Atrial fibrillation (AF) patients with mid-range left ventricular ejection fraction (mrEF) of 40-49% have neither preserved (pEF > 50%) nor reduced (rEF < 40%) EF and are increasingly being recognized as a distinct group with specific clinical risks. We aimed to retrospectively investigate clinical characteristics and associated thrombotic, bleeding and mortality risks of mrEF in comparison to pEF and rEF in a cohort of 1000 non-valvular AF patients presenting in our institution during the period 2013-2018. Patients with mrEF presented with older age (P < 0.001) and a higher frequency of arterial hypertension (P = 0.001) in comparison to both pEF and rEF patients. In comparison to pEF, mrEF patients were more likely to have diabetes mellitus (P = 0.004), lower HDL-cholesterol (P < 0.001) and lower estimated glomerular filtration rate (P < 0.001), significantly higher CHADS-VAS score (P < 0.001), significantly higher HAS-BLED score (P = 0.002) and had a higher likelihood of receiving anticoagulant therapy, mostly warfarin (P = 0.001). In addition, mrEF patients had a significantly higher risk of thrombotic events (HR = 2.22; P = 0.015), death (HR = 1.71; P = 0.005) and composite endpoint of thrombosis, bleeding or death (HR = 1.65; P = 0.003) in comparison to pEF patients, but did not significantly differ in comparison to rEF patients. There was no significant difference regarding major bleeding risk. Associations with clinical outcomes remained statistically significant in multivariate models independently of CHADS-VAS. Our findings support defining AF patients with mrEF as a subgroup with distinct clinical characteristics and increased risk for thrombotic events and death, irrespective of predetermined CHADS-VAS risk. These patients seem to require special clinical considerations and more intensive control of cardiovascular risk factors.

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