Heart Failure with Reduced Ejection Fraction (HFrEF) — Pharmacotherapy Sequencing

A 72-year-old man with a 20-year history of poorly controlled hypertension and previous anterior wall myocardial infarction (AWMI) 5 years ago presents with progressive dyspnea on exertion and orthopnea for 3 months. Physical examination reveals elevated JVP, bilateral basal crackles, and a laterally displaced apex beat. Echocardiography shows left ventricular ejection fraction (LVEF) of 32% with global hypokinesis. He is already on ramipril 10 mg daily, carvedilol 12.5 mg twice daily, and furosemide 40 mg daily. His current serum creatinine is 1.8 mg/dL (eGFR 38 mL/min/1.73m²) and serum potassium is 5.2 mEq/L. Which of the following is the MOST appropriate next therapeutic addition to his current regimen?