What is the QTC?

As a medical professional, I specialize in understanding and interpreting various medical parameters, including the QTc interval, which is a critical measurement in cardiology. The QTc, or corrected QT interval, is a heart rate-adjusted version of the QT interval on an electrocardiogram (ECG). The QT interval represents the time from the start of the Q wave to the end of the T wave, which corresponds to the time between the initial depolarization and the completion of repolarization of the ventricles. The QTc is important because it helps to identify potential issues with the heart's electrical activity, which can be a sign of certain heart conditions or the effect of certain medications. Normal QTc values are typically less than 440 milliseconds in men and less than 460 milliseconds in women. A QTc interval that is prolonged, meaning it exceeds these values, can be associated with an increased risk of a type of irregular heartbeat called torsades de pointes, which can be life-threatening. On the other hand, a QTc that is abnormally short, less than 350 milliseconds, can also indicate a problem. A useful rule of thumb for the normal QT interval is that it should be less than half the duration of the preceding RR interval, which is the time between two successive QRS complexes on the ECG.

Normal QTc values. QTc is prolonged if > 440ms in men or > 460ms in women. QTc > 500 is associated with increased risk of torsades de pointes. QTc is abnormally short if < 350ms. A useful rule of thumb is that a normal QT is less than half the preceding RR interval.