Cardiac Arrest - Ultrasound Detection of Occult Perfusion

The goal of this study is to describe the population of patients presenting after out of hospital cardiac arrest with occult perfusion, defined as a patient without a palpable pulse but with some evidence of pulsatile arterial flow. The main questions it aims to answer are: * To measure the prevalence of patients of patients presenting to the emergency department after out of hospital cardiac arrest with occult perfusion * To measure the association between occult perfusion and survival * Compare survival between patients with occult perfusion that were treated as pulseless by ACLS interventions vs those treated as hypotensive Researchers will describe the percentage of out-of-hospital cardiac arrest presenting to the emergency department without a pulse but with occult perfusion. Researchers will also compare survival endpoints (ROSC, Survival to hospital Admission, and Survival to Ho