His bundle activates faster than ventricular myocardium during prolonged ventricular fibrillation.

Nathan Angel,Li Li,Derek J Dosdall,Alena Talkachova

doi:10.1371/journal.pone.0101666

Abstract

BackgroundThe Purkinje fiber system has recently been implicated as an important driver of the rapid activation rate during long duration ventricular fibrillation (VF>2 minutes). The goal of this study is to determine whether this activity propagates to or occurs in the proximal specialized conduction system during VF as well.Methods and ResultsAn 8×8 array with 300 µm spaced electrodes was placed over the His bundles of isolated, perfused rabbit hearts (n = 12). Ventricular myocardial (VM) and His activations were differentiated by calculating Laplacian recordings from unipolar signals. Activation rates of the VM and His bundle were compared and the His bundle conduction velocity was measured during perfused VF followed by 8 minutes of unperfused VF. During perfused VF the average VM activation rate of 11.04 activations/sec was significantly higher than the His bundle activation rate of 6.88 activations/sec (p<0.05). However from 3–8 minutes of unperfused VF the His system activation rate (6.16, 5.53, 5.14, 5.22, 6.00, and 4.62 activations/sec significantly faster than the rate of the VM (4.67, 3.63, 2.94, 2.24, 3.45, and 2.31 activations/sec) (p<0.05). The conduction velocity of the His system immediately decreased to 94% of the sinus rate during perfused VF then gradually decreased to 67% of sinus rhythm conduction at 8 minutes of unperfused VF.ConclusionDuring prolonged VF the activation rate of the His bundle is faster than that of the VM. This suggests that the proximal conduction system, like the distal Purkinje system, may be an important driver during long duration VF and may be a target for interventional therapy.

Highlights

Sudden cardiac death due to ventricular fibrillation (VF) is one of the leading causes of death in the developed world[1]
During prolonged VF the activation rate of the His bundle is faster than that of the ventricular myocardium (VM). This suggests that the proximal conduction system, like the distal Purkinje system, may be an important driver during long duration VF and may be a target for interventional therapy
Hearts in which unperfused VF persisted less than 2 minutes were excluded from the analysis (n = 2)

Summary

Introduction

Sudden cardiac death due to ventricular fibrillation (VF) is one of the leading causes of death in the developed world[1]. Implantable cardiac defibrillators (ICD’s) have greatly reduced mortality due to VF, likely due to defibrillation shocks being applied to the myocardium soon after the onset of VF[3]. This treatment is only available for those that have been clinically diagnosed as high risk for VF. Successful resuscitation rate is thought to decrease during prolonged VF because of electrophysiological changes to cardiac tissue under ischemic conditions[6] These electrophysiological changes may cause permanent cardiac damage[7] and can result in failure to defibrillate successfully[8]. The goal of this study is to determine whether this activity propagates to or occurs in the proximal specialized conduction system during VF as well

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Discussion

Conclusion