Thromboembolic Phenomena and Vegetations

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15 Thromboembolic Phenomena and Vegetations

Peter J. Cawley, Brian D. Soriano

Background

Thrombi and vegetations may result in clinical symptoms when embolism occurs. Vegetations may result in clinical symptoms when significant valve destruction occurs or with systemic symptoms such as fever and malaise. Tumors may also present clinically due to embolism, but tumors are not covered in this section.

Thrombus

• Thrombus is predisposed to form in areas of the heart where there is low-velocity blood flow or flow stasis.

• The left atrium (LA) (especially the left atrial appendage [LAA] [Fig. 15-1]) is a common area of thrombus formation when associated with atrial arrhythmias or mitral stenosis.

• The left ventricle (LV) is a common area of thrombus formation when associated with left ventricular dysfunction (global or regional) (Fig. 15-2), aneurysm, or pseudoaneurysm (Fig. 15-3). The apex is a common area for thrombus formation.

• Thrombus formation within the right heart may occur in cases of severe right atrial enlargement (i.e., atriopulmonary Fontan) or right ventricular dysfunction. More commonly, thrombus formation occurs within veins and embolizes to the right heart. Thrombus may become trapped in the right atrium (RA) (Chiari network or Eustachian valve), in the right ventricle (RV) (tricuspid valve apparatus or right ventricular trabeculations), or pulmonary arteries (PAs) as it embolizes (Fig. 15-4).

• Thrombus formation may occur on intracardiac devices seen within the right heart such as pacing/defibrillator leads and central venous catheters. Thrombus formation can result on intracardiac walls of the right heart if a central venous catheter tip results in local trauma.

• Thrombus formation may occur in surgically placed conduits (Glenn shunt, Fontan shunt, RV-to-PA conduit). Thrombus can be difficult to visualize on echocardiography (echo) due to artifact from conduits or the lack of an ultrasound window. Magnetic resonance imaging (MRI) or computed tomography (CT) may be more helpful in this regard.

• Intracardiac shunting can result in venous thrombi embolizing to the arterial system. The most common shunts for which this may occur are a patent foramen ovale (PFO), atrial septal defects (ASDs), baffle/conduit leaks, and larger ventricular septal defects (VSDs) with right-to-left shunting such as Eisenmenger physiology.

• Thrombus can also occur on prosthetic valves. Clinical presentation may occur as a result of an embolic event or symptomatic valve dysfunction or may be directly visualized by echo in an asymptomatic patient.

Figure 15-1 A, Narrow-sector transesophageal (TEE) image of the left atrial appendage (LAA) without any thrombus. B, Narrow-sector TEE image of the LAA with thrombus (arrow).

Figure 15-2 A, Apical four-chamber (4C) view demonstrating the difficulty with imaging the left ventricular apex (near-field reflection artifact). No clear thrombus is identified. B, In the same patient, 4C single-state free-precession (SSFP) cine magnetic resonance imaging (MRI) showing a suspicion for an apical thrombus (arrow). C, In the same patient, delayed contrast imaging demonstrating scar (white part of myocardium) in the apex with an apical thrombus (arrow).

Figure 15-3 A, Vertical long axis (two-chamber [2C]) SSFP cine MRI demonstrating an apical pseudoaneurysm (arrow). B, In the same patient, delayed-enhancement imaging with a normal inversion time demonstrating the pseudoaneurysm. The arrow points to an area suspicious for thrombus but is best proved by prolonging the inversion time (C) and thus proving that thrombus did not take up the gadolinium contrast. D, Apical 4C transthoracic echocardiography (TTE) in the same patient demonstrates the apical pseudoaneurysm (arrow), but the echo images do not demonstrate the thrombus as clearly as the MRI, and it is harder to appreciate thrombus within pseudoaneurysm.

Figure 15-4 A, Right ventricular long axis SSFP cine MRI showing thrombus (arrow) entangled in the tricuspid subvalvular apparatus. B, In the same patient, a 4C SSFP cine demonstrating a thrombus (arrow) at the apex of the right ventricle.

Vegetations

• Vegetations are most commonly the result of bacterial or fungal infections.

