Left ventricular assist device

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Background

  • Commonly referred to as an LVAD
  • Developed in 1960s and used as a bridge to Cardiac Transplant but have evolved into permanent, or “destination therapy"
  • Indication is New York Heart Association class 4 heart failure, ejection fraction <25%, VO2 max less than 15 among other criteria[1]
  • Goal of a VAD is to assist the ventricle and augment cardiac output
    • LVAD (left ventricle), RVAD (right ventricle), BiVAD (both venticles via separate pumps)[2]
  • VADs have 3 major variables:
    1. Speed
    2. Flow
    3. Power

Components

  • Pump = Internal pump (usually placed in preperitoneal space), takes blood from a cannula in the apex of the left ventricle and pumps it into the aorta
  • Driveline = Percutaneous cable that exits the abdominal wall, connects pump to external components (controller, battery)
  • Controller = External "box" containing computer for the device that monitors pump performance, has a display screen and controls for settings/alarms/diagnostics, and will display will show pump speed in RPM and pump output in L/min
  • Power Supply = Controller can be connected to batteries for patient mobility, or to a "power base station" that plugs into the wall for home use

Devices Overview

Heartmate I
Heartmate II
Thoratec-VAD

HeartMate I or XVE

  1. Use: Destination Therapy
  2. Flow Type: Pulsatile
  3. Backup Method: Hand Pump
  4. Battery: 12volt MiMH - 10hrs
  5. Defib/Cardioversion: Use hand pump during defib/cardioversion

HeartMate II

(Most common type in use today)

  1. Use: Bridge to transplant or destination therapy
  2. Flow type: Continuous
  3. Backup Method: No external method
  4. Battery: 14V Li-Ion - 10 hrs
  5. Defib/Cardioversion: No precautions

Thoratec VAD (HeartMate III)

  1. Use: Bridge to Transplant
  2. Flow Type: Pulsatile
  3. Backup Method: No external method
  4. Battery: 12V lead acid gel battery - 7.2 Ah - up to 3 hrs
  5. Defib/Cardioversion: No precautions

Complications/Differential Diagnosis[3]

Evaluation[3]

  • Assess perfusion and general state (mental status, skin temp/color, capillary refill, etc)
    • LVADs are preload dependant - if symptoms of hypoperfusion, give fluid blous
  • HR measured via ECG or auscultation (may be difficult secondary to pump noise)
  • Get 12-lead ECG on all LVAD patients
    • Demonstrates primary cardiac disease[6]
    • Generally, VAD does not influence underlying cardiac rhythm
  • Blood pressure measured with manual BP cuff and Doppler ultrasound - MAP is identified when constant flow is heard
  • Basic labs (CBC, CMP, Coags) should be obtained on all LVAD patients
  • Assess LVAD status
    • Auscultate for pump noise
    • Device parameters (found on controller)
      • Pump speed - varies by device - 2,000-10,000 RPM
      • Power - normal 4-6 Watts
      • Flow - normal 4-6 L/min
      • Pulsatility Index (PI) - normal 1-10
        • Measures magnitude of pulsatile flow provided by native cardiac contractions
        • Higher PI = less LVAD support
    • Clinical status more important than LVAD parameters

Management

  • Immediately contact hospital or patient's LVAD coordinator to help coordinate care
  • Take special care to not twist, bend, cut, or otherwise damage the driveline
  • First generation LVADs had pulsatile flow
    • Subsequent designs use continuous flow - patient will not have a palpable pulse
  • Patient will be on anticoagulation and antiplatelet therapy secondary to high risk of pump thrombus, CVA, and other thromboembolic events
  • VADs are ECG independant, unlike ICD (many patients with a VAD will also have an ICD in place)
    • ICD discharges are common, and frequently inappropriate (possibly secondary to LVAD interference)[6]

Cardiac Arrest[3]

  • Unconscious, apneic, no evidence of LVAD function (auscultate for mechanical noise)
  • Immediately evaluate LVAD components and attach to reliable power source
    • Some first-generation LVADs have external hand pumps that can be used to provide circulation
  • Otherwise follow ACLS as in a normal patient
    • Patient should be intubated, given IV fluids and drugs, etc
  • Avoid chest compressions unless absolutely necessary - evaluate other causes of pump failure or lack of perfusion (e.g. pump thrombus) first
    • Compressions can potentially damage LVAD, disrupt its connection to the heart (risk of exsanguination), etc
    • Some studies available[7][8] indicate that CPR may not be as harmful as currently thought, or that abdominal compressions are an alternative[9] but further investigation needed
    • Use clinical judgement for initiation of compressions

Disposition

  • Immediately contact the patient's VAD coordinator
  • Almost all LVAD patient presenting to the ED will require admission

See Also

External Links

References

  1. Mancini D, Lietz K. Selection of cardiac transplantation candidates in 2010. Circulation. 2010;122(2):173-83.
  2. Mechem CC. Prehospital assessment and management of patients with ventricular-assist devices. Prehosp Emerg Care. 2013 Apr-Jun;17(2):223-9.
  3. 3.0 3.1 3.2 Partyka C, Taylor B. Review article: ventricular assist devices in the emergency department. Emerg Med Australas. 2014 Apr;26(2):104-12.
  4. 4.0 4.1 Rose EA, Gelijns AC, Moskowitz AJ et al. Long-term use of a left ventricular assist device for end-stage heart failure. N. Engl. J. Med. 2001; 345: 1435–1443.
  5. Jennings, D, et al. Safety of Anticoagulation Reversal in Patients Supported with Continuous-Flow Left Ventricular Assist Devices. ASAIO Journal. July 2014. 60:381–384
  6. 6.0 6.1 Pistono M, Corrà U, Gnemmi M, Imparato A, Temporelli PL, Tarro Genta F, Giannuzzi P. How to face emergencies in heart failure patients with ventricular assist device. Int J Cardiol. 2013 Oct 15;168(6):5143-8
  7. Shinar Z, Bellezzo J, Stahovich M, Cheskes S, Chillcott S, Dembitsky W. Chest compressions may be safe in arresting patients with left ventricular assist devices (LVADs). Resuscitation. 2014 May;85(5):702-4.
  8. Mabvuure NT, Rodrigues JN. External cardiac compression during cardiopulmonary resuscitation of patients with left ventricular assist devices. Interact Cardiovasc Thorac Surg. 2014 Aug;19(2):286-9.
  9. Eric M Rottenberg, Jarrett Heard, Robert Hamlin, Benjamin C Sun, and Hamdy Awad. Abdominal only CPR during cardiac arrest for a patient with an LVAD during resternotomy: A case report. J Cardiothorac Surg. 2011; 6: 91.

Authors

Neil Young