INTRODUCTION — Replacement of a diseased heart valve with a prosthetic heart valve exchanges the native disease for prosthesis-related complications [1-3]. Complications include prosthetic valve obstruction (including thrombosis and pannus formation), patient-prosthesis mismatch, embolic events, bleeding, prosthetic heart valve regurgitation (valvular and paravalvular), infective endocarditis, and prosthetic valve-related hemolysis.
Thrombus forming on a mechanical prosthetic valve can be nonobstructive or obstructive and may or may not cause clinical thromboembolic events [4-7].
Diagnosis of mechanical prosthetic valve thrombosis and obstruction are reviewed here. Related issues including when to suspect prosthetic valve thrombosis and obstruction and how to start the evaluation are reviewed separately:
●(See "Management of mechanical prosthetic valve thrombosis and obstruction".)
●(See "Bioprosthetic valve thrombosis, thromboembolism, and obstruction: Management".)
GENERAL APPROACH TO EVALUATION — Our general approach to evaluating patients with suspected mechanical prosthetic valve thrombosis (PVT) and/or obstruction is presented here.
Initial evaluation — The clinical manifestations and initial evaluation of prosthetic valve thrombosis or obstruction is detailed separately. Briefly, patients suspected of having PVT and/or obstruction should undergo clinical evaluation for any related symptoms or signs and transthoracic echocardiography (TTE) including determination of whether prosthetic valve obstruction is present. Prosthetic valve obstruction is identified as a mean transvalvular gradient increase by >50 percent (or >10 mmHg increase for an aortic prosthesis) compared with baseline, after exclusion of other causes such as a high-output state. (See "Bioprosthetic valve thrombosis, thromboembolism, and obstruction: Clinical manifestations and diagnosis", section on 'Initial evaluation'.)
Approach to further evaluation — We suggest the following approach if initial evaluation is suggestive of PVT and/or obstruction:
●Additional imaging of the mechanical valve is required. Options include transesophageal echocardiography (TEE) , multidetector computed tomography (MDCT) or fluoroscopy. Multiple advanced imaging options are often used.
•The urgency of further evaluation is based upon the clinical setting. Urgent multimodality imaging is recommended for patients with suspected PVT and/or prosthetic valve obstruction with moderate to severe symptoms (New York Heart Association functional class III or IV).
•Factors to consider when choosing between TEE and MDCT are described below. If the mechanical valve is not adequately visualized by TEE or MDCT, we suggest performing the alternate test, if feasible. (See 'Choice between TEE or MDCT' below.)
•If mechanical valve motion is not adequately assessed by TEE or MDCT, fluoroscopy may be helpful. Fluoroscopy is the gold standard in assessing mechanical valve motion, but it does not allow visualization of thrombus.
●Exclude prosthetic valve endocarditis. (See 'Exclude prosthetic valve endocarditis' below.)
●Differentiate between thrombus and pannus as main causes of prosthetic obstruction. (See 'Differentiate between thrombus and pannus as main cause of obstruction' below.)
Specific approaches to evaluation depending upon whether prosthetic valve obstruction is present are detailed below. In addition, for patients with a thromboembolic event (eg, stroke), comprehensive evaluation for alternative causes should be conducted. (See 'Specific approaches' below and "Bioprosthetic valve thrombosis, thromboembolism, and obstruction: Clinical manifestations and diagnosis".)
Additional imaging considerations
Characteristics of imaging tests — Imaging of normal and abnormal prosthetic valves is challenging, requiring experience and careful attention to detail in image acquisition and interpretation.
Transesophageal echocardiography — TEE enables assessment of prosthetic valve leaflet appearance, motion and function (obstruction and regurgitation), features of thrombus, and alternate causes of emboli. Three-dimensional (3D) TEE is suggested when available, as it may detect prosthetic thrombi that are missed or only partially visualized by two-dimensional (2D) TEE [8].
TEE is helpful in the assessment of mechanical mitral valves because thrombus is sometimes also located on the left atrial side of the valve and thus may be seen on TEE imaging. However, TEE is less useful for evaluation of mechanical aortic valve prostheses (particularly bileaflet valves and when more than one mechanical prosthesis is in place) because the posterior aspect of the valve shadows the valve itself in esophageal views. Transgastric views are often most helpful for assessing prosthetic leaflet motion.
If there are indeterminate TEE findings (eg, absence of mass in a patient with an aortic valve prosthesis, presence of an intermediate or high intensity ratio mass, or suboptimally visualized mitral valve prosthesis), then MDCT may be helpful in visualizing thrombus or pannus.
