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Ann Thorac Surg 2001;71:S297-S301
© 2001 The Society of Thoracic Surgeons

Bioprosthetic valves and conduits: new developments

Early and midterm results of model 300 CryoLife O’Brien stentless porcine aortic bioprosthesis

Sandro Gelsomino, MDa, Romeo Frassani, MDa, Lorenzo Porreca, MDa, Giorgio Morocutti, MDa, Angelo Morelli, MDa, Ugolino Livi, MDa

a Department of Cardiovascular Sciences, General Hospital "S. Maria della Misericordia," Udine, Italy

Address reprint requests to Dr Gelsomino, U. O. Cardiotoracica, Azienda Ospedaliera S. Maria della Misericordia, Piazzale S. Maria della Misericordia, 33100 Udine, Italy
e-mail: sandrogelsomino{at}virgilio.it

Presented at the VIII International Symposium on Cardiac Bioprostheses, Cancun, Mexico, Nov 3–5, 2000.


   Abstract
Top
 Abstract
Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
 References
 
Background. The Cryolife O’Brien (CLOB) is a composite stentless bioprosthesis constructed from noncoronary leaflets of three porcine aortic valves. This study aimed to investigate early and midterm results after aortic valve replacement with CLOB xenograft.

Methods. Between 1993 and 2000, the CLOB was implanted in 125 patients (62 men; mean age 71.3 ± 6.4 years). Mean prosthesis size was 23.6 ± 2 mm. Mean follow-up time was 37.0 ± 12.1 months. Patients underwent echocardiographic studies preoperatively, at discharge, at 6 and 12 months postoperatively, and yearly thereafter.

Results. Early (30-day) mortality rate was 2.4% (3 of 125 patients). Of the four late deaths, none was valve related. Actuarial 7-year survival was 93.6% ± 3%. Seven-year freedom from primary valve failure was 98.1% ± 1.8%. All patients showed an improvement of functional status (p < 0.001). ANOVA revealed a significant reduction over time in peak and mean systolic gradients (p < 0.001). Effective orifice area index increased (p < 0.001) and left ventricular mass index significantly reduced in all valve sizes (p < 0.001) during this time interval.

Conclusions. Because the early and midterm results with CLOB xenograft have been satisfactory, we encourage its use as a valve substitute, particularly in patients with small aortic roots.


   Introduction
Top
 Abstract
 Introduction
Material and methods
 Results
 Comment
 Acknowledgments
 References
 
The model 300 CryoLife O’Brien (CLOB) stentless xenograft (Cryolife International, Atlanta, GA) is a composite design constructed from noncoronary leaflets of three porcine aortic valves. It was first reported by O’Brien and colleagues [1] but the design failed to ensure durability because of formaldehyde preservation. Worldwide acceptance of stent mounting and glutaraldehyde preservation caused the use of unstented valves to be discontinued. Nevertheless, the drawbacks of conventional stented bioprostheses led to a renewed interest in stentless aortic valves that, becoming available again in 1985 [2], have been used increasingly with excellent functional and hemodynamic results in the past 10 years [3]. The concept of the composite design was reintroduced in 1992 with a porcine stent-deprived bioprosthesis, fixed in glutaraldehyde at very low or near zero pressure [4]. The model 300 CLOB stentless xenograft has been shown to provide low residual gradient and to favorably affect the left ventricular remodeling and regression of left ventricular hypertrophy after aortic valve replacement (AVR) [5]. This retrospective study was performed to assess the midterm clinical and hemodynamic results after AVR with the CLOB.


   Material and methods
Top
 Abstract
 Introduction
 Material and methods
Results
 Comment
 Acknowledgments
 References
 
Patient population
Among 878 patients undergoing AVR in our institution between 1993 and 2000, 125 (14.2%) consecutive patients had a CLOB stentless valve inserted in the aortic position. Clinical and operative data are summarized in Table 1. Mean size implanted was 23.6 ± 2.0 mm. Sixty-eight (54.4%) patients received a valve that was 23 mm or less in diameter, 57 (45.6%) patients received a valve that was 25 mm or larger. Patients with smaller valves were predominantly female (p < 0.001) and older (p = 0.03), with dominant aortic stenosis (p = 0.01) and smaller body surface area (BSA) (p < 0.001).


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  		Table 1. Perioperative Data

 
Contraindications for using the stentless valve were extensive calcification of the sinus aortic wall and root; an annulus diameter more than 30 mm that precluded the use of a 29-mm valve; or an extremely thin aortic wall. The implants were performed as described previously [6]. Follow-up was carried out by scheduled clinic visits or by direct telephone contact with the general practitioner and the patients. Mean follow-up was 37 ± 12 months (range 3 to 84 months). Operative and long-term mortality and morbidity were recorded according to The Society of Thoracic Surgeons’ guidelines for reporting morbidity and mortality after cardiac valvular operations [7]. No patient was lost to follow-up, which was 100% complete.

