Ann Thorac Surg 2004;78:786-793
© 2004 The Society of Thoracic Surgeons
Original article: cardiovascular
St. Jude Medical Toronto biologic aortic root prosthesis: Early FDA phase II IDE study results
Thomas G. Gleason, MD*,a,
Tirone E. David, MDb,
Joseph S. Coselli, MDc,
John W. Hammon, Jr, MDd,
Joseph E. Bavaria, MDa
a Division of Cardiothoracic Surgery, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA
b Division of Cardiothoracic Surgery, University of Toronto, Toronto General Hospital, Toronto, Ontario, Canada
c Division of Cardiothoracic Surgery, Baylor College of Medicine, Houston, Texas, USA
d Department of Cardiothoracic Surgery, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina, USA
Accepted for publication February 17, 2004.
* Address reprint requests to Dr Gleason, 3400 Spruce St, Silverstein 6, Division of Cardiothoracic Surgery, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
thomas.gleason{at}uphs.upenn.edu
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Abstract
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BACKGROUND: Several biological aortic root replacement techniques have distinct advantages over mechanical composite root replacement including better valvular hemodynamic characteristics and the lack of need for anticoagulation. Current biological root replacement options lack proven long-term durability or are limited by technical or practical concerns. We report the early results from a phase II multicenter clinical trial of the porcine St. Jude Toronto Bioprosthesis with BiLinx (Toronto root).
METHODS: 176 Toronto roots were implanted as total aortic root replacement from August 2001 through August 2003. Concomitant cardiac procedures including coronary artery bypass grafting (31%) and ascending aortic replacement (55%) were performed in 74%. Patients were followed clinically and were examined with an echocardiogram at discharge, 6 months, 12 months, and yearly thereafter. Root sizes implanted included 29 mm in 38%, 27 mm in 30%, 25 mm in 20%, 23 mm in 10%, and 21 mm in 2.2%.
RESULTS: There are 205 patient years of follow-up through October 2003. Operative mortality was 3.9% (none were valve related) and late mortality was 4%. Operative stroke rate was 1.1% and late stroke rate was 0.6%. Endocarditis developed in 1 patient. Freedom from aortic regurgitation is to date 100% at discharge, 6 months, and 1 year postimplant. Reoperation of the aortic valve/root was not required in any patient. Six-month mean transvalvular gradients for 21–29 mm valves were 12.8, 8.8, 5.3, 4.9, and 4.7 mm Hg, respectively.
CONCLUSIONS: Aortic root replacement with the Toronto root is safe and provides superb transvalvular hemodynamics with freedom from anticoagulation. The Toronto root seems widely applicable for all types of aortic root pathology and these early data offer very encouraging results. Long-term follow-up is required.
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Introduction
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Biological full aortic root replacement for treatment of aortic root pathology and concomitant aortic valve insufficiency or stenosis has several theoretical advantages including better valvular hemodynamic characteristics and very low thrombogenic properties. Biological aortic root replacement options include allografts, stented bovine pericardial composite grafts, pulmonary autografts, and porcine aortic xenografts. Porcine full aortic root xenografts have recently been engineered.
One concern regarding both xenograft and allograft valves has been their long-term durability and their tendency to calcify which would predispose them to structural deterioration. Older stented porcine valve products have had a propensity for structural deterioration at 10 years postimplantation, especially in younger patients [1–3]. As such, efforts to improve valve preservation techniques and to prevent long-term calcification have been ongoing. The porcine stentless full aortic root bioprosthesis was introduced as an investigational aortic root by Medtronic, Inc. (Freestyle Aortic Root Bioprosthesis; Medtronic, Inc., Minneapolis, MN) in 1992. This product is glutaraldehyde-fixed at physiologic pressures and is treated with an anticalcification compound derived from 2-amino oleic acid [4]. Follow-up of the initial Food and Drug Administration (FDA) trial population has demonstrated outstanding hemodynamic characteristics with no structural valve deterioration or aortic insufficiency at 8 years [5] and thus the porcine aortic root offers defined promise as a suitable biological alternative for aortic root replacement.
The St. Jude Medical (SJM) Toronto Root Bioprosthesis with BiLinx (St. Jude Medical, Inc., St. Paul, MN) (Toronto root, Fig 1) is a porcine aortic root that is glutaraldehyde-preserved and differentially treated with aluminum chloride-based and then ethanol-based agents to prevent distinct calcification of both the porcine aortic wall and the valve cusps (BiLinx treatment), respectively [6]. This preservation technology was presented to the FDA in 2001 as part of this trial. The original SJM Toronto subcoronary stentless porcine valve (SPV) was introduced in 1997 without BiLinx, but the BiLinx technology has since been added to this valve as well. We report the early results of the FDA Phase II Investigational Drug Exemption Study of the Toronto root as a full aortic root replacement. It began in North America in August 2001.
