Prolonged QT syndrome

Question 1

Prolonged QT syndrome: Definition

Answer 1

• a genetic/ acquired condition characterised by a prolonged QT interval on the surface ECG
• associated with a high risk of sudden cardiac death due to ventricular tachyarrhythmias
• Mutations within 13 identified genes result in a variety of channelopathies affecting myocardial repolarisation, thus prolonging the QT interval.

Question 2

Prolonged QT syndrome: Aetiology

Answer 2

• normally due to genetic mutations
  
  • Genetic mutations identified in 13 genes account for congenital LQTS, with those in the following 3 genes constituting 90% to 95% of cases
    
    • most mutations involve genes that encode K+/ Na+ channels
• can also occur in people without a genetic abnormality,
  
  • commonly due to a side effect of medications
  • or hypokalaemia
  • or hypomagnesaemia

Question 3

Prolonged QT syndrome: Risk Factors

Answer 3

• KCNQ1 gene mutations
• KCNH2 gene mutations
• SCN5A gene mutations
• QT interval-prolonging drugs

Question 4

Prolonged QT syndrome: Pathophysiology

Answer 4

• In congenital LQTS, a number of identified genetic mutations cause the alteration of a specific ion channel current, leading to the pathophysiological prolongation of repolarisation, which equates to QT interval prolongation on the ECG
• there are specifics explanations about LQTS 1, 2 and 3 but I think it’s too much detail so look on BMJ best practise to get more info

Question 5

Prolonged QT syndrome: Cinical manifestations: key presentations, other symptoms and signs

Answer 5

• The diagnosis of LQTS is not straightforward, as nearly 2.5% of the normal population may have a mildly prolonged QT interval, and nearly 25% of patients genotypically positive for LQTS may have normal-appearing QT intervals
• LQTS commonly presents in young people with cardiac arrest or unexplained syncope and is frequently misdiagnosed as epilepsy
• As mentioned, 2.5% of the population have LQTS so I assume it’s often asymptomatic - I can’t find much info on it
• May present with/ key diagnostic factors
  
  • syncope during heightened adrenergic tone
  • syncope during arousal or surprise
  • Clinical deafness
  • hx of known gene mutation
  • use of drugs or circumstances known to increase the QT interval

Question 6

Prolonged QT syndrome: Investigations (diagnosis): 1st line, gold standard & other

Answer 6

• Whilst the hallmark of LQTS is prolongation of the QT interval, the QT interval is highly variable among both those who are healthy and those who have LQTS.
• This leads to overlap between the QT intervals of those with and without LQTS and can make it hard to diagnose

ECG

• as it says on the tin - prolonged QT interval
  
  • see attatched image

Question 7

Prolonged QT syndrome: DDx

Answer 7

• Acquired structural heart disease
• Neurocardiogenic (vasovagal) syncope
• Neurological syncope

Question 8

Prolonged QT syndrome: Management

Answer 8

• The mainstay of treatment for LQTS, unless there is an identifiable reversible cause, is lifestyle modification and beta-blocker therapy
• with the implantation of a cardioverter-defibrillator (ICD) in patients who have had a previous cardiac arrest and in those continuing to have symptoms despite beta-blockade
• Lifestyle modification may include
  
  • Electrolyte losses due to vomiting, diarrhoea, or excessive sweating should be replaced with electrolyte solutions in order to avoid hypokalaemia and hypomagnesaemia.
  • Patients with LQT2 should avoid startling acoustic stimulation such as alarm clocks.
  • All patients must avoid other sympathomimetics and factors that may prolong the QT interval
  • Competitive sports or similar extreme exertion should be avoided