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Presentation Time:
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11/10/2004 11:00:00 AM
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Title:
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Upsurge in T-wave Alternans and Complex-Form Repolarization
Instability Precedes the Onset of Spontaneous Ventricular Tachyarrhythmias
in Humans
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Keywords:
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Arrhythmias,Ambulatory ECG,Ventricular arrhythmia,Ventricular action
potential,Electrocardiography
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Author Block:
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Vladimir Shusterman, Anna Goldberg, Univ of Pittsburgh, Pittsburgh,
PA
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Disclosure Block:
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V. Shusterman, None; A. Goldberg, None.
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Unlabeled/unapproved:
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There are no unlabeled/unapproved uses of drugs or products
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Analysis of T-wave alternans (TWA) has proved useful for arrhythmia
risk assessment. However, lack of information regarding temporal relations
between TWA and initiation of ventricular tachyarrhythmias (VTA) in humans
hampers the development of dynamic risk management and prevention of
arrhythmias. We hypothesized that repolarization instability increases
before VTA and examined continuous repolarization dynamics during 6hrs
before the onset of spontaneous sustained (>30s) VTA in Holter ECGs
(24pts, age:66±10y, all had structural heart disease, 88% ischemic, EF:30±19%).
Signals were digitized at 400Hz/2.5μV resolution, and TWA was examined using the Modified Moving Average
(MMA) and Intra-beat Average (IBA) analyses. Changes in EarlyTWA
(Tonset-Tpeak) and LateTWA (Tpeak-Tend) were compared. To examine complex-form
(longer-period) repolarization dynamics, spectral energy (SpectrEn, range:
.15-.4cycles/beat) of the mean amplitude of the T-wave was calculated for
all successive 5min intervals using the short-time Fourier transform. Heart
rate variability (HRV) was assessed using the Fourier transform. Results.
TWA increased 30min before VTA (p=.04 for MMA and IBA). The increase in
EarlyTWA (24%, p=.03) was greater than that in LateTWA (15%, p=.6). SpectrEn
increased two-fold (p=.001). In contrast, the low (0.04-0.15Hz) and
high-frequency (0.15-0.4Hz) HRV decreased (p=.022). Conclusions. 1)
TWA increased before the onset of VTA, predominantly in the early
portion of the T-wave. 2) An increase in the spectral energy of the T-wave
oscillations in the setting of a decreased HRV suggests an upsurge of
non-autonomic, complex repolarization instabilities. 
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