Effects of atrial fibrillation substrate and spatiotemporal organization on atrial defibrillation thresholds

We previously showed that canine models of atrial fibrillation (AF) have different substrates (either structural or electrical) that lead to differences in AF characteristics.

The purpose of this study was to determine whether the differences in AF characteristics also would lead to differences in atrial defibrillation thresholds (ADFTs).

Dogs were divided into five groups: control; MR-mitral regurgitation for 5 weeks; CHF-congestive heart failure for 4 weeks; RAP-rapid atrial pacing for 6 weeks; and METH-acetyl-beta-methylcholine acutely administered. A cross-sectional area of the left atrium was calculated, and AF was induced with rapid atrial pacing. Biphasic shocks with a pulse width of 3/3 ms were delivered through specially constructed shocking catheters with a surface area of 3.7 cm(2) that were placed in the right and left atria. An up-down-up protocol was used to determine the 50% ADFT threshold (ADFT(50)). A wide-bipole AF signal was digitally filtered, and a fast Fourier transform was calculated over a 2-second window every 1 second. The dominant frequency was determined, and the organization index was calculated as the ratio of the area under the dominant peak and its harmonics to the total area of the spectrum.

For left atrial size, the CHF and MR groups had a significantly larger atria than did control. ADFT(50) for control, MR, CHF, RAP, and METH groups were 160 +/- 30 V, 120 +/- 50 V, 132 +/- 20 V, 668 +/- 205 V, and 593 +/- 128 V, respectively (analysis of variance, P <.0001). Dominant frequencies were significantly higher and organization indexes significantly lower in the RAP and METH models compared with the other models.

RAP and METH canine models had a significantly higher ADFT(50) compared with the other AF models. The increase in ADFT(50) in these models corresponded with higher global dominant frequencies and lower measured organization indexes.