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Material and methods
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Twenty-one centers in North America are enrolled in the SJM Toronto Root Trial. Data presented hereafter represent the first 2 years of the study. Before initiation of the trial, each institution's internal review board approved the study design. Written and informed consent was obtained preoperatively from each patient enrolled in the study.
A total of 176 Toronto roots were implanted for aortic root replacement in 176 patients throughout 16 North American centers (five centers have not implanted full roots) from Aug 1, 2001 through August 1, 2003 (see Table 1). One-hundred thirteen (73%) patients were male. The mean age was 63 with a range of 20–85 years. The age distribution is illustrated in Figure 2. The frequency of comorbid factors are listed in Table 2. The distribution of preoperative symptoms of heart failure by New York Heart Association (NYHA) class is presented in Table 3.
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Fig 2. Age distribution of patients implanted with the Toronto root-by-root inclusion or full-root techniques.
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The majority (90%) of the aortic root replacements were performed using a full-root replacement technique. The remaining 10% (18 patients) were placed by a root inclusion technique. Coronary buttons were transferred in an orthotopic position to the new root.
Aortic root pathology was varied but most patients had aneurysmal aortic roots. Bicuspid aortic valve was present in 37% of the patients, rheumatic valvular disease was present in 2.8% of the patients, Marfan syndrome was present in 6.8% of the patients, aortic dissection was present in 8% of the patients, and the remainder exhibited degenerative aortic and/or valvular diseases. The distribution of aortic regurgitation and stenosis is listed in Table 4. Concomitant cardiac surgical procedures were performed in 74% of the patients (Table 5). Replacement of the ascending aorta and coronary artery bypass grafting (CABG) were the two most common concomitant procedures performed in 54% and 31% of the patients, respectively. Cardiac reoperations comprised 20% of the patients.
Ascending aortic replacements with or without arch reconstruction were completed using polyester grafts (Hemashield vascular graft; Meadox Medicals, Inc., Oakland, NJ or Vascutek Gelweave graft; Vascutek Ltd., Renfrewshire, UK) extending from the porcine root to the native aorta. The majority of these cases were performed with an open-distal anastomosis under deep hypothermic circulatory arrest with or without retrograde cerebral perfusion.
Echocardiograms were performed at discharge, 6 months, 1 year, and yearly thereafter. The echocardiograms were reviewed and the hemodynamic valvular characteristics were scored and calculated by an off-site core facility. Descriptive statistics were used to summarize the acquired preoperative and postoperative data. Parametric echocardiographically derived data were compared using f tests and subsequent t tests. Nonparametric data were compared using 
2 analyses.
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Results
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The distribution of the Toronto root sizes implanted are indicated in Figure 3. Toronto roots measuring either 27 mm or 29 mm were received by 67% of the patients. Mean aortic cross-clamp times for patients undergoing isolated aortic root replacement or aortic root replacement plus a concomitant cardiac procedure were 100 ± 28 minutes and 128 ± 44 minutes, respectively. The length of hospital stay averaged 8.6 ± 5.2 days with a range of 3–33 days. There was a considerable reduction of the functional symptoms of heart failure among the entire cohort at 6 months postoperatively (Table 3).
More than 205 patient years of follow-up have accrued as of October 2003. Operative (30-day) mortality was 3.9% with no valve-attributable mortality (Table 6). Overall late survival from August 2001 through October 2003 was 93.7%. Early and late morbidities are outlined in Tables 7 and 8, respectively. The operative (30-day) stroke rate was 1.1% and the overall late stroke rate within the study period was 1.7% (3 patients). None of the patients diagnosed with cerebrovascular accident (CVA) or reversible ischemic neurologic deficit (RIND) had a history of cardiac dysrhythmia before the event, although atrial fibrillation developed in the 1 patient with RIND before discharge. Two of the CVA/RIND events occurred in patients undergoing concomitant ascending aortic or arch replacement (2 out of 95 or 2.1% vs 1 out of 81 or 1.2% among patients without concomitant ascending aortic replacement.)
