Practice question

A 72-year-old woman with hypertension and coronary artery disease presents with exertional dyspnea and leg swelling. Echocardiogram shows a left ventricular ejection fraction of 30 percent and NYHA class III symptoms despite maximally tolerated lisinopril and metoprolol succinate. Her estimated glomerular filtration rate is 55 mL/min/1.73 m² and potassium is 4.4 mEq/L. Which additional medication class should be added to provide further mortality benefit for heart failure with reduced ejection fraction?