Primary Outcome Measures:
- clinical efficacy and value of ambulatory intrathoracic impedance measurement of the Optivol alert as an indicator of decompensated heart failure reflected by sensitivity and positive predictive value [ Time Frame: end of follow-up ]
Secondary Outcome Measures:
- influence of left ventricular filling pattern and brain natriuretic level on the positive predictive value of the Optivol alert [ Time Frame: end of follow-up ]
Patients who have a Medtronic (R) ICD equipped with the Optivol (TM) impedance monitoring will be included in your study after informed consent. The OptiVol (TM) feature will be activated and at baseline data is collected (blood sample including BNP, electrocardiography, echocardiography, chest X-ray and ICD check-up). During follow-up patients will be re-assessed in case of an OptiVol alert or in case of heart failure.