Investigation of the interaction between left ventricular assist devices and the native heart under normal and abnormal conditions
File(s)
Author(s)
Cheng, Audrey
Type
Thesis
Abstract
Left ventricular assist devices (LVADs) provide life-sustaining support for patients in end- stage heart failure until transplantation, recovery of the natural heart or as life-long treatment. Associated complications include stroke, blood clots in the LVAD (pump thrombosis) and acquired aortic valve regurgitation. There are aspects of the therapy that remain incompletely characterised, notably the interaction between LVADs and the left ventricle (LV). Moreover, diagnosis of pump thrombosis entails reliance on indirect methods. Assessment of recovery of the left ventricle (LV) during LVAD support continues to be challenging.
To address these deficits, a mock circulation loop was developed from which the acoustic and the magnetic signals from the HVAD, HeartMate 3 and Impella CP were recorded using a bespoke microphone and magnetometer. Analytical software developed for both in-vitro and clinical use included the Fast Fourier Transform method and the Hilbert Transform (HT) of dominant harmonics of the acoustic and magnetic signals generated by the LVAD. This allowed quantification of instantaneous impeller speed enabling elucidation of the mechanistic basis of the cardiac cycle-dependent LVAD impeller speed variation, attributable to the LV/LVAD interaction. This was investigated under both normal and abnormal operating conditions. The magnetic signal was shown to be of higher fidelity and was the signal of choice apart from for the diagnosis of impeller rotational instability which was better assessed acoustically. The magnitude of the change in instantaneous magnetic frequency correlated with underlying LV function and the waveform was modified during pump thrombosis or LVAD occlusion events. Preliminary clinical results concurred with in-vitro findings. A clinical trial is now justified to determine the utility of the novel techniques with the ultimate aims of improving i) pump thrombosis detection and treatment ii) the assessment and promotion of underlying LV function thereby improving clinical outcomes during and after LVAD explantation.
To address these deficits, a mock circulation loop was developed from which the acoustic and the magnetic signals from the HVAD, HeartMate 3 and Impella CP were recorded using a bespoke microphone and magnetometer. Analytical software developed for both in-vitro and clinical use included the Fast Fourier Transform method and the Hilbert Transform (HT) of dominant harmonics of the acoustic and magnetic signals generated by the LVAD. This allowed quantification of instantaneous impeller speed enabling elucidation of the mechanistic basis of the cardiac cycle-dependent LVAD impeller speed variation, attributable to the LV/LVAD interaction. This was investigated under both normal and abnormal operating conditions. The magnetic signal was shown to be of higher fidelity and was the signal of choice apart from for the diagnosis of impeller rotational instability which was better assessed acoustically. The magnitude of the change in instantaneous magnetic frequency correlated with underlying LV function and the waveform was modified during pump thrombosis or LVAD occlusion events. Preliminary clinical results concurred with in-vitro findings. A clinical trial is now justified to determine the utility of the novel techniques with the ultimate aims of improving i) pump thrombosis detection and treatment ii) the assessment and promotion of underlying LV function thereby improving clinical outcomes during and after LVAD explantation.
Version
Open Access
Date Issued
2024-01-13
Date Awarded
01/10/2024
License URL
Advisor
Parker, Kim
Bowles, Christopher
Publisher Department
Bioengineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)