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Ann Thorac Surg 1996;62:690
© 1996 The Society of Thoracic Surgeons
DR DEMETRE M. NICOLOFF (Minneapolis, MN): It seems that the peak gradient was about a 20-mm difference between your autograft and your stented valves, and yet you found that this did not show any regression, or the hypertrophy and the diastolic filling pressures stayed the same or did not regress. It is often said that a 10- or 15-mm gradient makes no difference once you replace a valve that has a 100-mm gradient. Could you make a comment on that?
DR L. HENRY EDMUNDS JR (Philadelphia, PA): Doctor Pepper, I would also like to know how much regression in left ventricular mass you saw within the first 6 months.
DR PEPPER: Perhaps I could take Dr Edmunds' question first. We saw most of the regression in the first 6 months. After 6 months there is very little change. With regard to the gradient, first this is not a peak-to-peak gradient as in a cardiac catheter. It is a pressure fall-off measured by Doppler echocardiography, and it is calculated using a modified Bernoulli theorem, which assumes resistive flow. That may be appropriate for a stented prosthesis, but in a stentless prosthesis, the flow is inertial and therefore this assumption may not be appropriate. Also the measurement is done at rest, but the gradient may be more significant on exercise.
But we think more important than the gradient is actually the reduction in wall stress, and here there are at least two other elements that come into play, that is, subendocardial blood flow and, in a minority of patients, the presence of incoordinate left ventricular relaxation due to abnormalities of the longitudinal fibers, which lie largely in the subendocardium.
DR VIVEK RAO (Toronto, Ont, Canada): As you heard from our group earlier today, we were unable to detect any differences in left ventricular mass regression between those patients who received mechanical valves, stented tissue valves, or stentless tissue valves. You have included mechanical valves in your stented valve group. Have you performed an analysis examining stented tissue valves alone, and if so, were you still able to detect differences between groups?
DR PEPPER: No, we did not do that. You will note from the presentation that the number of mechanical valves is small, and we are continuing to evaluate this group. We do not think the results will be very different with larger numbers; however, time will tell. The point we are trying to make is that it is the presence of a rigid stent that the left ventricle does not seem to like.
DR BRADLEY S. ALLEN (Chicago, IL): You stated you believe that the differences you demonstrated are due not to gradients across the valve, but to other forces or stresses produced by stented valves. Therefore, I am wondering whether you examined the effects of different gradients in stented valve patients. In other words, did you compare, say, patients with stented valves larger than 23 mm with those smaller than 23 mm where the gradient would be higher? This should either support or refute your conclusions that these findings are due to more than just a small valve with a high gradient.
DR PEPPER: Yes, we did look at different valve sizes. There was not a great impact, although over the size of 27 mm there was a slight improvement in the velocity of posterior wall thinning but no difference in any of the other parameters.
Related Article
Ann. Thorac. Surg. 1996 62: 683-690.
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