Cardiac repolarization wave dynamics and its role in arrhythmogenesis

Premature ventricular contractions (PVCs) are commonly associated with action potential duration (APD) prolongation through early afterdepolarizations (EADs) or repolarization failure (RF), yet the mechanisms linking spatial heterogeneity of repolarization to PVC initiation remain unclear. Previous studies have emphasized the role of repolarization gradients, but a unifying dynamical framework connecting repolarization wave (RW) propagation and PVC initiation is lacking. Here, we investigate PVC initiation in one-dimensional heterogeneous tissue using models of increasing biophysical complexity ranging from simplified two-variable to detailed ionic models. Across all models, we find that PVC initiation is governed by a dynamical competition at the interface between long- and short-APD regions. A PVC occurs when the short-APD region regains excitability before a retrograde RW succeeds to propagate into the long-APD region. The retrograde RW speed, therefore, provides a quantitative indicator of this competition and is determined by the stability of the high-voltage plateau fixed point associated with EADs or RF. Depending on this stability, retrograde RWs propagate as trigger waves when the fixed point is stable or as pushed or pulled fronts when unstable. A highly stable fixed point slows the RW, thereby promoting PVC initiation by allowing more time for the recovery of the short-APD region. For the two-variable models, we derive semi-analytical criteria predicting the conditions for PVC initiation. Finally, we show that the critical size of the prolonged APD region is comparable to the electrotonic coupling length under diffusive coupling and is significantly reduced by ephaptic coupling, which facilitates PVC initiation and arrhythmogenesis.