No Toronto roots have been explanted. There was 1 patient who required early reoperation for coronary ischemia caused by an acutely thrombosed vein graft. Eight patients (4.5%) experienced a bleeding complication and in 2 of these patients, the bleeding was anticoagulation-related. Seven of these patients (4.0% overall) required a reoperation for either immediate postoperative bleeding (4 out of 7) or delayed pericardial effusions (3 out of 7). There have not been any late reoperations. Postoperative cardiac arrhythmias developed in 31 patients (17.6%): 20 patients exhibited atrial fibrillation (9 out of 20 exhibited preoperative atrial fibrillation), 3 patients exhibited atrial flutter, 4 patients exhibited sinus tachycardia, and 4 patients had preoperative pacemakers that required continued pacing.
There was 1 patient who experienced postimplant endocarditis. This patient was readmitted 6 months postimplant for Enterococcal endocarditis when a vegetation was noted on the porcine valve. After 4 weeks of antibiotics transesophageal echocardiogram indicated that there was no residual vegetation and the patient was discharged. He was readmitted again at 11 months postimplant because of diarrhea, dehydration, and dyspnea. He sustained a cardiac arrest and died during this admission. This was the only valve-attributable death occurring at 359 days. A second patient, who initially presented with an embolic stroke, required aortic root replacement for aortic stenosis and despite the lack of gross evidence of native valve endocarditis, the excised aortic valve grew out Enterococcus. However, this patient is now 13 months postimplantation and remains free of endocarditis.
There has not been any evidence of hemolysis, structural valvular deterioration, or nonstructural dysfunction. No aortic regurgitation was observed in 100% of patients at discharge, 6 months, and 1 year postimplant (Fig 4). The hemodynamic performances by valve size as measured by mean and peak gradient and effective orifice area calculated by echocardiography are summarized in Table 9. Neither valve gradient nor effective orifice area changed substantially at 6 or 12 months postoperatively. There was a trend toward a reduction in valve gradient over time. On average, regardless of the operative indication, there was a statistically significant reduction in left ventricular (LV) mass index between discharge and 6 or 12 months by matched pair t tests (Table 10). When comparing discharge with follow-up data for individual valve sizes, a reduction in LV mass index was noted for valve sizes 23–29 mm implanted by full-root technique, but this reduction was only statistically significant for the 27 and 29 mm Toronto root. The change in LV mass index was less marked in patients in whom a root inclusion technique was used, however the numbers implanted were small.
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Fig 4. Incidence of aortic regurgitation after Toronto root implantation at discharge, 6 months, and 1 year. Severity of aortic regurgitation was graded by an off-site echocardiogram core facility.
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Comment
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Biological aortic roots provide more superior hemodynamic characteristics than either stented bioprosthetic or mechanical aortic-valved conduits [7–14]. Biological aortic root replacement also precludes the need for anticoagulation against aortic valve-related thromboembolic disease. These two features make biological aortic root replacement more attractive to patients and physicians. Options to achieve biological full root and valve replacement have included aortic allografts, pulmonary autografts, and, more recently, porcine bioprosthetic xenografts. The overriding concern regarding all of these biological alternatives is their long-term durability.
Limitations of aortic allografts include the lack of widespread availability and the calcification that both the aortic wall and valve cusps tend to develop over time which contribute to structural deterioration and aortic regurgitation within 10–15 years postimplantation [15–19]. There is a 15% incidence of grade 3/4 allograft aortic regurgitation at 8 years and a 7%–20% incidence of reoperation at 10 years [15–19]. Use of the pulmonary autograft exhibits the inherent disadvantage of placing both the aortic root and the pulmonic root at a long-term risk of reoperation. The rate of valve-related complications experienced by autograft patients (ie, autograft or homograft degeneration, reoperation, or valve-related death) is 17% at 10 years [20]. The autograft reoperation rate in adults is 11%–15% at 7 years [21, 22]. Autograft dilatation and aortic regurgitation occur at rates of 58% and 25%, respectively, by 7 years [22]. Single valvular disease is converted to two-valvular disease at the time of autograft transfer. Many aortic root pathologies that have a genetic basis (eg, connective tissue disorders and bicuspid aortic valve) likely contain the same genetic alterations within the pulmonic root and once subjected to aortic pressures may exhibit similar pathophysiologic changes in the autograft [23–25]. One example occurred during the current trial whereby marked dilatation of the entire pulmonary autograft and the remaining ascending aorta developed in a patient 9 years after a Ross procedure was performed for aortic stenosis and bicuspid aortic valve. He presented with severe aortic regurgitation, a markedly aneurysmal pulmonic autograft and ascending aorta. The pulmonary autograft and aorta were replaced with a Toronto root and a woven polyester graft, respectively.
