Management of Obstructive Hypertrophic Cardiomyopathy
A 74-year-old woman with a known history of hypertrophic cardiomyopathy (HCM) presents to the office for worsening shortness of breath and lightheadedness.
Her vital signs include heart rate (HR) 56 bpm, blood pressure (BP) 118/72 mm Hg, and oxygen saturation 99% on room air. Physical examination reveals unremarkable S1 and S2 with a grade 1/6 systolic ejection murmur, lung examination reveals no crackles, and there is no lower extremity edema. Echocardiography is notable for maximal basal septal thickness 2 cm, with systolic anterior motion (SAM) of the mitral valve leading to moderate posteriorly directed mitral regurgitation (Figure 1). At rest, Doppler gradient through the left ventricular outflow tract (LVOT) is 25 mm Hg. The gradient through the LVOT increases to 130 mm Hg with Valsalva maneuver. A 48-hour telemetric monitor demonstrates a few short runs of supraventricular tachycardia but no atrial fibrillation or ventricular arrhythmias (VAs).
She has been maintained on beta-blocker and calcium channel blocker therapy with metoprolol succinate 50 mg twice daily and extended-release verapamil 120 mg in the morning and 80 mg in the evening. Despite her medications, she notes worsening shortness of breath and lightheadedness while walking only a few steps. Electrocardiography (ECG) in the office shows sinus rhythm at a rate of 56 bpm and left ventricular hypertrophy (LVH) with repolarization abnormality consistent with HCM; her ECG findings are unchanged from prior.
Which one of the following is the best next step in the management of this patient?