Bazett formula

Description

  • A prolonged QT interval is associated with an increased risk of torsades de pointes. A rise in heart rate is associated with a shortening of the QT interval and similarly a slowing of the heart rate is associated with a longer QT interval.
  • Bazett formula ‘corrects‘ the measured QT interval to a value (QTc) attributable to a heart rate of 60 bpm. Thus providing a QT interval value that a particular patient would theoretically have if their heart rate was 60 beats/min
Bazett-Formula-Modern-usage-QTc

History

1891Augustus Desiré Waller provided a series of values for the duration of mechanical systole with different heart rates. He demonstrated that the period of mechanical contraction (systole) was shortened at faster heart rates

1919 – Lombard WP and Cope OM recorded measurements of the carotid pulse in patients standing, lying and sitting and following exercise to derive an equation for measuring the duration of systole.

Lombard-and-Cope-1919

1920Bazett used Waller’s 1891 data to create a formula which could estimate/calculate the duration of systole with varying pulse rates. He then reviewed electrical and mechanical data from Weitz, Wiggars, Lewis, Buchanan, Kraus and Nicholai to confirm his calculations. He concluded:

Waller gives values for the duration of mechanical systole with different heart rates, and it will be seen that almost exactly similar figures are obtained by calculation from the formula Systole = k √ cycle, where K has a value of 0.343.

The (Lombard, Cope 1919) results are confirmed by the figures here reported, in spite of the difference in the method employed, and I had independently arrived at the same relationship of systole to the square root of the cycle before the publication of their results.

The duration of the ventricular complex in an electrocardiogram is in the normal heart a function of the pulse rate, and may be determined by the formula: Systole = k √ cycle. The normal value for k is 0.37 for men and 0.40 for women.

Bazett Formula QTc 1920

1947Taran and Szilagyi related QT prolongation to acute rheumatic carditis in children. In doing so, they updated Bazett’s original formula:

QTc QT interval Taran-and-Szilagyi-1947

Associated Persons


Alternative names

  • Bazett’s formula
  • Taran and Szilagyi corrected QT interval
  • Bazett formula modified by Taran and Szilagyi

Controversies

  • Bazett QTc calculation unreliably identifies patients with prolonged QTc interval [Charbit 2006]

References


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the names behind the name

Emergency physician MA (Oxon) MBChB (Edin) FACEM FFSEM with a passion for rugby; medical history; medical education; and informatics. Asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | vocortex |

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