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Ann Thorac Surg 2002;73:1822-1829
© 2002 The Society of Thoracic Surgeons
a Division of Cardiovascular Surgery of Sunnybrook and Women’s College Health Sciences Centre, Toronto, Ontario, Canada
* Address reprint requests to Dr Christakis, Sunnybrook and Women’s College Health Sciences Centre, H406-2075 Bayview Ave, Toronto, Ontario M4N 3M5, Canada
e-mail: george.christakis{at}swchsc.on.ca
Presented at the Thirty-seventh Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 29–31, 2001.
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Abstract |
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Methods. To assess the prevalence of patient-prosthesis mismatch and the influence of small valve size on survival, we prospectively studied 1,129 consecutive patients undergoing aortic valve replacement between 1990 and 2000. Mean and peak gradients and indexed effective orifice area were measured by transthoracic echocardiography postoperatively (3 months to 10 years). Abnormal postoperative gradients were defined as those patients with mean or peak gradient above the 90th percentile (mean gradient 
21 or peak gradient 38 mm Hg). Patient-prosthesis mismatch was defined as those patients with indexed effective orifice area below the 10th percentile (< 0.60 cm2/m2).
Results. A multivariable analysis identified internal diameter of the implanted valve as the only independent predictor of abnormal gradients postoperatively. However, there was no significant difference in actuarial survival between normal and abnormal gradient groups (7 years: 91.2% ± 1.5% versus 95.0% ± 2.2%; p = 0.48). Freedom from New York Heart Association class III or IV (7 years: 74.5% ± 3.1% versus 74.6% ± 6.2%; p = 0.66) and left ventricular mass index were not different between normal and abnormal gradient groups. Patients with and without patient-prosthesis mismatch were similar with respect to postoperative left ventricular mass index, 7-year survival (95.1% ± 1.3% versus 94.7% ± 3.0%; p = 0.54), and 7-year freedom from New York Heart Association class III or IV (79.3% ± 6.6% versus 74.5% ± 2.5%; p = 0.40). In patients with patient-prosthesis mismatch and abnormal gradients, the majority had prosthesis dysfunction owing to degeneration.
Conclusions. Severe patient-prosthesis mismatch is rare after aortic valve replacement. Patient-prosthesis mismatch, abnormal gradient, and the size of valve implanted do not influence left ventricular mass index or intermediate-term survival.
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Introduction |
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Material and methods |
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TopAbstractIntroductionMaterial and methodsResultsCommentDiscussionReferences |
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Prostheses
The selection of the prosthesis was based on the patient’s age, history of previous thromboembolism or bleeding disorder, and the preferences of the patient, cardiologist, and surgeon. Prostheses included 7 homografts, 182 stented porcine bioprostheses (3 Carpentier Edwards porcine, 162 Hancock II, 17 Hancock modified orifice), 318 stented pericardial bioprostheses (297 Carpentier Edwards, 5 Mitroflow, 16 Medtronic Intact), 211 stentless porcine bioprostheses (199 Toronto SPV, 10 Prima Edwards, 2 Freestyle), 24 tilting disc mechanical valves (13 Björk-Shiley, 11 Medtronic Hall), and 387 bileaflet mechanical valves (169 Carbomedics, 64 Carbomedics tophat, 70 St. Jude mechanical, 84 St. Jude mechanical HP series).
We used two different methods for assessing prosthesis size: manufacturer’s labeled size and the true internal valve diameter. Manufacturer’s labeled size is commonly used to express prosthesis size. However, this method is nonuniform and may lead to erroneous comparisons among valves. We have previously recommended the use of internal diameter as a standard for assessment of valve size and for comparison of valve performance [2].
Echocardiography
Preoperative echocardiograms were performed 0 to 7 days before the operation. All patients were followed with serial transthoracic echocardiograms as previously described [2]. All measurements described in this study were derived directly from echocardiographic measurements (Appendix). The first examination was performed just before discharge. Subsequent follow-up examinations occurred at 3 to 6 months, 1 year, and annually thereafter. Echocardiographic data collected included mean and peak gradients, indexed effective orifice areas (IEOA), and left ventricular mass index (LVMI), as previously described [2]. Techniques used for assessment of hemodynamics follow the recommendations of ASE. Interobserver variability among the 3 physicians performing LVMI echocardiographic measurements has been documented as less than 10%.
