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Recent insights into the relation between haemodynamic severity and clinical outcome have altered our approach to the patient with moderate valvar aortic stenosis. At the heart of this discussion is the changing definition of “severe” (and hence “moderate”) aortic stenosis. Historically, severe stenosis was defined in terms of valve area based on the fluid dynamics concept that flow is not restricted until an orifice is reduced to a quarter its original size. As patients typically underwent cardiac catheterisation only after symptom onset, few data on disease progression or haemodynamic severity in asymptomatic patients were available. However, clinical experience supported this definition and it was used successfully for many years to identify patients likely to benefit from valve replacement.
Relation between haemodynamic severity and clinical symptoms
The first indication that the traditional definition of severe aortic stenosis might need revision came from clinical studies showing substantial overlap in haemodynamic severity between symptomatic and asymptomatic adults despite very different clinical outcomes.1-4 While the observed overlap in pressure gradients was not surprising given their flow dependence, the overlap in valve areas (even when indexed for body size) was unexpected, leading to the question: why do some patients become symptomatic with only “moderate” stenosis while others remain asymptomatic despite “severe” valvar obstruction?
The second piece of evidence suggesting that the traditional definition of severe stenosis might no longer be adequate for patient management was the demonstration that not only pressure gradients but also valve areas and other measures of stenosis severity including valve resistance vary with changes in volume flow rate, whether calculated by traditional invasive or newer non-invasive approaches.5 ,6The lack of a measure of stenosis severity that is constant for a given valve anatomy raised the question: what criteria should be used to define “severe” aortic stenosis?
New definition of aortic stenosis severity
If we …