Online QTc Calculator for Normal and Wide QRS (as may be seen with LBBB, RBBB)
There are 2 parts to this QTc Calculator. You should immediately see Part-1. You may need to scroll over to see Part-2 of this embedded Excel table.
- Part-1: Calculation of the QTc by the 5 most commonly used methods. Enter the Heart Rate and the QT interval that you measure (in msec.) — and after you click Return, you should see the 5 values!
- Part-2: Calculation of the modified QTc if the QRS is wide (ie, because of LBBB, RBBB, IVCD). Enter the Heart Rate — the QRS duration (in msec.) — and the QT interval that you measure (in msec.) — and the Rautaharju QTc (modified to account for QRS widening) should come up.
- The Bogossian value that comes up if for the QT has now been “modified” to account for the widened QRS. After getting this Bogossian QT value — Plug this QT value in to Part-1 to get the modified QTc.
- Smith: Clinically — “It is probably not a good idea to ‘correct’ for the QT interval when the heart rate is below 60/minute — because a slow rate puts the patient at higher risk of Torsades”. (See the July 12, 2025 post by Dr. Nossen for the post including this Smith quote — which reviews the fascinating case of a 70-something year old woman whose “Congenital” Long QT Syndrome was only discovered when she was in her 70s!). I would add that corrections for very slow heart rate tend to be less accurate — with relatively less “correction” below the QT measured at ~60/minute.
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NOTE: This QT calculator has been created by Arron Pearce.
- The calculator is a work in progress — as we aim to continue optimizing making it. In the meantime — we welcome your feedback (Send to Ken Grauer, MD — ekgpress@mac.com).
- The calculator was created on an Excel file, that we have embedded in this blog post in Dr. Smith’s ECG Blog (Easy access available by clicking in the Menu Bar at the TOP of every page in Dr. Smith’s ECG Blog.)
- ATTENTION: Some users have reported that the Calculator is not working for them … For some — this appears to be browser specific (ie, whether using Safari – Foxglove – Chrome, etc.) — but for me, the Calculator is working on Mac computer, ipad & iphone in all 3 of the above browsers.
- — KEY: Sometimes the Calculator needs to be “woken up”. For example, on smart phone or tablet — You may need to tap twice, quickly and firmly over the box where you enter data — and then it works! Similarly, on computer — You may need to tap more than once — and then it works.
- Please — Let me know if you are unable to get the application to work (and if so — what kind of device and which browsers is it not working on. Thank you! ).
- P.S.: For step-by-step on how I embedded this QTc Calculator Excel file — CLICK HERE —
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Grauer: The fact that you will see slightly different values in the above QTc calculator conveys the lack of universal agreement on QTc calculation at different heart rates. That said — 4 of the 5 methods are generally quite close to each other (You might mentally take an average of those readings for the value you select — or pick your “favorite” among the methods).
- In our experience — We find the Bazett method potentially problematic, in that it tends to overestimate the QTc for faster heart rates — and underestimate the QTc for slower heart rates.
- For QTc estimation when the QRS is wide — I find the Bogossian method to be problematic because the simplified formula that is used by the Bogossian method to calculate the modified QT = QT minus ~50% of QRS duration. But since all this entails is to subtract ~50% of QRS width (ie, for a widened QRS = 0.16 msec — 0.08 msec would be subtracted from the QT you measured) — there is no compensation for any change in heart rate (and since we know the QTc is altered by faster or slower heart rates — I believe the Bogossian method is fatally flawed).
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ADDENDUM (7/12/2025):
Our goal for this QTc Calculator is to facilitate QTc estimation (for any tracing — regardless of whether the QRS is normal or wide).
- We’ve added a quick link to the QTc calculator in the Menu at the top of every page in Dr. Smith’s ECG Blog (Figure-1).
Figure-1: Quick link to the QTc Calculator in the Menu at the TOP of every page in Dr. Smith’s ECG Blog.
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Add a quick link on your smart phone!
- Figures-2 and -3 below show how to easily do this on iphone.
- To find out how to do this for other brand smart phone — Simply do a Google Search for, “Can you add link to home screen of Android? (or other brand).
Figure-2: To add a quick link on iphone — GO TO the QTc Calculator page in Dr. Smith’s ECG Blog. Once there — Click in the bottom Menu on the icon within the BLUE rectangle (LEFT panel). This takes you to the page shown in the RIGHT panel — Scroll down that page until you get to, “Add to Home Screen”.
