Monitoring Intrathoracic Impedance with an Implantable Defibrillator Reduces Hospitalizations in Patients with Heart Failure


  • Conflict of interest disclosure: Annamaria Varbaro, Alessandra Denaro, and Sergio Valsecchi are employees of Medtronic, Inc. No other conflict of interest exists.

Address for reprints: Maurizio Lunati, M.D., Cardiology Department, Ospedale Niguarda Ca' Granda, Piazza Ospedale Maggiore, 3, 20162 Milano, Italy. Fax: +39-0266101716; e-mail:


Purpose: Some implantable cardioverter-defibrillators (ICDs) are now able to monitor intrathoracic impedance. The aim of the study was to describe the use of such monitoring in clinical practice and to evaluate the clinical impact of the fluid accumulation alert feature of these ICDs.

Methods and Results: Five hundred thirty-two heart failure (HF) patients implanted with these ICDs were followed up for 11 ± 7 months. A clinical event (CE) was deemed to have occurred if it resulted in hospitalization or milder manifestations of HF deterioration. Three hundred sixty-two acute decreases in intrathoracic impedance (Z events) occurred in 230 patients. Of these episodes, 171 (47%) were associated with a CE within 2 weeks of the Z event. In another 71 (20%) Z events, drug therapy was adjusted despite the absence of overt signs of clinical deterioration. The rate of unexplained Z events was 0.25 per patient-year and 25 hospitalizations were not associated with Z events. The audible alert was disabled in a group of 102 patients (OFF group). HF hospitalizations occurred in 29 (7%) patients in the ON group and 20 (20%, P < 0.001) patients in the OFF group. The rate of combined cardiac death and HF hospitalization was lower in patients with Alert ON (log-rank test, P = 0.007).

Conclusions: The ICD reliably detected CE and yielded low rates of unexplained and undetected events. The alert capability seemed to reduce the number of HF hospitalizations by allowing timely detection and therapeutic intervention.