Follow-up
Most patients presented for follow-up at 3 months and annually at the surgeon’s office. For those unable to attend, a telephone interview was conducted. Postoperative symptomatic status and survival data were obtained from these interviews. Follow-up was 98% complete in this group of patients.
Statistical analysis
Baseline comparisons between groups were performed with analysis of variance for continuous data and 
2 or Fisher’s exact test for categorical data. Early outcomes were compared by analysis of variance or 2 tests when appropriate. Covariant adjustment was performed using stepwise logistic regression model to assess the predictors of postoperative high gradient. Statistical significance is assumed for p less than 0.05. Late survival was compared between groups by log rank methods.
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Results |
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Definition of patient-prosthesis mismatch
The distribution of the postoperative IEOA (effective orifice area divided by body surface area) for all patients in this study (as measured by echocardiography) is shown in Figure 4.
The mean value of IEOA was 0.94 ± 0.32 cm2/m2. Patient-prosthesis mismatch was defined as occurring in those patients below the 10th percentile value for the lowest postoperative IEOA (< 0.60 cm2/m2). Table 2
shows patients’ preoperative characteristics in the nonmismatch and PPM groups. There were more female patients in the PPM group. Valve size and internal diameter of implanted prostheses were significantly smaller in the mismatch group. Annulus enlargement was more prevalent in the PPM group, and stentless valves were less frequently implanted in patients with PPM. Figure 5
shows postoperative LVMI for patients with and without PPM. There was no difference in LVMI between the two groups at any follow-up period. Figure 6
shows actuarial survival and freedom from New York Heart Association class III or IV of the two groups. There were no significant differences between patients with or without PPM.
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21 mm Hg and IEOA 
0.6 cm2/m2), group 2 (MG < 21 mm Hg and IEOA 0.6 cm2/m2), group 3 (MG 21 mm Hg and IEOA > 0.6 cm2/m2), and group 4 (MG < 21 mm Hg and IEOA > 0.6 cm2/m2). In patients with at least one postoperative echocardiogram in which both MG and IEOA were measured, the distribution of patients was as follows: group 1, 3.8%; group 2, 7.1%; group 3, 3.6%; and group 4, 85.5% (based on a total of 447 patients who had both measurements performed and survived).
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Comment |
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Abnormal gradients
In this study, we also assessed PPM on the basis of elevated gradients, picking the 90th percentile for mean or peak postoperative gradient. Pibarot and colleagues [6], who suggest PPM exists at an IEOA of 0.85 cm2/m2, demonstrated MG of 15 ± 8 and 22 ± 9 mm Hg in their nonmismatch and mismatch patient groups. The difference was statistically significant. However, the gradients were very low in both groups, and the difference in gradients was less than the sensitivity error of echocardiographic measurements. This calls into question the clinical relevance of these findings. Patients with abnormal gradients after aortic valve replacement in this study had equivalent left ventricular mass regression during follow-up as patients with low gradients. This suggests that gradients across aortic valve prostheses are low enough and clinically insignificant and do not influence left ventricular hypertrophy regression. Patients with high gradients also had similar survival and symptom-free status as patients with low gradients. This suggests that gradients (at least for the intermediate follow-up period) are clinically insignificant and do not influence patient outcomes.
The only independent predictor of abnormal gradients after aortic valve replacement in this study was the internal diameter of the prosthesis implanted. Valve type or other clinical criteria did not influence postoperative gradients. This suggests that although smaller valves produce higher gradients, they do not influence postoperative outcomes [11].
