Fx. Witkowski et al., SIGNIFICANCE OF INWARDLY DIRECTED TRANSMEMBRANE CURRENT IN DETERMINATION OF LOCAL MYOCARDIAL ELECTRICAL ACTIVATION DURING VENTRICULAR-FIBRILLATION, Circulation research, 74(3), 1994, pp. 507-524
Ventricular fibrillation (VF) is the principal cardiac rhythm disorder
responsible for sudden cardiac death in humans. The accurate determin
ation of local cardiac activation during VF is essential for its mecha
nistic elucidation. This has been hampered by the rapidly changing and
markedly heterogeneous electrophysiological nature of VF. These diffi
culties are manifested when attempting to differentiate true propagati
ng electrical activity from electrotonic signals and when identifying
local activation from complex and possibly fractionated electrograms.
The purpose of this investigation was to test the hypothesis that the
presence of a balanced inwardly and outwardly directed transmembrane c
harge, obtained from the ratio of the inward to outward area under the
cardiac transmembrane current curve (-/+ I-m area), could reliably di
fferentiate propagating from electrotonic deflections during VF. To te
st this hypothesis, we applied a recently described technique for the
in vivo estimation of the transmembrane current (I-m) during cardiac a
ctivation. A 17-element orthogonal epicardial electrode array was comb
ined with an immediately adjacent optical fiber array to record electr
ical and optically coupled transmembrane potential signals during VF.
Recordings were obtained during electrically induced VF in six dogs to
determine the I-m associated with activation and the time course of r
epolarization, as well as unipolar electrograms and bipolar electrogra
ms recorded at multiple center-to-center interelectrode distances from
0.2 to 3 mm. Propagat ing local activations were associated with the
presence of an easily identified inwardly directed I-m with a balanced
inward and outward charge (-/+ I-m area approximate to 1.0). Electrot
onic waveforms lacked this inward I-m (-/+ I-m area approximate to 0.0
). Normal Na+-mediated inward currents were directly demonstrated to b
e responsible for some activations during VF. (Circ Res. 1994;74:507-5
24.)