X-Change HF - Exchange of the Existing Pacemaker/ICD in Bradycardia Patients Suffering From Heart Failure

The goal of X-Change HF is to estimate the effect of biventricular stimulation in patients who need antibradycardia ventricular stimulation (more than 80%); are eligible for the exchange of an old pacemaker or implantable cardioverter defibrillator (ICD); and have ventricular dysfunction (left ventricular ejection fraction \[LVEF\] \< 35%). All patients eligible for participation in the study will be upgraded with a cardiac resynchronization therapy (CRT)-device and receive either right ventricular or biventricular stimulation in a crossover protocol. The endpoint is functional performance measured by spiroergometry.