Abstract Background The relationship between baseline heart rates and cardiac function in patients with atrial fibrillation (AF) remains unknown, as does its impact on long-term outcomes. Methods Patients with newly diagnosed AF and available echocardiography images were included. Conventional echocardiography measurement and myocardial deformation analyses using two-dimensional speckle-tracking echocardiography were performed during AF. Clinical endpoints included first-time hospitalization for ischemic stroke, heart failure (HF), all-cause mortality, and composite endpoint. Results Patients were categorized into groups according to baseline heart rates: 40-59, 60-69, 70-79, 80-89, 90-99, 100-109, 110-119, and ≥120 beats per minutes (bpm). As heart rates increased, there was a stepwise decrease of peak atrial longitudinal systolic strain (PALS: 14.6 ± 5.3%, 14.7 ± 5.5%, 14.1 ± 4.6%, 13.4 ± 4.7%,12.6 ± 4.9%, 12.1 ± 4.5%, 11.2 ± 5.2% and 10.8±4.1% in 40-59, 60-69, 70-79, 80-89, 90-99, 100-109, 110-119, and ≥120 bpm groups, respectively; P < 0.001)) and LV strain (-13.8 ± 3.9%, -14.5 ± 4.0%, -13.4 ± 3.4%, -13.4 ± 3.6%, -12.5 ± 3.6%, -11.9 ± 3.8%, -10.3 ± 3.8%, and -10.2 ± 3.8%, in 40-59, 60-69, 70-79, 80-89, 90-99, 100-109, 110-119, and ≥120 bpm groups, respectively; P < 0.001)(Figure). The lowest risk of composite endpoint was observed for patients whose heart rate between 60 to 69 bpm (Figure). Compared to the 60-69 heart rate group, faster heart rates were associated with increased risk of ischemic stroke (adjusted hazard ratios [aHR] 4.448 in the ≥120 bpm group), HF (aHR 1.909 in the ≥120 bpm group), mortality (aHRs 2.487, 2.810, 4.569, 4.760 in the 90-99, 100-109, 110-119, and ≥120 bpm groups, respectively), and composite endpoint (aHRs 2.034, 2.349, 3.492 in the 100-109, 110-119, and ≥120 bpm groups, respectively) (all P < 0.05). Conclusion In patients with AF, heart rate is closely linked to cardiac function and plays a pivotal role in long-term prognosis. Faster heart rates were associated with worse LA/LV functions and increased risk of clinical events. Favorable outcomes were found at heart rates below 100 bpm, with even better LA/LV function noted at heart rates below 80 bpm.
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