The correction conundrum: divergence of QTc formulae in a paediatric cardiac surgery cohort

BACKGROUND: The heart-rate correction formula used to compute the corrected QT interval (QTc) can influence risk classification, yet the effect in critically ill children after cardiac surgery is poorly quantified. We quantified disagreement between five correction formulas in classifying severe QTc prolongation, using Bazett as comparator, and explored the bundle branch block-specific Bogossian adjustment. METHODS: In this prospective observational study, 130 consecutive children in a paediatric cardiac ICU underwent 12-lead electrocardiography 24 hours after cardiac surgery. QTc was calculated with the Bazett, Fridericia, Framingham, Hodges, and Rautaharju formulas; the Bogossian formula was applied to patients with bundle branch block followed by Fridericia rate correction. Severe prolongation was defined as QTc≥ 500ms. No reference standard for arrhythmic risk was available. In an exploratory analysis of 6 children with bundle branch block, Bogossian adjustment moved 4 of 6 below 500 ms. No episodes of torsade de pointes occurred. CONCLUSIONS: Severe QTc prolongation prevalence varied by correction formula, with Bazett classifying more children as high risk. Without a reference standard or arrhythmic events, these data show disagreement but cannot establish which formula is more accurate; bundle branch block findings are exploratory. The formula used should be reported, and multicentre outcome studies are needed.