Multidetector computed tomography — MDCT enables assessment of prosthetic valve leaflet appearance and motion and features of thrombus [9]. MDCT and fluoroscopy correlate well in identifying restricted leaflet motion, but MDCT further enables assessment of paravalvular masses [10]. MDCT is also helpful for identifying alternative diagnoses (similar to TEE), as it can identify findings consistent of vegetations with accuracy approaching that of TEE [11], and MDCT with a delayed imaging acquisition protocol can identify atrial thrombi with accuracy nearing that of TEE [12,13]. However, thin, highly mobile masses may be challenging to detect by MDCT given its temporal resolution. (See "Echocardiographic evaluation of prosthetic heart valves".)
Fluoroscopy — Fluoroscopy provides the most reliable assessment of mechanical leaflet motion but does not enable assessment of soft tissue (eg, thrombus or pannus) associated with the valve. Valve fluoroscopy is generally best performed in the catheterization laboratory by experienced operator. Fluoroscopy or TEE may be used to evaluate Bjork-Shiley or Sorin monoleaflet motion, but TEE is generally preferred as it may additionally enable visualization of mass on the leaflet.
Choice between TEE or MDCT — The choice between TEE and MDCT as the next imaging test after TTE is made based upon availability, prior test results, patient characteristics, mechanical valve location, and clinician/institutional experience.
General recommendations — If both TEE and MDCT are feasible, we generally recommend the following approach:
●TEE is preferred for mechanical mitral and tricuspid valves. However, some experts prefer starting with MDCT as the primary test to evaluate prosthetic leaflet motion and appearance except for Bjork-Shiley or Sorin monoleaflet valves.
●TEE rather than MDCT is used to evaluate Bjork-Shiley or Sorin monoleaflet valves since MDCT evaluation of these valves is generally technically suboptimal due to artifact [14-16].
●MDCT is preferred for mechanical aortic or pulmonic valves (except Bjork-Shiley or Sorin monoleaflet valves) [17].
If the mechanical valve is not adequately visualized by TEE or MDCT, we suggest performing the alternate test, if feasible.
Fluoroscopy is frequently used as an adjunct to other imaging tests to assess mechanical prosthetic leaflet motion, but it does not permit assessment of thickening or mass on the prosthetic leaflet(s). (See 'Fluoroscopy' above.)
Additional factors to consider — Clinical experience as well as some clinical factors may influence the choice between TEE and MDCT:
●Factors that favor TEE (see 'Transesophageal echocardiography' above):
•If TTE assessment of prosthetic valve gradients is suboptimal, TEE is preferred as it may be helpful in assessing valve gradients.
•TEE is preferred to MDCT if other causes of emboli such as atrial thrombi or vegetations are suspected.
•TEE is preferred to MDCT in patients at risk for contrast nephropathy.
●Factors that favor MDCT (see 'Multidetector computed tomography' above):
•MDCT is preferred for the patient with contraindication to TEE.
•MDCT is preferred for a patient known to have suboptimal TEE prosthetic valve images (unless a Bjork-Shiley or Sorin valve is present, as discussed above). (See 'General recommendations' above.)
Exclude prosthetic valve endocarditis — A definitive tissue diagnosis of a mass attached to the prosthesis (eg, thrombus, pannus, or vegetation) cannot be made on an imaging test (TEE, MDCT, fluoroscopy), and ultimately it is the clinical context that helps guide diagnosis and therapy. For patients presenting with abnormal prosthetic valve appearance or mobility, it is important to exclude the presence of prosthetic valve endocarditis (PVE). PVE generally presents with signs and symptoms of invasive infection; clinical manifestations and diagnosis are discussed separately. (See "Prosthetic valve endocarditis: Epidemiology, clinical manifestations, and diagnosis".)
If imaging and clinical findings support a diagnosis of PVE (eg, presence of vegetations and bacteremia with typical bacteria), then appropriate management including antimicrobial therapy is indicated.
If a diagnosis of PVE is uncertain, follow-up testing (eg, repeat TEE in one week) is recommended to determine whether or not PVE is present. PET-CT is emerging as a useful imaging modality in assessment of endocarditis. (See "Prosthetic valve endocarditis: Epidemiology, clinical manifestations, and diagnosis", section on 'Additional imaging tools'.)
