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Left Ventricular Assist Devices: Physiologic Assessment using Echocardiography for Management and Optimization
Ultrasound in Med. & Biol., Vol. 38, No. 2, pp. 335–345, 2012 Copyright Ó 2012 World Federation for Ultrasound in Medicine & Biology Printed in the USA. All rights reserved 0301-5629/$ - see front matter
doi:10.1016/j.ultrasmedbio.2011.11.009
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Technical Note LEFT VENTRICULAR ASSIST DEVICES: PHYSIOLOGIC ASSESSMENT USING ECHOCARDIOGRAPHY FOR MANAGEMENT AND OPTIMIZATION FAROUK MOOKADAM,* CHRISTOPHER B. KENDALL,* RAYMOND K. WONG,y ANANTHARAM KALYA,* TAHLIL WARSAME,* FRANCISCO A. ARABIA,y JOAN LUSK,* SHERIF MOUSTAFA,* ERIC STEIDLEY,* NISHATH QUADER,* and KRISHNASWAMY CHANDRASEKARAN* * Division of Cardiovascular Diseases; and y Division of Cardiothoracic Surgery, Mayo Clinic Arizona, Scottsdale, AZ, USA (Received 9 August 2011; revised 12 October 2011; in final form 15 November 2011)
Abstract—Left ventricular assist devices (LVAD) are being deployed increasingly in patients with severe left ventricular dysfunction and medically refractory congestive heart failure of any etiology. The United States Food and Drug Administration (FDA) recently approved the use of the Thoratec Heartmate II (Thoratec Corporation, Pleasanton, CA, USA) for outpatient use. Echocardiography is fundamental during each stage of patient management, pre-LVAD placement, during LVAD placement, for postoperative LVAD optimization and longterm follow-up. We present a pragmatic and systematic echocardiographic approach that serves as a guide for the management of left ventricular assist devices. (E-mail: [email protected]) Ó 2012 World Federation for Ultrasound in Medicine & Biology. Key Words: 2-dimensional echocardiography, Congestive heart failure, Left ventricular assist devices, LVAD physiology and optimization.
LVAD technology use continuous axial flow pumps with fewer moving parts and is much smaller in size. As a result, long-term durability has improved and availability has been expanded to a larger group of patients. Transthoracic echocardiography (TTE), transesophageal echocardiography (TEE) and, less commonly, epicardial echocardiography (EE) can all be used in the management of LVAD patients before, during and after deployment of the assist device. With TEE and EE, visualization of cardiac anatomy can be superior and thus especially useful in guiding the cardiac surgeon during LVAD placement. It should be emphasized that for the preoperative evaluation and postextubation day-to-day optimization, fluid and hemodynamic assessment, TTE can provide much of the needed information if a technically directed approach is used for patient management.
INTRODUCTION Left ventricular assist devices (LVAD) are becoming increasingly important as a therapeutic intervention for appropriately selected individuals with advanced heart failure recalcitrant to medical therapy. Not all patients are eligible for transplantation and some of those who are candidates for cardiac transplant need immediate hemodynamic support beyond inotropes, without which, death or serious morbidity may supervene. The limitations to cardiac transplantation for both donor and recipient, coupled with technologic advancements have resulted in broader application of the LVAD, both as a bridge to transplantation (BTT) and as destination therapy (DT) (Jessup and Brozena 2003; Rose et al. 2001). LVAD ‘‘standbys’’ also provide the option for immediate and intermediate-term support in the highrisk post-cardiac surgical patient. Oftentimes, this support can be extended for longer periods of time when BTT or DT is later prescribed (Miller et al. 2007; Rose et al. 2001). Current second and third generation
Overview of ventricular assist devices Two main types of ventricular assist devices (VADs) are in use currently, pulsatile and continuous (axial) flow mechanical assist devices. First generation VADs provide pulsatile flow from blood pumps that are either extracorporeal or implanted within an abdominal pocket. Second generation VADs use axial flow impellers that provide continuous pump flow and dispenses with the need for
Address correspondence to: Dr. Farouk Mookadam, Division of Cardiovascular Diseases, Mayo Clinic, 13400 East Shea Boulevard, Scottsdale, AZ 85259 USA. E-mail: [email protected] 335
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Table 1. Pre-left ventricular device insertion (1) Examine LV systolic and diastolic function, and exclude ventricular thrombus. (2) Examine RV size, systolic and diastolic function. (3) Assess aortic valve for stenosis and regurgitation. (4) Examine ascending, descending and abdominal aorta for dissection and atherosclerosis. (5) Examine mitral valve function, regurgitation and rule out mitral valve stenosis. (6) Examine tricuspid valve annular size and regurgitation. (7) Exclude cardiac abnormalities that could lead to right to left shunting post-LVAD placement: PFO, ASD or iatrogenic atrial shunt. (8) Assess for ventricular scar and aneurysm with ischemic cardiomyopathy. (9) Assess pulmonary valve regurgitation. (10) Assess for pulmonary hypertension, increased pulmonary vascular resistance and pulmonary embolism. (11) Examine pericardial space for effusion or adhesions if prior cardiac surgery or history of pericarditis with constrictive physiology. LVAD 5 left ventricular assist device; RV 5 right ventricle; LV 5 left ventricle; PFO 5 patent foramen ovale; ASD 5 atrial septal defect.
Fig. 1. New generation left ventricular assist device.
unidirectional valves connected to the inflow/outflow cannula. Third and fourth generation devices employ centrifugal pumps that also provide continuous flow, with the latter generation sufficiently miniaturized that they can be positioned at the left ventricular apex (Scalia et al. 2000; Stainback et al. 2005). Left VADs are positioned in parallel with the normal blood circulation from the left ventricle into the aorta and have several essential components (Fig. 1), which include: (1) An inflow conduit from the LV apex to the VAD pump; (2) Propulsion pump (LVAD) that moves the blood; (3) An outflow graft conduit that returns blood to the aorta; (4) An external controller which receives and processes information from the pump and returns information for pump operation. (Frazier et al. 2001; Horton et al. 2004; Tittle et al. 2002). Role of echocardiography for management of patient with LVAD Axial flow VADs are currently approved for outpatient use. Due to the portability of these devices and the agrarian nature of the patient, medical attention may be sought at a facility that may be less familiar with the echocardiographic examination or may be uncertain of which echocardiographic parameters to measure, or which morphologic features to observe for during echocardiographic interrogation of the device and related hemodynamics. Hence, a good understanding of cardiac anatomy and physiology is needed to understand normal VAD function and potential complications that can occur. The purpose of this overview is to systematically guide
physicians and sonographers caring for patients with devices as a routine or when such a device may be encountered unexpectedly. Preoperative echocardiography A comprehensive transthoracic echocardiogram (TTE) for LVAD candidates should include standard two-dimensional (2-D) and Doppler interrogation per guidelines (Table 1). Important findings, which may influence hemodynamic status and encumber device function, should be evaluated before the patient arrives in the operating suite: Left ventricular (LV) thrombus; aortic valve function, rule out stenosis and greater than mild regurgitation; atrial septal shunt; ascending aorta pathology; atrial septal shunt; and mitral inflow stenosis. If LV thrombus is suspected, the use of ultrasound contrast agent can aid in LV opacification for visualization of thrombus size and location. The aortic valve (AoV) should be evaluated for significant stenosis and insufficiency. If greater than mild AoV regurgitation is present, the surgeon may suture repair the AoV cusps to prevent increased recirculation of pump flow (Rao et al. 2001) The potential site for the outflow cannula should be interrogated closely. Transthoracic echocardiography can be used to assess the size and appearance of the aorta. The aortic arch can be visualized from the suprasternal view; descending thoracic limited views and abdominal aorta limited views should be assessed for dissection, aneurysm, atherosclerosis or any potential pathology, which could compromise outflow cannula function, or interfere with the cross clamp procedure. Patent foramen ovale (PFO) is common in the adult population (Hagen et al. 1984). The presence of an atrial septal defect (ASD) or patent foramen ovale (PFO) should
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Fig. 2. (a) Optimal left ventricular assist device (LVAD) setting parasternal long axis. Interventricular septal (IVS) midline during live cine clip with no septal shift on respiration. Right ventricle (RV) is dilated. Mitral valve (MV), status post MV annuloplasty band (high grade mitral stenosis is a contraindication for ventricular assist device [VAD] due to increased inflow gradient from common tachycardia in these patients). NOTE: Apical four chamber is oriented with left heart chambers on left side of screen as is standard imaging protocol for Mayo Clinic. (b) Parasternal short axis. Mitral valve level. IVS centerline with some bowing to right at end diastole. (c) Papillary level. IVS maintains midline position; no ‘‘D’’ shaped left ventricle (LV). (d) LV apex. Inlet cannula noted in apex with 2-D. (e) Para-apical window. Off axis window, in between parasternal and true apical window. This can be the closest view to a four chamber secondary to insertion site of inlet cannula. Ultrasound images used in this manuscript follow institutional patient informed consent protocol and patient identity is protected.
