Intrathoracic Impedance Monitoring in Patients With Heart Failure

BACKGROUND: Cardiac resynchronization therapy/defibrillators (CRTD) and implantable cardioverter defibrillators (ICD) with continuous intrathoracic impedance monitoring might provide an early warning of thoracic fluid retention. In contrast, volume loss events such as dehydration and bleeding are also common events in heart failure patients treated with diuretics and anticoagulants. The correlation between intrathoracic impedance and a volume loss event is not known. METHODS AND RESULTS: This study evaluated the association between intrathoracic impedance and volume loss events in 36 patients with chronic heart failure (New York Heart Association [NYHA] II, III and IV) who had received CRTD/ICD implantation. Elevation of thoracic impedance above the reference line was defined as a positive deviation of thoracic impedance (PDI). This study recorded 249 PDIs including 60 spike PDIs defined as over 5 ohms elevation from the reference line and 17 large PDIs as over 5 ohms elevation and continuing for at least 4 days. Clinically, 96 dehydration events and 2 bleeding events were observed over a 1-year period. The sensitivity and positive predictive value (PPV) for spike PDI was 31.6% and 51.7%, respectively, while those for large PDI were 17.3% and 100%, respectively. CONCLUSIONS: A large PDI reflected dehydration and bleeding events with a high PPV in severe heart failure patients. The large PDI criteria might therefore be useful for predicting volume loss events in chronic heart failure patients.