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Ann Thorac Surg 1996;62:683-690
© 1996 The Society of Thoracic Surgeons
Departments of Cardiothoracic Surgery and Cardiology, Royal Brompton Hospital, London, United Kingdom
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Abstract |
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Methods. One hundred thirty-seven patients receiving single aortic valve replacement (52 with concomitant coronary artery bypass graft) were enrolled in this study. Ninety-eight were men, and the mean age was 68 years (range, 55 to 90 years). Of the 137 patients, 39 had an aortic homograft, 72 a Toronto stentless porcine valve, and 26 had a stented porcine or bileaflet mechanical valve, with mean valve size of 25 ± 2.5 mm (mean ± standard deviation). Left ventricular muscle mass and function were assessed by M-mode echocardiography performed before and 0.5, 6, 12, 24, and 36 months after operation, and recorded on paper for off-line digitizing. Peak valve prosthesis pressure gradients were quantified by continuous wave Doppler.
Results. A total of 330 echocardiograms obtained during this study were adequate for computer digitizing. Clinical data, preoperative left ventricular function, and hypertrophy were similar between the three groups. Significant improvement in left ventricular function and major regression of left ventricular hypertrophy had occurred in the entire population by 6 months after operation. Multivariate analysis of variance showed that patients with previous aortic regurgitation had a larger left ventricular cavity size (p < 0.001) and greater mass index (p = 0.001) postoperatively than those with previous aortic stenosis. In addition, peak valvular gradient was lower (p < 0.001), mass index less (p < 0.001), and left ventricular function more normal both systolic, by a greater peak velocity of dimension shortening (p = 0.05) and wall thickening (p = 0.002), and diastolic, by a greater peak velocity of dimension lengthening (p = 0.046), with an aortic homograft or stentless porcine valve compared with a mechanical or stented biological valve. There was no significant difference in peak valve gradient, left ventricular mass index, or function between the aortic homograft and the stentless porcine valve. Age, sex, and concomitant coronary artery bypass graft, as well as aortic cross-clamp time, cardioplegia method, and valve size all proved to be insignificant determinants of postoperative left ventricular hypertrophy or function.
Conclusions. In the first 2 years after implantation, the superior hemodynamic performance of aortic homograft and stentless porcine valve appears to result in more extensive regression of ventricular hypertrophy and greater improvement of left ventricular function than occurs with a mechanical or stented biological valve. These findings encourage the use of a stentless biological valve in older patients requiring aortic valve replacement, and a larger scale long-term randomized study of stentless versus stented biological valve or mechanical valve seems warranted.
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Introduction |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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Changes in left ventricular function and muscle mass after aortic valve replacement have been extensively studied during the past several decades [1–4]. It is well established that, provided a significant pressure drop does not persist, hypertrophy regresses and function improves regardless of whether a biological or a mechanical valve substitute is used [5–7]. Nevertheless, residual hypertrophy has proved to be an important determinant of long-term ventricular function [8–10], arrhythmias [11, 12], and thus survival. Although the superior hemodynamic performance of the stentless biological valve is increasingly being recognized [13–16], it is still uncertain whether this is translated into regression of hypertrophy and improved long-term ventricular function [17]. The present study was designed to investigate this question by comparing changes in ventricular mass, cavity size, as well as systolic and diastolic function in comparable groups of patients after aortic valve replacement with an aortic homograft, a stentless porcine valve, or a mechanical or stented biological valve, over a period of up to 3 years after operation.
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Patients and Methods |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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. Of these, 39 patients received an aortic homograft, 72, a Toronto stentless porcine valve (St. Jude Medical, Inc, St Paul, MN), and 26, a stented porcine (Carpentier-Edwards porcine valve, in 13 patients) or a mechanical bileaflet valve (St Jude bileaflet mechanical prosthesis, 13 patients). Fifty-two patients with additional coronary artery disease received full revascularization (2 ± 1 graft). Valve selection in individual patients was based on randomization to either an aortic homograft or a stentless porcine valve. When no suitable aortic homograft was available, a mechanical or a stented biological valve was used according to patient's preference. Nine patients underwent a redo aortic valve replacement: 7 received an aortic homograft and 2 a mechanical prosthesis. The stentless porcine valve was not considered in this circumstance due to its investigational status. The randomization protocol between aortic homograft and stentless porcine valve had been approved by the Ethics Committee of the Royal Brompton Hospital.
