A 65-year-old man with a history of type 2 diabetes mellitus and hypertension presents to the community

A 65-year-old man with a history of type 2 diabetes mellitus and hypertension presents to the community clinic with concerns for fatigue, lightheadedness, and difficulty breathing. He is currently taking lisinopril 20 mg daily, metoprolol succinate 50 mg BID, and metformin 1,000 mg BID. He reports that these symptoms began 2 days ago and worsen with physical activity. He reports no chest pain or syncope. On examination, he appears pale. His pulse is 42 beats/min and irregular. His other vital signs are within normal limits. His ECG shows intermittent nonconducted P waves (i.e., dropped QRS complexes), constant PR intervals of 0.20 seconds in the conducted beats, and constant intervals between P waves. There are three P waves for every two QRS complexes. Which of the following is the suspected diagnosis? First-degree atrioventricular block Mobitz type I second-degree atrioventricular block Mobitz type II second-degree atrioventricular block Third-degree atrioventricular block