Echocardiography
Echocardiograms were recorded by a Hewlett Packard Sonos 5500 ultrasound system with a 2.5 MHz transducer (Hewlett Packard, Andover, MA). All examinations were performed by the same technician with a consensus of a cardiologist (G.M.). Patients underwent echocardiographic studies preoperatively, at discharge, 6 and 12 months postoperatively, and yearly thereafter. Measurements and calculations were carried out as described in the literature [8].

Statistical analysis
SPSS for Windows release 8.0 (SPSS Inc, Chicago, IL) was used to perform data analyses. Continuous variables were expressed as mean ± standard deviation (SD). Discrete variables were presented as percentages. Paired and unpaired Student’s t tests were used as appropriate to analyze continuous data, and the {chi}2 test and Fisher’s exact test were used to analyze discrete data. The one-way analysis of variance (ANOVA) was performed where appropriate, and multiple group comparisons were performed using the Bonferroni post hoc test. Data from the 7-year study were excluded from analysis because of the small number of patients. Cox’s proportional hazard models were used for multivariable analyses to test for independent effects of each variable on outcome. Death and event-free survival estimates were calculated by the product-limit method of Kaplan and Meier, reported with 95% of confidence limit and expressed ± standard error (SE); the Mantel–Cox (log-rank) test was used to test the hypothesis that there was no difference in survival among groups. In all cases p values lower than 0.05 were considered significant.


   Results
Top
 Abstract
 Introduction
 Material and methods
 Results
Comment
 Acknowledgments
 References
 
Early outcome
Mortality and complication rates are summarized in Table 2. There were three early (30-day) deaths (2.4%): myocardial infarction, multiorgan failure, and sepsis were the respective causes of these fatal outcomes. Postmortem examination was performed in all 3 patients and no technical or valve failure was demonstrated. Nonfatal complications occurred in 4% (5 of 125) of cases: 2 patients were reexplored for bleeding, 2 had sternal infection, and 1 developed respiratory failure.


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  		Table 2. Survival and Complication Rates

 
Late mortality
Four patients died during follow-up (3.2%). There was one (0.8%) cardiac death due to myocardial infarction and one (0.8%) valve-related death caused by a sepsis secondary to prosthesis endocarditis 34 months postoperatively. One patient died from stroke and one cause of death remained unknown. Multivariable analysis identified the presence of significant coronary artery disease (CAD) (p = 0.02) and a low ejection fraction (p < 0.001) as factors affecting the 7-year survival. Seven-year survival with and without concomitant CAD were 81.8% ± 11.6% and 93.2% ± 3.3%, respectively (log-rank, p = 0.04).

Unfavorable events
Apart from events leading to death, 1 more patient had active endocarditis 41 months postoperatively and 2 patients (1.6%) had thromboembolic events: one transitory ischemic attack (TIA) and one stroke after 32 and 77 months from intervention, respectively. There were no episodes of significant anticoagulation-related hemorrhage. One valve was explanted 47 months after AVR because of primitive prosthetic failure: at reoperation, a retraction of a cusp was responsible for valve incompetence. Two more patients underwent valve-related reoperation for nonstructural valve deterioration: the patient with infective endocarditis underwent successful root replacement with a homograft. The second patient developed aortic incompetence early (6 months) after AVR because of technical failure and had the prosthesis replaced with a stented xenograft.

Functional status
At recent follow-up all patients showed an improvement in functional status: among 118 survivors mean New York Heart Association functional class (NYHA) was 1.3 ± 0.2 (p < 0.001 versus preoperatively). Seventy-five patients (63.6%) were in NYHA I, 43 (36.4%) were in functional class II, and none was in class III or IV. Patient age (p < 0.001), NYHA class IV (p = 0.01), concomitant CAD (p < 0.001), and a left ventricular ejection fraction (LVEF) of 0.35 or less (p < 0.001) were preoperative determinants of functional status after AVR.

Aortic regurgitation
At discharge aortic regurgitation was absent in 76 (67.2%) patients and was graded trivial in 26 (23%), mild in 4 (3.5%), and moderate in 1 (0.8%). At 7-year follow-up, 75% (9 of 12) and 25% (3 of 12) of patients had no or trivial aortic insufficiency (AI), respectively.

