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Cellular mechanisms underlying the long QT syndrome
Charles Antzelevitch1, Wataru Shimizu
1Masonic Medical Research Laboratory, Utica, New York, USA; National Cardiovascular Center, Osaka, Japan. ca@mmrl.edu
Current Opinion in Cardiology
|January 16, 2002
Summary
Dispersion of repolarization, not just QT prolongation, is key to life-threatening torsades de pointes arrhythmias. Understanding this electrical heterogeneity is crucial for preventing cardiac events.
Area of Science:
- Cardiology
- Electrophysiology
- Molecular Biology
Background:
- QT prolongation is linked to dangerous torsades de pointes (TdP) arrhythmias.
- Ventricular myocardium electrical heterogeneities arise from differing cell repolarization.
- These heterogeneities cause transmural voltage gradients and repolarization dispersion, affecting the ECG T wave.
Purpose of the Study:
- To investigate the relationship between QT interval prolongation, repolarization dispersion, and TdP.
- To determine the primary cause of TdP in long QT syndrome.
Main Methods:
- Analysis of factors influencing ventricular myocardial repolarization.
- Examination of the role of spatial dispersion of repolarization in arrhythmia development.
- Distinguishing between QT prolongation alone and QT prolongation with increased dispersion.
Main Results:
- Agents reducing net repolarizing current amplify spatial repolarization dispersion.
- This amplified dispersion creates a substrate for re-entry, leading to TdP.
- Early afterdepolarizations in M cells and Purkinje fibers may trigger TdP.
Conclusions:
- Torsades de pointes is primarily caused by increased dispersion of repolarization, not solely by QT interval prolongation.
- Agents that prolong QT without increasing transmural dispersion do not induce TdP.
- The critical issue in long QT syndrome is the dispersion of repolarization accompanying QT prolongation.