A prospective evaluation of the immediate reproducibility of the signal-averaged ECG

The purpose of this investigation was to prospectively evaluate the immediate reproducibility of the signal-averaged electrocardiogram (SAECG). A total of 114 patients undergoing evaluation for ventricular arrhythmias were enrolled in this protocol. Two consecutive SAECG's (40 Hz bidirectional high-pass filtering with a computer-automated system) were performed 10 minutes apart. Abnormal SAECG parameters were defined as (1) vector QRS duration more than 120 msec, (2) terminal root mean square (RMS) voltage less than 20 μV, and (3) low-amplitude signal (LAS) duration more than 40 msec. An SAECG was defined as abnormal if at least one vector parameter was abnormal. There was close correlation between vector parameters during the two SAECG observations: QRS duration had the highest reproducibility (r2 = 0.97, p < 0.001) followed by terminal RMS voltage (r2 = 0.92, p < 0.001), and LAS duration (r2 = 0.90, p < 0.001). The mean (± SD) percentage of change between the two recordings was 2% ± 2% of the ORS duration, 13% ± 22% for terminal RMS voltage, and 7% ± 11% for LAS duration. The reproducibility of an initially normal SAECG was 92% and of an initially abnormal SAECG, 96%. Seventeen patients (15%) had a change in one of the three vector parameters between the two recordings. There were no clinically significant differences between the 17 patients in whom the SAECG was nonreproducible and the 97 patients in whom the SAECG was reproducible. However, reproducibility was significantly higher in patients with an initially normal versus an initially abnormal SAECG (92% vs 76%, p = 0.03). In conclusion, the reproducibility of an initially normal or abnormal SAECG was high. ORS duration had the highest reproducibility, but terminal RMS voltage and LAS duration showed mean percentage changes of 13% and 7%, respectively. Patients with an initially abnormal SAECG had frequent variability of one SAECG parameter. This variability should be considered when changes in the absolute values of these measurements or parameter changes are examined in natural history studies or trials examining the effects of therapeutic modalities on the SAECG.