be ruled out using color flow Doppler and/or agitated saline bubbles during preoperative "baseline" TTE. As seen with heart failure patients, severe hypoxemia can occur with PFO after LVAD (Daniels et al. 2004).
The mitral valve, chordae and papillary muscles should be evaluated for normal structural anatomy and position. Mitral chordae, aberrant LV chordae, aberrant or displaced papillary muscle or a hypertrophied
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Fig. 3. (a) Pre-optimization parasternal long axis. Device flow too high. Interventricular septum (IVS) shifted to left during diastole (‘‘Hourglass’’ left ventricle [LV]). (b) Postoptimization parasternal long axis. IVS in centerline position during end diastole or when mitral valve closes due to higher pressure gradient between LV and left atrium (LA) (arrow). Device flow was decreased. Note heart rate has increased and there is less ectopy.
papillary muscle can potentially obstruct the inflow cannula. The presence of mitral valve stenosis can impede LV and device filling during commonly encountered tachycardia. Mitral valve stenosis is a contraindication for LVAD deployment but in cases of mitral valve repair and annular rings, a take-down procedure can open the mitral valve for unobstructed cannula flow (Fig. 2a–e). The right-sided structures impact overall cardiac function post-VAD implantation and, therefore, mandates thorough echocardiographic interrogation. The tricuspid valve is assessed for the degree of insufficiency and peak tricuspid regurgitant jet velocity is necessary before surgery. If tricuspid annular dilatation is present and the annulus is greater than 4 cm, the patient may require TV annuloplasty to prevent increased dilatation and regurgitation with RV volume changes in the postoperative period. The RV systolic function can be assessed by fractional area change (normal value 5 35%–63%) (Rudski et al.
2010). Tricuspid annular tissue Doppler (TAPSE) can be used to further evaluate RV systolic and diastolic function. Pulmonary valve regurgitation is an important finding in patients requiring ventricular assist device support. Careful examination with color flow Doppler (CFD), pulsed wave (PW) Doppler, and continuous wave (CW) Doppler for assessing the degree of regurgitation is prudent, since right ventricular volume overload can occur with pulmonary insufficiency greater than moderate. Pulmonary artery embolus, if suspected, may be detected uncommonly in proximal main pulmonary artery or within flow divider. RIGHT VENTRICULAR FUNCTION Right ventricular systolic function has been evaluated per published guidance (Rudski et al. 2010). Right ventricular diastolic function is evaluated by pulsed Doppler of the tricuspid inflow, tissue Doppler of the
Fig. 4. (a) Preoptimization apical four chamber. Device flow too high, intra-ventricular septum shifted toward left ventricle. (b) Postoptimization apical four chamber. Device flow reduced and inter-ventricular septum in a more desirable centerline position.
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Fig. 5. (a) Preoptimization apical long axis. Near left ventricle (LV) mid-cavity obliteration. (b) Postoptimization apical long axis. LV cavity size increased with a lower setting for left ventricular assist device (LVAD) flow.
lateral tricuspid annulus, pulsed Doppler of the hepatic vein and measurements of inferior vena cava (IVC) size and collapsibility (Rudski et al. 2010). Periprocedural device implantation TEE The baseline preoperative TTE information gleaned is supplemented by an intraoperative TEE. During LVAD implantation, in the operating room, transesophageal echocardiography (TEE) provides an opportunity to assess several features essential to confirm optimal positioning of the inflow and outflow conduits, detect complications and to assist in hemodynamic optimization. When TEE is contraindicated or if TEE views are limited, epicardial echocardiography (EE) can be used to evaluate cardiac anatomy. (Eltzschig et al. 2003; Reeves et al. 2007). The morphology of the left and right ventricles and the interventricular septum must be interrogated in concert. Left ventricular filling is usually assessed by transesophageal echocardiography or by invasive measurements of left atrial pressure. Right ventricular
deterioration with progressive tricuspid regurgitation can be readily identified. Transesophageal inspection of the inflow cannula site placement is performed prior to cannula placement. Once the cannula has been placed, TEE is used to help direct the cannula orifice toward mitral valve inflow, and away from the interventricular septum. With impellers set at a fixed speed, regardless of inflow to the ventricular conduit, the LVAD is capable of providing hemodynamic support only if there is adequate inflow into the device. The axial flow devices use impellers rotating at high speeds (2000–13,000 revolutions per minute (RPMs), depending on device type, allowing for maximal outputs of 10 L/min, tailored to each patient’s clinical status. Immediate postimplantation TEE (While surgical team closing) Upon insertion of the LVAD, the initial weaning process from cardiopulmonary bypass should be gradual with meticulous attention being paid to LV filling.
Fig. 6. (a) M-mode aortic valve. Aortic valve does not open during ventricular systole. (b) M mode. Aortic valve opening with each beat while weaning from left ventricular assist device (LVAD).
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Fig. 7. (a) Outlet cannula high left parasternal window. Color flow Doppler image of inlet cannula and ascending aorta. This is usually a difficult image to attain with patient in left lateral decubitus position. Having the patient lay supine or turn to right lateral decubitus can help find the optimal image. (b) Outlet cannula Doppler. Pulsed wave (PW) Doppler signal from outlet cannula, peak velocity 0.7 m/s.
If the RPM (output) of the device is increased too rapidly without adequate LV filling, a suction event occurs whereby the ventricular septum and less commonly the LV free wall will collapse, resulting in LVAD inflow conduit obstruction. The configuration of the interventricular septum will then be convex to the left ventricle and the right ventricle assumes an undesirable geometry resulting in RV dysfunction, further worsening volume delivery to the LV and subsequently to the LVAD. Adjustments to the LVAD flow settings are made based on the morphologic findings, reflecting the hemodynamic function (Chumnanvej et al. 2007; Frazier et al. 2001; Miller et al. 2007; Rose et al. 2001). Complications early postinsertion of the LVAD can be identified, especially in patients with hemodynamic
compromise using echocardiography (TEE or TTE). These complications can include new pericardial effusion, hematoma within the pericardial cavity or occult bleeding that may result in hypovolemia identified by tachycardia and LV end-diastolic volume reduction. In patients that are hemodynamically unstable, reflexively increasing the device RPM in an attempt to increase cardiac output may further worsen the clinical condition because of potential LV wall collapse and inflow catheter obstruction. The appropriate maneuver in these suction events is to decrease the RPM, restore intravascular volume and when the patient is considered euvolemic, LVAD flow can be incrementally raised to optimal levels depending upon the morphologic findings of the LV, RV and interventricular septum (Miller et al. 2007;
Fig. 8. (a) Inlet cannula apical four chamber with color flow Doppler (CFD). With CFD during ventricular systole, while mitral valve is closed, we see left ventricle (LV) intracavitary flow with aortic insufficiency. (b) Inlet cannula Doppler. Apical four chamber. PW Doppler of inlet cannula, peak velocity 0.5 m/s. This is one window to line up with turbulent flow in inlet cannula, try multiple windows, i.e. apical long axis, apical two, parasternal, para-apical, to get parallel to flow and peak velocity.
