abstract
presented
at the 1997 NASPE
New Orleans, Louisiana
May 7-10, 1997
Mechanism of Initiation
of Ventricular Fibrillation During T Wave Alternans
PACE 1997;20:II-584
Joseph M. Pastore, Steven D. Girouard, David S. Rosenbaum,
Case Western Reserve University, Cleveland, OH
Although T wave alternans (TWA) of the surface
ECG has been closely associated with vulnerability to ventricular
arrhythmias, an explanation for this relationship is unknown. To determine
if TWA plays a role in the initiation of ventricular fibrillation
(VF), TWA was induced by steady-state pacing in 4 Langendorff
perfused (27°C) guinea pig hearts. Action potentials were recorded
simultaneously from 128 left ventricular sites (1 cm2 area)
using high resolution optical mapping with the voltage-sensitive dye di-4-ANEPPS
(15 µM). Above a threshold heart rate (213±51 bpm), alternations
of the plateau and late repolarization of the action potential were elicited
from all ventricular recording sites such that action potential duration
(APD) oscillated from beat to beat with identical phase at each
recording site (i.e. concordant alternans). However, at faster heart rates
(> 300 bpm), APDs prolonged in some regions while shortening
in others during the same beat (i.e. discordant alternans). Discordant
alternans produced a marked increase in the spatial dispersion of repolarization
(DOR) as measured form the variance of repolarization times across
the ventricle (Figure).
The DOR was characterized by large gradients of
repolarization whose orientation changed by 180° on consecutive beats.
This, in turn, caused regional conduction slowing (14±7 cm/s @ 315
bpm) compared to control (36±16 cm/s @120 bpm) into areas of delayed
repolarization. Moreover, during discordant alternans, a small (3 bpm)
increase in heart rate produced conduction block into areas of delayed
repolarization, followed by reentry and VF.
Conclusions: Discordant alternans causes increased
spatial inhomogeneity of repolarization which leads to conduction block,
reentry, and VF. These data suggest that there is indeed a mechanistic
relationship between TWA and initiation of VF.
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