Why do we correct the QT interval for heart rate?

  Since heart rate is the major modifier of ventricular action potential,

      the QT interval changes with heart rate. This is the basis for QT interval correction.

      To compare the QT intervals between different individuals, they must be corrected according to the

      heart rate.

  Heart rate is INVERSELY related to the QT interval:

      As the heart rate increases, the QT interval decreases.

      As the heart rate decreases, the QT interval increases.




Proposed formulae for QT interval correction





Linearity of the QT interval correction formulae

  Nonlinear formuale

            - Bazett

            - Fridericia

  Linear formuale

            - Framingham

            - Hodges




Which QT interval correction formula is the best?

  The most frequently used one is the Bazett's formula (1920).

      However it is also the most criticized formula.

      Bazett's formula

                  - overcorrects the QT interval at fast heart rates

                  - undercorrects the QT interval at slow heart rates.

  Hodges formula is suggested to be the best one.




References

  Journal of Electrocardiology 2004, Vol 37, Suppl:81-90.

  J Cardiovasc Electrophysiol 2010;21:905-913.

  J Am Coll Cardiol 1983;12:694.Am J Cardiol 79:797,1992

  Am J Cardiol 1992;79:797

  Acta Med Scan 1920;53:469.

  Heart 1920;7:353.J Cardiovasc Electrophysiol 2010;21:905-913.

  Clinical Arrhythmology and Electrophysiology: A Companion to Braunwald's Heart Disease.

      2nd edition. 2012.