All areas of clinical practice · UKMLA & AKT
Drug-induced prolonged QT and arrhythmias
A free high-yield preview for the UKMLA Applied Knowledge Test, covering how to recognise this condition. The full SA Note notes add investigations, management and complications, with practice questions on this topic.
Key high-yield points
- Drug-induced QT prolongation occurs when drugs block the hERG (IKr) potassium channel, slowing phase 3 repolarisation. This prolongs the action potential, predisposes to early afterdepolarisations (EADs), and can trigger torsades de pointes (TdP) - a polymorphic VT that may degenerate into VF.
- QTc calculated using Bazett formula: QTc = QT / √RR
- Prolonged QTc: >440 ms (males), >460 ms (females); QTc >500 ms = high-risk threshold
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