Why the study?
Does intravenous isoproterenol alter QT and RR intervals differently in children with positive versus negative orthostatic tests for syncope?
Does intravenous isoproterenol alter QT and RR intervals differently in children with positive versus negative orthostatic tests for syncope?
Children with orthostatic positive neurocardiogenic syncope exhibit a different QT response to beta-adrenergic stimulation, supporting the theory of altered beta-adrenergic sensitivity.
Altered QT response to isoproterenol may reflect beta-adrenergic differences in pediatric syncope; supports mechanistic hypothesis but leaves clinical utility open.
The effect of intravenous bolus doses (0.25, 0.5, 1.0 microgram) of isoproterenol on the QT and RR intervals was reviewed in a group of 34 children undergoing autonomic testing for syncope. Twenty-one patients had a positive orthostatic test and 13 were negative. The two groups (positive and negative) were compared. Baseline QT and RR intervals were similar. The RR interval was shortened by isoproterenol in both groups. Isoproterenol shortened the QT interval in the negative group (as seen in normal persons), but produced QT prolongation in the positive group, although neither reached statistical significance when compared to baseline within the respective group. Comparing the values for RR and QT at each dose of isoproterenol (including baseline) between the two groups showed a significant difference in the QT interval after the 1.0-microgram dose of isoproterenol. Thus children with orthostatic positive neurocardiogenic syncope showed a different QT response to beta-adrenergic stimulation. This lends support to the theory of altered beta-adrenergic sensitivity being present in children with neurocardiogenic syncope.
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Balaji et al. (1994) studied this question.
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