Both these methods can have significant deviation from the 'true' valve area, they are both dependent on the flow rate across the valve.
The cath is less dependent on operator error and is the more "direct" measurement, its questionable if it is more accurate
In my instance, my echos had so much noise in them from the valve that the heart cath was the more accurate. In general it's a toss up as to which is more accurate. Your physician should carefully weigh the results of both the cath and the echo to determine when your surgery is needed.<!-- / message --><!-- sig -->