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Table 2. Postoperative recovery period echo evaluation (1) Reassessment of the LV chamber size (geometry), function and interventricular septum direction. (2) Examination of the LV apex with inflow conduit alignment and exclude obstruction using Doppler ultrasound techniques. (3) Reassessment of the RV chamber size (geometry), function and interventricular septum direction. (4) Examine interventricular septum bowing direction with respect to LVAD setting and on changes to LV/RV size. IVS should be midline at optimal device flows. (5) Assess tricuspid regurgitation with color Doppler and CW for right ventricular systolic pressure, assess for pulmonary hypertension. (6) Reassessment of aorta for outflow conduit flow (Doppler) and exclude evidence of new dissection. (7) Examine aortic valve for opening (long cine loop cycle), significant regurgitation (. 11) and sinus of Valsalva thrombus. (8) Reassessment of LA, RA and atrial septum for new atrial shunt. (9) Assess pulmonary veins to exclude obstructions/compressions. LVAD 5 left ventricular assist device; RV 5 right ventricle; LV 5 left ventricle; IVS 5 interventricular septal; CW 5 continuous wave Doppler; LA = left atrium; RA = right atrium.
Rose et al. 2001). Once implantation is complete, optimization of chamber morphology and cannula flows can be achieved under 2-D echocardiographic guidance during inpatient or outpatient follow-up. (Figs. 3a–8b). The inflow cannula Doppler profile should be obtained to evaluate flow from the LV into the device. This is usually obtained from an apical or off axis apical view (Fig. 8a and b). The inter-atrial septum should be evaluated again immediately postprocedure for an atrial shunt that may not have been evident in preoperative scans. Postprocedure inpatient or ambulatory follow-up using TTE/TEE When evaluating the patient and device in the ambulatory setting, most LVAD adjustments are directed to optimize for volume shifts. Routine TTE windows can be limited in the early postoperative period due to healing incision sites and the sling immobilizer which aids in securing the external controller, cannula and chest tubes. It may be prudent for the sonographer to request nursing assistance to remove the sling for the purpose of accomplishing a comprehensive TTE examination. For optimal clinical outcomes in the VAD patient, a systematic approach for echocardiographic examinations is outlined in Tables 1 and 2. Recommended 2-D TTE views and targeted findings are listed in Tables 3 (left heart) and 4 (right heart) (Joffe et al. 1996; Peterson et al. 2003; American Society of Anesthesiologists and Society of Cardiovascular Anesthesiologists 1996). The VAD flow performance can be assessed using continuous wave (CW) or pulsed wave (PW) Doppler signals from the cannula (Figs. 7b and 8b) (Scalia et al. 2000; Stainback et al. 2005). For the follow-up TTE, the following protocol is recommended as a guide.
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Primary echocardiographic findings for axial flow VAD optimization are: (1) LVAD inflow and outflow conduits; (2) Ventricular septal position and motion (respirometry); (3) Left ventricular size (and function if contractility restored); (4) Intermittent opening of the aortic valve and aortic valve regurgitation; (5) Right ventricular size and function (RV cardiac output); (6) Tricuspid valve inflow, regurgitation and regurgitant peak velocity; (7) Pericardial effusion: presence. Cannula flow velocities should be estimated in the presence of suction events to rule out obstruction from LV chamber walls (ventricular septum, papillary muscle, mitral valve) or from cannula thrombus. Obtaining velocities can be challenging and requires patience, skill and knowledge of cannula position and direction. With the inflow cannula position at the LV apex, Doppler flow should be attempted from the most parallel echo window using the parasternal short axis, para-apical, and if possible apical window. The outflow cannula position and direction of flow poses a greater challenge for the cardiac sonographer because of its location within the ascending aorta (Fig. 8a). The outflow cannula, when placed in the ascending aorta, can be assessed in either the left lateral or right lateral decubitus position from the parasternal window. Peak systolic Doppler velocity, either CW or PW, for the inflow and outflow cannula should be comparatively similar (Figs. 7b and 8b). A discrepancy between inflow and outflow cannula flow velocity must be accounted for, particularly when a suction event occurs. The LV and RV should be evaluated with respect to the interventricular septal (IVS) position. Left ventricular function (ejection fraction or EF) is not routinely reported post- device implantation, but if needed, temporary interruption of the LVAD is necessary to calculate the EF. The LVAD flow rate can be optimized if the IVS is shifted to the left or right side during echocardiographic interrogation. Device flow is optimal when the IVS is midline and the LV chamber is not collapsed (‘‘hour-glass’’ shape) (Fig. 3a). When assessing the IVS in the postoperative period, the use of a respirometer is essential to aid in distinguishing abnormal IVS motion that can be due to pericardial effusion or hematoma causing hemodynamic effects on LV and RV function. A careful exploration should be undertaken looking for thrombus in the left-sided chambers that may embolize and obstruct the LVAD. Multiple TTE windows and TEE planes should be used to assess the LVAD inflow conduit (Chumnanvej et al. 2007; Frazier et al. 2001).
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Table 3. TTE views and common key findings for long-term LVAD usage Anatomy
Views
Key findings
Left ventricle
PLAX, para-apical, apical
Size and function Intra ventricular septal shift Wall thickness Rule out thrombus Inflow cannula position
Outlet cannula/ascending aorta
High left PLAX and high right PLAX (right lateral decubitus to examine ascending aorta)
Annotate device output and flow rate on U/S screen Ascending aorta size Color flow Doppler PW peak velocity
Inlet cannula
PSAX, para-apical, apical
Annotate device output and flow rate on ultrasound system screen Usually at LV apex Cannula position and direction Color flow Doppler PW Doppler inflow velocities (,2.0–2.3 m/s)
Mitral valve and apparatus
PLAX, PSAX, para-apical
MV mobility Papillary muscle obstructing cannula MV regurgitation MV diastolic inflow velocity (CW and PW)
Aortic valve
PLAX, PSAX, para-apical
Closed and/or open-to-closed ratio PW LVOT (if AV opens) Aortic valve regurgitation Rule out thrombus (Sinus of Valsalva)
Right ventricle
PLAX, RV inflow, para-apical
Size and function RVSP Tissue Doppler (s’/e’/a’)
Tricuspid valve
PSAX, RV inflow, para-apical
Pulmonary valve
PSAX, RV outflow
RVOT diameter (cardiac output calculation) PW RVOT TVI CW peak velocity and TVI
Left atrium
PLAX, para-apical, apical
Size Pulmonary vein flow Rule out thrombus
Pericardium
Parasternal, apical
Pericardial effusion Pericardial adhesions
Vena cava and hepatic vein
PSAX, RV inflow, subcostal, transhepatic
Size with respiratory cycle Color flow Doppler PW hepatic vein noting any respiratory variation
Leaflet mobility Tricuspid annulus Regurgitation Diastolic inflow
TTE 5 transthoracic echocardiography; LVAD 5 left ventricular assist device; PLAX 5 parasternal long axis; PSAX 5 parasternal short axis; PW 5 pulsed wave Doppler; LVOT 5 left ventricular outflow tract; MV 5 mitral valve; AV 5 aortic valve; CW 5 continuous wave Doppler; RVSP 5 right ventricle systolic pressure; RV 5 right ventricle.
