MSFinals-5759
A 68-year-old man with lung cancer presents to the Emergency Department complaining of chest pain and shortness of breath. He reports no cough or sputum production. Upon auscultation, his chest is clear. His pulse is irregularly irregular and measures 110 bpm, while his oxygen saturation is 86% on room air. He is breathing at a rate of 26 breaths per minute. What diagnostic investigation is most likely to be effective in this scenario?