Key result
During electrically induced atrial fibrillation in canine hearts, the mode external work efficiency of arrhythmic beats remained normal at 15%, although the mean efficiency of 13.3% was significantly lower than the 15.3% seen in regular beats.
Absolute Event Rate: 13.3% vs 15.3%
p-value: p=<0.05
In normal canine hearts, the most frequent (mode) external work efficiency of individual beats during atrial fibrillation remains comparable to that of regular tachycardia, despite a lower overall mean efficiency.
Preserved mode efficiency in canine AF suggests beat resilience; leaves open translation to human ventricular energetics.
The external work (EW) efficiency of individual arrhythmic beats of the left ventricle (LV) cannot directly be obtained since LV O(2) consumption (VO(2)) of each beat cannot directly be measured under beat-to-beat varying contractile and loading conditions. We, however, have recently reported that VO(2) of each arrhythmic beat can reasonably be estimated by VO(2) = aPVA + bE(max) + c even under varying PVA and E(max). Here, PVA is the LV pressure-volume (P-V) area as a measure of the LV total mechanical energy, E(max) is the LV end-systolic elastance as an index of the LV contractility, a is a constant O(2) cost of PVA, b is a constant O(2) cost of E(max), and c is the basal metabolic VO(2) of the beat, all on a per-beat basis. Using the above formula in this study, we calculated VO(2) of the individual arrhythmic beats from their measured PVA and E(max) during electrically induced atrial fibrillation (AF) in normal canine hearts. We then calculated their LV EW efficiency by dividing their measured EW with the estimated VO(2). We found that the thus calculated EW efficiency of the arrhythmic beats had a rightward skewed distribution with a mode of 15% and a maximum of 18% around a mean of 13% on average in six hearts. This mode remained comparable to the efficiency (15%) at regular tachycardia though 22% lower than mean arrhythmic tachycardia.
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Shimizu et al. (2009) studied Atrial fibrillation (n=6). Electrically induced atrial fibrillation vs. Regular tachycardiac pacing was evaluated on Mean external work efficiency (p=<0.05). During electrically induced atrial fibrillation in canine hearts, the mode external work efficiency of arrhythmic beats remained normal at 15%, although the mean efficiency of 13.3% was significantly lower than the 15.3% seen in regular beats.
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