EKG annotation example using a paired Observation with valuePeriod (id = "ekg-abnormal-period")

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

<!--  A paired Observation annotates an abnormal interval in the referenced EKG waveform.
  --><Observation xmlns="http://hl7.org/fhir">
  <id value="ekg-abnormal-period"/> 
  <text> 
    <status value="generated"/> <div xmlns="http://www.w3.org/1999/xhtml">
      <p> This Observation identifies the abnormal interval from 09:30:35.240 to 09:30:35.320
         in the EKG waveform referenced by derivedFrom.</p> 
    </div> 
  </text> 
  <status value="final"/> 
  <code> 
    <text value="Abnormal EKG period"/> 
  </code> 
  <subject> 
    <reference value="Patient/f001"/> 
    <display value="P. van de Heuvel"/> 
  </subject> 
  <effectiveDateTime value="2015-02-19T10:00:00+01:00"/> 
  <performer> 
    <reference value="Practitioner/f005"/> 
    <display value="A. Langeveld"/> 
  </performer> 
  <valuePeriod> 
    <start value="2015-02-19T09:30:35.240+01:00"/> 
    <end value="2015-02-19T09:30:35.320+01:00"/> 
  </valuePeriod> 
  <derivedFrom> 
    <reference value="Observation/ekg"/> 
    <display value="EKG waveform"/> 
  </derivedFrom> 
</Observation>