Differentiating AVNRT and JT. Introduction: Junctional tachycardia (JT) and atrioventricular nodal reentrant tachycardia (AVNRT) can be difficult to differentiate. Yet, the two arrhythmias require distinct diagnostic and therapeutic approaches. We explored the utility of the delta H-A interval as a novel technique to differentiate these two tachycardias.Methods: We included 35 patients undergoing electrophysiology study who had typical AVNRT, 31 of whom also had JT during slow pathway ablation, and four of whom had spontaneous JT during isoproterenol administration. We measured the H-A interval during tachycardia (H-A T ) and during ventricular pacing (H-A P ) from the basal right ventricle. Interobserver and intraobserver reliability of measurements was assessed. Ventricular pacing was performed at approximately the same rate as tachycardia. The delta H-A interval was calculated as the H-A P minus the H-A T .Results: There was excellent interobserver and intraobserver agreement for measurement of the H-A interval. The average delta H-A interval was −10 ms during AVNRT and 9 ms during JT (P < 0.00001). For the diagnosis of JT, a delta H-A interval ≥ 0 ms had the sensitivity of 89%, specificity of 83%, positive predictive value of 84%, and negative predictive value of 88%. The delta H-A interval was longer in men than in women with JT, but no gender-based differences were seen with AVNRT. There was no difference in the H-A interval based on age ≤ 60 years. Conclusion:The delta H-A interval is a novel and reproducibly measurable interval that aids the differentiation of JT and AVNRT during electrophysiology

Hyponatremia occurred in nearly half of the infants and children receiving arginine vasopressin therapy in this study. Clinicians should be aware of this association, monitor serum sodium values closely, and consider providing less free water to these patients before hyponatremia occurs.

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