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Ann Thorac Surg 2005;80:480-487
© 2005 The Society of Thoracic Surgeons

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Original article: Cardiovascular

Ten-Year Outcome After Aortic Valve Replacement with the Freestyle Stentless Bioprosthesis

^a Department of Medicine, Division of Cardiology, University of Michigan, Ann Arbor, Michigan
^b Department of Surgery, Section of Cardiothoracic Surgery, Wake Forest University School of Medicine, Winston-Salem, North Carolina
^c Department of Medicine, Division of Cardiology, University Laval, Ste-Foy, Quebec, Canada
^d Department of Cardiac Surgery, Kaiser Permanente Hospital, Los Angeles, California
^e LDS Hospital, Salt Lake City, Utah

Accepted for publication March 4, 2005.

^_* Address reprint requests to Dr Bach, L3119 Women’s-0273, 1500 E Medical Center Dr, Ann Arbor, MI48109 (Email: dbach{at}umich.edu).

Presented at the Forty-first Annual Meeting of The Society of Thoracic Surgeons, Tampa, FL, Jan 24–26, 2005.

	Abstract

Top Abstract Introduction Patients and Methods Results Comment Discussion References

 
BACKGROUND: Stentless aortic bioprostheses offer excellent hemodynamics and potentially improved durability compared with other bioprostheses. The present report describes the clinical and hemodynamic outcomes for the Freestyle aortic root bioprosthesis in a large, multicenter cohort prospectively followed up for 10 years.

METHODS: A total of 725 patients at 8 centers in North America (668 [92%] aged more than 60 years) were followed up prospectively after aortic valve replacement with the Freestyle stentless bioprosthesis. Implant technique was subcoronary in 509, total root in 178, and root inclusion in 38. Follow-up was 4,488 patient-years (mean 6.2 years/patient).

RESULTS: For subcoronary, full root, and root inclusion groups, 10-year actuarial freedom from structural valve deterioration was 97.0% ± 2.2%, 96.0% ± 4.5%, and 90.9% ± 11.2%, respectively; and actuarial freedom from reoperation was 91.7% ± 3.5%, 92.3% ± 6.0%, and 92.0% ± 10.7%, respectively. Mean pressure gradient at 10 years was 8.9 ± 7.9 mm Hg for subcoronary, 7.0 ± 4.1 mm Hg for full root, and 10.0 ± 11.1 mm Hg for root inclusion groups; effective orifice area was 1.6 ± 0.5 cm², 1.6 ± 0.6 cm², and 1.7 ± 0.5 cm², respectively. Freedom from moderate or more aortic regurgitation at 10 years was good for all three implant groups, but slightly higher for full root (97.7% ± 1.6%) compared with subcoronary (87.2% ± 2.8%) patients (p < 0.005).

CONCLUSIONS: The Freestyle stentless aortic root bioprosthesis is a versatile option for aortic valve replacement. Measures of clinical outcomes and prosthesis durability remain excellent through 10 years.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment Discussion References

 

Doctors Bach, Kon, Dumesnil, and Doty disclose that they have a financial relationship with Medtronic.

 

Stentless aortic bioprostheses may offer hemodynamic advantages as well as the potential for improved durability compared with other bioprostheses, with no requirement for long-term anticoagulation. Previously published reports confirm excellent hemodynamics associated with stentless valves as a group [1–3]. Because of unique features associated with different stentless aortic bioprostheses, mechanisms of failure and therefore valve durability could differ for various prostheses and between stentless bioprosthesis implant techniques.

The Freestyle aortic root bioprosthesis is a stentless porcine aortic root prepared using a proprietary low-pressure and zero-pressure fixation process and alpha-amino oleic acid (AOA) leaflet anticalcification treatment, with the aim of optimizing both hemodynamics and bioprosthesis durability. The device can be implanted as a subcoronary valve replacement, as a complete aortic root replacement (full root), or as a root inclusion. Initial implantation in humans began in 1992, and the device has been approved for clinical use in the United States since 1997. Existing data suggest good midterm durability [4–6]. The purpose of the present report is to describe the hemodynamic and clinical outcomes for the Freestyle aortic root bioprosthesis in a large, multicenter cohort prospectively followed up for as long as 10 years.

