Ambulatory ECG Methods Amplify
T-Wave Alternans Compared to Traditional Spectral Analysis
Category: 09 Signal Average ECG/T-Wave
Alternans
Presentation Time: Friday, 3:30 p.m. - 4:30 p.m.
Presentation Number: P5-29
Keyword: T-wave alternans, Ambulatory monitoring
Background: T-wave alternans (TWA) is a promising
risk-stratifier for sudden death, yet the spectral method for its detection
uses specialized equipment for non-continuous testing. Modified moving average
(MMA) analysis has recently become available to detect TWA from ambulatory
ECGs. However, the clinical utility of MMA-TWA is unclear relative to
spectral-TWA.
Methods and Results: We compared MMA and traditional spectral analyses
of TWA in 43 patients (age 69+11 years), with coronary disease and LVEF
32+9 % referred to EPS for risk stratification. TWA was calculated
during pacing at 550 ms (109 beats/min). MMA-TWA, calculated as a weighted
rolling-mean, was detectable in more patients than spectral TWA (97 % versus 36
%, p<0.001) due to its method of computation and its resilience to ectopic
beats and ECG noise. Moreover, MMA amplified TWA magnitude roughly 3-fold
versus spectral TWA in X- (13.4+ 10.0 vs 4.3+7.5 mcV; p=0.004),
Y- (15.6+7.5 mcV vs 4.4 + 5.9 mcV; p<0.00001) and Z-
(18.0+12.9 mcV vs 7.5+12.4 mcV; p=0.015) ECG axes. Linear plots
confirmed TWA amplification by MMA versus spectral analysis in X- (r=0.50;
p<0.05), Y- (r=0.63; p<0.005), and Z- (r=0.72; p<0.001) ECG axes. On
534+284 days’ follow-up, 15 patients suffered ‘events’ (4 died, 11 had
sustained ventricular arrhythmias). Receiver operating characteristics for
MMA-TWA gave an area under the curve of 0.545, lower than for spectral TWA (ROC
area 0.6630). As a result, spectral TWA predicted events on Kaplan-Meier
analysis (p=0.05), while MMA-TWA did not.
Conclusions. Computing TWA using MMA amplifies TWA magnitude and is
resistant to noise compared to spectral analyses, but cannot be used with
existing TWA diagnostic criteria. Further studies should define how best to
apply MMA to ambulatory ECGs for continuous measurements of TWA.