Short-term left ventricular mechanical circulatory support: Use of echocardiography during initiation and management

INTRODUCTION — Temporary short- and intermediate-term left ventricular (LV) mechanical circulatory support (MCS) devices may be used for patients with cardiogenic shock or cardiorespiratory failure when medical therapy has failed. Typical indications include failure to wean from cardiopulmonary bypass (CPB), acute myocardial infarction, or as a bridge to a durable left ventricular assist device (VAD) or heart transplantation. Temporary LV support is also used during selected high-risk interventional cardiology and electrophysiology cases.

This topic addresses the role of transesophageal echocardiography (TEE) imaging during short-term MCS for the LV (eg, to guide insertion and positioning of device cannulae, monitor device function, and facilitate eventual weaning from the device).

Other topics address:

●Use of TEE to guide insertion, positioning, monitoring, and weaning of short-term right ventricular (RV) MCS devices - (See "Short-term right ventricular or biventricular mechanical circulatory support: Use of echocardiography during initiation and management".)

●Use of TEE imaging to facilitate initiation, monitoring, and weaning of extracorporeal membrane oxygenation (ECMO) – (See "Extracorporeal life support in adults in the intensive care unit: The role of transesophageal echocardiography (TEE)".)

Indications, device selection, and general management of patients who require short-term LV and/or RV MCS are addressed in a separate topic. (See "Short-term mechanical circulatory assist devices".)

OVERVIEW OF LV SUPPORT — Devices typically used to provide short-term LV support include the percutaneously inserted intra-aortic balloon pump (IABP), LV-to-aorta axial flow device (Impella), left atrium (LA)-to-aorta device with a centrifugal pump containing a spinning impeller (TandemHeart), and nonpercutaneous continuous flow centrifugal blood pump (CentriMag) (table 1). Device selection depends on the setting, the specific indication for hemodynamic support, the urgency of need, and patient-related or device-related risks or contraindications, as well as variable availability and institutional experience with specific device(s). (See "Short-term mechanical circulatory assist devices".)

Short-term LV support increases cardiac output (CO) to improve end-organ and coronary perfusion, decreases myocardial oxygen consumption, improves LV unloading to provide an opportunity for myocardial recovery, and reduces pulmonary edema associated with refractory LV dysfunction.

Weaning and removal of temporary MCS to the LV is considered in hemodynamically stable patients who exhibit evidence of myocardial recovery (ie, increased systemic arterial pulsatility and increased native CO with only low levels of inotropic, vasopressor, and device support), as well as end-organ recovery.

ECHOCARDIOGRAPHY BEFORE INITIATING LV SUPPORT — Transesophageal echocardiography (TEE) or transthoracic echocardiography (TTE) is often used before initiation of short-term MCS for the LV [1-3]. Notably, use of TEE or TTE is not always necessary during emergency implantation of some temporary MCS devices. For example, intra-aortic balloon pump (IABP) and percutaneous axial flow devices are often inserted in the cardiac catheterization suite using fluoroscopy to guide placement of cannulae.

When available, echocardiography is useful to:

●Confirm the presumed diagnosis and need for an MCS device to support the LV.

●Determine whether abnormalities that may contraindicate device placement or interfere with device function are present, such as:

•Aortic regurgitation (AR) (movie 1 and image 1 and image 2). AR limits the effectiveness of a temporary MCS device since a significant amount of the blood delivered to the aorta would be directly returned to the LV, resulting in LV distention and possibly pulmonary edema if left atrial (LA) pressures are persistently elevated. Notably, AR may occur intermittently, during diastole, or throughout the entire cardiac cycle in the case of continuous flow devices [4]. Assessment of severity of AR is typically based on the width of the color-flow Doppler (CFD) AR jet vena contracta or the ratio of vena contracta width to LV outflow tract (LVOT) diameter, but may be affected by reduction in the volume of blood ejected by a severely dysfunctional LV. (See "Echocardiographic evaluation of the aortic valve", section on 'Doppler echocardiography' and "Clinical manifestations and diagnosis of chronic aortic regurgitation in adults", section on 'Echocardiogram' and "Acute aortic regurgitation in adults", section on 'Echocardiography'.)

