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FOCUS ISSUE: ATRIAL FIBRILLATION: CLINICAL RESEARCH: LEFT ATRIAL STRUCTURE AND CONDUCTION DELAY

Anatomically Determined Functional Conduction Delay in the Posterior Left Atrium

Relationship to Structural Heart Disease

Kurt C. Roberts-Thomson, MBBS^_*,1, Irene H. Stevenson, MBBS^_*,2, Peter M. Kistler, MBBS, PhD^_*,3, Haris M. Haqqani, MBBS^_*,1, John C. Goldblatt, MBBS^_*, Prashanthan Sanders, MBBS, PhD and Jonathan M. Kalman, MBBS, PhD, FACC^_*,_*

^_* Departments of Cardiology and Cardiothoracic Surgery, Royal Melbourne Hospital, and the University of Melbourne, Melbourne, Australia
Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Discipline of Medicine, University of Adelaide, Adelaide, Australia.

Manuscript received June 18, 2007; revised manuscript received October 29, 2007, accepted November 8, 2007.

^_* Reprint requests and correspondence: Dr. Jonathan M. Kalman, Department of Cardiology, Royal Melbourne Hospital, Royal Pde. Melbourne 3050, Australia. (Email: jon.kalman{at}mh.org.au).

Objectives: This study sought to characterize the conduction properties of the posterior left atrium (PLA) in patients with different forms of structural heart disease undergoing cardiac surgery.

Background: The PLA plays an important role in the initiation and maintenance of atrial fibrillation.

Methods: This study included 34 patients having elective cardiac surgery. There were 4 groups of patients: normal left ventricular (LV) function (coronary artery bypass grafting [CABG]); severe LV dysfunction (LVF/CABG); severe mitral regurgitation (MR); severe aortic stenosis (AS). Epicardial mapping of the PLA was performed in sinus rhythm and during differential pacing. Activation patterns, regional conduction velocity (CV), conduction heterogeneity, anisotropy, and total plaque activation time (TAT) were assessed.

Results: Left atrial size in patients with LVF/CABG (47 ± 7 mm) and MR (54 ± 6 mm) was larger than patients with CABG (39 ± 7 mm) and AS (42 ± 6 mm; p < 0.05). During pacing, all patients developed a vertical line of conduction delay running between the pulmonary veins. The extent of this conduction delay was greater in patients with LVF/CABG and MR than patients with AS and CABG (p < 0.05). Conduction heterogeneity, anisotropy, and TAT were greater in patients with LVF/CABG and MR than patients with CABG (p < 0.05). These changes resulted in circuitous wave front propagation.

Conclusions: There is a line of functional conduction delay in a consistent anatomical location in the PLA in patients with structural heart disease. This is most marked in conditions associated with significant chronic atrial enlargement and leads to circuitous wave front propagation, suggesting a potential role in arrhythmogenesis.

Abbreviations and Acronyms   AERP = atrial effective refractory period   AF = atrial fibrillation   AS = aortic stenosis   CABG = coronary artery bypass grafting   LVF = left ventricular failure   MR = mitral regurgitation   PLA = posterior left atrium.

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