Elimination of Purkinje Fibers by Electroporation Reduces Ventricular Fibrillation Vulnerability

Abstract

Background The Purkinje network appears to play a pivotal role in the triggering as well as maintenance of ventricular fibrillation. Irreversible electroporation ( IRE ) using direct current has shown promise as a nonthermal ablation modality in the heart, but its ability to target and ablate the Purkinje tissue is undefined. Our aim was to investigate the potential for selective ablation of Purkinje/fascicular fibers using IRE . Methods and Results In an ex vivo Langendorff model of canine heart (n=8), direct current was delivered in a unipolar manner at various dosages from 750 to 2500 V, in 10 pulses with a 90-μs duration at a frequency of 1 Hz. The window of ventricular fibrillation vulnerability was assessed before and after delivery of electroporation energy using a shock on T-wave method. IRE consistently eradicated all Purkinje potentials at voltages between 750 and 2500 V (minimum field strength of 250-833 V/cm). The ventricular electrogram amplitude was only minimally reduced by ablation: 0.6±2.3 mV ( P=0.03). In 4 hearts after IRE delivery, ventricular fibrillation could not be reinduced. At baseline, the lower limit of vulnerability to ventricular fibrillation was 1.8±0.4 J, and the upper limit of vulnerability was 19.5±3.0 J. The window of vulnerability was 17.8±2.9 J. Delivery of electroporation energy significantly reduced the window of vulnerability to 5.7±2.9 J ( P=0.0003), with a postablation lower limit of vulnerability=7.3±2.63 J, and the upper limit of vulnerability=18.8±5.2 J. Conclusions Our study highlights that Purkinje tissue can be ablated with IRE without any evidence of underlying myocardial damage.

Keywords: Purkinje fibers; ablation; direct current ablation; irreversible electroporation; ventricular fibrillation; window of vulnerability.

Figure 1

Endoscopic view of the left ventricular endocardium, demonstrating both the mapping catheter and ablation catheter separated by at least 10 to 25 mm.

Figure 2

Representative electroanatomical map before (A) and after (B) electroporation. The fascicular/Purkinje signal is well seen before direct current delivery of 1000 V and electroporation (yellow arrow). The electroanatomical map showed that the mapping catheter has not moved. Yet, the fascicular signal is no longer present (blue arrow). Furthermore, the electrogram amplitude is essentially unchanged.

Figure 3

Vulnerability to ventricular fibrillation. A, Limits of vulnerability showing both the upper and lower limits. B, Window of vulnerability.