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Echocardiography
Echocardiograms were recorded by Hewlett Packard Sonos 1500 Ultrasound system. From a parasternal left ventricular long-axis view, standard recordings [18] of left ventricular M-mode echocardiograms were obtained and printed photographically at a paper speed of 100 mm/s, with simultaneous electrocardiogram and phonocardiogram. Peak pressure drop across the valve prosthesis was estimated by the simplified Bernoulli equation from peak velocity measured by continuous-wave Doppler echocardiography.
The echocardiograms were digitized off-line using a computer system (sample rate, 100 Hz) along with depth and time calibration [19]. The onset of the QRS complex on the electrocardiogram was used to identify left ventricular end-diastole, and the second heart sound (A2, the onset of first high frequency vibration of the aortic component) was taken as end-systole. At least three successive heart beats were digitized at each time interval and mean values derived. From these results, the following measurements were made: (1) left ventricular minor axis (dimension, D), posterior wall and septal thickness at end-diastole and end-systole; (2) shortening fraction, peak normalized rates of change of left ventricular minor dimension: shortening velocity (-dD/dt/D) and lengthening velocity (+dD/dt/D); (3) shortening fraction of the posterior wall, peak normalized velocity of posterior wall thickening and thinning; and (4) left ventricular muscle mass was calculated according to the Penn convention [20].
To assess the reproducibility of the digitizing of M-mode echocardiogram, a random sample of 10% beats was redigitized after a period of 6 months. Variables included left ventricular dimension, wall thickness, and their normalized rates of change.
Statistical Methods
Continuous data are presented as mean ± 1 standard deviation. Using Minitab statistical software (PC Version, Release 8, 1991; Minitab Inc, Philadelphia, PA) [21], clinical data and preoperative echocardiographic measurements were compared by one-way analysis of variance or 
2 test (for qualitative clinical data) among patients who had an aortic homograft, a stentless valve, or a stented or mechanical valve. One-way analysis of variance was also used to test the significance of changes of each parameter over time in whole patients, and combined with 95% confidence interval (Dunnett's method). Possible significant effects on postoperative left ventricular function and hypertrophy, of age (68 or less years or more than 68 years), sex, nature of valve disease (predominant aortic stenosis or regurgitation), with or without coronary artery bypass graft, duration of aortic cross-clamp (95 or less minutes or more than 95 minutes), cardioplegia method (crystalloid or blood cardioplegia), implanted valve size (valve sewing ring area, 2.6 or less cm2/m2 or more than 2.6 cm2/m2), valve type (aortic homograft, stentless porcine valve, or stented or mechanical valve), and follow-up time (0.5, 6, 12, 24, 36 months) were initially identified by one-way analysis of variance, respectively. Factors thus shown to be significant were entered into a multivariate analysis of variance (General Linear Model), and their independent role on each echocardiographic parameter was further defined. A p value of 0.05 or less was considered as significant in statistics. When assessing reproducibility, pairs of duplicate determinations were first examined for consistent differences between them. If these were absent, the root-mean-square of the difference between the two determinations was calculated, along with the mean of the two determinations of the variable itself. Variability was derived as (root-mean-square of difference)/mean value, and expressed as a percentage.
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Results |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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). No significant aortic or mitral regurgitation was found in these postoperative echocardiograms.
Preoperative Left Ventricular Function and Hypertrophy
Preoperative echocardiographic data showed similar disturbances of left ventricular function and the extent of hypertrophy among the three groups (Table 2).
