Updated comprehensive guidelines for the multimodality imaging of LVADs were recently published in 2024. We propose a succinct TTE protocol for assessment of HM3 which can be utilized in the clinical management of LVAD patients, seen in Table 1 , Table 2 , and Figure 1 . TTE evaluation of LVADs includes the assessment of (1) positioning and function of the inflow and outflow cannulas; (2) left and right atria, and interatrial septum; (3) left and right ventricular function; (4) valvular function (5) LVAD echocardiographic ramp study and (6) use of TEE in LVAD patients. When obtaining TTE images, vital signs, including blood pressure and heart rate, LVAD model, pump speed, and pump flow at the time of the study should be listed on the initial image acquired. LVAD patients often do not have a palpable pulse, and the blood pressure must be measured using a Doppler probe with the understanding that in patients with little to no aortic valve (AV) opening, the first Korotkoff sound correlates with the mean arterial pressure and in patients with full AV opening, the first Korotkoff sound correlates to the systolic blood pressure.

• (1) Assessment of pump positioning and function: ( Figure 1 )

  • a. The inflow cannula:

    The inflow cannula is inserted into the left ventricular (LV) apex and should be pointed toward the mitral valve (MV). Laminar flow towards the inflow cannula should be seen using color Doppler on parasternal long axis (PLAX) or apical 4-chamber (A4C) views. A low diastolic and higher systolic velocity should be seen on pulsed wave (PW) Doppler with sample volume placed in the inflow cannula where it is best visualized either in PLAX or A4C views. As HM3 LVADs alter rotor speeds every 2 seconds to create an artificial “pulse,” intermittent changes in flow may appear on PW Doppler, which is a normal finding. ^,, The systolic velocity should be <1.5 m/s and the flow should be continuous and laminar.

  • b. The outflow cannula:

    The outflow cannula is made from a woven polyester material and is anastomosed to the ascending aorta. The proximal end travels within and through the bend relief, a reinforced tube that prevents kinking and abrasion, and attaches to the pump which is inserted in the LV apex. The distal end is sutured to the ascending aorta by an end-to-side anastomosis. The outflow cannula is often difficult to visualize on TTE though velocities can be assessed. Standardized velocities have not been established, as peak and mean velocities vary with pump speed and changes in LV preload and end-diastolic volume. However, an outflow cannula peak systolic velocity greater than 2 m/s may be abnormal. If the outflow velocity can only be seen in diastole, this suggests there is excessive unloading of the ventricle by the LVAD. Color Doppler should be used to locate the outflow cannula and align the PW Doppler to assess velocities. If the outflow graft can be visualized in the modified right parasternal view or suprasternal notch view, PW Doppler of the graft should be acquired within 1.0-1.5 cm from the site of anastomosis. ^, To better visualize the outflow cannula, CT scans may be utilized, the details of which will be discussed later.

• (2) Assessment of the left and right atria and interatrial septum: ( Figures 1 and 2 )

  

  Echocardiographic ramp study and transesophageal echocardiography of LVAD patients. Caption: positioning of the interventricular septum during ideal LV unloading, inadequate LV unloading, and excessive LV unloading as seen during ramp studies. Transesophageal echocardiographic assessment of LVAD inflow cannula. A4C = apical 4-chamber; LV = left ventricular; LVAD = left ventricular assist device; MR = mitral regurgitation; RPM = revolutions per minute.

  The left atrium (LA) and right atrium (RA) volumes should be measured per standard guidelines. A patient’s volume status can be evaluated by assessing the position of the interatrial septum. lnteratrial septum (IAS) should be positioned at midline. Rightward shift may mean underdecompression of the LV; for which increase in LVAD speed should be considered. Leftward shift of the IAS may indicate increased RA pressure or overdecompression of the LV and reduction of LVAD speed should be considered.

• (3) Assessment of the left and right ventricles:

  • (a) Left ventricle: ( Figures 1 , 2 , and Table 2 )

