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Gating-dependent mechanisms for flecainide action in SCN5A-linked arrhythmia syndromes
P C Viswanathan1, C R Bezzina, A L George
1Department of Anesthesiology, Vanderbilt University, Nashville, Tennessee, USA.
Circulation
|September 6, 2001
Summary
Cardiac sodium channel (SCN5A) mutations cause LQT3 and Brugada syndromes. Inactivation gating defects in these mutations increase sensitivity to flecainide, potentially causing dangerous arrhythmias.
Area of Science:
- Cardiovascular genetics
- Molecular cardiology
- Electrophysiology
Background:
- Mutations in the cardiac sodium channel gene (SCN5A) are linked to LQT3 and Brugada syndromes.
- Antiarrhythmic drugs targeting sodium channels can have opposing effects on these conditions.
- Flecainide, a sodium channel blocker, can paradoxically worsen Brugada syndrome and induce similar effects in LQT3 patients.
Purpose of the Study:
- To investigate how SCN5A inactivation gating defects in LQT3 and Brugada syndromes contribute to proarrhythmic sensitivity to flecainide.
- To elucidate the mechanistic basis for flecainide-induced arrhythmias in these genetic heart conditions.
Main Methods:
- Whole-cell sodium current (I(Na)) was measured in tsA-201 cells expressing LQT3 (DeltaKPQ) and combined LQT3/Brugada (1795insD) mutations.
- The effect of flecainide (1 micromol/L) on I(Na) and recovery from inactivation was assessed.
- Comparison of flecainide block and recovery kinetics between mutant and wild-type sodium channels.
Main Results:
- Both DeltaKPQ and 1795insD mutations altered inactivation gating, leading to potentiated tonic I(Na) block by flecainide.
- Flecainide caused significantly greater tonic block in 1795insD (58.0%) and DeltaKPQ (39.4%) channels compared to wild type (16.8%).
- The 1795insD mutation also delayed recovery from inactivation, indicating enhanced intermediate inactivation and use-dependent flecainide block.
Conclusions:
- Two specific inactivation gating defects (closed-state fast inactivation and intermediate inactivation) were identified as key factors in flecainide sensitivity for LQT3 and Brugada syndrome mutations.
- These findings provide a mechanistic rationale for predicting flecainide's proarrhythmic potential based on SCN5A mutation type.
- Identifying these SCN5A inactivation gating defects can aid in risk stratification and personalized treatment strategies for patients with these channelopathies.
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