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Neonatal cardiac output heart-rate dependence — MRCPCH TAS MCQ

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HardPhysiologyNeonatal cardiac output heart-rate dependenceMRCPCH TAS

A septic 10-day-old has poor perfusion, heart rate 80/min and normal blood pressure initially. Echocardiography shows no structural lesion. Why can bradycardia rapidly reduce cardiac output in this age group?

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Correct answer: E — Stroke volume reserve is limited in neonates

Neonatal cardiac output is relatively heart-rate dependent because stroke volume reserve is limited by myocardial immaturity and lower compliance. Higher myocardial compliance would imply a larger stroke volume reserve, which is not typical of neonates. The pearl is that bradycardia in a sick neonate is an important sign of impending decompensation.

Reference: Rennie and Robertson Textbook of Neonatology; Ganong's Review of Medical Physiology; RCPCH Theory examination syllabi