Long QT (including) syndrome
- a genetic syndrome of many different gene mutations with resultant K+ (60% cases) or Na+ channel dysfunction
- QT>450ms, QTc>440ms in men & QTc>460ms in women
- life-threatening cardiac arrhythmia syndrome and leading cause of sudden death in young people. Without treatment ~20% mortality in 1st year of 1st syncope
- prolonged ventricular repolarisation predisposes to malignant tachyarrhythmia - especially Torsade's de Pointes
Often stimulated by:
- stress and activities with increased sympathetic activity.
- variety of drugs including amiodarone, TCA's, antibiotics, opioids and antipsychotic agents
- Metabolic derangement including low K+, Ca++, Mg++
- hypothermia
NOT just an ECG diagnosis - requires supporting Hx
- History of syncope especially exercise induced, cardiac arrest, FHx of long QT
- 3 main types recognised on ECG:
- LQTI - broad T waves
- LQT2 - notched or bifid T in V2,3 and inferior leads
- LQT3 - long isoelectric ST with normal T wave
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Management
- β blockers
- treat metabolic abnormalities
- avoidance of increased sympathetic tone (stressful exercise)
- avoidance of hypokalaemia
- review of medications to avoid enhanced risk
- pacing, ICD
- there is some interest in what has become known as QT dispersion, defined as the difference between the max & min QT interval on a 12 lead ECG
- some suggestion that there is a link between increased QT dispersion and death from a cardiac cause
- a variation of >50ms or probably >80ms is seen to be more predictive
References include
https://www.thecardiologyadvisor.com/home/decision-support-in-medicine/cardiology/long-qt-syndromes-and-torsade-de-pointes/
https://litfl.com/long-qt-syndrome/
Circulation - arrhythmia and electrophysiology: Long QT syndrome
BMJ: QT dispersion article