Overview of Left Ventricular Assist Devices (LVADs)

This page was authored by Chris Partyka. It was originally published on the amazing Blunt Dissection Blog and based on a fantastic review article by Dr. Partyka.

Left Ventricular Assist Devices (LVADs)

These are intricate mechanical pumps utilised in the management of end-stage cardiac failure refractory to aggressive medical therapy, typically bridging a patient to cardiac transplantation.

The first implantation of an LVAD occurred back in 1984, however their technology and success have markedly improved since then. The landmark REMATCH paper demonstrated significant survival increase [52% vs 25% at 1 year, p=0.002] with an improved quality of life. Currently over 90% of LVAD-supported patients will survive to 1 year post-implantation.

Indications.

  • Bridge to cardiac transplant.
  • Bridge to recovery – potential reversible myocardial pathology.
  • Destination therapy – long-term assistance for patients ineligible for transplant

The components.

  • Inflow cannula.
    • placed within the left-ventricle
    • draws blood from the LV into the pump.
  • The pump.
    • is located at the apex of the LV.
    • houses the impeller – a frictionless rotor which is magnetically levitated. This rotates at speeds of >3000 rpm & can generate up to 10 litres per minute of blood flow.
  • Outflow graft.
    • flexible & gel-impregnated
    • conveys blood from the pump to the ascending aorta.
  • Driveline.
    • tunneled subcutaneously from the pump & exits typically in the patients epigastrium or right-upper quadrant
    • contains wires from external controller.
  • Controller.
    • regulates power, monitors VAD performance & displays alarms,
    • displays battery life & function.
    • allows data to be downloaded for analysis.
  • Batteries.
    • at least two rechargeable lithium-ion batteries are carried at all times
    • the device is also capable of recharging on standard power supply.

What do they look like ?

HeartWare HVAD. A continuous flow device designed to draw blood from the LV & propel it through an outflow graft connected to the patient’s ascending aorta. The inflow cannula is surgically implanted into the left ventricle & blood is conveyed through the pump via an impeller at operating speeds of 2400-3200 rpm (resulting in up to 10L/min of blood flow)(Courtesy of HeartWare International Inc, Framingham, Massachusetts, USA.)

HeartWare HVAD. A continuous flow device designed to draw blood from the LV & propel it through an outflow graft connected to the patient’s ascending aorta. The inflow cannula is surgically implanted into the left ventricle & blood is conveyed through the pump via an impeller at operating speeds of 2400-3200 rpm (resulting in up to 10L/min of blood flow)(Courtesy of HeartWare International Inc, Framingham, Massachusetts, USA.)

Thoratec HeartMate II. An axial-flow VAD with an impeller [the only moving part] that propels blood from the inflow cannula in the left ventricle to the ascending aorta. (Reprinted with the permission of Thoratec Corporation)

Thoratec HeartMate II. An axial-flow VAD with an impeller [the only moving part] that propels blood from the inflow cannula in the left ventricle to the ascending aorta. (Reprinted with the permission of Thoratec Corporation)

HeartWare LVAD controller. Displays battery life, impeller RPM, cardiac output & power usage. Alarms are also displayed here

HeartWare LVAD controller. Displays battery life, impeller RPM, cardiac output & power usage. Alarms are also displayed here

A typical CXR for a patient with an implanted left ventricular assist device. These patients will often have pacemakers or AICDs implanted also.

A typical CXR for a patient with an implanted left ventricular assist device. These patients will often have pacemakers or AICDs implanted also.

 

How do you assess a VAD Patient?

The assessment of a patient with a VAD begins like any other; a primary survey !! However, there are a few specifics we should mention.

1) BLOOD PRESSURE MEASUREMENT.

Due to diminished [& sometimes absent] peripheral pulses in the continuous-flow VADs, standard non-invasive blood pressure is difficult [perhaps impossible] to obtain.

Blood pressure can be measured with (1) a manual sphygmomanometer & (2) Doppler ultrasound over the radial or brachial artery. Cuff pressure is gradually reduced until a constant sound is heard – signifying the mean arterial pressure. Alternatively, in a critically ill patient just place an ultrasound-guided arterial line !

Mean arterial pressure in patient with left ventricular assist device [LVAD]. Doppler gate through radial artery. Regular spikes indicate minor pressure augmentation from native LV function.

Mean arterial pressure in patient with left ventricular assist device [LVAD]. Doppler gate through radial artery. Regular spikes indicate minor pressure augmentation from native LV function.

Radial artery doppler with falling manual sphygmomanometer pressure. Pulse returns due to native LV function.

Radial artery doppler with falling manual sphygmomanometer pressure. Pulse returns due to native LV function.

