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The Biology Project > Biomath > Applications > Heart Activity

Heart Activity

Electrocardiograms (ECGs or EKGs) provide information about heart activity. They are most often used by doctors to identify potential arrhythmias. The QT interval on an ECG is the time interval representing ventricular depolarization and subsequent repolarization (i.e. the duration of activation and recovery of the heart). The RR interval on an ECG is the interval used to calculate the heart rate.

The QT interval varies with heart rate (i.e. RR interval); normal QT decreases with increasing heart rate. Therefore, a QTc interval (corrected QT interval) is often calculated to adjust for the heart rate. The most common correction is called the Bazett correction. This commonly used correction has been criticized as being inaccurate, and numerous other corrections have been proposed.

A more complicated exponential equation to compute QTc was found by using nonlinear regression analysis to fit data from young healthy volunteers in [1]. This equation is given by,

QTc = 425 - 676 · e -0.0037·RR ,

where RR is the RR interval from an ECG (all units are in milliseconds).

Use this equation to solve the three problems in this section.


Compute the QTc interval for an individual with an RR interval of 900 ms.

Round you answer to the nearest whole millisecond.

Answer:   ≈


Problem 1- Calculate the corrected QT interval

Problem 2- Calculate the RR interval

Problem 3- When can you use this correction?

[1] Lecocq, B., Lecocq, V., and P. Jaillon (1989). Physiologic relation between cardiac cycle and QT duration in healthy volunteers. Am J Cardiol 64:481-486.


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The Biology Project > Biomath > Applications > Heart Activity

Credits and Citation

The Biology Project
Department of Biochemistry and Molecular Biophysics
The University of Arizona

December 2005
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