Performance of the signal-averaged electrocardiogram: Relation to baseline QRS duration

Abstract

Analysis of the duration and terminal components of the filtered QRS complex on the signal-averaged electrocardiogram (ECG) has been widely used for the detection of late potentials. Although filtered QRS duration is strongly related to 12-lead QRS duration, the relation of performance of the signal-averaged ECG to baseline QRS duration has not been critically examined. To examine the relation of test performance of the signal-averaged ECG to 12-lead QRS duration and to test the hypothesis that the difference between filtered and baseline 12-lead QRS duration would reflect more accurately the presence of late potentials than would analysis of the filtered QRS alone, we evaluated signal-averaged and 12-lead ECGs in 144 normal subjects and in 132 patients who were examined by electrophysiologic study and of whom 45 had inducible sustained monomorphic ventricular tachycardia. The signal-averaged ECG was considered positive by standard late potential criteria when the filtered vector QRS duration was >114 msec and either the root-mean-square voltage of the terminal 40 msec of the filtered QRS was <20 μV or the low-amplitude signal of the terminal filtered QRS was >38 msec. A new signal-averaged ECG criterion for the presence of late potentials was developed in the 144 normal subjects on the basis of the difference between the longest filtered QRS duration in any of the orthogonal leads and QRS duration on the baseline 12-lead ECG (“the QRS difference”), which was adjusted by regression analysis for the decreasing QRS difference found with increasing baseline QRS duration. Among patients who underwent electrophysiologic study, performance of standard late potential criteria was highly dependent on underlying 12-lead QRS duration: when subgrouped according to a median QRS duration of 92 msec on the routine ECG, patients with longer QRS durations had significantly lower specificity (61% vs 96%; p = 0.0001) and higher sensitivity (71% vs 36%; p < 0.05) than did those with shorter QRS durations. The new regression-based QRS difference criteria had specificity (96% vs 92%; p not significant [NS]) equivalent to that of standard late potential criteria in the normal subjects, and when applied to the 132 patients who underwent electrophysiologic study, analysis of the QRS difference significantly improved specificity (89% vs 79%; p < 0.05) with no loss in sensitivity (58% vs 60%; p NS). In addition, performance of the regression-based QRS difference criteria was less dependent on 12-lead QRS duration than was performance of standard late potential criteria, with similar specificity (83% vs 93%; p NS) and a trend toward higher sensitivity (65% vs 43%; p NS) at QRS durations >92 msec. These data demonstrate that test performance of standard late potential criteria is highly dependent on baseline QRS duration, However, new signal-averaged ECG criteria that can be derived on the basis of the difference between standard and filtered QRS duration improve accuracy of the signal-averaged ECG, are less dependent on 12-lead QRS duration, and are independent of terminal QRS root-mean-square voltage and low-amplitude-signal magnitude measurements.