Admittance to detect alterations in left ventricular stroke volume.

Area of Science:

• Cardiovascular physiology
• Biomedical engineering
• Medical device technology

Background:

• Implantable cardioverter-defibrillators (ICDs) use electrograms (EGMs) to distinguish arrhythmias.
• High rates of inappropriate shocks occur due to misclassification of hemodynamically stable tachycardias.
• Integrating left ventricular (LV) stroke volume (SV) assessment with EGMs could improve hemodynamic evaluation during arrhythmias.

Purpose of the Study:

• To accurately derive LV SV using the admittance method.
• To assess the feasibility of using biventricular pacing leads for SV monitoring.

Main Methods:

• Canine models (n=12) utilized ultrasonic flow probes and LV endocardial crystals for SV measurement.
• Biventricular pacing leads enabled admittance measurements via tetrapolar impedance analysis.
• Derived instantaneous blood conductance (Gb) by separating myocardial and blood impedance components.

Main Results:

• Gb demonstrated more accurate tracking of SV changes than traditional methods during pacing and dopamine infusion (P=.004).
• Gb also showed superior accuracy in tracking instantaneous LV volume during vena cava occlusions (n=5, P=.025).
• Finite element modeling indicated improved measurement sensitivity to the LV blood chamber with the admittance method.

Conclusions:

• LV SV monitoring is achievable with the admittance method employing biventricular pacing leads.
• This technique offers potential to augment EGMs for determining arrhythmia hemodynamic instability.
• The method could reduce inappropriate shocks in ICD patients by providing better hemodynamic context.