Question 1

Why does Bazett's formula overcorrect at high heart rates?

Accepted Answer

Bazett divides by the square root of RR, which shrinks the denominator disproportionately at fast rates, yielding an artificially prolonged QTc. Fridericia's cubic-root correction is more robust at high heart rates, which is why multiple formulas should be inspected.

Question 2

What is the most common cause of acquired QTc prolongation in hospital?

Accepted Answer

Drug-induced QT prolongation. Common offenders include macrolide and fluoroquinolone antibiotics, fluconazole, haloperidol, ondansetron, methadone, and many antiarrhythmics (amiodarone, sotalol, dofetilide). Polypharmacy with additive QT effects is especially dangerous. Always review the patient's medication list.

Question 3

When should I take a patient off QT-prolonging medications?

Accepted Answer

Discontinuation should be discussed if the QTc exceeds 500 ms or if the patient has risk factors for TdP (hypokalaemia, hypomagnesaemia, bradycardia, recent conversion from atrial fibrillation, or a personal/family history of long QT syndrome). Correct electrolytes first.