Rate control in atrial fibrillation: role of atrial inputs to the AV node
Authors: A Rankin
Journal: Cardiovascular Research (1999)

See article by Garrigue et al. [11] ( pages 344 -355) inand ventricular rate is observed at all high rates above that this issue.at which Wenckebach occurs [7].The anatomical complexities of the AV nodal region are also relevant, with two A vital property of the atrioventricular (AV) node is its functional inputs to the AV node, a posterior input via the ability to prevent excessive ventricular rates in the pres-crista terminalis and an anterior interatrial septal input.The ence of high atrial rates, in particular atrial fibrillation, a direction of atrial wave front [9] and the relative timing of common clinical arrhythmia during which atrial rates may activation at the atrial inputs [10] may influence the be up to 600 beats per minute.The mechanisms involved patterns of AV nodal propagation.The potential role of the have been studied for over a century, but remain incom-atrial inputs is further demonstrated in the paper by pletely understood (for reviews see [1,2]).Many factors Garrigue et al. in this issue [11], which shows the play a role in determining the ventricular rate and irregu-importance of the differential bombardment of the inputs larity in response to rapid atrial rate.The refractory period to the AV node in determining the ventricular response in a of the AV node is of major importance [3,4], related to the rabbit model of simulated atrial fibrillation.unique electrophysiological properties of the AV nodal In this paper [11], the inverse relationship between cells, in which the refractory period [3,4] extends beyond increasing atrial rate and ventricular response is confirmed, the time of repolarisation of the action potential, in contrast both with regular and irregular atrial pacing, and the to atrial cells [5,6].The atrial rate is also important and has complexity of this relationship is illustrated.Regular atrial a complex relationship with the ventricular response [7].pacing could result in irregularity of ventricular response, With increasing atrial rate there is an initial corresponding depending on intra-atrial block, AV nodal refractoriness, rise in ventricular rate, with 1:1 conduction.However, with concealed conduction and atrial input activation.At critical further increase in atrial rate the phenomenon of Wenck-regular atrial rates, the ventricular irregularity observed ebach block occurs, with intermittent block of conduction was very similar to that produced by random atrial pacing.to the ventricle, and there is subsequently an inverse High rate atrial pacing was used which was random but relationship between atrial rate and ventricular response reproducible, and the same sequence of random intervals i.e. the ventricular rate decreases as atrial rate increases.was delivered to multiple atrial sites.When the total events This is due to the effects of concealed conduction, first at both atrial inputs to the AV node were considered, the defined by Langendorf in 1948, as ''an impulse which inverse relationship between atrial rate and ventricular affects the A-V junction by penetrating into it without response was confirmed but the correlation was weak with traversing it'' but is evident from its ''influence . . . on the a large range of overlap e.g. a 300 ms His-His (HH) transmission time or on the formation of a subsequent interval could result from 2 to 7 atrial input events.This impulse'' [8].Irregularity of atrial rhythm is also im-indicated that more than overall atrial rate was influencing portant.With regular atrial pacing the inverse relationship AV nodal output.The site of pacing was found to be may be lost over ranges of atrial rate that allow a fixed important, although variable between preparations.The ratio of conduction (e.g.2:1, 3:1).With irregular atrial direction of the activation wavefront and the subsequent pacing, however, the inverse relationship between atrial pattern of engagement of the AV nodal inputs affected the functional refractory period, as indicated by the shortest HH intervals.Pacing sites associated with the greatest