The AV synchrogram: A novel approach to quantify atrioventricular coupling during atrial arrhythmias

The generation of ventricular response during atrial arrhythmias and its dependence on atrial activity is poorly understood. This paper introduces the atrioventricular (AV) synchrogram, a novel method for the beat-to-beat assessment of AV coupling during atrial arrhythmias, based on the stroboscopic observation of the ventricular phase at times triggered by atrial activation. The method was applied on a database of 120 atrial electrograms and ECG signals recorded in patients during typical atrial flutter (AFL), rapid atrial flutter (rAFL), and atrial fibrillation (AF). Synchronized epochs of different n:m order were automatically detected in the AV synchrogram and characterized in terms of percentage of significantly coupled beats (p_lb), maximal length of coupling segments (l_max), average conduction ratio (CR). Synchrogram analysis demonstrated that AV coupling and degree of conduction were significantly affected by the rate and regularity of atrial activity. The occurrence and stability of AV coupled epochs was maximal during regular atrial activation in AFL (median (interquartile range) of p_lb = 100 (100–100)%, l_max = 29.0 (28.5–29.4) s), and significantly (p < 0.001) decreased at faster atrial rates in rAFL (p_lb = 74.3 (57.6–100)%, l_max = 7.4 (3.9–28.7) s). A further decrease of coupling indexes occurred at higher irregularity of atrial activity in AF (p_lb = 25.7 (19.9–30.2)%, l_max = 2.1 (1.8–2.6) s). The increase of atrial rate led to a significant (p < 0.001) reduction of CRs from 0.50 (0.29–0.50) in AFL to 0.25 (0.22–0.25) in rAFL and 0.30 (0.24–0.35) in AF. Application of the analysis to the time course of AF showed the presence of a Farey sequence structure in n:m coupling patterns at increasing atrial rate, which was consistent with the scaling effect of nodal recovery on atrial beats. In conclusion, AV synchrogram analysis enables beat-to-beat assessment of AV coupling and dynamical tracking of AV response during atrial arrhythmias, which may favor mechanistic insight about the genesis of ventricular rhythms and potentially the development of efficacious rate control strategies.