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CLINICAL RESEARCH: HEART RHYTHM DISORDERS

Paroxysmal Lone Atrial Fibrillation Is Associated With an Abnormal Atrial Substrate

Characterizing the "Second Factor"

Cardiovascular Research Centre, Department of Cardiology, Royal Adelaide Hospital, and the Disciplines of Medicine and Physiology, University of Adelaide, Adelaide, Australia

Manuscript received August 15, 2008; revised manuscript received November 3, 2008, accepted November 26, 2008.

^_* Reprint requests and correspondence: Dr. Prashanthan Sanders, Cardiovascular Research Centre, Department of Cardiology, Level 5 McEwin Building, Royal Adelaide Hospital, Adelaide, South Australia 5000, Australia (Email: prash.sanders{at}adelaide.edu.au).

Objectives: The purpose of this study was to determine whether patients with paroxysmal "lone" atrial fibrillation (AF) have an abnormal atrial substrate.

Background: While "AF begets AF," prompt termination to prevent electrical remodeling does not prevent disease progression.

Methods: Twenty-five patients with paroxysmal lone AF, without arrhythmia in the week prior, and 25 reference patients with left-sided accessory pathways were studied. Multipolar catheters placed at the lateral right atrium (RA), crista terminalis, coronary sinus, septal RA, and sequentially within the left atrium (LA) determined the effective refractory period (ERP) at 10 sites, conduction time along linear catheters, and conduction characteristics at the crista terminalis. Bi-atrial electroanatomic maps were created to determine regional differences in conduction velocity and voltage.

Results: Patients with AF demonstrated the following compared with reference patients: larger atrial volumes (RA: 94 ± 18 ml vs. 69 ± 9 ml, p = 0.003; LA: 99 ± 19 ml vs. 77 ± 17 ml, p = 0.006); longer ERP (at 600 ms: 255 ± 25 ms vs. 222 ± 16 ms, p < 0.001; at 450 ms: 234 ± 20 ms vs. 212 ± 14 ms, p = 0.004); longer conduction time along linear catheters (57 ± 18 ms vs. 47 ± 10 ms, p = 0.01); longer bi-atrial activation time (128 ± 17 ms vs. 89 ± 10 ms, p < 0.001); slower conduction velocity (RA: 1.3 ± 0.3 mm/ms vs. 2.1 ± 0.5 mm/ms; LA: 1.2 ± 0.2 mm/ms vs. 2.2 ± 0.4 mm/ms, p < 0.001); greater proportion of fractionated electrograms (27 ± 8% vs. 8 ± 5%, p < 0.001); longer corrected sinus node recovery time (265 ± 57 ms vs. 185 ± 60 ms, p = 0.002); and lower voltage (RA: 1.7 ± 0.4 mV vs. 2.9 ± 0.4 mV; LA: 1.7 ± 0.7 mV vs. 3.3 ± 0.7 mV, p < 0.001).

Conclusions: Patients with paroxysmal lone AF, remote from arrhythmia, demonstrate bi-atrial abnormalities characterized by structural change, conduction abnormalities, and sinus node dysfunction. These factors are likely contributors to the "second factor" that predisposes to the development and progression of AF.

Key Words: atrial fibrillation • arrhythmia • electrophysiology • atrial remodeling • atrial substrate

Abbreviations and Acronyms   AF = atrial fibrillation   CI = confidence interval   CSNRT = corrected sinus node recovery time   ERP = effective refractory period   LA = left atrium/atrial   OR = odds ratio   RA = right atrium/atrial   SACT = sinoatrial conduction time

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