Age-dependent and 'pathologic' changes in ICG waveforms resulting from superposition of pre-ejection and ejection...

Area of Science:

• Biomedical Engineering
• Cardiovascular Physiology
• Medical Instrumentation

Background:

• Impedance cardiography (ICG) is a non-invasive method for evaluating cardiac function, including left ventricular stroke volume and contractility.
• Accurate identification of ejection onset and key waveform parameters in ICG is crucial but often challenging, particularly in cardiac patients, due to waveform complexities.

Purpose of the Study:

• To investigate the underlying mechanisms contributing to abnormal impedance cardiogram (ICG) waveforms.
• To develop a theoretical model explaining the influence of pre-ejection and ejection phases on ICG signals.
• To propose a method for improving the accuracy of ICG-derived parameters, such as ejection onset and amplitude.

Main Methods:

• A theoretical model was developed to simulate the formation of impedance systolic waves.
• The model considered two main processes: pre-ejection cardiac/vascular changes and aortic expansion during ejection.
• A "two-bell" model was proposed to explain abnormal dZ/dt waveforms and their impact on ICG parameters.
• An alternative interpretation of the dZ/dt B-point notch was explored.

Main Results:

• The theoretical model successfully predicted potential mechanisms for abnormal dZ/dt waveforms in ICG.
• The study identified pre-ejection waves as a contributor to waveform abnormalities and errors in systolic time intervals and amplitude measurements.
• The proposed two-bell model offers an explanation for the dZ/dt B-point notch.
• A decomposition method was suggested to overcome masking effects and accurately determine ejection onset and peak amplitudes.

Conclusions:

• The presence of pre-ejection waves can significantly distort ICG waveforms, leading to inaccuracies in cardiac function assessment.
• The new theoretical model provides a framework for understanding these distortions and their impact on key ICG parameters.
• A novel decomposition technique holds promise for enhancing the accuracy of ICG analysis, especially in patients with complex cardiac conditions.