QTc_Calculation v.1

Calculates the corrected QT interval (QTc), which is an estimate of the QT interval at a heart rate of 60 beats per minute (bpm). QTc allows comparison of QT values over time at different heart rates and improves detection of patients at increased risk of arrhythmias. QTc is expressed in milliseconds and is estimated using the heart rate (bpm) and QT interval (milliseconds) as variously expressed by the Bazett, Fredericia, Framingham and Hodges formulae. QTc is prolonged if > 440ms in men or > 460ms in women, and associated with increased risk of torsades de pointes if > 500ms in any sex. QTc is abnormally short if < 350ms.

Eneimi Allwell-Brown

models@cambiocds.com

© Cambio Healthcare Systems

To estimate the QTc which represents the QT interval at a heart rate of 60 bpm, allows comparison of QT interval values at different heart rates, and improves detection of patients at increased risk of arrythmia.

Use to calculate QTc based on heart rate (obtainable by palpation or ECG) and QT interval (obtained from the ECG). QTc is expressed in milliseconds (msecs) and is estimated using the heart rate (bpm) and QT interval (msecs) as variously expressed by the following formulae: Bazett: QTc = QT / RR^0.5 Fredericia: QTc = QT / RR^0.333 Framingham: QTc = QT + 0.154 (1 – RR) Hodges: QTc = QT + 1.75 (heart rate – 60) where RR = R-R interval = 60 / heart rate. QTc is prolonged if > 440ms in men or > 460ms in women, and associated with increased risk of torsades de pointes if > 500ms in any sex. QTc is abnormally short if < 350ms. Bazett’s formula is simple and is the most commonly used. It provides an adequate correction for heart rates ranging from 60 – 100 bpm. It over-corrects at heart rates > 100 bpm and under-corrects at heart rates < 60 bpm. Fredericia or Framingham corrections are more accurate at heart rates outside of the 60 – 100 bpm range.

Bazett HC. AN ANALYSIS OF THE TIME‐RELATIONS OF ELECTROCARDIOGRAMS. Annals of Noninvasive Electrocardiology. 1997 Apr 1;2(2):177-94. Fridericia LS. The duration of systole in an electrocardiogram in normal humans and in patients with heart disease. Annals of Noninvasive Electrocardiology. 2003 Oct 1;8(4):343-51. Hodges M, Salerno D, Erlien D. BAZETT QT CORRECTION REVIEWED-EVIDENCE THAT A LINEAR QT CORRECTION FOR HEART-RATE IS BETTER. InJournal of the American College of Cardiology 1983 Jan 1 (Vol. 1, No. 2, pp. 694-694). 655 AVENUE OF THE AMERICAS, NEW YORK, NY 10010: ELSEVIER SCIENCE INC. Sagie A, Larson MG, Goldberg RJ, Bengtson JR, Levy D. An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study). The American journal of cardiology. 1992 Sep 15;70(7):797-801.

OBSERVATION.ecg.v1, OBSERVATION.pulse.v2