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J Thorac Cardiovasc Surg 2007;133:1045-1050
© 2007 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease

A randomized comparison of the Cryolife O’Brien and Toronto stentless replacement aortic valves

John B. Chambers, MD, FACC*, Helen M. Rimington, BSc, Ronak Rajani, MB, BS, MRCP, Fiona Hodson, RGN, Fikrat Shabbo, MS, FRCS

The Valve Study Group, St Thomas Hospital, London, UK.

Received for publication August 17, 2006; revisions received October 13, 2006; accepted for publication October 23, 2006.

* Address for reprints: Dr John Chambers, Cardiothoracic Centre, St Thomas Hospital, London SE1 7EH, UK. (Email: jboydchambers{at}aol.com).


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Limitations
 Conclusions
 References
 
Objective: A composite stentless valve might be less obstructive than a preparation incorporating the porcine right coronary muscle bar. The aim of this study was to compare early hemodynamic function in a prospective series of 78 patients randomized to receive either a Toronto or Cryolife O’Brien stentless valve.

Methods: Echocardiography was performed early after surgery, between 3 and 6 months, and at 1 year after surgery.

Results: The groups were matched demographically. The Cryolife O’Brien valve was significantly less obstructive in terms of effective orifice area (1.81 vs 1.30 cm2; P < .0001), mean pressure difference (7.1 vs 11.7 mm Hg; P < .0001), and peak velocity (1.7 vs 2.2 m/s) assessed at 1 year (P = .001). Bypass time was 91 (SD 22) minutes for the Cryolife O’Brien compared with 125 (SD 22) minutes (P < .0001) for the Toronto. There was a higher incidence of paraprosthetic regurgitation in the Cryolife O’Brien valve (16.7% vs 3.2%). Mortality and clinical events were similar.

Conclusion: The composite valve was less obstructive than the porcine valve, suggesting that stentless valves cannot be considered as a homogeneous class.

Abbreviations and Acronyms ANOVA = analysis of variance; CSA = left ventricular outflow cross-sectional area; {Delta}P = pressure difference; EOA = effective orifice area; LV = left ventricular; LVDD = left ventricular diastolic diameter; NYHA = New York Heart Association; v1 = subaortic peak velocity; v2 = transaortic peak velocity; VTI1 = subaortic velocity integral; VTI2 = aortic velocity integral


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Limitations
 Conclusions
 References
 
All replacement valves are obstructive compared with normal native valves,1Go but the orifice area available for flow is expected to be larger with a stentless than a stented valve. Although this was confirmed in early studies,2,3Go larger randomized studies4-7Go show conflicting results. It is possible that apparent discrepancies are partly caused by differences in the comparator stented valve, as there is some evidence that pericardial valves are hemodynamically superior to porcine valves.8Go However, it is also possible that a stentless valve manufactured from a whole porcine aortic root is more obstructive than a composite stentless valve lacking the muscle bar at the base of the right coronary cusp.

The aim of this study was therefore to compare hemodynamic function in patients prospectively randomized to either the Toronto (St Jude Medical Inc, Minneapolis MN) porcine stentless valve or the Cryolife O’Brien (Cryolife O’Brien International, NW Kennesaw, GA) tricomposite stentless valve.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Limitations
 Conclusions
 References
 
Patients
A total of 80 consecutive patients scheduled to have single bioprosthetic valve replacement in the aortic position were recruited. The population sizes were calculated to detect a difference in mean effective orifice area of 0.2 cm2 and standard deviation of 0.3 cm2 with 80% power. A random number sequence with a block of 16 was applied at the time of listing for surgery. However, 2 patients randomized to receive a Toronto required a stented biologic valve because of dilatation of the aortic root. The study group, therefore, comprised 78 patients. The mean age was 73 (range 55-88) years and 39 (50%) were men. Demographic details are given in Table 1. The study was accepted by the Local Committee on Ethical Practice, and all patients gave written consent.


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  		TABLE 1 Demographic comparison of patients receiving Toronto or Perimount valves (mean ± standard deviation)
 
Surgery
The Toronto valve was chosen as the porcine stentless replacement. It consists of a preparation of porcine aortic root sculpted to accommodate the coronary ostia and lined externally with Dacron. The valves were implanted using a subcoronary technique with interrupted sutures for the lower suture line at the level of the annulus joining the lower midpoints of previous cuspal attachment and passing across the intercommissural triangles. The porcine commissures were suspended independently, and a running polypropylene suture was used for the upper suture line. The Cryolife O’Brien model 300 valve was chosen as the composite stentless valve. It is composed of 3 individual noncoronary porcine cusps and has no Dacron lining. The profile is lower than for the Toronto, and it is sewn using a single continuous suture to the aortic wall just above the annulus.9Go

