title: Prediction of All-Cause Mortality Based on the Direct Measurement of Intrathoracic Impedance.
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.
  
  
  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.
authors.affiliation: 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.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Zile
authors.affiliation: 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.).
authors.forename: Vinod
authors.initials: V
authors.lastname: Sharma
authors.affiliation: 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.).
authors.forename: James W
authors.initials: JW
authors.lastname: Johnson
authors.affiliation: 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.).
authors.forename: Eduardo N
authors.initials: EN
authors.lastname: Warman
authors.affiliation: 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.).
authors.forename: Catalin F
authors.initials: CF
authors.lastname: Baicu
authors.affiliation: 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.).
authors.forename: Tom D
authors.initials: TD
authors.lastname: Bennett
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D058406:Cardiac Resynchronization Therapy; D058409:Cardiac Resynchronization Therapy Devices; D002307:Cardiography, Impedance / Q000295:instrumentation; D002423:Cause of Death; D016208:Databases, Factual; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000295:instrumentation; D005260:Female; D006333:Heart Failure / Q000175:diagnosis / Q000401:mortality* / Q000503:physiopathology / Q000628:therapy; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D013686:Telemetry / Q000295:instrumentation; D013997:Time Factors; D016896:Treatment Outcome
keywords: all-cause mortality; heart failure; impedance; risk