• Noninfectious vegetations may also occur and are commonly referred to as marantic or nonbacterial thrombotic endocarditis (NBTE). NBTE usually occurs in the context of a malignancy or autoimmune disease (Fig. 15-5). A metastatic malignancy does not necessarily have to be present. Although blood cultures and an accurate determination of whether the patient was exposed to antibiotics at the time of blood sampling for culture are essential in identifying vegetations as infectious or noninfectious, there are some imaging characteristics of NBTE: vegetations tend to be less mobile, more sessile, and located toward the base of the leaflets. Because the base of the valve leaflets is more commonly affected, less severe valve regurgitation is noted. Anticoagulation should be considered in patients with NBTE.

• Mobility and location are important distinguishing features of a vegetation. Vegetations have motion independent of a valve leaflet and are most commonly associated with the upstream surface of a valve leaflet (e.g., the right atrial side of the tricuspid valve [Fig. 15-6]) but have also been reported on the Eustachian valve, residual Chiari network, subvalvular apparatus, and chamber wall. Commonly, the vegetations are not rounded in appearance. Vegetations usually have low reflectance of ultrasound waves but over time may become more calcified (high reflectance). Visualization of vegetations in more than one ultrasound window decreases the likelihood of an ultrasound artifact.

• Vegetations can occur on intracardiac devices such as pacing/defibrillator leads and central venous catheters (Fig. 15-7).

• Destruction of the valve apparatus (annulus or leaflet) can result in a fistulous connection between adjacent cardiac chambers (e.g., aorta to RA) or valve regurgitation.

• Paravalvular abscesses may occur as a result of endocarditis and typically occur in the annular part of the valve apparatus. Abscesses may be echogenic or echolucent spaces near the valve annulus.

• Infections of bioprosthetic or prosthetic valves are more typically an annular disease, which can result in valve dehiscence or annular abscess (Fig. 15-8).

• Adequate sampling of blood for culture and obtaining blood cultures before the commencement of antibiotics are critical for the timely diagnosis of infectious endocarditis.

Figure 15-5 Narrow-sector TEE image (midesophageal long axis view) in a patient with nonbacterial thrombotic endocarditis secondary to lupus. These vegetations (arrows) tend to be more sessile and less mobile.

Figure 15-6 4C SSFP cine MRI demonstrating a tricuspid valve vegetation (arrow) on the atrial side of the valve.

Figure 15-7 Transgastric right ventricular inflow view on TEE demonstrates a large mass (solid arrow) attached to a right-sided pacing/defibrillator lead (dashed arrow) as it crosses the tricuspid valve.

Figure 15-8 Narrow-sector TEE image of a bioprosthetic aortic valve in short axis. Note the echolucent spaces (arrows) along the annulus in this patient with an annular abscess.

A more detailed discussion of the evaluation of endocarditis can be found in Chapter 14 of the Echocardiography Review Guide by C. M. Otto and R. G. Schwaegler.

Overview of Echocardiographic Approach

In many infants and young children, transthoracic acoustic windows are typically adequate enough that the structures of the heart are well visualized and there is little incremental benefit to transesophageal echo (TEE). TEE should be considered when transthoracic findings are equivocal or if specific structures of the heart are not well visualized. TEE may also be useful in guiding the surgical approach.

M-Mode

• Displaying cardiac motion over time in a “pencil-beam” portion of the heart can be very helpful diagnostically to demonstrate the rapid movements of a valve vegetation or thrombus.

Two-Dimensional

• Transthoracic echo (TTE) allows direct visualization of the cardiac chambers such as the left and right ventricles.

• The left ventricular apex is better visualized by TTE than TEE. Thus TTE ismore sensitive for the detection of ventricular thrombi.

• The LA and the LAA are better visualized by TEE than TTE. Thus TEE is more sensitive for the detection of atrial thrombi.

• TEE has a higher degree of sensitivity for detecting valve thrombosis.

• TTE can detect PFOs and ASDs, but TEE has a higher degree of sensitivity and specificity. The addition of saline microbubbles testing with two-dimensional (2D) imaging increases the sensitivity of detecting shunting.

• TTE can detect vegetations and paravalvular abscesses, but TEE has a higher degree of sensitivity and specificity (Figs. 15-9 and 15-10).

Figure 15-9 Diastolic TEE image (multiplane at 129 degrees) of a bioprosthetic pulmonary valve demonstrating normal valve leaflets (arrowhead) with thick, mobile densities adherent to the hinge points of the valve cuffs (arrows). The distal end of the conduit is partially obscured by a right pulmonary artery stent (asterisk).

