FRCA Notes

Ventricular Assist Devices

Ventricular assist devices may seem an unlikely candidate for a Final FRCA CRQ, though a recent BJA Education article may point to one in the not-too-distant future.

The curriculum only mentions them in passing: 'Describes the principles of action, and the use of, intra-aortic balloon counter-pulsation and other assist devices'.

Resources

  • Ventricular assist devices (VADs) provide circulatory support, subclassified as supporting:
    • The left ventricle (LVAD) - most common
    • The right ventricle (RVAD)
    • Both ventricles (BiVAD)
  • They may be inserted for temporary support as a bridge to definitive treatment, or for long-term use ('durable VADs')
  • The goal is to reduce LV workload and maintain adequate cardiac output
  • Generally consist of:
    • An inflow cannula from the LV apex, which drains blood to a pump
    • A pumping mechanism
    • An outflow cannula to the ascending aorta
    • A percutaneous lead ('driveline') connecting the pump to a controller and battery
    • Battery; generally has both a portable function (10hrs) and mains plug

Generations

Generation 1st 2nd 3rd
Flow Pulsatile Continuous Continuous
Pump Axial Axial Centrifugal
  • Third generation pumps have reduced incidence of thrombotic and haemolytic complications
    • Still necessitate anticoagulation e.g. warfarin to an INR of 2-3
  • Only third generation pumps are now implanted, but some patients may still have second generation pumps in situ

Controller values

  • The VAD pump speed is set during insertion, often at 5,200 - 5,800rpm

  • The device calculates pump flow using the pump speed, power (in Watts) and haematocrit
    • Typically 3-6L/min
    • This calculated value may differ from actual flow depending on patient state, but trends in calculated flow may be useful

  • As a bridge to:
    • Cardiac transplant [only valid indication in the UK]
    • Candidacy for cardiac transplant
    • Recovery
  • As a 'destination' i.e. last line therapy
Typical pathologies requiring VAD insertion
End-stage heart failure
Cardiogenic shock
Fulminant myocarditis
Failure to wean from bypass
Post-cardiac arrest

Benefits


  • 1/3rd of patients require unplanned hospital admission within 6 months of device implantation
  • 2yr survival 83%, comparable to heart transplantation
Haemorrhagic Infection (up to 50%) Thrombotic Cardiac Other organ dysfunction
Any bleeding (44%) Driveline infections Any stroke (10%) RV failure Respiratory
GI bleeding (25-40%) Pump pocket infection Disabling stroke (5%) Arrhythmia (25-36%) Renal
Intracerebral bleeding Pump thrombosis (1.4%) Hepatic


  • Present for an array of surgeries including:
    • Elective cardiac surgery e.g. transplant
    • Elective non-cardiac surgery
    • Emergency surgery e.g. endoscopy for UGIB, neurosurgery for ICH, management of device complications

  • They are at an increased, and overall high, risk of perioperative complications

Perioperative complications

General Cardiovascular Thrombotic/haemorrhagic Device-related Other
30-day re-admission (39%) Heart failure (10%) Ischaemic stroke (7%) Thrombosis (0.6%) AKI (18-44%)
30-day mortality (5-10%) MACE (17%) Intracranial haemorrhage (3.3%) Failure (0.1%) LRTI (7%)
Intra-operative hypotension (27%) Need for transfusion (38-43%) Infection (0.1%) Sepsis (11%)
Malignant arrhythmia (1.3%)


Perioperative management of the patient with a ventricular assist device


  • Patients should be managed and have surgery in a VAD specialist centre
  • MDT assessment prior to elective surgery, with input from cardiology, anaesthetics, proceduralist, perfusionists, cardiac surgery, haematology and intensive care
  • Generally plan for (cardiac) ICU stay post-operatively

Assessment

  • Functional status
  • End-organ function
  • Medication history inc. heart failure medication and anticoagulation
  • VAD history inc. previous complications or hospitalisation

Investigations

  • FBC: check for anaemia and haemolysis
  • LFT + U&E: check for end-organ dysfunction
  • Clotting profile
  • Group and cross-match as typically higher-than-usual blood loss

  • CXR: for device position
  • ECG: check for dysrhythmias
  • TTE: up-to-date to check both device and ventricular functioning
  • Consider CT chest/abdomen if surgery includes upper abdomen or chest, to check device and line positions relative to surgical site(s)

  • VAD interrogation
  • Management of PPM and/or ICD if present

Drug management

  • Continue heart failure medications
  • Typically continue aspirin
  • Stop warfarin 5 days prior to surgery and bridge with IV heparin
    • Avoid use of vitamin K as will need post-operative re-warfarinisation
    • FFP may be suitable, but PCC generally avoided due to risk of device thrombus

  • Minimise fasting time to reduce dehydration and effect on preload

Monitoring and access

  • Non-pulsatile flow renders NIBP unreliable
    • Can still be measured using a manual cuff and Doppler probe, though this is largely impractical intra-operatively
    • Arterial line used instead; generally need ultrasound to insert as no pulse!