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). This was accomplished by an increase of peak velocity of left ventricular dimensional shortening and lengthening, and that of posterior wall thickening and thinning already apparent by 2 weeks after operation. In addition, there was a small decrease of peak gradient across the aortic valve during follow-up.
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) with factors that had a significant effect on one or more parameters in univariate analysis, further excluded any significant influence of concomitant coronary artery disease, and the longer duration of aortic cross-clamp time to ventricular function or hypertrophy. Significant findings include that female sex was associated with a smaller left ventricular cavity size (4.8 ± 0.13 cm versus 5.2 ± 0.10 cm, p = 0.019) possibly due to a smaller body surface area (1.7 ± 0.2 m2 versus 1.9 ± 0.12 m2 , p < 0.001), along with slightly faster heart rate (84 ± 2 beats/minute versus 77 ± 2 beats/minute, p = 0.002), and a higher peak velocity of dimensional lengthening (3.0 ± 0.2/second versus 2.5 ± 0.1/second, p = 0.017), but sex had no effect on left ventricular systolic function or mass index. Apart from a higher velocity of posterior wall thinning (4.9 ± 0.3/second versus 4.1 ± 0.3/second, p = 0.036), a larger valve size had no other significant effect.
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. Left ventricular dimensions were greater and dimension shortening fraction somewhat less after correction of aortic regurgitation. Although wall thickness and its thickening velocity were similar in these patients, the larger left ventricular cavity size led to a greater left ventricular mass than in patients with previous aortic stenosis. With similar cavity size and heart rate, the peak pressure gradient across a stented biological or mechanical valve was significantly higher than an aortic homograft or a stentless porcine valve (20 ± 2 mm Hg versus 8 ± 1, 6 ± 1 mm Hg, p < 0.001). The left ventricular posterior wall and septum were also both significantly thicker with a stented biological or mechanical valve than with an aortic homograft or a stentless porcine valve. This was associated with a 20% increase in left ventricular mass index.
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Comment |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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Regression of Ventricular Hypertrophy and Improvement of Myocardial Function After Aortic Valve Replacement
In aortic valve disease, ventricular hypertrophy develops with pressure or volume overload, and its significant regression after aortic valve replacement has been extensively reported, with a 20% to 30% decrease of left ventricular mass index within the first year, and 30% to 35% by 5 years [5, 6]. However, this regression is not usually complete. Persistent cellular hypertrophy and interstitial fibrosis are likely to be the result of the residual pressure gradient across the prosthetic valve [22]. A stentless porcine valve in the aortic position is associated with a greater decrease in left ventricular systolic wall stress, a decrease in transvalvular pressure gradient, and a decrease in valvular energy loss, than that occurring with a stented biological valve [16]. It is possible, therefore, that the extent of postoperative left ventricular hypertrophy might also be less [16, 17]. Results from the present study confirm previous speculation in showing that the major changes in left ventricular mass index have occurred by 6 months, and furthermore demonstrate that the extent of the changes is greater with an aortic homograft or stentless porcine valve than with a mechanical or stented biological valve. This suggests that the favorable hemodynamics of a stentless biological valve can indeed be translated into a greater and more rapid regression of ventricular hypertrophy. The greater ventricular mass with a mechanical or stented biological valve proved to be attributable to a greater wall thickness rather than larger cavity size, compatible with the existence of a higher cavity systolic pressure. Although the peak pressure gradient across a mechanical or a stented biological valve was consistently higher, the increase was small at rest in viewing absolute values, and represented no more than 10% of the normal ventricular systolic pressure in patients with a mean age of approximately 70 years. It is possible that the pressure decrease is proportionately greater on exercise. A further factor may be that the early decrease in peak systolic wall stress is almost 50% greater after replacement with a stentless biological valve compared with a stented one [16], suggesting that simple measurement of peak transvalvular velocity by Doppler, whether or not expressed as a pressure gradient, may underestimate the severity of the persisting disturbance to left ventricular ejection.