Inflow conduit obstruction either by septal suck-down or thrombi is usually detected by turbulent, high aliasing velocity flow with color flow Doppler or by previously reported peak velocities higher than 2.3 m/s using continuous wave Doppler (Chumnanvej et al. 2007). It may be challenging with 2-D imaging to visualize the track flow to the inlet conduit from the left ventricle depending on the VAD being employed because of reverberation
artifacts. Color flow Doppler is useful in tracking intraventricular blood flow from the mitral orifice into the device in these instances, using an apical window (Fig. 9a and b). For optimal LVAD function, the aortic valve should remain closed throughout the cardiac cycle. In addition, greater than mild aortic regurgitation may result in abnormal LVAD function because of reduced efficiency
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Fig. 9. (a) Apical four chamber. 2-D view from the apex with poor acoustic window, image shadowing from scar tissue and inlet cannula. (b) Apical four chamber with color flow Doppler (CFD). During CFD imaging at low velocity scale we can appreciate blood flow to the inlet cannula after atrial contribution.
of flow from the outflow cannula into the aorta as well as volume overload to the LV inflow cannula (Chumnanvej et al. 2007; Frazier et al. 2001; Miller et al. 2007; Rose et al. 2001). With the outflow cannula anastomosed to the mid ascending aorta, the device circulates blood flow retrograde toward the sinus of Valsalva and the aortic valve (DiGiorgi et al. 2004). This type of retrograde flow is disruptive to the ‘‘normal’’ physiology of pericannula aortic tissue and fluid dynamics (John et al. 2010). In this hemodynamic situation, thrombosis at the level of the sinus of Valsalva and, over time, aortic valve cusp fusion through fibrosis can occur (John et al. 2010). It has been suggested that adjusting pump flow rate to Table 4. Right heart Anatomy
Views
allow intermittent opening of the aortic valve cusps can improve cusp physiology (Zamarripa Garcia et al. 2008) and reduce the incidence of sinus of Valsalva thrombus formation (Crestanello et al. 2009). If aortic valve opening does occur, the ratio of opento-closed beats is an important finding when assessing the LVand mechanical pump function. Using a long cine loop clip, $ 6 cardiac cycles, is sufficient to capture possible aortic valve opening. M-mode provides high frame rate images that may assist in detecting a small opening of aortic valve cusps or to confirm that the valve remains closed (Fig. 6a and b). Color flow Doppler is used at the level of the aortic valve to assess aortic valve regurgitation, which is usually a central jet. Aortic valve regurgitation can be visualized with CFD with intra-cavitary flow within the LV during ventricular systole (Fig. 8a).
Key findings
Right ventricle
PLAX, RV inflow, para-apical
Function RVSP Tissue Doppler (s’/e’/a’)
Tricuspid valve
PSAX, RV inflow, para-apical
Pulmonary valve
PSAX, RV outflow
RVOT diameter (cardiac output calculation) PW RVOT TVI CW peak velocity and TVI
Vena cava and hepatic vein
PSAX, RV inflow, subcostal, transhepatic
Size with respiratory cycle Color flow Doppler PW hepatic vein noting any respiratory variation
Leaflet mobility Tricuspid annulus Regurgitation Diastolic inflow
PLAX 5 parasternal long axis; PSAX 5 parasternal short axis; PW 5 pulsed wave Doppler; RVOT 5 right ventricular outflow tract; CW 5 continuous wave Doppler; RVSP 5 right ventricle systolic pressure; RV 5 right ventricle; TVI 5 time velocity integral.
The right heart Variable degrees of right heart failure are common during the postoperative period for LVAD patients, hence, mandating close monitoring of RV function is needed (Patel et al. 2008). Right ventricular function can be assessed from the parasternal window, RV inflow view and the para-apical echo windows. Pulse wave Doppler (PW) of the RVOT is required for computing the right ventricular cardiac output and pulmonary vascular resistance. A simple method for noninvasive estimation of pulmonary vascular resistance has previously been described by Abbas et al. (2003). Right atrial pressure (RAP) is estimated based on the appearance and collapse of the inferior vena cava (IVC) (Kircher et al. 1990). Placement of the drive component is within an intraabdominal pocket. This placement obscures the subcostal echo window. In this instance, a right transhepatic view should be attempted to visualize the IVC. The
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pericardium should be assessed for signs of fluid and clot accumulation. Cardiac tamponade is a clinical diagnosis, which can be confirmed with typical echocardiographic findings and respiro-phasic changes that indicate ventricular interdependence by interpretation of the transmitral and tricuspid inflow Doppler velocities (Mookadam et al. 2009). In cases where TTE is sub-optimal because of cardiac imaging window limitations, TEE can provide an unobstructed view of cardiac anatomy to aid in identifying the cause of hemodynamic instability.
CONCLUSION Cardiac transplantation remains the primary treatment for patients with intractable heart failure. With donor organs in short supply, we can expect to see an increase in the deployment of LVAD for bridge to transplantation or as destination therapy. Recent Food and Drug Administration (FDA) approval of continuous flow LVADs for outpatient use increases the likelihood of non-device specialty clinics or hospitals coming into contact with these patients. To help assess these patients in a meaningful way, a meticulous and systematic cardiac ultrasound is essential. Echocardiography when used appropriately can help assess the physiologic and hemodynamic function of the continuous flow LVAD and can diagnose the cause of malfunction. We have outlined a systematic approach that may be used in the assessment of LVADs using cardiac ultrasound that may be useful to both sonographers and cardiologists who may be involved in the management of this unique but growing group of patients. Familiarity with these cardiac assist devices and the anatomical or morphologic echocardiographic landmarks will be useful in caring for these patients.
REFERENCES American Society of Anesthesiologists and Society of Cardiovascular Anesthesiologists. Practice guidelines for perioperative transesophageal echocardiography. A report by the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists Task Force on Transesophageal Echocardiography. Anesthesiology 1996;84:986–1006. Abbas AE, Fortuin FD, Schiller NB, Appleton CP, Moreno CA, Lester SJ. A simple method for noninvasive estimation of pulmonary vascular resistance. J Am Coll Cardiol 2003;41:1021–1027. Chumnanvej S, Wood MJ, MacGillivray TE, Melo MF. Perioperative echocardiographic examination for ventricular assist device implantation. Anesth Analg 2007;105:583–601. Crestanello JA, Orsinelli DA, Firstenberg MS, Sai-Sudhakar C. Aortic valve thrombosis after implantation of temporary left ventricular assist device. Interact Cardiovasc Thorac Surg 2009;8:661–662. Daniels C, Weytjens C, Cosyns B, Schoors D, De Sutter J, Paelinck B, Muyldermans L, Van Camp G. Second harmonic transthoracic echocardiography: The new reference screening
