CORRESPONDENCE
Reply
Helmut Baumgartner, MD, FACCa
a Department of Cardiology, Vienna General Hospital, University of Vienna, Wahringer Gurtel 18-20, A-1090 Vienna, Austria
We appreciate the letter by DeGroff and colleagues regarding our recent article and their awareness of the importance of pressure recovery for the assessment of aortic stenosis. These authors apparently misunderstood our statement, which they criticize in their letter. As a matter of fact, almost all of the references listed by DeGroff et al. are cited in our article, as far as original publications are concerned. Of course, we are not aware of articles in press. All six published original articles (including our own previous work [1]) listed in the letter are, however, in vitro studies, three of which refer to aortic stenosis. As stated in our article, pressure recovery has indeed been demonstrated by other investigators and by us in experimental studies. However, all the extensive clinical work that has been done so far on the Doppler assessment of aortic stenosis has generally neglected pressure recovery as a source of discrepancy between Doppler and catheter gradients. To the best of our knowledge, our study was the first to demonstrate that pressure recovery can indeed cause clinically relevant "overestimation" of catheter gradients by Doppler echocardiography in the clinical setting of aortic stenosis. The referenced study of Lemler et al. (2) (two authors of the letter contributed to this report) may be another one, but has apparently not been published yet.
It is correct that Doppler and catheter measurements should ideally be obtained simultaneously. However, accurate measurement of maximal transvalvular velocities in aortic stenosis needs careful interrogation of the jet from various windows (apical, right parasternal, suprasternal), requiring various patient positions including the left and right lateral (sometimes extreme) position. Conditions that allow for such demanding Doppler examinations, however, can hardly be provided in the catheterization laboratory while simultaneously performing proper invasive pressure measurements. Thus, invasive and noninvasive studies were performed within 24 h at stable conditions in all patients, and special care was taken to collect the data at comparable heart rates with all patients being in sinus rhythm. Nevertheless, we agree that nonsimultaneous measurement remains a limitation, as discussed in our article. However, simultaneous measurement would have suffered from the limitations discussed earlier.
Of course, we agree that all well-known sources of error for invasive pressure measurements with fluid-filled catheters and echocardiographic measurements, such as Doppler gradients, orifice areas and dimensions of the ascending aorta, remain limitations for such clinical studies. Nevertheless, it was possible to clearly demonstrate the effect of pressure recovery on the relation between Doppler and catheter gradients despite the acknowledged limitations of measurement techniques currently used in clinical practice. Finally, we cannot agree that our article should have included more information on previous data regarding discrepancies between Doppler and catheter gradients across aortic stenosis. As far as pressure recovery is concerned, these published reports comprise only in vitro studies. As a matter of fact, these studies (including our own work [1]) are extensively discussed and form the basis of this clinical study, which sought to confirm previous in vitro findings.
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References
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1. Niederberger J, Schima H, Maurer G, Baumgartner H. Importance of pressure recovery for the assessment of aortic stenosis by Doppler ultrasound: role of aortic size, aortic valve area, and direction of the stenotic jet in vitro. Circulation. 1996;94:1934–1940[Abstract/Free Full Text]
2. Lemler MS, Valdes-Cruz LM, Shandas R, Cape EG. Insights into catheter/Doppler discrepancies: a clinical study of congenital aortic stenosis. Am J Cardiol. In press.
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References