QTc in Bundle Branch Block Calculator

A wide QRS inflates the QT without lengthening repolarisation. This applies Bogossian’s modified QT — the measured QT minus 48.5% of the QRS — and corrects it with Hodges, the pairing that agreed most closely with the narrow-QRS QTc.

Last updated 8 Oct 2026

Bogossian modified QTc

QT − 48.5% QRS, then Hodges

Measured QT interval (ms)Earliest QRS onset to latest T-wave offset, in the lead where the QT is longest (usually II, V5 or V6), by the tangent method. Do not include a U wave; where T and U merge the measurement is unreliable and so is everything below it. In bundle branch block, take the QRS offset as the point where the terminal deflection returns to the baseline — mistaking it for the start of the ST segment shortens the measured QT.

QRS duration (ms)The widest QRS across the 12 leads. 120 ms or more defines a complete bundle branch block or a paced complex; below that the adjustment on this page does not apply.

Heart rate or RR intervalFrom the same beat the QT and QRS were measured on.

Rate unitSet the unit to match what you are holding. Every rate correction here was published with RR in SECONDS, so a heart rate typed into an RR field is the commonest way these formulas are got wrong: at 100 bpm it divides the QT by 10 instead of by 0.775. Both quantities are printed back under the answer.

442ms (Bogossian, Hodges)Example

QT 480 ms, QRS 150 ms, heart rate 80 bpm

Formula

QT_m = QT − 0.485 × QRS
QTc = QT_m + 1.75 × (HR − 60)
QT, QRS in ms; HR in bpm

48.5%: Bogossian’s fraction, from 60 patients with narrow intrinsic QRS paced at the right ventricular apex and outflow tract. The QT lengthened by 48.3% and 48.8% of the paced QRS width, mean 48.5%, and the JT interval did not lengthen at all — the evidence that the extra QT is excitation, not repolarisation
Hodges rather than Bazett: the Clinical Cardiology 2020 study of 71 patients with artificially created bifascicular blocks found “the Bogossian formula in combination with the Hodge formula delivered the best results”, with mean deviations from the narrow-QRS QTc of −3 ± 24 ms and −6 ± 25 ms
what it does not fix: only the arithmetic contribution of QRS width. A bundle branch block changes the activation sequence and so changes repolarisation itself, and no subtraction separates that from a drug effect. The 2020 ICD validation found it over-estimates by about 25 ± 21 ms during right ventricular pacing
the rival forms: the published alternatives disagree. Some reviews round the fraction to 50% of the QRS; the AHA recommends the JT interval instead, which is QTc minus QRS; and a widely quoted clinical form is (QT − (QRS − 120)) / √RR. All three are printed beside the answer, and on a 150 ms QRS they span tens of milliseconds

Worked example

QT 480 ms, QRS 150 ms, heart rate 80 bpm
Modified QT = 480 − 0.485 × 150 = 407 ms
Hodges: 407.25 + 1.75 × (80 − 60) = 442 ms
The unadjusted trace by Bazett: 480 / √0.75 = 554 ms — 112 ms above the adjusted figure. 554 ms is past every published threshold; 442 is under all of them, and the difference is QRS width
The JT approach gives 554 − 150 = 404 ms; the (QT − (QRS − 120)) / √RR form gives 520 ms. The three published approaches span 116 ms on one complex, which is why the page prints all of them
Set the QRS to 100 ms and the adjustment no longer applies: this is not a wide-QRS complex, and subtracting 48.5 ms would remove repolarisation time the QRS is not responsible for

The published ways to handle a wide QRS, and what each gives here

Five answers to one complex, spanning 150 ms. The order is not an accident: the JT approach removes the whole QRS and under-states, the 120 ms allowance removes only the excess over a normal QRS and over-states, and Bogossian’s 48.5% sits between them because that is what the pacing experiment measured.
Approach	Form	Source	QT 480, QRS 150, 80 bpm
Bogossian modified QT, Hodges correction	(QT − 0.485 × QRS) + 1.75 × (HR − 60)	Bogossian, Heart Rhythm 2014; pairing from Clin Cardiol 2020	442 ms
Bogossian modified QT, Bazett correction	(QT − 0.485 × QRS) / √RR	Bogossian, Heart Rhythm 2014	470 ms
JT interval	QTc − QRS duration	AHA/ACCF/HRS part IV recommends the JT interval when a BBB is present	404 ms
Fixed 120 ms allowance	(QT − (QRS − 120)) / √RR	Widely quoted clinical form, reproduced in hospital-medicine guidance	520 ms
No adjustment	QT / √RR	What an ECG cart prints	554 ms