Indexed effective orifice area
Comparing patients with and without PPM by our definition, we demonstrated that patients with PPM had similar postoperative MG, reduction in left ventricular hypertrophy, intermediate-term survival, and freedom from symptoms. These data suggest that even with the most conservative definition of PPM, there is no significant survival or hemodynamic difference between patients in the two groups. Pibarot and associates [5], who have championed the PPM theory, studied the impact of PPM on survival and found no difference between those with and without mismatch (7-year survival, 79% ± 3% and 75% ± 4%; p = 0.59, for nonmismatch and mismatch groups, respectively). Rao and associates [12] studied PPM in 2,504 patients undergoing aortic valve replacement. They demonstrated only valve-related mortality was higher in the PPM group at 10 years, but overall survival was no different. This retrospective study was not randomized, and valve-related mortality included mechanisms of death that are totally unrelated to PPM (embolic stroke, valve failure, endocarditis, bleeding, reoperation, and so forth). Furthermore, this study had no echocardiographic data. Effective orifice area was obtained from in vitro data supplied by the manufacturers according to the valve size implanted. Patient-prosthesis mismatch was simply assumed on the basis of calculated numbers unrelated to individual patients. He and associates [13], who assessed 30-year survival after aortic valve replacement in the small aortic root, concluded that body surface area (even in this high-risk group) influenced survival only in patients with concomitant coronary artery bypass grafting. Sawant and coworkers [14] demonstrated that in patients with small aortic roots, body surface area and valve size were not determinants of long-term survival. Although it has been suggested that there is less regression of left ventricular hypertrophy in patients with PPM [15], we found no differences. Even among a group of 10 patients with IEOA less than 0.6 cm2/m2 and MG more than 21 mm Hg, only 3 patients had persistently elevated LVMI at more than 5 years postoperatively. This suggests that even under the most severe definition, PPM is rare if not clinically insignificant.
Consistent perspective for patient-prosthesis mismatch
There is very little evidence in the literature to support the hypothesis that PPM decreases long-term survival. Patient-prosthesis mismatch has been accepted on the basis of assumptions, indirect evidence, and intuitive reasoning. Patient-prosthesis mismatch has mostly been defined by the presence of abnormal gradients in a setting of decreased IEOA. The commonly accepted principle is that the combination of high gradients and low effective orifice area leads to poor long-term survival. This was not supported by the data in the current study. A recent study by Medalion and associates [11] has very scientifically demonstrated that PPM does not adversely impact on long-term survival, and that valve size may be unimportant.
The scientific logic used to assess PPM must be congruent with the logic and scientific evidence used in treating patients with native aortic valve disease in general. One should not use one set of assumptions and logic for PPM and a completely different set for treating patients with native aortic valve disease. The scientific evidence and logic that surgeons and cardiologists currently use to treat patients with aortic stenosis is based on a study by Ross and Braunwald [16]. Except for asymptomatic patients with severe aortic stenosis (gradient > 100 mm Hg or effective orifice area < 0.6 cm2, American College of Cardiology/American Heart Association guidelines [17]), we currently replace the aortic valve in patients with aortic stenosis who have significant gradients (MG > 50 mm Hg) and symptoms of congestive heart failure, chest pain, or syncope based on the survival data of Ross and Braunwald [16]. It is rare to operate on patients with moderate gradients (mean, 21 to 35 mm Hg) and no symptoms (except for other concomitant cardiac surgery) inasmuch as long-term survival is not improved in these patients. Using this consistent logic, the authors question why a surgeon would consider an asymptomatic patient after aortic valve replacement with mild to moderate gradients to be at risk of death owing to PPM. If there truly was scientific evidence that PPM with mild to moderate gradients and IEOA less than 0.85 cm2/m2 decreased long-term survival, then we should be operating on all patients with mild to moderate aortic stenosis. Similarly, a criticism often used to support the PPM theory is the evidence from exercise gradients. The commonly espoused theory is that patients with mild to moderate gradients at rest have much higher gradients during exercise. The logical extension is that patients with high exercise gradients (especially young patients) will have incomplete regression of left ventricular hypertrophy, and therefore poor long-term survival. If one were to use consistent logic, the corollary to this theory is that we should exercise all patients (especially young patients) with mild to moderate native aortic stenosis, and operate on patients with high exercise gradients to improve long-term survival. We do not do this because there is no evidence to support this. Using consistent logic based on known scientific data, one should conclude that PPM is rare and even when it does exist, it does not influence long-term survival.
Limitations of the study
We have used an equally empirical and arbitrary method of defining abnormal gradients and PPM as all previous investigators have. Therefore, the continuum between abnormal or normal gradients and between PPM and no PPM is blunted by creating two supposedly distinct groups. Outcome differences may be accentuated or diminished by patients being placed in one group or another arbitrarily. Patients with intermediate or moderate PPM (IEOA > 0.6 cm2/m2 and < 0.75 cm2/m2) have been placed in the non-PPM group in our study, and could have influenced outcomes. This study, however, was prospectively designed to assess abnormal gradients and PPM in two distinct categorical groupings to compare our data to the work of previous authors who have also used two groups. In future, we plan to divide patients in a more continuous grouping as suggested by Rahimtoola [10]. In addition, it is possible that patients with very low cardiac outputs could have deceivingly low gradients. However, the incidence of very low cardiac output in a population of patients who are asymptomatic is unknown.