Left ventricular function
Echocardiographic data are shown in Table 3. In the early postoperative period, LVEF increased by 0.26 ± 0.06 (p < 0.001) at the 6-month examination with a further but not statistically significant increment over time. By univariate analysis, the improvement of LVEF was directly related to a higher preoperative gradient (p = 0.02) and adversely affected by the presence of concomitant coronary artery bypass grafting (p = 0.01) and by low preoperative mean and peak gradients (p < 0.001). At multivariate analysis, extent of CAD (p < 0.001) and low preoperative gradients (p < 0.001) adversely affected LVEF.


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  		Table 3. Echocardiographic Results

 
Hemodynamic performance
Peak and mean gradients across the aortic valve decreased significantly at the discharge (p < 0.001) and the 6-month examinations (p = 0.02) without further significant changes at late controls. ANOVA failed to show significant differences in reduction of transvalvular gradients between valve sizes (p = 0.412). There was a significant increase in effective orifice area and effective orifice area index (EOAI) at discharge (p < 0.001) and at 6 months (p < 0.001). No further significant change in these measurements was noticed at late controls. Twenty-four patients (19.2%) receiving a valve 23 mm or narrower and 14 (1.2%) with a prosthesis 25 mm or larger showed an EOAI of 0.8 cm/m2 or less in the early postoperative period. At late studies only 2 patients, both with a valve 23 mm or narrower, still had EOAI of 0.8 cm/m2 or less.

Left ventricular remodeling
At discharge left ventricular mass index (LVMI) decreased significantly from preoperatively and reduced again at 6 months without further significant modifications. Preoperatively, LVMI was higher in patients who received a valve that was 23 mm or narrower compared with patients who had larger prostheses (206 ± 38 g/m2 versus 175 ± 36 g/m2, p = 0.01), but no difference in LVMI changes was noticed between valve size by ANOVA. Multivariate analysis (Table 4) identified base line BSA of 1.75 m2 or more, male sex, preoperative systolic arterial blood pressure of 150 mm Hg or more, LVEF 0.35 or less, NYHA of III or higher, atrial fibrillation, mean gradient of 40 mm Hg or more, and the pure or prevalent AI as factors affecting LVMI postoperatively. At the preoperative study LVMI was greater in patients with AI than in patients with prevalent valve stenosis (220 ± 35 g/m2 versus 162 ± 28 g/m2, p < 0.001). The value remained still higher in the AI group at the discharge (p < 0.001), 6-month (p < 0.001), 1-year (p = 0.01) and 2-year (p = 0.03) echocardiograms; by the 3-year echocardiogram there were no significant differences in LVMI between valve stenosis and AI. ANOVA revealed significant changes over time in septum thickness, posterior wall thickness, left ventricular end systolic and end diastolic dimensions and shortening fraction, but failed to demonstrate differences in changes of these measurements by valve size (p = NS).


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  		Table 4. Multivariable Logistic Regression Analysis of Risk Factors for High LVMI After Stentless AVR

 

   Comment
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
Acknowledgments
 References
 
An increasing interest has developed in stentless bioprostheses since they were reintroduced in the mid-1980s [2]. Recent studies [4, 9, 10] have confirmed the benefits of stentless AVR, with excellent hemodynamics, superior to stented valve [11] and comparable with homografts [12]. In addition, an improvement in survival [13] and a greater recovery of left ventricular function [14] have been shown after implantation of unstented valves and, finally, durability of stentless xenografts has not been shown to differ from conventional porcine bioprostheses despite the improvement in clinical outcome and patient survival [10]. O’Brien and colleagues first reported the use of a formaldehyde-fixed composite porcine stentless valve [1]. This bioprosthesis, fixed in glutaraldehyde at 2 to 3 mm Hg pressure, was reintroduced in 1992 [4]. The advantages of the model 300 CLOB can be summarized as follows: The supraannular design allows a prosthesis larger than the measured host annulus to be implanted. The lack of any synthetic material lessens the risk of postoperative infections. Lastly, this valve offers lower flow resistance because all ventricular muscle is completely removed.