Both systolic and diastolic left ventricular function may be impaired preoperatively in patients with aortic stenosis, even if cavity size and shortening fraction are normal. In our patients, preoperative values of peak velocities of dimension shortening and wall thickening were both reduced, compatible with the increased resistance to ejection. These values returned toward normal after operation, although the increase was significantly greater in patients receiving a stentless valve. This difference was much more in line with that in ventricular mass index than in estimated peak ventricular pressure, again suggesting that Doppler-derived valve gradients do not reflect the overall disturbance to ejection. Diastolic dysfunction is also common in left ventricular hypertrophy, and was documented preoperatively in the present study as a reduction in peak rates of dimension lengthening and wall thinning. We used M-mode echocardiographic measurements of diastolic function because we have previously shown them to be more consistently abnormal and less affected by events earlier in the cardiac cycle than the more commonly used ones based on Doppler estimates of transmitral flow velocity [23]. Again, these diastolic disturbances regressed toward normal after valve replacement. The extent of the change in peak rate of dimension increase being significantly greater in the patients with stentless valves. This difference cannot be explained directly on the basis of the dynamics of ejection, but may be attributable to a more complete regression of hypertrophy.
In contrast to the consistent differences between stentless and mechanical or stented valve, the performance of the stentless porcine valve and that of the aortic homograft was effectively identical during the follow-up period, not only in terms of valve pressure gradient, but also in the extent of regression of left ventricular hypertrophy and the improvement of function. The larger size of stentless porcine valve compared to that of the aortic homograft and mechanical or stented biological valve was not a significant factor affecting postoperative left ventricular mass index or function. The actual aortic annulus diameter was no larger in patients in whom the stentless porcine valve was inserted, as the difference of body surface area and left ventricular cavity dimension was insignificant between the three groups. It is technically possible to implant a stentless biological valve with a size of 1 to 2 mm larger than that of aortic annulus diameter, but this is usually not the case with mechanical or stented biological valve. In practice in our hospital, few aortic homografts have a diameter more that 25 mm. Thus the larger size of stentless porcine valve implanted is simply the result both of technical feasibility and valve availability in a variety of sizes.
Other Factors Related to Long-term Outcome After Aortic Valve Replacement
In line with the previous reports, the nature of the original valve disease remains an independent factor determining postoperative left ventricular mass and function within first 2 to 3 years. Aortic regurgitation is associated with greater cavity size, thus, a lower dimensional shortening fraction and a greater mass index, although the end-diastolic wall thickness and the extent and velocity of wall thickening do not differ from those of previous aortic stenosis. However, sex, increasing age, and concomitant coronary artery disease, which might have affected left ventricular function [24–26], were not found to be significant over the first 2 to 3 years. Whether this is due to the favorable effect of a stentless biological valve, used in majority of patients, a policy of full revascularization, or a relatively short follow-up time remains to be clarified. Implanting a stentless biological valve inevitably needs a longer aortic cross-clamp time than that required for a stented or mechanical valve. A perioperative study of left ventricular function has not shown any adverse effect due to longer cardioplegia time [16], and our present results extend this conclusion to at least 24 months after operation. Although the extent of reversible myocardial injury at the time of operation can be significantly reduced by using cold blood cardioplegia rather than crystalloid cardioplegia [27], this difference was no longer significant during intermediate follow-up, a finding compatible with a previous study after coronary artery bypass grafting [28].
