Schematic representation of normal ECG trace (sinus rhythm), with waves, segments, and intervals labeled.

In medicine, specifically cardiology, the QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle. The QT interval is dependent on the heart rate in an obvious way (the faster the heart rate, the shorter the QT interval) and has to be adjusted to aid interpretation. Image File history File links Download high resolution version (1156x1145, 30 KB) Summary Schematic diagram of normal sinus rhythm for a human heart as seen on ECG. Author: Agateller (Anthony Atkielski) Licensing I, the creator of this work, hereby release it into the public domain. ... Image File history File links Download high resolution version (1156x1145, 30 KB) Summary Schematic diagram of normal sinus rhythm for a human heart as seen on ECG. Author: Agateller (Anthony Atkielski) Licensing I, the creator of this work, hereby release it into the public domain. ... Sinus rhythm is indicative of normal electrical conductance of the heart. ... Cardiology is the branch of medicine dealing with disorders of the heart and blood vessels. ... The EKG complex. ... The infant/neonatal rate of heartbeat is around 130-150 bpm, the toddlers about 100–130 bpm, the older childs about 90–110 bpm, and the adolescents about 80–100 bpm. ...

The standard clinical correction is to use Bazett's formula,^[1] named after physiologist Henry Cuthbert Bazett, calculating the heartrate-corrected QT interval QTc.

The formula is as follows:

,

where QTc is the QT interval corrected for rate, and RR is the interval from the onset of one QRS complex to the onset of the next QRS complex, measured in seconds. However, this formula tends to not be accurate, and over-corrects at high heart rates and under-corrects at low heart rates. Physiology (in Greek physis = nature and logos = word) is the study of the mechanical, physical, and biochemical functions of living organisms. ... The QRS complex is a record of the measurement of the movement of electrical impulses through the lower heart chambers (ventricles). ...

In the same year, Fridericia ^[2] published an alternative adjustment:
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A more accurate method to correct the QT interval for the rate was developed by Rautaharju et al.^[3], who developed the formula

This method is not widely used by clinicians. There are several other methods, but a regression based approach is the most accurate according to the current knowledge.

Normal values for the QT interval are between 0.30 and 0.44 (0.45 for women) seconds. If abnormally prolonged or shortened, there is a risk of developing ventricular arrhythmias. An abnormal prolonged QT interval could be due to Long QT syndrome, whereas an abnormal shortened QT interval could be due to Short QT syndrome. In anatomy, a ventricle is a part of the body filled with fluid. ... A cardiac arrhythmia, also called cardiac dysrhythmia, is a disturbance in the regular rhythm of the heartbeat. ... The long QT syndrome (LQTS) is a heart disease in which there is an abnormally long delay between the electrical excitation (or depolarization) and relaxation (repolarization) of the ventricles of the heart. ... Short QT syndrome is a genetic disease of the electrical system of the heart. ...

See also

• Electrocardiogram

Lead II An electrocardiogram (ECG or EKG, abbreviated from the German Elektrokardiogramm) is a graphic produced by an electrocardiograph, which records the electrical activity of the heart over time. ...

References