Left atrium in cardiac resynchronization therapy: Active participant or innocent bystander

BACKGROUND: Cardiac resynchronization therapy (CRT) is an established treatment for patients with advanced heart failure that results in improvement of left ventricle (LV) systolic function and LV reverse remodeling. This may have a positive effect on the size and the function of the left atrium (LA). We assessed the LA function, dimensions, and volumes before and after CRT implantation. METHODS: A total of 37 patients with mean age of 55.3 ± 9.64 years including 11 (29.7%) females, having symptomatic heart failure [ejection fraction (EF) <35%, left bundle branch block >120 ms, with New York Heart Association III or ambulatory class IV] were enrolled, and underwent CRT implantation. M-mode, two-dimensional (2D) echocardiography, tissue Doppler imaging, and 2D strain (ɛ) imaging were done assessing LV volumes, ejection fraction, and diastolic function, LA diameter, area, maximal and minimal volumes, LA EF, and longitudinal strain (ɛ). Patients were reassessed after 3 months. A reduction in LV end-systolic volume of ≥10% was defined as volumetric responders to CRT. Patients with decompensated New York Heart Association class IV, sustained atrial arrhythmias, rheumatic or congenital heart diseases, nonleft bundle branch block, and those who were poorly echogenic, were excluded. RESULTS: Twenty-four (64.8%) patients were volumetric responders (group A). Both groups were matched regarding demographic, clinical, electrocardiographic, and echocardiographic criteria apart from the LA dimension and volumes which were significantly lower in the responders group prior to CRT. At the end of the follow-up, only the responders group had further significant reduction in LA diameter (41.6 ± 1.67 vs. 43.88 ± 1.82 mm, p < 0.01), maximal volume (62.2 ± 18.3 vs. 73.04 ± 21.78 ml, p < 0.01), minimal volume (32.6 ± 12.3 vs. 41.8 ± 13.97, p < 0.01), together with a significant increase in LA EF (48.3 ± 11.3 vs. 41.99 ± 13.9, p < 0.01), positive longitudinal strain (16.59% ± 5.89 vs. 12.45% ± 6.12, p < 0.01), and negative longitudinal strain (−3.3 ± 1.9 vs. −1.62 ± 1.2, p < 0.01) compared to baseline readings, a finding that was not present in the nonresponders group. In addition, atrial fibrillation was significantly higher in the nonresponders group. Baseline LA diameter and volumes were found to be independent predictors of response to CRT by multivariate analysis. CONCLUSIONS: CRT induces LA anatomic, electrical, and structural reverse remodeling that could be assessed by conventional 2D echocardiography and 2D (ɛ) strain imaging. LA dimension and volumes were independent predictors of response to CRT and can help in selection of candidates for it.