The patients in this study were not homogeneous and included patients with aortic insufficiency and patients undergoing double valve replacement and root procedures. A more homogeneous group of patients would be preferable, although the loading conditions on a prosthetic valve should be similar in all patient subgroups. Patients with echocardiographic data from centers outside our own were excluded prospectively to remove the variability and quality issues of echocardiograms performed outside our institution. This was a prospective criterion of this study. We do not expect a selection bias for PPM based on patient referral patterns from outside this institution. We also identified a statistically higher operative mortality in the patients with PPM (2.6% versus 0.14%), which may be an argument to suggest PPM influences early mortality. This study was not designed to assess determinants of early mortality. In previous studies, we have not found PPM to be an independent predictor of early mortality. The results are also skewed by selection bias, as only patients who survived for at least 3 months could have follow-up echocardiograms.
Severe PPM with excessive gradients and incomplete left ventricular hypertrophy regression is rare after aortic valve replacement. We demonstrated no difference in medium-term survival, symptom-free status, or left ventricular hypertrophy regression in patients with conservatively defined criteria for PPM and elevated postoperative gradients. Our data support recent suggestions that small valve size does not influence intermediate survival.
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Appendix |
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2. Peak Pressure Gradient. Peak velocities, obtained from pulsed-wave and continuous-wave Doppler, were converted to peak pressure gradient using Bernoulli’s equation:
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PPeak is peak systolic aortic pressure gradient in millimeters of mercury; V2 is prosthetic peak velocity in meters per second, measured with continuous-wave Doppler; and V1 is peak velocity proximal to valve in meters per second, measured with pulsed-wave Doppler.
3. Mean Pressure Gradient. Mean transvalvular pressure gradient was calculated by subtraction of the mean pressure proximal to the valve from the mean distal pressure:
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PMean is mean transvalvular pressure gradient in millimeters of mercury; P2 is prosthetic mean pressure measured with continuous-wave Doppler; and P1 is proximal mean pressure measured with pulsed-wave Doppler in the left ventricular outflow tract.
4. Left Ventricular Mass Index. Left ventricular mass was calculated by the ASE cube method:
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Discussion |
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DR CHRISTAKIS: That is a very good point. Operative deaths sometimes can be attributed to patient-prosthesis mismatch. This was not part of our prospective study but we did look at it,and we found that there were no differences in operative mortality between patients with or without patient-prosthesis mismatch, nor between patients with normal and abnormal gradients. My feeling would be that if there were such a condition and there were increased deaths, it would probably be caused by poor myocardial protection from a hypertrophied ventricle, inasmuch as by relieving the obstruction, even by palliating the obstruction, you should still have better function postoperatively than you did preoperatively. But that is a valid point and it needs to be studied. This study did not address that at all, but it is a very valid point.
