[1] Med Univ Plovdiv, Cardiol Sect, Dept Internal Dis 1, Plovdiv, Bulgaria
[2] Natl Heart Hosp, Dept Noninvas Cardiol, Sofia, Bulgaria
[3] Med Univ Pleven, Pleven, Bulgaria
[4] Natl Heart Hosp, Clin Cardiol, Sofia, Bulgaria
[5] Med Univ Varna, Varna, Bulgaria
[6] Med Univ Pleven, Dept Cardiol, Pulmunol, Endocrinol, Pleven, Bulgaria
[7] Med Univ Sofia, Fac Publ Hlth Prof Tsekomir Vodenicharov MD DSc, Sofia, Bulgaria
[8] Boehringer Ingelheim RCV GmbH & Co KG Bulgarian B, Sofia, Bulgaria