Louis Sigurd Fridericia

Louis Sigurd Fridericia (1881 – 1947)

Louis Sigurd Fridericia (1881 – 1947) was a Danish physician.

In 1920 Fridericia found that the duration of the QT interval was related to the cube root of the RR interval (Fridericia’s formula) – independent of the relationship defined by Bazett (1920) where he related the corrected QT interval to the square root of the RR interval (Bazett formula)

Fridericia investigated the relationship between vitamin deficiency and night blindness in rats. He introduced the term ‘refection‘ following studies demonstrating rats could grow and thrive without ‘vitamin B’ in their diet. Refection enabled rats to make use of the vitamins synthesized in the caecum by ‘microbial agents’ activated in vitamin B deficiency

We propose to name this restoring change: refection (Latin: reficere = restore). To induce refection will be termed to refect: and agencies capable of refecting will be termed refectious

Fridericia LS, 1925


  • Born 24 February 1881 Copenhagen, Denmark
  • 1906 – Medical degree, University of Copenhagen
  • 1907 – Assistant to Christian Bohr at the Physiological Laboratory, University of Copenhagen
  • 1909 – Assistant to Carl Julius Salomonsen at the Institute of General Pathology, University of Copenhagen
  • 1910 – Doctoral thesis – Undersøgelser over fosterstofskifte [Fetal metabolism studies]
  • 1913-18 assistant physician at the Rigshospitalet, Kommunehospitalet and Bispebjerg Hospital with special interest in cardiology
  • 1918 – Professor of hygiene, Hygienic Institute of the University of Copenhagen
  • 1920 – Country Editor of the Nordic Hygiene Journal
  • 1935 – President, Medical Society of Copenhagen
  • 1943 – Escaped Nazi persecution in Denmark being smuggled in a fishing boat to Sweden and then to London
  • Died 26 February 1947

Medical Eponyms

Fridericia formula (1920)

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

In 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.

Fridericia 1

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.

Major Publications


eponymictionary CTA


the person 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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