    LV remodeling in the setting of myocardial injury or alterations in loading conditions can result in modification of LV shape from elliptical to spherical. With effective unloading of the LV by the LVAD, there can be normalization of LV size and shape. This can be assessed in the usual TTE views. ^, LV volumes and LV ejection fraction (EF) should be calculated using Simpson’s biplane method of discs. The interventricular septum (IVS) should ideally be positioned in the middle between the left and right ventricles (RV), taking into consideration postsurgical septal motion changes. ^, Septal shift to the right indicates inadequate unloading while septal shift to the left indicates excessive unloading, which can worsen RV function. Excessive LV unloading can lead to suction events of the inflow cannula and ventricular arrhythmias. If TTE windows are severely limited, a transhepatic approach has been suggested. In the apical views, LV global longitudinal strain can be measured using speckle tracking. A standard dose of contrast can be used safely in patients with LVADs to improve visualization of LV endocardial borders. If the 2-dimensional echocardiography (2DE) images obtained are of adequate quality, 3-dimensional echocardiography (3DE) should be attempted as it offers more accurate LV volume measurements and better visualization of both ventricles. ^,, However, in the LVAD population, adequate 3DE imaging can only be acquired in about half of patients due to pump artifact, body habitus, and arrhythmias. To best optimize 3DE, volume assessments should be performed using electrocardiographic gating over 4 to 6 cardiac cycles during a single breath-hold. Decreasing the sector width and minimizing the depth by excluding the atria allows for maximal frame rates. Using commercial software, LV and right ventricular end-diastolic volume (EDV), end-systolic volume (ESV), and EF can be calculated. Comparisons of 2DE and 3DE in the LVAD population have been performed and investigation of clinical and prognostic utility of 3DE is an active area of research. LV EDV is expected to decrease after LVAD implantation on 2DE and 3DE, though LV EF and global longitudinal strain may not change significantly.

  • (b) Right ventricle: ( Figure 3 and Table 2 )

    

    Echocardiographic evaluation of the right ventricle. Evaluation of the right ventricle in patients with heartmate 3 devices using doppler and 2D echocardiography. A4C = apical 4-chamber; CW = continuous wave; EDA = end diastolic area; ESA = end systolic area; FAC = fractional area change; LV = left ventricular; PSAX =parasternal short axis; PW = pulsed wave; RV = right ventricular; RVOT = right ventricular outflow tract; TAPSE = tricuspid annular plane systolic excursion; VTI = velocity time integral.

    A critical factor in successful LVAD implantation is optimizing RV function. Assessment of RV anatomy and function on TTE can be challenging. In addition to routine 2D, M mode and tissue Doppler assessment, current guidelines recommend obtaining RV strain data. RV free-wall strain (RVFWS) is obtained in the RV-focused A4C view using speckle tracking. ^, RV global longitudinal strain (RVGLS) is argued to be more accurate in determination of RV function as the RV relies heavily on septal contraction to generate cardiac output. Nonetheless, both RVFWS and RVGLS are effective tools in predicting RV failure in patients with LVADs. Standardized RV strain values in HM3 LVADs have not been established, however, RV absolute longitudinal strain < 9.6% has been associated with development of RV failure in HeartMate II LVADs. If 3DE images in the modified RV-focused A4C view are obtained, it is recommended that the contours of the RV endocardial border tracings include the trabeculae, papillary muscles, and moderator band.

• (4) Assessment of valvular function: ( Figures 1 and 4 )

  • (a) Aortic valve:

    The AV may be closed, open intermittently, or open on each beat, and this should be reported. If the AV opens with every beat, LV unloading may be inadequate. If an inadequate volume is unloaded from the ventricle via the LVAD, the excess volume generates increased LV pressures which can exceed the aortic pressure, causing the aortic valve to open with every beat. If the AV remains persistently closed, LV unloading may be excessive, which can lead to AV commissural fusion and leaflet deterioration, with the risk of progressing to moderate to severe aortic regurgitation (AR). ^, AV opening frequency can be visualized in the PLAX and parasternal short axis (PSAX) views; M-mode can be used as well. Lack of opening of the AV in the early post implantation period, when the patient is not fully anticoagulated, may result in aortic root thrombus formation. Although the optimal rate of the AV opening is a clinical judgement, the findings should be adequately reflected in the report.

    In native hearts, AR occurs in the diastolic phase of the cardiac cycle. As LVADs do not have a true diastolic phase, regurgitant flow occurs throughout the entire cardiac cycle, driven by an LVAD–induced reverse transaortic pressure gradient, thus conventional methods of quantifying AR (vena contracta, proximal isovelocity surface area, etc.) are inaccurate and underestimate the severity of AR. Consequently, the outflow cannula has become an essential component of AR evaluation in LVAD patients, by measuring outflow cannula diastolic acceleration time and outflow cannula systolic-to-diastolic (S/D) peak velocity ratio. ^,, LV preload will progressively increase with constant regurgitant flow across the AV. Simultaneously, there is decreased antegrade flow into the aorta from the outflow cannula, resulting in decreased aortic pressure predominantly during ventricular diastole. This elevated preload and decreased afterload physiology creates a flow gradient across the AV that can be measured by the S/D peak velocity ratio at the outflow cannula on echocardiography. Ultimately, S/D peak velocity ratio decreases and outflow cannula diastolic acceleration time increases with worsening AR. These new parameters better correlate to invasive hemodynamic assessment of AR compared to standard vena contracta measurements in HeartWare and HeartMate II LVAD patients, however, validation of this technique in HM3 patients is necessary. Of note, obtaining the spectral profiles of the outflow cannula in the ascending aorta can be challenging. They can typically be obtained using the modified right parasternal view or suprasternal notch view. Both parameters are measured via PW Doppler. Diastolic acceleration time measures the diastolic slope from the onset to the end of the diastolic phase, and S/D peak velocity ratio measures peak systolic velocity to peak diastolic velocity on PW Doppler. ^,