Volume 38, Number 2, 2012 method for the detection of patent foramen ovale. Eur J Echocardiogr 2004;5:449–452. DiGiorgi PL, Smith DL, Naka Y, Oz MC. In vitro characterization of aortic retrograde and antegrade flow from pulsatile and nonpulsatile ventricular assist devices. J Heart Lung Transplant 2004; 23:186–192. Eltzschig HK, Kallmeyer IJ, Mihaljevic T, Alapati S, Shernan SK. A practical approach to a comprehensive epicardial and epiaortic echocardiographic examination. J Cardiothorac Vasc Anesth 2003; 17:422–429. Frazier OH, Myers TJ, Jarvik RK, Westaby S, Pigott DW, Gregoric ID, Khan T, Tamez DW, Conger JL, Macris MP. Research and development of an implantable, axial-flow left ventricular assist device: The Jarvik 2000 Heart. Ann Thorac Surg 2001;71:S125–S132. discussion S44–S46. Hagen PT, Scholz DG, Edwards WD. Incidence and size of patent foramen ovale during the first 10 decades of life: An autopsy study of 965 normal hearts. Mayo Clinic Proc 1984;59:17–20. Horton SC, Khodaverdian R, Powers A, Revenaugh J, Renlund DG, Moore SA, Rasmusson B, Nelson KE, Long JW. Left ventricular assist device malfunction: A systematic approach to diagnosis. J Am Coll Cardiol 2004;43:1574–1583. Jessup M, Brozena S. Heart failure. New Engl J Med 2003;348: 2007–2018. Joffe II, Jacobs LE, Lampert C, Owen AA, Ioli AW, Kotler MN. Role of echocardiography in perioperative management of patients undergoing open heart surgery. Am Heart J 1996;131:162–176. John R, Mantz K, Eckman P, Rose A, May-Newman K. Aortic valve pathophysiology during left ventricular assist device support. J Heart Lung Transplant 2010;29:1321–1329. Kircher BJ, Himelman RB, Schiller NB. Noninvasive estimation of right atrial pressure from the inspiratory collapse of the inferior vena cava. Am J Cardiol 1990;66:493–496. Miller LW, Pagani FD, Russell SD, John R, Boyle AJ, Aaronson KD, Conte JV, Naka Y, Mancini D, Delgado RM, MacGillivray TE, Farrar DJ, Frazier OH. Use of a continuous-flow device in patients awaiting heart transplantation. N Engl J Med 2007;357: 885–896. Mookadam F, Jiamsripong P, Oh JK, Khandheria BK. Spectrum of pericardial disease: Part I. Exp Rev Cardiovasc Ther 2009;7: 1149–1157. Patel ND, Weiss ES, Schaffer J, Ullrich SL, Rivard DC, Shah AS, Russell SD, Conte JV. Right heart dysfunction after left ventricular assist device implantation: A comparison of the pulsatile HeartMate I and axial-flow HeartMate II devices. Ann Thorac Surg 2008;86: 832–840. discussion 32–40. Peterson GE, Brickner ME, Reimold SC. Transesophageal echocardiography: Clinical indications and applications. Circulation 2003;107: 2398–2402. Rao V, Slater JP, Edwards NM, Naka Y, Oz MC. Surgical management of valvular disease in patients requiring left ventricular assist device support. Ann Thorac Surg 2001;71:1448–1153. Reeves ST, Glas KE, Eltzschig H, Mathew JP, Rubenson DS, Hartman GS, Shernan SK. Guidelines for performing a comprehensive epicardial echocardiography examination: Recommendations of the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists. Anesth Analg 2007;105: 22–28. Rose EA, Gelijns AC, Moskowitz AJ, Heitjan DF, Stevenson LW, Dembitsky W, Long JW, Ascheim DD, Tierney AR, Levitan RG, Watson JT, Meier P, Ronan NS, Shapiro PA, Lazar RM, Miller LW, Gupta L, Frazier OH, Desvigne-Nickens P, Oz MC, Poirier VL. Long-term use of a left ventricular assist device for end-stage heart failure. N Engl J Med 2001;345:1435–1443. Rudski LG, Lai WW, Afilalo J, Hua L, Handschumacher MD, Chandrasekaran K, Solomon SD, Louie EK, Schiller NB. Guidelines for the echocardiographic assessment of the right heart in adults: a report from the American Society of Echocardiography endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology, and the Canadian Society of Echocardiography. J Am Soc Echocardiogr 2010;23: 685–713. quiz 86–88.
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Tittle SL, Mandapati D, Kopf GS, Elefteriades JA. Alternate technique for implantation of left ventricular assist system: left thoracotomy for reoperative cases. Ann Thorac Surg 2002;73:994–996. Zamarripa Garcia MA, Enriquez LA, Dembitsky W, May-Newman K. The effect of aortic valve incompetence on the hemodynamics of a continuous flow ventricular assist device in a mock circulation. Asaio J 2008;54:237–244.
doi:10.1016/j.ultrasmedbio.2011.11.009
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Technical Note LEFT VENTRICULAR ASSIST DEVICES: PHYSIOLOGIC ASSESSMENT USING ECHOCARDIOGRAPHY FOR MANAGEMENT AND OPTIMIZATION FAROUK MOOKADAM,* CHRISTOPHER B. KENDALL,* RAYMOND K. WONG,y ANANTHARAM KALYA,* TAHLIL WARSAME,* FRANCISCO A. ARABIA,y JOAN LUSK,* SHERIF MOUSTAFA,* ERIC STEIDLEY,* NISHATH QUADER,* and KRISHNASWAMY CHANDRASEKARAN* * Division of Cardiovascular Diseases; and y Division of Cardiothoracic Surgery, Mayo Clinic Arizona, Scottsdale, AZ, USA (Received 9 August 2011; revised 12 October 2011; in final form 15 November 2011)
Abstract—Left ventricular assist devices (LVAD) are being deployed increasingly in patients with severe left ventricular dysfunction and medically refractory congestive heart failure of any etiology. The United States Food and Drug Administration (FDA) recently approved the use of the Thoratec Heartmate II (Thoratec Corporation, Pleasanton, CA, USA) for outpatient use. Echocardiography is fundamental during each stage of patient management, pre-LVAD placement, during LVAD placement, for postoperative LVAD optimization and longterm follow-up. We present a pragmatic and systematic echocardiographic approach that serves as a guide for the management of left ventricular assist devices. (E-mail: [email protected]) Ó 2012 World Federation for Ultrasound in Medicine & Biology. Key Words: 2-dimensional echocardiography, Congestive heart failure, Left ventricular assist devices, LVAD physiology and optimization.
LVAD technology use continuous axial flow pumps with fewer moving parts and is much smaller in size. As a result, long-term durability has improved and availability has been expanded to a larger group of patients. Transthoracic echocardiography (TTE), transesophageal echocardiography (TEE) and, less commonly, epicardial echocardiography (EE) can all be used in the management of LVAD patients before, during and after deployment of the assist device. With TEE and EE, visualization of cardiac anatomy can be superior and thus especially useful in guiding the cardiac surgeon during LVAD placement. It should be emphasized that for the preoperative evaluation and postextubation day-to-day optimization, fluid and hemodynamic assessment, TTE can provide much of the needed information if a technically directed approach is used for patient management.
INTRODUCTION Left ventricular assist devices (LVAD) are becoming increasingly important as a therapeutic intervention for appropriately selected individuals with advanced heart failure recalcitrant to medical therapy. Not all patients are eligible for transplantation and some of those who are candidates for cardiac transplant need immediate hemodynamic support beyond inotropes, without which, death or serious morbidity may supervene. The limitations to cardiac transplantation for both donor and recipient, coupled with technologic advancements have resulted in broader application of the LVAD, both as a bridge to transplantation (BTT) and as destination therapy (DT) (Jessup and Brozena 2003; Rose et al. 2001). LVAD ‘‘standbys’’ also provide the option for immediate and intermediate-term support in the highrisk post-cardiac surgical patient. Oftentimes, this support can be extended for longer periods of time when BTT or DT is later prescribed (Miller et al. 2007; Rose et al. 2001). Current second and third generation
Overview of ventricular assist devices Two main types of ventricular assist devices (VADs) are in use currently, pulsatile and continuous (axial) flow mechanical assist devices. First generation VADs provide pulsatile flow from blood pumps that are either extracorporeal or implanted within an abdominal pocket. Second generation VADs use axial flow impellers that provide continuous pump flow and dispenses with the need for
Address correspondence to: Dr. Farouk Mookadam, Division of Cardiovascular Diseases, Mayo Clinic, 13400 East Shea Boulevard, Scottsdale, AZ 85259 USA. E-mail: [email protected] 335
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Table 1. Pre-left ventricular device insertion (1) Examine LV systolic and diastolic function, and exclude ventricular thrombus. (2) Examine RV size, systolic and diastolic function. (3) Assess aortic valve for stenosis and regurgitation. (4) Examine ascending, descending and abdominal aorta for dissection and atherosclerosis. (5) Examine mitral valve function, regurgitation and rule out mitral valve stenosis. (6) Examine tricuspid valve annular size and regurgitation. (7) Exclude cardiac abnormalities that could lead to right to left shunting post-LVAD placement: PFO, ASD or iatrogenic atrial shunt. (8) Assess for ventricular scar and aneurysm with ischemic cardiomyopathy. (9) Assess pulmonary valve regurgitation. (10) Assess for pulmonary hypertension, increased pulmonary vascular resistance and pulmonary embolism. (11) Examine pericardial space for effusion or adhesions if prior cardiac surgery or history of pericarditis with constrictive physiology. LVAD 5 left ventricular assist device; RV 5 right ventricle; LV 5 left ventricle; PFO 5 patent foramen ovale; ASD 5 atrial septal defect.
