A 1-hour-old boy is evaluated for respiratory distress. The patient was born at 39 weeks gestation via cesarean delivery. The mother's pregnancy was complicated by gestational diabetes, and she was nonadherent with treatment. Birth weight was at the 95th percentile. Apgar scores were 5 and 7 at 1 and 5 minutes, respectively. Temperature is 36.6 C (97.9 F), pulse is 160/min, and respirations are 70/min. Oxygen saturation is 94% on room air. The patient is in mild respiratory distress with a plethoric appearance. Cardiac examination reveals a 3/6 systolic ejection murmur. Physical examination is otherwise unremarkable. Bedside echocardiography shows increased thickness of the interventricular septal wall. Which of the following is the best initial therapy for this patient?
Hypertrophic cardiomyopathy in infants of diabetic mothers | |
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LVOT = left ventricular outflow tract. | |
This newborn has mild respiratory distress and a systolic ejection murmur with sonographic evidence of interventricular septal wall thickening, consistent with hypertrophic cardiomyopathy (HCM). Infants of mothers with gestational diabetes are at risk of developing a transient form of HCM. Exposure to excess glucose in utero leads to fetal hyperglycemia, hyperinsulinemia, and increased fat and glycogen deposition that is prominent within interventricular septum cardiomyocytes, causing HCM. Although most affected infants are asymptomatic, some develop heart failure due to severe left ventricular outflow tract (LVOT) obstruction (eg, respiratory distress, hypotension, systolic ejection murmur). Other neonatal consequences of maternal diabetes may be present, such as macrosomia and plethora (due to polycythemia).
Management of symptomatic HCM is aimed at increasing LV blood volume in order to alleviate LVOT obstruction and improve cardiac output. It includes intravenous fluids and beta blockers (eg, propranolol).
Beta blockers reduce heart rate (negative chronotropic effect), which increases LV diastolic filling time, as well as end-diastolic volume (ie, preload).
In addition, the negative inotropic effect of beta blockers decreases the pressure gradient between the LVOT and aorta, further reducing dynamic LVOT obstruction.
Treatment is rarely required for more than a few weeks because insulin levels quickly normalize, leading to reduced septal thickening and self-resolution of HCM.
(Choice A) Dobutamine is primarily a beta-1 agonist with positive chronotropic and inotropic effects. It decreases LV blood volume and increases the pressure gradient between the LVOT and the aorta, likely worsening LVOT obstruction in HCM.
(Choices B and D) Furosemide (diuretic) and nitroprusside (venous and arterial dilator) decrease preload and LV blood volume. These medications are expected to worsen LVOT obstruction in HCM.
(Choice C) Indomethacin is a nonsteroidal anti-inflammatory drug indicated for closure of a patent ductus arteriosus, a condition with increased incidence in infants of diabetic mothers. However, the ductus arteriosus is physiologically open immediately after birth, and symptoms (eg, continuous machine-like murmur, poor feeding, respiratory distress) do not occur unless it fails to close after the newborn period.
Educational objective:
Infants of diabetic mothers are at increased risk for transient hypertrophic cardiomyopathy with dynamic left ventricular outflow tract obstruction (LVOT). Management includes beta blockers (eg, propranolol), which reduce LVOT obstruction by increasing LV filling time and end-diastolic volume (due to reduction in heart rate) and decreasing the pressure gradient between the LVOT and aorta (due to reduction in contractility).