A formula for calculating the QT interval on an electrocardiogram (ECG) according to heart rate. Using this formula, Fridericia postulated that QT values >0.43 seconds were considered prolonged
1891 – Augustus 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
1920 – Fridericia hypothesised a relationship between the duration of the ventricular electrocardiogram (s) and the duration of the pulse period (p). He studied 50 healthy individuals (age 3-81 years; 28 males and 32 females) at rest to determine the accuracy and the error rate in the measurement of both the pulse period (p) and the duration of the ventricular electrocardiogram (s).
He found that QT could be predicted accurately from the following formula: s = K (p0.3558) which he then simplified (p0.3558) to ³√p without any significant error; then calculated k (=8.22) for normal healthy individuals.
He concluded that in a normal, resting subject, the duration of electrical systole on an ECG is proportional to the cube root of the duration of the pulse period.
By applying this equation to his data set, Fridericia defined an average (Gauss) error of 0.015 seconds for a single duration. Variations of the observed duration of electrical systole >3 times the average error were considered to be pathological. Therefore the upper value for a ‘normal QT interval’ at a heart rate of 60 bpm was defined as 0.427 seconds (0.382 sec+0.045 s), and so QT values>0.43 seconds were deemed prolonged.
- Augustus Desiré Waller (1856-1922)
- Henry Cuthbert Bazett (1885-1950)
- Louis Sigurd Fridericia (1881-1947)
- Charbit B et al in a study of 108 patients found that automatic QT correction using Bazett formula had a sensitivity for detection of QT prolongation of 54% while automatic QT correction using Fridericia formula had 100% sensitivity
- Moss AJ Introductory note to a translated classic article of L. S. Fridericia. Ann Noninvasive Electrocardiol. 2003 Oct;8(4):341-2. [PMID 14516291]
- Fridericia LS. Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken [The Duration of Systole in an Electrocardiogram in Normal Humans and in Patients with Heart Disease]. Part I: Beziehung zwischen der Pulsfrequenz und der Dauer des Ventrikelelektrokardiogramms bei normalen Menschen in der Ruhe [Relationship of the pulse frequency and the duration of the ventricular electrocardiogram in normal humans at rest]. Acta Med Scand 1920;53:469–486 [Translated reprint: Ann Noninvasive Electrocardiol. 2003 Oct;8(4):343-51.]
- Luo S, Michler K, Johnston P, Macfarlane PW. A comparison of commonly used QT correction formulae: the effect of heart rate on the QTc of normal ECGs. J Electrocardiol. 2004;37 Suppl:81-90. [PMID 15534815]
- Charbit B, Samain E, Merckx P, Funck-Brentano C. QT interval measurement: evaluation of automatic QTc measurement and new simple method to calculate and interpret corrected QT interval. Anesthesiology. 2006 Feb;104(2):255-60. [PMID 16436843]
- Indik JH, Pearson EC, Fried K, Woosley RL. Bazett and Fridericia QT correction formulas interfere with measurement of drug-induced changes in QT interval. Heart Rhythm. 2006 Sep;3(9):1003-7 [PMID 16945790]