Prolonged QT

Question 1

What is the definition of a Long QT interval in men and women?

Answer 1

QT interval is abnormally long when;
> 440 m/s in males
>460 m/s in females

Question 2

What is the pathophysiology of a prolonged Q-T interval?

Answer 2

1. QT interval is longer than normally which should typically be less than half of a cardiac cycle.
2. Ventricles take longer to repolarise
3. This can be due to L- type calcium channels dysfunction
   which normally make the cell membranes more positive in the cardiac action potential and propagate the plateau phase.

Question 3

What is the definition of corrected QT interval?

Answer 3

• QT interval changes depending on the rate
• As the rate increases, the QT interval decreased
• Thus - correct QT or QTc allows for comparison of the QT interval at a standard 60 beats per minute

Question 4

What is Bazett’s formula?

Answer 4

Qtc = QT (in milliseconds) / Square root (R-R interval in seconds)/1 second

Question 5

What are the complications ofa prolonged QT interval?

Answer 5

• Re-entract tachycardia
• Torsade de Pointes } Polymorphic ventricular tachycardia

Question 6

Which drugs cause prolonged QT?

(5)

Answer 6

1. Amiodorone, Sotalol
2. Tricyclic antidepressants, SSRI (Citalopram), Haloperidol
3. Methadone
4. Erythromycin
5. Electrolyte abnormalities : Hypokalaemia, Hypomagnesaemia, Hypocalcaemia

Question 7

What is the management of a long QT isyndrome?

Answer 7

1. Avoid drugs which prolong Q-T interval and strenuous exercise
2. Beta blockers (except for sotalol)
3. Implantable Cardioverter defibrillators in high risk cases

Question 8

What is the definition of Torsade de Pointes?

Answer 8

• a form of polymorphic Ventricular tachycardia associated with a long Q-T interval.
• Can deteriorate into ventricular fibrillation and lead to sudden death.

Question 9

What is the management of Torsade de Pointes?

Answer 9

IV Magnesium Sulphate