Makindo Medical Notes

Early therapy with implanted cardioverter/defibrillators (ICDs) must be considered in high-risk cases of congenital Long QT syndrome (LQTS). ⚡

📖 About

• Inherited cause of Long QT syndrome (LQTS).
• Particularly associated with the Jervell and Lange-Nielsen syndrome, which combines congenital deafness with prolonged QT interval.
• Inheritance is typically autosomal recessive for this severe form, while other LQTS variants can be autosomal dominant (Romano-Ward syndrome).

🧬 Aetiology

• Caused by mutations in the KCNQ1 and KCNE1 genes.
• These genes encode subunits of a potassium channel that helps repolarize cardiac cells after depolarization.
• Potassium ion movement is also important in the inner ear → explains the sensorineural deafness often associated.
• Defective ion channels → delayed repolarisation → prolonged QT interval → risk of arrhythmias.

🩺 Clinical Features

• May be asymptomatic until a trigger.
• Arrhythmias: Syncope, torsades de pointes, ventricular tachycardia.
• Triggers: Emotional stress, exercise (particularly swimming), or sudden fright.
• Sensorineural deafness: Seen in Jervell and Lange-Nielsen variant.
• Sudden cardiac death (SCD): Often first presentation in undiagnosed cases.

🔍 Differentials

• Other inherited arrhythmia syndromes (Brugada, catecholaminergic polymorphic VT).
• Drug-induced QT prolongation (antiarrhythmics, macrolides, fluoroquinolones, antipsychotics).
• Electrolyte disturbances (hypokalaemia, hypocalcaemia, hypomagnesaemia).

🧪 Investigations

• ECG: Prolonged QT interval, torsades de pointes episodes.
• Holter monitoring: Detects intermittent arrhythmias.
• Genetic testing: Confirms mutations in KCNQ1/KCNE1.
• Audiometry: Assesses associated congenital deafness.

💊 Management

• β-blockers: First-line (e.g., propranolol, nadolol), but limited efficacy in Jervell and Lange-Nielsen type.
• ICD (Implantable Cardioverter-Defibrillator): Recommended in high-risk patients or survivors of cardiac arrest.
• Lifestyle modification: Avoid QT-prolonging drugs, correct electrolytes, restrict strenuous exercise/swimming.
• Potassium supplementation: May help reduce arrhythmic risk in some patients.
• Family screening: ECG + genetic testing of relatives is essential.

📚 References

• ESC – Congenital Long QT Syndrome
• GeneReviews: Long QT Syndrome
• NHS – Long QT Syndrome