  • (b) Mitral valve:

    The presence of an LVAD leads to improved LV unloading with reverse remodeling of the LV, decreased mitral annular size, better leaflet coaptation, and reduction in mitral regurgitation (MR) severity. Despite this, secondary MR is a common finding on TTE in patients with LVADs. MR can be assessed using standard TTE guidelines. Persistence of MR is a sign of insufficient LV unloading and can predispose patients to increased risk of RV failure in the setting of elevated RV afterload. Monitoring of MR on interval TTE examinations and mitigating MR with LVAD setting modifications during ramp studies can optimize sufficient LV unloading and prevent RV decompensation.

  • (c) Tricuspid valve:

    While many patients experience improvement of tricuspid valve regurgitation (TR) after LVAD implantation, LVAD support can sometimes worsen the severity of TR. Both preoperative and postoperative TR is associated with increased mortality and right heart failure. Unloading the LV results in a leftward shift of the IVS, increased venous return, and increased RV stroke volume, leading to dilation of the tricuspid annulus and worsening TR. Patients with advanced heart failure who require LVAD support often have implantable cardiac devices and leads passing through the tricuspid valve can impair valve closure, leading to TR as well. Low Doppler velocities of <2 m/s are seen in severe TR due to the equalization of pressures between the RV and RA. Significant TR leads to decreased forward flow from the RV and reduces LV preload.

  

  Assessment of valvular regurgitation. Evaluation of regurgitant valvular lesions in patients with Heartmate 3 devices using Doppler and 2D echocardiography. CW = continuous wave; PW = pulsed wave.

• (5) LVAD ramp testing: ( Figure 2 )

  Echocardiographic ramp speed optimization evaluations help achieve optimal biventricular geometry and function in patients with HM3s. While the ideal frequency for performing ramp studies is uncertain, the International Society for Heart and Lung Transplantation (ISHLT) recommends regular echocardiographic evaluation to monitor myocardial recovery in stable patients as well as to assess for device malfunction in patients with persistent HF symptoms or concerns for pump thrombosis. Ramp tests have been noted to improve LV unloading with increased final LVAD speed settings without compromising RV function when performed immediately after implantation and at 1-to-3 months postimplantation in clinically stable patients. Recent guidelines provide a framework to perform ramp studies and provide values to suggest myocardial recovery. The optimal LVAD speed is defined as one at which there is intermittent AV opening, a neutral position of the IVS, with preservation of RV function, without increase in AR or TR, and ideally, mild or minimal MR. Generally, the pump speed is increased in increments from a specific lower speed limit to a predetermined upper limit until suction events occur, frequent premature ventricular contractions (PVCs) are noted, or LV end-diastolic diameter (LVEDD) decreases to <3 cm, at which time the ramp test should be stopped. ^, At each stage of the ramp study, standard 2DE and 3DE views are obtained to determine the optimal speed setting. Ideally, the LV volume should decrease and the LV shape should change from spherical to conical, whereas the RV volume only changes at higher pump speeds due to changes in IVS curvature. LVAD parameters, such as the pulsatility index, pump power, and pump flow, should remain within acceptable ranges and be closely monitored during each stage of the study as well.

  Some centers perform right heart catheterization (RHC) simultaneously with echocardiographic ramp studies, coined “hemodynamic ramp” studies. Hemodynamic ramp studies are associated with more speed increases than echocardiographic guided ramp studies, thus providing more personalized hemodynamic evaluation and optimization of LVAD patients. Ramp study protocols vary across institutions; however, Rubenstein et al. recently published a hemodynamic ramp study protocol of HM3 LVADs that focuses on altering speed to achieve optimized biventricular filling pressures (central venous pressure and pulmonary capillary wedge pressure) which led to decreased hospitalizations at 1 year follow up.

• 6. Use of transesophageal echocardiography in LVAD patients: ( Figure 2 )

  TEE is most frequently used in the perioperative period. Prior to LVAD implantation, TEE is utilized for assessment of the IAS with bubble study to identify patent foramen ovale (PFO), which if detected warrants closure prior to LVAD implantation. In patients with chronic HF, altered hemodynamics with low interatrial pressure gradients may result in difficulty identifying a PFO prior to LVAD placement. In such cases, TEE interrogation with bubble study is repeated immediately post implant to identify shunt and surgical repair is considered at that time. Additionally, during implantation, TEE is used to evaluate air trapping in the LV and to guide deairing maneuvers to prevent air embolism on activation of the LVAD. Air usually appears as white hyperechoic specks in the anterior portions of the LV and LA. Immediately after implantation, LVAD speed optimization, evaluation of inflow cannula position and flow, and monitoring for intracardiac shunting is performed. ^, The midesophageal 4C and 2C views are the best views for assessing inflow cannula position with color and PW Doppler interrogation of laminar flow and flow velocities. Outside of the perioperative period, TEE should be considered if TTE images are suboptimal in at least 2 windows, if hemodynamic instability occurs, recurrent low flow LVAD alarms are present, or if there is concern for endocarditis.