The native aortic valve was completely excised with aggressive debridement of all calcium to leave a smooth tissue annulus. Both valve types were sized from the sinotubular junction as discussed by David and colleagues10Go using a cylindrical independent sizer. This had been confirmed to correspond to the sizers provided by the 2 manufacturers. The patient tissue annulus was also measured using the independent sizer to exclude oversizing. In most cases, a valve of 1 label size larger than the patient tissue annulus diameter was selected,11Go but in the presence of a large sinotubular junction, a valve of 2 label sizes larger was occasionally used. However, if the sinotubular diameter was more than 2 sizes larger than the patient tissue annulus diameter, a stented valve was implanted instead and the patient was excluded. This occurred on 2 occasions. Aortoplasty or enlargement of the sinotubular junction was not required. Standard operative procedures were used with a median sternotomy, cardiopulmonary bypass, cooling to 32°C, and cold blood cardioplegia for myocardial preservation.

Echocardiography
Studies were performed immediately before discharge, at the first postoperative visit at 6 weeks, then between 3 and 6 months, and again at 1 year. Five patients refused echocardiography at 3 to 6 months and 1 was in hospital elsewhere, and 3 patients refused restudy at 1 year. Measurements were made as recommended by the American Society of Echocardiography12Go over 3 cycles in sinus rhythm or over 6 cycles in atrial fibrillation. Left ventricular (LV) outflow diameter was measured from inner to inner edge just below the replacement aortic valve in a parasternal long-axis view frozen in systole. The largest of 3 measurements was used. Regurgitant jets were localized, then graded by a combination of the jet height and the density, and pressure half-time of the aortic regurgitant signal on continuous wave Doppler. Moderate regurgitation was defined by a jet height between 25% and 65% of the outflow diameter with a pressure half-time longer than 300 ms. Mild regurgitation was defined by a jet height less than 25% of the outflow diameter and a complete, low-intensity continuous wave-form with pressure half-time longer than 500 ms. Trivial regurgitation was defined by a thin, low-momentum jet ending close to the valve with an incomplete continuous waveform. No jet in this study was found to be severe.

Calculations
The following calculations were performed: (1) effective orifice area (EOA) by the continuity equation (EOA in cm2) = CSA x VTI1/VTI2 where CSA is LV outflow cross-sectional area (cm2) calculated from the diameter assuming circular cross section, VTI1 is subaortic velocity integral (cm), and VTI2 is aortic velocity integral (cm); (2) peak pressure difference across the aortic valve (peak {Delta}P in mm Hg) = 4 (v2 2 – v1 2) where v2 is transaortic peak velocity (m/s) and v1 is subaortic peak velocity (m/s); (3) mean pressure difference across the aortic valve (mean {Delta}P in mm Hg) = aortic mean {Delta}P – subaortic mean {Delta}P; (4) LV mass (g) = 0.83 (left ventricular diastolic diameter [LVDD] + septal thickness + posterior wall thickness)3 – (LVDD)3. LV mass and EOA were indexed to body surface area.

Analysis
The mean and standard deviation values were calculated for variables that were approximately normally distributed and the median and range for those that were skewed. Comparisons were made between valve types using the unpaired t test or nonparametric Mann–Whitney U test as appropriate. The hemodynamic results were compared over the 4 postoperative visits using 1-way analysis of variance (ANOVA). The incidence of regurgitation was compared using Fisher exact test as the numbers in some categories were expected to be small. Standard definitions of clinical events were used.13Go Sizing was compared by plotting the LV outflow diameter measured by echocardiography against the label size for each valve design. Analyses were performed using the statistical package social sciences version 11.5.1.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Limitations
 Conclusions
 References
 
The groups were similar with respect to demographic characteristics (Table 1). The mean label size was 25.05 (standard deviation 2.62) for the Cryolife O’Brien and 24.80 (2.62; P = .66) for the Toronto valves. LV outflow tract diameter was similar for both valve types for label sizes 21 through 25, and approximately 2 mm smaller for the Toronto at label size 27 and 29 (Figure 1). Crossclamp time for the Cryolife O’Brien group was 67 (SD 12) minutes, which was statistically shorter than for the Toronto group at 102 (SD 21) minutes (P < .0001). Total bypass time for the Cryolife O’Brien group was 91 (SD 22) minutes compared with 125 (SD 22) minutes for the Toronto group (P < .0001). Two patients died in the early postoperative period (2.6%), 1 in each group. There were 6 deaths between 30 days and 1 year, 4 in the Toronto group and 2 in the Cryolife O’Brien group. One patient developed endocarditis in each group, which was fatal for the patient in the Cryolife O’Brien group but not fatal for the patient in the Toronto group. There were no thromboembolic events and no valve thromboses.


