Key result
Low baseline intrathoracic impedance linked to ~38% higher all-cause mortality.
Why the study?
Does directly measured baseline intrathoracic impedance predict all-cause mortality in patients with implanted ICD or CRT-D devices?
Cohort (n=146,238)
Yes
Does directly measured baseline intrathoracic impedance predict all-cause mortality in patients with implanted ICD or CRT-D devices?
Directly measured intrathoracic impedance independently predicts all-cause mortality in device patients and adds prognostic value to established fluid index thresholds.
May refine mortality risk assessment in ICD/CRT-D patients; leaves open whether impedance-guided management improves outcomes.
BACKGROUND: Intrathoracic impedance-derived OptiVol fluid index calculated using implanted devices has been shown to predict mortality; direct measurements of impedance have not been examined. We hypothesized that baseline measured impedance predicts all-cause mortality; changes in measured impedance result in a change in the predicted mortality; and the prognostic value of measured impedance is additive to the calculated OptiVol fluid index. METHODS AND RESULTS: A retrospective analysis of 146,238 patients within the Medtronic CareLink database with implanted devices was performed. Baseline measured impedance was determined using daily values averaged from month 6 to 9 after implant and were used to divide patients into tertiles: group L = low impedance, ≤ 65 ohms; group M = medium impedance, 66 to 72 ohms; group H = high impedance, ≥ 73 ohms. Change in measured impedance was determined from values averaged from month 9 to 12 post implant compared with the 6- to 9-month values. OptiVol fluid index was calculated using published methods. All-cause mortality was assessed beginning 9 months post implant; changes in mortality was assessed beginning 12 months post implant. Baseline measured impedance predicted all-cause mortality; 5-year mortality for group L was 41%, M was 29%, and H was 25%, P < 0.001 among all groups. Changes in measured impedance resulted in a change in the predicted mortality; the prognostic value of measured impedance was additive to the OptiVol fluid index. CONCLUSIONS: Direct measurements of intrathoracic impedance using an implanted device can be used to stratify patients at varying mortality risk.
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Zile et al. (2015) conducted a cohort in Heart failure with implanted ICD or CRT-D devices (n=146,238). Low baseline intrathoracic impedance (≤ 65 ohms) vs. Medium intrathoracic impedance (66-72 ohms) was evaluated on All-cause mortality (HR 1.38, 95% CI 1.33-1.42, p=<0.001). Low baseline intrathoracic impedance (≤ 65 ohms) was associated with a higher risk of all-cause mortality compared to medium impedance (66-72 ohms) with an adjusted HR of 1.38.
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