QTc values among children and adolescents presenting to the emergency department

Long-QT syndrome (LQTS) is both underdiagnosed and overdiagnosed. Many patients are incorrectly diagnosed as having LQTS after presenting to an emergency department (ED) with presyncope/syncope and demonstrating "borderline" QT-interval prolongation (QTc ≥ 440 milliseconds) in a sentinel ED-obtained electrocardiogram (ECG). We sought to evaluate the distribution and clinical significance of QT intervals in the ED.

We retrospectively reviewed data for all patients 22 years of age or younger (N = 626; 369 females; age, mean ± SD: 17 ± 5 years) who had ECGs obtained in our ED between July 1, 2007, and June 30, 2008. A total of 223 patients were excluded because of known structural heart disease, arrhythmias, electrolyte abnormalities, or exposure to QT-interval-prolonging medications.

The average QTc was 428 ± 28 milliseconds (range: 344-566 milliseconds), and approximately one-third of patients had QTc values of ≥440 milliseconds (females: 41%; males: 21%). Overall, 104 patients presented with presyncope/syncope, of whom 14 (13%) had follow-up ECGs. On follow-up, these patients demonstrated significant decreases in QTc values of 33 ± 43 milliseconds (P < .04). Only 8 (31%) of 26 patients with presyncope/syncope with borderline QT values had follow-up ECGs performed, in 5 of which the QTc values were decreased significantly. No patients ultimately received LQTS diagnoses.

In the ED setting, approximately one-third of pediatric patients exhibited QTc values of ≥440 milliseconds and had significant normalization of QTc values in follow-up evaluations. First-time ECGs obtained after a syncopal episode must be interpreted with caution, particularly in the context of so-called borderline QT intervals.