What the validation studies found

All three create the wide QRS by pacing a patient whose own QRS is narrow, which is the only design that can compare an adjusted wide-QRS QTc against the same heart’s true value. It is also the limitation: a paced left bundle branch block is not a diseased one, and none of these cohorts was a drug-safety population.
Study	Population	Agreement with the narrow-QRS QTc
Bogossian, Heart Rhythm 2014 (derivation)	60 patients in sinus rhythm with narrow intrinsic QRS, paced from the right ventricular apex and outflow tract	QT prolongation was 48.3% of the paced QRS from the apex and 48.8% from the outflow tract, mean 48.5%, with no prolongation of the JT interval
Prospective multicentre ICD study	145 ICD recipients, intrinsic QRS under 120 ms and reduced left ventricular function; 74 apical and 71 non-apical pacing	QTc 461 ± 34 ms by the formula during pacing against 436 ± 34 ms in intrinsic rhythm — an over-estimate of about 25 ± 21 ms, roughly 5.7%
Clin Cardiol 2020	71 patients, intrinsic QRS under 120 ms, with bifascicular blocks created by left ventricular pacing	Mean deviation −3 ± 24 ms in RBBB with left posterior fascicular block (P = 0.44) and −6 ± 25 ms with left anterior fascicular block (P = 0.15), using Bogossian with Hodges

Why a wide QRS breaks every rate correction

The QT interval contains two different things. The QRS complex is ventricular excitation; the JT interval that follows it is repolarisation. Only repolarisation carries the risk of torsades de pointes, and only repolarisation is what a QT-prolonging drug or a channelopathy acts on. When conduction is normal the QRS is short enough that the distinction rarely matters. When a bundle branch block or a paced rhythm widens the QRS to 150 or 180 ms, most of the apparent QT prolongation is excitation time, and an unadjusted QTc describes a danger that is not there.

Bogossian’s experiment settled the arithmetic cleanly. Sixty patients with their own narrow QRS were paced from the right ventricular apex and the outflow tract, which creates a left-bundle-branch-block pattern on demand. The QT lengthened by 48.3% and 48.8% of the paced QRS width — and the JT interval did not lengthen at all. Repolarisation was unchanged; the QT had absorbed about half the extra excitation time. Hence the formula: subtract 48.5% of the QRS, then rate-correct as usual. A later study of 71 patients with artificially created bifascicular blocks found that pairing it with Hodges brought the adjusted value within a few milliseconds of the same patients’ narrow-QRS QTc, which is the pairing here.

Three other published approaches exist and they do not agree. The AHA/ACCF/HRS statement recommends the JT interval, effectively subtracting the whole QRS, which under-states. A widely quoted clinical form subtracts only the excess over a normal QRS, which over-states. Some reviews round Bogossian’s fraction to 50%. On a 150 ms QRS at 80 bpm these span 116 ms, so the page prints all of them rather than pretending to a consensus that does not exist.

What none of them fixes is the deeper problem. A bundle branch block does not merely add excitation time; it changes the activation sequence and therefore changes repolarisation itself, and no subtraction can separate that from a drug effect. The validation in 145 ICD recipients found the formula over-estimates by about 25 ms during right ventricular pacing, and in atrial fibrillation the problem compounds because the QT must also be averaged across beats. Treat the adjusted figure as the better of two imperfect numbers, not as a measurement. This supports a clinician’s judgement rather than replacing it. An ECG interval is read alongside the patient, the drug chart and the electrolytes, and never instead of them.

Frequently asked questions

How do you measure QTc in bundle branch block?

Account for the wide QRS first. The Bogossian formula subtracts 48.5% of the QRS from the measured QT and then rate-corrects; the AHA/ACCF/HRS statement recommends the JT interval instead. On a 480 ms QT with a 150 ms QRS at 80 bpm, the unadjusted Bazett QTc is 554 ms and the Bogossian-with-Hodges figure 442 ms.

What is the Bogossian formula?

Modified QT = measured QT minus 48.5% of the QRS duration, then rate-corrected as usual. The fraction came from 60 patients with narrow intrinsic QRS paced from the right ventricle: the QT lengthened by 48.3% of the paced QRS from the apex and 48.8% from the outflow tract, while the JT interval did not lengthen at all.

Why does a wide QRS inflate the QTc?

Because the QT includes the QRS. The QT is excitation plus repolarisation and only repolarisation carries arrhythmic risk, so a QRS of 150 ms rather than 90 adds 60 ms of excitation — which a rate correction then multiplies rather than removes.

Which rate correction should follow the Bogossian adjustment?

The 2020 bifascicular-block study of 71 patients concluded that “the Bogossian formula in combination with the Hodge formula delivered the best results”, with mean deviations from the narrow-QRS QTc of −3 ± 24 ms and −6 ± 25 ms.

How accurate is the adjusted QTc in a paced rhythm?

A prospective study of 145 ICD recipients found the formula gave 461 ± 34 ms during right ventricular pacing against 436 ± 34 ms in the same patients’ intrinsic rhythm — an over-estimate of about 25 ± 21 ms, or 5.7%. The authors called it reliable but said the over-estimation “must be respected”.

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References

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(12):2273–2277.
Bogossian H, Linz D, Heijman J, et al. QTc interval evaluation in patients with right bundle branch block or bifascicular blocks. Clin Cardiol. 2020;43(9):957–962.
Bogossian H, Linz D, Heijman J, et al. Applicability of a novel formula (Bogossian formula) for evaluation of the QT interval in patients with right ventricular pacing: a prospective multicentre observational study of 145 ICD recipients.
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. J Am Coll Cardiol. 2009;53(11):982–991.

Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/