•Intracardiac shunting via an atrial septal defect (ASD) (movie 2), ventricular septal defect (VSD), or patent foramen ovale (PFO) (movie 3). When blood is drawn from the LV during MCS, exacerbation of right-to-left shunting may result in worsening hypoxemia or paradoxical embolism. Larger PFOs are typically closed at the time of placement of an MCS device, particularly if the patient has pulmonary hypertension, hypoxemia, or a history of paradoxical embolization. (See "Patent foramen ovale", section on 'TEE, TTE, and ICE' and "Clinical manifestations and diagnosis of atrial septal defects in adults", section on 'Echocardiography'.)

•LA or ventricular thrombi (figure 1), which may become dislodged and embolize into the systemic circulation or into the MCS device to occlude the outflow cannula.

•Aortic dissection, which creates a false lumen where a wire or catheter may be placed unintentionally during attempts to insert device cannulae (movie 4 and image 3). This may result in extension of the dissection and ineffective MCS.

•Severe aortic atheromatous disease with large (ie, >5 mm height) or mobile atheroma on TEE, due to risk of embolization to mesenteric vessels or peripheral arteries (image 4 and movie 5).

•Significant right ventricular (RV) dysfunction that may impair flow from RV to LV (movie 6 and movie 7). In addition, increased venous return to the RV (which occurs with effective LV mechanical support) may precipitate acute RV distention and failure. In some cases, an RV support device is added to manage this. (See "Short-term mechanical circulatory assist devices", section on 'Right ventricular assist devices'.)

•Other device-specific contraindications, which may include severe aortic stenosis or presence of a mechanical aortic valve. These abnormalities are particularly relevant for devices passed over a guidewire and through the aortic valve, with final positioning within the LV cavity. (See 'Impella device for LV support' below.)

PROCEDURES FOR SPECIFIC LV SUPPORT DEVICES

Intra-aortic balloon pump — The intra-aortic balloon pump (IABP) is the most widely used temporary MCS device for support of the LV and is commonly employed to manage cardiogenic shock after cardiopulmonary bypass (CPB) [5,6]. Basic principles regarding uses and complications of IABP counterpulsation are presented separately. (See "Intraaortic balloon pump counterpulsation".)

●Overview of IABP support – During diastole, inflation of the IABP balloon, which is positioned below the takeoff of the left subclavian artery in the descending aorta, displaces blood toward the aortic root and into the coronary arteries, which augments diastolic blood pressure (BP) to increase coronary blood flow and improve coronary perfusion [5]. In addition, rapid deflation of the balloon during the systolic phase of the cardiac cycle (just prior to aortic valve opening) reduces LV afterload and LV end-diastolic pressure, which decreases myocardial oxygen consumption and myocardial work by reducing the isovolumic phase of ventricular systole. Expected changes in hemodynamic variables include increased cardiac output (CO) and mean arterial pressure, with decreased systolic BP, increased (augmented) diastolic BP, reduced heart rate (HR), and decreased pulmonary artery wedge pressure (PAWP) [5]. (See "Intraaortic balloon pump counterpulsation", section on 'Hemodynamic effects'.)

●Imaging prior to IABP insertion

•Evaluation for possible contraindications – Transesophageal echocardiography (TEE) may be used in intubated patients immediately before IABP placement to assure that there are no contraindications to its utilization [5-7]. (See 'Echocardiography before initiating LV support' above and "Intraaortic balloon pump counterpulsation", section on 'Contraindications'.)

•Assessment of alternative cannulation sites – An IABP is typically placed through a percutaneously inserted sheath in a common femoral artery using a Seldinger technique. In rare circumstances (eg, severe or mobile aortic atheroma, prior repair of aortic dissection), an IABP may be inserted via a graft to the subclavian artery, aortic arch, or left axillary artery [8]. Ultrasonography may be used to examine these potential alternative sites for atherosclerotic disease.

●Imaging during IABP insertion – Fluoroscopic guidance is often employed for insertion of an IABP in the cardiac catheterization laboratory. Although TEE is not always necessary for IABP placement, it is typically used in perioperative settings to [9]:

•Confirm positioning of the guidewire in the proximal descending thoracic aorta using both long-axis (LAX) and short-axis (SAX) views (image 5). The IABP is then threaded over the guidewire, and then the wire is removed. When an IABP is inserted following surgical repair of an aortic dissection, confirm that it is located correctly in the true lumen of the aorta [10].

