A pretreatment ECG should be performed ... If the patient has a Q-Tc interval of 450-500 msec, the patient should be monitored more frequently and the patient should be informed of the increased ...

She returns for a follow-up visit for palpitations, and a 12-lead ECG is obtained ... The QT/QTc intervals are normal (280/440 msec). Prominent atrial waveforms occur before each QRS complex ...