Subaortic Stenosis With Elevated Aortic Gradients in a Pregnant Patient.

Subaortic stenosis is an obstructive lesion that may be exacerbated by pregnancy. We describe the management of a 39-year-old woman presenting at 37 weeks of pregnancy with a murmur who is found to have a subaortic membrane with severely elevated left ventricular outflow gradients. (Level of Difficulty: Beginner.).

Subvalvular aortic stenosis (SAS) is the second most prevalent type of aortic stenosis, accounting for 6.5% of adult congenital heart disease (1). There are 3 anatomic variants: a thin crescent-shaped membrane below the aortic valve (most predominant), a fibromuscular ridge, or a fibromuscular channel along the left ventricular outflow tract (LVOT) causing obstruction (2). Although SAS may be associated with congenital defects in 60% of cases, it is rarely diagnosed before the first decade of life (3) and is considered an acquired heart disease. Women with SAS may be diagnosed after discovering a murmur or unmasking of symptoms during hemodynamically stressful events such as pregnancy. Pregnancy increases cardiac output by increasing heart rate and stroke volume, and reduces systemic vascular resistance (4). The natural history of SAS in pregnancy is not well understood, with limited data extrapolated from case reports and small studies (5, 6, 7). We describe the case of a 39-year-old woman presenting for induction of labor, found to have a murmur and subaortic membrane with severe LVOT obstruction.

Learning Objectives

To recognize the importance of the physical examination in guiding management of subvalvular stenosis in pregnant patients.

To learn the appropriate management of asymptomatic patients with subvalvular stenosis during pregnancy and delivery.

History of Presentation

The patient is a 39-year-old woman G2P0101 who presented to obstetric triage at 37 weeks for abdominal pain. Fetal monitoring showed late decelerations, so the patient was admitted for induction of labor. Physical examination on admission was notable for a normal jugular venous pressure of 10 cm, normal S1 and S2, and harsh mid-peaking systolic murmur heard best at the left upper sternal border without radiation or change with Valsalva. Abdomen was gravid and firm, her lungs were clear, and she had no lower extremity edema.

Medical History

LM had a preterm uncomplicated vaginal delivery for cervical dilatation 13 years before presentation. She had 2 visits for chest pain 5 to 6 years before presentation and was diagnosed with anxiety. Since then she has had no recurrent chest pain, dyspnea, or syncope. She had no limitations to exercise tolerance before pregnancy. Her pregnancy thus far was uncomplicated without chest pain, shortness of breath, lower extremity edema, or hypertension.

Differential Diagnosis

The differential diagnosis for systolic murmur in pregnancy includes valvular aortic stenosis (including bicuspid aortic valve), subvalvular and supravalvular aortic stenosis, hypertrophic obstructive cardiomyopathy, and physiologic flow murmur of pregnancy.

Investigations

Laboratory tests on presentation were unremarkable. Electrocardiogram showed sinus rhythm with mild tachycardia, no ST changes or hypertrophy. Echocardiogram showed left ventricular (LV) ejection fraction of 71%, small LV size (LV end diastolic diameter 3.7 cm), moderate mid-LV cavitary obstruction (∼35 mm Hg), a subaortic membrane, and peak gradient of 50 mm Hg. There was no LV hypertrophy (posterior diameter 0.9 cm, intraventricular septum 0.8 cm) or mitral valve anterior septal motion. She had a normal-appearing trileaflet aortic valve with no regurgitation (Figure 1). Because of the echocardiogram findings, cardiology was consulted regarding management during labor and delivery.

Figure 1

Subaortic Membrane on Echocardiogram

(A) Parasternal long-axis view of subaortic membrane (arrow) in the peripartum period with (B) color Doppler showing left ventricular outflow tract (LVOT) turbulence. (C) Three-chamber view of subaortic membrane (arrow) with (D) color Doppler of LVOT turbulence. Continuous-wave Doppler illustrating LVOT gradient of 50 mm Hg peripartum (E), improved to 33 mm Hg postpartum (F). Pulse-wave Doppler showing midcavitary gradient peripartum (G,I), which resolves postpartum (H,J).

Management

LM’s case was discussed among maternal fetal medicine, obstetrical anesthesia, and adult cardiology. Fetal status warranted immediate induction of labor. An early epidural was placed with adequate pain control. Because the patient was stable and asymptomatic, vaginal delivery was deemed to be safe with an assisted second stage if cardiac symptoms occurred. The patient tolerated induction; however, her fetus developed recurrent prolonged decelerations, so a cesarean delivery was performed without maternal complications.

