Comparative measures of systolic ejection during treadmill exercise by impedance cardiography and Doppler
P N Kizakevich1, S M Teague, D B Nissman
1Research Triangle Institute, Biomedical Engineering Program Office, Research Triangle Park, NC 27709.
Insights
Impedance cardiography (ICG) measurements closely correlate with Doppler echocardiography for assessing systolic ejection dynamics. While timing features of ICG show moderate agreement, alternative impedance metrics may enhance accuracy for valvular events.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Diagnostic Imaging
Background:
- Systolic ejection dynamics are crucial for cardiovascular health assessment.
- Impedance cardiography (ICG) offers a non-invasive method to evaluate these dynamics.
- Correlating ICG with Doppler echocardiography can validate its clinical utility.
Purpose of the Study:
- To compare systolic ejection dynamics measured by ICG with simultaneous Doppler echocardiography.
- To assess the accuracy of ICG in normal subjects and coronary artery disease patients during exercise.
- To evaluate specific ICG indices against Doppler-derived parameters.
Main Methods:
- Simultaneous monitoring of patients using ICG and Doppler echocardiography during treadmill exercise.
- Analysis of ensemble-averaged ECG, ICG, dZ/dt, and Doppler waveforms.
- Correlation analysis of timing events (aortic valve opening/closure) and acceleration indices.
Main Results:
- Strong correlation (r=0.86) between ICG and Doppler for peak ejection velocity timing.
- Moderate correlations (r=0.69-0.74) for aortic valve closure timing and impedance acceleration indices.
- ICG waveforms reflect both aortic blood velocity and acceleration.
Conclusions:
- ICG is a viable tool for assessing systolic ejection dynamics, showing good correlation with Doppler echocardiography.
- Specific timing features derived from the first derivative of ICG (dZ/dt) may require refinement for optimal accuracy.
- Exploring alternative impedance cardiography features could improve the assessment of aortic valvular events.
Abstract:
Measurements of systolic ejection dynamics by impedance cardiography were compared with simultaneous Doppler echocardiography in normal subjects and coronary artery disease patients. Patients with chest pain admitted for elective coronary angiography were monitored by simultaneous impedance cardiography and Doppler echocardiography before, during, and after treadmill exercise. Ensemble-averaged ECG, impedance cardiogram (ICG), the first derivative of ICG (dZ/dt), and Doppler waveforms were analyzed to identify systolic ejection variables. The timing of aortic valve opening was well correlated (r = 0.78) the timing of peak ejection velocity was very well correlated (r = 0.86), and the timing of aortic valve closure was moderately correlated (r = 0.69 and r = 0.73) in these subjects. The thoracic electrical impedance acceleration and normalized impedance acceleration indices were moderately correlated with Doppler model acceleration (r = 0.74, r = 0.79). The impedance cardiogram waveforms are of complex origin and are related to both aortic blood velocity and aortic blood acceleration. Users of dZ/dt timing features for determining aortic valvular events might consider alternative impedance features to improve ejection time accuracy.
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