About small aortic prostheses.

We read with interest the case report of Oswal et al. [1], but were greatly concerned with their conclusion about the use of very small Carbomedics prostheses for aortic valve replacement in adults, based on the hemodynamics of one prosthesis only! The authors demonstrated with their patient a resting gradient that was felt to be acceptable. They demonstrated an increase in the cardiac output with dobutamine, but failed to demonstrate any increase in the mean gradient across the prosthesis. They thus concluded that the hemodynamic performance of the 16 mm Carbomedics prosthesis is favorable. First, it is a fact that a resting transvalvar gradient may not represent the person’s status during exercise [2]. Second, this response to dobutamine is unusual [3], though not unheard of. Some patients with native aortic stenosis may not increase their transvalvar flow rate or transvalvar gradient with exercise or pharmacological stress [4]. This could be caused by failure of a diseased myocardium to respond to the stress. Unfortunately, there was no mention in the report of the left ventricular systolic function, but of note was the low resting cardiac output. Lastly, an unusual and unexplained finding with their measurements was the increase in the left ventricular outflow tract systolic diameter with dobutamine. This unexpected increase might have contributed to the increase in the cardiac output, which otherwise might not have been so favorable in spite of the contribution by the expected increase in heart rate. There has always been much concern about patients being given small size prostheses because of small aortic roots [5]. Smaller prostheses may not provide clinical or hemodynamic relief both at rest and with exercise, with persistently high transvalvar gradients and left ventricular hypertrophy. In the young with a large body surface area, the usually present high cardiac output across the small effective orifice area of the small prosthesis continue to produce high transvalvar gradient. In our population of patients with rheumatic valve disease, operated on in their early teens and given small mechanical prostheses, increasing gradient across the prosthesis and increasing left ventricular wall thickness has been noted on follow-up with time. The same has also been noted with older patients given smaller prostheses for one reason or another. Many of these patients became symptomatic and had to have repeat surgery and given larger prostheses. Except for the odd prosthesis with excessive pannus formation or thrombosis as the underlying cause for the increasing gradients, most of the other prostheses were found to be functioning normally. Hence it is our belief that in adults, small aortic prostheses whether biological or mechanical should be avoided as much as possible even if one has to revert to enlarging the aortic root. What is more, we believe that findings based on unusual hemodynamics in a case report that the authors described as unique, should not be the basis for general statements about the use of small aortic prostheses in the adult that may be misleading and carry grave consequences.