I had a echo back in July 2009 shortly before I had a ton of other testing including a cath that showed quite a difference in my pressures and EF from echo, MRI and cath.
My ep told me then there was such a difference possibly due to tech and reader error...so I started doing research and found that there's a +/- 10% for echo's and sometimes more depending on the tech & reader's expertise some reports show up to +/- 15% errors which can mean alot.
Here's some info I found and what brought up a conversation with dr's I've seen: http://www.medhelp.org/user_journals/show/305549/One-size-fits-all?personal_page_id=861727 not
one dr I've asked can tell me what echo parameter standards their office uses - they have to do some research was the answer I got, this included the largest teaching university here in FL.
This info isn't meant to start a heated debate just what I've found for my personal use and what information my dr's have given me.
Ask your dr what echo parameter standards they use, you may get an answer and be able to research the variables on it and error rates.