Figure 15-10 Short axis TEE image (multiplane at 90 degrees) of a bioprosthetic valve. The valve leaflets remain thin (arrow) but a prominent, elliptical vegetation is seated within the cusp (arrowhead).

Color Doppler

• Doppler imaging is not useful for detecting the presence or absence of thrombus but is useful for detecting shunting when paradoxical embolization is clinically suspected.

• Useful for determining the presence of valve regurgitation and distinguishing between physiologic and pathologic valve regurgitation. Regurgitation or leaflet perforation may be a consequence of valve vegetations.

• Useful for distinguishing abnormal fistulous connections. A fistula may be a consequence of annular infections.

• Useful for determining flow disturbances, which are often the first echocardiographic signs of an abnormality that can then be further characterized by 2D imaging.

• Limited value for determining the severity of valve regurgitation.

Continuous Wave Doppler

• Useful for determining the severity of regurgitation.

• Useful for determining the location of fistulous connections by determining the peak velocity and the timing of the flow with the cardiac cycle.

Anatomic Imaging

Left Atrial Thrombus

Image Acquisition

• Decrease the image depth to maximize the entire LA. Scan the LA while repositioning the probe in the esophagus from superior to inferior and turning the probe left to right to capture the entire LA. Rotate the multiplane knob to scan the LA from 0 to 180 degrees.

• The exam must be individualized but commonly the LAA is best located by rotating the multiplane knob to between 60 and 100 degrees. Center the LAA in the imaging sector. Narrow the sector to maximize imaging resolution. Attempt to look into the LAA by avoiding the ridge of cardiac tissue between the left superior pulmonary vein (PV) and the LAA.

Pitfalls

• Spontaneous echocardiographic contrast is indicative of decreased flow areas and may be mistaken for cardiac thrombus.

• Reverberation artifact may be mistaken for a thrombus when the ridge of tissue between the left superior PV and the LAA is located between the source of the ultrasound beam and the LAA.

• Pectinate muscles are normal structures found within the LAA and can be mistaken for thrombi (Fig. 15-11).

• Alternative approaches: contrast-enhanced MRI and contrast-enhanced CT. However, either one may give a false filling defect if contrast does not get into the LAA due to poor LAA contraction.

Figure 15-11 Narrow sector TEE images in different multiplane angles (A, B) of the LAA demonstrating normal pectinate muscles (arrows) that can sometimes be mistaken for abnormal masses.

Left Ventricular Thrombus

Image Acquisition

• Use standard and off-axis views to optimize visualization of the apex. Care should be undertaken to avoid foreshortening the apex.

• Increase the transducer frequency.

• Left ventricular thrombus is commonly associated with abnormal wall motion. Carefully examine for the presence of wall motion abnormalities.

• Mural thrombus is typically laminated against the left ventricular wall and may be more difficult to visualize than mobile thrombus.

Pitfalls

• Near-field reflection artifact is commonly encountered when imaging from the apical window. Strong reflectors are noted at the apex, which give the appearance of a mass in the apex.

• Normal variants within the ventricular apex that may be mistaken for cardiac thrombi are trabeculations or false tendons.

• Contrast agents may be useful to delineate normal structures from thrombus.

Valve Vegetations

Image Acquisition (Whether TEE or TTE)

• Narrow the imaging sector around the valve structure (Fig. 15-12).

• Examine all leaflets of the valves using multiple angles and windows.

• Examine the entire annulus closely.

• For prosthetic valves, look for valve/annular stability. The presence of annular motion may indicate valve dehiscence.

• Examine all intracardiac devices such as pacing leads and central venous catheters.

Figure 15-12 Narrow sector midesophageal TEE image of the mitral valve in a patient with streptococcal endocarditis (solid arrows). Note that there is associated mitral annular calcification (dashed arrow) that causes acoustic shadowing.

Pitfalls

• Normal variants such as Lambl excrescence (degenerative changes commonly found on the left ventricular surface of the aortic valve usually having the appearance of linear strands [Fig. 15-13]) or nodules of Arantius (focal thickening at the coaptation point of the valve leaflets) may be mistaken for valve vegetations.

• Image artifacts such as beam width artifacts may be mistaken for valve vegetations. Identifying valve vegetations in two ultrasound windows minimizes the likelihood of an imaging artifact.

• Mitral valve prolapse or flail chords/leaflets may be mistaken for valve vegetations.

Figure 15-13 Narrow sector midesophageal TEE image of the aortic valve demonstrating a normal variant associated with aging: Lambl excrescence (arrow).

