Echocardiographic Evaluation of Ventricular Support Devices

12 Echocardiographic Evaluation of Ventricular Support Devices

James N. Kirkpatrick

Background

• Ventricular assist devices (VADs) were initially used to stabilize patients with acute cardiogenic shock (particularly post–cardiac surgery).
• Subsequently, they have been used as a “bridge to transplant,” “bridge to recovery,” or “bridge to decision” (stabilizing patients during work-up to decide transplantation candidacy) and as “destination therapy” (lifelong use).
• Early-generation left ventricular assist devices (LVADs) mimic the pulsatile action of the heart and have inlet and outlet valves (Figure 12-1A; Table 12-1).
• Pulsatile pumps can be set to fixed heart rate or automatic modes.
• Automatic mode on pulsatile pumps varies heart rate to maintain constant volume; therefore, pumping is asynchronous with the electrocardiogram (ECG).
• More recent LVADs are continuous flow, involving axial (rotating propeller) pumps, and have no valves (making them more durable) (see Figure 12-1B; see Table 12-1).
• In continuous-flow LVADs, rotor speed (in rotations per minute, rpm) and pressure difference between inflow chamber and outflow chamber (usually left ventricle and aorta, respectively) determine flow.
• In continuous-flow LVADs, increasing rotor speed leads to ventricular unloading.
• Even in continuous-flow LVADs, pulsatility is present as a result of residual ventricular function and the fact that LVAD flow is higher when the aorta-LV pressure differential is low (systole) and lower when the differential is higher (diastole).
• Third-generation VADs are magnetically or hydrodynamically levitated, continuous-flow centrifugal (rotating plate) pumps with no bearings or valves, theoretically making them even more durable than second-generation VADs (see Table 12-1).
• The dysfunctional RV can respond well to LVAD implantation because of reduced afterload from lower pulmonary pressures.
• Alternatively, the RV function may worsen because of high preload from increased venous return secondary to increased left-sided output.
• Some patients receiving LVADs will require RV mechanical support, either temporarily (separate right ventricular assist device [RVAD]) or permanently (biventricular assist device [BiVAD]).
• Other patients with RV dysfunction can be supported medically with pulmonary vasodilators and inotropes.
• RVADs generally involve an inflow cannula placed in the right atrium and an outflow cannula placed in the proximal pulmonary artery.
• The total artificial heart is an alternative to VADs as a bridge to transplantation and consists of right and left pumping chambers attached to the native atria.
• The intra-aortic balloon pump (IABP) reduces systolic afterload on the left ventricle and can improve diastolic coronary flow via counterpulsation in the descending aorta.
• Percutaneous ventricular assist devices (PVADs) involve cannulae inserted via peripheral arteries and veins.
• PVADs can provide 2 to 6 L/min of cardiac output support and can be placed quickly in acute cardiogenic shock from (usually left but also right) ventricular decompensation and/or acute severe mitral regurgitation.
• PVADs are used primarily as a bridge to recovery and “bridge to bridge” (acute stabilization with subsequent implantation of a standard LVAD).
• PVADs are also used in high-risk percutaneous coronary interventions in patients with severely reduced LV ejection fraction (LVEF), and in percutaneous aortic valve procedures.
• PVADs provide better hemodynamic support than IABPs, but studies have not demonstrated improvements in mortality.
• The Impella Recover (Abiomed, Danvers, MA) can support the right or left ventricle and consists of a catheter in an inflow port and an outflow port that is advanced retrograde through the aorta or pulmonary artery into the ventricle (Figure 12-2A).
• The inflow port placed below the aortic or pulmonic valve draws blood from the ventricle and ejects it from the outflow port positioned above the valve.
• The TandemHeart (Cardiac Assist, Pittsburgh, PA) involves an inflow cannula placed through the femoral vein in the RA, across an interatrial septotomy, and into the left atrium. The outflow cannula is placed through the femoral artery into the abdominal aorta (see Figure 12-2B).
• The TandemHeart can also be used to support the RV.
• Extracorporeal membrane oxygenation (ECMO) provides temporary cardiopulmonary support for patients with reversible cardiogenic shock and/or severe pulmonary failure.
• ECMO systems include an inflow cannula placed into the right atrium via the femoral vein or right internal jugular vein, and an outflow cannula in the femoral artery or ascending aorta.
image

