NONINVASIVE RECORDING OF SINUS NODE ACTIVITY BY P-WAVE-TRIGGERED SIGNAL-AVERAGED ELECTROCARDIOGRAM - VALIDATION USING DIRECT INTRAATRIAL RECORDING OF SINUS NODE ELECTROGRAM

In order to evaluate if sinus node activity can be detected by surface ECG, at least 200 sinus beats of 3 bipolar orthogonal leads (horizont al, vertical, and sagittal position) were averaged in 33 consecutive p atients (mean age: 58 +/- 19 years). Each lead signal (0.5-300 Hz) was independently averaged triggering P wave by the template-comparing me thod 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 obser ved atrial activation in the 3 nonamplified and nonfiltered leads (mea n voltage: 9.3 +/- 6.4 muV). Such pre-P signal was always lost with 50 -Hz high-pass filtering, and could be present in 1 or more leads; in t he latter case, the longest duration was considered. The length of pre -P signal proved to be strictly correlated (r = 0.9932, p < 0.001) wit h that contemporaneously furnished by the direct intra-atrial recordin g of sinus node electrogram (0.05-35 Hz, mean of at least 20 measureme nts). 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 si nus node signal. These findings suggest the possibility of a clinical use of noninvasive sinus node activity recording for diagnostic purpos es.