•Confirm that the balloon is positioned 1 to 2 cm below the takeoff of the left subclavian artery and aortic arch. This is determined by identifying the descending aorta and tip of the balloon, then withdrawing the TEE probe until the left subclavian artery is identified (image 6) [9].

•Verify balloon placement prior to initiating counterpulsation. Accurate assessment of IABP position is more difficult once the balloon is filled with gas, since this will create significant acoustic shadowing and reverberation artifacts during each diastolic inflation phase [9,11].

•Confirm final positioning of the IABP by obtaining a chest radiograph (CXR) as soon as possible after initial insertion. The IABP tip should lie between the anterior portion of the second intercostal space at the level of the carina at least 2 cm below the aortic arch (image 7 and image 8) [12].

●Use of TEE to monitor IABP support – Proper timing for inflation and deflation of the IABP balloon is shown in the figures (waveform 1 and figure 2). After initiation of balloon assistance, TEE may be used to reassess ventricular function, the degree of aortic regurgitation (AR), changes in previously identified atheroma locations, or the rare complication of iatrogenic aortic dissection [13].

●Use of TEE during weaning of IABP support – Weaning of support from an IABP is generally accomplished by monitoring hemodynamic variables and laboratory measures of adequate circulatory function while IABP support ratios are gradually decreased from 1:1 to 1:4 (image 9) as inotropic and vasoactive medications are appropriately adjusted until support can be discontinued. Although echocardiography is not a key component of weaning, TEE may be used to assess ventricular function as support is gradually withdrawn in patients that are intubated.

Impella device for LV support

●Overview of Impella devices – Impella MCS devices may be used to support the LV or right ventricle (RV) or used in tandem to support both ventricles [14-17]. The Impella LV-to-aorta axial flow ventricular assist device (VAD) has become more common to treat postcardiotomy shock [1,18]. Occasionally, an Impella device is used to reduce distention of the LV caused by AR during venoarterial extracorporeal membrane oxygenation (ECMO) [19]. These devices have also been employed to manage high-risk percutaneous coronary interventions [7,20,21]. (See "Short-term mechanical circulatory assist devices", section on 'Left ventricle to aorta'.)

Impella devices for LV support include the 2.5 (figure 3), cardiac power (CP) (picture 1), and 5.5 device (picture 2), which provide different levels of hemodynamic assistance. However, all require the same positioning across the aortic valve within the LV to achieve optimal effectiveness as blood is withdrawn from the LV cavity and expelled via the outflow port into the aortic root.

Versions of this device that generate blood flow of up to 2.5 L/minute are typically placed percutaneously through the femoral artery or via a surgically placed graft to the axillary artery, then across the aortic valve for final positioning in the LV (Impella 2.5 (figure 3)). A larger percutaneous version of the Impella device may generate flows up to 4.3 L/minute (Impella CP (picture 1)). The Impella 5.5 can generate up to 5.5 L/minute. This device is inserted via a graft attached to the ascending aorta or the axillary artery since it is too large to be inserted percutaneously (picture 2).

●TEE evaluation for possible contraindications prior to Impella device insertion – In addition to TEE evaluation for typical contraindications (significant AR, intracardiac shunting or thrombus, or dissection or mobile atheroma in the aorta), TEE is used to rule out severe aortic stenosis or the presence of a mechanical aortic valve since the Impella device will be passed across the aortic valve for final positioning within the LV cavity [22]. A relative contraindication is asymmetric septal hypertrophy because of the risk of worsening the obstruction associated with emptying the LV. However, one case series notes successful use of short-term MCS devices to treat reversible cardiogenic shock in patients with obstructive cardiomyopathy, including one patient who received an Impella device [23].

●Imaging during Impella device insertion – The Impella CP device is usually placed via a femoral percutaneous approach with the use of fluoroscopy. Supplemental information is often obtained from TEE imaging [1,22]. Successful bedside placement with TEE alone has been reported in patients with hemodynamic instability [24].

TEE is used to guide the following sequential steps during a femoral arterial approach for Impella device insertion [1,22]:

•Confirmation of wire positioning within the aortic lumen of the descending thoracic aorta, with no evidence of aortic dissection (image 5). Both SAX and LAX views of the descending aorta are imaged for accurate confirmation.

