Dynamics of AV coupling during human atrial fibrillation . 2 Role of atrial rate

26 27 The causal relationship between atrial and ventricular activities during human atrial fibrillation (AF) 28 is poorly understood. 29 This study analyzed the effects of an increase in atrial rate on the link between atrial and ventricular 30 activities during AF. Atrial and ventricular time series were determined in fourteen patients during 31 the spontaneous acceleration of the atrial rhythm at AF onset. The dynamical relationship between 32 atrial and ventricular activities was quantified in terms of atrioventricular (AV) coupling by AV 33 synchrogram analysis. The technique identified n:m coupling patterns (n atrial beats in m 34 ventricular cycles), quantifying their percentage (pc), maximal length (lmax) and conduction ratio 35 (CR=m/n). Simulations with a difference-equations AV model were performed to correlate the 36 observed dynamics to specific atrial/nodal properties. 37 The atrial rate increase significantly affected AV coupling and ventricular response during AF. The 38 shortening of atrial intervals from 185±32 to 165±24 ms (p<0.001) determined transitions towards 39 AV patterns with progressively decreasing m/n ratios (from CR=0.34±0.09 to 0.29±0.08, p<0.01), 40 lower occurrence (from pc=27.1±8.0 to 21.8±6.9%, p<0.05) and higher instability (from 41 lmax=3.9±1.5 to 2.8±0.7 s, p<0.01). Advanced levels of AV block and coupling instability at higher 42 atrial rates were associated with increased ventricular interval variability (from 123±52 to 133±55 43 ms, p<0.05). AV pattern transitions and coupling instability in patients were predicted, assuming 44 the filtering of high-rate irregular atrial beats by the slow recovery of nodal excitability. These 45 results support the role of atrial rate in determining AV coupling and ventricular response, and may 46 have implications for rate-control in AF. 47 48