Overview
Clinical Meaning
The QT interval on the ECG represents ventricular depolarization and repolarization — from the beginning of the QRS complex to the end of the T wave.
PNP-PC
PNP-PC
The QT interval on the ECG represents ventricular depolarization and repolarization — from the beginning of the QRS complex to the end of the T wave. It is corrected for heart rate using Bazett's formula (QTc = QT / √RR interval). Normal QTc is < 440 ms in males and < 460 ms in females. QTc prolongation (> 500 ms is highest risk) predisposes to torsades de pointes (TdP), a polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation and sudden cardiac death. Mechanism: prolonged repolarization creates unequal recovery of excitability across the ventricular myocardium, leading to early afterdepolarizations (EADs) that trigger re-entrant circuits. Drug-induced QT prolongation occurs through blockade of the hERG (IKr) potassium channel, which is responsible for the rapid delayed rectifier potassium current critical for phase 3 repolarization. Major drug categories causing QT prolongation include: antiarrhythmics (sotalol, amiodarone, procainamide, dofetilide), antipsychotics (haloperidol, ziprasidone, thioridazine), antibiotics (fluoroquinolones, macrolides, azole antifungals), antiemetics (ondansetron, droperidol), and methadone. Risk factors for TdP include female sex, hypokalemia, hypomagnesemia, bradycardia, congenital long QT syndrome, structural heart disease, and the combination of multiple QT-prolonging...
Unlock full lesson + practice questions
4 more sections with scenarios, priorities, and review drills.
Final rapid review before practice
Next study step
Finish the lesson first, then choose a focused activity to apply what you just reviewed.
Continue studying
Sign in to save progress on this lesson.
Unlock the interactive lesson quiz with a plan that includes this PNP-PC pathway. You can still explore topic-filtered questions from the bank hubs below.