Abstract Body (Do not enter title and authors here): Goals:
To describe the clinical course of a 27-year-old woman with hypertrophic obstructive cardiomyopathy (HoCM) who developed a severe left ventricular outflow tract (LVOT) obstruction with a stress cardiomyopathy following discontinuation of Mavacamten due to an unplanned pregnancy. This case highlights the challenges of managing HoCM during pregnancy, consequences of treatment interruption, and postpartum decision-making.

Description of the Case:
This is a case of a 27-year-old woman with HoCM who was treated with Metoprolol and Mavacamten for 20 months, reducing her LVOT gradient from 70 mmHg to 9 mmHg at rest (Figure 1A and 1B). Despite oral contraceptive use, she had an unplanned pregnancy and immediately discontinued therapy due to teratogenicity concerns.

Six weeks later, she was hospitalized for shortness of breath and lightheadedness and found to have elevated troponins. Transthoracic echocardiography (TTE) showed new mid-septal wall motion abnormalities, reduced EF to 40%, and severe mitral regurgitation with systolic anterior motion of the mitral valve. Gradients were not assessed. Due to concern for acute coronary syndrome, a left heart catheterization was normal, and stress cardiomyopathy was suspected. After receiving 3L IV fluids, she developed flash pulmonary edema and was transferred to our center for worsening hypotension.

On arrival, TTE showed a severe LVOT obstruction (peak gradient 110 mmHg with Valsalva). She was started on IV esmolol and phenylephrine. Over several days, her LVOT gradient improved to 70 mmHg at rest. Pressors were weaned and she was transitioned to oral metoprolol. The pregnancy was electively terminated, and she was discharged home.

One month later, the wall motion abnormalities resolved and her LVOT gradient at rest was 51 mmHg (Figure 1C) and Mavacamten was resumed at 5 mg daily, and a non-hormonal intrauterine device was placed. Three months later, her LVOT gradient improved to 8 mmHg at rest (Figure 1D), and reported no functional limitations.

Discussion:
Despite prior excellent response, abrupt mavacamten discontinuation due to pregnancy led to recurrence of severe obstruction, exacerbated by stress cardiomyopathy (Table 1). Mavacamten may reduce the efficacy of combined hormonal contraceptives, contributing to contraceptive failure. This case underscores the need for preconception counseling and multidisciplinary monitoring for women of childbearing age prior to initiating myosin inhibitors.