Impella

Catheter-based microaxial flow pump indicated in cardiogenic shock secondary to LV failure, which provides:

This is in strong contradistinction to VA, which provides systemic perfusion at the expense of ↑ LV afterload and ↑ LV wall tension.

Indications

  • Cardiogenic shock secondary to LV failure

Contraindications

  • Mechanical aortic valve
  • LV thrombus
  • Peripheral vascular disease
  • Right ventricular failure

Anatomy

Equipment

  • Impella catheter
    From proximal to distal, consists of:
    • Blood inlet
    • Axial flow pump
      Rotational speed is directly proportional to flow.
    • Radio-opaque strip
      Aids placement, as this line should straddle the aortic valve.
    • Blood outlet
    • Optical pressure sensor
    • Suture hub
  • Automated Impella Controller
    Provides:
    • Interface for monitoring and control
    • Display
      • Aortic root pressure
      • LV pressure
      • Flow control
        Adjust between ordinal P-levels.
      • Current calculated flow and P-level
        Includes maximal systolic and minimal diastolic flow rate.
    • Purge system
      Adjusted to maintain a pressure level of 300-1100mmHg; at a rate of 2-30mL/hr.
    • Battery backup
      60 minutes.
  • Purge fluid
    Purge fluid provides a pressure head inside the device to prevent blood entering the motor. Fluid options include:
    • Dextrose 5% with heparin (25U/mL)
    • Dextrose 5% with bicarbonate
      If concern for bleeding or HITT.

With respect to measurements:

  • Aortic pressure is monitored by the optical sensor
  • Aortic-LV pressure differential is proportional to the motor current
  • LV pressure is calculated by the differential between the aortic and LV pressure
Flow ranges of the Impella 5.5
P-level Mean Flow (L/min) Revolutions per Minute
P-0 0 0
P-1 0 12,000
P-2 0 - 1.9 17,000
P-3 1.1 - 2.7 20,000
P-4 1.9 - 3.3 22,000
P-5 2.8 - 3.7 24,000
P-6 3.4 - 4.1 26,000
P-7 3.9 - 4.5 28,000
P-8 4.3 - 4.9 30,000
P-9 5.0 - 5.5 33,000

Notes on Impella flow:

  • Pressure gradient through the device is ~30 - 60 mmHg
  • Flow varies at each P-level due to ventricular loading
  • The Impella is preload dependent and afterload sensitive

Technique

Insertion

Management

Haemodynamics:

  • Maintain correct positioning
    Indicated by:
    • A true difference between the aortic and LV pressure waveform
    • Inlet 5cm from aortic valve annulus, with the Impella bend at the annulus
  • Cardiac arrest
    ↓ Impella flow rate during arrest.

Weaning:

  • ↓ Impella flow rate by 2 P-level increments
    Avoid ↓ flow rate <P-2, until immediately prior to removal.
  • Monitor trend in MAP and LVEDP
  • Goal is maintenance of total cardiac output and cardiac power, with stable MAP and LVEDP

Anticoagulation:

  • Maintain ACT 160-180
    May be achieved with the heparin in the purge fluid.

Removal:

  • Continue support at P-2 until immediately prior to removal
  • ↓ Flow to P-1 and then withdraw into the aorta
  • ↓ Flow to P-0 and remove device
  • Surgical closure of graft site

Complications

  • Aortic dislodgement
    Withdrawal of the device into the aorta.
    • Indicated by:
      • Overlap of the LV and aortic pressure waveform
      • Both waveforms consistent with an arterial pressure wave
      • Absence of motor current
    • Actions
      • Reduce P-level to P2
      • Reposition catheter under imaging guidance
  • Ventricular dislodgement
    Advancement of the device into the ventricle.
    • Indicated by:
      • Overlap of the LV and aortic pressure waveform
      • Both waveforms consistent with an= ventricular pressure wave
      • Absence of motor current
    • Actions
      • Reduce P-level to P2
      • Reposition catheter under:
        • Without imaging guidance
          Gentle withdrawal until pressure and current differential is seen.
        • With echocardiographic guidance
  • Unknown position
    May occur when:
    • The catheter has migrated, but the pressure waveforms are not definitively aortic or arterial
    • Native heart function is too impaired to produce a significant pressure differential
  • Suction
    • Indicated by:
      • Suction alarm
      • Negative left ventricular diastolic pressure
      • Flow lower than expected
      • Hypotension
      • ↓ Motor current
    • May occur when:
      • Incorrect ventricular positioning
      • RV failure
      • Hypovolaemia
    • Actions
      • Reduce P-level
      • Review volume state
      • Check RV function
      • Check Impella position
  • Haemolysis
    Always pathological, and indicates catheter obstruction:
    • Inflow obstruction
      • Papillary muscles
      • Suck-down
    • Pump obstruction
      • Fibrin
      • Clot
    • Outflow obstruction
      • AV
      • Aortic wall

References