Role of Purkinje Fibers in the Maintenance of Ventricular Fibrillation

Abstract

any experimental and clinical studies on the mechanisms of ventricular fibrillation (VF) have been performed over the past 10 decades. The underlying mechanisms of VF have been discussed from different points of view: initiation and maintenance. It is beyond question that reentry, triggered activity or automaticity initiates VF, but the mechanism of its maintenance is not fully determined. Although the duration from the onset of VF may affect its electrophysiological features, maintenance of VF has been explained by the coexistence of 2 or more unstable multiple wavelets or mother rotors. 1 Article p 1803In recent studies, however, attention has been directed to the role of Purkinje fibers in the initiation and maintenance of VF. 2-6 The Purkinje fiber system, which plays a critical role in harmonious myocardial contraction and relaxation via its efficient propagation properties and unique geometrical distribution, 7 is naturally worthy of note when discussing a possible source of VF. Because of the conspicuous heterogeneity in the action potential duration of Purkinje fibers compared with the working myocardium, it is likely that this system offers a substrate for reentry to sustain VF.The VF threshold (VFT), expressed by the amount of electrical stimulation to induce VF, has been used to quantify the susceptibility of the heart to VF. [8][9][10] Horowitz et al reported a significant difference between endocardial and epicardial VFTs in the left ventricle. 8 They considered that the coexistence of ordinary myocardium with shorter repolarization characteristics and Purkinje fibers with a long refractory period in the endocardium facilitated the induction of VF. Later, Damiano et al attempted to clarify the role of the Purkinje network on ventricular vulnerability. 9 In their study, the baseline VFT was 26±2 mA and increased to 53±6 mA after total ablation of the endocardial surface by applying Lugol's solution. This observation was in agreement with Horowitz's suggestion. In a more recent study using a 3-dimensional model of the ventricles, 2 the Purkinje system was shown to give rise to initial reentry, which led to the establishment of intramyocardial reentry independent of the Purkinje network.Purkinje fibers are known to be so resistant to ischemia that they survive and continue to function even during longlasting VF, 11 which may explain why VF terminates spontaneously in hearts with subendocardial chemical ablation, and suggests that Purkinje fibers play a significant role in the maintenance of VF. 5 Recently, Tabereaux et al investigated the activation pattern during VF. 3 They found that Purkinje fibers are highly active even 10 min after the onset of VF. In addition to retrograde propagation from the working ventricular myocardium to the Purkinje fibers, they noticed antegrade propagation also occurred from the Purkinje fibers to the working ventricular myocardium. This phenomenon supports the hypothesis that Purkinje fibers play an important role in the maintenance of VF, as well as in its initiation.I...