Prolonged QT

Question 1

What defines Prolonged QT on an ECG?

Answer 1

QT interval > 0.45s in men or > 0.46s in women (upper normal limit ≈ 0.45s).

Question 2

What does the QT interval represent?

Answer 2

Ventricular depolarisation + repolarisation time (QRS to end of T wave).

Question 3

What causes Prolonged QT physiologically?

Answer 3

Prolonged ST segment due to delayed ventricular repolarisation.

Question 4

Why is a long QT dangerous?

Answer 4

Increases risk of torsades de pointes → can lead to sudden cardiac death.

Question 5

What arrhythmia is most associated with Prolonged QT?

Answer 5

Torsades de Pointes (polymorphic VT).

Question 6

List two broad categories of Prolonged QT causes.

Answer 6

Genetic (congenital LQTS) and acquired (secondary to drugs, electrolyte imbalance, etc.).

Question 7

Name 3 common acquired causes of Prolonged QT.

Answer 7

Medications (antiarrhythmics, antipsychotics, antibiotics).

• Electrolyte imbalance (↓K⁺, ↓Mg²⁺, ↓Ca²⁺).
• Myocardial ischaemia.

Question 8

What is the normal QTc interval range?

Answer 8

0.33–0.45 seconds (corrected for HR).

Question 9

What drugs are classically known to prolong QT?

Answer 9

Class III antiarrhythmics (e.g., amiodarone, sotalol).

• Macrolide antibiotics.
• Antipsychotics (e.g., haloperidol).

Question 10

What ECG features suggest Prolonged QT?

Answer 10

Wide separation between QRS onset and T-wave end; stretched ST–T complex.

Question 11

What electrolyte should you check first in suspected Prolonged QT?

Answer 11

Potassium (K⁺) – hypokalaemia is a classic reversible cause.

Question 12

What’s the main risk if QT prolongation is not corrected?

Answer 12

What’s the main risk if QT prolongation is not corrected?

Question 13

How does congenital LQTS typically present?

Answer 13

Family history of sudden death, recurrent fainting, and syncope triggered by stress/exercise.

Question 14

What’s the management of drug-induced Prolonged QT?

Answer 14

Stop offending drug, correct electrolytes, IV magnesium if torsades develops.

Question 15

What is the first-line emergency treatment for torsades caused by prolonged QT?

Answer 15

IV magnesium sulfate.