title: Assessment of intrathoracic impedance algorithm in the pediatric and adult congenital population.
abstract: BACKGROUND
  Decreased intrathoracic impedance has been used in adults to predict heart failure (HF) exacerbations. A commercial algorithm, OptiVol® (Medtronic Inc., Minneapolis, MN, USA), identifies patients with decreased impedance. We sought to determine the specificity, sensitivity, and positive predictive value (PPV) of OptiVol for predicting HF exacerbation or increased arrhythmia burden in pediatric and adult congenital heart disease (CHD) patients.
  
  
  METHODS
  A multicenter retrospective chart review was undertaken. Inclusion criteria were: (1) <19 years or CHD adults, (2) an implanted device with OptiVol capability, (3) implanted between April 9 and September 6, and (4) follow-up of >30 days postimplant. Clinical events were defined as clinical HF exacerbation/hospital admission, initiation/uptitration of medication, or increased arrhythmia burden.
  
  
  RESULTS
  Seventy-two patients (19 ± 9 years) were identified with the following indications: 20% dilated cardiomyopathy (DCM), 11% hypertrophic cardiomyopathy (HCM), 43% CHD, 15% channelopathy, and 11% other. Thirty-nine had 122 OptiVol crossings (median 2, range 1-11); 30% were linked to a cause. The remaining 33 had no crossing, though 17 had 89 clinical events. The clinical event rate was 19% greater in patients with crossings, though not statistically significant (P = 0.4). The algorithm had a 59% sensitivity, 52% specificity, and 62% PPV. Clinical HF exacerbation and arrhythmia burden did not significantly correlate with decreased impedance though uptitration or initiation of HF medication did correlate significantly (P = 0.03).
  
  
  CONCLUSIONS
  The algorithm sensitivity for pediatric DCM, HCM, CHD, and adult CHD was equivalent to the general adult population. Further studies are warranted to assess whether inaccuracy in prediction is secondary to the algorithm or to differences in the clinical response of pediatric/CHD patients.
authors.affiliation: Division of Pediatric Cardiology, Washington University School of Medicine/St. Louis Children's Hospital, St. Louis, Missouri.
authors.forename: Jennifer N A
authors.initials: JN
authors.lastname: Silva
authors.forename: Nicholas H
authors.initials: NH
authors.lastname: VON Bergen
authors.forename: Anne M
authors.initials: AM
authors.lastname: Dubin
authors.forename: Kathryn K
authors.initials: KK
authors.lastname: Collins
authors.forename: Jiajing
authors.initials: J
authors.lastname: Chen
authors.forename: Tammy M
authors.initials: TM
authors.lastname: Bowman
authors.forename: George F
authors.initials: GF
authors.lastname: Van Hare
mesh_terms: D000465:Algorithms; D002307:Cardiography, Impedance / Q000295:instrumentation*; D009202:Cardiomyopathies / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D006330:Heart Defects, Congenital / Q000150:complications* / Q000503:physiopathology; D006333:Heart Failure / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: device diagnostics; heart failure exacerbation; intrathoracic impedance