Table of contents

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    Introduction

    • LVADs have become popular in recent years
      • Few donors, large need
      • Improved short and medium-term outcomes with VADs
    • LVADs can be used for:
      • 1. Bridge to transplant
      • 2. Destination therapy (if ineligible for transplant)
    • VADs are composed of:
      • 1. Blood Pump
        • Inflow Cannula, Impeller, Outflow Cannula  --> dacron graft --> aorta
      • 2. Percutaneous Lead
      • 3. External Power
      • 4. System Controller

     

    Hemodynamics

    • Pump differential pressure (difference between pump LV pressure and aortic pressure)
      • Flow inversely correlated to differential pressure
    • Similar kinetics in LVAD as heart
      • Sensitive to preload and afterload
      • Pulsatility is achieved by systole (ventricle contracts, pushing more blood into LV) and diastole
      • Centrifugal pumps are more sensitive to pressure changes (more pulsatility)
      • Pumps MORE sensitive to afterload changes than the biologic LV (3-4 times)
      • Pumps are LESS sensitive to preload than biologic LV
    • Preload is VERY important for heart flow.
    • Afterload dose change output as well
    • R-heart is extremely important to supply enough blood for VAD preload (maintain LV filling)
    • During conditions of low ventricular preload, axial pumps tend to “suck” harder than centrifugal pumps, and may even lead to a self-latching condition, as the pump continues to increase suction as flows fall, resulting in suck-down of the ventricular wall around the inflow cannula. In this regard, centrifugal pumps are less likely than axial pumps to create ventricular suck-down at low flow.
    • Suction Events
      • Occur when not enough preload for the LV and LVAD, suction occurs of ventricular wall on the inflow cannula. 
      • When this happens, LVAD shifts to lower preprogrammed pump speed
      • Suction events can trigger arrhythmias and need to be avoided.
      • Poor preload and high flows can trigger arrhythmias.  Patients with RV failure are at HIGHEST RISK. 
    • LVAD can improve native LV function by decreasing LV diameter, which improves passive pressure-volume relationship.
    • RV function can also improve by dropping RV afterload and improving venous return.
      • Can improve pulmonary hypertension, and slowly improve PVR
      • Can exacerbate TR
    • RAMP Study
      • RAMP Study =  measurement of central venous and pulmonary artery wedge pressures and cardiac output at increasing pump speeds
      • Sequential increase in pump speeds to see if they can tolerate higher speeds (find optimal speed)
      • To decrease risk of suction events
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