Figure-3: After the actions in Figure-2 — You’ll be taken to the page shown in the LEFT panel. You need to choose a short title in order to “fit” on your iphone screen. We suggest, “QTc Calculator”. Then click on “Add” — and you are done! You’ll find your quick link to the QTc Calculator on the home screen of your iphone (within the YELLOW rectangle, as shown in the RIGHT panel).
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— Please give us your feedback! (Ken Grauer, MD — ekgpress@mac.com )
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NOTE: What follows below is My Comment found at the bottom of the page from the July 12, 2025 post — in which Dr. Nossen reviews the fascinating case of a patient with “Congenital” Long QT Syndrome that was not detected until this patient was in her 70s!
- Figure-2 at the bottom of the page illustrates how to measure the QT interval when there are large U waves that overlap with the preceding T wave.
- For more on assessment of this patient with Congenital Long QT Syndrome — Please check out the complete post from July 12, 2025.
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MY Comment, by KEN GRAUER, MD (7/12/2025):
Fascinating case by Dr. Nossen — of a “congenital” ECG abnormality that did not present for medical attention until today’s patient was in her 70s!
- I focus My Comment on a number of additional points to those brought out in Dr. Nossen’s excellent discussion above.
- For clarity in Figure-1 — I’ve labeled the KEY areas in today’s initial ECG that left me uncertain about what I was seeing.
How Long is the QTc in Today’s ECG?
Reminder: Accurate determination of the QTc ( = the QT interval corrected for heart rate) is essential for optimal management of a number of important clinical conditions. This is especially true for today’s case, in which the patient developed arrhythmic storm, with episodes of Torsades de Pointes ( = a condition that depends on accurate determination of the QTc to distinguish it from polymorphic VT, in which the QTc is normal).
- To facilitate QTc determination at various heart rates — We’ve added a QTc Calculator that is readily accessible from the Menu found at the TOP of every page in Dr. Smith’s ECG Blog.
- Go to Tools & Guides in the TOP Menu. From the pull-down menu, click on QT Calculator. This will take you to THIS PAGE —
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Dr. Nossen estimates the QTc in today’s initial ECG at ~630 msec.
- Dr. Nossen may be correct.
- My Thought — I do not know what the QTc is for today’s initial ECG (which for clarity, I’ve reproduced in Figure-1).
- The reason I do not know what the QTc is in ECG #1 — is that a form of electrical alternans is present, in which either the T wave or the U wave is changing in size and shape every-other-beat.
- I simply am not sure in Figure-1 — where the T wave ends (and where the U wave begins). Without being able to determine this — it’s not possible to be certain about the QTc interval.
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Figure-1: I’ve labeled the initial ECG in today’s case. Where does the T wave end and the U wave begin? (Is there T wave or U wave alternans?).
Looking Closer at Today’s Initial ECG:
Why is it so difficult to assess the QTc interval in ECG #1? Does this make a difference in our management of today’s patient?
- The 1st challenge in assessing today’s tracing — is that we only have 5 beats to look at in Figure-1 (ie, The same 5 beats that are seen in the chest leads — are also seen in the limb leads). In addition — the R-R interval is not completely regular. Thus, we only have 5 beats in this sinus arrhythmia from which to determine the QTc.
- Next — some form of T wave or U wave alternans is present (See My Comment at the bottom of the page in the October 23, 2023 post in Dr. Smith’s ECG Blog for review about the various forms and clinical significance of Electrical Alternans). As per the above discussion by Dr. Nossen (and as was brought out in the above-cited October 23, 2023 case) — the presence of T wave (and presumably also U wave) alternans should serve to alert providers of a significantly increased the risk of Torsades — unless precipitating factors are promptly corrected, and especially serum electrolytes are normalized (often assisted by administration of supplemental IV Magnesium).
For example — Take Another LOOK at Figure-1:
- Note the alternating size and morphology that occurs after every-other QRS complex (Best seen in leads I,II — and in leads V1,V2).
- Doesn’t it look in leads I and V1 — that the T wave is dramatically changing (becoming much larger for the T wave of beats #1,3,5?).
- But what about leads II and V2? Doesn’t it look like it is the U wave (and not the T wave) that gets much larger with alternate beats? (with a giant negative U wave now seen in lead V2 for beats #1,3,5?).
- Or perhaps, rather than either the T wave or the U wave — fusion of these 2 ECG waves is responsible for the unusual change in morphology seen after alternate QRS complexes?
- NOTE: Most of the time — it is not difficult to distinguish between the end of the T wave and the beginning of the U wave. But today’s case illustrates one occasion in which I can not be confident doing so.
