Left Ventricular Assist Device

Pathophysiology

Parameters

Key LVAD parameters include:

Speed
Pump speed in RPM. The speed is:
- The only value that is set
- Generally, ↑ pump speed should ↑ flow
Power
Measure of pump work.
- ↑ Power occurs with:
  - ↑ Pump speed
  - ↑ Pump flow
    This can occur independent of speed with pathology, e.g. AR or ↓ SVR states.
  - Rotor thrombosis
- ↓ Power occurs with:
  - ↓ Pump speed
  - ↓ Pump flow
  - Obstruction
    Inflow cannula obstruction.
Flow
LVAD flow is a measure of LVAD output, and is estimated based on:
- Speed
- RPM
- Haematocrit
Pulsatility Index
Measure of the variation in flow. The PI is:
- Calculated as:
  $P I = \frac{F l o w_{M a x} - F l o w_{M i n}}{F l o w_{M e a n}}$
- A marker of native cardiac function
- Assessed over 15s
- Used to determine PI Events
  - Period where PI is >45%
  - Results in a transient ↓ LVAD speed
  - May trigger a suction event

Normal ranges for LVAD parameters vary depending on the model.

For the HeartMate 3:

Speed: 4700-6500
Power: 3-7
Flow: 3-6L/min
PI: 1-10

Assessment

Vital signs:

Palpable pulse may not be present due to low native CO
NIBP similarly ineffective
MAP can be calculated:
- Via invasive measurement
- Via pressure cuff with doppler
  - Inflate cuff above SBP
  - Deflate cuff until doppler pulse returns
  - This pressure is the MAP

LVAD Assessment:

Driveline intact
Driveline connected to controller
Controller not alarming
LVAD connected to power source
Auscultate for mechanical hum

Investigations

Bedside:

Laboratory:

Imaging:

Other:

Management

Resuscitation:

ABC approach. Comment on team coordination and clinical priorities. Specific therapy:

Pharmacological
Procedural
Physical

Supportive care:

Disposition:

Preventative:

Anaesthetic Considerations

Complications

Include:

Changes in LVAD Parameters by Condition
Condition	Flow	Power	PI
Inflow/Outflow Obstruction	↓	↓	↓
Rotor Thrombus	Machine: ↑ Reality: ↓	↑↑
Hypovolaemia	↓	↓	↑/↓
Hypervolaemia	↑	↑	↑/↓
Hypertension	↓	↓	↑
RV Failure	↓	↓	↑/↓
Sepsis	↑	↑	↓
Aortic Regurgitation	↑	↑	↓
Ventricular arrhythmia	↓	↓	↓

Direct
- Suction event
- Pump thrombosis
Indirect

Direct

Suction event:

LV collapse due to either:
- ↓ LV preload
  Intervention is very different depending on the cause, and usually needs echo guidance:
  - True hypovolaemia
    - Bleeding
  - RV failure
  - Tamponade
  - Arrhythmia
- Excessive LVAD speed
Leads to:
- ↓ LVAD output
  - Alarms
  - ↓ LVAD CO and likely total CO
    - Hypotension

Pump thrombosis:

Consider if clinically ↓ CO with ↑ power
Assess for haemolysis:
- ↑ LDH
- ↓ Haptoglobin
- ↑ Plasma Free haemoglobin
Usually requires device exchange, though thrombolysis may be possible

Device failure:

Treat as cardiogenic shock in a patient with terrible ventricular function
- Adrenaline
- Noradrenaline/dobutamine
Consider VA ECMO

Indirect

C
- RV failure
  Major complication of LVAD support.
  - 10-40% by 2 years
  - Multifactorial
    - ↑ RV preload secondary to ↑ CO and ↑ VR
    - Altered ventricular dynamics
      Septal shift with LV unloading.
    - Pulmonary hypertension
    - Arrhythmias
- Ventricular arrhythmias
  - Can be surprisingly well-tolerated in short term
  - Require treatment due to:
    - RV dysfunction
    - Loss of native CO
      - Thrombosis risk
- Aortic Regurgitation
  - Consider if clinically ↓ CO despite ↑ flow
  - Results in ineffective LVAD function with recirculation through device
    - Cardiogenic shock
    - RV failure
D
- Stroke
  10% by 2 years.
G
- GI bleeding
  - Multiple risk factors
    - Therapeutic anticoagulation
    - Acquired von Willebrand syndrome
    - Gastrointestinal AVM formation
      Attributed to non-pulsatile flow.