After the Freestyle bioroot, the Toronto root is the second porcine bioprosthetic root introduced. Eight-year follow-up of the Freestyle bioroot trial has demonstrated superb hemodynamic characteristics with 100% freedom from reoperation and structural deterioration and 0% aortic regurgitation [5, 26]. Differences in the Toronto root include its preservation with the BiLinx anticalcification technology. The system uses stepwise pretreatment of the valve cusps with ethanol and the aortic root with aluminum chloride and, in combination, these treatments synergistically inhibit calcification [27–29]. In part this inhibition is caused by the extraction of cholesterol and phospholipids from the tissue and subsequent aluminum binding to elastin reduces calcium binding [27–29]. The Toronto root's fixation process yields a porcine aortic wall that is stiffer than the Freestyle bioroot. The Toronto root is also a longer graft with a few more millimeters of porcine aortic length. This has proven to be advantageous in certain cases involving reconstruction of the ascending aorta.
The majority of surgeons involved in this current trial have used a full freestanding aortic root replacement technique (158 patients). A root inclusion technique was used in 18 patients at one center with promising results. There can be up to a 30°–60° discrepancy in coronary orientation between the porcine coronary ostia and the human coronary buttons. This potential limitation has been raised previously in the Freestyle trial [5]. An alternative implant technique was suggested in which the porcine root was rotated 120° and the porcine noncoronary sinus used for the new left coronary sinus. However this has not been a particular concern with respect to the Toronto root. We rotate the Toronto root slightly clockwise (15°–20°) relative to the aortic annulus to accommodate any coronary angle discrepancy across both the new left and right coronary sinuses. This maneuver coupled with adequate coronary button mobilization allows proper coronary alignment and we have not observed any problems with either right or left main coronary artery kinking or a need for subsequent coronary artery grafting due to an alignment issue. Occasionally during reoperative aortic root procedures in which dense scarring has occurred around the previously dissected coronary buttons, there is not enough length for the right coronary button to adequately reach the porcine right coronary sinus. In this case we have used a Cabrol technique for the right coronary artery with a short segment of vein graft. When ascending aortic replacement was required it was done using polyester woven grafts. It is not clear what the long-term fate of the porcine-to-polyester graft anastomosis will be, however 10-year data are now surfacing from the Freestyle bioroot trial and these bioroots do not seem calcified. There has been no pseudoaneurysm formation around any Toronto root implant to date. Operative times for full-root replacement are commensurate with subcoronary valve implant techniques. The new Toronto SPV valve with BiLinx has been under concomitant investigation with the current Toronto full-root trial and cross-clamp times for subcoronary implantation with or without concomitant cardiac procedures averaged 117 minutes and 94 minutes, respectively, compared with 128 minutes and 100 minutes for full-root replacement.
Operative morbidity and mortality with Toronto root replacement was acceptably low and compares favorably with recently published literature despite the fact that 75% of patients underwent concomitant cardiac procedures and 20% were reoperations [19, 30–33]. For example, the operative mortality in the Freestyle bioroot trial was identical at 3.9% [5]. The operative and late stroke rates of 1.1% and 1.7%, respectively, are also comparable with other reports [34, 35]. Although operative stroke rate was not reported in the Freestyle trial, the 1-year rate of freedom from thromboembolic events was 94% [5].
The hemodynamic characteristics of the Toronto root have been exceptional, particularly for the larger root sizes of 27 mm and 29 mm with mean valvular gradients less than 5 mm Hg at 1-year postimplantation. Toronto roots measuring either 27 mm or 29 mm were received by 67% of the patients (N = 118). Not uncommonly we have been able to upsize the aortic root implanted relative to the annular size measured offering truly optimal postoperative hemodynamics for each patient. Over time there has not been a decrease in effective orifice area. Both peak and mean gradients actually decreased with time in both this Toronto root trial and the Freestyle bioroot trial occurring largely over the first 6 months. This early reduction in valve gradient is likely a reflection of the resolution of postoperative edema and remodeling of the annular suture line. To date there has not been any hemodynamically significant aortic insufficiency observed: 97% had no insufficiency and 3% had a trivial degree of insufficiency at discharge and at 1-year postimplantation. There was an average reduction in the LV mass index of 65 g/m2 at 12 months postimplant regardless of the indication for root replacement. Larger Toronto roots imparted, on average, a greater reduction in LV mass index.
