Long QT syndrome

Disorder of ventricular repolarization (congenital or acquired) causing a prolonged QT interval on ECG (usually QTc >450 ms) and risk of syncope or sudden death from torsades de pointes.

• A leading cause of sudden cardiac death in otherwise healthy young people (due to polymorphic VT/torsades). Early identification and treatment (beta-blockers, avoiding triggers) can be life-saving.

• Often discovered after syncope or seizure-like fainting episodes or even sudden cardiac arrest. Congenital LQTS typically presents in childhood/adolescence; acquired LQTS can occur at any age (e.g., hospital patient on multiple QT-prolonging meds).
• Congenital: recurrent syncope during exercise or high emotion (LQT1) or after sudden auditory stimuli (alarm clock, LQT2), or episodes during sleep/rest (LQT3). Family history of sudden death may be present. Jervell & Lange-Nielsen syndrome features congenital deafness in addition to long QT.
• Acquired: look for medication triggers (e.g., antiarrhythmics, macrolide or fluoroquinolone antibiotics, antipsychotics, antidepressants, antiemetics) especially in the setting of electrolyte disturbances (hypokalemia, hypomagnesemia). Patient may develop palpitations, syncope, or torsades de pointes (a transient polymorphic VT that can cause fainting or degeneration to VF).
• ECG: QT interval is prolonged (best measured in lead II or V5-6). A quick clue is if the QT is more than half of the RR interval. QTc (corrected QT) is used to account for heart rate (Bazett formula); >440 ms in men or >460 ms in women is prolonged, and >500 ms indicates high arrhythmia risk. T-wave morphology may be abnormal (notched or biphasic T waves) in congenital LQTS.

1. Measure the QT interval correctly: take the longest QT in lead II or V5-6 across several beats; include large, fused U-waves if present, and correct for heart rate (Bazett's formula). Check that QTc is truly prolonged (≥ ~450 ms).
2. Exclude secondary causes of QT prolongation: review the medication list (stop any offending QT-prolonging drugs) and correct electrolyte abnormalities (especially low K, Mg, Ca). Also check for hypothyroidism.
3. If no reversible cause is found and QT remains prolonged, evaluate for congenital LQTS. Use clinical criteria (e.g., Schwartz score ≥3.5 points supports diagnosis) and inquire about family history of sudden death. Genetic testing can confirm a pathogenic mutation (commonly KCNQ1, KCNH2, SCN5A genes) and help subtype, but is costly.
4. Screen first-degree relatives of a patient with confirmed congenital LQTS (ECG ± genetic testing) since Romano-Ward LQTS is autosomal dominant and Jervell-Lange-Nielsen is autosomal recessive. Family screening can identify asymptomatic carriers who may benefit from precautions or therapy.
5. Consider referral to electrophysiology/cardiology for risk stratification. High-risk features (QTc >500 ms, history of cardiac arrest, or syncope on therapy) warrant discussion of ICD placement in addition to medical therapy.

1. First-line for congenital LQTS: beta blockers (nonselective, e.g., propranolol or nadolol) to blunt adrenergic surges. Advise lifestyle modifications: avoid strenuous exercise or loud noise triggers (depending on LQT subtype), maintain adequate electrolytes, and strictly avoid drugs that prolong QT.
2. ICD (implantable cardioverter-defibrillator) is recommended in survivors of cardiac arrest and in those with high-risk features (e.g., syncope or ventricular arrhythmias despite beta-blockade, or very prolonged QT). In refractory cases, left stellate ganglion sympathectomy is a surgical option to reduce arrhythmic risk.
3. Acute torsades de pointes: initiate IV magnesium sulfate promptly (even if Mg level is normal). If unstable, perform immediate defibrillation. Also consider accelerating the heart rate (IV isoproterenol infusion or overdrive pacing) to suppress further torsades while correcting underlying causes.

• Mnemonic "ABCDE" for long QT–inducing drug classes: A: antiArrhythmics (class I & III), B: antiBiotics (macrolides, fluoroquinolones), C: antiPsychotics (e.g., haloperidol), D: antiDepressants (TCAs, SSRIs), E: antiEmetics (ondansetron).
• Romano-Ward syndrome is the autosomal dominant form of congenital LQTS (pure cardiac phenotype, no deafness). Jervell & Lange-Nielsen is the rare autosomal recessive form with sensorineural deafness.
• Normal QT rule of thumb: QT interval should be less than half of the RR interval. If it looks abnormally long (especially with T-wave abnormalities), think LQTS.

• Unexplained syncope (especially without prodrome) during exertion, emotional stress, or sudden noise → raises concern for LQTS (arrhythmic syncope). These events can be misdiagnosed as seizures; always evaluate with an ECG.
• Torsades de pointes (polymorphic VT with twisting QRS complexes) is a life-threatening emergency. Treat immediately with magnesium and cardioversion as needed, and remove/correct any precipitating factors (drugs, electrolyte disturbances) to prevent progression to ventricular fibrillation.

1. Suspected LQTS (young patient with syncope/seizure during stress, or incidental long QT on ECG) → obtain a 12-lead ECG and check QTc.
2. If QTc is prolonged, identify and address any acquired causes: stop offending drugs, correct electrolytes (K, Mg, Ca), and treat conditions like hypothyroidism.
3. If QT remains prolonged without secondary causes, diagnose congenital LQTS. Apply diagnostic criteria (QTc ≥480–500 ms, positive LQTS score, or a confirmed gene mutation) and refer to cardiology. Notify the patient's family to undergo screening ECG/genetic evaluation.
4. Start beta-blocker therapy for confirmed or strongly suspected congenital LQTS. Counsel on trigger avoidance (per subtype) and list of prohibited medications (from credible sources like CredibleMeds).
5. For high-risk patients (e.g., LQTS with prior arrest or persistent symptoms), implement advanced therapies: consider ICD placement in addition to beta-blockers, and/or left cardiac sympathetic denervation for refractory cases, in consultation with a specialist.

• Teen athlete who faints during swimming or exercise, with QTc >500 ms on ECG → congenital long QT syndrome (often LQT1 subtype).
• Young patient with congenital deafness and episodes of syncope → Jervell & Lange-Nielsen syndrome (AR long QT syndrome).
• Patient on a QT-prolonging drug (e.g., sotalol or haloperidol) with hypokalemia develops sudden syncope; ECG shows polymorphic VT (torsades) → acquired long QT syndrome leading to torsades de pointes.