Expansion
The As: antiarrhythmics, antibiotics, antipsychotics, antidepressants, antiemetics
Expansion
The As, which covers most of them:
- Antiarrhythmics: amiodarone, sotalol, quinidine, procainamide
- Antibiotics: macrolides (erythromycin, clarithromycin), quinolones, fluconazole
- Antipsychotics: haloperidol, quetiapine, risperidone
- Antidepressants: citalopram and escitalopram, tricyclics
- Antiemetics: ondansetron, domperidone
- Antihistamines, and methadone
Normal QTc: under 440 ms in men, 460 ms in women. Over 500 ms carries a markedly increased risk of torsades de pointes.
Risk factors that multiply the drug effect
- Hypokalaemia, hypomagnesaemia, hypocalcaemia
- Bradycardia
- Female sex, age, structural heart disease, hepatic or renal impairment
- Congenital long QT syndrome
- Two QT prolonging drugs together, or a CYP inhibitor raising the level of one
“Correct the electrolytes, stop the drug, and treat torsades with magnesium.”
Torsades de pointes is a polymorphic ventricular tachycardia with a twisting axis: treat with intravenous magnesium sulphate, correct electrolytes, stop the offending drugs, and consider overdrive pacing for recurrent episodes.