RESUMO
To test the hypothesis that late potentials may be more enhanced by signal processing of intracardiac and epicardial electrograms, we performed a comparative analysis of signal averaging (SA) of the surface QRS complex (method I), signal averaging of an endocardial electrode catheter recording (method II), and epicardial recording (method III) in 24 patients (mean age = 55 +/- 14 years). Sixteen of the 24 patients (66%) had spontaneous as well as induced sustained ventricular tachycardia (VT), whereas the remaining 8 patients (33%) had spontaneous non-sustained VT. SA by the three methods was performed within less than or equal to 24 hours of each other, utilizing a band pass filter frequency of 25 to 250 Hz. The duration of the SA-QRS complex, low amplitude signals (LAS) of less than 40 microV and the RMS-voltage (V) of the terminal 40 ms were determined for the three methods. There was a significant correlation between method I and methods II and III for the SA-QRS duration (r = .928, p less than .001), RMS-V (r = .634, p less than .002) and LAS (r = .783, p less than .001). There was no significant difference in the quantitative signal-averaged parameters between the three methods. The incidence of the RMS-V of less than 25 microV (37.5% vs 21%); LAS of greater than 32 ms (46% vs 37.5%) and SA-QRS of greater than 120 ms (54% vs 42%) was higher but statistically non-significant by methods II and III when compared to method I. We concluded that: (1) SA of intracardiac electrograms correlate well with SA of the surface QRS. This observation further validates the technique of surface SA to detect delayed ventricular activation. (2) SA of intracardiac electrograms may provide additional information on quantitative SA parameters relative to surface QRS in some patients with VT.