[Evaluation of late potential by using--event-related signal-averaging technique]

Event-related (ER) signal-averaging technique was used to evaluate whether beat-to-beat changes of filtered QRS complex possibly relate to the appearance of ventricular arrhythmias (VA) or not. 82 patients with premature ventricular contractions (PVC) were studied. ANALYSIS-I:56 pts (16 with VT): a conventional method, in which all sinus beats were averaged (ALL), was compared with the new ER methods, in which only sinus beats immediately before (B) or after (A) each PVC can be separately averaged. ANALYSIS-II: 26 pts (10 with VT): five modes of ER averaging, 2nd preceding (2-B), just preceding (1-B), immediately after (1-A), 2 beat after (2-A), and isolated (ISO) from each PVC, were compared.

I: Significantly longer F-QRS and smaller RMS40 than ALL were observed at B both in VT+ and VT- pts. These transient changes tended to remain even at A only in VT+ not in VT+ pts.II: No significant changes compared with ISO were seen at 2-B and 2-A at all. The widening of F-QRS and the decrease of RMS40 occurred only at 1-B in VT- and unti 1-A in VT+ pts. In conclusion, pre- and post- extra-systolic changes of filtered QRS complex were very transient and event-related, suggesting the close relationship to the mechanism of VA.