Congenital Heart Disease — SAQ

Stem

A newborn becomes cyanosed at 24 hours of age. Oxygen saturation is 75% in room air. On 100% oxygen for 10 minutes, SpO2 rises to 82%. Chest is clear with equal air entry. Murmur is not audible. [1]

Questions

a) What is the most likely diagnosis? (2 marks) [1]

Cyanotic congenital heart disease (positive hyperoxia test: minimal response to 100% oxygen suggests right-to-left shunting). Most likely duct-dependent lesion (presents at duct closure 24-48h). Top differentials: TGA, TOF, tricuspid atresia, HLHS. Absence of murmur does NOT exclude CHD. [1]

b) What is the immediate management? (3 marks) [1]

1. Start PGE1 (prostaglandin E1) 0.05-0.1 mcg/kg/min IV to maintain ductal patency
2. Urgent echocardiography to confirm diagnosis
3. Refer to paediatric cardiology/cardiac surgery
4. Monitor for PGE1 side effects: apnoea (may need intubation), hypotension, fever, hyperglycaemia
5. Correct metabolic acidosis if present
6. Maintain normothermia, normoglycaemia [1]

c) What investigation confirms the diagnosis? (2 marks) [1]

Echocardiography is the gold standard — defines anatomy, shunt direction, ductal dependence, cardiac function. 4-chamber view, great vessel relationship, ductal flow, pulmonary venous return. [1]

d) Describe the hyperoxia test and its interpretation. (3 marks) [1]

Place infant in 100% oxygen for 10 minutes, then measure PaO2 (arterial blood gas):

• PaO2 over 150 mmHg (20 kPa) = PULMONARY cause (CHD effectively excluded)
• PaO2 under 100 mmHg (13 kPa) = CARDIAC cause (right-to-left shunting)
• This infant: SpO2 only 82% on 100% O2 = positive test = cardiac cause
• Note: hyperoxia test is less reliable in very sick infants; echo is definitive [1]

References

1. [1]van der Linde D, Konings EEM, Slager MA, Witsenburg M, Helbing WA, Takkenberg JJM, Roos-Hesselink JW. Birth prevalence of congenital heart disease worldwide: a systematic review and meta-analysis. J Am Coll Cardiol, 2011.PMID 22078432