Ventricular Assist Device (VAD)

Reviewed and revised 20 July 2015

OVERVIEW

A Ventricular Assist Device (VAD) is a mechanical pump used to provide adequate cardiac output when heart failure is resistant to medical therapy

USES/INDICATIONS

Severe heart failure and cardiogenic shock (patients selected typically are NYHA Class IV, with EF <25% and VO2max <15) in the setting of:

• bridge to recovery — temporizing measure to optimize ventricular function while awaiting native ventricular function to return
  (e.g. unable to wean off bypass, transient cardiomyopathy)
• bridge to heart transplantation
• bridge to decision — temporizing measure until a decision can be made on one of the above
• destination therapy if not eligible for cardiac transplantation (not currently funded in Australia)

Contraindications

• Irreversible hepatic or renal failure not due to poor cardiac output
• Metastatic cancer
• Cerebral accident with neurological deficits

Relative contraindications

• Refractory tachyarrhythmias
• Active coagulopathy
• Active infection
• Mechanical cardiac valves
• Severe valvular regurgitation (especially aortic)

DESCRIPTION

• a small tube that carries blood out of the heart into a pump then blood pumped back into the aorta (LVAD) or pulmonary artery (RVAD)
• can be continuous flow (cf-VAD) rather than pulsatile (generally older models); cf-VADs are smaller, quieter, and durable
• 2 main types of pumps currently used:
  1. centrifugal (~2,500 rpm)
  2. axial flow (~10,000 rpm)
• may be right, left or biventricular
• either transcutaneous or implantable
• good control of cardiac output

Components that may be present:

• inflow cannula — stationed inside the left ventricle to direct blood into the pump
• pump — located at the apex of the left ventricle and houses the impeller (magnetically levitated frictionless rotor)
• outflow graft — flexible, gel-impregnated conduit that directs blood from the pump to the ascending aorta
• controller — monitors pump function (flow, speed, power), controls pump speed and manages power supply, records pump data and alarms; displays battery life and function; data can be downloaded for analysis
• driveline — subcutaneously tunneled from the epigastrium or RUQ to the pump;   contains wires that provide power and operating details to the pump from the controller
• stabilisation belt — supports and anchors the driveline at the exit site, reduces risk of infection, minimises tissue injury and promotes tissue growth
• batteries — patients carry at least 2 lithium batteries at all times; VAD can be recharged using standard power supply

METHOD OF INSERTION AND/OR USE

Site

• surgically placed
• varies with device e.g. HEARTMATE II has a subdiaphragmatic pocket

Flow

• LVAD — LV to aorta
• RVAD — RA or RV to pulmonary artery
• BiVAD — both of the above

OTHER INFORMATION

Key issues

• VADs are preload dependent and afterload sensitive
• requires anticoagulation to prevent pump or intracardiac thrombosis
• cardioversion is safe
• CPR can be performed (controversial)
• perioperative antibiotic prophylaxis is use following insertion (e.g. vancomycin and ceftazidime)

Assessment of VAD patients

• Most patients have tag located on their controller around their waist indicating what type of device it is, what institution put it in, and a number to call.
• pulse may be impalpable with cf-VAD (DBP increases)
• always auscultate (e.g. epigastrium/ precordium) to hear if the VAD is working
• assess blood pressure (typically aim for MAP 60-90 mmHg)
  • may be difficult or impossible with standard non-invasive blood pressure measurement
  • intra-arterial line is ideal
  • can use brachial artery doppler to to detect loud contiuous noise during non-invasive blood pressure measure, this corresponds to the MAP
• check battery life and performance parameters on controller
• perform bedside echocardiography (see below)
• perform ECG — VAD pateints may tolerate otherwise lethal dysrhythmias (unless RV dysfunction occurs)
• assess for sepsis (including exit site swabs)
• also discuss patients with a VAD center

Key parameters (HEARTMATE II)

