Poor feeding and weak femoral pulses in a 6-week-old
Sara is a 6-week-old girl, born at term and discharged on day 2. She now takes only 40 mL of formula every 3 hours instead of 90 mL, and sweats during feeds. She has no fever. Weight is 3.4 kg (birth weight 3.2 kg). Respiratory rate is 70/min, heart rate 180/min, and oxygen saturation 96% in the right hand and 95% in the right foot. Blood pressure is 92/56 mmHg in the right arm, 88/54 mmHg in the left arm, 68/40 mmHg in the right leg, and 66/42 mmHg in the left leg. There is a precordial bulge, a grade 3/6 systolic murmur heard at the left infraclavicular area and back, a gallop rhythm, and the liver edge 3 cm below the costal margin. Femoral pulses are weak and capillary refill is 3 seconds.
1. Interpret the four-limb blood pressures and oxygen saturations. What is the most likely diagnosis, and which features argue against a simple innocent murmur?
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The four-limb pressures show a 24-26 mmHg arm-leg gradient with weak femoral pulses, which localizes the obstruction to the aortic arch or isthmus. The oxygen saturations are equal, so there is no right-to-left shunt. The murmur in the left infraclavicular area and back is consistent with coarctation; the gallop, hepatomegaly, tachypnea, and poor feeding indicate heart failure, not an innocent murmur.
Most likely: coarctation of the aorta, probably with a bicuspid aortic valve and a closing duct. The differential includes interrupted aortic arch, critical aortic stenosis, hypoplastic left heart syndrome, myocarditis, and sepsis. Against an innocent murmur are the weak femoral pulses, the blood pressure gradient, a gallop, hepatomegaly, and failure to thrive.
A normal oxygen saturation does not exclude a duct-dependent lesion: the obstruction is to systemic flow, not to pulmonary blood flow. In a sick neonate the arm-leg gradient may be absent when the left ventricle is failing, so a normal gradient does not rule out coarctation.
2. Describe your immediate management, including the place of prostaglandin E1, fluid and inotrope strategy, and what you would avoid before echocardiography.
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Immediate.
- Admit to a unit with pediatric cardiology and transfer after stabilization.
- Obtain IV access, ECG, and continuous monitoring; arrange urgent echocardiography.
- Correct hypoglycemia and anemia; keep the infant warm.
- Prostaglandin E1 if there is shock, acidosis, or absent femoral pulses with poor perfusion: start 0.01-0.05 microgram/kg/min and titrate. It keeps the duct open and can improve systemic perfusion, but it can worsen pulmonary edema and causes apnea, so have airway support ready. In coarctation with a closed duct and preserved perfusion, discuss with cardiology before starting.
- Fluids: restrict to about 100-120 mL/kg/day if there is pulmonary edema; give a cautious 10 mL/kg bolus only for shock.
- Diuretics for pulmonary congestion, and inotropes such as dobutamine if there is hypotension, with cardiology input.
Avoid ACE inhibitors or aggressive afterload reduction before the obstruction is relieved, large fluid boluses, and femoral arterial puncture if it will delay transfer. Do not label it sepsis and stop there: the blood pressure gradient and weak femoral pulses are the key.
3. What long-term complications would you discuss with the family, and how would you monitor for them?
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Long-term issues to discuss:
- Recoarctation in about 10-20%; it may need balloon angioplasty or stenting, so regular blood pressure measurement and echocardiography are needed.
- Bicuspid aortic valve in the majority; risk of aortic stenosis, regurgitation, and endocarditis.
- Hypertension can persist even after successful repair; monitor at every visit and treat.
- Aortic aneurysm or dissection later in life; surveillance imaging with MRI or CT in adolescence and adulthood.
- Endocarditis prophylaxis is now limited to high-risk patients; discuss with cardiology.
- Exercise is usually allowed but should be individualized; avoid heavy isometric strain if there is significant aortic disease.
- Pregnancy needs preconception counseling and specialist care.
Monitoring: blood pressure in all four limbs at each visit, echocardiography, and transition to adult congenital heart services.