ABNORMAL SIGNAL-AVERAGED ELECTROCARDIOGRAMS IN PATIENTS WITH INCOMPLETE RIGHT BUNDLE-BRANCH BLOCK

Background and hypothesis: A hypothesis was formulated that regional d elayed activation of the right ventricle, as seen in incomplete right bundle-branch (IRBBB) aberrancy, may simulate late potential activity and may be responsible for abnormal signal-averaged electrocardiograms (SAECGs). No previous studies have specifically addressed this issue in this particular group of patients (with IRBBB). Therefore, the aim of the present study was to investigate the incidence of abnormal SAEC Gs in patients with IRBBB. If this were confirmed, our purpose would f urther be to investigate ways of reducing the false positive results. Methods: The study group included 53 patients (28 men and 25 women), a ged 53 +/- 13 years, with no history of previous myocardial infarction or ventricular tachycardia and who had an electrocardiogram (ECG) sho wing IRBBB. An SAECG was also performed in a control group of 19 age-m atched individuals with a normal ECG. Time domain analysis was perform ed using a band pass filter of 40-250 Hz. The following parameters wer e considered normal: filtered QRS duration (QRSD) < 114 ms, root mean square of the voltage of the last 40 ms of the QRS complex (RMS) > 20 mu V, and the duration of the low amplitude signal (< 40 mu V) at the terminal portion of the QRS (LAS)< 38 ms. An SAECG was considered abno rmal if any two of these criteria were abnormal. Results: The mean val ues of the SAECG parameters were: QRSD 101 +/- 11 ms, RMS 32 +/- 20 mu V, LAS 32 +/- 12 ms, and noise 0.29 +/- 0.13 mu V. Abnormal SAECGs wi th at least two criteria satisfied were present in 16 of 53 (30%) pati ents compared with 0 (0%) of 19 individuals in the control group (p = 0.02). Abnormal values included the combination of RMS and LAS in 12 p atients and all three parameters in 4 patients. However, if the defini tion of late potentials were limited to the combination of abnormal QR SD and either RMS or LAS values, the incidence of false positive resul ts (4 patients) (7.5%) would be significantly decreased (p = 0.007). A t 21 months of follow-up, no arrhythmic events occurred. Conclusions: Delayed terminal conduction observed in IRBBB may cause a high inciden ce of false positive late potentials on SAECGs. Based on this study, w e propose that this can be largely remedied if the optimal criteria fo r the presence of late potentials in patients with IRBBB always includ e the combination of QRSD and either RMS or LAS.