Differentiate between thrombus and pannus as main cause of obstruction — In patients presenting with prosthetic valve obstruction, once endocarditis has been excluded it is important to distinguish thrombus from pannus given the differences in treatment options. In some cases, pannus and thrombus may both contribute to valve obstruction. The evaluation of mechanical valve obstruction is closely linked to management since some therapies (such as fibrinolysis or valve surgery) may both identify the cause of prosthetic valve obstruction and treat it.
Approach to presumptive diagnosis — We suggest the following approach to make a presumptive diagnosis of thrombus or pannus in patients with mechanical valves (algorithm 1) based upon the features described below. Some patients may have both thrombus and pannus. (See 'Features of thrombus and pannus' below.)
●For mitral and tricuspid mechanical valves or Bjork-Shiley or Sorin monoleaflet valves in any position, perform TEE first.
•If normal leaflet motion is detected, but there is evidence of an increased gradient compared with baseline (not explained by a high cardiac output state), pannus is likely.
•If impaired leaflet motion is detected or if leaflet motion is not well visualized, assess if mass is present:
-If mass is present, we suggest evaluating the echodensity of the mass. Echodensity can be evaluated qualitatively (low intensity: similar to myocardial echodensity; high-intensity, similar to the prosthetic hardware echodensity) or quantitatively using the intensity ratio (defined as the intensity of mass/intensity of prosthesis).
•A low intensity mass (ratio ≤0.45) suggests a presumptive diagnosis of thrombus.
•If a high intensity mass (ratio >0.45) is detected (and a Bjork-Shiley or Sorin monoleaflet valve is NOT present), we suggest performing MDCT and assessing valve appearance as follows:
-Pannus is likely if one or more of the following features are present: normal leaflet motion, high attenuation (Hounsfield units [HU] ≥145), and extension along the valve ring.
-Thrombus is likely if one or more of the following features are present: low attenuation (HU <90) or irregular shape with attachment to leaflets or hinge points.
-MDCT findings are indeterminate if there is intermediate attenuation (HU 90 to 145) and other features not diagnostic of thrombus.
•Bjork-Shiley and Sorin monoleaflet valves are not well visualized by CT due to severe artifact, so fluoroscopy or TEE is preferred for visualization of leaflet motion for these valve types.
●For aortic and pulmonary mechanical valve (other than Bjork-Shiley or Sorin monoleaflet valve), we suggest starting with MDCT and assessing the valve appearance as described above.
Features of thrombus and pannus
●Features favoring thrombus:
•Clinical features – More acute onset of symptoms and a history of inadequate anticoagulation.
•Restricted leaflet motion [10,18].
•Detection of mass consistent with thrombus suggests thrombus, but absence of visible mass does not exclude thrombus [10]. Thrombus on bileaflet valves usually starts at the pivot mechanism of the occluders. Thrombus located upstream of the valve (left or right atrium for atrioventricular valves, left or right ventricle for replaced semilunar valves) is easier to detect, but imagers must be aware that it may not reflect the entire thrombus burden. Indeed, thrombus located downstream of the valve (left or right ventricular side for AV valves, aorta/pulmonary artery side for replaced semilunar valves) is often difficult to visualize by either echocardiography or CT.
The following features suggest thrombus:
-Lower echodensity compared with pannus. Although the echodensities of thrombus and pannus overlap, masses with the lowest intensity ratios (ratio of intensity of mass compared with the intensity of prosthesis <0.45) were thrombi in two small series [19,20].
-On MDCT, low attenuation (similar to the interventricular septum; eg, HU <145, particularly HU <90, [16,17]). In a small series, complete disappearance of periprosthetic mass with restoration of valve function was more frequent for masses with HU <90 compared with those with HU 90 to 145 (100 versus 42 percent) [16].
-Thrombus may have an irregular shape and attachment to prosthetic heart valve leaflets or hinge points [14].
-A mobile mass is common in patients with thrombus or thrombus plus pannus [20].
●Features favoring pannus:
•Generally more dense than thrombus [19].
•Leaflet motion may be normal or restricted (eg, restricted motion in 60 percent in one series [19]). In a patient with new mechanical valve obstruction, if leaflet motion is well visualized and normal by TEE, then pannus is likely [10].
•A mass is often not visualized by 2D TEE in patients with pannus (eg, not seen in 67 percent in one systematic review [10]).
-A mobile mass is uncommon with pannus alone but may be seen in patients with pannus plus thrombus [20]. (See "Echocardiographic evaluation of prosthetic heart valves", section on 'Distinction between thrombus and pannus'.)