Fig. 1. New generation left ventricular assist device.
unidirectional valves connected to the inflow/outflow cannula. Third and fourth generation devices employ centrifugal pumps that also provide continuous flow, with the latter generation sufficiently miniaturized that they can be positioned at the left ventricular apex (Scalia et al. 2000; Stainback et al. 2005). Left VADs are positioned in parallel with the normal blood circulation from the left ventricle into the aorta and have several essential components (Fig. 1), which include: (1) An inflow conduit from the LV apex to the VAD pump; (2) Propulsion pump (LVAD) that moves the blood; (3) An outflow graft conduit that returns blood to the aorta; (4) An external controller which receives and processes information from the pump and returns information for pump operation. (Frazier et al. 2001; Horton et al. 2004; Tittle et al. 2002). Role of echocardiography for management of patient with LVAD Axial flow VADs are currently approved for outpatient use. Due to the portability of these devices and the agrarian nature of the patient, medical attention may be sought at a facility that may be less familiar with the echocardiographic examination or may be uncertain of which echocardiographic parameters to measure, or which morphologic features to observe for during echocardiographic interrogation of the device and related hemodynamics. Hence, a good understanding of cardiac anatomy and physiology is needed to understand normal VAD function and potential complications that can occur. The purpose of this overview is to systematically guide
physicians and sonographers caring for patients with devices as a routine or when such a device may be encountered unexpectedly. Preoperative echocardiography A comprehensive transthoracic echocardiogram (TTE) for LVAD candidates should include standard two-dimensional (2-D) and Doppler interrogation per guidelines (Table 1). Important findings, which may influence hemodynamic status and encumber device function, should be evaluated before the patient arrives in the operating suite: Left ventricular (LV) thrombus; aortic valve function, rule out stenosis and greater than mild regurgitation; atrial septal shunt; ascending aorta pathology; atrial septal shunt; and mitral inflow stenosis. If LV thrombus is suspected, the use of ultrasound contrast agent can aid in LV opacification for visualization of thrombus size and location. The aortic valve (AoV) should be evaluated for significant stenosis and insufficiency. If greater than mild AoV regurgitation is present, the surgeon may suture repair the AoV cusps to prevent increased recirculation of pump flow (Rao et al. 2001) The potential site for the outflow cannula should be interrogated closely. Transthoracic echocardiography can be used to assess the size and appearance of the aorta. The aortic arch can be visualized from the suprasternal view; descending thoracic limited views and abdominal aorta limited views should be assessed for dissection, aneurysm, atherosclerosis or any potential pathology, which could compromise outflow cannula function, or interfere with the cross clamp procedure. Patent foramen ovale (PFO) is common in the adult population (Hagen et al. 1984). The presence of an atrial septal defect (ASD) or patent foramen ovale (PFO) should
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Fig. 2. (a) Optimal left ventricular assist device (LVAD) setting parasternal long axis. Interventricular septal (IVS) midline during live cine clip with no septal shift on respiration. Right ventricle (RV) is dilated. Mitral valve (MV), status post MV annuloplasty band (high grade mitral stenosis is a contraindication for ventricular assist device [VAD] due to increased inflow gradient from common tachycardia in these patients). NOTE: Apical four chamber is oriented with left heart chambers on left side of screen as is standard imaging protocol for Mayo Clinic. (b) Parasternal short axis. Mitral valve level. IVS centerline with some bowing to right at end diastole. (c) Papillary level. IVS maintains midline position; no ‘‘D’’ shaped left ventricle (LV). (d) LV apex. Inlet cannula noted in apex with 2-D. (e) Para-apical window. Off axis window, in between parasternal and true apical window. This can be the closest view to a four chamber secondary to insertion site of inlet cannula. Ultrasound images used in this manuscript follow institutional patient informed consent protocol and patient identity is protected.
be ruled out using color flow Doppler and/or agitated saline bubbles during preoperative "baseline" TTE. As seen with heart failure patients, severe hypoxemia can occur with PFO after LVAD (Daniels et al. 2004).
The mitral valve, chordae and papillary muscles should be evaluated for normal structural anatomy and position. Mitral chordae, aberrant LV chordae, aberrant or displaced papillary muscle or a hypertrophied
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Fig. 3. (a) Pre-optimization parasternal long axis. Device flow too high. Interventricular septum (IVS) shifted to left during diastole (‘‘Hourglass’’ left ventricle [LV]). (b) Postoptimization parasternal long axis. IVS in centerline position during end diastole or when mitral valve closes due to higher pressure gradient between LV and left atrium (LA) (arrow). Device flow was decreased. Note heart rate has increased and there is less ectopy.
papillary muscle can potentially obstruct the inflow cannula. The presence of mitral valve stenosis can impede LV and device filling during commonly encountered tachycardia. Mitral valve stenosis is a contraindication for LVAD deployment but in cases of mitral valve repair and annular rings, a take-down procedure can open the mitral valve for unobstructed cannula flow (Fig. 2a–e). The right-sided structures impact overall cardiac function post-VAD implantation and, therefore, mandates thorough echocardiographic interrogation. The tricuspid valve is assessed for the degree of insufficiency and peak tricuspid regurgitant jet velocity is necessary before surgery. If tricuspid annular dilatation is present and the annulus is greater than 4 cm, the patient may require TV annuloplasty to prevent increased dilatation and regurgitation with RV volume changes in the postoperative period. The RV systolic function can be assessed by fractional area change (normal value 5 35%–63%) (Rudski et al.
2010). Tricuspid annular tissue Doppler (TAPSE) can be used to further evaluate RV systolic and diastolic function. Pulmonary valve regurgitation is an important finding in patients requiring ventricular assist device support. Careful examination with color flow Doppler (CFD), pulsed wave (PW) Doppler, and continuous wave (CW) Doppler for assessing the degree of regurgitation is prudent, since right ventricular volume overload can occur with pulmonary insufficiency greater than moderate. Pulmonary artery embolus, if suspected, may be detected uncommonly in proximal main pulmonary artery or within flow divider. RIGHT VENTRICULAR FUNCTION Right ventricular systolic function has been evaluated per published guidance (Rudski et al. 2010). Right ventricular diastolic function is evaluated by pulsed Doppler of the tricuspid inflow, tissue Doppler of the
Fig. 4. (a) Preoptimization apical four chamber. Device flow too high, intra-ventricular septum shifted toward left ventricle. (b) Postoptimization apical four chamber. Device flow reduced and inter-ventricular septum in a more desirable centerline position.
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Fig. 5. (a) Preoptimization apical long axis. Near left ventricle (LV) mid-cavity obliteration. (b) Postoptimization apical long axis. LV cavity size increased with a lower setting for left ventricular assist device (LVAD) flow.
lateral tricuspid annulus, pulsed Doppler of the hepatic vein and measurements of inferior vena cava (IVC) size and collapsibility (Rudski et al. 2010). Periprocedural device implantation TEE The baseline preoperative TTE information gleaned is supplemented by an intraoperative TEE. During LVAD implantation, in the operating room, transesophageal echocardiography (TEE) provides an opportunity to assess several features essential to confirm optimal positioning of the inflow and outflow conduits, detect complications and to assist in hemodynamic optimization. When TEE is contraindicated or if TEE views are limited, epicardial echocardiography (EE) can be used to evaluate cardiac anatomy. (Eltzschig et al. 2003; Reeves et al. 2007). The morphology of the left and right ventricles and the interventricular septum must be interrogated in concert. Left ventricular filling is usually assessed by transesophageal echocardiography or by invasive measurements of left atrial pressure. Right ventricular
deterioration with progressive tricuspid regurgitation can be readily identified. Transesophageal inspection of the inflow cannula site placement is performed prior to cannula placement. Once the cannula has been placed, TEE is used to help direct the cannula orifice toward mitral valve inflow, and away from the interventricular septum. With impellers set at a fixed speed, regardless of inflow to the ventricular conduit, the LVAD is capable of providing hemodynamic support only if there is adequate inflow into the device. The axial flow devices use impellers rotating at high speeds (2000–13,000 revolutions per minute (RPMs), depending on device type, allowing for maximal outputs of 10 L/min, tailored to each patient’s clinical status. Immediate postimplantation TEE (While surgical team closing) Upon insertion of the LVAD, the initial weaning process from cardiopulmonary bypass should be gradual with meticulous attention being paid to LV filling.
