Threshold Crossing of Device-Based Intrathoracic Impedance Trends Identifies Relatively Increased Mortality Risk

Study Questions:

Do reductions in intrathoracic impedance (IImp) have prognostic significance in patients with heart failure (HF)?


This was a retrospective analysis of uploaded data from remote monitoring of 21,217 patients (mean age 68 years) with an implantable cardioverter-defibrillator (ICD). IImp trends were analyzed and an early threshold crossing (ETC) was defined as a reduction in IImp, resulting in a rise in the fluid index above the nominal threshold of 60 ohm-days. The mean duration of remote monitoring was 20 months. Mortality data were collected starting at 6 months of follow-up from a device registry and the Social Security Death Index.


In the first 6 months of monitoring, 36% of patients had a mean of 1.3 ETCs. After the first 6 months of monitoring, the mortality rate was significantly higher in the patients with ETCs (11.2%) than in the patients without ETCs (5.5%). ETCs were associated with approximately a twofold higher risk of death independent of age, gender, ICD shocks, atrial fibrillation, and cardiac resynchronization therapy. The risk of death was lower when there were no threshold crossings after the first 6 months.


The authors concluded that ETCs are associated with a higher risk of death in patients with an ICD.


A reduction in IImp correlates with pulmonary congestion and has been used as an indicator of decompensation in patients with HF. The results of this study validate the clinical significance of IImp monitoring by demonstrating that ETCs are associated with a higher risk of death independent of ventricular tachycardia/fibrillation.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure

Keywords: Risk, Defibrillators, Follow-Up Studies, Shock, Ventricular Fibrillation, Tachycardia, Cardiac Resynchronization Therapy, Heart Diseases, Death, Cardiology, Heart Failure

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