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The standard clinical correction is to use Bazett's formula1 calculating the heart rate corrected QT interval QTc. Bazett's formula is QTc = rac{QT}{\sqrt {RR} },

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.

A more accurate method to correct the QT interval for the rate was developed by Rautaharju et al.2, who developed the formula QTp= rac{656}{1+ rac{heart\ rate}{100}}.

This method is ''not'' widely used by clinicians.

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 Arrhythmia s. 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 .


SEE ALSO



REFERENCES

1. Bazett HC. An analysis of the time-relations of electrocardiograms. Heart 1920; 7:353-370

2. Rautaharju PM, Warren JW, Calhoun HP. Estimation of QT prolongation. A persistent, avoidable error in computer electrocardiography. J Electrocardiol. 1990;23 Suppl:111-7. PMID 2090728.