Figure 12-1 Schematic drawings of a pulsatile LVAD (Thoratec XVE; A) and a continuous-flow LVAD (HeartMate II, Thoratec Corp.; B). Components of each LVAD are labeled. The pump is implanted in the upper abdomen. Inflow cannula connects the left ventricular apex to the pumping chamber, which is connected, in turn, to the ascending aorta via an outflow cannula. A drive line runs from the pump, through the skin, to the externalized system controller. The system controller is connected to battery packs. The pulsatile LVADs employ a compressible chamber that fills with blood via an inlet valve. A pusher plate mechanism then squeezes the chamber to expel blood through an outlet valve. The valves have limited durability and contribute to the reduced longevity of first-generation LVADs. The continuous-flow LVADs use either a rotor device (second generation) or a rotating disk (third generation) to accelerate and expel blood. Continuous-flow VADs do not have valves and have proven to be more durable.

(From Thoratec Corp.)

TABLE 12-1 EXAMPLES OF VAD GENERATIONS

Examples Type
First Generation  
HeartMate XVE (Thoratec Corp.) Pulsatile
Novacor pumps (WorldHeart Corp.) Pulsatile
Second Generation  
HeartMate II (Thoratec Corp.) Axial Flow
Jarvik 2000 (Jarvik Heart Corp.) Axial Flow
Micromed DeBakey (Micromed Cardiovascular Inc.) Axial Flow
Third Generation  
HeartWare HVAD (HeartWare Inc.) Centrifugal
Duraheart (Terumo Heart Inc.) Centrifugal
Levacor (WorldHeart Corp.) Centrifugal
Total Artificial Heart  
Abiocor (Abiomed Corp.)  
Cardiowest (Syncardia Inc.)  
image

Figure 12-2 Schematic drawings of percutaneous VADs: Impella Recover (A) and TandemHeart (B). The Impella Recover is advanced retrograde through femoral artery access, across the aortic valve and into the left ventricular cavity. The inlet port (at the tip) is positioned 3 to 4 cm below the aortic valve via a pigtail catheter. The outlet port is positioned 1.5 to 2 cm above the sinus of Valsalva in the proximal ascending aorta. The TandemHeart inflow catheter is advanced through femoral vein access, antegrade into the right atrium and across an interatrial septal puncture, into the left atrium. The separate, outflow catheter is placed in the femoral artery or abdominal or descending aorta.

(A, from Abiomed Corp. B, from CardiacAssist Corp.)

Overview of Echocardiographic Approach (Table 12-2)

LVADs

Preimplantation Echocardiographic Assessment

• Echocardiography establishes severely reduced LVEF, one of the criteria for LVAD implantation.
• Echocardiography excludes diagnoses that complicate LVAD placement.
• Echocardiography assesses preimplantation RV function and can predict the need for RVAD.

TABLE 12-2 APPROACH TO ECHOCARDIOGRAPHY IN LVADS

Preoperative
• Establish criteria for VAD candidacy (LVEF < 25%–30%)
• Assess need for RVAD
• Detect intracavitary thrombi
• Detect aortic atheroma, aneurysms, dissection
• Detect shunts
• Evaluate for valvulopathy, esp. mitral stenosis, aortic insufficiency
Intraoperative
• Direct cannulae placement away from potential obstructions
• De-airing
Diagnosis of LVAD dysfunction
Diagnose Obstruction
• Septum shifted toward RV
• LVEDD increased compared to baseline
• Spontaneous echocardiographic contrast
• High velocities in cannulae
Diagnose Underfilling
• Septum shifted toward LV
• LVEDD reduced compared to baseline
• Pericardial effusion with chamber collapse
• Septum shifting into LV
Diagnose Regurgitation
• Aortic regurgitation
• Mitral regurgitation
• LVAD regurgitation
• Tricuspid regurgitation
Detect Vegetations and Thrombi on Valves and Cannulae
LVAD Optimization
• Changes in LVEDD
• Alignment of interventricular septum
• Changes in degree and frequency of aortic valve opening
• Reductions in aortic, mitral, or tricuspid regurgitation
• LVAD weaning
• Changes in LVEDD, LVEF, aortic valve opening with reductions in level of VAD support
Percutaneous VADs
• Aortic abnormalities
• Aortic stenosis and regurgitation
• Ventricular septal defect
• Positioning of Impella Recovery device across aortic valve
• Guidence of trans-septal puncture for TandemHeart
• Positioning of IABP
• Positioning of ECMO cannulae
• Assessment of catheter migration and obstruction

Implantation/Intraoperative Echocardiographic Assessment

• Echocardiography guides placement of cannulae and de-airing.

