Usefulness of anaerobic threshold to peak oxygen uptake ratio to determine the severity and pathophysiological condition of chronic heart failure.

BACKGROUND

Anaerobic threshold (AT) and peak oxygen uptake (V˙O) are well known as indicators of severity and prognosis of heart failure. Since these parameters are regulated by many factors, multiple organ dysfunction may occur in chronic heart failure, and these two parameters would vary among patients. However, it is not clear whether AT and peak V˙O deteriorate similarly. Therefore, we planned to compare the degree of deterioration of these two parameters using a ratio of AT and peak V˙O (%AT/peak), and evaluated its significance in heart failure subjects.

METHODS

One hundred ninety-four stable heart failure patients who had optimal medical treatment for at least 3 months were enrolled. Cardiopulmonary exercise testing, echocardiography, and blood sampling were examined within one week. Since %AT/peak varied from 50.3% to 108.5%, we divided patients into tertiles of %AT/peak [Group A, 50.1-70.0 (n=112), Group B, 70.1-90.0 (n=64), Group C, 90.1-110.0 (n=18)], and compared factors relating with skeletal muscle and heart failure among these 3 groups.

RESULTS

In Group A, ratio of measured AT against predicted value (%AT) and measured peak V˙O against predicted value (%peak V˙O) were similar (80.3±19.0% and 80.4±17.1%, respectively). Peak V˙O became lower as %AT/peak increased (Group B; 65.6±14.8%, p<0.01 vs. Group A, Group C; 38.3±9.7%, p<0.01 vs. Group B). On the other hand, %AT in Group B (77.1±18.5%) was similar to Group A, and diminished in Group C (58.0±8.2%, p<0.05 vs. Group B). Peak work rate and lean body mass were smaller in Group B than those in Group A. Although, left ventricular ejection fraction and E/E' deteriorated in Group B compared with Group A, plasma B-type natriuretic peptide and estimated glomerular filtration rate stayed constant in Group B and deteriorated in Group C.

CONCLUSIONS

%AT/peak showed negative correlation with peak V˙O. In chronic heart failure, muscle weakness occurs at an early stage, and this can be evaluated using %AT/peak.