Formulas and sources
Tap any formula name in the results to jump to its entry.
Bazett
QTc = QT / √RR
RR in seconds. Over-corrects with tachycardia and under-corrects with bradycardia; in a 6,609-patient monitoring cohort it performed worst of the common formulas, with Fridericia and Framingham best.
Bazett HC. An analysis of the time-relations of electrocardiograms. Heart 1920;7:353–370.
Vandenberk B, Vandael E, Robyns T, et al. Which QT correction formulae to use for QT monitoring? J Am Heart Assoc 2016;5:e003264. DOI
Fridericia
QTc = QT / ∛RR
RR in seconds. Cube-root correction; far less rate-dependent than Bazett and the usual choice when the rate is outside 60–100 bpm.
Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. Acta Med Scand 1920;53:469–486.
Framingham
QTc = QT + 154 × (1 − RR)
RR in seconds, QT in ms. Linear correction fitted to 5,018 Framingham Heart Study participants.
Sagie A, Larson MG, Goldberg RJ, Bengtson JR, Levy D. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). Am J Cardiol 1992;70:797–801.
Hodges
QTc = QT + 1.75 × (HR − 60)
Linear correction expressed in heart rate rather than RR.
Hodges M, Salerno D, Erlien D. Bazett's QT correction reviewed: evidence that a linear QT correction for heart rate is better. J Am Coll Cardiol 1983;1:694 (abstract).
Thresholds
Prolonged ≥ 450 ms (men), ≥ 460 ms (women); markedly prolonged ≥ 500 ms; short ≤ 360 ms
The 450/460 ms cut-offs are the AHA/ACCF/HRS values for normal conduction; 500 ms is the usual threshold for high torsades risk. A QTc ≤ 360 ms is the screening level for short-QT syndrome when symptoms, family history or a pathogenic variant are present; ≤ 330 ms is diagnostic on its own.
Rautaharju PM, Surawicz B, Gettes LS, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, part IV: the ST segment, T and U waves, and the QT interval. Circulation 2009;119:e241–e250. DOI
Priori SG, Wilde AA, Horie M, et al. HRS/EHRA/APHRS expert consensus statement on the diagnosis and management of patients with inherited primary arrhythmia syndromes. Heart Rhythm 2013;10:1932–1963. DOI
Bogossian
QTm = QT − 0.485 × QRS, then rate-correct QTm as usual
Derived from right-ventricular pacing in patients with intrinsic narrow QRS: the QT prolongation caused by the paced LBBB averaged 48.5 % of the QRS width while the JT interval was unchanged. Later confirmed in pacemaker patients with paced LBBB and in intermittent LBBB.
Bogossian H, Frommeyer G, Ninios I, et al. New formula for evaluation of the QT interval in patients with left bundle branch block. Heart Rhythm 2014;11:2273–2277. PubMed
Weipert KF, Bogossian H, Conzen P, et al. Application of the Bogossian formula for evaluation of the QT interval in pacemaker patients with stimulated left bundle branch block. Clin Res Cardiol 2018;107:1033–1039. DOI
Yankelson
QTc(BBB) = QTc − QRS + 95 (men) or + 88 (women)
Rate-correct first (Bazett in the original), then swap the wide QRS for a fixed normal one. Derived in 48 patients who developed LBBB in hospital and had a recent narrow-QRS ECG for comparison; it outperformed Bogossian in that cohort and was the most consistent formula in RBBB. The Fridericia column applies the same replacement to the Fridericia QTc.
Yankelson L, Hochstadt A, Sadeh B, et al. New formula for defining "normal" and "prolonged" QT in patients with bundle branch block. J Electrocardiol 2018;51:481–486. PubMed
Wang
QT-LBBB = QT − (0.86 × QRS − 71), then rate-correct as usual
Derived from right-ventricular apical pacing in 62 patients, where the net increase in QRS made up 92 % of the net increase in QT; tested in 22 patients with intermittent LBBB.
Wang B, Zhang L, Cong P, et al. A new formula for estimating the true QT interval in left bundle branch block. J Cardiovasc Electrophysiol 2017;28:684–689. PubMed
Rautaharju
QTc = QT − 155 × (60/HR − 1) − 0.93 × (QRS − 139) + k, with k = −22 ms (men) or −34 ms (women)
A single linear model in RR, QRS and sex, fitted in 1,251 adults with major ventricular conduction defects (QRS ≥ 120 ms). It removes the rate dependence and gives upper 5 % and 2 % normal limits of 450 and 460 ms, the same as in normal conduction. The same paper shows that "QTc − QRS" keeps a strong residual rate dependence and should not be used.
Rautaharju PM, Zhang ZM, Prineas R, Heiss G. Assessment of prolonged QT and JT intervals in ventricular conduction defects. Am J Cardiol 2004;93:1017–1021. PubMed
JT index
JTI = (QT − QRS) × (HR + 100) / 518; prolonged when ≥ 112
Rate-adjusted JT interval that leaves depolarization out entirely. Derived in a community sample of 23,552 ECGs, with and without conduction defects.
Zhou SH, Wong S, Rautaharju PM, Karnik N, Calhoun HP. Should the JT rather than the QT interval be used to detect prolongation of ventricular repolarization? An assessment in normal conduction and in ventricular conduction defects. J Electrocardiol 1992;25(Suppl):131–136.
Right bundle branch block
No RBBB row is shown; in RBBB, ΔQT ≈ 23 % of the QRS (≈ 25 % for bedside use)
The block adds only about a quarter of the QRS to the QT in RBBB, so LBBB-derived subtractions (Bogossian, Wang) over-correct. In a 100-patient comparison Yankelson was the most consistent of the LBBB formulas in RBBB; for bifascicular block, Bogossian combined with Hodges rate correction performed best.
Alizadeh A, Shahrbaf MA, Khorgami M, et al. QTc interval measurement in patients with right bundle branch block: a practical method. Ann Noninvasive Electrocardiol 2023;28:e13047. DOI
García-Izquierdo E, García-Gómez S, Aguilera-Agudo C, et al. Estimation of the QTc interval in the presence of right bundle branch block: a comparative study using validated formulae for left bundle branch block. J Electrocardiol 2022;74:26–31. PubMed
Erkapic D, Frommeyer G, Brettner N, et al. QTc interval evaluation in patients with right bundle branch block or bifascicular blocks. Clin Cardiol 2020;43:957–962. DOI