Aerobic capacity and functional classification of patients with severe left-ventricular dysfunction

Classes I/II and III of the classification systems of the New York Heart Association (NYHA), Canadian Cardiovascular Society (CCS) and American Medical Association (AMA) were compared with each other and with the Weber classification (O2 uptake, VO2/kg during treadmill walking) in 35 male patients with severe left ventricular dysfunction. Measured end points were ventilatory threshold (VT) and peak exercise. Also investigated was whether the CCS and AMA scales, due to their more stringent differentiation, are more precise than the NYHA system in determining a limited physical capacity and whether there are other differentiating factors useful in classification which may be derived from cardiopulmonary exercise testing. At the VT, the mean VO2/kg did not differ significantly in any classification system between classes I/II and III (12.8 +/- 2.5 vs. 11.1 +/- 2.3 ml/kg/min) and corresponded to Weber class B. At peak exercise, the mean VO2/kg only differed significantly within the NYHA classification; classes I/II (16.3 +/- 3.1 ml/kg/min) corresponded to Weber class B, and class III (13 +/- 3 ml/kg/min) to Weber class C. The individual values displayed a large scatter. Factors differing in classes I/II and III of all three systems at peak exercise were the ventilatory equivalent of O2 and CO2 as well as end-tidal partial pressure for O2 and CO2. At VT these factors showed a separating character only in the AMA classification. It is not possible to determine objective functional impairment by use of the NYHA, CCS and AMA systems because they are not analogous to the Weber system. Nevertheless, these classification systems can be used for clinical assessment and follow-up.