Summary
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, 24 h 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.
Résumé
Justification
L’hyperréactivité vagale (HRV) est une étiologie fréquente des malaises chez le nourrisson; son diagnostic est parfois difficile. Un test biochimique serait donc utile, d’autant que l’innocuité de l’épreuve du reflexe oculocardiaque (ROC) n’est pas absolue.
Objectif
Répondre à la question: les excrétions urinaires de noradrénaline, adrénaline et dopamine sont-elles marqueurs d’HRV ?
Méthodes
Les excrétions urinaires de noradrénaline, adrénaline et dopamine totales de 24 heures ont été mesurées pour évaluer l’activité sympathique chez 55 nourrissons de 0,5 à 11 mois présentant des malaises et soumis au bilan habituel clinique et électrocardiographique incluant le ROC et l’enregistrement Holter de 24 heures.
Résultats
Les excrétions urinaires d’adrénaline et noradrénaline sont négativement corrélées avec l’intensité d’HRV appréciée par les paramètres électrocardiographiques du ROC: RRmax, pourcentage de décélération et fréquence minimale cardiaques. Lorsque RRmax au ROC est supérieur ou égal à 800 ms, l’excrétion nycthémérale d’adrénaline tend à être inférieure ou égale à 9 nmol/mmol de créatinine, celle de noradrénaline inférieure ou égale à 190 nmol/mmol de créatinine.
Conclusion
Un retard de maturation du système sympathique et/ou des médullosurrénales avec hyposécrétion de noradrénaline et d’adrénaline entraînant un déséquilibre de la balance parasympathique/sympathique pourrait contribuer aux malaises associés à une HRV. Les excrétions nycthémérales d’adrénaline et noradrénaline pourraient constituer des marqueurs complémentaires intéressants et non invasifs d’HRV.
Introduction
Vagal hyperreactivity (VHR) is a frequent etiology in infant fainting spells or in apparent life threatening events (ALTE). It appears isolated, without any other cause of fainting spell, in about 12 to 15% of all cases . It is more frequently found in association with gastro-esophagal reflux. VHR is also associated with reflex anoxic seizures (white breath-holding) . It is suspected to participate in the etiology of sudden infants death syndrome (SIDS) .
Even though VHR is that frequent and systematically investigated for infant discomfort evaluation in our centre of infant cardiology, it is still difficult to diagnose and even controversial. Diagnosis relies on a stack of clinical, historical and electrocardiographic arguments. Two complementary tests currently used for that purpose in infants are oculocardiac reflex (OCR) and 24-h Holter ECG . But normal limits for these two tests, particularly for OCR, are discussed and falsely negative results were reported with secondary evidence of VHR . Furthermore, the innocuity of OCR is not absolute. Besides infant relapsing fainting spells with VHR may be treated by atropinic drugs . We thought that complementary biochemical tests exploring the sympathetic and parasympathetic nervous systems would be welcome for the diagnosis, the follow-up under treatment and a better comprehension of the physiopathology of VHR. Since noninvasive, urinary tests are preferred in infants.
In a previous experimental study, we observed a decrease in norepinephrine (NE) urinary excretion (U) in rats with experimental vagal hypertonia induced by reserpine. Opposite variations were found in a model of vagal hypotonia induced by diphemanil-methylsulfate .
We therefore determined UNE, but also U epinephrine (E) and U dopamine (D) in infants with fainting spells who were tested for VHR.
Subjects and methods
Subjects
Fifty-five infants from 0.5 to 11 months of age were investigated at the “Centre de cardiologie infantile du Château-des-Côtes” for VHR, 51 after fainting spells, four as siblings of SIDS victims. The investigation includes routinely, besides the history and the clinical examination, OCR and 24-h Holter ECG . At the end of the evaluation, diagnosis was established, ranging from frank VHR (score 4) to absence of VHR (score 1). Positive diagnosis of VHR (score 4) is admitted in the presence of one major criterium, or three minor criteria. Possible VHR (score 3) or doubtful VHR (score 2) are considered in the presence of two minor criteria or one minor criterion respectively.
Major criteria:
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fainting or syncope during the Holter ECG monitoring with a simultaneous prolonged sinus pause;
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inducibility of fainting or syncope during OCR reproducing the same type of faint described by the family.
Minor criteria:
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history of familial VHR;
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identification of vagally mediated signs induced by factors like pain, vomiting, crying;
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clinical symptoms such as pallor, hypotonia, cyanosis of the lips;
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positive OCR test or indexes of VHR on the Holter recording.
The study complied with the Helsinki declaration. After informed and written consent of the parents, as recommended by Huriet Law, two consecutive noninvasive urinary collections were carried out. A urinary bag was installed for a 3-h collection starting between 9 h and 10 h 30 a.m. just after the clinical examination and the OCR test; then a 21-h collection followed immediately and covered the whole night period. Results for 24 h were obtained by calculation. This protocol was established to test the diagnostic value of the 3-h versus the 24-h collection.
