A 17 year-old male presents to the Emergency Department with palpitations and shortness of breath that started suddenly one hour ago while driving with his friends. No prior medical/surgical history. Patient denies any drugs, alcohol, tobacco use. On your exam, he appears short of breath. Heart rate is regular and tachycardic.
A 63 year old male arrives via EMS in acute respiratory distress. Medics note he is in atrial fibrillation with a heart rate in the 150s. You ponder the age old question as you walk to the resuscitation bay: "Is the high heart rate causing the respiratory distress or vice versa?"