Scenario: This cardiac rhythm strip (leads I and II) is from a 19-year-old college student who came to a local emergency department after sustaining a football injury involving his arm. After a thorough physical assessment, it was determined that he did not sustain any other injuries or trauma. A radiograph revealed a fracture of his humerus that would require an immediate surgical procedure. He had been given intravenous pain medications and cardiac monitoring had been started in surgery when this irregular rhythm was noted. His current state of health is excellent and he has no prior medical problems and is not taking any medications or supplements. All vital signs are within normal range.

Sinus arrhythmia. Sinus arrhythmia is under the control of the sinus node, as evidenced by the normal P-wave morphology and the fixed PR interval; however, the P-P intervals...

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