Fig. 6. (a) M-mode aortic valve. Aortic valve does not open during ventricular systole. (b) M mode. Aortic valve opening with each beat while weaning from left ventricular assist device (LVAD).
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Fig. 7. (a) Outlet cannula high left parasternal window. Color flow Doppler image of inlet cannula and ascending aorta. This is usually a difficult image to attain with patient in left lateral decubitus position. Having the patient lay supine or turn to right lateral decubitus can help find the optimal image. (b) Outlet cannula Doppler. Pulsed wave (PW) Doppler signal from outlet cannula, peak velocity 0.7 m/s.
If the RPM (output) of the device is increased too rapidly without adequate LV filling, a suction event occurs whereby the ventricular septum and less commonly the LV free wall will collapse, resulting in LVAD inflow conduit obstruction. The configuration of the interventricular septum will then be convex to the left ventricle and the right ventricle assumes an undesirable geometry resulting in RV dysfunction, further worsening volume delivery to the LV and subsequently to the LVAD. Adjustments to the LVAD flow settings are made based on the morphologic findings, reflecting the hemodynamic function (Chumnanvej et al. 2007; Frazier et al. 2001; Miller et al. 2007; Rose et al. 2001). Complications early postinsertion of the LVAD can be identified, especially in patients with hemodynamic
compromise using echocardiography (TEE or TTE). These complications can include new pericardial effusion, hematoma within the pericardial cavity or occult bleeding that may result in hypovolemia identified by tachycardia and LV end-diastolic volume reduction. In patients that are hemodynamically unstable, reflexively increasing the device RPM in an attempt to increase cardiac output may further worsen the clinical condition because of potential LV wall collapse and inflow catheter obstruction. The appropriate maneuver in these suction events is to decrease the RPM, restore intravascular volume and when the patient is considered euvolemic, LVAD flow can be incrementally raised to optimal levels depending upon the morphologic findings of the LV, RV and interventricular septum (Miller et al. 2007;
Fig. 8. (a) Inlet cannula apical four chamber with color flow Doppler (CFD). With CFD during ventricular systole, while mitral valve is closed, we see left ventricle (LV) intracavitary flow with aortic insufficiency. (b) Inlet cannula Doppler. Apical four chamber. PW Doppler of inlet cannula, peak velocity 0.5 m/s. This is one window to line up with turbulent flow in inlet cannula, try multiple windows, i.e. apical long axis, apical two, parasternal, para-apical, to get parallel to flow and peak velocity.
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Table 2. Postoperative recovery period echo evaluation (1) Reassessment of the LV chamber size (geometry), function and interventricular septum direction. (2) Examination of the LV apex with inflow conduit alignment and exclude obstruction using Doppler ultrasound techniques. (3) Reassessment of the RV chamber size (geometry), function and interventricular septum direction. (4) Examine interventricular septum bowing direction with respect to LVAD setting and on changes to LV/RV size. IVS should be midline at optimal device flows. (5) Assess tricuspid regurgitation with color Doppler and CW for right ventricular systolic pressure, assess for pulmonary hypertension. (6) Reassessment of aorta for outflow conduit flow (Doppler) and exclude evidence of new dissection. (7) Examine aortic valve for opening (long cine loop cycle), significant regurgitation (. 11) and sinus of Valsalva thrombus. (8) Reassessment of LA, RA and atrial septum for new atrial shunt. (9) Assess pulmonary veins to exclude obstructions/compressions. LVAD 5 left ventricular assist device; RV 5 right ventricle; LV 5 left ventricle; IVS 5 interventricular septal; CW 5 continuous wave Doppler; LA = left atrium; RA = right atrium.
Rose et al. 2001). Once implantation is complete, optimization of chamber morphology and cannula flows can be achieved under 2-D echocardiographic guidance during inpatient or outpatient follow-up. (Figs. 3a–8b). The inflow cannula Doppler profile should be obtained to evaluate flow from the LV into the device. This is usually obtained from an apical or off axis apical view (Fig. 8a and b). The inter-atrial septum should be evaluated again immediately postprocedure for an atrial shunt that may not have been evident in preoperative scans. Postprocedure inpatient or ambulatory follow-up using TTE/TEE When evaluating the patient and device in the ambulatory setting, most LVAD adjustments are directed to optimize for volume shifts. Routine TTE windows can be limited in the early postoperative period due to healing incision sites and the sling immobilizer which aids in securing the external controller, cannula and chest tubes. It may be prudent for the sonographer to request nursing assistance to remove the sling for the purpose of accomplishing a comprehensive TTE examination. For optimal clinical outcomes in the VAD patient, a systematic approach for echocardiographic examinations is outlined in Tables 1 and 2. Recommended 2-D TTE views and targeted findings are listed in Tables 3 (left heart) and 4 (right heart) (Joffe et al. 1996; Peterson et al. 2003; American Society of Anesthesiologists and Society of Cardiovascular Anesthesiologists 1996). The VAD flow performance can be assessed using continuous wave (CW) or pulsed wave (PW) Doppler signals from the cannula (Figs. 7b and 8b) (Scalia et al. 2000; Stainback et al. 2005). For the follow-up TTE, the following protocol is recommended as a guide.
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Primary echocardiographic findings for axial flow VAD optimization are: (1) LVAD inflow and outflow conduits; (2) Ventricular septal position and motion (respirometry); (3) Left ventricular size (and function if contractility restored); (4) Intermittent opening of the aortic valve and aortic valve regurgitation; (5) Right ventricular size and function (RV cardiac output); (6) Tricuspid valve inflow, regurgitation and regurgitant peak velocity; (7) Pericardial effusion: presence. Cannula flow velocities should be estimated in the presence of suction events to rule out obstruction from LV chamber walls (ventricular septum, papillary muscle, mitral valve) or from cannula thrombus. Obtaining velocities can be challenging and requires patience, skill and knowledge of cannula position and direction. With the inflow cannula position at the LV apex, Doppler flow should be attempted from the most parallel echo window using the parasternal short axis, para-apical, and if possible apical window. The outflow cannula position and direction of flow poses a greater challenge for the cardiac sonographer because of its location within the ascending aorta (Fig. 8a). The outflow cannula, when placed in the ascending aorta, can be assessed in either the left lateral or right lateral decubitus position from the parasternal window. Peak systolic Doppler velocity, either CW or PW, for the inflow and outflow cannula should be comparatively similar (Figs. 7b and 8b). A discrepancy between inflow and outflow cannula flow velocity must be accounted for, particularly when a suction event occurs. The LV and RV should be evaluated with respect to the interventricular septal (IVS) position. Left ventricular function (ejection fraction or EF) is not routinely reported post- device implantation, but if needed, temporary interruption of the LVAD is necessary to calculate the EF. The LVAD flow rate can be optimized if the IVS is shifted to the left or right side during echocardiographic interrogation. Device flow is optimal when the IVS is midline and the LV chamber is not collapsed (‘‘hour-glass’’ shape) (Fig. 3a). When assessing the IVS in the postoperative period, the use of a respirometer is essential to aid in distinguishing abnormal IVS motion that can be due to pericardial effusion or hematoma causing hemodynamic effects on LV and RV function. A careful exploration should be undertaken looking for thrombus in the left-sided chambers that may embolize and obstruct the LVAD. Multiple TTE windows and TEE planes should be used to assess the LVAD inflow conduit (Chumnanvej et al. 2007; Frazier et al. 2001).
