<?xml version="1.0" encoding="utf-8"?>

<ECG xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <id root="1.2.392.200111.1.2.2.20191015.141109"/>
  <name>李思思</name>
  <effectiveTime>
    <low value="20191011110754.000" inclusive="true"/>
    <high value="20191011110809.000" inclusive="false"/>
  </effectiveTime>
</ECG>

XmlDocument doc = new XmlDocument();
doc.Load(@"D:\XMLFile\FtSampledData.xml");

XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
nsmgr.AddNamespace("xsi", "http://www.w3.org/2001/XMLSchema-instance");

XmlElement root = doc.DocumentElement;

XmlNode name = root.SelectSingleNode("name", nsmgr);