Real-Time Ventricular Volume Measured Using the Intracardiac Electromyogram

Figures

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  Figure 1.. Surgical implantation. A: A cannula encompassing four electrodes (B1–B4) was implanted in the left ventricular cavity. The electrodes measured the intracardiac electromyogram (iEMG). B: Explanted heart showing the attachment with an HVAD suture ring. (C) Intracavity view of the cannula showing the shielded (B3, B4) and unshielded electrodes (B1–B2).

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  Figure 2.. Design of the unipolar amplifier. The reference electrode is referenced to its own low-pass filtered signal. The low-pass filtered signal is further used for the other three electrodes. The amplifier consists of two amplifier stages and two filters.15,16

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  Figure 3.. Experimental protocol. During all interventions, left ventricular volume was recorded through (A) echocardiography and (B) electric impedance. (C) The amount of blood in the circulation was altered using a cardiopulmonary bypass resulting in small and large changes in volume (ΔV). (D) The hematocrit was altered using hemorrhage and subsequent reinfusion of 0.9% NaCl. (E) Afterload was increased using a balloon catheter.

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  Figure 4.. Recorded waveforms. Representative waveforms are obtained from the electrocardiogram (ECG), the intracardiac electromyogram (iEMG), and the left ventricular volume (LVV) using electric impedance. Data are obtained from animal 3 at a high (left) and low (right) preload state. DA, depolarization amplitude.

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  Figure 5.. The depolarization amplitude and the end-diastolic volume (EDV). A mixed-effect model relates the depolarization amplitude of the intracardiac electromyogram with the end-diastolic volume measured by electric impedance. Each measurement point represents the median of a steady-state segment of 15 seconds.

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  Figure 6.. Positioning of the electrodes. A: The number of permissible intracardiac electromyogram recordings varied across the different electrodes B1–B4. Electrodes B3 and B4 were shielded from the blood pool, by a three-dimensional (3D) printed cage. B: The depolarization amplitude (DA) varied consistently over time. C: The offset of the relationship between the DA and the end-diastolic volume is preserved, whereas the offset differs across electrodes. Includes data only from small ΔV.

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  Figure 7.. The intracardiac electromyogram (iEMG) during dynamic change in afterload during occlusion of the descending aorta (dashed line). One out of three representative occlusion maneuver is depicted per column for animal 3, animal 4, and animal 5. The beat-wise end-diastolic volume (EDV) was estimated using the iEMG and compared against the EDVimp derived from the left ventricular volume (LVV) signal measured by electric impedance.