Copyright © 1996 by the European Society of Cardiology.
© 1996 The European Society of Cardiology
Noise in the signal-averaged electrocardiogram and accuracy for identification of patients with sustained monomorphic ventricular tachycardia after myocardial infarction
Department of cardiology, Skejby Sygehus, University Hospital Aarhus, Denmark
Received 18 September 1995; accepted 25 October 1995.
Correspondence: Evald Høj Christiansen, Department of Cardiology, Skejby Sygehus, University Hospital, KD-8200 Aarhus N, Denmark
Abstract
Late potentials are detected at various noise levels in clinical studies. The aim of this study was, in a case-control design, to assess the effect of residual noise level on the identification of patients with sustained monomorphic ventncular tachycardia after myocardial infarction. Electrocardiograms from 16 patients with prior myocardial infarction and documented sustained monomorphic ventricular tachycardia and 41 patients with prior myocardial infarction and without ventncular tachycardia, were analysed by two signal averaging procedures to noise level 0·2 and 0·4 µV Standard time domain parameters were measured. Two definitions of late potential were analysed: (1) if any two of the following criteria were present (signal-averaged QRS duration >120 ms, late potential duration >40 ms, and root-mean-square voltage of the terminal 40 ms of the filtered QRS <25µV); or (2) if the signal-averaged QRS duration
120 ms. Overall the signal-averaged electrocardiogram performed better at noise level 0·4µV compared to noise level 0·2µV with respect to identification of patients with or without ventricular tachycardia after myocordial infarction. Reducing noise level from 0·4 to 0·2 µV increased the sensitivity, but the consequence was a substantial decrease in specificity. Our data indicate that when a high sensitivity is the goal, the definition based only on signal-averaged QRS duration
120 ms should be applied; sensitivity was 88% and specificity 59% at noise level 0·4 µV. If a high specificity is the goal, the definition should be based on the definition with two abnormal parameters; sensitivity was 69% and specificity 68% at noise level 0·4µV.
Key Words: Signal averaging late potentials ventricular tachyarrhythmia noise reduction electrocardiography