Fig. 4 |. Atrial fibrillation is associated with heterogeneous changes in left atrial myosin isoform expression.
a, Langendorff-perfused rabbit hearts from control (blue, top) or heart failure rabbits (red, bottom panel) were tested for atrial fibrillation inducibility and duration following burst pacing at 50 ms cycle length. Heart failure was induced by chronic left circumflex artery ligation and was allowed to develop over 6 weeks. During heart failure progression, severe left atrial hypertrophy occurred. b, Heart failure hearts (n = 4) developed long-lasting atrial fibrillation (> 60 s) when intra-atrial pressure was increased to 10 cm H2O. Control hearts (n = 4) did not develop long-lasting atrial fibrillation until intra-atrial pressure was increased to 30 cm H2O. The colored bars represent mean atrial fibrillation duration and the black error bars represent the corresponding standard errors of the mean. All individual data points are shown in the more detailed Supplementary Fig. 4. c, Western blotting for MYH7 expression (β -MyHC protein) indicates MYH7 expression exclusively in the remodeled heart failure left atrium. The experiment was repeated for two independent heart failure animals and two control animals with similar results. An uncropped version of the western blot is shown as Supplementary Fig. 5. d, Immunostaining and confocal microscopy revealed heterogeneous MYH7 expression (green) in the heart failure left atrium. Consistent with western blotting data, the heart failure right atrium did not express MYH7. The experiment was repeated for two independent heart failure animals with similar results. Supplementary Figure 6 shows an additional image. LAA, left atrial appendage; RAA, right atrial appendage; V, ventricle; AF, atrial fibrillation; HF, heart failure; SR, sinus rhythm; w, week; LA, left atrium; RA, right atrium.