Interaction of the left ventricle and left ventricular assist device during mechanical circulatory support for advanced heart failure
Creators: name: Noor, Mumin
Publisher: name: Imperial College London
Year: 2015

description: The work in this thesis was undertaken to examine clinically significant questions at a time of evolving Left Ventricular Assist Device (LVAD) technology. The main theme of the research was to increase our understanding of the interaction between left ventricle and newer continuous flow LVADs through both in-vitro models and clinical studies with the ultimate aim of improving patient care. The hydrodynamic performance of the two continuous flow LVADs (Thoratec HeartMate II and HeartWare HVAD) was compared in a normothermic, human blood-filled pulsatile mock circulation model under conditions of steady flow and under simulated physiological conditions. These experiments were repeated using dextrose in order to determine its suitability as a mock circulation blood analogue. This study found that clinically representative pulsatile relationships are better represented as H/Q loops instead of linear plots. This allows for greater understanding of the instantaneous H/Q relationship of LVADs with the native LV. The relationship between LVAD pump speed and exercise capacity was studied in patients receiving support from a continuous flow HM II and examined the influence of residual LV function on this relationship. This study found that exercise time and pkVO2 are sensitive to pump speed in patients with poor LV function receiving HM II support. By contrast, insensitivity of exercise parameters such as pkVO2 and exercise time to changes in pump speed may be a non-invasive indicator for LV functional recovery in patients receiving support with rotary LVADs. Effect of temporarily increasing pump speed on exercise capacity was then studied in a group of patients supported with continuous flow LVADs. The study showed that it was safe and feasible to temporarily increase LVAD speed during exercise and this resulted in a significant increase in peak oxygen consumption. Furthermore, improved exercise capacity was observed in both axial and centrifugal pump devices. Radial strain and radial strain rate values were measured by Speckle Tracking Echocardiography to assess LV function and mechanics. The effect of reducing pump speed on these measurements was also examined. My result showed that the radial strain values are significantly lower than normal range and in keeping with advanced heart failure patients. I found the measurements to be relatively independent of degree of LVAD speed and may potentially reflect underlying LV function. Lastly, I investigated the feasibility of recording acoustic waveforms from a LVAD using an electronic stethoscope and analysing the frequency components of the LVAD acoustic spectrum. After recording the findings in patients with normal pump function, we compared it to patients with pump thrombosis. The acoustic profile is primarily determined by rotation speed and device design. In pump thrombosis cases, there were atypical spectral peaks during pump thrombus episodes. Acoustic monitoring is a simple non-invasive method which may have clinical utility in the diagnosis of pump thrombus episodes in patients supported by a rotary LVAD.