Reproducibility of impedance cardiography parameters in outpatients with clinically stable coronary artery disease.

BACKGROUND Impedance cardiography (ICG) is a noninvasive method of determining hemodynamic parameters. It is clinically important to determine whether any change in ICG parameters occur due to changes in disease status or therapeutic interventions, or due to normal hemodynamic and technology variability. The objective of this study was to establish the intra- and inter-day reproducibility of ICG in a stable population with coronary artery disease (CAD). METHODS A prospective, time series design was used. The study group consisted of 96 clinically stable CAD patients in an outpatient cardiac rehabilitation program. Measurements of ICG hemodynamic parameters were obtained at four points in time: after 5 and 10 min of rest on the first day and after 5 and 10 min of rest on a second day, 1 week later. RESULTS There were small but significant intra-day changes between the 5- and 10-min hemodynamic measures. Mean absolute percent changes in intra-day hemodynamic measures were <8%. High intra-day correlation was observed, ranging from 0.85 for mean arterial pressure to 0.99 for thoracic fluid content. There were expectedly larger inter-day hemodynamic variation of up to 18% and lower inter-day correlation for all ICG parameters ranging from 0.66 to 0.88. CONCLUSIONS Impedance cardiography measurements demonstrate both intra- and inter-day reproducibility within clinically acceptable ranges in a clinically stable population of CAD patients. The expected ranges of variation can be used to gauge whether a patient's hemodynamic status has changed because of disease or intervention.