Limitation of the Study
To achieve a reasonable case load, this study has been based on noninvasive measurements of left ventricular mass and function. Estimates of mass, using the Penn convention, have been fully documented in the setting of left ventricular hypertrophy [6, 20]. It is a method based on M-mode echocardiography and therefore would potentially be invalidated by abnormalities of ventricular shape such as aneurysm or major areas of dyskinesia. These were not present on two-dimensional echocardiogram in our patients. In 20% of patients, preoperative echocardiograms were not included for digitizing due to suboptimal quality of echocardiographic image and M-mode recordings. However, their absence was distributed similarly among the three groups. Thus, it is unlikely that the validation of a comparable baseline among three groups would have been affected by this limitation, nor would this have any impact on the postoperative data analysis. Doppler estimates of valve stenosis also have well-recognized limitations. Peak velocity across a stenotic valve is a measure of peak pressure drop, not the peak-to-peak value measured by cardiac catheterization. These estimates are based on the simplified Bernoulli equation, which assumes resistive flow across the valve. This may well be present with an aortic prosthesis [29], but flow across the normal valve (aortic homograft) is dominantly inertial, to which the simplified Bernoulli equation may not apply. Although stroke volume was not measured directly, the fact that cavity dimensions were similar in all groups of patients makes it very unlikely that the large differences in peak velocity could have been explained on this basis. The overall reproducibility of digitizing was adequate to sustain the significant changes in both ventricular function and hypertrophy after aortic valve replacement. The number of patients studied at 3 years is small, therefore, we regard the conclusion of this study being adequately supported up to 2 years after operation. We studied fewer stented biological or mechanical prostheses compared with stentless valves, but this did not prevent very consistent differences between the two being identified. However, a larger scale randomized study should be considered to confirm the long-term result, the present figures might be used to derive appropriate values for power and sample size calculation.
In conclusion, this study provides intermediate-term evidence suggesting that the stentless porcine valve can be used satisfactorily in older patients who need aortic valve replacement. In addition, it suggests greater regression of ventricular hypertrophy and corresponding improvement of left ventricular function than occurs with conventional mechanical or stented biological valve. Over the first 2 years, the performance of the Toronto stentless porcine valve remains essentially similar to that of the aortic homograft. Apart from the type of valve substitute, the nature of original valve disease, the follow-up time also determines the postoperative changes in hypertrophy and ventricular function. However, the effects of sex, advanced age, and concomitant coronary artery disease, as well as increased intraoperative ischemic time and different cardioplegia methods have insignificant effects on left ventricular function and hypertrophy during this follow-up period. Our results thus encourage the use of a stentless porcine valve in older patients requiring aortic valve replacement.
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Acknowledgments |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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Footnotes |
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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Address reprint requests to Dr Pepper, Department of Cardiothoracic Surgery, Royal Brompton Hospital, Sydney St, London, SW3 6NP, United Kingdom.
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TopFootnotesAbstractIntroductionPatients and MethodsResultsCommentAcknowledgmentsReferences |