•Confirmation of guidewire passage across the aortic valve into the LV cavity short of the LV apex to avoid arrhythmias. The midesophageal (ME) aortic valve LAX view is used to confirm guidewire passage across the aortic valve. The tip of the wire should be directed toward the apex of the ventricle while avoiding the mitral apparatus.

•Reassessment of competency of the aortic valve after passage of the guidewire into the LV cavity, as well as the degree of mitral regurgitation, which may increase if the wire distorts the mitral subvalvular apparatus.

•Placement of the Impella device over the guidewire and through the aortic valve, with positioning of the device tip in the mid-LV cavity (image 10). The distance from the aortic valve to the device inlet should be approximately 3.5 cm for all Impella devices, with the exception of Impella 5.5, for which this distance should be 5 cm. Placement too far into the LV may result in the outlet port remaining in the LV and failure to improve systemic blood flow. Final positioning of the device should show it curving toward the apex of the LV and away from the mitral valve, with the outlet positioned distal to the aortic valve (image 10).

•Immediately after Impella placement, a comprehensive TEE examination should be performed, including color-flow Doppler (CFD) imaging to evaluate for blood flow into the ventricular inlet port of a properly positioned device within the LV, and from the outlet of the device into the aorta (image 10). The ME LAX TEE view allows assessment of device positioning including distance of the ventricular inflow port from the aortic valve, presence of aortic insufficiency, and outflow into the aortic root. CFD imaging should demonstrate laminar flow into the device proximal to the tip (image 10). This TEE examination should also confirm proper function of the mitral and aortic valves without significant or new increases in regurgitation or evidence of aortic or mitral valve perforation, aortic dissection, or pericardial effusion [1,22].

Subsequently, device positioning is also checked with a CXR, which should demonstrate the inflow portion of the device projected over the LV while the outflow is projected over the aortic root (image 11).

●Supplemental confirmation of proper Impella positioning – Correct positioning of the Impella MCS device is also confirmed through interpretation of placement signal waveforms (image 12) [25].

•The presence of ventricular and aortic waveforms indicates proper positioning:

-The aortic waveform is a fiberoptic sensor-derived pressure measurement.

-The ventricular waveform is a value that is calculated from the aortic pressure detected by the optical pressure sensor and the motor current. The motor current recognizes differences in pressure gradients during both systole and diastole during the cardiac cycle. For example, recognition of a 5 mmHg gradient during systole indicates that the LV pressure is 5 mmHg higher than the aortic pressure. A 50 mmHg difference during diastole indicates that the LV pressure is 50 mmHg lower.

•The motor current waveform measures energy intake. Variations in the waveform occur due to motor speed changes and pressure differentials across the aortic valve that occur during the cardiac cycle. Damping or flattening of this waveform indicates that the inlet and outlet areas are on the same side of the valve (which would render the device ineffective), or that there is minimal native pulsatility.

●Use of TEE to monitor Impella device function – During LV support with an Impella device, TEE imaging may be used to ensure that proper positioning has been maintained, and to monitor for adequate device function [1,22]. A malpositioned Impella device will cause recirculation and ineffective circulatory support (eg, if the inlet and outlet ports are located on the same side of the aortic valve). This may occur if [22,26]:

•The device is positioned too deep within the LV. TEE can reveal the flow color mosaic located of the outlet port within the ventricle if the device is too deep.

•The device migrates outside the LV into the aorta. The flow color mosaic of the inlet port may be visualized in the aortic root if the device has been malpositioned in that location rather than being in the LV.

●Echocardiography during weaning from Impella device support – Myocardial recovery can be evaluated with TEE during weaning of LV support in conjunction with monitoring hemodynamic values including arterial BP, CO, central venous pressure (CVP), and pulmonary artery pressure (PAP).

After removal of the device, a complete echocardiographic examination with either TEE or transthoracic echocardiography (TTE) is performed to establish a new "baseline" of ventricular function. It is also important to detect any new or worsened aortic or mitral regurgitation due to direct damage from the device [1,22].

