TNNT2 and chronic obstructive pulmonary disease: ECG: Electrocardiogram, AECOPD: Acute exacerbated chronic obstructive pulmonary disease, COPD: Chronic obstructive pulmonary disease, cTnT: Cardiac troponin T, cTnI: Cardiac troponin I, ICU: Intensive care unit, Hs- cTnT: High sensitivity-cardiac troponin T, BNP: Brain natriuretic peptide