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O. Lund, K. Emmertsen, I. Dorup, F. T. Jensen, and C. Flo Regression of left ventricular hypertrophy during 10 years after valve replacement for aortic stenosis is related to the preoperative risk profile Eur. Heart J., August 1, 2003; 24(15): 1437 - 1446. [Abstract] [Full Text] [PDF]
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 S A Olenchock Jr, J F Reed III, A Brown, and F M Garzia Improved postoperative outcomes with stentless aortic valve: a community hospital experience Heart, May 1, 2003; 89(5): 551 - 552. [Full Text] [PDF]
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M. Doss, S. Martens, J.P. Wood, T. Aybek, P. Kleine, G. Wimmer Greinecker, and A. Moritz Performance of stentless versus stented aortic valve bioprostheses in the elderly patient: a prospective randomized trial Eur. J. Cardiothorac. Surg., March 1, 2003; 23(3): 299 - 304. [Abstract] [Full Text] [PDF]
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D. B. Doty and J. R. Doty Stentless Aortic Valve Replacement: Bioprostheses Card. Surg. Adult, January 1, 2003; 2(2003): 889 - 898. [Full Text]
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G. Dellgren, M.J. Eriksson, L.A. Brodin, and K. Radegran Eleven years' experience with the Biocor stentless aortic bioprosthesis: clinical and hemodynamic follow-up with long-term relative survival rate Eur. J. Cardiothorac. Surg., December 1, 2002; 22(6): 912 - 921. [Abstract] [Full Text] [PDF]
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S. Bevilacqua, J. Gianetti, A. Ripoli, U. Paradossi, A. Giuseppe Cerillo, M. Glauber, M. L. Sacha Matteucci, M. Senni, A. Gamba, E. Quaini, et al. Aortic valve disease with severe ventricular dysfunction: stentless valve for better recovery Ann. Thorac. Surg., December 1, 2002; 74(6): 2016 - 2021. [Abstract] [Full Text] [PDF]
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X. Y. Jin and J. R. Pepper Do stentless valves make a difference? Eur. J. Cardiothorac. Surg., July 1, 2002; 22(1): 95 - 100. [Abstract] [Full Text] [PDF]
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G. Dellgren, C. M. Feindel, J. Bos, J. Ivanov, and T. E. David Aortic valve replacement with the Toronto SPV: long-term clinical and hemodynamic results Eur. J. Cardiothorac. Surg., April 1, 2002; 21(4): 698 - 702. [Abstract] [Full Text] [PDF]
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S. Silberman, J. Shaheen, O. Merin, D. Fink, N. Shapira, N. Liviatan-Strauss, and D. Bitran Exercise hemodynamics of aortic prostheses: comparison between stentless bioprostheses and mechanical valves Ann. Thorac. Surg., October 1, 2001; 72(4): 1217 - 1221. [Abstract] [Full Text] [PDF]
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I. Knez, R. Rienmuller, R. Maier, P. Rehak, B. Schrottner, H. Machler, M. Anelli-Monti, and B. Rigler Left ventricular architecture after valve replacement due to critical aortic stenosis: an approach to dis-/qualify the myth of valve prosthesis-patient mismatch? Eur. J. Cardiothorac. Surg., June 1, 2001; 19(6): 797 - 805. [Abstract] [Full Text] [PDF]
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D. J. Thomson, W.R. E. Jamieson, J. G. Dumesnil, J. J. Burgess, C. M. Peniston, J. Metras, J. A. Sullivan, J. C.W. Parrott, A. Maitland, and I. J. Cybulsky Medtronic mosaic porcine bioprosthesis: midterm investigational trial results Ann. Thorac. Surg., May 1, 2001; 71 (2007): S269 - S272. [Abstract] [Full Text] [PDF]
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W.R. E. Jamieson, M. T. Janusz, J. MacNab, and C. Henderson Hemodynamic comparison of second- and third-generation stented bioprostheses in aortic valve replacement Ann. Thorac. Surg., May 1, 2001; 71 (2007): S282 - S284. [Abstract] [Full Text] [PDF]
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X. Y. Jin and S. Westaby Pericardial and porcine stentless aortic valves: are they hemodynamically different? Ann. Thorac. Surg., May 1, 2001; 71 (2007): S311 - S314. [Abstract] [Full Text] [PDF]
