Noninvasive Recording of Sinus Node Activity by P-Wave-Triggered Signal-Averaged Electrocardiogram: Validation Using Direct Intra-Atrial Recording of Sinus Node Electrogram

Abstract

In order to evaluate if sinus node activity can be detected by surface ECG, at least 200 sinus beats of 3 bipolar orthogonal leads (horizontal, vertical, and sagittal position) were averaged in 33 consecutive patients (mean age: 58 ± 19 years). Each lead signal (0.5-300 Hz) was independently averaged triggering P wave by the template-comparing method and then filtered (0.5-25 Hz) and amplified. In 29 patients (88%), amplification revealed the presence of a progressive upstroke slope beginning during the isoelectric line and ending at the earliest observed atrial activation in the 3 nonamplified and nonfiltered leads (mean voltage: 9.3 ± 6.4 pV). Such pre-P signal was always lost with 50-Hz high-pass filtering, and could be present in 1 or more leads; in the latter case, the longest duration was considered. The length of pre-P signal proved to be strictly correlated (r = 0.9932, p < 0.001) with that contemporaneously furnished by the direct intra-atrial recording of sinus node electrogram (0.05-35 Hz, mean of at least 20 measurements). Mean values of noninvasive and invasive pre-P lengths were 76 ± 29 and 74 ± 30 ms, respectively. In conclusion, it seems possible to detect from surface ECG a pre-P activity whose character and timing are well correlated to those obtained by endocavitary recording of sinus node signal. These findings suggest the possibility of a clinical use of noninvasive sinus node activity recording for diagnostic purposes.