Figure 27-7 Measurement of the QTC interval (properly termed QETC to indicate that it begins with the start of the Q wave, lasts throughout the QT interval, ends with the end of the T wave, and is corrected for heart rate). RR is the RR interval in seconds. (From Hensel P, Roizen MF: Patients with disorders of parathyroid function. Anesthesiol Clin North Am 5:287, 1987.)