Defibrillation success with high frequency electric fields is related to degree and location of conduction block.
BACKGROUND
We recently demonstrated that high frequency alternating current (HFAC) electric fields can reversibly block propagation in the heart by inducing an oscillating, elevated transmembrane potential (Vm) that maintains myocytes in a refractory state for the field duration and can terminate arrhythmias, including ventricular fibrillation (VF).


OBJECTIVE
To quantify and characterize conduction block (CB) induced by HFAC fields and to determine whether the degree of CB can be used to predict defibrillation success.


METHODS
Optical mapping was performed in adult guinea pig hearts (n = 14), and simulations were performed in an anatomically accurate rabbit ventricular model. HFAC fields (50-500 Hz) were applied to the ventricles. A novel power spectrum metric of CB-the loss of spectral power in the 1-30 Hz range, termed loss of conduction power (LCP)-was assessed during the HFAC field and compared with defibrillation success and VF vulnerability.


RESULTS
LCP increased with field strength and decreased with frequency. Optical mapping experiments conducted on the epicardial surface showed that LCP and the size of CB regions were significantly correlated with VF initiation and termination. In simulations, subsurface myocardial LCP and CB sizes were more closely correlated with VF termination than surface values. Multilinear regression analysis of simulation results revealed that while CB on both the surface and the subsurface myocardium was predictive, subsurface myocardial CB was the better predictor of defibrillation success.


CONCLUSIONS
HFAC fields induce a field-dependent state of CB, and defibrillation success is related to the degree and location of the CB.
Department of Applied Science, College of William and Mary, Williamsburg, Virginia, USA.
Seth H
SH
Weinberg
Kelly C
KC
Chang
Renjun
R
Zhu
Harikrishna
H
Tandri
Ronald D
RD
Berger
Natalia A
NA
Trayanova
Leslie
L
Tung
D000818:Animals; D054537:Atrioventricular Block / Q000503:physiopathology / Q000628:therapy*; D003198:Computer Simulation; D004554:Electric Countershock / Q000379:methods*; D004562:Electrocardiography; D006168:Guinea Pigs; D006321:Heart / Q000503:physiopathology*; D066298:In Vitro Techniques; D011817:Rabbits; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy*; D056969:Voltage-Sensitive Dye Imaging / Q000379:methods*