RESUMO
BACKGROUND: Vagal hyperreactivity (VHR) is a frequent etiology of infant fainting spells; but it is sometimes difficult to diagnose. A biochemical test would therefore be useful, especially as the oculocardiac reflex (OCR) test innocuity is not absolute. AIMS: To evaluate urinary excretions of norepinephrine, epinephrine and dopamine as markers for vagal hyperreactivity. METHODS: During check-up of 55 infants from 0.5 to 11 months of age, for discomfort episodes, including OCR and Holter recording, 24h urinary assays of total norepinephrine, epinephrine and dopamine were carried out to evaluate sympathetic activity. RESULTS: Epinephrine and norepinephrine urinary excretions were negatively correlated with VHR intensity, as measured by the OCR ECG parameters: RRmax, % cardiac deceleration and minimal frequency; dopamine excretion was not. When RRmax(OCR) was greater or equal to 800 ms, epinephrine urinary excretion tended to be less or equal to 9 nmol/mmol creatinine and norepinephrine excretion less or equal to 190 nmol/mmol creatinine. CONCLUSION: A delay in maturation of the sympathetic system and/or adrenomedullary glands with low secretion of norepinephrine and epinephrine inducing a desequilibrium of the sympathetic/parasympathetic balance may contribute to the fainting spells observed with VHR. Epinephrine and norepinephrine urinary excretions may provide informative complementary noninvasive markers for VHR.
