title: Transthoracic impedance compared to magnetic resonance imaging in the assessment of cardiac output.
abstract: BACKGROUND
  Cardiac magnetic resonance imaging is considered the gold-standard method for the calculation of cardiac volumes. Transthoracic impedance cardiography assesses the cardiac output. No studies validating this measurement, in comparison to that obtained by magnetic resonance imaging, are available.
  
  
  OBJECTIVE
  To evaluate the performance of transthoracic impedance cardiography in the calculation of the cardiac output, cardiac index and stroke volume using magnetic resonance imaging as the gold-standard.
  
  
  METHODS
  31 patients with a mean age of 56.7 ± 18 years were assessed; of these, 18 (58%) were males. Patients whose indication for magnetic resonance imaging required pharmacologic stress test were excluded. Correlation between methods was assessed using the Pearson's coefficient, and dispersion of absolute differences in relation to the mean was demonstrated using the Bland-Altman's method. Agreement between methods was analyzed using the intraclass correlation coefficient.
  
  
  RESULTS
  The mean cardiac output by transthoracic impedance cardiography and by magnetic resonance imaging was 5.16 ± 0.9 and 5.13 ± 0.9 L/min, respectively. Good agreement between methods was observed for cardiac output (r = 0.79; p = 0.0001), cardiac index (r = 0.74; p = 0.0001) and stroke volume (r = 0.88; p = 0.0001). The analysis by the Bland-Altman plot showed low dispersion of differences in relation to the mean, with a low amplitude of agreement intervals. Good agreement between the two methods was observed when analyzed by the intraclass correlation coefficient, with coefficients for cardiac output, cardiac index and stroke volume of 0.78, 0.73 and 0.88, respectively (p < 0.0001 for all comparisons).
  
  
  CONCLUSIONS
  Transthoracic impedance cardiography proved accurate in the calculation of the cardiac output in comparison to cardiac magnetic resonance imaging.
authors.affiliation: Universidade Federal Fluminense, Rio de Janeiro, Brasil. hvillacorta@cardiol.br
authors.forename: Humberto
authors.initials: H
authors.lastname: Villacorta Junior
authors.forename: Aline Sterque
authors.initials: AS
authors.lastname: Villacorta
authors.forename: Fernanda
authors.initials: F
authors.lastname: Amador
authors.forename: Marcelo
authors.initials: M
authors.lastname: Hadlich
authors.forename: Denilson Campos de
authors.initials: DC
authors.lastname: Albuquerque
authors.forename: Clerio Francisco
authors.initials: CF
authors.lastname: Azevedo
mesh_terms: D000328:Adult; D000368:Aged; D002302:Cardiac Output / Q000502:physiology*; D002307:Cardiography, Impedance / Q000592:standards*; D005260:Female; D006333:Heart Failure / Q000175:diagnosis; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000592:standards*; D008297:Male; D008875:Middle Aged; D013318:Stroke Volume