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G. Ismeno, A. Renzulli, M. De Feo, A. Della Corte, F. E. Covino, and M. Cotrufo Standard versus hemodynamic plus 19-mm St Jude Medical aortic valves J. Thorac. Cardiovasc. Surg., April 1, 2001; 121(4): 723 - 728. [Abstract] [Full Text] [PDF]
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R.M Grocott-Mason, O Lund, H Elwidaa, R Mazhar, V Chandrasakeran, A.G Mitchell, C Ilsley, A Khaghani, A Rees, and M Yacoub Long-term results after aortic valve replacement in patients with congestive heart failure. Homografts vs prosthetic valves Eur. Heart J., October 2, 2000; 21(20): 1698 - 1707. [Abstract] [PDF]
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P. Pibarot and J. G. Dumesnil Hemodynamic and clinical impact of prosthesis-patient mismatch in the aortic valve position and its prevention J. Am. Coll. Cardiol., October 1, 2000; 36(4): 1131 - 1141. [Abstract] [Full Text] [PDF]
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S. Westaby, M. Horton, X. Y. Jin, T. Katsumata, O. Ahmed, S. Saito, H.-H. Li, and G. L. Grunkemeier Survival advantage of stentless aortic bioprostheses Ann. Thorac. Surg., September 1, 2000; 70(3): 785 - 791. [Abstract] [Full Text] [PDF]
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R. D. Riley, J. W. Hammon Jr, S. M. Adair, A. R. Cordell, and N. D. Kon Stentless aortic valve replacement with freestyle or Toronto SPV: an early comparison Ann. Thorac. Surg., July 1, 2000; 70(1): 48 - 51. [Abstract] [Full Text] [PDF]
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A. Kalangos, P. Trigo-Trindade, D. Vala, A. Panos, and B. Faidutti AORTIC VALVE REPLACEMENT WITH THE FREESTYLE STENTLESS BIOPROSTHESIS WITH RESPECT TO SPACIAL ORIENTATION OF PATIENT CORONARY OSTIA J. Thorac. Cardiovasc. Surg., June 1, 2000; 119(6): 1185 - 1192. [Abstract] [Full Text] [PDF]
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R. Fries, O. Wendler, H. Schieffer, and H.-J. Schafers Comparative rest and exercise hemodynamics of 23-mm stentless versus 23-mm stented aortic bioprostheses Ann. Thorac. Surg., March 1, 2000; 69(3): 817 - 822. [Abstract] [Full Text] [PDF]
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S. S. Khan, R. J. Siegel, M. A. DeRobertis, C. E. Blanche, R. M. Kass, W. Cheng, G. P. Fontana, and A. Trento Regression of hypertrophy after Carpentier-Edwards pericardial aortic valve replacement Ann. Thorac. Surg., February 1, 2000; 69(2): 531 - 535. [Abstract] [Full Text] [PDF]
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T. Walther, V. Falk, G. Langebartels, M. Kruger, U. Bernhardt, A. Diegeler, J. Gummert, R. Autschbach, and F. W. Mohr Prospectively Randomized Evaluation of Stentless Versus Conventional Biological Aortic Valves : Impact on Early Regression of Left Ventricular Hypertrophy Circulation, November 9, 1999; 100 (2009): II-6 - II-10. [Abstract] [Full Text] [PDF]
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P. Pibarot, J. G. Dumesnil, J. Jobin, P. Cartier, G. Honos, and L.-G. Durand Hemodynamic and physical performance during maximal exercise in patients with an aortic bioprosthetic valve: Comparison of stentless versus stented bioprostheses J. Am. Coll. Cardiol., November 1, 1999; 34(5): 1609 - 1617. [Abstract] [Full Text] [PDF]
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K. Niwaya, R. C. Elkins, C. J. Knott-Craig, K. Santangelo, M. B. Cannon, and M. M. Lane Normalization of left ventricular dimensions after ross operation with aortic annular reduction Ann. Thorac. Surg., September 1, 1999; 68(3): 812 - 818. [Abstract] [Full Text] [PDF]
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C. Gross, W. Harringer, H. Beran, R. Mair, K. Sihorsch, R. Hofmann, and P. Brucke Aortic valve replacement: is the stentless xenograft an alternative to the homograft? midterm results Ann. Thorac. Surg., September 1, 1999; 68(3): 919 - 924. [Abstract] [Full Text] [PDF]