Diagnosis of the Causes of LVAD Dysfunction

• Etiologies include obstruction, underfilling, and valvulopathy.
• Comprehensive two-dimensional (2D), M-mode, and color and spectral Doppler echocardiographic examination is crucial for diagnosing the cause of LVAD dysfunction.

Echocardiography-Guided LVAD Optimization

• Optimizing LVAD pumping rates, pumping volumes, or rotor speeds uses echocardiographic measurements to balance proper preload and adequate decompression with excessive unloading leading to “suck-down” events (obstruction of the inflow cannula by trabeculation, chamber walls, papillary muscles, or chordal structures in the setting of an underfilled chamber).

Echocardiography-Guided LVAD Weaning (“Turndown”)

• Decrease in LVAD support will lead to increases in afterload and preload.
• A ventricle that maintains its size and improves its function may have recovered to the point that the LVAD can be explanted.

Percutaneous VADs, IABP, and ECMO

• Echocardiography is useful in preimplantation assessment, placement, and follow-up of two of the currently available PVADs, IABPs, and ECMO.

Key Points

• Comprehensive echocardiography is necessary preimplantation to establish criteria for LVAD implantation, uncover findings that complicate LVAD placement, and assess the need for concomitant RVAD.
• Intraoperative echocardiography guides cannula placement and de-airing.
• Postimplantation use of echocardiography includes diagnosis of the cause of LVAD dysfunction, and guidance of LVAD optimization and weaning.

Preimplantation Echocardiographic Assessment

Anatomic Imaging

Acquisition

• Standard echocardiographic imaging techniques are used to evaluate cardiac anatomy, with particular attention to ventricles, the left atrium, the great vessels, and the interatrial and interventricular septae.
• In patients with limited echocardiographic windows, the use of microbubble contrast for LV opacification may be necessary to provide an accurate LVEF assessment.
• Microbubble contrast may be necessary to detect LV thrombi prior to LVAD implantation.
• Transesophageal echocardiography (TEE) is necessary to exclude LA and LA appendage thrombus, especially before planned LA cannulation.
• Agitated saline contrast study is necessary to examine the interatrial septum for evidence of atrial septal defect (ASD) or patent foramen ovale (PFO) prior to implantation. TEE may be required for optimal visualization of the septum.

Analysis

• Standard measurement and interpretation is done, with careful measurements of ventricular size (LV end-diastolic diameter [LVEDD]) and function, and detection of thrombi, aortopathy, and shunts.
• Echocardiography establishes LVEF criteria for LVAD (<25% to 30%).
• Real-time three-dimensional (3D) echocardiography may provide more accurate and reproducible measurements of LV volumes and LVEF.
• Severely enlarged RVs (defined in single-center experiences as > 85-mm end-diastolic diameter, > 200-mL end-diastolic volume, > 177-mL end-systolic volume, or short-axis to long-axis ratio ≥0.6), severe qualitative systolic RV dysfunction, tricuspid annular planar systolic motion (<7.5 mm in one study), or moderate to severe tricuspid regurgitation (TR), may require RVAD support (Table 12-3).

TABLE 12-3 PREDICTORS OF THE NEED FOR RVAD

Echocardiographic Finding Measurement
RV enlargement
• RVEDD > 85 mm
• RVEDV > 200 mL
• RVESV > 177 mL

Related posts:

  1. Evaluation of the Patient with Diastolic Dysfunction
  2. Echocardiography in the Patient with Right Heart Failure
  3. Distinguishing Systolic versus Diastolic Heart FailureA Practical Approach by Echocardiography
  4. Echocardiographic Assessment of Heart Failure Resulting from Coronary Artery Disease

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Jun 11, 2016 | Posted by in CARDIOLOGY | Comments Off on Echocardiographic Evaluation of Ventricular Support Devices

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