Andersen-Tawil Syndrome (LQT7)
Details
Andersen-Tawil syndrome (ATS) is a rare autosomal dominant multisystem channelopathy caused by loss-of-function variants in KCNJ2, encoding the Kir2.1 inward rectifier potassium channel (IK1). It is classified as LQT7 within the long QT syndrome spectrum. The hallmark is a clinical triad of: (1) prominent U waves with or without QT prolongation, (2) bidirectional and/or polymorphic PVCs/VT, and (3) extra-cardiac features — dysmorphic features and periodic paralysis.
Key Facts
- Gene: KCNJ2 (Kir2.1 inward rectifier K⁺ channel); loss-of-function reduces IK1 → impaired terminal repolarization → prominent U waves and susceptibility to DAD-triggered VA. (sources/VA-SCD-ESC-2022)
- Extra-cardiac features: Dysmorphic features (low-set ears, hypertelorism, small mandible, fifth-digit clinodactyly, short stature) and periodic paralysis (hypo-, normo-, or hyperkalaemic). Not all three elements required for diagnosis. (sources/VA-SCD-ESC-2022)
- ECG pattern: Prolonged QU interval (often mistaken for long QT), prominent U waves, bidirectional VT (beat-to-beat 180° QRS axis alternation — resembling CPVT), and frequent polymorphic PVCs. (sources/VA-SCD-ESC-2022)
- Arrhythmia burden is often high but SCD is less common than in other LQTS subtypes; bidirectional VT in ATS is frequently well-tolerated. (sources/VA-SCD-ESC-2022)
- Diagnosis (Class IIa, ESC 2022): Consider ATS in patients without structural heart disease who present with ≥2 of: prominent U waves ± QT prolongation; bidirectional/polymorphic PVCs or VT; dysmorphic features; periodic paralysis; KCNJ2 pathogenic loss-of-function mutation.
- Genetic testing (Class I, ESC 2022): Recommended in all patients with suspected ATS.
- ILR (Class IIa): Consider implantable loop recorder in ATS with unexplained syncope.
Management (ESC 2022)
- ICD (Class I): After aborted cardiac arrest or haemodynamically not-tolerated sustained VT.
- ICD (Class IIb): May be considered in ATS with history of unexplained syncope or haemodynamically tolerated sustained VT.
- Pharmacotherapy (Class IIa): Beta-blockers and/or flecainide with or without acetazolamide to treat VA.
- Acetazolamide targets periodic paralysis by reducing hypokalaemic episodes; may also reduce arrhythmia burden by stabilizing serum potassium. (sources/VA-SCD-ESC-2022)
Contradictions / Open Questions
- ATS classified as LQT7 — mechanistic misclassification: ATS is categorized within the LQTS spectrum as LQT7, but the predominant ECG finding is QU prolongation (not true QT prolongation), the arrhythmia mechanism differs from IKr/IKs-related TdP, and SCD risk is substantially lower than in other LQTS subtypes. This classification creates clinical ambiguity — QT-prolonging drugs, contraindicated in LQTS, may be used in ATS without the same risk, yet the LQT7 label suggests otherwise. (sources/VA-SCD-ESC-2022)
- Bidirectional VT in ATS — high arrhythmia burden with paradoxically benign prognosis: ATS patients frequently have high-frequency bidirectional VT and PVCs, resembling CPVT on ECG. However, SCD is substantially less common than in CPVT, and the bidirectional VT in ATS is often hemodynamically well-tolerated. The ICD recommendation after aborted cardiac arrest (Class I) is appropriate, but the Class IIb recommendation for ICD in unexplained syncope reflects genuine uncertainty about the threshold for implantation given the relatively benign natural history in non-arrested ATS patients. (sources/VA-SCD-ESC-2022)
- QU vs. QT distinction — diagnostic pitfall: Prominent U waves in ATS are frequently misinterpreted as prolonged QT on standard ECG, creating risk of incorrect LQTS diagnosis and inappropriate use of QTc as the primary monitoring parameter. No guideline provides specific guidance on how to measure or interpret the QU interval in ATS for risk stratification. (sources/VA-SCD-ESC-2022)
Connections
- Related to entities/Long-QT-Syndrome
- Related to concepts/Bidirectional-Ventricular-Tachycardia
- Related to entities/CPVT
- Related to concepts/Sudden-Cardiac-Death
- Related to entities/KCNJ2