title: Influence of electrode positioning on accuracy and reproducibility of electrical velocimetry cardiac output measurements.
abstract: Electrical velocimetry (EV) is one of the most recent adaptions of impedance cardiography. Previous studies yielded diverging results identifying several factors negatively influencing accuracy. Although electrode arrangement is suspected to be an influencing factor for impedance cardiography in general, no data for EV is available. We aimed to prospectively assess the influence of electrode position on the accuracy and reproducibility of cardiac output (CO) measurements obtained by EV. Two pairs of standard electrocardiographic electrodes were placed at predefined positions of the thorax in 81 patients. The inter-electrode gap was varied between either 5 or 15 cm by caudal movement of the lowest electrode. Measurements were averaged over 20 s and performed twice at each electrode position. Reference values were determined using cardiac magnetic resonance imaging (CMR). Mean bias was 1.2  ±  1.6 l min(-1) (percentage error 22  ±  28%) between COCMR and COEV at the 5 cm gap significantly improving to 0.5  ±  1.6 l min(-1) (8  ±  28%) when increasing the gap (p  <  0.0001). The mean difference between repeated measurements was 0.0  ±  0.3 l min(-1) for the 5 cm and 0.1  ±  0.3 l min(-1) for the 15 cm gap, respectively (p  =  0.3). The accuracy of EV can be significantly improved when increasing the lower inter-electrode gap still exceeding the Critchley and Critchley recommendations. Therefore, absolute values should not be used interchangeably in clinical routine. As the reproducibility was not negatively affected, serial hemodynamic measurements can be reliably acquired in stable patients when the electrode position remains unchanged.
authors.affiliation: 1st Department of Medicine (Cardiology, Angiology, Pulmonology, Intensive Care), University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
authors.forename: Frederik
authors.initials: F
authors.lastname: Trinkmann
authors.forename: Manuel
authors.initials: M
authors.lastname: Berger
authors.forename: Julia D
authors.initials: JD
authors.lastname: Michels
authors.forename: Christina
authors.initials: C
authors.lastname: Doesch
authors.forename: Christel
authors.initials: C
authors.lastname: Weiss
authors.forename: Stefan O
authors.initials: SO
authors.lastname: Schoenberg
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Akin
authors.forename: Martin
authors.initials: M
authors.lastname: Borggrefe
authors.forename: Theano
authors.initials: T
authors.lastname: Papavassiliu
authors.forename: Joachim
authors.initials: J
authors.lastname: Saur
mesh_terms: D002302:Cardiac Output; D002307:Cardiography, Impedance; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012212:Rheology / Q000295:instrumentation*