Figure 1
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  		Figure 1. LV outflow tract diameter (mean and 95% confidence interval) for each label size by valve type. LV, left ventricular.

 
There were minor changes in results over time (Table 2), but these did not attain statistical significance within each group. At 1 year, the effective orifice area was 1.81 (0.50) cm2 for the Cryolife O’Brien and 1.30 (0.42) cm2 for the Toronto group (P < .0001; Table 2). Patient–prosthesis mismatch defined by indexed effective orifice area < 0.8 cm2/m2 occurred in 16 patients in the Toronto group and 4 patients in the Cryolife group (P < .0001). The peak transaortic velocity was 1.7 (0.4) m/s for the Cryolife O’Brien group and 2.2 (0.5) m/s for the Toronto group (P < .0001), and the mean gradient for the Cryolife O’Brien group was 7.1 (3.7) mm Hg compared with 11.6 (5.7) mm Hg (P = .001) for the Toronto group. For comparison with the literature, hemodynamic results by label size are given for 3-6 months and 1 year in Table 3.


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  		TABLE 2 Hemodynamic results for whole Cryolife O’Brien group and whole Toronto group (mean ± standard deviation)
 

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  		TABLE 3 Hemodynamic results at 3-6 and 12 months displayed for convenience by label size * (mean ± standard deviation)
 
There was no change in the incidence or degree of regurgitation during the short study period. At 1 year there was mild regurgitation through the valve in 2 (6.5%) patients in the Toronto group and 2 (5.6%) patients in the Cryolife O’Brien group. None had moderate or severe regurgitation. There was mild paraprosthetic regurgitation in 6 (16.7%) patients in the Cryolife O’Brien group but none in the Toronto group, while there was moderate paraprosthetic regurgitation in 1 (3.2%) patient in the Toronto group and none in the Cryolife O’Brien group. Of the 5 patients with functionally bicuspid native valves who received a Cryolife O’Brien valve, only 1 had mild paraprosthetic regurgitation, and the single patient receiving a Toronto valve had no regurgitation. There was no significant difference in the incidence of regurgitation using Fisher exact test. There was no significant difference in LV mass index or indices of systolic function between the 2 valve types at any point after surgery (Table 4). New York Heart Association (NYHA) class was similar in the 2 groups at 1 year, with 30 of 37 (81%) patients in the Cryolife group and 27 of 31 (87%) patients in the Toronto group in NYHA I, 6 (16%) and 3 (10%) patients, respectively, in NYHA II, 1 patient in each group in NYHA III, and none in NYHA IV.


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  		TABLE 4 Measures of LV structure and function (mean ± standard deviation)
 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Limitations
 Conclusions
 References
 
Stentless xenograft replacement valves are usually considered as a homogeneous class. This study suggests that differences within the class may be important as the Cryolife O’Brien valve was hemodynamically superior to the Toronto valve.

This is likely to be related predominantly to the difference in design and implantation site. The Toronto valve is prepared from a whole porcine aortic root with the possibility of a reduction in the compliance of the annulus and increased stiffness of the paracommissural parts of the cusps caused by the retained muscle bar at the base of the right coronary cusp and the use of a Dacron lining. By comparison, the Cryolife O’Brien valve has no Dacron lining and is composed of 3 noncoronary cusps and therefore has no muscle bar. Furthermore, the Toronto valve is sewn with the lower sutures at the annulus, and the Cryolife O’Brien valve is sited just above the annulus. Similar results were shown in a comparison of the cryopreserved homograft and Prima,14Go (Edwards Lifesciences, Irvine, Calif) which is a porcine preparation with the septal muscle shelf removed but with a Dacron-covered annulus. The mean pressure drop was 5 mm Hg in the homograft group compared with 12 mm Hg in the Prima group. By contrast, another study15Go found a similar pressure drop in homografts and the Toronto stentless valve, but this was measured only a few hours after surgery using a regression equation to calculate pressure difference. In the present study, there were small differences in the size of the aorta in favor of the Cryolife valve. The mean label size, which reflects sinotubular junction diameter, differed by only 0.2 mm. However, the LV outflow diameter on echocardiography, which reflects patient tissue annulus diameter, was approximately 2 mm smaller for the Toronto than for the Cryolife valves in the 27-mm and 29-mm sizes, although similar for the other sizes (Figure 1).