- Guidelines have been been cited for measuring the QT interval in cases in which prominent U waves are present (See below). But as for Panel D in my Figure-2 below — including a large U wave that looks to be fused with the preceding T wave in determination of the QT — risks overestimation of the QTc level when uncertainty prevails as to where the T wave ends.
- Riera et al (Cardiol J 15(5):408-421, 2008) suggests use of the term, “Q(T + U) interval” — when there is marked prolongation of this interval, in which an apparent huge U wave masks the T wave end point.
- Riera also cites the recommendation when debating the difference between a 2-peaked T wave vs a T wave and U wave — to measure the distance between the 2 peaks that are seen (as I schematically show in lead V5 of Figure-2). If the distance between these 2 peaks is <150 msec. ==> then Assume this is a dual-peaked T wave. But if the distance between peaks is >150 msec. ==> Assume there is both a T wave and a U wave. (ie, In Figure-2 — the distance between peaks = 1 large box on ECG paper = 200 msec., which if the above recommendation is accurate suggests that we are seeing a T wave and a U wave in Figure-2). However, given the discrepancy I cited earlier between what we see in leads I,II and V1,V2 in Figure-2 — I find it difficult to accept the between-peak distance recommendation.
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BOTTOM Line:
I still have no idea as to where the T wave ends in Figure-1 (ie, at the point where the light BLUE vertical line crosses the baseline — or where the RED vertical line crosses the baseline?).
- Clinically — This distinction does not matter. Although my estimate of the QTc interval for ECG #1 in today’s case is less than the 630 msec. estimated by Dr. Nossen — both of us agree that the QTc is significantly prolonged!
- Both of us also agree that the unusual alternate beat morphology change (regardless of whether this is a change in T wave vs U wave vs some indiscernible fusion of the two) — indicates either T wave or U wave alternans, which serves as a high-risk warning for development of Torsades unless metabolic conditions (and especially serum K+ and Mg++ levels) are quickly optimized.
- Along the way — The cause of U waves on ECG remains uncertain. Among the hypotheses for the generation of U waves include repolarization of Purkinje fibers — delayed repolarization of papillary muscles — afterpotentials caused by mechanical forces in the ventricular wall — prolonged repolarization of mid-myocardial “M-cells”. But — No one really knows …
- PEARL #1: Regardless of its T wave or U wave etiology — the marked degree of apparent T-U wave merging seen in today’s initial ECG is typical of the LQTS, Type 1 that today’s patient was found to have.
- PEARL #2: I long ago developed the easy-to-remember but surprisingly useful LIST of 3 Causes to consider whenever you encounter a long QTc in a patient who does not have a wide QRS. Think of the following! — i) Drugs (as noted above in Dr. Nossen’s discussion); — ii) Lytes (especially low serum K+ and Mg++ — but also low Ca++); and, iii) CNS disturbances (ie, Stroke [as for the patient in today’s case] — CNS Bleed — Brain Tumor — Coma — Seizure — Head Trauma — as some of the most abnormal ECGs are seen in patients with some form of CNS emergency).
- In 2025 — I’ll amend the above LIST by adding, under the right clinical circumstances — iv) Takotsubo (Stress) Cardiomyopathy (with an unusual anatomic distribution of ST-T wave abnormalites on ECG, that occurs in association with a surprisingly long QTc interval — suggesting this entity in a patient with new CP, heart failure, severe stress, etc.).
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How to Measure the QTc when U Waves are Present:
In Figure-2 — I’ve adapted the figure published by Rawshani in the first reference cited above by Dr. Nossen (Rawshani — Cardiovasc Med, 2025). I’ve consolidated below several helpful tips put forth by Rawshani:
- For optimal accuracy — Measure the QT manually, ideally using a series of consecutive beats — taken from more than a single lead — selecting the longest QT interval for which you can clearly see the onset and offset landmarks of the QT.
- The QT interval should be measured from the onset of QRS complex until the end of the T wave (ie, If no Q wave is present — begin measuring from the R wave).
- Leads with large U waves are ideally avoided. While recommended to include large U waves that are fused with the preceding T wave in your measurement — Realize that doing so may result in overestimation of the QT interval (with this being a significant problem in today’s case! ).
- Be sure to adjust the QT interval for heart rate! (See My Reminder above, near the beginning of My Comment).
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Figure-2: How to measure the QTc when U waves are present (Figure adapted from Rawshani — Cardiovasc Med, 2025).