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment Discussion References

 
Study Population
The multicenter evaluation of the Freestyle (Medtronic, Minneapolis, Minnesota) stentless aortic root bioprosthesis began in 1992 at 21 centers in North America and Europe. In 1997, a long-term study of the valve began at 8 of these centers (see Appendix), selected for patient volume and protocol adherence. The study protocol was reviewed and approved by each participating hospital’s ethics review board; all subjects provided written informed consent. The long-term study group includes 725 consecutive patients having undergone implantation of the Freestyle valve. The present study is based on data to July 2004, extending the previously published clinical experience that was through November 2001 [5]. Implant technique was subcoronary in 509 patients (70.2%), total root in 178 (24.6%), and root inclusion in 38 (5.2%). The preponderance of subcoronary implants were modified subcoronary, with retention of the noncoronary sinus of Valsalva. Demographic data and patient characteristics are shown in Table 1. Of 725 patients, 668 (92%) were older than 60 years at the time of surgery. Operative technique has been previously described [4]. Valve sizes 19 mm, 21 mm, 23 mm, 25 mm, 27 mm, and 29 mm were implanted as follows: in the subcoronary group, 31 (6.1%), 103 (20.2%), 133 (26.1%), 137 (26.9%), 96 (18.9%), and 9 (1.8%), respectively; in the full root group, 8 (4.5%), 22 (12.4%), 33 (18.5%), 35 (19.7%), 64 (36.0%), and 16 (9.0%), respectively; and in the root inclusion group, 0 (0.0%), 4 (10.5%), 11 (28.9%), 13 (34.2%), 10 (26.3%), and 0 (0.0%), respectively. Follow-up was 4,488 patient-years (mean 6.2 years/patient; range, 0 to 11). Follow-up was complete in 678 of 725 patients (93.5%), and was 10 years or more for 105 patients (14.5%).

Echocardiograms were obtained at the respective investigational centers using clinically standard criteria for analysis. Mean pressure gradient was calculated using the modified Bernoulli equation, correcting for proximal velocity [9]. Effective orifice area (EOA) was calculated using the continuity equation [9]. Aortic regurgitation was graded as absent, trivial, mild, moderate, or severe based on standard clinical criteria, including assessment of jet width, circumference and eccentricity [10].

Statistical Methods
Continuous data are expressed as mean ± 1 SD. Categorical data are expressed as percentages. Survival analyses using the Kaplan-Meier method were used to estimate survival, freedom from valve-related adverse events, and freedom from aortic regurgitation; Peto’s formula was used to calculate the standard error of the estimates. A log-rank test was used to test for differences in adverse events between implant groups; pair-wise comparisons were used to determine differences between specific implant techniques. Analysis of covariance was used to test for differences in hemodynamics between implant techniques and across time. Statistical analysis was performed using SAS statistical software (SAS Institute, Cary, North Carolina). Differences were considered significant at a value of p less than 0.05.

	Results

Top Abstract Introduction Patients and Methods Results Comment Discussion References

 
Clinical Outcomes
Operative death for this population has been previously described [4, 7]. Actuarial survival and freedom from valve-related death through 10 years are shown in Figures 1 and 2; actuarial freedom from structural valve deterioration and freedom from reoperation are shown in Figures 3 and 4. There were no significant differences in adverse event rates between implant groups (survival, p = 0.89; valve-related death, p = 0.17; structural deterioration, p = 0.54; reoperation, p = 0.82). For subcoronary, full root, and root inclusion techniques, the 10-year actual freedom from valve-related death was 96.2% ± 1.0%, 95.0% ± 2.2%, and 88.8% ± 5.3%, respectively; the actual freedom from structural valve deterioration was 98.3% ± 0.8%, 97.6% ± 1.7%, and 95.9% ± 4.0%, respectively; and the actual freedom from reoperation was 94.6% ± 1.3%, 94.9% ± 2.2%, and 92.1% ± 4.4%, respectively. Linearized rates of adverse events are shown in Table 2. Anticoagulation and antiplatelet therapy is shown in Table 3.

