AUTHOR=Tse Gary , Du Yimei , Hao Guoliang , Li Ka Hou Christien , Chan Fiona Yin Wah , Liu Tong , Li Guangping , Bazoukis George , Letsas Konstantinos P. , Wu William K. K. , Cheng Shuk Han , Wong Wing Tak 

TITLE=Quantification of Beat-To-Beat Variability of Action Potential Durations in Langendorff-Perfused Mouse Hearts

JOURNAL=Frontiers in Physiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2018.01578

DOI=10.3389/fphys.2018.01578

ISSN=1664-042X

ABSTRACT=<p><bold>Background:</bold> Beat-to-beat variability in action potential duration (APD) is an intrinsic property of cardiac tissue and is altered in pro-arrhythmic states. However, it has never been examined in mice.</p><p><bold>Methods:</bold> Left atrial or ventricular monophasic action potentials (MAPs) were recorded from Langendorff-perfused mouse hearts during regular 8 Hz pacing. Time-domain, frequency-domain and non-linear analyses were used to quantify APD variability.</p><p><bold>Results:</bold> Mean atrial APD (90% repolarization) was 23.5 ± 6.3 ms and standard deviation (SD) was 0.9 ± 0.5 ms (<italic>n</italic>  =  6 hearts). Coefficient of variation (CoV) was 4.0 ± 1.9% and root mean square (RMS) of successive differences in APDs was 0.3 ± 0.2 ms. The peaks for low- and high-frequency were 0.7 ± 0.5 and 2.7 ± 0.9 Hz, respectively, with percentage powers of 39.0 ± 20.5 and 59.3 ± 22.9%. Poincaré plots of APD<sub>n+1</sub> against APD<sub>n</sub> revealed ellipsoid shapes. The ratio of the SD along the line-of-identity (SD2) to the SD perpendicular to the line-of-identity (SD1) was 8.28 ± 4.78. Approximate and sample entropy were 0.57 ± 0.12 and 0.57 ± 0.15, respectively. Detrended fluctuation analysis revealed short- and long-term fluctuation slopes of 1.80 ± 0.15 and 0.85 ± 0.29, respectively. When compared to atrial APDs, ventricular APDs were longer (ANOVA, <italic>P</italic> &lt; 0.05), showed lower mean SD and CoV but similar RMS of successive differences in APDs and showed lower SD2 (<italic>P</italic> &lt; 0.05). No difference in the remaining parameters was observed.</p><p><bold>Conclusion:</bold> Beat-to-beat variability in APD is observed in mouse hearts during regular pacing. Atrial MAPs showed greater degree of variability than ventricular MAPs. Non-linear techniques offer further insights on short-term and long-term variability and signal complexity.</p>