Reduced Left Atrial Emptying Fraction and Chymase Activation in Pathophysiology of Primary Mitral Regurgitation

Visual Abstract
Highlights • Extensive LA fibrosis is related to an increase in LA size and decrease in total LA EF. This supports the contention that the LA is not merely a bystander of MR but rather is actively involved in the pathophysiology of MR. • Chymase is plentiful in the human heart, especially in the LA, and correlates with extracellular matrix accumulation in primary MR. • Because of the unreliability of the LV ejection fraction in primary MR, future studies may consider LA size and total LA EF for timing of surgical intervention of asymptomatic moderate to severe MR.
Summary Increasing left atrial (LA) size predicts outcomes in patients with isolated mitral regurgitation (MR). Chymase is plentiful in the human heart and affects extracellular matrix remodeling. Chymase activation correlates to LA fibrosis, LA enlargement, and a decreased total LA emptying fraction in addition to having a potential intracellular role in mediating myofibrillar breakdown in LA myocytes. Because of the unreliability of the left ventricular ejection fraction in predicting outcomes in MR, LA size and the total LA emptying fraction may be more suitable indicators for timing of surgical intervention.