Prevention of Atrial Fibrillation:

The article by Betts et al.1 in this issue of the Journal reports detailed high-density mapping of left atrial (LA) endocardial activation by a noncontact system performed during sinus rhythm and coronary sinus (CS) pacing in nine patients with paroxysmal atrial fibrillation (AF). They accurately describe areas of block in the posterior LA wall in close proximity to the pulmonary veins (PVs) during sinus rhythm and CS pacing. They suggest that these lines of block contribute to the substrate for reentrant arrhythmias, including AF or LA flutter. The site of earliest LA endocardial activation was on the superior interatrial septum, anterior to the ostium of the right upper PV in 5 patients, in the midposterior septum, anterior to the ostium of the right lower PV in 2 patients, and on the anterosuperior septum in 2 patients. A vertical line of conduction block running from the superior to inferior right PVs was seen during sinus rhythm and CS pacing in 5 of 9 patients. Their results are important, emphasizing the role of a “posterior” rather “anterior” (Bachmann’s bundle) site of interatrial breakthrough that is the first site to show disorganized activity at AF onset. Conduction block or delay in the posterior LA may provide the additional component allowing triggers to induce reentrant wavelets that may degenerate into AF. The maps appear to be accurate. Using a non-contact mapping system with a 64-electrode array on a 9-French balloon catheter, thousands of points can be collected and detailed LA geometry can be acquired. The entire endocardial activation can be mapped continuously during every beat in sinus rhythm as well as during CS pacing. The main limitation of the study is the lack of a control group, as mapping was not performed in patients without a history of AF. A better understanding of transseptal activation pattern and its role in a large population of AF patients may be important for treatment, but little is known about the prevalence and clinical significance of preferential routes of conduction from the LA to the right atrium in humans.2-6 The position and orientation of interatrial connections appear to be speculative and essentially based on published anatomic studies. Knowledge of the anatomic and functional components of interatrial conduction has progressed dramatically. Increased knowledge of the sequence of LA activation and the way in which triggers interact with the LA to initiate AF will be useful in the evolution of treatment strategies aimed specifically at the initiating process.3 These findings