获取XML 属性值

<controlActProcess classCode="CACT" moodCode="EVN">
    <queryByParameter>
      <statusCode code="new"/>
      <queryByParameterPayload>
       
        <statusCode code="new"/>
        <actId>
          <value>
            <!--申请单编号-->
            <item extension="" root="2.16.156.10011.1.24"/>
            <!--住院号-->
            <item extension="" root="2.16.156.10011.1.12"/>
            <!--门诊号-->
            <item extension="" root="2.16.156.10011.1.11"/>
          </value>
        </actId>
        <!--申请单开立者ID(医务人员ID)-->
        <authorId>
          <value>
            <item extension="" root="2.16.156.10011.1.4"/>
          </value>
        </authorId>
        <!--申请单有效期间-->
        <effectiveTime>
          <value>
            <low value="20211031090047"/>
            <high value="20241226201025"/>
          </value>
        </effectiveTime>
        <!--患者ID-->
        <patientId>
          <value>
            <!-- 身份证号 -->
            <item extension="" root="2.16.156.10011.1.3"/>
            <!-- 医保卡号 -->
            <item extension="000110012131231" root="2.16.156.10011.1.15"/>
            <!-- 患者ID -->
            <item extension="" root="2.16.156.10011.2.5.1.4"/>
          </value>
        </patientId>
      </queryByParameterPayload>
    </queryByParameter>
  </controlActProcess>

XmlNode strMenCardNo = document1.DocumentElement.SelectSingleNode("xsi:controlActProcess/xsi:queryByParameter/xsi:queryByParameterPayload/xsi:patientId/xsi:value/xsi:item@root='2.16.156.10011.1.15'", nsmgr);