  • Non-pulsatile flow renders saturations monitoring unreliable or degrades the signal excessively
    • Can use near-infrared spectroscopy as a surrogate marker of tissue oxygenation, as it is non-reliant on pulsatile flow

  • ECG, placed as far as possible from the device

  • ± CVC
  • ± Depth of anaesthesia monitoring (as sympathetic responses to pain or awareness may be blunted)
  • ± TOE in major surgery to assess haemodynamics and VAD function

  • Continuous monitoring of the device function by a perfusionist/VAD nurse specialist
  • External defibrillator pads on (or at least nearby) all patients

Anaesthetic technique

  • Neuraxial anaesthetic generally contraindicated because of anticoagulation and to avoid large decreases in SVR
  • No GA technique shown to be superior
  • Should ensure responses to anaesthetic intervention e.g. laryngoscopy are blunted as excessive afterload can reduce pump flow
  • Equally may need to carefully titrate induction agents to avoid large decreases in SVR
  • Meticulous positioning to avoid damaging the driveline, which may result in catastrophic device failure

Haemodynamic goals

  • Third generation devices are:
    1. Preload-dependent
      • Requires adequate input from the LV to maintain output
      • Pump flow will either decrease (low LV preload) or increase (high LV preload) depending on LV preload
      • Excessively low preload can lead to a 'suction event' (see below)
      • Manage with fluids (or diuretics if fluid overloaded)

    2. Afterload-sensitive
      • Pump flow will either decrease (high LV aferload) or increase (low LV afterload) to a limited extent depending on LV afterload
      • Manage low afterload with vasopressors
      • Manage excessive afterload with magnesium or nitrates
  • Pump speed rarely needs to be adjusted
Cardiovascular feature Goal of management Rationale
Heart rate
& rhythm		 Maintain normal rate and sinus rhythm
Rapid treatment of arrhythmia		 Tachyarrhythmia may cause RV dysfunction and impaired preload
Preload Maintain preload with fluid boluses LVAD is preload dependent
RV Afterload
LV Afterload		 Prevent increases in PVR
Prevent large decreases or increases in SVR		 High PVR compromises RV function and LV preload
Limited compensatory increase in view of changing SVR
MAP 60-80mmHg <60mmHg risks end-organ damage, esp. renal, so should be managed with fluids and vasopressors
>90mmHg risks AR, pump thrombosis and stroke, or reduced pump flow
  • Echocardiography can help determine the cause of any haemodynamic instability, e.g.
Cardiovascular Device-related
Hypo-/hyper-volaemia Excessive pump speed (over-pumping)
MR Under-pumping
RV dysfunction Inflow cannula obstruction e.g. from thrombus

RV dysfunction

  • Pre-existing RV dysfunction is common in patients with VADs
  • Acute deterioration in RV function associated with changing perioperative physiology can reduce LV preload and therefore cause reduced pump flow
  • Potential causes:
    • High intrathoracic pressure e.g. PPV, excess PEEP
    • Volume overload e.g. excessive IV fluids, steep Trendelenburg position
    • Any cause of raised PVR e.g. hypoxia, hypercarbia

  • In general, the benefit of mechanical (positive pressure) ventilation to prevent hypoxia and hypercarbia outweighs the risk of precipitating RV failure
  • Treatment of RV failure, beyond correcting causative factors, may involve RV inotropic support e.g. dobutamine, milrinone

Infection control

  • Infections of the pump or driveline are serious complications which may necessitate device removal
  • Patients are also at high risk of being colonised by MDR organisms

  • Meticulous infection control and aseptic technique is required
  • Aseptic technique for all procedures including peripheral IV acces
  • Prophylactic antimicrobials
    • Liaise with Microbiology
    • Broad-spectrum antibiotics for procedures e.g. pip/taz for GI surgery, vancomycin/cephalosporin for others
    • Consider anti-fungal cover

Blood products

  • Increase risk of requiring perioperative red cell transfusion, due to:
    • Residual effects of anticoagulation
    • Acquired vWF factor deficiency due to degradation by the pump

  • Transfusion is associated with poorer outomes, and an increased risk of alloimmunisation in patients who are likely to require future transfusion ± transplant

Surgical considerations

  • Avoid prolonged head-up (reduced LV preload) or head-down positioning (risks RV failure)
  • Prone positioning generally avoided but is described

  • If pneumoperitoneum is required:
    • Place ports as far from the device/driveline as possible
    • Establish gradually to allow titration of cardiovascular support
    • Maximum pressure 12cmH2O

  • Bipolar diathermy to minimise electromagnetic interference
  • If unipolar diathermy required, place pad as far from device as possible

Suction event

  • Due to inadequate preload to the pump (of any cause e.g. pneumoperitoneum, hypovolaemia, RV failure, steep head-up, Valsalva, couhging)
  • LV pressure decreases such that the ventricle collapses and occludes the inflow cannula
  • Pump flow precipitously decreases
  • Severe hypotension ± malignant arrhythmia develops
  • May cause cardiac arrest

  • Management
    • Reduce pump speed by 200rpm every 30-60s
    • Give IV fluid bolus guided by echocardiography
    • Correct precipitating factors

Thrombotic occlusions

  • New thrombus formation in the inflow cannula or pump
  • Increased risk perioperatively due to cessation of anticoagulation
  • Leads to reduced pump flow
  • Identified with echocardiography
  • Necessitates restarting anticoagulation + urgent VAD cardiologist referral

Cardiac arrest

  • May be difficult to diagnose in the (normal) absence of a pulse
  • Aetiology
    • The commonest causes in patients with VADs are suction events or malignant arrhythmias
    • Device malfunction; rare to occur spontaneously but may do so secondary to surgical damage of the device or driveline
    • Any normal cause for perioperative cardiac arrest e.g. anaphylaxis

  • Management
    • Cardioversion and defibrillation are safe
    • Chest compressions relatively contra-indicated due to fears over device damage/displacement but should be used if necessary

  • Ensure anaesthetic fully reversed and aim to extubate if possible
  • HDU management
  • Multimodal analgesia to prevent increased SVR associated with pain
  • Return ICD/PPM to pre-operative settings
  • Discuss timing of restarting anticoagulation with surgeons; bridge with heparin until then
  • Urgent TTE if persistent hypotension