Full Text
The Full Text of this article is available as a PDF (87.8 KB).
. 1999 Jun;81(6):671. doi: 10.1136/hrt.81.6.671
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.