VADs

Question 1

LVAD Indications

Answer 1

• Bridge to transplantation — main indication
• Temporary support — reverse neurohumoral response to heart failure
• Destination therapy — palliative therapy

Question 2

Pre-bypass

Answer 2

•Aortic valve function (most important valve)
-significant AI is detrimental -> repair/replace/sew closed
-if replaced -> bio prosthetic valve d/t decrease flow across mechanical valve creates nidus for thrombus
-sewn closed if won’t be weaned from device
•Intracardiac shunts (interatrial septal defect)
- R —> L shunt creates hypoxia and paradoxical emboli
- L —> R shunt will quickly revert to R —> L shunt after LVAD implant
- needs repaired
•Intracardiac thrombus
- low EF predisposes to thrombus
- PWD at opening of LAA and velocity > 45 cm/s suggests thrombus unlikely [ > 55 cm/s has a 100% NPV ]
•RV function
- RV supplies preload to the device
- FAC of RV in ME4C view
- measure lateral TAPSE
- assess for TR — greater than moderate may need repair
•Aortic atherosclerosis (epiaortic exam)
- assess outflow cannula site and where cross clamp placed
•Mitral valve exam — stenosis?
- reduces preload to the device and decreases effective systemic perfusion

Question 3

Weaning from bypass

Answer 3

•Evaluated LVAD inflow cannula
- make sure not obstructed by thrombus or septum not getting sucked up against it (“suck down effect”) — treat by increased preload, increased afterload, decreased flow through device
- inflow obstruction seen with pulsatile device with velocity > 230 cm/s or axial device with velocity > 100 - 200 cm/s
- most have diameter of 16 mm and flow of 65 ml
- inflow cannula sites : LV apex (conventional, obstruction?) ; Trans-aortic (Impella, possible SAM) ; Trans-atrial septum (Tandem heart) ; LA (posterior aspect of LA)
•Outflow cannula sites
- ascending aorta (conventional) - make sure no outflow obstruction
- trans-aortic valve (impella)
- femoral artery (tandem heart , P-VAD)
- descending aorta (Jarvik 2000)
•Adequate flow (appropriate LV volume)
•Aortic valve function — now subject to LVAD flow w/ higher systolic pressures which may cause AI and reentrant flow decreasing systemic perfusion
•Intracardiac shunts (interatrial septal defects) — lower left side pressures facilitate R —> L shunt creating hypoxia and paradoxical emboli
•De-airing — important so aire doesn’t go down RCA and make RV worse
•RV function — may need augmented with phosphodiesterase inhibitors, beta agonists, nitric oxide — optimize oxygenation and ventilation

Question 4

Post bypass

Answer 4

• RV function (biggest concern) — frequently needs augmentation
• Unobstructed inflow cannula — Vpeak < 230 cm/s
• Volume status
• Intact septum

Question 5

Post op (ICU)

Answer 5

•Hypoxia —> look for PFO and optimize lung function
•CVA —> look for PFO or thrombus
•Hemodynamic instability
- hypovolemia due to bleeding most common
- tamponade
- RV failure
- infection d/t sepsis (late finding)
- device failure — axial flow devices less likely to fail compared to older pulsatile devices due to valve insufficiency

Question 6

Intra-aortic balloon pumps

Answer 6

•Blows up right after AV closes to provide augmented diastolic perfusion of the coronaries
•Deflates rapidly as AV opening to create a vacuum to offload the LV
•Indications:
- LV systolic failure
- post bypass HD collapse
- unstable angina
- preop for high risk patients
•Contraindications:
- significant AI
- aortic dissection
- prosthetic graft in descending aorta
- severe arotoiliac disease
- aorta-pulmonary shunt (BT shunt)
•Complications:
- aortic dissection and arterial perforation
- limb ischemia
- thrombocytopenia
- thromboembolic complications
- balloon rupture with helium embolus
- hematoma
- pseudo aneurysm 
- arteriovenous fistula
- infection
- bleeding
•Position 1 cm distal to left subclavian artery

Question 7

LVAD low flow alarm differential

Answer 7

• LVAD suction event
• hypovolemia
• RV failure
• tamponade
• malignant hypertension
• inflow thrombus or outflow graft kinking / obstruction
• arrhythmias

Question 8

LVAD high flow (high power) alarm differential

Answer 8

• sepsis with vasodilation
• medication with vasodilation effect
• rotor/bearing thrombosis with pump malfunction
• significant AR

Question 9

IABP

Answer 9

• unloads the ventricle (lower pressure but volume doesn’t change)
• pre-existing dysfunctional ventricle will not have CO augmented as much — balloon pump increases diastolic pressure which increases coronary perfusion but need a functioning LV to increase CO
• positioned 1 - 2 cm distal to left subclavian artery
• consider aortic pathologies before placing : dissection, AR, coarctation, severe / mobile atheroma

Question 10

Impella

Answer 10

• axial device that goes through AV and directly unloads the LV
• decreases afterload and decompresses the ventricle [P-V loop becomes more triangular] — primary unloading prior to reperfusion may reduce size of infarct
• correct placement approximately 3.5 cm from annulus into ventricle
• too far may injure tissue or cause recirculation in LV
• anatomic considerations: AI, AS, PFO, LV thrombus

Question 11

Tandem Heart

Answer 11

•requires a transeptal puncture
- right side from SVC
- left side from IVC
•acts more similar to ECMO resulting in loading of the LV although decompressed and decreased volume from cannula in atrium but the afterload similar to that with ECMO (higher LV pressures but lower volumes)
•can be used with LV closet due to location of cannula in the atrium

Question 12

ECMO

Answer 12

•loads the LV — good tool to treat hypotension
•can combine ECMO to increase blood pressure with Impella to unload the LV
•”North-South Syndrome” — occurs in VA ECMO as the heart recovers and starts to eject before lungs recovered —> pumps deoxygenated blood
- diagnose with pulse ox on right arm and look for desaturation
- transition zone on ECHO from native CO and blood ejected from ECMO device
•Avalon catheter : VV ECMO
- avoid placement into hepatic veins

Question 13

RV function abnormal threshold values

Answer 13

TAPSE < 16 - 17 mm
RV FAC < 35%
RV dp/dt < 400 mmHg/sec
3D RVEF by cMRI < 45%
RV free wall strain >  -20
RV IVA < 2.2 m/s^2
TDI lateral TV annulus S’ < 10 cm/s
MPI by TDI > 0.55
MPI by PWD > 0.4