Interatrial Features of Length-Dependent Regulation of Myocardial Force in Paroxysmal Atrial Fibrillation in Rats

Myocardial stretch is a factor that forms an arrhythmogenic substrate for the progression of atrial fibrillation (AF). The features of force generation remodeling during stretching in the atrial myocardium in AF remain poorly understood. In this study, we analyzed changes in active and passive tension of left and right rat atrial myocardial strips at their diastolic stretching and the slopes of the "length-tension" relationship in acetylcholine-CaCl₂-induced paroxysmal AF. In AF, neither magnitudes of the active and passive tension, nor the slope coefficients of the "length-tension" relationship changed significantly relative to the intact control values. However, the differences between the left and right atria in the parameters of length-dependent regulation of passive tension typical of normal atrial myocardium disappeared in paroxysmal AF.