Electrical, morphological, and ultrastructural remodeling and reverse remodeling in a canine model of chronic atrial fibrillation

Background-In patients with recurrent persistent atrial fibrillation (AF), vulnerability to AF persists indefinitely despite presumed completion of re verse electrical remodeling within days of return to normal sinus rhythm. A trial electrical and anatomic remodeling and reverse remodeling were studie d in a canine model of chronic AF. Methods and Results-Chronic AF was induced in 8 dogs by creating moderate m itral regurgitation and rapidly pacing the right atrium at 640 bpm for >8 w eeks. Measurements performed at baseline, after establishment of chronic AF , and then at 4 hours and again at 7 to 14 days after cardioversion to sinu s rhythm included atrial effective refractory periods, AF cycle lengths, le ft atrial dimensions, premature atrial contraction (PAC) frequency, and atr ial vulnerability to atrial extrastimuli. After establishing chronic AF, at rial effective refractory period shortening, increases in spontaneous PAC f requency, increases in left atrial size with loss of contractility, and mul tiple ultrastructural abnormalities were demonstrated. Complete reverse ele ctrical remodeling and decreases in PACs were observed after 7 to 14 days o f sinus rhythm, but there was no resolution of anatomic and ultrastructural abnormalities. Occurrence of spontaneous AF paralleled PAC frequency, but vulnerability to AF induction persisted (75% immediately after conversion v ersus 63% at 4 hours and 50% at 7 to 14 days) despite reverse electrical re modeling. Conclusions-After conversion from chronic AF to sinus rhythm in this canine model, electrical remodeling occurs rapidly. However, gross and ultrastruc tural anatomic changes persist, as does vulnerability to induced AF, Vulner ability to AF initiation 7 to 14 days after cardioversion is more dependent on persisting structural abnormalities than on electrophysiological abnorm alities.