prolongedqtc
Table of Contents
prolonged QTc
see also:
- avoid prescribing drugs known to cause prolonged QTc to patients at high risk of, or known to have prolonged QTc!
- patients are particularly at risk if they also have bradycardia
introduction
- the QT interval on the ECG is measured from the start of QRS complex to end of the T wave
- QTc refers to a QT interval “corrected” for the effect of differing heart rate to give a QT value as if the heart rate is 60bpm
- prolonged QTc represents delayed repolarisation & predisposes to early after-depolarisations, re-entrant tachycardias, especially potentially fatal torsade de pointes VT which is most likely if bradycardia is present too.
calculating QTc
- if rate 60-100bpm, then QT should be less than half the RR interval
- Bazett's formula: QTc = QT / square root (RR interval)
aetiology of prolonged QTc
- V-W class Ia drugs: quinidine, disopyramide, procainamide
- V-W class III drugs: amiodarone, sotalol
- other drugs with class Ia activity: tricyclic antidepressants, particularly in overdose, phenothiazines, non-sedating antihistamines (H1)
- high dose iv ondansetron
- cerebrovascular disease incl. subarachnoid haemorrhage (SAH)
- rheumatic fever
- myocarditis
- mitral valve prolapse
- hypokalaemia - actually a flat T with a prominent U wave
- liquid protein diets
- congenital prolonged QT syndrome
prolongedqtc.txt · Last modified: 2026/03/20 23:49 by wh