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Table 3. TTE views and common key findings for long-term LVAD usage Anatomy
Views
Key findings
Left ventricle
PLAX, para-apical, apical
Size and function Intra ventricular septal shift Wall thickness Rule out thrombus Inflow cannula position
Outlet cannula/ascending aorta
High left PLAX and high right PLAX (right lateral decubitus to examine ascending aorta)
Annotate device output and flow rate on U/S screen Ascending aorta size Color flow Doppler PW peak velocity
Inlet cannula
PSAX, para-apical, apical
Annotate device output and flow rate on ultrasound system screen Usually at LV apex Cannula position and direction Color flow Doppler PW Doppler inflow velocities (,2.0–2.3 m/s)
Mitral valve and apparatus
PLAX, PSAX, para-apical
MV mobility Papillary muscle obstructing cannula MV regurgitation MV diastolic inflow velocity (CW and PW)
Aortic valve
PLAX, PSAX, para-apical
Closed and/or open-to-closed ratio PW LVOT (if AV opens) Aortic valve regurgitation Rule out thrombus (Sinus of Valsalva)
Right ventricle
PLAX, RV inflow, para-apical
Size and function RVSP Tissue Doppler (s’/e’/a’)
Tricuspid valve
PSAX, RV inflow, para-apical
Pulmonary valve
PSAX, RV outflow
RVOT diameter (cardiac output calculation) PW RVOT TVI CW peak velocity and TVI
Left atrium
PLAX, para-apical, apical
Size Pulmonary vein flow Rule out thrombus
Pericardium
Parasternal, apical
Pericardial effusion Pericardial adhesions
Vena cava and hepatic vein
PSAX, RV inflow, subcostal, transhepatic
Size with respiratory cycle Color flow Doppler PW hepatic vein noting any respiratory variation
Leaflet mobility Tricuspid annulus Regurgitation Diastolic inflow
TTE 5 transthoracic echocardiography; LVAD 5 left ventricular assist device; PLAX 5 parasternal long axis; PSAX 5 parasternal short axis; PW 5 pulsed wave Doppler; LVOT 5 left ventricular outflow tract; MV 5 mitral valve; AV 5 aortic valve; CW 5 continuous wave Doppler; RVSP 5 right ventricle systolic pressure; RV 5 right ventricle.
Inflow conduit obstruction either by septal suck-down or thrombi is usually detected by turbulent, high aliasing velocity flow with color flow Doppler or by previously reported peak velocities higher than 2.3 m/s using continuous wave Doppler (Chumnanvej et al. 2007). It may be challenging with 2-D imaging to visualize the track flow to the inlet conduit from the left ventricle depending on the VAD being employed because of reverberation
artifacts. Color flow Doppler is useful in tracking intraventricular blood flow from the mitral orifice into the device in these instances, using an apical window (Fig. 9a and b). For optimal LVAD function, the aortic valve should remain closed throughout the cardiac cycle. In addition, greater than mild aortic regurgitation may result in abnormal LVAD function because of reduced efficiency
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Fig. 9. (a) Apical four chamber. 2-D view from the apex with poor acoustic window, image shadowing from scar tissue and inlet cannula. (b) Apical four chamber with color flow Doppler (CFD). During CFD imaging at low velocity scale we can appreciate blood flow to the inlet cannula after atrial contribution.
of flow from the outflow cannula into the aorta as well as volume overload to the LV inflow cannula (Chumnanvej et al. 2007; Frazier et al. 2001; Miller et al. 2007; Rose et al. 2001). With the outflow cannula anastomosed to the mid ascending aorta, the device circulates blood flow retrograde toward the sinus of Valsalva and the aortic valve (DiGiorgi et al. 2004). This type of retrograde flow is disruptive to the ‘‘normal’’ physiology of pericannula aortic tissue and fluid dynamics (John et al. 2010). In this hemodynamic situation, thrombosis at the level of the sinus of Valsalva and, over time, aortic valve cusp fusion through fibrosis can occur (John et al. 2010). It has been suggested that adjusting pump flow rate to Table 4. Right heart Anatomy
Views
allow intermittent opening of the aortic valve cusps can improve cusp physiology (Zamarripa Garcia et al. 2008) and reduce the incidence of sinus of Valsalva thrombus formation (Crestanello et al. 2009). If aortic valve opening does occur, the ratio of opento-closed beats is an important finding when assessing the LVand mechanical pump function. Using a long cine loop clip, $ 6 cardiac cycles, is sufficient to capture possible aortic valve opening. M-mode provides high frame rate images that may assist in detecting a small opening of aortic valve cusps or to confirm that the valve remains closed (Fig. 6a and b). Color flow Doppler is used at the level of the aortic valve to assess aortic valve regurgitation, which is usually a central jet. Aortic valve regurgitation can be visualized with CFD with intra-cavitary flow within the LV during ventricular systole (Fig. 8a).
Key findings
Right ventricle
PLAX, RV inflow, para-apical
Function RVSP Tissue Doppler (s’/e’/a’)
Tricuspid valve
PSAX, RV inflow, para-apical
Pulmonary valve
PSAX, RV outflow
RVOT diameter (cardiac output calculation) PW RVOT TVI CW peak velocity and TVI
Vena cava and hepatic vein
PSAX, RV inflow, subcostal, transhepatic
Size with respiratory cycle Color flow Doppler PW hepatic vein noting any respiratory variation
Leaflet mobility Tricuspid annulus Regurgitation Diastolic inflow
PLAX 5 parasternal long axis; PSAX 5 parasternal short axis; PW 5 pulsed wave Doppler; RVOT 5 right ventricular outflow tract; CW 5 continuous wave Doppler; RVSP 5 right ventricle systolic pressure; RV 5 right ventricle; TVI 5 time velocity integral.
The right heart Variable degrees of right heart failure are common during the postoperative period for LVAD patients, hence, mandating close monitoring of RV function is needed (Patel et al. 2008). Right ventricular function can be assessed from the parasternal window, RV inflow view and the para-apical echo windows. Pulse wave Doppler (PW) of the RVOT is required for computing the right ventricular cardiac output and pulmonary vascular resistance. A simple method for noninvasive estimation of pulmonary vascular resistance has previously been described by Abbas et al. (2003). Right atrial pressure (RAP) is estimated based on the appearance and collapse of the inferior vena cava (IVC) (Kircher et al. 1990). Placement of the drive component is within an intraabdominal pocket. This placement obscures the subcostal echo window. In this instance, a right transhepatic view should be attempted to visualize the IVC. The
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pericardium should be assessed for signs of fluid and clot accumulation. Cardiac tamponade is a clinical diagnosis, which can be confirmed with typical echocardiographic findings and respiro-phasic changes that indicate ventricular interdependence by interpretation of the transmitral and tricuspid inflow Doppler velocities (Mookadam et al. 2009). In cases where TTE is sub-optimal because of cardiac imaging window limitations, TEE can provide an unobstructed view of cardiac anatomy to aid in identifying the cause of hemodynamic instability.
CONCLUSION Cardiac transplantation remains the primary treatment for patients with intractable heart failure. With donor organs in short supply, we can expect to see an increase in the deployment of LVAD for bridge to transplantation or as destination therapy. Recent Food and Drug Administration (FDA) approval of continuous flow LVADs for outpatient use increases the likelihood of non-device specialty clinics or hospitals coming into contact with these patients. To help assess these patients in a meaningful way, a meticulous and systematic cardiac ultrasound is essential. Echocardiography when used appropriately can help assess the physiologic and hemodynamic function of the continuous flow LVAD and can diagnose the cause of malfunction. We have outlined a systematic approach that may be used in the assessment of LVADs using cardiac ultrasound that may be useful to both sonographers and cardiologists who may be involved in the management of this unique but growing group of patients. Familiarity with these cardiac assist devices and the anatomical or morphologic echocardiographic landmarks will be useful in caring for these patients.
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