Thank you for your inquiry regarding CMS996v4, Appropriate Treatment for ST-Segment Elevation Myocardial Infarction (STEMI) Patients in the Emergency Department (ED). The measure’s denominator exclusion criteria uses the relevantPeriod attribute in relation to their respective QDM datatypes rather than the locationPeriod attribute. As defined in the QDM v5.6, the relevantPeriod for the “Encounter, Performed” datatype is the time the encounter began (admission time) to the time the encounter ended (discharge time) [ https://ecqi.healthit.gov/sites/default/files/QDM-v5.6-508.pdf ]. The relevantPeriod attribute does not consider the patient’s location during the ED encounter, unlike the locationPeriod attribute which addresses the time the patient arrived at a particular location to the time the patient departed the location. CMS996v4 only uses locationPeriod in its measure numerator definitions and uses relevantPeriod in its denominator exclusion definitions. The physical location of the patient is not relevant to measure's denominator exclusion criteria. In the example depicted in the inquiry, even though the patient experienced cardiac arrest requiring CPR during transport to or in the cardiac catheterization lab, as long as there is proper EHR documentation that the ED encounter had not yet ended and there was no patient discharge disposition, the encounter would be excluded from the measure denominator. Lastly, we want to clarify that the measure denominator builds from the “Encounter, Performed: Emergency Department Evaluation and Management Visit” QDM datatype and value set rather than "Encounter, Performed: Emergency Department Visit". The "Encounter, Performed: Emergency Department Visit" datatype and ED Visit value set are used in the ED arrival and departure time functions to define the measure's numerator criteria.