Makindo Medical Notes

Related Subjects: |ECG-QT interval |Brugada Syndrome |Long QT syndrome (LQTS) Acquired |Long QT syndrome (LQTS) Congenital |Torsade de Pointes |Ventricular Fibrillation |Ventricular Tachycardia |Resuscitation - Adult Tachycardia Algorithm |Automatic Implantable Cardioverter Defibrillator (AICD)

⚠️ Always consider Long QT Syndrome in any patient with polymorphic ventricular tachycardia (VT) or unexplained syncope. Drug- and electrolyte-induced causes are common. QTc >440 ms is abnormal, and risk of arrhythmia is highest once QTc exceeds 500 ms.

📌 About

• LQTS is a cardiac condition that prolongs ventricular repolarisation, increasing the risk of Torsades de Pointes (TdP), VF, and sudden death.
• Over 50 medications are known to prolong QT; see QTDrugs.org for up-to-date lists.
• Can be congenital (channelopathy) or acquired (drug/electrolyte-related).

⚡ Torsades de Pointes

🧬 Aetiology

• QT interval reflects ventricular repolarisation. Prolongation provides a substrate for re-entrant arrhythmias.
• Often due to drug effects, electrolyte imbalance, or underlying cardiac disease.
• HERG potassium channel inhibition is a common mechanism for drug-induced cases.

💊 Causes

• Medications: Antiarrhythmics (sotalol, amiodarone), macrolides, fluoroquinolones, antipsychotics (haloperidol, ziprasidone), tricyclic antidepressants, cisapride, chloroquine.
• Electrolyte imbalance: Hypokalaemia, hypomagnesaemia, hypocalcaemia.
• Bradycardia: Especially in the presence of QT-prolonging drugs.
• Structural disease: MI, heart failure, myocarditis, HCM, RV dysplasia.
• Other risks: Starvation, hypothermia, methadone, severe systemic illness.

📈 ECG Appearance

• QTc >450 ms in men, >460 ms in women = prolonged.
• QTc >500 ms = high risk of TdP and sudden death.

👩‍⚕️ Clinical Presentation

• Often more common in women.
• Can present with syncope, seizures, palpitations, cardiac arrest, or sudden death.
• May be precipitated by exertion, rest, or emotional stress.
• Family history of sudden cardiac death (SCD) is a red flag.

🧪 Investigations

• ECG: Prolonged QTc (repeat if borderline).
• Bloods: U&E, Ca²⁺, Mg²⁺ to correct reversible causes.
• Consider arrhythmia monitoring if symptomatic.

🩺 Management

• Torsades de Pointes: Immediate IV magnesium sulfate 2 g (even if Mg²⁺ normal); repeat infusion if needed.
• Stop QT-prolonging drugs and correct electrolytes (esp. K⁺ & Mg²⁺).
• Potassium supplementation: May shorten QT interval, esp. in hypokalaemia or LQT2.
• Bradycardia-related TdP: Consider overdrive pacing or isoprenaline to prevent long RR pauses.
• Defibrillation: If unstable VT/VF occurs.
• Monitoring: QTc ≥500 ms requires admission and cardiology input.

📚 References

• NHS: Acquired Drug-Induced Long QT Syndrome
• Mechanisms, Risk Factors & Management of Acquired LQTS