View larger version (25K): [in this window] [in a new window]   Fig 1. Survival. There were no differences between implant techniques in overall survival (p = 0.89). Numbers below the graph represent patients at risk. Squares = full root (FR); diamonds = root inclusion (RI); circles = subcoronary (SC).

View larger version (24K): [in this window] [in a new window]   Fig 3. Freedom from structural valve deterioration (SVD). There were no differences between implant techniques in freedom from structural valve deterioration (p = 0.54). Numbers below the graph represent patients at risk. Squares = full root (FR); diamonds = root inclusion (RI); circles = subcoronary (SC).

Hemodynamics
Hemodynamics by valve size early after surgery have been previously reported [4, 7]. Mean gradients, EOA and indexed EOA at 1 year, 8 years, and 10 years postoperative are shown in Table 4. As anticipated, gradients were lower (p < 0.0001) and EOA was higher (p < 0.0001) for larger (25, 27, 29 mm) compared with smaller (19, 21, 23 mm) valve sizes. Gradients were lower among patients implanted using a full root or root inclusion technique than among those implanted using the subcoronary technique (p < 0.0001). The EOA was higher among patients implanted using a full root compared with a subcoronary technique (p < 0.0001); no differences were observed between subcoronary and root inclusion, or full root and root inclusion techniques.

Aortic Regurgitation
The preponderance of patients in all three implant groups had no or trivial aortic regurgitation through 10 years; no patient had severe aortic regurgitation throughout the follow-up period. Freedom from hemodynamically significant (moderate or more) aortic regurgitation is shown in Figure 5. Although the prevalence of aortic regurgitation was low in all three groups, there was a statistically significant difference between implant techniques in the presence of moderate or more aortic regurgitation (p = 0.02). There was a greater freedom from moderate or more aortic regurgitation in the full root group compared with the subcoronary group (p = 0.005), but no differences between full root and root inclusion (p = 0.22) or subcoronary and root inclusion groups (p = 0.53).

View larger version (26K): [in this window] [in a new window]   Fig 5. Freedom from moderate or greater aortic regurgitation (AR). Freedom from aortic regurgitation was greater after full root compared with subcoronary implantation (p = 0.005). Numbers below the graph represent patients at risk. Squares = full root (FR); diamonds = root inclusion (RI); circles = subcoronary (SC).

	Comment

Top Abstract Introduction Patients and Methods Results Comment Discussion References

Survival at 10 years in the present study was relatively low, but within the range of that reported among other patients after bioprosthetic aortic valve replacement [12–18]. An older population in the present study (aged 69 to 72 years at the time of surgery) compared with patients in many other reports [12, 13, 15, 17, 18] likely contributed to the observed late mortality. Survival was similar to that observed in populations of similar age [14, 16].

Hemodynamics
Stentless valves have excellent hemodynamic characteristics that approximate those of aortic allografts [3]. Previous studies have documented an early postoperative decrease in gradients and increase in EOA associated with stentless valves in general and the Freestyle valve in particular [4, 7]. The present work confirms that low gradients and large EOA are maintained at least 8 years after implantation. However, relatively few data points were available at 10 years. Based on available data, there appears to be a small but statistically significant decrease in EOA between 1 year and 10 years after surgery. Although no matching increase in gradient was observed, there was a trend toward slightly higher gradients at 10 years. Ultimately, additional data at 10 years and beyond are required to further assess late hemodynamics. From a clinical perspective, both gradient and EOA remain very good at 10 years.

Aortic Regurgitation
Previously published studies demonstrated a low prevalence of aortic regurgitation with the Freestyle valve through 8 years [5, 6]. The present study confirms that there is preserved freedom from significant aortic regurgitation through 10 years. Similar to the pattern noted at 8 years [5], the full root implant technique was associated with somewhat greater freedom from hemodynamically significant aortic regurgitation compared with subcoronary implants, possibly mediated by more stable valve geometry with retention of the porcine aortic root.

