A comparison of systolic time intervals measured by impedance cardiography and carotid pulse tracing.

: The purpose of this study was to compare the systolic time intervals (STI) obtained by impedance cardiography and by the conventional carotid technique. This comparison was done with respect to: 1) correlations between variables obtained by the two methods, 2) ability to reflect drug-induced changes, 3) reliability in terms of reproducibility and 4) heart rate dependency of the variables measured. The study included 25 unmedicated patients with ischaemic heart disease and 36 healthy subjects. We obtained significant correlations between STI-variables measured by the two methods (p less than 0.001) and found that left ventricular ejection times were longer when determined by the carotid technique (p less than 0.01). We found a significant correlation between drug-induced changes in STI-variables measured by the two methods (p less than 0.001). Both methods had a high degree of reproducibility and this parameter was significantly better within the same day, when impedance cardiography was used (p less than 0.01). The error due to the reading of STI-tracings obtained by impedance cardiography was very small when performed by the same observer. We found the pre-ejection period to be independent upon heart rate, while the left ventricular ejection time depended upon this parameter. We conclude that impedance cardiography and carotid technique differ with respect to the measurement of left ventricular ejection times, but not with respect to the measurement of other STI-variables. We furthermore conclude that both methods are reliable, but we recommend the use of impedance cardiography because it is easier to apply, it may be more precise and it can be used for simultaneous measurements of other haemodynamic variables.