Corrected QT (Bazett, Fridericia, Framingham)

The Corrected QT Comparison Calculator displays QTc using all three major correction formulas simultaneously: Bazett, Fridericia, and Framingham. This side-by-side comparison reveals how different formulas yield varying QTc values from the same raw QT and heart rate, enabling more informed clinical decisions about QT prolongation risk assessment.

QT correction is needed because QT has an inverse relationship with heart rate. Bazett (QTc = QT/√RR) is most widely used and FDA-required, but overcorrects above 90 bpm and undercorrects below 60 bpm. Fridericia (QTc = QT/RR^(1/3)) provides more accurate correction across a wider range and is preferred by ICH E14 guidelines. Framingham (QTc = QT + 154×(1-RR)) uses linear correction avoiding all nonlinear distortions.

Clinical significance: a patient with HR 110 and QT 340 ms might have Bazett QTc 460 ms (concerning) but Fridericia 420 ms (normal). Understanding these differences prevents unnecessary medication changes or false reassurance. All formulas converge at exactly 60 bpm (RR = 1.0 s) where no correction is needed.

Expert consensus: Fridericia is generally most reliable at non-60 bpm rates. Framingham serves as tiebreaker when Bazett and Fridericia disagree. For regulatory submissions, Bazett remains required. For clinical decision-making at borderline values, comparing all three formulas provides the most robust assessment.

Discrepancies exceeding 20-30 ms between formulas at extreme heart rates are expected and reflect inherent formula limitations rather than measurement error. When a discrepancy changes clinical classification (normal vs prolonged), the formula most appropriate for that specific heart rate should be prioritized in clinical decision-making.

QTc from any formula should always be interpreted with clinical context including medication history, electrolyte status, ECG morphology, and patient risk factors for arrhythmia. No formula alone determines clinical action; rather, the corrected values inform a broader risk assessment.