• rpm (pump speed — this is set according to ECHO results)
• flow (this is calculated from power, rpm and hematocrit/ blood viscosity) — paradoxically increased flow reading can be caused by obstruction as also leads to increased power requirement
• PI (pulsatility index — how much cardiac output is provided by the patient vs pump)
• power (required by the VAD — averaged over cardiac cycle

General VAD parameter ranges

Lowest safe VAD operating speeds (e.g. for use during cardiac arrest)

• Heartware — Manually decrease speed to 1,800 rpm; No flow estimation given
• Heartmate II — Manually decrease speed to 8,000 rpm; No flow estimation if < 3L/min
• Heartmate III — Manually decrease speed to 4,000 rpm

Trouble-shooting power abnormalities (e.g. for HEARTMATE II) — note that pump speed (rpm) will remain constant unless there is a suction event:

• low power with low pulsatility index and steady pump speed
  • causes: inflow/ outflow obstruction, LV failure, dysrhythmia, hypertension
• low power with normal or high pulsatility index
  • suckdown
• high power with low pulsatility index fluctuating pump speed
  • pump thrombosis, vasodilation, hypotension, initial response to exercise
• high power with high pulsatility index
  • normal physiological response to increased demand; myocardial recovery; fluid retention

Echocardiography findings

• small RV suggests inadequate preload
• small LV suggests suckdown
• large RV and small LV suggests RV failure or pulmonary hypertension
• large RV and large LV suggests pump thrombosis/ obstruction

Causes of hypotension

• VAD-related:
  • suckdown
  • malposition
  • pump failure/ obstruction (thrombosis, kinking, etc)
  • excessive pump speed
• non-VAD-related:
  • hypovolemia (dehydration or haemorrhage)
  • cardiac tamponade
  • aortic regurgitation
  • dysrhythmias
  • vasodilation

Causes of dysrhythmia

• local physical effects (e.g. malposition, suck down), electrolyte disturbance, ischemia, underlying cardiomyopathy

COMPLICATIONS

Main issues with LVAD post-insertion

• right heart failure (due to mechanical interdependence and haemodynamic reasons)
• bleeding/ clotting
• suckdown

Cardiovascular

• right heart dysfunction
  • up to 20% develop acute right heart failure post-VAD
• aortic regurgitation
  • often induced by LVAD
• dysrhythmia
  • typically due to a “suction event” (where the inflow cannula contacts the ventricular septum), most common in the first month
  • Suction events can be caused by hypovolemia, small ventricular size, or RV failure and are treated with fluid resuscitation and decreasing the LVAD speed
• CVA
  • prevent with aggressive management of hypertension with ACEI/ B-blockers

Device-related

• suckdown
  • due to right ventricular failure, hypovolaemia, tamponade, dysrhythmias, inflow cannula malposition
• device failure
• malposition/ migration
• mobility restrictions

Hematological

• bleeding (e.g. epistaxis, intracranial, intrathoracic)
  • anticoagulation
  • post-surgical bleeding
  • intracranial haemorrhage (higher with axial flow pumps)
  • acquired von Willebrand factor deficiency
  • gastrointestinal angiodysplasia and AV malformations
• thromboembolism (higher with centrifugal pumps, see above)
• haemolysis
  • check haptoglobin, free Hb, LDH, Hb in urine; consider inflow/ outflow obstructions and pump dysfunction

Infection

• VAD-specific infections
  • pump and/or cannula infections, pocket infections, and driveline infections (usually Staphylococcus or Enterococcus; for pump pocket and deeper wound infections need to cover pseudomonas)
• VAD-related infections
  • infective endocarditis, bloodstream infections, and mediastinitis
• non-VAD-related infections
  • e.g. LRTI, UTI