Physiologic Data

Valve Vegetations

• Use color Doppler to identify pathologic valve regurgitation, leaflet perforation, fistulous connections, and abnormal flow signals.

• Useful for determining the location of fistulous connections by determining the peak velocity and the timing of the flow with the cardiac cycle.

Alternate Approaches

• As with echo, MRI uses different imaging techniques to answer clinical questions. Cine MRI allows improved visualization of the cardiac apex when an ultrasound window is poor or when visualizing the cardiac apex by echo is limited by lung or rib interference. Cine MRI also allows improved endocardial delineation (Fig. 15-14). Contrast-enhanced MRI can help distinguish normal adjacent myocardium from thrombus on the basis of tissue characterization (Fig. 15-15). MRI angiography may also be helpful for distinguishing thrombus by looking for filling defects within the LAA.

• CT angiography may also be helpful to identify thrombus within the cardiac chambers by identifying filling defects.

• Invasive angiography may also be helpful to identify thrombus within the cardiac chambers.

Figure 15-14 A, 4C SSFP cine MRI demonstrating a flow disturbance (arrow) from the LV into the right atrium (RA) (Gerbode-type ventricular septal defect [VSD]). B, In the same patient, this coronal cine demonstrates a prosthetic aortic valve (dashed arrow) with the Gerbode-type VSD defect (solid arrow) from the LV into the RA.

Figure 15-15 A, Short axis SSFP cine MRI at the level of the atria demonstrating an irregular mass (arrow) protruding into the lumen of the LA. B, Delayed-enhancement imaging with a long inversion time at the same corresponding area demonstrating laminar thrombus (arrow).

Key Points

• The most common sources of cardiac embolization include thrombus, vegetations, and tumor.

• The location of embolization depends on the location of the source within the heart (right side versus left side) and the presence of shunts within the heart.

• Intracardiac thrombus commonly occurs in the LAA (in conjunction with mitral stenosis or atrial arrhythmias), in the LV (in the presence of regional or global dysfunction), or in the right heart (dysfunction, chamber enlargement, or trapped as the thrombus is embolizing from a deep vein).

• TTE is helpful for detecting ventricular thrombus, whereas TEE is more sensitive for the detection of atrial thrombus.

• MRI and CT are alternative modalities for the detection of intracardiac thrombus. Tissue characterization with MRI can be especially helpful in distinguishing thrombus from tumor.

• Echo remains the best modality to identify valve vegetations because of its superior temporal resolution.

• Vegetations can be visualized by 2D echo. Doppler is also helpful to suspect vegetations by identifying pathologic regurgitation, leaflet perforation, or fistulous connections.

• Prosthetic valve endocarditis is more commonly an annular disease than a leaflet disease.

• Other intracardiac devices such as pacing/defibrillator leads are increasingly common sources of thrombus and vegetations.

Suggested Reading

1 Shanewise JS, Cheung AT, Aronson S, et al. ASE/SCA guidelines for performing a comprehensive intraoperative multiplane transesophageal echocardiography examination: recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography. J Am Soc Echocardiogr. 1999;12:884-900.

2 Bonow RO, Carabello BA, Chatterjee K, et al. ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (writing Committee to Revise the 1998 guidelines for the management of patients with valvular heart disease) developed in collaboration with the Society of Cardvascular Anesthesiologists endorsed by the Society for Cardiovascular Angiography and Interventions and the Society of Thoracic Surgeons. J Am Coll Cardiol. 2006;48:e1-e148.

3 Zoghbi WA, Chambers JB, Dumesnil JG, et al. Recommendations for evaluation of prosthetic valves with echocardiography and Doppler ultrasound: a report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Task Force on Prosthetic Valves, developed in conjunction with the American College of Cardiology Cardiovascular Imaging Committee, Cardiac Imaging Committee of the American Heart Association, the European Association of Echocardiography, a registered branch of the European Society of Cardiology, the Japanese Society of Echocardiography and the Canadian Society of Echocardiography, endorsed by the American College of Cardiology Foundation, American Heart Association, European Association of Echocardiography, a registered branch of the European Society of Cardiology, the Japanese Society of Echocardiography, and Canadian Society of Echocardiography. J Am Soc Echocardiogr. 2009;22:975-1014.

4 Otto CM, Schwaegler RG. Echocardiography Review Guide. Philadelphia: Saunders; 2007.

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