REPRODUCIBILITY OF THE SIGNAL-AVERAGED P-WAVE - TIME AND FREQUENCY-DOMAIN ANALYSIS

Objective-To assess the reproducibility of time and frequency domain v ariables derived from the signal averaged P wave. Design-Longitudinal within patient study. Setting-Regional cardiothoracic centre. Patients -20 patients (10 with documented paroxysmal atrial fibrillation and 10 normal controls) were studied on three occasions to assess the reprod ucibility of repeated signal averaged P wave recordings. Digital P wav e recordings were made on a further 10 patients on a single occasion a nd the recordings signal averaged twice in order to assess the reprodu cibility of the averaging system itself in the absence of biological v ariation. Main outcome measures-P wave duration, spatial velocity, and energies contained in frequency bands from 20, 30, and 60-150 Hz of t he P wave spectrum were measured after P wave specific signal averagin g. Coefficients of reproducibility were calculated for paired signal a veraged P waves derived by signal averaging the same digital recording s on two separate occasions, for recordings performed in the same pati ents immediately after each other (((back to back))) and those perform ed one week apart. Results-System reproducibility when the same digita l P wave recordings were signal averaged on two separate occasions was high (< 11% for all variables). For P wave duration the coefficient o f reproducibility was 11.4% for back to back recordings and 13.1% for those one week apart. The reproducibility of spatial velocity and P wa ve energy was low. Variation in P wave morphology was noted when succe ssive P waves from the same subject were examined. If recordings with the same P wave morphology were analysed the reproducibility of spatia l velocity and P wave energy improved but remained significantly poore r than that for P wave duration. Conclusions-P wave duration is reprod ucible within subjects in the short and medium term. Frequency domain and spatial velocity analysis are poorly reproducible, due more to spo ntaneous variation in P wave morphology than to instability of the sig nal averaging process. This may limit the utility of signal averaged P wave variables other than duration for the prediction of atrial arrhy thmia.