Hey everyone,
Today’s POTD will be all about LVADs, something we encounter rarely, but vitally important to know about. Feel free to skip to the bottom for the TL;DR!
What are LVADs?
Left ventricular assistance devices (LVADs) were developed in 1960s as a bridge to cardiac transplant, but is now also used as destination therapy, meaning it is the patient’s final therapy for heart failure during their lifetime. They are typically powered by two batteries with a power base unit that can be plugged into the wall. Indicated for NYHA class 4 HF, ejection < 25%. Note the Heartmate II is the most common one in use today.
Components
Pump: takes blood from cannula in apex of LV and pumps it directly into aorta.
Driveline: percutaneous cable that exits the abdominal wall and connects pump to external components such as controller and battery.
Controller: external “box” containing computer for device. Monitors pump performance and has controls for settings/alarms/diagnostics. Will show pump speed and output. Listed here are the normal range of values.
Pump Speed: 2200 – 2800 rpm (HeartWare VAD) and 8000 – 10000 rpm (HeartMate II VAD)
Power: 4 – 6 Watts
Flow: 4 – 6 L/min
Pulsatility Index (PI): 1 – 10
Power supply: connected to batteries or power base station which plugs into wall
FOR EMS PROVIDERS: In an emergency, all efforts should be made to transport patients with LVADs to their respective LVAD center. If a patient is brought to a non-device center, it is crucial that EMS personnel make every effort to bring the patient’s peripheral equipment needed to support them until they can be transferred to an LVAD center.
Common complications
Bleeding: most common reason for ED visit, most commonly in first month after implant. Tx with anticoagulant reversal, transfuse if needed. LVADs can cause acquired von Willebrand Disease, thought to be from the action of rotary or axial flow pump of the LVAD which causes high shear stress that may increase lysis of large vWF multimers.
Infection: from driveline and pocket, cover broadly with vanc/cefepime
Pump thrombosis: tx with heparin/antiplatelets or tPA in life-threatening situations. Pts will be on anticoagulation but pump thrombosis can still be common due to prosthetic material inflammatory reaction with blood and intrinsic endothelial activation in response to a continuous flow.
Arrhythmia: tx like you would in pt without LVAD either chemically or with electricity - place pads in anterior/posterior positioning
Suction event: when LV myocardium partially occludes the LVAD inflow cannula reducing inflow. Caused by low LV preload relative to pump speed. Tx by giving fluids, consider reducing LV speed in conjunction with LVAD team.
Cardiac tamponade: refer to LVAD center, pericardiocentesis discouraged b/c of low yield and potential for harm as the LVAD outflow graft may traverse typical course of needle.
Initial assessment FOCUSES ON CIRCULATION:
CONTACT THE LVAD TEAM: here at Maimo, the number is 35CHF
Note patients with LVADs will have NO PALPABLE PULSE and NO DISCERNIBLE HEART SOUNDS. Instead you will hear a continuous hum to confirm device is operating, though newest Heartmate 3 may have some interruptions to hum.
Measure the BP (must use doppler US and sphygmomanometer with doppler placed over brachial or radial artery).
1. Cuff inflated until pulse no longer audible and then deflated.
2. BP reading made when arterial flow audible again, giving single reading as MAP.
Goal MAP 70-80 and no more than 90 as this high afterload may compromise optimal function of LVAD. Should place A-line in hemodynamically unstable/hypotensive patients to more closely monitor BP.
Work-up will be the usual things you do for a cardiac patient: EKG, labs including trop, BNP, CXR. BEDSIDE ECHO AND COAGS/HEMOLYSIS LABS will be key because they can lead you down different diagnostic pathways.
Approach to conscious hypotensive patient with LVAD: check flow and power
Low flow vs high flow?
· Low flow suggests hypovolemia
· High flow state
o Normal power or high power?
· Normal power – distributive shock
· High power – obstructive shock from thrombosis vs suction event vs cardiac tamponade
Differing schools of thought on CPR in LVAD:
Some argue you should analyze the LVAD first, others say you should begin CPR immediately if a patient comes in with circulatory collapse like you would any other patient.
If you were to analyze the LVAD first, then LOOK, LISTEN, FEEL:
Look at all connections
Listen for hum
Feel (hot control box usually means thrombosis or other obstruction)
Sometimes there is a hand pump attached to LVAD, but if pt unresponsive with MAP < 50 and etCO2 <20, or LVAD cannot be restarted, it is reasonable to proceed with CPR if you're in a setting without an LVAD team.
TL;DR of what to do when an LVAD patient arrives:
CONTACT THE LVAD TEAM through extension 35CHF here at Maimo.
Patients with LVADs may have no palpable pulse and that is normal! You should hear a continuous hum on auscultation to verify that it is working.
Look at all connections, listen for hum, analyze settings on the box.
Measure the BP with a cuff and doppler and aim for a MAP of 70-80, no more than 90. An A-line should be placed for close hemodynamic monitoring.
Do a bedside echo and get the usual labs but include hemolysis labs/coags.
In a hypotensive patient with an LVAD, low flow is from hypovolemic shock; high flow will either be distributive (normal power reading) or obstructive shock (high power reading).
Shocks are okay for the appropriate arrhythmias.
If a patient is in circulatory collapse and the LVAD is not working/can't be restarted/there is no handpump, it is reasonable to proceed with CPR if you're in a setting without an LVAD team, but follow your institutional recs. Note that here at Maimo, it is advised not to start compressions.
References
https://emcrit.org/emcrit/left-ventricular-assist-devices-lvads-2/
https://criticalcarenow.com/when-a-vad-goes-bad/