Cardiac action potential repolarization revisited: early repolarization shows all-or-none behaviour

Area of Science:

• Cardiology
• Electrophysiology
• Pharmacology

Background:

• The cardiac action potential (AP) waveform governs heart contractions.
• Action potential duration (APD) and its stability are vital biomarkers for cardiac electrophysiology.
• Current drug safety guidelines focus on late repolarization (APD, Q-T interval), but early repolarization is emerging as critical for arrhythmogenesis.

Purpose of the Study:

• To provide a mechanistic understanding of early repolarization syndrome.
• To highlight the significance of both early and late phases of the cardiac action potential in arrhythmogenesis.
• To explain how cell-to-cell interactions influence APD and drug responses.

Main Methods:

• Review of mechanistic evidence for early repolarization syndrome.
• Analysis of regenerative, all-or-none behavior in cardiac depolarization and repolarization.
• Consideration of factors influencing APD, including cell-to-cell current flow and drug effects.

Main Results:

• Both early and late phases of the cardiac AP exhibit distinct thresholds and regenerative properties.
• Early repolarization, alongside late repolarization, is an important biomarker for predicting arrhythmias.
• Single myocyte data may not fully capture ventricular repolarization dynamics due to complex cell interactions.

Conclusions:

• Early repolarization syndrome is mechanistically significant for cardiac arrhythmogenesis.
• APD stability and responsiveness to drugs are influenced by myocardial conduction and repolarization reserve.
• A comprehensive understanding of cardiac AP dynamics, including early repolarization, is essential for drug safety and arrhythmia prediction.