Corrected QT Intervals in the Pediatric Emergency Department: Don't Be Misled

Pediatric health care providers request electrocardiograms (ECGs) for diverse clinical presentations, and are understandably concerned when the corrected QT (QTc) interval is prolonged. Subsequent confirmation by pediatric cardiologists often finds that the unconfirmed QTc intervals previously displayed on ECGs were inaccurate. We evaluated the principal factors responsible for disparate QT/QTc intervals, and highlight the impact on decision-making. We include a straightforward approach to determine accurate QTc intervals for providers awaiting finalized interpretations.

Two hundred pediatric cardiologist-confirmed pediatric ECGs were analyzed to evaluate differences between automated unconfirmed and cardiologist-confirmed QT interval measurements. QTc intervals were calculated using Bazett formula (QTcB), and frequency of normal, borderline, and abnormally prolonged QTcB were compared between unconfirmed and confirmed interpretations. The mean QT interval and heart rate for the cohort were used to calculate QTc values using contemporary non-Bazett formulae.

Automated QT and QTcB intervals were longer than confirmed values by ~25 ms and ~30 ms, respectively ( P < 0.0001). The QTcB of 19/200 (~10%) unconfirmed ECGs were borderline or abnormally prolonged, compared with a single confirmed ECG with a borderline QTcB. QTc values using common non-Bazett formulae were markedly shorter than QTcB.

The QTc values displayed on unconfirmed pediatric ECGs are often different from those subsequently adjudicated by cardiologists, and may substantially influence clinical impressions and decision-making by primary providers. Providers in the pediatric ED should be aware that variable methods and algorithms "behind the scenes" cause these variations, and have tools to confirm QTc values in advance of delayed confirmation by a cardiologist.