title: Intrathoracic and ventricular impedances are associated with changes in ventricular volume in patients receiving defibrillators for CRT.
abstract: BACKGROUND
  Some implantable cardioverter defibrillators (ICD) are able to monitor intrathoracic impedance to detect pulmonary fluid overload. This is achieved by measuring impedance between the ICD case and the right ventricular (RV) lead. We hypothesized that the measured impedance would rise with improvement in left ventricular (LV) volumes during cardiac resynchronization therapy (CRT), and that such impedance changes would be more apparent when measured with an alternative pacing vector.
  
  
  METHODS
  We analyzed echocardiographic and impedance data from heart failure patients implanted with a CRT-ICD capable of intrathoracic impedance measurement for fluid accumulation diagnosis, and LV pacing impedance recording for lead integrity monitoring.
  
  
  RESULTS
  In 127 out of 170 patients that received de novo CRT implantation, the LV end-systolic volume (LVESV) decreased at 6-month follow-up (LVESV at 6 month-LVESV at baseline <0: group A). For the remaining 43 patients (group B) the change was > or = 0. Despite comparable values at baseline (P = 0.262), the impedances of groups A and B gradually diverged soon after the implant, resulting in significant difference between the two groups at the 6-month visit (P = 0.001). The changes in LV dimensions produced larger differences between groups in the impedance measured between the LV and the RV leads (P < 0.001). The regression analysis demonstrated an inverse correlation between paired changes of volume and intrathoracic impedance. Higher correlation coefficient was obtained using the LV-to-RV measurement vector (r =-0.635, P < 0.001).
  
  
  CONCLUSIONS
  The changes in ICD-measured impedance seem associated with the LV volume changes induced by CRT. Specifically, the LV-to-RV impedance estimations seem to better correlate with paired changes of ventricular volumes.
authors.affiliation: Division of Cardiology, Santa Maria del Carmine Hospital, Corso Verona, 4, 38068 Rovereto (TN), Italy. mainesdrmax@hotmail.com
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Maines
authors.forename: Maurizio
authors.initials: M
authors.lastname: Landolina
authors.forename: Maurizio
authors.initials: M
authors.lastname: Lunati
authors.forename: Gabriele
authors.initials: G
authors.lastname: Lonardi
authors.forename: Alessia
authors.initials: A
authors.lastname: Pappone
authors.forename: Alessandro
authors.initials: A
authors.lastname: Proclemer
authors.forename: Gabriele
authors.initials: G
authors.lastname: Zanotto
authors.forename: Massimo
authors.initials: M
authors.lastname: Santini
authors.forename: Annamaria
authors.initials: A
authors.lastname: Varbaro
authors.forename: Marco
authors.initials: M
authors.lastname: Vimercati
authors.forename: Sergio
authors.initials: S
authors.lastname: Valsecchi
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D017147:Defibrillators, Implantable; D004452:Echocardiography; D017097:Electric Impedance; D005260:Female; D005500:Follow-Up Studies; D006333:Heart Failure / Q000628:therapy; D006352:Heart Ventricles / Q000033:anatomy & histology*; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D009929:Organ Size; D013909:Thorax / Q000502:physiology*; D016276:Ventricular Function / Q000502:physiology*