Table 1

Transthoracic echocardiographic evaluation of heartmate 3 left ventricular assist devices

• Record the patient’s vital signs (heart rate and blood pressure), LVAD device type, and pump speed on the initial image ○ When measuring blood pressure, attempt to measure a cuff pressure first and if it cannot be obtained, then attempt a manual Doppler blood pressure (Doppler opening pressure correlates to the mean arterial pressure) • Use contrast agents to improve endocardial border definition • Consider performing transesophageal echocardiogram if: 1) images are suboptimal in at least 2 windows (i.e. parasternal long axis and apical 4-chamber views), 2) hemodynamic instability is present, 3) recurrent low flow LVAD alarms are occurring

Parasternal long axis view: Aortic valve (AV): • M-mode of the AV with 10 beat acquisition and decreased sweep speed to determine how frequently the AV opens ○ Assess if AV opens normally, partially, or remains closed ○ During ramp studies, AV opening should be recorded at the highest and lowest speed settings tested • Assess severity of aortic insufficiency (AI), if present ○ Measure the vena contracta and width of the regurgitant jet ○ Use M-mode and color Doppler to determine whether AI is diastolic or continuous If AI is continuous, upgrade severity by half a grade Mitral valve: • M-mode of the mitral valve • Color Doppler to assess severity of mitral regurgitation ○ Measure the vena contracta Left ventricle (LV): • Include the apex with the outflow cannula in this view • Measure the following linear dimensions: ○ LV end diastolic dimension ○ LV end systolic dimension ○ Interventricular Septum ○ Posterior Wall • During ramp studies, measure the maximal LV dimension at the lowest speed and the minimal LV dimension at the highest speed Aorta: • Evaluate for dilation and/or dissection flap ○ If a dissection flap is seen, use color Doppler to assess flow • High parasternal/off axis view may allow for visualization of part of the outflow graft as it travels over the right ventricle prior to anastomosis to the ascending aorta Pericardium: • Determine presence of effusion and if present, measure the size of the effusion in diastole

Apical views: Inflow cannula: • May need off-axis apical positions to show 2D view and may need to decrease sweep speed • Color and PW Doppler on-axis with the inflow cannula Aortic valve: • Can attempt M-mode in this view if AV opening was not well visualized previously • Continue assessment as in the parasternal long axis view Mitral valve: • Continue assessment as in the parasternal long axis view Tricuspid valve: • Assess for severity of tricuspid regurgitation, if any, using color and CW Doppler ○ Measure the vena contracta • Measure the tricuspid annulus at end-diastole • Assess RVSP using CW Doppler of the tricuspid valve for TR velocity ○ Estimate right atrial pressure using IVC size and collapsibility Right ventricle (RV): • In the apical 4-chamber view with focus on the RV, measure the following: ○ RV basal linear dimension ○ RV end diastolic area ○ RV end systolic area ○ RV fractional area change • M-mode of the tricuspid annulus for TAPSE measurement • Assess interventricular septal position; the ideal septal position is midline ○ During ramp studies, assess the septal position at different speeds

Subcostal views: Inferior vena cava: • Estimate right atrial pressure using IVC size and collapsibility with inspiration Pericardium: • Assess for pericardial effusion and/or pericardial hematoma • Assess for cardiac tamponade by observing for collapse of the right atrium and/or right ventricle

Suprasternal notch views: Outflow Cannula: Located at the ascending aorta • May need off-axis views in the suprasternal and right parasternal views to show 2D view of the cannula • Perform color, CW, and PW Doppler of the outflow cannula

Additional instructions for ramp studies: • Use the same window to reliably assess changes in LV dimensions when ramp studies are performed • Record pump speed, heart rate, and blood pressure on the acquired images serially when the pump speed is adjusted • In the parasternal long axis: measure LVEDD, LVESD, AV opening, presence of AI and MR, position of the interventricular septum • In the parasternal short axis, evaluate the position of the septum again which should ideally be midline

Additional instructions for LVAD weaning: • Perform baseline TTE as previously outlined • Depending on the LVAD center’s experience, TTE evaluation should be performed at the recommended lowest pump speed with close hemodynamic monitoring (apical, parasternal, and subcostal views as above)

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