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Prolonged QT Inverval Prolonged QT Interval (Example 1) Prolonged QT Interval (Example 2) Prolonged QT Interval (Example 3) Prolonged QT Interval (Example 4) Prolonged QT Interval (Example 5) A prolonged QT interval has a variety of causes and can be a very serious EKG finding since it may lead to the potentially fatal arrhythmia Torsades de Pointes. A normal QT interval varies, but when corrected for heart rate it should be < 420 milliseconds or 0.42 seconds. The QT interval is measured from the start of the QRS complex to the end of the T wave. In general, the QT interval should be less than half of the R to R interval. Anything longer can be considered prolonged. The QT interval varies greatly depending upon the heart rate and the gender of the person. The slower the heart rate, the longer the QT interval and vise versa. Females have a longer QT interval in general when compared to their male counterparts. To correct for the QT interval's change with different heart rates, a corrected QT interval can be calculated (QTc). The QTc is the measured QT interval divided by the square root of the R to R interval. The equation is below (Bazett's formula): QTc = (QT measured) / (R-R interval)½ Many drugs, electrolyte disturbances, or congenital syndromes can cause a prolonged QT interval. |
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