Discussion

This case highlights the management of severe SAS during labor and delivery. There are few reports detailing SAS in pregnancy (5, 6, 7), therefore data are extrapolated from patients with valvular aortic stenosis. Older studies showed a high mortality rate of 15% to 20% for patients with severe stenosis (8), although contemporary studies suggest mortality closer to 10% (9). These patients are at high risk for cardiac complications during pregnancy, with heart failure rates ranging from 10.0% to 26.3% (7,9).

The 2008 American Heart Association guidelines recommend consideration of surgical resection in patients with peak gradient above 50 mm Hg, mean gradient above 30 mm Hg, ejection fraction <50%, marked LV hypertrophy, or abnormal blood pressure response on exercise testing. In patients with mean gradient below 30 mm Hg and no LV hypertrophy, the recommendation is for annual follow-up and stress testing (10). For our patient, although her peak gradient met criteria for surgery, she was compensated without heart failure or structural changes. This highlights the importance of a detailed history and physical in assessing severity of subvalvular stenosis, especially during pregnancy. Cardiac output is increased during pregnancy (4), which may increase the obstructive gradient measured on imaging. Therefore, relying on the gradient alone may not be appropriate for determining the need for surgical intervention. Additionally in LM, her peak gradient decreased postpartum, validating the effect of pregnancy on cardiac parameters. Therefore, the preceding guidelines may need reconsideration during pregnancy.

Expectant management of SAS in pregnancy includes accounting for possible cardiac complications. An interdisciplinary approach to management is recommended. Hemodynamic changes in pregnancy and labor/delivery may precipitate volume overload, arrhythmias, or heart failure in women with LV obstruction. Volume management is paramount: fluids may be required for preload during labor, but diuresis might be needed postpartum as peripheral vascular resistance increases. Telemetry monitoring may be considered if symptoms suggest arrhythmias. Adequate pain control is recommended to reduce tachycardia resulting from pain and anxiety. While this is achieved with an epidural/spinal anesthesia, the associated hypotension may worsen LVOT gradients and precipitate obstruction. If vasopressors are needed, pure vasoconstrictors are recommended over inopressors. Mode of delivery depends on severity of LVOT obstruction. In asymptomatic patients, a vaginal delivery is preferred, with cesarean delivery reserved for obstetrical indications. Reducing Valsalva or an assisted seconds stage may be considered in severe LVOT obstruction or if cardiac symptoms are present. Cardiac indications for cesarean delivery include symptoms of LVOT obstruction or hemodynamic instability, with postoperative monitoring in an intensive care unit.

After discharge, cardiology follow-up is imperative for symptom monitoring and serial echocardiograms to guide the need for future surgical intervention. Exercise testing also may be beneficial to unmask symptoms. Transesophageal echocardiogram, cardiac computed tomography, or cardiac magnetic resonance imaging also can be considered to clarify anatomy. Reliable birth control is also necessary to avoid pregnancy until the patient has been optimized. Patients contemplating subsequent pregnancies should undergo preconception counseling with cardiology and obstetrics before attempting conception.

Follow-Up

LM remained asymptomatic during the remainder of her hospital admission. Repeat echocardiogram on postoperative day 2 showed hyperdynamic LV, resolution of midcavitary obstruction, and no significant change in LVOT gradients (peak gradient 47 mm Hg), which may have been due to early postpartum hemodynamics. She was discharged on postoperative day 3 on progesterone-only birth control with cardiology follow-up. At 1-month postpartum, she remained asymptomatic. Repeat echocardiogram performed at this time showed normal LV and right ventricle size and function, resolution of midcavitary obstruction, reduction in LVOT gradients (peak gradient 33 mm Hg), and normal aortic valve (Figure 1).

Conclusions

To our knowledge, this is the first published description of a patient with an isolated subaortic membrane in the late third trimester of pregnancy, including management through labor, delivery, and the postpartum period. Her case highlights the importance of the physical examination in guiding management of SAS in pregnant patients, given that the hemodynamics of pregnancy may cause an overestimation of subvalvular gradients in the perinatal period. We demonstrate that in asymptomatic patients it is safe to pursue vaginal delivery and monitor with serial echocardiograms unless the presence of symptoms causes changes in management. This case also emphasizes the importance of a multidisciplinary approach to SAS during pregnancy and the need for cardiac follow-up postpartum to determine the need for surgery.