of perioperative deaths or early postoperative hemorrhage, stroke, renal failure, and respiratory failure requiring tracheostomy (Table 3). Episodes of atrial fibrillation occurred more frequently in the MECH group. Thirty-day mortality was similar for both groups (ALLO, 8.8% versus MECH, 5.5%; p = 0.4). When performed emergently, aortic root replacement resulted in significantly elevated 30-day mortality overall (21% versus 4%; p < 0.01).
Of the 28 emergently performed aortic root replacements, 6 early (30-day) deaths occurred. Of the 2 intraoperative deaths, 1 occurred in a patient in acute cardiogenic shock who underwent emergent redo aortic root replacement secondary to anastomotic dehiscence and profuse hemorrhage. The second intraoperative death occurred in a patient with a ruptured sinus of Valsalva aneurysm who arrested immediately before undergoing emergent aortic root replacement. Of the remaining 4 early deaths, 1 patient expired on postoperative day 15 after emergent repair for prosthetic valve endocarditis and cardiogenic shock. Another patient expired on postoperative day 6 after emergent repair for severe, acute endocarditis involving the native mitral and aortic valves with concomitant septic shock. An additional patient with acute prosthetic valve endocarditis and hemodynamic instability was emergently managed and died on postoperative day 15. The final early death occurred in a patient with acute type A dissection, cardiogenic shock, and hemodynamic instability who expired on postoperative day 4. Thus, all deaths in the emergent group occurred in patients with preoperative shock.
Unadjusted actuarial survival at 1, 5, and 10 years was 90%, 81%, 67%, and 86%, 70%, 67%, for the MECH and ALLO groups, respectively (Fig 1). Kaplan–Meier analysis of survival for both groups did not reveal a statistically significant difference in survival (p = 0.09). In the entire series, 5 patients (2.9%, 0.6% per patient-year), experienced late thromboembolic complications (Table 4). Eleven patients (6.4%, 1.3% per patient-year) exhibited episodes of clinically significant hemorrhage, and 3 patients (1.7%, 0.4% per patient year) had endocarditis. Surgical revision of the replaced aortic root was necessary in 8 patients (4.7%, 0.9% per patient-year) owing to structural valve degeneration (n = 4, all ALLO), endocarditis (n = 2, all MECH), thoracic aortic aneurysm (n = 1, MECH), and hemorrhage at the right coronary anastomosis (n = 1, ALLO). No significant differences in the incidences of these valve-related complications were observed between both groups (Fig 2). Ten-year survival of patients stratified into etiology-specific groups of aortic root pathologic disease included the following (±standard error of the mean): annuloaortic ectasia (77% ± 8%), endocarditis (47% ± 10%), aortic dissection (64% ± 17%), prosthetic valve dysfunction (33% ± 24%), and ascending aortic aneurysm with other valve pathology (62% ± 10%). 2 analysis for equivalence of death rates revealed no significant impact of aortic root cause on overall survival among the groups (p = 0.12). Ten-year survival for Marfan patients, specifically, was favorable after aortic root replacement (81% ± 10%; Fig 3).
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Fig 1. Survival of patients undergoing aortic root replacement with St. Jude mechanical valve conduit (MECH; black line) versus aortic allograft (ALLO; gray line).
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Fig 2. Freedom from valve-related events after St. Jude mechanical valve conduit (MECH; black line) and aortic allograft (ALLO; gray line) aortic root replacement. (A) Overall event-free survival is shown. Events included in this analysis were death, thromboembolism, endocarditis, hemorrhage, and reoperation. (B) Freedom from late hemorrhage. (C) Freedom from reoperation secondary to structural valve degeneration (SVD). Differences between the curves depicting overall event-free survival, freedom from late hemorrhage, and freedom from reoperation secondary to structural valve degeneration for the St. Jude mechanical valve conduit and aortic allograft groups did not reach statistical significance.
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Fig 3. Survival after aortic root replacement in patient groups stratified by cause of aortic root disease. The three groups represented included patients with Marfan syndrome (medium gray line), aortic dissection (black line), and endocarditis (light gray line).
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A total of 49 deaths occurred during the 15 years of follow-up. In the univariate Cox model, significant predictors of long-term mortality included female sex, age older than 65 years, preoperative New York Heart Association class III or IV, emergently performed aortic root replacement, postoperative renal failure, and postoperative respiratory failure (Table 5). In the full multivariate Cox model, the following variables were independent predictors of long-term mortality: age older than 65 years, preoperative New York Heart Association class III or IV, emergently performed aortic root replacement, and postoperative respiratory failure (all p < 0.02; Table 6). By both univariate and multivariate Cox model analysis, insertion of a mechanical valve conduit did not confer a survival benefit relative to ALLO aortic root replacement (Tables 5, 6) in intermediate follow-up.
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Comment
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This study represents a large series of aortic root replacements performed with either aortic allografts or St. Jude mechanical valve conduits. Importantly, unlike prior series [12], which excluded patients with endocarditis, acute dissection, and emergent operative status, this current analysis includes patients with these important operative indications for aortic root replacement. Inclusion of these variables provides two study groups that are more representative of patients with aortic root disease routinely encountered in surgical practice, but also significantly diminishes the degree of similarity between these groups, thereby precluding statistical comparisons of outcome.