TandemHeart device for LV support

●Overview of TandemHeart device – The TandemHeart for LV support is a percutaneous left atrium (LA)-to-aorta VAD with a centrifugal pump containing a spinning impeller (figure 4) [27-29]. The venous 21 Fr cannula is inserted into the LA by transseptal puncture, and the 15 to 19 Fr arterial cannula is inserted into the iliofemoral arterial system. Oxygenated blood is then withdrawn from the LA into the pump and returned to the systemic circulation via the cannula in the iliofemoral artery. Flows of 3.5 to 4.0 L/minute can be generated. However, adequate RV function is necessary to drive blood through the pulmonary system and achieve effective circulatory support. (See "Short-term mechanical circulatory assist devices", section on 'Left-atrium-to-aorta assist device'.)

●Imaging during TandemHeart device insertion

•Venous inflow cannula placement – The venous inflow cannula of the TandemHeart is introduced into the femoral vein and guided into the LA via a transseptal puncture across the interatrial septum (IAS). This procedure is commonly performed with fluoroscopy, but TEE may be used to guide the initial transseptal puncture and subsequent cannula positioning [30].

TEE may be used to guide the following sequential steps for TandemHeart venous cannula placement via a femoral vein:

-An ME bicaval view is used to visualize guidewire placement from the femoral vein into the IVC, RA, and SVC [31]. A sheath is then placed over the wire. Then the guidewire is removed and replaced within the catheter tip. Then the apparatus is pulled down to the level of the IAS.

-An ME RV inflow-outflow view or ME aortic valve SAX view (40 to 50°) will demonstrate the thinnest part of the IAS. Needle contact with the IAS will demonstrate "tenting" of the IAS, then penetration of the needle into the LA (image 13 and image 14).

-A wire is placed through the puncture needle into the LA and directed into the left upper pulmonary vein. Alternatively, the sheath can be advanced over the needle directly. This may be visualized starting from an ME four-chamber view and then rotating the omniplane angle to approximately 70° (image 15).

-A puncture of the mid-fossa ovalis is preferred because it leaves more room in the LA for the device and reduces the likelihood of device malfunction due to contact with the LA wall [32]. When the catheter is located in the LA, the needle is removed and replaced with a guidewire, which is positioned in the left upper pulmonary vein [33].

-A sheath and dilator are advanced over the guidewire into the LA after dilation of the IAS hole.

-The inflow cannula is then positioned such that all of its holes are visualized within the LA (image 16 and image 17). The distance from the IAS to the tip of the TandemHeart cannula within the LA can be measured (image 18). If changes in TandemHeart function occur, its positioning can be reassessed to determine if the device has migrated.

•Arterial outflow cannula placement – After venous cannula placement, TEE may be used to guide the following sequential steps for arterial cannula placement into the descending aorta:

-Placement of a guidewire via the iliofemoral arterial system into the descending aorta, followed by introduction of the arterial outflow cannula over the guidewire.

-Although final positioning of the outflow cannula within the descending aorta is below the diaphragm beyond the limits of TEE imaging, blood flow into the arterial outflow cannula can be demonstrated using CFD

●Use of TEE to monitor TandemHeart device function – TEE imaging with CFD is employed to demonstrate appropriate flow into the cannula from the LA without entrainment of blood from the RA (image 17) [31,34]. Malposition of the inflow cannula across the IAS would unintentionally drain RA blood (image 19), while iatrogenic atrial septal defect (ASD) creation would result in mixing of RA and LA blood (image 20) [35].

It is standard practice to maintain some LV ejection with aortic valve opening during support with the TandemHeart device. This reduces the likelihood of LV blood stasis with clot formation in the LV apex or in the aortic root.

●Assessment for complications – The complication rate for transseptal puncture is approximately 1 percent, including the following:

•Creation of an iatrogenic ASD is the most common complication (image 20) [36]. By six months most iatrogenic ASDs have closed, although 7 percent remain open after one year [37].

•Cardiac tamponade may occur due to perforation of the atrium, pulmonary veins, or aortic root.

•Transient ST elevation may be evident during transseptal puncture. Proposed mechanisms include parasympathetic stimulation resulting in autonomic imbalance and coronary spasm, thrombus, or air embolism [38].

•Device-related neurologic dysfunction in patients with cardiogenic shock managed with the TandemHeart is reported at 2 percent [39]. Stroke may be evident after the procedure, but the incidence of this complication is not higher in patients with a new ASD [40].

●Echocardiography after weaning from TandemHeart device support – Upon removal of the device, a complete TEE or TTE is typically performed to establish a new "baseline" of ventricular and valvular function.

