Long QT syndrome + Loop diuretics

Question 1

What is long QT syndrome?

Answer 1

• Long QT syndrome (LQTS) is associated with delayed repolarization of the ventricles
• May lead to ventricular tachycardia/torsade de pointes and can therefore cause collapse/sudden death

Question 2

What are the most common variants of LQTS?

Answer 2

• The most common variants of LQTS (LQT1 & LQT2) are caused by defects in the alpha subunit of the slow delayed rectifier potassium channel
• A normal corrected QT interval is less than 430 ms in males and 450 ms in females

Question 3

What are congenital long QT interval?

Answer 3

• Jervell-Lange-Nielsen syndrome (includes deafness and is due to an abnormal potassium channel)
• Romano-Ward syndrome (no deafness)

Question 4

What drugs cause long QT syndrome?

Answer 4

• Amiodarone, sotalol, class 1a antiarrhythmic drugs
• Tricyclic antidepressants, selective serotonin reuptake inhibitors (especially citalopram)
• Methadone
• Chloroquine
• Terfenadine**
• Erythromycin
• Haloperidol
• Ondanestron

Question 5

What other causes of long QT syndrome are there?

Answer 5

• Electrolyte: hypocalcaemia, hypokalaemia, hypomagnesaemia
• Acute myocardial infarction
• Myocarditis
• Hypothermia
• Subarachnoid haemorrhage

Question 6

What are the features of long QT syndrome?

Answer 6

• May be picked up on routine ECG or following family screening
• Long QT1 - usually associated with exertional syncope, often swimming
• Long QT2 - often associated with syncope occurring following emotional stress, exercise or auditory stimuli
• Long QT3 - events often occur at night or at rest
• Sudden cardiac death

Question 7

What is the management of long QT syndrome?

Answer 7

• Avoid drugs which prolong the QT interval and other precipitants if appropriate (e.g. Strenuous exercise)
• Beta-blockers*** (solatolol may excerbate)
• Implantable cardioverter defibrillators in high risk cases

Question 8

How do drugs usually prolong QT interval?

Answer 8

Blockage of potassium channels

Question 9

What are examples of loop diuretics?

Answer 9

Furosemide and bumetanide

Question 10

How do loop diuretics work?

Answer 10

1. Inhibiting the Na-K-Cl cotransporter (NKCC2) in the thick ascending limb of the loop of Henle

:. reducing the absorption of NaCl

:. there are two variants of NKCC; loop diuretics act on NKCC2, which is more prevalent in the kidneys

Question 11

What are the indications of loop diuretics?

Answer 11

• Heart failure: both acute (usually intravenously) and chronic (usually orally)
• Resistant hypertension, particularly in patients with renal impairment

Question 12

What are adverse effects of loop diuretics?

Answer 12

• Hypotension
• Hyponatraemia
• Hypokalaemia, hypomagnesaemia
• Hypochloraemic alkalosis
• Ototoxicity
• Hypocalcaemia
• Renal impairment (from dehydration + direct toxic effect)
• Hyperglycaemia (less common than with thiazides)
• Gout