Published Online
on February 3, 2003

A more recent version of this article appeared on February 11, 2003

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Submitted on April 29, 2002
Revised on October 24, 2002
Accepted on October 28, 2002

Characterization of Left Atrial Activation in the Intact Human Heart

Vias Markides MRCP, Richard J. Schilling MD, Siew Yen Ho PhD, Anthony W.C. Chow MRCP, D. Wyn Davies MD, and Nicholas S. Peters MD^*

From St Mary's Hospital (V.M., R.J.S., A.W.C.C., D.W.D., N.S.P.) and Imperial College (V.M., S.W.H., A.W.C.C., N.S.P.), London, UK.

^* To whom correspondence should be addressed. E-mail: n.peters{at}ic.ac.uk.

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.

Key words: atrium • fibrillation • conduction • arrhythmia • mapping

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