Calculators for Qtc and risk for drug associated Qt prolongation

These two calculators have been elaborated to increase prescribers' awareness of the factors that may increase the risk of QT prolongation, particularly in the context of the use of Hydroxychloriquine and/or Azithromycin, as experimental traitement for Covid 19.

The approach is constructed upon a list of references and follows the two steps below:

Step 1: QTc calculator Step 2: Tisdale's score calculator

This application is developped by the Centre Hospitalier Sud-Francilien (CHSF) and IBISC laboratory from Evry/Paris-Saclay University.

For any feedback or comment to improve quality and performance of calculators, please Contact Dr. MAHFOUD Mohanad, Head of Arrhythmia Unit, Centre Hospitalier Sud-Francilien, Corbeil-Essonnes, France, mohanad_dot_mahfoud_at_chsf_dot_fr.

QTc calculator

How to use

Insert measured QT duration as well as either heart rate or R-R interval and select one of the QT estimator.
The form will then be able to compute the corrected QT duration.
QRS duration can be added in order to compute the wide QRS adjusted QTC.
Once these steps are completed, you can compute Tisdale's score.

Corrected QT estimator [1][2]


Please fill out the required fields.

Next step: Tisdale's score

QT measurement methods


Wide QRS adjusted QTc

In the case of a wide QRS, QTc needs to be adjusted. It is then computed as follows :

QTca = QTc - ( QRS - 100 )

where QTca stands for wide QRS adjusted QTc.

For example, if a patient’s left bundle branch block has yielded a QRS of 200 ms, and a QTc of 520 ms, this would appear to be long.
However, the wide-QRS adjusted QTc would be 520 ms – [200 – 100 ms] = 520 – 100 = 420 ms.


Bazett estimator is computed as follows:

QTc = QTm RR

Fridericia estimator is computed as follows:

QTc = QTm RR 3

Wide QRS adjusted QTc is computed as follows :

QTca = QTc - ( QRS - 100 )


  • QTm is the measured QT interval (in ms).
  • QTc is the corrected QT interval (in ms).
  • QTca is wide QRS adjusted QTc (in ms).
  • RR is the R-R interval (in s) and equals to 60/HR.
  • HR is the heart rate (in bpm).

Fridericia Formula is recommended when heart rate ≤ 60 BPM or > 90 BPM.
Fridericia Formula is recommended when R-R intervalle > 1000ms or ≤ 667ms.

Tisdale's score calculator

How to use

Just input the different parameters. Tisdale's score [4] will be adjusted in real-time. The risk is considered as:

  • low, if the score is below 6 (included)
  • moderate, if the score is between 7 and 11 (included)
  • high, if the score is above 11 (excluded)
Tisdale's score ranges from 0 to 21.


Tisdale's score

Please fill out the required fields.

(Please take in consideration that Tisdale's score has been developed and validated on hospitalized patients).

Recommendations to minimize arrhythmia risk include:

Previous step: QTc calculator

The following link can help you to determine if a drug is in the list of drugs that prolong QT & induce Torsades de Pointes (TdP):


  1. Bazett HC (1920). "An analysis of the time-relations of electrocardiograms". Heart (7): 353–370.
  2. Fridericia LS (1920). "Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken. [The duration of systole in the electrocardiogram of normal subjects and of patients with heart disease.]" Acta Medica Scandinavica 53:469–486.
  3. Giudicessi JR, Noseworthy PA, Friedman PA, Ackerman MJ (2020). "Urgent Guidance for Navigating and Circumventing the QTc Prolonging and Torsadogenic Potential of Possible Pharmacotherapies for COVID-19". Mayo Clinic Proceedings. 2020;95. (link)
  4. Tisdale JE, Jayes HA, Kingery JR, et al (2013). "Development and validation of a risk score to predict QT interval prolongation in hospitalized patients". Circ Cardiovasc Qual Outcomes. 2013;6:479-487.
  5. Simpson TF, Kovacs RJ, Stecker EC (2020). "Ventricular Arrhythmia Risk Due to Hydroxychloroquine-Azithromycin Treatment For COVID-19". ACC Cardiology magazine. (link)
  6. Vink AS, Neumann B, Lieve KV, Sinner MF, Hofman N, El Kadi S, Schoenmaker MH, Slaghekke HM, de Jong JS, Clur SB, Blom NA, Kääb S, Wilde AA, Postema PG (2018). "Determination and interpretation of the QT interval". Circulation 138 (21), 2345-2358.
  7. Roden DM, Harrington RA, Poppas A, Russo AM (2020). "Considerations for Drug Interactions on QTc in Exploratory COVID-19 (Coronavirus Disease 2019) Treatment.", Circulation, 8 Apr 2020. (link)

Legal Disclaimer

This application (the “Application”) is intended for physicians and other healthcare professionals.

The information and tools that the Application make available through the Application are provided for educational and informational purposes only. While we hope you find the Application useful to you as a healthcare professional, they are in no way intended to serve as a diagnostic service or platform, to provide certainty with respect to a diagnosis, to recommend a particular product or therapy or to otherwise substitute for the clinical judgment of a qualified healthcare professional. You are solely responsible, as a physician or healthcare professional, for evaluating the information obtained from the Application and for your use or misuse of such information in connection with your treatment decisions or otherwise. You agree that you shall be solely responsible for your compliance with all laws and standards of professional practice applicable to you and the practice of medicine or other relevant health profession.

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