VAD thrombosis

• dramatic increase in the rate of thrombosis since 2011 in the HeartMate II device (Starling et al, 2014)
  • increase in pump thrombosis at 3 months after implantation from 2.2% to 8.4%
  • median time from implantation to thrombosis was 18.6 months prior to March 2011, to 2.7 months after
• up to 50% mortality
• may present as
  • power spikes or low pump flow alarms on the patient’s control box Pump (VAD) failure, recurrent/new heart failure, ltered mental status, hypotension (MAP < 65), or signs of peripheral emboli (including acute CVA), evidence of hemolysis (LDH > 1,500 mg/dL or 2.5-3 times the upper limit of normal, haemoglobinuria and elevated plasma free hemoglobin)
• management
  • anticoagulation (e.g. heparin), may require thrombolysis/ thrombectomy/ surgical intervention

DEVICE TYPES

HeartMate I or XVE

• Use: Destination Therapy
• Flow Type: Pulsatile
• Pulse: Has pulse but may not match ECG rhythm
• Backup Method: Hand Pump
• Battery: 12volt MiMH – 10hrs
• Defib/Cardioversion: Use hand pump during defib/cardioversion
• Anticoagulation: patient on aspirin

HeartMate II

• Use: Bridge to transplant or destination therapy
• Flow type: axial flow
• Backup Method: No external method
• Pulse: No palpable pulse or BP. Doppler Only
• Battery: 14V Li-Ion – 10 hrs
• Defib/Cardioversion: No precautions necessary
• Anticoagulation: Warfarin

Thoratec VAD

• Use: Bridge to Transplant
• Flow Type: Patient will have pulse and BP but may not match ECG rhythm
• Backup Method: No external method
• Battery: 12V lead acid gel battery – 7.2 Ah – up to 3 hrs
• Defibrillation/Cardioversion: No precautions
• Anticoagulation: Warfarin

References and Links

Journal articles

• Felix SE et al. Continuous-flow left ventricular assist device support in patients with advanced heart failure: points of interest for the daily management. Eur J Heart Fail. 2012 Apr;14(4):351-6. PMID: 22308012.
• Partyka C, Taylor B. Review article: Ventricular assist devices in the emergency department. Emerg Med Australas. 2014 Apr;26(2):104-12. PMID: 24707998.
• Pratt AK, Shah NS, Boyce SW. Left ventricular assist device management in the ICU. Crit Care Med. 2014 Jan;42(1):158-68. PMID: 24240731.
• Rose EA, et al; Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) Study Group. Long-term use of a left ventricular assist device for end-stage heart failure. N Engl J Med. 2001 Nov 15;345(20):1435-43. PMID: 11794191.
• Slaughter MS, et al; HeartMate II Clinical Investigators. Clinical management of continuous-flow left ventricular assist devices in advanced heart failure. J Heart Lung Transplant. 2010 Apr;29(4 Suppl):S1-39. PMID: 20181499.
• Starling RC et al. Unexpected abrupt increase in left ventricular assist device thrombosis. N Engl J Med. 2014 Jan 2;370(1):33-40. PMID: 24283197.

FOAM and web resources

• Blunt Dissection — Part man… Part machine (2014)
• ED ECMO — LVAD Problems and Troubleshooting (2014)
• EMCrit — Left Ventricular Assist Devices (LVADs) (2013)
• EM Docs — Ventricular Assist Device Management (2014)
• EM Nerd — The Adventure of the Resident Patient (2013)
• EP Monthly — The LVAD: Walking, Talking … and Pulseless by Stuart Swadron (2012)
• ICN — Podcast 105. SIN Talk: Nair on LVADs in ICU (2013)
• JEMS — Patients with a Ventricular Assist Device Need Special Considerations (2012)
• Maryland CC Project — Introduction to the Left Ventricular Assist Device (2013)
• Maryland CC Project — Ventricular Arrhythmias in the LVAD Patient (2014)
• Maryland CC Project — LVAD Troubleshooting – Low flow & power drops (2014)
• MyLVAD.com — EMS Field Guides
• UMEM Education Pearls — VAD thrombosis (2013)
• Video lectures by Arie Blitz — VAD lecture and Heartmate II LVAD insertion (2011)