Radial artery doppler with ongoing falling manual sphygmomanometer pressure approaching mean arterial pressure…

Radial artery doppler with ongoing falling manual sphygmomanometer pressure approaching mean arterial pressure…

In this case the patients’ mean arterial pressure was measured at 59 mmHg. He normally runs at 70-80mmHg.

2) ASSESSING DEVICE FUNCTION.

  • Check that the pump is running. Auscultate the epigastrium/precordium for a continuous noise ! This is the pump operating.
  • Check the controller for;
    • BATTERY FUNCTION !
    • Flow
    • Power etc…

3) A BEDSIDE ECHO CAN BE A VERY POWERFUL TOOL.

  • VAD malfunction can result in catastrophic consequences & marked haemodynamic instability.
  • ECHO will allow rapid assessment of RV:LV chamber size comparison.
    • Small RV: consider Hypovolaemia [check IVC also]
    • Large RV: consider Pulmonary hypertension [correct hypoxia & acidosis]
    • Large RV + LV: consider VAD-thrombus !!
  • ECHO will also allow assessment of IVC diameter & collapsibility as well as the presence of pericardial effusion ± tamponade.
    • Will also confirm the correct positioning of the inflow cannula [which can migrate or kink overtime].

The GOLDEN RULE OF VADS

Call your nearest LVAD or Cardiac-transplant center as soon as possible for assistance in the care of these complex patients !!

So what can be causing his hypotension?

Click on over to the LVAD Troubleshooting Page to find out

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

Ventricular assist devices are implanted medical equipment to augment cardiac output. Left ventricular assist devices (LVADs) are the most common version you will encounter.

Currently, the best review article is (Crit Care Med 2014;42:158)

and this article is great as well (Clinical Management of VADS)

These devices augment the left ventricular flow for patients in severe congestive heart failure (CHF).  The recent popular form of this is through an internal pump and an external power supply.  These are connected through a driveline that exits the body through the right upper quadrant of the abdomen.

Indications

The indications for LVAD placement are patient with severe CHF limiting activities of daily living and often times requiring home inotropes to maintain perfusion.  Strict indications for implantation exist in United States for medicare reimbursement.  These include New York Heart Failure class 4 with ejection fraction less than 25%.

LVAD low res labeledDevice Functions

The LVAD has two cannulas.  The inflow cannula is inserted into the left ventricle apex and draws blood into the pump.  The pump has had various forms over the years.  Initial LVAD models were pulsatile.  While this concept succeeds in keeping with the body’s natural flow and may consequently have some physiologic benefits, continuous non-pulsatile pumps have become standard.  These types of pumps have the advantage of better durability as the pulsatile pumps required many moving parts.  Each of these parts were susceptible to failure.  Decreasing the number of moving parts has therefore become paramount with the most recent model claiming zero moving parts.

Beyond the pump lies the outflow cannula which connects the pump to the aorta.  This allows blood to be drawn out of the left ventricle and pumped into the aorta without need for left ventricle induced flow.  The outflow cannula is attached to aorta such that coronary flow is maintained along with the periphery.

Exiting the pump is the driveline.  This exits the body in the right upper quadrant and attaches to the controller.  The controller attaches to two batteries.  All three of these components are held in a vest-like garment or belt that allows the patient to be mobile when desired.  The controller contains the electronic circuitry required to maintain desired revolutions per minutes (rpm).  It also records adverse events and decreased flow periods with the machine.  It additionally has advanced functions to deal with specific LVAD problems like suction events and power shortages.

LVAD physiology

LVAD patients pose an interesting physiology not seen in other patients.  The design of the machine allows the left ventricle to still function normally.  This means some blood will exit the left ventricle (LV) through the aortic valve secondary to the native heart function.  The level of LV function and the compliance of the aorta will determine the pulsatility of the patient.  Due to low levels of LV function and the continuous nature of current generation pumps, most patients will not have a palpable pulse.  Additionally, most standard automatic blood pressure machines will not be able to determine the correct blood pressure on these patients.  A manual blood pressure will usually be successful at determining the mean arterial pressure (MAP) without a significant pulse pressure.

next see LVAD Problems and Troubleshooting

 


Keep up with the EDECMO Project


This post was brought to you by .



Trackbacks

  1. […] a thorough description of components, functionality and indications for LVAD’s, check out EDECMO’s blog post for an excellent LVAD overview. Below is a more in depth approach to the complications […]

  2. […] EDECMO (2017). Overview of Left Ventricular Assist Devices (LVADs). Accessed on 24th October at: http://edecmo.org/additional-technologies/ventricular-assist-devices-vads/lvads/ […]