Prolonged QT interval

An ECG finding in which the ventricular repolarization period (QT interval or rate-corrected QTc interval) is prolonged beyond normal limits (typically QTc ≥470 ms), reflecting delayed ventricular action potential duration and increasing the risk of polymorphic ventricular tachycardia, particularly torsades de pointes.

Causes

• Medications

  • Antibiotics: Macrolides (azithromycin, erythromycin), Fluoroquinolones

  • Antidepressants: TCA, SSRI

  • Antihistamines

  • Antipsychotics

  • Antiarrhythmic drugs: Quinidine, procainamide, amiodarone, sotalol

• Electrolyte disturbances affecting cardiac repolarization

  • Hypokalemia

  • Hypomagnesemia

  • Hypocalcemia

• Hypothyroidism

• Hypothermia

• Cardiac causes

  • Myocardial infarction

  • Myocardial ischemia

  • Cardiomyopathy

  • Myocarditis

  • Heart failure

• Neurological causes affecting autonomic regulation

  • Stroke

  • Intracranial hemorrhage

• Genetic causes

  • Congenital long QT syndromes

    • Romano–Ward syndrome

    • Jervell and Lange-Nielsen syndrome

  • Mutations affecting cardiac ion channels (potassium or sodium channel genes)