 |
| Fig.3.17 |
It should
be recognized that knowledge of the gradient across a stenotic valve
does not provide all the information necessary to assess the severity
of obstruction. The gradient will vary with flow across the stenotic
valve orifice and will increase in high flow situations and decrease
in low flow situations. Thus, a patient with a fixed valve area
will have a higher gradient during exercise when cardiac output
is increased, than at rest when cardiac output is lower. Figure
3.17 shows the idealized relationship of valve gradient to flow.
As flow across a valve rises, as with rapid tachycardia, the gradients
will vary.
Valve orifice size is generally considered not to vary with the
amount of flow across the valve and is, therefore, a preferred expression
of the severity of a given stenosis. The following discussion will
begin with estimates of gradients across stenotic valves and then
review some of the simplified methods for estimating valve orifice
area.
2004