However, all three implant techniques of the Freestyle valve were associated with lower rates of aortic regurgitation compared with the complete subcoronary Toronto SPV. Based on published data from a multicenter study, freedom from hemodynamically significant aortic regurgitation for the Toronto SPV decreased from 96.9% at 5 years to 82.5% at 9 years [17], probably mediated by progressive dilation of the aortic root sinotubular junction [19]. The full root and root inclusion techniques for the Freestyle valve, as well as retention of the noncoronary sinus of Valsalva using the modified subcoronary technique [21], appear to mitigate against dilation of the sinotubular junction, likely contributing to the relatively low rate of observed aortic regurgitation.

Study Limitations
The present study is an observational assessment of outcomes. Patients were not randomly assigned to various therapies, and comparison between inherently dissimilar groups is problematic. Clinical follow-up was available through 10 years, and continued study will be necessary for truly long-term follow-up. Although hemodynamic outcomes were measured through 10 years, limited data were available after 8 years, and additional data are required at the later time point. Finally, the present cohort represents the longest multicenter follow-up for the Freestyle valve. However, patient age predominantly greater than 60 years does not allow extrapolation of durability data to younger patients.

Conclusion
In conclusion, the Freestyle stentless aortic bioprosthesis has very good associated hemodynamics, with low gradients that are maintained at least through 10 years; small changes in EOA between 1 and 10 years after surgery are of statistical but not clinical significance. Measures of clinical outcomes and prosthesis durability remain excellent in multicenter follow-up through 10 years. The Freestyle stentless aortic root bioprosthesis is a versatile option for aortic valve replacement with excellent durability through 10 years in a population predominantly older than 60 years at the time of surgery.

	Appendix

 

	Discussion

Top Abstract Introduction Patients and Methods Results Comment Discussion References

DR BACH: This was surgeon-dependent, and there were no proscribed rules for which patient should get which implant technique. This obviously makes it difficult to compare between implant techniques in the study, because different surgeons used different criteria. For instance, Dr Neal Kon, one of the implanters, used a full root technique in everybody. I believe that all of the other surgeons used a root technique, either full root or root inclusion, only if there was aortic root pathology.

DR JORGE A. WERNLY (Albuquerque, NM): I have been following the literature with the most common stentless valves with a great deal of interest and attention, and I have a couple of observations and together a couple of questions. One is the fact that you stated this is a relatively old population. So making comparison with some of the more recent biological valve series, that should be clearly taken into account.

Second is the fact that undoubtedly, and I believe published by your group, there is an increased surgical mortality risk for patients undergoing the full root. Therefore, while the composite root seems to hold very well, in making the decision to proceed with a full root replacement, that has to be taken into account.

So going now to the subcoronary implantation group over which I am going to ask a couple of questions is that I am very curious about the mechanism of failure of the valves. The Toronto and Freestyle, they don’t seem to be failing because of calcification, but they seem to be failing because of tears, and at least in the other valves, that phenomenon seemed to have been related to the dilatation of the sinotubular junction. So my questions go towards that area.

Have you measured that, have you observed dilatation of the sinotubular junction, do you do anything to control the potential for dilatation at the junction, and whether you would comment on the mechanism of failure of these valves?

DR BACH: Thank you for the comments and the questions. Let me first address your second comment and say that the operative mortality associated with the full root technique is a bit arguable. In the original experience reported for this patient cohort, there was a relatively high operative mortality. But the users of the valve at present do not find a high operative mortality associated with a full root. It can be argued both ways, whether initial experience versus current experience should inhibit or encourage people with regard to the full root technique. This may rely more than anything on an individual surgeon’s level of experience and comfort with this technique.

With respect to mechanisms of failure, calcification did not appear to be prominent. In the initial experience with the Toronto SPV, a complete subcoronary stentless valve, structural failure appeared to be related to progressive dilatation of the sinotubular junction. Now, most surgeons use some sort of buttress to prevent this. The Freestyle valve reported here was implanted in roughly the same time period as the Toronto valve. I previously published data on shorter-term follow-up for the Freestyle valve, finding no evidence of sinotubular junction dilation associated with the modified subcoronary implant technique. The overall failure rate for the Freestyle valve is low and appears to be associated with leaflet tear more than calcification. I don’t have data for the Freestyle valve to suggest any correlation with progressive dilation of the STJ.

