Michael R Zile1, Vinod Sharma2, James W Johnson2, Eduardo N Warman2, Catalin F Baicu2, Tom D Bennett2. 1. From the Division of Cardiology, Department of Medicine, Medical University of South Carolina and RHJ Department of Veterans Affairs Medical Center, Charleston (M.R.Z., C.F.B.); and Medtronic, Plc., Minneapolis, MN (V.S., J.W.J., E.N.W., T.D.B.). zilem@musc.edu. 2. From the Division of Cardiology, Department of Medicine, Medical University of South Carolina and RHJ Department of Veterans Affairs Medical Center, Charleston (M.R.Z., C.F.B.); and Medtronic, Plc., Minneapolis, MN (V.S., J.W.J., E.N.W., T.D.B.).
Abstract
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.
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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