There are no significantly discrepant results compared with published information on the Cryolife O’Brien valve10,12,16-20Go and for the Toronto valve.2,3,6,21,22Go However, there is significant variation in the methodology and findings of previously published studies such that until our randomized comparison, it has not been possible to draw conclusions about the relative hemodynamic performance of the 2 valve types. We showed a fall in gradient between the postoperative study and 1 year for both valve types, as also shown by others.18,19Go However, these changes were not significant on ANOVA. The hemodynamic differences were not associated with differences in NYHA class, LV mass regression, or clinical events.

The Cryolife O’Brien valve has a relatively large coaptation region. This avoids the tendency of valve prepared from a whole root to distort leading to regurgitation through the valve. We showed a low incidence of regurgitation through the valve in agreement with other authors,18,20Go although this was no different from the regurgitation through the Toronto valve.23Go Previous work has shown a slightly higher incidence of regurgitation through the Toronto valve.24-27Go The incidence of paraprosthetic regurgitation was higher for the Cryolife O’Brien valve than for the Toronto valve, although this difference did not attain statistical significance. The presence of regurgitation was not associated with native bicuspid valve disease, and in neither valve type was the regurgitation graded more than moderate.


   Limitations
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Limitations
Conclusions
 References
 
This study compared patients of similar body size and sinotubular junction diameter as measured by an independent sizer. The echocardiographic LV outflow diameters, reflecting tissue annulus diameters, were similar for the 21-mm through 25-mm valves but smaller for the Toronto than the Cryolife O’Brien for the 27- and 29-mm valves. This suggests a slight weighting in favor of the Cryolife O’Brien but is insufficient to explain the overall better performance as results were better at the smaller as well as the larger sizes. The study was powered only to compare hemodynamic function, and the trend toward a higher incidence in paraprosthetic regurgitation in the Cryolife O’Brien valves might become significant with larger population sizes. This study was also concerned with early results and cannot exclude differences in durability or late events. Furthermore, the Toronto valves were implanted in a subcoronary position, and hemodynamic function is expected to be better with implantation as a total root replacement.


   Conclusions
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Limitations
 Conclusions
References
 
This study showed superior forward flow characteristics with a trend toward more paraprosthetic regurgitation for the Cryolife O’Brien valve compared with the Toronto stentless valve. This suggests that stentless valves should not be considered as a uniform class but must be subdivided according to design and implantation site. The Cryolife O’Brien valve is a tricomposite supra-annular valve, and the Toronto valve for this study was implanted in a subcoronary position.


   Footnotes
 
Research echocardiography was funded by educational grants from Cryolife and St Jude Medical.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Limitations
 Conclusions
 References
 