CentriMag device for LV support

●Overview of CentriMag device for LV support – The CentriMag is a continuous flow centrifugal blood pump with a console and motor, flow probe, and tubing, which may be used with a variety of different cannulae or cannula configurations to provide MCS. Insertion of cannulae or grafts for use with this centrifugal pump generally requires a sternotomy. During cardiac surgery, the surgical median sternotomy allows direct access to the heart and great vessels for central cannulation. The LV inflow cannula of the CentriMag device is placed under direct visualization into the LA via a pulmonary vein (or a graft to a pulmonary vein), or directly into the apex of the LV [41]. The arterial outflow cannula may be placed directly into the ascending aorta or into a graft to the ascending aorta.

The CentriMag VAD can generate flows up to 9.9 L/minute at 5500 rotations per minute and is approved for left, right, or biventricular support for up to 30 days [42-44]. Most commonly, the CentriMag is used to treat postcardiotomy shock, or as a bridge to transplantation in patients who do not qualify for more durable VADs [43]. Although such devices are occasionally selected to provide short-term support, they are more typically selected for patients likely to need support for a longer duration than can be provided by an IABP, Impella, or TandemHeart device [43]. (See "Short-term mechanical circulatory assist devices", section on 'Nonpercutaneous centrifugal pumps'.)

●TEE during CentriMag device placement – TEE is used to guide the following sequential steps during CentriMag device placement for LV support:

•Just before initiation of CentriMag flow, TEE is used to guide removal of intracardiac air (seen as hyperechoic white speckles) that may be present in the LV. Air tends to accumulate in areas of the heart that are nondependent (more superior in a supine patient). Although several different TEE views should be obtained, air is usually best demonstrated in the ME views at the LV apex or along the interventricular septum [45].

•Immediately after initiation of CentriMag function for LV support, CFD is used to demonstrate blood inflow into the atrial cannula, as well as outflow exiting via a cannula or graft into the ascending aorta (image 21). Outflow velocities are generally <2 m/second as measured with pulse wave Doppler, although smaller aortic graft sizes may result in higher velocities [11].

After flow is initiated, the LV should appear decompressed on TEE imaging. A shift of the interventricular septum and dilatation of the RV may indicate excessive LV unloading and/or RV dysfunction.

●Use of TEE to diagnose CentriMag device malfunction – During ongoing CentriMag support, TEE can be used to diagnose the cause of inadequate pump flow, including [46]:

•Hypovolemia

•RV dysfunction

•Graft kinking

•Outflow obstruction

•Cardiac tamponade

•Severe tricuspid regurgitation

•Aortic dissection

●Use of TEE during CentriMag removal – Removal of the cannulae connecting the patient to the CentriMag device is generally accomplished in the operating room. Removal may be scheduled electively after recovery of LV function or urgently at the time of heart transplantation. Intraoperative TEE is subsequently used to assess ventricular function of the native heart after device removal or the donor heart after transplantation.

SUMMARY AND RECOMMENDATIONS

●Overview of left ventricular (LV) support – Mechanical circulatory support (MCS) devices to provide short-term LV support include the percutaneously inserted intra-aortic balloon pump (IABP), LV-to-aorta axial flow device (Impella), left atrium (LA)-to-aorta centrifugal pump (TandemHeart), and nonpercutaneous continuous flow centrifugal pump (CentriMag) (table 1). (See 'Overview of LV support' above.)

●Transesophageal echocardiography (TEE) before initiating LV MCS – TEE is useful to confirm the presumed diagnosis and need for MCS support of the LV and to assess for abnormalities that may contraindicate device placement or interfere with device function. These include aortic regurgitation (AR) (movie 1 and image 1 and image 2) and intracardiac shunting (eg, atrial septal defect [ASD] (movie 2), ventricular septal defect [VSD] , patent foramen ovale [PFO] (movie 3), intracardiac thrombus (figure 1), aortic dissection (movie 4 and image 3), severe aortic atheromatous disease with large or mobile atheromas (image 4 and movie 5), or severe right ventricular [RV] dysfunction (movie 6 and movie 7)). (See 'Echocardiography before initiating LV support' above.)

●Imaging for IABP device (see 'Intra-aortic balloon pump' above):

•Prior to insertion – TEE may be used to evaluate for contraindications and, in selected patients, to assess alternative cannulation sites (eg, subclavian artery, aortic arch, left axillary artery) rather than a common femoral artery.

