VADs

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