Why Ablation of Sites With Purkinje Activation Is Antiarrhythmic: The Interplay Between Fast Activation and Arrhythmogenesis

Abstract

Ablation of sites showing Purkinje activity is antiarrhythmic in some patients with idiopathic ventricular fibrillation (iVF). The mechanism for the therapeutic success of ablation is not fully understood. We propose that deeper penetrance of the Purkinje network allows faster activation of the ventricles and is proarrhythmic in the presence of steep repolarization gradients. Reduction of Purkinje penetrance, or its indirect reducing effect on apparent propagation velocity may be a therapeutic target in patients with iVF.

Keywords: Purkinje; ablation; arrhythmias; early repolarization syndrome; electrophysiology; idiopathic ventricular fibrillation.

Figure 1

Computer simulations show that penetration of Purkinje fibers into the ventricular wall results in QRS slurring and short QRS50. (A) Torso model used for simulation. (B) The traces show simulated electrocardiograms (Lead II and III) with Purkinje fibers penetrating 2 mm (black) and 5 mm (red) into the ventricular wall. The dashed lines refer to the QRS duration at 50, 90, and 100% at 5 mm penetrance into the ventricular wall. Note that these moments of QRS50, QRS90, and QRS100 slightly differ at 2 mm penetrance because of different QRS amplitudes.

Figure 2

Purkinje-muscle junctions (PMJs) close to repolarization gradients may cause reentrant arrhythmias. (A) The graph shows time (vertical axis) and myocardial distances (horizontal axis). The blue line represents the repolarization time along the myocardial axis of beat 1 (supposedly a sinus activation). The orange and black lines show activation time along the myocardial axis of beat 2 (a ventricular premature activation). The orange line represents conduction through working myocardium and the black line through Purkinje fibers. If the PMJ activates the working myocardium far from the repolarization gradient (location A) the activation front propagates at low speed toward repolarization gradient, which will have disappeared when the activation front arrives (location C). If the PMJ activates the working myocardium close to the repolarization front (location B), the activation front meets still depolarized myocardium and conduction will block (location D) setting the stage for re-entry. Inset: A slowly conducting premature activation front (blue) arrives late at the site of prolonged repolarization causing activation whereas a fast conducting activation front (red) results in unidirectional block and re-entry. PMJ, Purkinje-muscle junction. (B) In the normal human heart, the Purkinje system is located at the endocardial side of the ventricular myocardium (left panel). If the Purkinje system penetrates into the transmural wall of the ventricle, the change is higher the working myocardium is activated close to depolarized myocardium (blue) and conduction block occurs.