[Functional capacity as a criterion for patient selection--too poor or too good for CRT?].

The article analyses the status of functional tests used in patient selection for cardiac resynchronization therapy (CRT). Based on published randomized trials, the NYHA classification, the quality of life score, the 6-minute walk and the cardio-pulmonary exercise test (CPX) are reviewed. The NYHA classification is a weak and unspecific test and should be used only as a basic consideration in patient selection. The 6-minute walk test shows a wide spread of values and high dependency on patients' motivation. Patients' functional capacity is measured most objectively by the CPX test, which additionally stratifies prognosis. We conclude that functional capacity is an important criterion in patient selection for CRT. However, primary functional status is of minor importance in estimating the expected functional benefit since multiple factors influence the success of CRT.