Refractory gradient is responsible for the increase in ventricular vulnerability under sodium channel blockade

Area of Science:

• Cardiovascular Electrophysiology
• Computational Cardiology
• Arrhythmia Mechanisms

Background:

• Sodium channel (I(Na)) blockade is known to increase ventricular vulnerability.
• Variations in the degree of increased vulnerability suggest underlying mechanisms.
• Preshock refractory gradients (RG) influence the vulnerable window (VW).

Purpose of the Study:

• To investigate if differences in arrhythmogenesis caused by I(Na) blockade are due to varying preshock refractory gradients (RG).

Main Methods:

• Simulations were performed on 2D bidomain myocardial sheets under I(Na) blockade.
• Three types of preshock RG were used: longitudinally tilted (LRG), transversely tilted (TRG), and non-tilted (NRG).
• Conduction velocity and action potential duration were analyzed in response to I(Na) blockade and RG type.

Main Results:

• Increased I(Na) blockade linearly decreased conduction velocity.
• Action potential duration was non-linearly shortened in LRG and TRG, but slightly prolonged in NRG.
• The vulnerable window (VW) for reentry induction widened with I(Na) blockade in LRG and TRG, but narrowed in NRG.

Conclusions:

• The type of preshock refractory gradient (RG) significantly alters ventricular vulnerability during I(Na) blockade.
• This highlights the importance of RG in understanding I(Na) blockade-induced arrhythmogenesis.
• Findings suggest RG is a critical factor in predicting the arrhythmic risk associated with I(Na) channel modulation.