Role of atrial arrhythmia and ventricular response in atrial fibrillation induced atrial remodelling.

No studies have assessed the specific contributions of atrial fibrillation (AF)-related atrial vs. associated ventricular arrhythmia to remodelling. This study assessed the roles of atrial arrhythmia vs. high ventricular rate in AF-associated remodelling. Four primary dog-groups (12/group) were subjected to 3-week pacing: 600-b.p.m. atrial tachypacing maintaining AF [AF w/o- atrioventricular block (AVB)]; atrial tachypacing with atrioventricular-node ablation (AF+AVB) and ventricular-demand pacing (80 b.p.m.); 160-b.p.m. ventricular-tachypacing (V160) reproducing the response rate during AF; and sinus rhythm with AVB/ventricular-pacing at 80-b.p.m. (control group). At terminal study, left-atrial (LA) effective refractory period (ERP) was reduced equally in both AF groups (w/o-AVB and AF+AVB). AF-inducibility was increased strongly in AF groups (w/o-AVB and AF+AVB) and modestly in V160. AF duration was significantly increased in AF w/o-AVB but not in AF+AVB or V160. Conduction velocity was decreased in AF w/o-AVB, to a greater extent than in AF+AVB and V160. Atrial fibrous-tissue content was increased in AF w/o-AVB, AF+AVB and V160, with collagen-gene up-regulation only in AF w/o-AVB. Connexin43 gene expression was reduced only in AF w/o-AVB. An additional group of 240-b.p.m. ventricular tachypacing dogs (VTP240; to induce heart failure) was studied: vs. other tachypaced groups, VTP240 caused greater fibrosis, but no change in LA-ERP or AF-inducibility. VTP240 also increased AF duration, strongly decreased left ventricular ejection fraction, and was the only group with LA natriuretic-peptide activation. The atrial tachyarrhythmia and rapid ventricular response during AF produce distinct atrial remodelling; both contribute to the arrhythmogenic substrate, providing new insights into AF-related remodelling and novel considerations for ventricular rate-control.