We report our experience with the stentless xenograft over 7 years in terms of clinical results and hemodynamic performance. Clinical outcomes and valve-related complications after AVR with the CLOB stentless valve have been satisfactory. The report of David and coworkers [10] of 10-year follow-up is the longest documented for stentless valves: despite the improvement in patient survival (93% and 89% at 5 and 9 years, respectively) and excellent hemodynamics after AVR with Toronto SPV (St. Jude Medical, St. Paul, MN) they reported a degeneration rate no different from stented porcine bioprostheses (100% and 85% at 5 and 9 years, respectively). Patient survival in the present study was 92.2% ± 3.2% and freedom from structural valve deterioration was 98.1% ± 1.8%. Mean and peak gradients showed a significant reduction over time: expansion of the annulus, which represents a dynamic structure, remodeling of the left ventricular outflow tract as well as changes in transvalvular velocity are believed to play an important rule in these reductions. Finally, ANOVA showed a significant reduction in LVMI after AVR with the CLOB stentless valve. Most (37.5%) of the left ventricular mass regression (LVMR) occurred in the first postoperative year with further, but not significant reductions after this period; LVMR was negatively influenced by male sex, BSA 1.75 m2 or more, preoperative arterial blood pressure 150 mm Hg or higher, LVEF 0.35 or less, NYHA functional class III or higher, presence of atrial fibrillation, mean transvalvular gradient 40 mm Hg or higher, and pure or prevalent AI. The size of the implanted valve did not affect LVMR.

Our study presents several limitations. First, the study had only a small number of patients. Because of the retrospective nature of the study, we did not compare the CLOB with other stentless or conventional stented bioprostheses. The short follow-up time did not provide adequate information about long-term valve durability. The small number of postoperative events limited the strength of our statistical analyses. The hemodynamic evaluations were performed at rest without findings collected during exercise. Lastly, left ventricular mass was measured by M-mode echocardiography, although more recent methods such as magnetic resonance would have been more accurate.

Despite these limitations, early and midterm results with the CLOB stentless bioprosthesis have been satisfactory thus encouraging the use of this valve in patients selected for a biological AVR and particularly in subjects with small aortic roots.


   Acknowledgments
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
References
 
We gratefully acknowledge Dr Orlando Parise for the statistical analysis.


   References
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 Acknowledgments
 References
 

  1. O’Brien M.F., Neilson G.H., Galea E.G., Molphy R., Power W., Stephen B.J. Heterograft valves: an analysis of clinical results of valve replacement. Circulation 1970;41(Suppl II):16-18.
  2. Sievers H.H., Lange P.E., Bernhard A. Implantation of a xenogeneic stentless aortic bioprosthesis: first experience. J Thorac Cardiovasc Surg 1985;33:225-226.
  3. Westaby S., Huysmans H., David T.E. Stentless aortic bioprostheses: compelling data from the second international symposium. Ann Thorac Surg 1998;65:235-240.[Abstract/Free Full Text]
  4. O’Brien M. Composite stentless xenograft for aortic valve replacement: clinical evaluation of function. Ann Thorac Surg 1995;60:S406-S409.
  5. Hvass U., Palatianos G., Frassani R., Puricelli C., O’Brien M. Multicenter study of stentless valves in small aortic roots: do stentless valves rule out replacement device mismatch?. J Thorac Cardiovasc Surg 1999;117:267-272.[Abstract/Free Full Text]
  6. O’Brien M. Implantation technique of the Cryolife-O’Brien stentless xenograft aortic valve: the simple, rapid and correct way to implant and the errors to avoid. Semin Thorac Cardiovasc Surg 1999;11(Suppl 1):121-125.[Medline]
  7. Edmunds L.H., Jr, Clark R.E., Cohn L.H., Grunkemeier G.L., Miller D.C., Weisel R.D. Guidelines for reporting morbidity and mortality after valvular cardiac operations. Ann Thorac Surg 1996;62:932-935.[Abstract/Free Full Text]
  8. Bach D.S., David T.E., Yacoub M., et al. Hemodynamics and left ventricular mass regression following implantation of the Toronto SPV stentless porcine valve. Am J Cardiol 1998;82:1214-1219.[Medline]
  9. Cartier P.C., Dumesnil J.G., Metras J., et al. Clinical and hemodynamic performance of the Freestyle aortic root bioprosthesis. Ann Thorac Surg 1999;67:345-351.[Abstract/Free Full Text]
  10. David T.E., Feindel C.M., Scully H.E., Bos J., Rakowsky H. Aortic valve replacement with stentless porcine aortic valves: a ten-year experience. J Heart Valve Dis 1998;7:250-254.[Medline]
  11. Fries R., Wendler O., Schieffer H., Schäfers H.-J. Comparative rest and exercise hemodynamics of 23-mm stentless versus 23-mm stented aortic bioprostheses. Ann Thorac Surg 2000;69:817-822.[Abstract/Free Full Text]
  12. Gross C., Harringer W., Beran H., et al. Aortic valve replacement: is the stentless xenograft an alternative to the homograft? Midterm results. Ann Thorac Surg 1999;68:919-924.[Abstract/Free Full Text]
  13. Westaby S., Horton M., Jin X.Y., et al. Survival advantages of stentless bioprostheses. Ann Thorac Surg 2000;70:785-791.[Abstract/Free Full Text]
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