The HCM Patient with Symptoms
A 49-year-old female high school teacher is referred for evaluation of hypertrophic cardiomyopathy (HCM). She had presented to her primary care provider with symptoms of mild exertional angina and dyspnea. A transthoracic echocardiogram is obtained and reveals increased left ventricular (LV) wall thickness concerning for HCM.
Vital signs included heart rate 72 bpm and blood pressure 121/82 mm Hg. Her body mass index is 24 kg/m2. Physical examination reveals a grade 2/6 crescendo–decrescendo systolic murmur at the lower left sternal border that increases to a grade 4/6 with Valsalva. Lungs are clear to auscultation and there is no lower extremity edema. A repeat transthoracic echocardiogram reveals ejection fraction 61%, increased LV wall thickness with asymmetric involvement of the septum extending to the apex, systolic anterior motion (SAM) of the mitral valve with obstruction, and secondary mitral regurgitation (MR), which is severe. The maximal LV wall thickness is measured at 15 mm (Figure 1), and a maximal instantaneous Doppler gradient in the left ventricular outflow tract (LVOT) is measured at 90 mm Hg.
Figure 1: Transthoracic echocardiogram showing the left ventricle in the parasternal long axis view. A, The thickened ventricular septum measuring 15 mm. B, Continuous wave Doppler assessment through the aortic valve with a peak gradient measuring 90 mmHg.
She is initiated on beta-blocker therapy with metoprolol succinate 25 mg daily. A 24-hour ambulator monitor does not reveal any arrhythmias, including absence of ventricular tachycardia. A cardiac magnetic resonance imaging confirms LV asymmetric hypertrophy with a sigmoid-shaped septum measuring up to 18 mm (Figure 2).
Figure 2: Cardiac magnetic resonance imaging confirming the presence of an asymmetric thickened ventricular septum measuring 18 mm.
At her 1-month follow-up visit, she reports worsening angina, particularly after meals, and worsening shortness of breath with minimal exertion despite compliant use of a beta-blocker. Heart rates at home have been consistently around 60 bpm. Her physical examination and repeat echocardiogram confirm that the systolic murmur and LVOT gradient are both unchanged.
Which one of the following is the best next step for the management of this patient's symptoms?