Frequency analysis of atrial fibrillation

Atrial fibrillation (AF) is a common arrhythmia which can have serious clinical consequences. Different characteristics of AF may be more amenable to treatment, but it is not easy to assess the characteristics of the atrial rhythm from ECG recordings since the atrial complexes are small relative to the ventricular complexes. AF is usually seen on the ECG as apparently irregular deviations of the baseline. Our aim was to develop a technique which would allow researchers to retrieve information about the atrial rhythm non-invasively from body-surface ECGs and to assess the stability of the atrial rhythm. We recorded 300 s of simultaneous 12-lead ECGs at 500 Hz directly to a computer from six patients with AF for subsequent analysis. For stability analysis, we split the 300 s recordings into two sections of 150 s each. These were then subdivided into sections of approximately 10 s, and principal component analysis was performed on each 12-lead section, generating 12 orthogonal data components. A frequency analysis of each component was carried out using a fast Fourier transform algorithm and the average spectrum calculated for each 150 s section. From this the dominant AF frequency was identified from the peak in the spectrum between 5 and 10 Hz. The atrial waveform was most commonly observed in principal components 6, 7 and 8 with mean (SD) frequency 6.8 Hz (0.9 Hz) and range 5.9 Hz to 8.2 Hz across the subjects. The difference between the paired 150 s sections was 0.3 Hz (0.3 Hz), showing that the dominant atrial frequency could be identified consistently and that there was little short term variability