Thank you for your inquiry regarding CMS996: Appropriate Treatment for ST-Segment Elevation Myocardial Infarction (STEMI) Patients in the Emergency Department (ED). The measure excludes cardiopulmonary arrest, including cardiac arrest, if it occurs 24 hours or less before the start of the ED encounter or during the ED encounter. The scenario described in the inquiry, where the patient experienced cardiac arrest en route to or in the cardiac catheterization lab before a percutaneous coronary intervention (PCI), would be excluded from the measure denominator as long as documentation of the onset dateTime of the cardiac arrest diagnosis occurred within the ED encounter relevantPeriod or occurred 24 hours or less before the start of the ED encounter relevantPeriod. As defined in the QDM v5.6, the ED encounter relevantPeriod 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 ]. We emphasize that the QDM does not prescribe the source of 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. Therefore, we recommend accurate EHR documentation to ensure that encounters meeting exclusion criteria are properly excluded from the denominator.