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W. B. Eichinger, F. Botzenhardt, A. Keithahn, R. Guenzinger, S. Bleiziffer, I. Wagner, R. Bauernschmitt, and R. Lange Exercise hemodynamics of bovine versus porcine bioprostheses: A prospective randomized comparison of the mosaic and perimount aortic valves J. Thorac. Cardiovasc. Surg., May 1, 2005; 129(5): 1056 - 1063. [Abstract] [Full Text] [PDF]
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 F. A. Crawford Jr Residual pulmonary artery hypertension after mitral valve replacement: Size matters! J. Am. Coll. Cardiol., April 5, 2005; 45(7): 1041 - 1042. [Full Text] [PDF]
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G. Tasca, F. Brunelli, M. Cirillo, M. Dalla Tomba, Z. Mhagna, G. Troise, and E. Quaini Impact of the Improvement of Valve Area Achieved With Aortic Valve Replacement on the Regression of Left Ventricular Hypertrophy in Patients With Pure Aortic Stenosis Ann. Thorac. Surg., April 1, 2005; 79(4): 1291 - 1296. [Abstract] [Full Text] [PDF]
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R. G. Fuster, J. A. M. Argudo, O. G. Albarova, F. H. Sos, S. C. Lopez, M. B. Codoner, J. A. B. Minano, and I. R. Albarran Patient-prosthesis mismatch in aortic valve replacement: really tolerable? Eur. J. Cardiothorac. Surg., March 1, 2005; 27(3): 441 - 449. [Abstract] [Full Text] [PDF]
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R.-U. Kuehnel, R. Puchner, A. Pohl, M. O. Wendt, M. Hartrumpf, M. Pohl, and J. M. Albes Characteristic resistance curves of aortic valve substitutes facilitate individualized decision for a particular type Eur. J. Cardiothorac. Surg., March 1, 2005; 27(3): 450 - 455. [Abstract] [Full Text] [PDF]
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C. Amarelli, A. Della Corte, G. Romano, G. Iasevoli, G. Dialetto, L. S. De Santo, M. De Feo, M. Torella, M. Scardone, and M. Cotrufo Left ventricular mass regression after aortic valve replacement with 17-mm St Jude Medical mechanical prostheses in isolated aortic stenosis J. Thorac. Cardiovasc. Surg., March 1, 2005; 129(3): 512 - 517. [Abstract] [Full Text] [PDF]
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G. Tasca, F. Brunelli, M. Cirillo, M. DallaTomba, Z. Mhagna, G. Troise, and E. Quaini Impact of Valve Prosthesis-Patient Mismatch on Left Ventricular Mass Regression Following Aortic Valve Replacement Ann. Thorac. Surg., February 1, 2005; 79(2): 505 - 510. [Abstract] [Full Text] [PDF]
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T. Bottio, L. Caprili, D. Casarotto, and G. Gerosa Small aortic annulus: The hydrodynamic performances of 5 commercially available bileaflet mechanical valves J. Thorac. Cardiovasc. Surg., September 1, 2004; 128(3): 457 - 462. [Abstract] [Full Text] [PDF]
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T. Bottio, G. Rizzoli, G. Thiene, G. Nesseris, D. Casarotto, and G. Gerosa Hemodynamic and clinical outcomes with the Biocor valve in the aortic position: An 8-year experience J. Thorac. Cardiovasc. Surg., June 1, 2004; 127(6): 1616 - 1623. [Abstract] [Full Text] [PDF]
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M. Ruel, F. D. Rubens, R. G. Masters, A. L. Pipe, P. Bedard, P. J. Hendry, B. K. Lam, I. G. Burwash, W. G. Goldstein, M. P. Brais, et al. Late incidence and predictors of persistent or recurrent heart failure in patients with aortic prosthetic valves J. Thorac. Cardiovasc. Surg., January 1, 2004; 127(1): 149 - 159. [Abstract] [Full Text] [PDF]
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G. Tasca, F. Brunelli, M. Cirillo, A. Amaducci, Z. Mhagna, G. Troise, and E. Quaini Mass regression in aortic stenosis after valve replacement with small size pericardial bioprosthesis Ann. Thorac. Surg., October 1, 2003; 76(4): 1107 - 1113. [Abstract] [Full Text] [PDF]
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E. H. Blackstone, D. M. Cosgrove, W.R. E. Jamieson, N. J. Birkmeyer, J. H. Lemmer Jr, D. C. Miller, E. G. Butchart, G. Rizzoli, M. Yacoub, and A. Chai Prosthesis size and long-term survival after aortic valve replacement J. Thorac. Cardiovasc. Surg., September 1, 2003; 126(3): 783 - 793. [Abstract] [Full Text] [PDF]
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C. Blais, J. G. Dumesnil, R. Baillot, S. Simard, D. Doyle, and P. Pibarot Impact of Valve Prosthesis-Patient Mismatch on Short-Term Mortality After Aortic Valve Replacement Circulation, August 26, 2003; 108(8): 983 - 988. [Abstract] [Full Text] [PDF]
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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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A. M. Gillinov, E. H. Blackstone, and L. L. Rodriguez Prosthesis-patient size: measurement and clinical implications J. Thorac. Cardiovasc. Surg., August 1, 2003; 126(2): 313 - 316. [Full Text] [PDF]
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N. D. Desai and G. T. Christakis Stented Mechanical/Bioprosthetic Aortic Valve Replacement Card. Surg. Adult, January 1, 2003; 2(2003): 825 - 856. [Full Text]
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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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