10th May 2025

Long QT Syndrome

Long QT syndrome (LQTS) is a disease of ventricular repolarization identified by the prolongation of the QT interval on ECG. Normal QT interval is <440 msec in male and <460 msec in female when corrected for heart rate of 60/min.

Diagnostic criteria

• Corrected QT interval (QTc) ≥ 480ms
• LQTS score >3 (See modified long QT syndrome diagnostic score)
• In the presence of cardiac arrest or syncope, a QTc ≥ 460 ms
• Pathogenic genetic mutation irrespective of QT interval

 Classification

• Congenital:
  • Autosomal recessive: Jervell and Lange-Nielsen syndrome (associated with deafness)
  • Autosomal dominant: Also known as Romano Ward Syndrome (has 3 main phenotypes: LQT1, LQT2 and LQT3)
• Acquired: Caused by drugs or electrolyte imbalance

Table 3: Acquired causes of LQTS

Clinical features

• Asymptomatic
• Sudden cardiac death
• Syncope
• Aborted ventricular arrhythmia including Torsades de pointes (Figure-2)
• Patients with LQT 1 are triggered by physical exercise, specially swimming
• Patients with LQT2 are triggered by noise
• Patients with LQT3 are triggered during sleep

ECG findings

Image Source: Wikimedia Commons (2020). ECG, Licensed under a creative commons licence. Available for free at:  https://commons.wikimedia.org/w/index.php?search=long+qt+ecg&title=Special:MediaSearch&go=Go&type=image (Accessed 7 May 2025).

Image Source: Wikimedia Commons (2010). Torsade ECG, Licensed under a creative commons licence.  Available for free at: https://commons.wikimedia.org/w/index.php?search=torsade+pointes+ecg&title=Special:MediaSearch&go=Go&type=image (Accessed 7 May 2025).

Management

• Torsades de pointes should be terminated by intravenous Magnesium sulfate. Alternatives are, overdrive pacing and intravenous isoprenaline. Although, isoprenaline should be avoided in congenital long QT syndrome.
• Avoidance of QT prolonging drugs, electrolyte imbalance and genotype specific triggers in all patients
• Asymptomatic congenital LQTS are advised to be treated with beta blockers
• Implantable cardioverted defibrillator (ICD) implantation should be considered in patients with previous cardiac arrest, syncope despite beta blockers and in asymptomatic cases with QTc >500 msec
• Left cardiac sympathetic denervation can be considered in patients who remain symptomatic.