Active Mechanical Circulatory Systems

Surgically placed LVADs are used to bridge to recovery or cardiac transplantation, or as "destination therapy". These are generally continuous-flow (CF) and either work by axial-flow or centrifugal-flow pumps.

In addition to surgically placed LVADs, the percutaneously placed MCS also work via centrifugally-driven pumps or axial-flow pumps.

Three primary CF percutaneous MCS are currently used in clinical practice for LV support:

1. TandemHeart (centrifugally driven left atrial to femoral artery bypass)
2. VA-ECMO
3. Microaxial flow catheters (Impella)

These differ from pulsatile support such as the IABP which is generally classified as "passive" circulatory support.

Physiology of MCS

• MCS increases vital organ perfusion, augments coronary perfusion and reduces filling pressures and volumes which reduces myocardial oxygen consumption.
• MCS are dependent on preload and afterload optimization: Low preload or high afterload leads to flow reduction.
• For all CF MCS devices, flow is directly related to RPM and indirectly related to the "pressure head" (H) which is defined as the difference between the pressure at the inlet and outlet of the impeller.

Impella Devices

• Impella devices are a series of catheter-based, axial-flow, peripherally inserted heart pumps: the Impella 2.5, CP, 5.0, LD, and RP models.
• Left-sided Impellas are placed retrograde across the AV into the LV and generate antegrade bloodflow in the ascending aorta while unloading the LV.
• The Impella RP is placed antegrade across the TV and PV, and the inlet is in the RA and the outlet is in the main PA. It can be used in tandem with the left sided Impella (i.e. "BiPella").
• These devices require some preservation of contralateral ventricular function for maximal flows.
• All Impellas require systemic anticoagulation.
• Approved for <6 hours for high risk PCI, and <4 days for cardiogenic shock.
• Powered by AC energy, and have internal batteries that can last 1 hour
• LV Impellas are contraindicated in the presence of a mechanical AV or LV thrombus. Relatively contraindicated in RV failure, AR, aortic dissection, bleeding diathesses, and uncontrolled sepsis.

Indications for Impellas

TandemHeart

The TandemHeart device (TandemLife, Pittsburgh, PA) is a left atrial to femoro-iliac bypass, powered by an external centrifugal pump that provides up to 5 L/min of forward flow.

Small randomized trials have been performed comparing the TandemHeart with IABP in patients with CGS, demonstrating superior hemodynamics but higher complication rates with the TandemHeart.