DR DANIEL H. DRAKE (Traverse City, MI): We have implanted about 250 of these to date and have also enjoyed excellent results with the Freestyle. One trick that we have used to control enlargement of the S-T junction is to a nearly circumferential transverse aortotomy at the S-T junction for initial valve exposure. We are careful to try to position the aortotomy correctly such that subsequent closure with Teflon felt will reduce the likelihood of dilation in this area.

My question is after looking at your own results, in an otherwise healthy adult, what is the minimum age that you would recommend routine placement of this device?

DR BACH: I don’t think that there is a minimum age. I realize that that is controversial and may go against some published guidelines, but I am a believer in discussing with patients the relative merits of bioprosthetic versus mechanical valves; in essence, trying to avoid reoperation or avoiding anticoagulants. We implant these valves in patients who are in their 20s, in patients who are in their 40s, and in patients who are older. As long as the patient is making an informed choice about relative risks and what is known and what is not known, I feel comfortable with no lower age limit.

DR DRAKE: Let me rephrase the question then. In the individual who insists on the goal of only one open heart operation in their life, what would be the minimum age that you would recommend this implant?

DR BACH: Obviously a difficult question. This comes down to factoring in the durability of the valve and the anticipated life expectancy of the patient. We know that patients who undergo valve replacement do not have a normal life expectancy. Without hesitation, I think this could be a single operation for a patient age 65 and older. For patients younger than that, I would look at comorbidities and anticipated survival of the patient, which is quite variable.

DR GEORGE TOLIS (New York, NY): My reoperative experience with this conduit includes one patient for an acute failure at 10 years after implantation, and on reoperation the entire root was frozen, calcified, and one leaflet had actually torn off almost completely. Do you think that is the standard mode of failure for this long term, number one?

And number two, if that is the case, we know from homografts that they seem to be doing fairly well until the 10-year mark, at which point the curve starts pointing downward fairly rapidly. Do you anticipate the same long-term issues with this conduit?

DR BACH: My understanding is that the failures were not abrupt failures with acute tearing of a leaflet and fulminant aortic regurgitation. Obviously, the longer follow-up we have, the more we will know. I’ll look forward to 12-year and 14-year data, but from what we have now, I feel confident that durability is good at 10 years. There are some hypothetical reasons to expect this valve to have better durability than a homograft, and I’ll wait for the data to see if that is confirmed.

View larger version (26K): [in this window] [in a new window]   Fig 2. Freedom from valve-related death. There were no differences between implant techniques in freedom from valve-related death (p = 0.17). Numbers below the graph represent patients at risk. Squares = full root (FR); diamonds = root inclusion (RI); circles = subcoronary (SC).

View larger version (25K): [in this window] [in a new window]   Fig 4. Freedom from reoperation. There were no differences between implant techniques in freedom from reoperation (p = 0.82). Numbers below the graph represent patients at risk. Squares = full root (FR); diamonds = root inclusion (RI); circles = subcoronary (SC).

	References

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1. Pibarot P, Dumesnil JG, Jobin J, Cartier P, Honos G, Durand LG. Hemodynamic and physical performance during maximal exercise in patients with an aortic bioprosthetic valvecomparison of stentless versus stented bioprostheses. J Am Coll Cardiol 1999;34:1609-1617.[Abstract/Free Full Text]
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3. Kon ND, Adair SM, Kitzman DW, et al. Comparison of results using the Freestyle stentless porcine aortic root bioprosthesis with the cryopreserved aortic allograftIn: Huysmans HA, David TE, Westaby S, editors. Stentless bioprosthesis. 2nd ed.. Oxford, United Kingdom: Isis Medical Media; 1999. pp. 127-133.
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6. Kon ND, Riley RD, Adair SM, Kitzman DW, Cordell AR. Eight-year results of aortic root replacement with the Freestyle stentless porcine aortic root bioprosthesis Ann Thorac Surg 2002;73:1817-1821.[Abstract/Free Full Text]
7. Bach DS, Cartier PA, Kon N, Johnson KG, Deeb GM, Doty DB. Impact of implant technique following Freestyle stentless aortic valve replacement Ann Thorac Surg 2002;74:1107-1114.[Abstract/Free Full Text]
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