The surface electrocardiogram (ECG) is an indirect measure of the heart’s electrical activity and is one of the most commonly used diagnostic tools. Measuring the QT interval on the surface ECG is important because when it is long, it is associated with syncope, the arrhythmia torsade de pointes, and death.1–7  The QT interval is an indirect measure of ventricular repolarization and is measured in seconds (s) or milliseconds (ms) from the onset of the QRS complex to the end of the T wave. Including the QRS complex in the QT interval measurement is necessary because the start of a ventricular repolarization is buried somewhere within the QRS complex. Therefore, as the QRS complex is usually less than 120 ms and its onset is easily identifiable, the QRS complex is included. However a second step after the measurement of the QT...

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