•During insertion – TEE or fluoroscopy may be used during a femoral approach to confirm positioning of the guidewire in the proximal descending thoracic aorta (image 5), followed by balloon advancement to a position 1 to 2 cm below the takeoff of the left subclavian artery in the aortic arch (image 6). Final positioning of an IABP is confirmed with a chest radiograph (CXR) (image 8).

•Monitoring during support – Proper timing for inflation and deflation of the IABP balloon is shown in the figures (waveform 1 and figure 2). TEE may be used to reassess ventricular function, the degree of AR, changes in previously identified atheroma locations, or the rare occurrence of aortic dissection.

•Weaning from support – Ventricular function can be assessed with TEE as IABP support ratios are gradually decreased from 1:1 to 1:4 (image 9).

●Impella devices – Impella devices for LV support include the 2.5 (figure 3), cardiac power (CP) (picture 1 and image 11), and 5.5 device (picture 2) (see 'Impella device for LV support' above):

•Prior to insertion – In addition to evaluation for typical contraindications, TEE is used to rule out severe aortic stenosis, presence of a mechanical aortic valve, asymmetric septal hypertrophy, or a myxomatous mitral valve.

•During insertion – Although Impella devices are usually placed via a femoral approach under fluoroscopic guidance, supplemental information from TEE imaging includes:

-Confirmation of wire positioning within the aortic lumen of the descending thoracic aorta (image 5), followed by passage of the guidewire then the Impella device itself across the aortic valve into the LV cavity, with positioning of the tip in the middle of the LV cavity (image 10).

-Subsequent TEE examination with color-flow Doppler (CFD) imaging can evaluate appropriate laminar blood flow into the inlet of the device within the LV and from the outlet into the aorta, as well as proper mitral and aortic valve function (image 10).

-Impella positioning is further confirmed by noting the presence of ventricular and aortic waveforms and variations in the motor current waveform, indicating pressure differentials across the aortic valve that occur during the cardiac cycle (image 12).

•Monitoring during support – TEE may be used to ensure that proper positioning has been maintained and that device function is adequate.

•Weaning from support – After device removal, a complete TEE or transthoracic echocardiography (TTE) examination is performed to establish a new "baseline" for ventricular function and to detect new or worsened AR or mitral regurgitation caused by direct damage from the device.

●TandemHeart device (figure 4) (see 'TandemHeart device for LV support' above):

•During insertion

-Venous inflow cannula insertion – Fluoroscopy is commonly used during introduction of the venous inflow cannula into the femoral vein and up into the right atrium (RA), then across the interatrial septum (IAS) into the LA. TEE may be used to guide the transseptal puncture and subsequent inflow cannula positioning (image 13 and image 14).

-Arterial outflow cannula insertion – TEE can be used to visualize guidewire placement into the descending aorta via the iliofemoral arterial system (image 15). Although final positioning of the outflow cannula within the descending aorta is below the diaphragm beyond the limits of TEE imaging, blood flow into the arterial outflow cannula can be demonstrated using CFD (image 16 and image 18 and image 17).

•Monitoring during support and assessment for complications – Malposition of the inflow cannula across the IAS would unintentionally drain RA blood (image 19), while iatrogenic ASD creation would result in mixing of RA and LA blood (image 20). Other complications include tamponade due to perforation of the atrium, pulmonary veins, or aortic root.

•Weaning from support – After device removal, a complete TTE or TEE examination is performed to establish a new "baseline" of ventricular and valvular function.

●CentriMag device (see 'CentriMag device for LV support' above):

•During insertion – Just before initiation of CentriMag flow, TEE is used to guide removal of intracardiac air. Immediately after initiation of CentriMag function for LV support, CFD is used to demonstrate blood inflow into the atrial cannula, as well as outflow exiting via a graft into the ascending aorta (image 21).

•Diagnosis of device malfunction during support – Later causes of inability to achieve adequate flows may be diagnosed using TEE, including RV dysfunction, graft kinking, outflow obstruction, cardiac tamponade, hypovolemia, severe tricuspid regurgitation, and aortic dissection.

•During device removal – Intraoperative TEE is used to assess ventricular function of the native heart after device removal or the donor heart after transplantation.