Two important questions concern which patients are appropriate candidates for Toronto root placement and how long the valves will last. For patients older than 70 years of age that have aortic root pathology which requires replacement, the porcine bioprosthetic root is likely to be the best conduit because it will be widely available, can be sized precisely, has a sewing ring that facilitates easy suturing to the aortic annulus, has excellent hemodynamic characteristics, and does not require anticoagulation. This conduit will provide adequate durability for this population.
A younger patient with pathology requiring aortic root replacement must weigh the risks of long-term anticoagulation with the risk of probable reoperation when comparing mechanical and biological aortic root options of all types. We agree that when aortic valve-sparing root replacement for aortic root pathology is possible, it is optimal provided that the valve can be preserved without aortic regurgitation. Whenever the valve cannot be spared because of inherent pathology, then the porcine bioprosthetic root is a suitable option amidst all of the biological alternatives. Based on 8-year data it seems that the Freestyle porcine bioroot demonstrates 100% freedom from aortic insufficiency and reoperation compared with rates of 85%–90% for allografts [5, 15–18]. This signifies that modern porcine bioroots will conceivably provide at least as favorable and probably even greater long-term durability and freedom from reoperation than allografts. Pulmonary autografts may be appropriate for a select group of patients and pathologies, particularly for children and young adults with aortic stenosis. However 7- to 10-year aortic regurgitation rates of 25% and reoperation rates of 10%–15% are reported in the older adult patient populations [20–22]. The early Toronto root data presented here demonstrate equivalent hemodynamic indices as those indicated by the Freestyle bioroot at the same time periods.
Currently we see the primary indication for the porcine bioprosthetic root as an elderly patient who exhibits aortic root pathology necessitating full aortic root replacement. However well-informed patients younger than 70 years of age that require aortic root and valve replacement and in whom anticoagulation is either contraindicated or clearly refused by the patient are seemingly reasonable candidates for bioprosthetic root replacement. Placement of the largest possible porcine bioroot may allow subsequent aortic valve replacement with favorable hemodynamic characteristics within the bioroot if and when long-term valve replacement becomes necessary.
Full biological aortic root replacement for aortic valve pathology alone remains controversial. Data suggests that the benefit afforded by improved transvalvular hemodynamics with stentless biological aortic valve replacement may translate to greater survival [36–39]. Several studies demonstrate a survival advantage to using aortic valve replacement with a stentless valve over a stented biological valve [36, 37, 39, 40]. Porcine full-root replacement when compared with subcoronary stentless replacement results in both considerably less aortic regurgitation and lower mean systolic gradients [41–43]. Therefore usage of porcine bioprosthetic aortic roots for aortic valve replacement indications in populations younger than 70 years of age may also be justified in terms of better long-term hemodynamics and ultimately improved left ventricular performance if this benefit is not obliterated by the risk of subsequent aortic root surgery many years later. In the current era when placing bioprosthetic aortic roots in younger patients we rely on an overtly stipulated understanding between both the surgeon and the patient that eventual reoperation may be required because of structural valve deterioration. When that reoperation will be necessary is not yet clear but based on the data now available from the Medtronic Freestyle trial of the early 1990s, it is likely to be well beyond 10 years. The Freestyle bioroot clearly has greater durability than older stented porcine valves. If the anticalcification processes used in the Toronto root or other porcine roots demonstrate considerable long-term (> 15 years) durability, then these products will be useful across a much broader patient population.
| Dr David discloses that he has a financial relationship with St. Jude.
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Acknowledgments
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All authors of this paper are with The St. Jude Toronto Bioroot Investigators and Dr Joseph E. Bavaria is the Principal Investigator.
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W. Y. Szeto, J. E. Bavaria, F. W. Bowen, A. Geirsson, K. Cornelius, W. C. Hargrove, and A. Pochettino
Reoperative Aortic Root Replacement in Patients With Previous Aortic Surgery
Ann. Thorac. Surg.,
November 1, 2007;
84(5):
1592 - 1599.
[Abstract]
[Full Text]
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B. Lima, G. C. Hughes, A. Lemaire, J. Jaggers, D. D. Glower, and W. G. Wolfe
Short-Term and Intermediate-Term Outcomes of Aortic Root Replacement with St. Jude Mechanical Conduits and Aortic Allografts
Ann. Thorac. Surg.,
August 1, 2006;
82(2):
579 - 585.
[Abstract]
[Full Text]
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Abstract
Introduction
30 Days