<qa>  What is the standard operation procedure of the Medical Clinic I?The surgery is then terminated as planned and postoperative care is performed according to the standard operation procedure SOP of the Medical Clinic I. Within the framework of a control visit routinely performed in the Medical Clinic I , an echocardiographic follow-up of heart failure, a history assessment and a laboratory-based blood analysis are performed 6 months after CRT implantation. In the context of this visit peripheral venous blood is collected again for the study. In addition, the 6-minute walk test is performed once more and the patient receives the same questionnaire again. 