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J R Gonzalez-Juanatey, M V Fernandez, F G Sampedro, J M Garcia-Acuna, J B Garcia-Bengoechea, A A Cendon, and M G de la Pena Haemodynamic performance of aortic pericardial bioprostheses and bileaflet prostheses at rest and during exercise: implications for the surgical management of patients with small aortic roots Heart, August 1, 1999; 82(2): 149 - 155. [Abstract] [Full Text] [PDF]
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H. L. Thomson, M. F. O'Brien, A. A. Almeida, P. J. Tesar, M. B. Davison, and D. J. Burstow Haemodynamics and left ventricular mass regression: a comparison of the stentless, stented and mechanical aortic valve replacement Eur. J. Cardiothorac. Surg., May 1, 1999; 13(5): 572 - 575. [Abstract] [Full Text] [PDF]
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D. Maselli, R. Pizio, L. P. Bruno, I. Di Bella, and C. De Gasperis Left ventricular mass reduction after aortic valve replacement: homografts, stentless and stented valves Ann. Thorac. Surg., April 1, 1999; 67(4): 966 - 971. [Abstract] [Full Text] [PDF]
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X. Y. Jin, R. Pillai, and S. Westaby Medium-term determinants of left ventricular mass index after stentless aortic valve replacement Ann. Thorac. Surg., February 1, 1999; 67(2): 411 - 416. [Abstract] [Full Text] [PDF]
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U. Hvass, G. M. Palatianos, R. Frassani, C. Puricelli, and M. O'Brien MULTICENTER STUDY OF STENTLESS VALVE REPLACEMENT IN THE SMALL AORTIC ROOT J. Thorac. Cardiovasc. Surg., February 1, 1999; 117(2): 267 - 272. [Abstract] [Full Text] [PDF]
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O. Lund, V. Chandrasekaran, R. Grocott-Mason, H. Elwidaa, R. Mazhar, A. Khaghani, A. Mitchell, C. Ilsley, and M. H. Yacoub PRIMARY AORTIC VALVE REPLACEMENT WITH ALLOGRAFTS OVER TWENTY-FIVE YEARS: VALVE-RELATED AND PROCEDURE-RELATED DETERMINANTS OF OUTCOME J. Thorac. Cardiovasc. Surg., January 1, 1999; 117(1): 77 - 91. [Abstract] [Full Text] [PDF]
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R. D. Paulis, MD, L. Sommariva, MD, L. Colagrande, MD, G. M. De Matteis, MD, S. Fratini, MD, F. Tomai, MD, C. Bassano, MD, A. P. de Peppo, MD, and L. Chiariello, MD REGRESSION OF LEFT VENTRICULAR HYPERTROPHY AFTER AORTIC VALVE REPLACEMENT FOR AORTIC STENOSIS WITH DIFFERENT VALVE SUBSTITUTES J. Thorac. Cardiovasc. Surg., October 1, 1998; 116(4): 590 - 598. [Abstract] [Full Text] [PDF]
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X. Y. Jin, K. Dhital, K. Bhattacharya, R. Pieris, N. Amarasena, and R. Pillai Fifth-year hemodynamic performance of the prima stentless aortic valve Ann. Thorac. Surg., September 1, 1998; 66(3): 805 - 809. [Abstract] [Full Text] [PDF]
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S. Westaby, X. Y. Jin, T. Katsumata, A. Arifi, and P. Braidley Valve replacement with a stentless bioprosthesis: Versatility of theporcine aortic root J. Thorac. Cardiovasc. Surg., September 1, 1998; 116(3): 477 - 481. [Abstract] [Full Text]
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T. E. David, R. Puschmann, J. Ivanov, J. Bos, S. Armstrong, C. M. Feindel, and H. E. Scully Aortic valve replacement with stentless and stented porcine valves: a case-match study J. Thorac. Cardiovasc. Surg., August 1, 1998; 116(2): 236 - 240. [Abstract] [Full Text] [PDF]
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S. Westaby, H. A. Huysmans, and T. E. David Stentless Aortic Bioprostheses: Compelling Data From the Second International Symposium Ann. Thorac. Surg., January 1, 1998; 65(1): 235 - 235. [Abstract] [Full Text] [PDF]
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R. P. Siebenmann Implantation of the Toronto SPV Stentless Porcine Bioprosthesis in Dilated Ascending Aorta Ann. Thorac. Surg., October 1, 1997; 64(4): 1197 - 1200. [Abstract] [Full Text]
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D. F. Del Rizzo, B. S. Goldman, G. T. Christakis, and T. E. David HEMODYNAMIC BENEFITS OF THE TORONTO STENTLESS VALVE J. Thorac. Cardiovasc. Surg., December 1, 1996; 112(6): 1431 - 1446. [Abstract] [Full Text]
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