Thank you for your inquiry regarding CMS996: Appropriate Treatment for ST-Segment Elevation Myocardial Infarction (STEMI) Patients in the Emergency Department (ED). The measure’s initial population includes all emergency department (ED) encounters for patients 18 years and older at the start of the encounter with a diagnosis of STEMI during the ED encounter, that ends during the measurement period (aside from those meeting measure denominator exclusions or exceptions). We emphasize that STEMIs occurring during a subsequent inpatient encounter are not captured in the measure denominator. The QDM does not prescribe the source of STEMI diagnosis data in the EHR. Diagnoses may be found in a patient’s problem list, encounter diagnosis list, claims data, or other sources within the EHR. A patient with a STEMI diagnosis may be captured in the measure in two ways. First, a STEMI diagnosis can be pulled directly from the ED encounter if a STEMI diagnosis was coded during the encounter, as indicated by the measure logic definition below.   ED Encounter with Encounter Diagnosis of STEMI “ED Encounter During MP” EDEncounter   with EDEncounter.diagnoses EncounterDiagnosis    such that EncounterDiagnosis.code in “STEMI”   Second, the patient can have a diagnosis pulled from a claim, problem list, or other source in the EHR as long as the prevalencePeriod of the STEMI diagnosis started during the ED encounter relevantPeriod. PrevalencePeriod is an attribute of the “Diagnosis” datatype and signifies the onset dateTime to abatement dateTime of the STEMI diagnosis. RelevantPeriod is an attribute of the “Encounter, Performed”: “Emergency Department Evaluation and Management Visit” datatype and signifies the startTime that the encounter began (admission time) to the stopTime that the encounter ended (discharge time). The definition describing this measure logic can be found below.   ED Encounter with a Diagnosis of STEMI “ED Encounter During MP” EDEncounter   with [“Diagnosis”: “STEMI”] DxSTEMI    such that DxSTEMI.prevalencePeriod starts during EDEncounter.relevantPeriod   To differentiate between active and historic diagnoses in the problem list, we recommend working with your EHR vendor to ensure that both the onset and abatement times are populated in the EHR accurately and mapped to the appropriate QDM data elements to avoid misattribution. We encourage you to ensure that the timing components associated with the measure are captured accurately, even if the STEMI diagnosis is being pulled from a source other than the encounter diagnosis.