This retrospective review of aortic root replacement outcomes in 172 patients represents the second largest study to examine results with mechanical and biologic valve conduits. The first study of this kind, by Byrne and associates [12], included 231 elective aortic root replacements (biologic, n = 136; mechanical, n = 85), and concluded there were no meaningful differences in early-term or mid-term valve-related outcomes between biologic and mechanical groups. Five-year survival rates in the biologic and mechanical groups (92.4% versus 88.2%; p = 0.07) were similar, and independent predictors of late death included age, previous valve replacement, concomitant coronary artery bypass grafting, and perioperative stroke. Relative to this prior study, 5-year survival was reduced in this current series (MECH 81% versus ALLO 70%) and may be directly attributable to the inclusion of emergently performed aortic root replacements (16%), a higher proportion of reoperative cases (41% versus 13% in Byrne and colleagues [12]) and concomitant operative procedures (30% versus 24% in Byrne and colleagues [12]), and patients with endocarditis and acute dissection. These factors are important to consider, particularly as emergent aortic root replacement was found to be an independent predictor of late mortality by multivariate analysis in this study. Similarly, Gott and coworkers [14] have previously documented that elective aortic root replacement is associated with significantly reduced morbidity and mortality compared with emergent reconstruction. That advanced age and heart failure class were independently predictive of long-term mortality in this study is also consistent with data from other studies in which these predictors were validated [12, 15, 16].
Overall, the low rate of valve-related events in this study, such as thromboembolism, endocarditis, and reoperation, compare favorably with the results obtained from other larger series of aortic root replacements [16, 17]. Ten-year survival in this series was similar to other series [6, 18, 19], but less than those reported in younger Marfan patients (81%) [20]. Recent 10-year outcomes of aortic root replacement with the Freestyle stentless porcine bioprosthesis (n = 178) in an older group of patients (mean age, 71 years) include 5- and 10-year actuarial survival rates of 73% and 47%, respectively [10].
As previously noted in comparisons of biologic versus mechanical aortic valve replacement, performing aortic root replacement does not appear to alter the similarity in long-term patient survival observed for biologic versus mechanical prostheses [21, 22]. The low 30-day mortality (7% overall, 4.2% in elective cases) observed in this heterogeneous group of patients is also similar to that of published outcomes in aortic valve replacement operations [22] and emphasizes the safety and efficacy with which aortic root replacement can be reproducibly performed.
The limitations of this study include that it is not a prospective, randomized, controlled study but is, instead, a single-institution retrospective review susceptible to the inherent selection biases associated with retrospective analyses. The patients in the MECH and ALLO groups were also very heterogeneous and dissimilar with regard to preoperative characteristics and operative indications. The size of the series is also relatively small, and the extent of follow-up is limited beyond 10 years. This latter point is quite important, particularly because it is in the 10- to 15-year time interval when most of the reported structural valve degenerations occur in aortic allografts [6, 23–25]. Nevertheless, in this series and others, only one half of the patients who undergo aortic root replacement are expected to live longer than 10 years. Therefore, a specific comparison of long-term durability between MECH and ALLO aortic root replacement would require a lengthier period of follow-up than provided in this study.
In the end, the question still stands as to which valve conduit type might yield optimal outcomes from aortic root replacement in any given patient indication. Any selection of biologic versus mechanical conduits should be at least partially based on technical and availability issues along with the usual considerations of biologic versus mechanical prostheses. Specifically, just as with simple aortic valve replacement, aortic root replacement using aortic allografts has an established role in the management of patients with native or prosthetic valve endocarditis [17, 20, 26], in women anticipating pregnancy, in young adults with small annular size, and in patients with contraindications to systemic anticoagulation. In the setting of endocarditis, aortic allografts may be associated with a reduced early risk of recurrent endocarditis relative to mechanical conduits. Allografts were predominantly used in our series of patients with endocarditis (Fig 3), with 5- and 10-year survival of 65% and 47%, respectively. Mechanical aortic root replacement may have advantages in patients with larger annular size or life expectancy greater than 15 years, as well as in patients with connective tissue disorders, such as Marfan syndrome. As reported by other groups, we preferentially used mechanical conduits for aortic root replacements in Marfan patients and observed favorable long-term survival (Fig 3). In deciding mechanical versus biologic aortic root replacement, the risk associated with life-long anticoagulation must be weighed against the age-related limited durability and lifetime risk of reoperation well characterized in allograft root replacement [25]. The results from this study suggest no clear difference in short-term and intermediate-term event-free survival between aortic allografts and St. Jude composite grafts. Thus, the choice of mechanical versus allograft aortic root replacement should largely be one of long-term durability versus ability to tolerate anticoagulation. More definitive data will require long-term (>15 years), larger population studies, preferably at the multiinstitutional level.
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Discussion
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DR THORALF SUNDT (Rochester, MN): That was a beautifully presented paper and outstanding results, as we would expect from your institution. I am glad you have still got that slide there, because I would take issue with it on a fundamental level, which is that it shouldn't read "surgeon preference," it should read "patient preference." I think that we write a lot of papers where we are trying to determine differences in survival when the issue really boils down to the patient's preference. It is like trying to determine statistically whether a patient would prefer apples to oranges. The patient really makes the decision, anticoagulation versus reoperation, and we can look at survival all we want. We are not going to answer that. So it is important for you to add patient preference as well as patient factors to that list of considerations. Thanks.
DR LIMA: Thank you, sir. I certainly agree with that comment. It is very insightful.
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Abstract
Introduction
