CNS Pharmacology USMLE Step 1 Practice Question

A 60-year-old man with a history of anterior myocardial infarction two years ago presents to his cardiologist reporting palpitations, mild dyspnea on exertion, and occasional lightheadedness over the past three weeks. His blood pressure is 128/76 mmHg, heart rate is irregularly irregular at 94 beats per minute, and oxygen saturation is 97% on room air. An electrocardiogram confirms atrial fibrillation with no acute ischemic changes. Echocardiography reveals a left ventricular ejection fraction of 40% with an area of anteroseptal hypokinesis consistent with prior infarction. Serum electrolytes, TSH, and renal function are within normal limits. The cardiologist considers pharmacologic rhythm control but advises against a potent sodium channel blocker because it can precipitate life-threatening ventricular arrhythmias in patients with structural heart disease. Which of the following agents is most likely being avoided?