Characterization of Left Atrial Activation in the Intact Human Heart

Abstract

Background-The patterns of activation of the human left atrium (LA), how they relate to atrial myocardial architecture, and their role in arrhythmogenesis remain largely unknown. Methods and Results-Left atrial endocardial activation was mapped in 19 patients with a percutaneous noncontact mapping system. Earliest endocardial breakthrough during sinus rhythm (SR) occurred more frequently in the septal (63%, principally posteroseptal) than anterosuperior (37%) LA and varied little with isoproterenol or high right atrial pacing rate. Regardless of site of breakthrough, LA activation was characterized in all patients by propagation around a variably complete line of functional conduction block, descending on the posterior wall from the roof, passing between the ostia of the superior and then inferior pulmonary veins (PVs) before turning septally, passing below the oval fossa, and merging further anteriorly with the septal mitral annulus. Examination of the myocardial architecture in 10 normal adult postmortem hearts revealed an abrupt change in subendocardial fiber orientation along a line following the same course. During episodes of focal initiation of atrial fibrillation (AF), interaction was observed between wavefronts entering the LA from PVs and this functional line of conduction block that resulted in LA macroreentry or formation of daughter wavefronts. Conclusions-The LA endocardium has complex but characteristic patterns of activation during sinus rhythm, pacing, and AF initiation by PV ectopy that are determined largely by the functional properties of atrial musculature. These findings have important implications for both pacing and ablative strategies for the prevention of initiation of AF.

Interatrial conduction can be accurately determined using standard 12-lead electrocardiography: Validation of P-wave morphology using electroanatomic mapping in man

“…Bachmann's bundle being lower in some reports 1,5 than in others. [2][3][4] Nevertheless, based on the data available, it seems reasonable to conclude that Bachmann's bundle is the most common interatrial conductive route, although other routes, located posteriorly 6,7 and inferiorly, [8][9][10] also participate in interatrial conduction in most patients.…”

“…However, knowledge about normal interatrial conduction during sinus rhythm in the intact human heart is based on a few reports on patients with clinical arrhythmia, using various invasive techniques. [1][2][3][4][5] The results are to a certain degree conflicting, with the proportion of patients showing activation of the left atrium via…”

Left atrial posterior wall isolation: the icing on the cake

“…The incorporated PVs form the smooth posterior wall of the LA, while the trabeculated portion of the LA comes to occupy a more ventral aspect [7,8]. Anatomically, there is an abrupt change in LA subendocardial fiber orientation as this bundle traverses the posterior LA between the PVs, which create a basis of reentry [9,10]. Indeed, previous work using noncontact mapping has demonstrated significant conduction abnormalities in the posterior LA during sinus rhythm in patients with PAF [9].…”

“…Anatomically, there is an abrupt change in LA subendocardial fiber orientation as this bundle traverses the posterior LA between the PVs, which create a basis of reentry [9,10]. Indeed, previous work using noncontact mapping has demonstrated significant conduction abnormalities in the posterior LA during sinus rhythm in patients with PAF [9]. Additionally, the LAPW myocytes have a higher incidence of delayed afterdepolarizations, larger late sodium currents, but smaller inward rectifier potassium currents.…”

Box Isolation for Atrial Fibrillation

“…22) Non-PV foci originated mainly from the PV ostium or from the posterior LA, 23) and the posterior LA and the LA roof serve as a substrate for maintenance of AF in patients with AF. 24,25) It has been proposed that surgical procedures for isolating the posterior LA and PVs could cure AF in 93% of patients with lone AF 26) and 86% with chronic AF. 27) These findings support that isolation of not only PVs but also the whole posterior LA can result in a much better cure rate in the patients with paroxysmal and persistent AF.…”