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.
Veronica L. Cox, BA, Mitul Patel, MD, Gowri Sivaraman, MBBS, Taylor Liu, MD, PhD and Sanjiv M. Narayan, MD, PhD. University of CA, San Diego, CA, University of California and VA Medical Centers, San Diego, CA
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.