EPIT-HF survey chronického srdcového zlyhávania s redukovanou, mid-range a zachovanou ejekčnou frakciou na Slovensku = EPIT-HF survey of chronic heart failure with reduced, mid-range and preserved ejection fraction in Slovakia. Part 1: Focus on epidemiology / Dúbrava J., Šidlo R.. Cardiology letters Vol. 26, no. 6 (2017), s. 323-335