| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
J Thorac Cardiovasc Surg 2004;127:1852-1854
© 2004 The American Association for Thoracic Surgery
Letter to the editor |
Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, Cleveland, OH 44195, USA
Reply to the Editor:
We have long respected the excellent and prolific work of Dumesnil and Pibarot, so it is not surprising that we referred to their publications in our articles. However, they are unhappy in part with the way we have interpreted (or misinterpreted) their work,1,2 and in part with the surgical recommendations we based on survival data from our multicenter meta-analysis,1 which differ from their own, which were based largely on functional prosthesis performance data.
 |
What we studied |
|---|
 Top What we studied What we did not...Alternative proposalTwo notes of cautionDisclaimerReferences |
|---|
Long-term survival is a relevant and important goal of aortic valve replacement,3 although how it is associated with efficiency of prosthetic devices remains controversial. Use of small label-size prostheses has been presumed by many surgeons to reduce survival after valve replacement. When patients were stratified by label size in our large study, however, prosthesis size was found to have little impact on survival (in contrast to substantial impact of patient factors, such as age). Unlike all previous studies, ours had the statistical power to detect even small differences in survival, with 1109 prostheses of label size 19 mm or smaller and 2984 of label size 21 mm.
To increase sensitivity, we focused our survival analysis on the geometric dimension of the internal orifice of the prosthesis normalized to patient size (prosthesis-patient size), a concept familiar in congenital heart disease but less so in adult heart disease.4 Stratifying patients by prosthesis-patient size revealed no impact on long-term or intermediate survival. However, in risk-adjusted and balancing score–adjusted analyses, when geometric orifice size was less than about the lower 95% confidence limit for normal human aortic valve size, which is uncommon in prudent aortic valve replacement (only 85 patients had prosthesis-patient size smaller than 0.85 cm2/m2), early survival was affected to a small extent (1% to 2%).
Adjusting prosthesis-patient size for prosthesis model
Physics of blood flow dictates that as prosthesis geometric orifice size decreases, energy loss at a given flow rate increases. However, inertia, turbulence, other disturbances of blood flow velocity profile, and many other factors also affect energy loss. Therefore, as described in the multi-institutional article,1 we searched for a relation of prosthesis-patient size to survival that was specific for each model of prosthesis by means of interaction terms. We found none of these to be statistically significant, indicating similarity of the relationship of geometric prosthesis-patient size to survival.
Surgical inferences
Surgical inferences drawn concerning prosthesis size selection were based on survival data within the context of prudent valve replacement in these numerous representative institutions. We had no functional prosthesis performance data after operation for these patients, which might have further increased sensitivity of the survival analysis, thereby further refining prognosis and possibly surgical recommendations.
|
What we did not study |
|---|
|
TopWhat we studiedWhat we did not...Alternative proposalTwo notes of cautionDisclaimerReferences |
|---|
We also studiously avoided the term prosthesis-patient mismatch. No doubt a clinical syndrome of prosthesis-patient mismatch occurs, as described by Rahimtoola5 and Rahimtoola and Murphy.6 However, through the years its definition has ceased being a clinical diagnosis and has become arbitrarily inferred from postoperative echocardiographic velocity measurements. We had no postoperative echocardiographic data in the assembled databases to address this issue, so we cannot discuss it further.
|
Alternative proposal |
|---|
|
TopWhat we studiedWhat we did not...Alternative proposalTwo notes of cautionDisclaimerReferences |
|---|
Prerequisites
Before accepting this alternative, several things need to be in place and clarified. Just as we had available an equation relating patient size to normal aortic valve size derived from 6801 measurements,9 so we need an equation relating patient size to functional prosthesis size that is based on a substantial number of measurements. For this, high-quality individual patient postoperative Doppler velocity data for each label size of current aortic valve prostheses would need to be assembled, along with height and weight, and an appropriate analysis would need to be performed to obtain the equation. However, accurate (unbiased), precise (reproducible), and extensive (power) functional estimates of prosthesis size are elusive. They are related to many patient characteristics, left ventricular outflow complex factors, time, measurement variability, interobserver variability, method of computation, and myriad other factors. It is sobering that even in vitro laboratory estimates of hemodynamic properties of prostheses are fraught with important institutional variation (as much as 200% to 400%)!10 Thus, it is likely that the in vivo relation will have substantial scatter. Then an association should be sought between survival and functional prosthesis-patient size, with reference to the normalizations suggested in the articles.1,2
|
Two notes of caution |
|---|
|
TopWhat we studiedWhat we did not...Alternative proposalTwo notes of cautionDisclaimerReferences |
|---|
Avoiding 1000 deaths per year
The second note of caution is the notion that if a policy of liberal aortic root enlargement accompanying aortic valve replacement were adopted, then "each year in North America...approximately 1000 operative deaths could potentially be avoided." This too is a stretch of statistics. The extrapolation is based on Castro and colleagues' observation11 of a single death among 114 patients (70% confidence limits 0.1%-3.0% mortality) in the concurrent setting of 543 patients deemed not in need of aortic root enlargement; the latter sustained a mortality of 4.1% with 70% confidence limits of 3.2% to 5.1%.11 These confidence limits and the context caution against concluding that widespread application of the proposed algorithm is likely to lower operative mortality.
Small sets of data pose two dangers, identifying spurious relations in small subgroups and failing to identify relations because of lack of statistical power. These concerns motivated collaborators in the multi-institutional study to contribute more than 13,000 patients with 70,000 patient years of follow-up.
|
Disclaimer |
|---|
|
TopWhat we studiedWhat we did not...Alternative proposalTwo notes of cautionDisclaimerReferences |
|---|
We remain interested in performance of prostheses, but we believe that available evidence suggests that other factors have more impact on long-term all-cause mortality than does prosthesis-patient size, however expressed.
|
References |
|---|
|
TopWhat we studiedWhat we did not...Alternative proposalTwo notes of cautionDisclaimerReferences |
|---|
15 to 20 years. J Am Coll Cardiol. 2003;42:1720–1721Related Article
This article has been cited by other articles:
|
|
 |
|
  P. Pibarot, J. G. Dumesnil, G. Tasca, C. G. Koch, F. Khandwala, F. G. Estafanous, F. D. Loop, and E. H. Blackstone Letter Regarding Article by Koch et al, "Impact of Prothesis-Patient Size on Functional Recovery After Aortic Valve Replacement" * Response Circulation, November 22, 2005; 112(21): e333 - e333. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
