Question: A 66-year-old patient presents with a report of dyspnea, fatigue, and occasional palpitations for the past several days. The nurse practitioner detects an irregular heart rhythm on auscultation, with variable intensity of S1 and no audible S3 or S4. Which of the following is the most likely diagnosis? Group of answer choices First-degree heart block Mitral stenosis Atrial fibrillation Aortic stenosis