Electrophysiological cardiac parameters
The quantitative parameters of OCR were studied as in :
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minimum heart rate (Fmin OCR ), calculated on three successive beats, expressed as beats per minute (bpm);
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RRmax OCR (maximum interval between two R waves, in ms);
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ΔFi OCR , percentage of heart rate (HR) deceleration:
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ΔFi = [(HR before the test – HR during the test)/HR before the test] × 100.
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Evident VHR criteria under 3 months are: Fmin OCR ≤ 50 bpm, RRmax OCR ≥ 1200 ms or ΔFi OCR ≥ 66%.
Moderate VHR criteria under 3 months are: Fmin OCR ≤ 75 bpm, RRmax OCR ≥ 800 ms or ΔFi OCR ≥ 50%.
The Holter quantitative parameters were :
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Fmin Holter , minimum cardiac frequency observed during the 24 h (in bpm);
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ΔFi Holter , maximal deceleration upon 10 s, observed during the 24 h.
VHR criteria are Fmin Holter ≤ 80 bpm under 1 month, ≤ 70 bpm under 2 months, ≤ 60 bpm between 2 months and 1 year, or ΔFi Holter ≥ 55% or ΔFi Holter ≥ 100 bpm absolute deceleration.
Urinary collection and biochemical assays
Urine collection was carried out after addition of 0.5 mL of HCl for 3 h and 2 mL for 21 h in the storage bottles, kept at 4 °C during the collection and frozen at −30 °C thereafter. Urine acidity was checked (pH between 1 and 3).
Total norepinephrine, epinephrine and dopamine (free and conjugated) were measured by high performance liquid chromatography (HPLC) in reverse phase with amperometric electrochemical detection, after hydrolysis (20 min at 80 °C, at a pH of 0.8 to 1) and extraction by ionic exchange on Biorad column .
Creatinine (Cr) was determined by the Jaffé method on KONE “Optima” analyzer. The first 20 samples were measured with and without previous pH neutralization. The results obtained were similar. Therefore pH neutralization was omitted further on.
All results of biochemical assays of catecholamines were expressed as nmol per mmol Cr.
Statistical methods
In the whole group infants from 0.5 to 11 months or in different groups of age, the urinary excretions of the different catecholamines are represented by the mean ± SD and/or the (range). Log e of the values was used to normalize their distribution if necessary.
For studying correlations between urinary excretion of each catecholamine and A 37 age or electrocardiographic parameters, Pearson’s correlation as well as multiple correlation coefficients were determined, using the statistical Analysis System SAS 9.2 software (SAS Institute Inc, Cary, NC, USA) with the CORR procedure; adjustment for age was effected by the REG procedure (0 if ≤ 3 months, 1 if > 3 months, since 3 months of age has been found to be a critical milestone, see discussion).
For studying the variations of excretion of each metabolite in function of age (age sections of 1 month) or collection time (3 h/21 h) or VHR score (1 to 4), analysis of variance was used, followed by comparison of means by the Bonferoni-Student t test.
The level of significance was considered as P ≤ 0.05.
Results
Clinical characteristics of the infants
Age
Out of 55 infants, six were under 1 month (0.5 to 0.9 months), 15 from 1.0 to 1.9 months, 18 from 2.0 to 2.9 months, eight from 3.0 to 3.9 months, three from 4.0 to 4.9 months, five older than 5 months (5.3, 7.6, 9.5, 10, 10.3). Five children were preterms, (30 to 36 weeks). Maturation of the cardiac control being in relation with the gestational age , we used for these children an A 37 age, as if they had been born at 37 weeks. Eighty-five percent of the children had their first fainting spell before 3 months of age.
Diagnosis of VHR
Sixteen children had positive VHR (score 4), 15 possible VHR (score 3), nine doubtful VHR (score 2), 15 absence of VHR (score 1). None of the four siblings of SIDS victims had VHR.
Urinary epinephrine
Variations of excretion in function of age or collection time
For the infants of all ages, the mean UE 24h = 14.8 ± 10.1 nmol/mmolCr (with high individual variations, from 1 to 43.8 nmol/mmolCr). In contrast with norepinephrine excretion (see below), neither UE 24h nor LogUE 24h were correlated with the A 37 age ( r = 0.077 and r = 0 respectively).
For what concerns the effect of collection time, UE 21h was lower than UE 3h only in children aged less than 2 months (8.7 ± 5.6 nmol/mmolCr vs 24.4 ± 24.2 nmol/mmolCr, P < 0.005). Beyond 2 months of age, the difference disappeared.
Correlations with OCR ECG parameters
In all children between 0.5 and 11 months, LogUE 24h was negatively correlated with RR maxOCR ( r = −0.34; P = 0.012), positively correlated with Fmin OCR ( r = +0.31; P = 0.024), marginally correlated with ΔFi OCR ( r = −0.24; P = 0.084) ( Table 1 ).
