What determines wall thickness? investigating compensatory ventricular remodeling in a sheep model of acute onset - chronic left bundle branch block

Abstract Introduction A left bundle branch block (LBBB) induces an early activation of the septal wall and late activation of the lateral wall of the left ventricle. This mechanical dyssynchrony causes the septal wall to shorten against low left ventricular (LV) pressure, whereas the lateral wall will shorten against higher LV pressure. This loading asymmetry has been hypothesized as the trigger for compensatory remodeling – septal thinning and lateral thickening – which has been suggested to rebalance wall stresses in the left ventricle. Yet, empirical measurements of wall stress during chronic LBBB are sparse. Purpose This study aimed to investigate how wall stress distribution within the left ventricle relates to regional remodelling in an animal model with chronic exposure to LBBB. Methods Fifteen sheep underwent DDD pacing of the right ventricle at 180 bpm to induce LBBB-like conduction delay and accelerate remodeling. Echocardiography allowed to measure septal and lateral wall thickness; speckle-tracking provided septal and lateral strain and curvature; and LV pressure was recorded via a Millar catheter. Dynamic wall stress was assessed by the Law of Laplace – [wall stress = pressure x (radius of curvature / 2 x wall thickness)] – and was measured at the onset of regional shortening and at peak. All measurements were performed at baseline, 8 weeks, and 16 weeks. A "control" setting was recorded at baseline without pacing. Results LBBB induced mechanical dyssynchrony (Fig. A vs. B). By week 16, septal thickness decreased by 29% (p