  1. Wang Z, Grainger N, Chambers J. Doppler echocardiography in normally functioning replacement heart valves: a literature review. J Heart Valve Dis 1995;4:591-614.[Medline]
  2. David TE, Pollick C, Bos J. Aortic valve replacement with stentless porcine aortic bioprosthesis. J Thorac Cardiovasc Surg 1990;99:113-118.[Abstract]
  3. Cohen G, Christakis GT, Buth KJ, Joyner CD, Morgan CD, Sever JY, et al. Early experience with stentless versus stented valves. Circulation 1997;96(suppl II):II76-II82.
  4. Santini F, Bertolini P, Montalbano G, Vecchi B, Pessotto R, Prioli A, et al. Hancock versus stentless bioprostheses for aortic valve replacement in patients older than 75 years. Ann Thorac Surg 1998;66:S99-S103.[Medline]
  5. Cohen G, Christakis GT, Joyner CD, Morgan CD, Tamariz M, Hanayama N, et al. Are stentless valves hemodynamically superior to stented valves?. A prospective randomized trial. Ann Thorac Surg 2002;73:767-778.[Abstract/Free Full Text]
  6. Chambers JB, Rimington HM, Hodson F, Rajani R, Blauth CI. The subcoronary Toronto stentless versus supra-annular Perimount stented replacement aortic valve: early clinical and hemodynamic results of a randomised comparison in 160 patients. J Thorac Cardiovasc Surg 2006;131:878-882.[Abstract/Free Full Text]
  7. Ali A, Halstead JC, Cafferty F, Sharples L, Rose F, Coulden R, et al. Are stentless valves superior to modern stented valves?. Circulation 2006;114(suppl I):I535-I540.[Medline]
  8. Walther T, Lehmann S, Falk V, Metz S, Doll N, Rastan A, et al. Prospectively randomized evaluation of stented xenograft hemodynamic function in the aortic position. Circulation 2004;110(suppl II):II74-II78.[Medline]
  9. O’Brien MF. The Cryolife O’Brien-O’Brien composite aortic stentless xenograft: surgical technique of implantation. Ann Thorac Surg 1995;60:S410-S413.[Medline]
  10. David TE, Feindel CM, Bos J, Sun Z, Scully HE, Rakowski H. Aortic valve replacement with a stentless porcine aortic valve. J Thorac Cardiovasc Surg 1994;108:1030-1036.[Abstract/Free Full Text]
  11. Hvass U, Baron F, Elsebaey A, Nguyen D, Flecher E. The stentless Cryo-Life O’Brien aortic valve at 10 years. J Heart Valve Dis 2004;13:977-983.[Medline]
  12. Sahn DJ, De Maria A, Kisslo J, Weyman AE. The Committee on M-mode Standardization of the American Society of Echocardiography: recommendations regarding quantitation in M-mode echocardiography: results of a survey of echocardiographic measurements. Circulation 1978;58:1072-1081.[Abstract/Free Full Text]
  13. Edmunds LH, Clark RE, Cohn LH, Grunkemeier GL, Miller DC, Weisel RD. Guidelines for reporting morbidity and mortality after cardiac valvular operations. J Thorac Cardiovasc Surg 1996;112:708-711.[Free Full Text]
  14. Gross C, Harringer W, Mair R, Wimmer-Greinecker G, Klima U, Sihorsch K, et al. Aortic valve replacement: is the stentless xenograft an alternative to the homograft?. Early results of a randomised study. Ann Thorac Surg 1995;60:S418-S421.[Medline]
  15. Jin XY, Gibson DG, Yacoub MH, Pepper JR. Perioperative assessment of aortic homograft, Toronto stentless valve, and stented valve in the aortic position. Ann Thorac Surg 1995;60:S395-S401.[Medline]
  16. Hvass U, Chatel D, Assayag P, Ouroudji M, Pamsard Y, Lenormand C, et al. The O’Brien-Angell stentless porcine valve: early results with 150 implants. Ann Thorac Surg 1995;60:S414-S417.[Medline]
  17. Gelsomino S, Morocutti G, Frassani R, Da Col P, Carella R, et al. Usefulness of the Cryolife O’Brien stentless suprannular aortic valve to prevent prosthesis-patient mismatch in the small aortic root. J Am Coll Cardiol 2002;39:1845-1851.[Abstract/Free Full Text]
  18. Hvass U, O’Brien MF. The stentless Cryolife-O’Brien aortic porcine xenograft: a 5-year follow-up. Ann Thorac Surg 1998;66:S134-S138.[Medline]
  19. Martinovic I, Farah I, Everlien M, Knez I, Greve H, Vogt P. Aortic valve replacement with the Cryolife O’Brien-O’Brien stentless aortic bioprosthesis: five-year experience. J Cardiovasc Surg (Torino) 2004;45:557-563.[Medline]
  20. O’Brien MF, Gardner MAH, Garlick B, Jalali H, Gordon JAS, Whitehouse SL, et al. Cryolife O’Brien-O’Brien stentless valve: 10-year results of 402 implants. Ann Thorac Surg 2005;79:757-766.[Abstract/Free Full Text]
  21. Del Rizzo DF, Goldman BS, Christakis GT, David TE. Hemodynamic benefits of the Toronto stentless valve. J Thorac Cardiovasc Surg 1996;112:1431-1436.[Abstract/Free Full Text]
  22. Walther T, Autschbach R, Falk V, Baryalei M, Scheidt A, Dalichau H, et al. The stentless Toronto SPV bioprosthesis for aortic valve replacement. Cardiovasc Surg 1996;4:536-542.[Medline]
  23. Walther T, Langebartels G, Kruger M, Bernhardt U, Diegeler A, Gummert J, et al. Prospectively randomised evaluation of stentless versus conventional biological aortic valves. Circulation 1999;100(suppl II):II6-II10.[Medline]
  24. David TE, Bos J, Rakowski H. Aortic valve replacement with the Toronto SPV bioprosthesis. J Heart Valve Dis 1992;1:244-248.[Medline]
  25. Bach DS, David T, Yacoub M, Pepper J, Goldman B, Wood J, 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]
  26. Walther T, Falk V, Autschbach R, Scheidt A, Baryalei M, Schindewolf K, et al. Hemodynamic assessment of the stentless Toronto SPVTM bioprosthesis by echocardiography. J Heart Valve Dis 1994;3:657-665.[Medline]
  27. David TE, Feindel CM, Scully HE, Bos J, Rakowski H. Aortic valve replacement with stentless porcine aortic valves: a ten-year experience. J Heart Valve Dis 1998;7:250-254.[Medline]



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