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QTc (Fridericia)

Fridericia: A cube-root correction formula often preferred in research and for patients with tachycardia or bradycardia.

Guidelines & Evidence

Verified

Last Review: 2026

When to Use

When to Use

To calculate the heart rate-corrected QT interval (QTc) on a standard 12-lead ECG.
Preferred over Bazett’s formula in patients with tachycardia (> 100 bpm) or bradycardia (< 60 bpm).
Widely used in clinical research and by the FDA for drug safety evaluations.

How it Works

Formula

QTc = QT / ∛(RR) Where RR is the interval between two consecutive R waves (in seconds).

Mathematical Rationale

Fridericia’s formula uses a cube root (∛) of the RR interval rather than the square root (√) used in Bazett’s. This cube-root correction better accounts for the physiologic relationship between repolarization and heart rate at the extremes of the spectrum.

Clinical Pearls

Superior Accuracy

Fridericia’s formula significantly reduces the rate of false-positive QTc prolongation across a wide range of heart rates. It is considered more reliable than Bazett’s in patients with persistent sinus tachycardia.

Next Steps

Complementary Calculators

Bazett’s Formula (QTc)
Framingham Formula (QTc)
Brugada Algorithm
VEREKEI Algorithm
Sokolow-Lyon Voltage

The Evidence

Foundational Reference

Die Systolendauer im Elektrokardiogramm bei normalen Menschen und bei Herzkranken.

Fridericia LS. • Acta Med Scand.. 1920;53:469–486. The original derivation of the cube-root correction.

Last Comprehensive Review: 2026

In Recent Clinical News

Scanning Medical Journals

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