Objective: 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.
Methods: 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.
Results: 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.
Conclusions: 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.