Left Atrial Dynamics During Exercise in Mitral Regurgitation of Primary and Secondary Origin Pathophysiological Insights by Exercise Echocardiography Combined With Gas Exchange Analysis

OBJECTIVES The aim of this study was to identify the pattern of exercise left atrial (LA) dynamics, its gas exchange correlates, and prognosis in mitral regurgitation (MR) of primary and secondary origin. BACKGROUND The adaptive response and clinical significance of LA function during exercise in MR is undefined. METHODS A total of 196 patients with MR (81 with primary MR, 115 with secondary MR) and 54 control subjects underwent exercise stress echocardiography and cardiopulmonary exercise testing with LA function assessment. Patients with MR were divided into 4 groups according to etiology and severity using a cutoff of 3+. RESULTS LA dynamics was studied using speckle-tracking echocardiography. Compared with control subjects, patients with MR had a lower LA strain and strain rate at rest. Exercise LA strain and LA strain rate progressively worsened from primary MR <3+ through secondary MR >= 3+. In primary MR, some reserve in exercise LA strain and LA strain rate was observed, but not in secondary MR. In secondary MR, LA strain at rest and during exercise (18.1 +/- 5.7 s(-1), 18.3 +/- 6.9 s(-1), 18.6 +/- 5.5 s(-1), 13.9 +/- 3.8 s(-1)) and peak oxygen consumption (11.7 +/- 3 ml/min/kg) were decreased compared with the other groups. In secondary MR $3+, the slope of ventilation versus carbon dioxide was higher compared with the other groups: 35.1 (interquartile range [IQR]: 29.0 to 44.2) compared with control subjects: 26.5 (IQR: 24.4 to 29.0); patients with primary MR <3+ (26.9; IQR: 24.0 to 31.9); those with primary MR >3+ (25.5; IQR: 23.4 to 29.0); and those with secondary MR <3+ (29.5; IQR: 26.5 to 33.7) (p < 0.05 for all). A progressive impairment in exercise LA mechanics combined with limited cardiac output increase and right ventricular-to-pulmonary circulation uncoupling was observed from primary to secondary MR. LAS during exercise was predictive of all-cause mortality and hospitalization for heart failure. CONCLUSIONS In MR of any origin, exercise LA reservoir and pump function are impaired. For similar MR extent, secondary MR exhibits worse atrial function, resulting in the lowest exercise performance, limited cardiac output increase, impaired right ventricular-to-pulmonary circulation coupling, and the highest event rate. (C) 2020 by the American College of Cardiology Foundation.