The mechanisms of an increased dominant frequency in the left atrial posterior wall during atrial fibrillation in acute atrial dilatation.
BACKGROUND
Previous studies have shown that the highest dominant frequency (DF) is located in the left atrium (LA) during atrial fibrillation (AF) in pacing-induced AF. However, there have been few studies on the mechanisms of the increased DF of AF during acute atrial dilatation. The purpose of this study was to investigate the mechanisms of the increased maximal DF (max DF) in pacing-induced AF during acute atrial dilatation.


METHODS
In eight Langendorff-perfused canine hearts (26 +/- 2 kg), noncontact balloon catheters were placed into the right atrium (RA) and LA, respectively. AF was induced by extrastimulation pre- and postdilatation in the atrium (0 and 15 cm H(2)O, respectively). Fast Fourier transformation analysis was performed to analyze the max DF and harmonic index (HI) from the bi-atrial unipolar virtual electrograms during AF. The fibrillation cycle lengths were obtained from different atrial sites. The number of wavefronts was analyzed during AF. The frequency of regional splitting was defined as the number of wavefront splits per second in different atrial regions during AF. The percentage of the low-voltage zones (<0.5 mV) was defined as the ratio of the area of the low-voltage zones to the total atrial surface area.


RESULTS
The DF was measured during AF. The shortest fibrillation cycle length was located in the LA posterior wall and became shorter during acute atrial dilatation. The max DF was located in the LA posterior wall and increased during acute atrial dilatation (7.1 +/- 0.8 vs 8.8 +/- 2.1, P = 0.02). The max DF of the LA correlated with the wavefront number (r = 0.797, P < 0.001 predilatation; r = 0.860, P < 0.001 postdilatation). The splitting of wavefronts facilitated the formation of new wavefronts. During acute atrial dilatation, the frequency of regional splitting was closely correlated with the percentage of the low-voltage zones (r = 0.876, P < 0.001). Furthermore, the LA posterior wall had a higher percentage of the low-voltage zones than the other sites.


CONCLUSIONS
In acute atrial dilatation, the percentage of the low-voltage zones increased, especially in the LA posterior wall, which correlated with the regional splitting of the AF wavefronts. The increase in the splitting facilitated the formation of new wavefronts and resulted in a higher max DF during acute atrial dilatation.
Huang
Jin-Long
JL
Division of Cardiology, Department of Internal Medicine, Taichung Veterans General Hospital, Taipei, Taiwan.
Tai
Ching-Tai
CT
Lin
Yenn-Jiang
YJ
Ting
Chih-Tai
CT
Chen
Ying-Tsung
YT
Chang
Mau-Song
MS
Lin
Fan-Yue
FY
Lai
Wen-Ter
WT
Chen
Shih-Ann
SA
D000818:Animals; D001281:Atrial Fibrillation / Q000503:physiopathology*; D004108:Dilatation, Pathologic; D004285:Dogs; D005583:Fourier Analysis; D006325:Heart Atria / Q000473:pathology / Q000503:physiopathology*