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Impedance cardiographic waveforms in children: Involvement in left ventricular ejection time determination during
Eric Wodey1, Lotfi Senhadji, Jean Yves Bansard
1Departments of Anesthesiology and Surgical Intensive Care (Drs. Wodey, Beneux, and Ecoffey) and Physiology (Dr. Carre), Université Rennes, 1, Rennes, France; Laboratoire de Traitement du Signal et de l'Image, Rennes, France (Dr. Senhadji); and Institut National de la Santé et de la Recherche Médicale, Paris, France (Drs. Senhadji, Bansard, and Carre).
Insights
Impedance cardiography (ICG) signal shapes in children do not accurately determine left ventricular ejection time (LVET) or stroke volume. This study highlights limitations in using ICG for hemodynamic monitoring in pediatric critical care.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Pediatric Critical Care
Background:
- The physiologic basis of impedance cardiography (ICG) signals remains debated.
- Accurate left ventricular ejection time (LVET) determination is crucial for calculating stroke volume.
- Varied ICG signal morphologies are observed in pediatric patients during anesthesia and critical care.
Purpose of the Study:
- To investigate the relationship between ICG signal shape and echocardiographically derived hemodynamic parameters in children.
- To assess the impact of different ICG signal shapes on the accuracy of LVET determination.
- To explore the utility of ICG for stroke volume calculation in pediatric surgical patients.
Main Methods:
- Prospective study involving 103 pediatric surgical patients (ASA I or II) under general anesthesia.
- Simultaneous recording of electrocardiography, ICG, and Doppler echocardiography.
- Mathematical modeling of ICG signal shape using normalized harmonic amplitudes (NHA) and phase (NHP) analyzed via multiple correspondence analysis.
Main Results:
- ICG-derived LVET showed no significant correlation with Doppler-derived LVET or heart rate.
- NHA and NHP were not significantly related to Doppler-derived LVET or stroke volume.
- NHA demonstrated a link to heart rate and the relative duration of the cardiac diastolic period.
Conclusions:
- The lack of correlation between ICG signal shape variables and Doppler-derived LVET indicates limitations in ICG's accuracy for stroke volume determination in children.
- Arterial compliance may influence ICG signal shape, as suggested by the relationship between NHA, heart rate, and diastolic period length.
Abstract:
OBJECTIVE: The physiologic basis of the impedance cardiographic (ICG) signal is still a matter of debate. An accurate determination of left ventricular ejection time (LVET) is needed to calculate stroke volume. In children, several shapes of the ICG signal are observed during anesthesia or in critical care. The aim of this study was to determine the relationship between the shape of the ICG signal and various morphologic and hemodynamic determinants obtained with Doppler echocardiography to highlight the effect of the various shapes in the accuracy of LVET determination. DESIGN: Prospective study. SETTING: Pediatric surgery in a university hospital. PATIENTS: 103 children, ASA physical status I or II. INTERVENTIONS: General anesthesia for elective surgery. Measurements: Electrocardiography, ICG, and Doppler echocardiography were recorded simultaneously. Classic hemodynamic variables, such as heart rate, LVET, stroke volume, or systemic vascular resistance, were measured or calculated. A mathematical model of the ICG signal was used to determine the shape of the ICG signal and its potential relationship to various morphologic and hemodynamic determinants. The ICG signal shape was then modeled with the normalized amplitudes (NHA) and phase (NHP) of the three harmonics of the fundamental signal. Analysis was performed with a multiple correspondence analysis. RESULTS: ICG method LVET did not significantly correlate with LVET determined with Doppler or with heart rate. NHA and NHP of the ICG signal were not significantly related to LVET determined with Doppler or to stroke volume. NHA were linked to heart rate and the relative length of the cardiac diastolic period. CONCLUSION: The absence of relationship between LVET determined with Doppler and the main variables defining the shape of the ICG signal highlight the relative limit of stroke volume determination with ICG method. The involvement of the arterial compliance in the ICG signal shape can be discussed in regard to the links between NHA and both heart rate and the relative length of the cardiac diastolic period, respectively.
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