Effect of QRS width on QT interval

Cicy Bastian, Raihanathul Misiriya Kamarudheen Jameela, Sudhayakumar N

Abstract


EFFECT OF QRS WIDTH ON QT INTERVAL.

Abstract

Background.

In the surface ECG, ventricular depolarization is represented by the QRS and ventricular repolarization by the ST and T which together forms the JT interval. When the QRS duration is normal,  we take QT interval as a measure of repolarization. But when there is QRS widening, what happens to this QT interval? If there is prolongation of the QT , is it due to prolongation of depolarization alone or  prolongation of repolarization?  We tried to find out this by analyzing 50 cases of intermittent narrow and wide QRS.

Methods.

50 patients with intermittent right bundle branch block (RBBB), pacing in Sick sinus syndrome (SSS), pacing in brad arrhythmias during Myocardial infarction (MI), and intermittent preexcitation were included in the study. Patients with pre existing broad QRS were excluded from the study. Simultaneous  single channel 12 lead  ECG was taken during narrow QRS and broad QRS . QT interval was calculated as the mean QT of six leads in which QT could be easily measured.  JT interval was  calculated by subtracting QRS duration from QT interval. Corrected QT interval (QTc) was calculated by Bazett’s formula.  From this corrected JT ( JTc) was also calculated. All the measurements were taken during narrow QRS rhythm and broad QRS rhythm.

Results

As the QRS width prolonged to 110 ms or more , QT and QTc were also prolonged. There was no change in JT and JTc.

Conclusion

JT and JTc intervals are more reliable than QT and QTc intervals  in case of wide QRS.

Key words

Broad QRS, JT interval ,QRS width , QT interval.


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References


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