Absence of Correlation between Microvolt T-Wave Alternans by Spectral Analysis and Newly Developed Ambulatory Electrocardiogram-Based T-Wave Alternans by Time-Domain Analysis
Presentation Start/End Time:	Thursday, May 10, 2007, 3:30 PM - 4:30 PM
Location:	Exhibit Hall
Author Block:	Katsura Sakaki, MD, Hideaki Yoshino, MD, Yosuke Miwa, MD, Mutsumi Miyakoshi, MD, Haruhisa Ishiguro, MD, Takehiro Tsukada, MD, Atsuko Abe, MD, Hisaaki Mera, MD, Kentaro Nakamura, MD, Satoru Yusu, MD and Takanori Ikeda, MD. Kyorin University, Tokyo, Japan
Introduction: Extensive clinical evidence supports the utility of microvolt T-wave alternans (M-TWA), which is measured by spectral analysis, as an index of risk for ventricular arrhythmias or sudden cardiac death. Recently, ambulatory electrocardiogram-based tracking of TWA (A-TWA), which is measured by time-domain analysis, has been used in clinical practice for risk stratification. We assessed correlation between M-TWA and A-TWA in high risk patients. Methods: This study included 68 consecutive patients who had serious cardiac disorders, ventricular tachyarrhythmic events, or unknown syncope. Patients with persistent atrial fibrillation and cardiac pacemakers were excluded from the study. M-TWA was assessed using FFT analysis during treadmill exercise at a level of 110-120 beats/min in leads X, Y, Z, and V1-V5. After M-TWA acquisition, A-TWA was assessed using the modified moving average method (i.e., a time-domain algorithm), which is based on 24-hour Holter electrocardiograms. This time-domain method had three time points for TWA determinations (8:00 a.m., maximum heart rate, and maximum ST-segment deviation) in leads CM5 and NASA. We compared magnitudes of TWA between both methods. Results: In M-TWA method, successful measurements were done in 50 patients (74%). The remaining 18 patients (26%) had an indeterminate test result and were excluded from analysis. A mean maximal TWA voltage in any orthogonal or precordial leads was 3.8 ± 5.5 μV. In A-TWA method, all patients had successful measurements for TWA. Although A-TWA had three parameters of A-TWA in two available leads, the maximal voltage among these parameters was chosen for analysis. A mean maximal TWA voltage was 41.5 ± 23.7 μV. There was no linear correlation between both methods (y = 42.1-0.16x, r=0.04). Conclusions: Although both TWA techniques are designed to detect temporal abnormalities of ventricular repolarization, no close correlation exists between the voltages acquired by both methods. The yield of both methods may be independently in risk stratification for arrhythmic death.