-High attenuation mass (greater than the interventricular septum; eg, HU ≥145 [16,17]). In a series of 62 patients with suspected mechanical prosthetic valve dysfunction, an MDCT threshold HU ≥145 provided a sensitivity of 87.5 percent and a specificity of 95.5 percent for discriminating pannus from thrombus [16].
-Mass extending along the valve ring [14].
SPECIFIC APPROACHES
For valve obstruction with or without symptoms — After initial evaluation identifying mechanical valve obstruction (see 'Initial evaluation' above), the approach to evaluation depends upon the severity of symptoms of obstruction as outlined here (algorithm 1).
If moderate to severe symptoms — For patients with new mechanical valve obstruction causing moderate to severe symptoms (New York Heart Association [NYHA] functional class III or IV), urgent evaluation and management is indicated:
●Urgent initiation of therapeutic intravenous anticoagulation if INR is subtherapeutic.
●Urgent multimodality imaging (after initial transthoracic echocardiography, generally transesophageal echocardiography or multidetector computed tomography) is performed to assess the prosthetic transvalvular gradient, leaflet motion, and the cause of the obstruction (thrombus versus pannus). (See 'Differentiate between thrombus and pannus as main cause of obstruction' above.)
●Urgent referral to a Heart Valve Team is indicated to guide the choice among valve surgery, fibrinolytic therapy (if thrombus is suspected), and palliative care. (See "Management of mechanical prosthetic valve thrombosis and obstruction", section on 'Urgent management of mechanical valve obstruction'.)
If no or mild symptoms — For patients with mechanical valve obstruction causing no or mild symptoms (NYHA functional class I or II), we suggest the following approach:
●Urgent initiation of therapeutic intravenous anticoagulation if INR is subtherapeutic.
●After initial evaluation reveals valve obstruction (see 'Initial evaluation' above), proceed with further evaluation to identify the probable cause of obstruction as described above. (See 'Approach to further evaluation' above.)
●The following diagnoses are made based upon the evaluation:
•Presumptive diagnosis of mechanical valve thrombosis with valve obstruction
•Presumptive diagnosis of mechanical valve pannus with valve obstruction
•Presumptive diagnosis of mechanical valve thrombosis plus pannus
The management of each of these disorders is discussed separately. (See "Management of mechanical prosthetic valve thrombosis and obstruction".)
For valve thrombosis without obstruction — We suggest the following approach for suspected mechanical valve thrombosis without obstruction:
●After the initial evaluation of suspected mechanical valve thrombosis reveals no significant obstruction (see 'Initial evaluation' above), proceed with the further urgent evaluation as described above. (See 'Approach to further evaluation' above.)
●The following diagnoses are made based upon the above evaluation:
•Presumptive diagnosis of mechanical valve thrombosis with no valve obstruction. Management is discussed separately. (See "Management of mechanical prosthetic valve thrombosis and obstruction", section on 'For valve thrombosis without obstruction'.)
•No mechanical valve abnormalities with no valve obstruction. Routine follow-up is recommended for these patients. (See "Overview of the management of patients with prosthetic heart valves", section on 'Schedule of follow-up'.)
•Mechanical leaflet thickening/mass strongly suggestive of thrombus with normal cusp motion and no mechanical valve obstruction. If there is leaflet thickening or mass strongly suggestive of thrombus, we suggest treatment similar to that for patients with a presumptive diagnosis of thrombosis. (See "Management of mechanical prosthetic valve thrombosis and obstruction", section on 'For valve thrombosis without obstruction'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Cardiac valve disease".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Prosthetic valves (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Initial evaluation of patients suspected of having prosthetic valve thrombosis (PVT) and/or obstruction should include clinical assessment of symptoms and signs and transthoracic echocardiography (TTE) with determination of whether prosthetic valve obstruction is present. (See 'Initial evaluation' above.)
●Prosthetic valve obstruction is defined as mean transvalvular gradient increase by >50 percent (or >10 mmHg increase for an aortic prosthesis) compared with baseline, after exclusion of other causes such as a high-output state. (See 'Initial evaluation' above.)
●Further evaluation of mechanical valve thrombosis and/or obstruction includes further imaging of the mechanical valve by transesophageal echocardiography (TEE) and/or multidetector computed tomography (MDCT), exclusion of prosthetic valve endocarditis, and determining whether imaging findings are consistent with PVT. For patients with a thromboembolic event, comprehensive evaluation for alternative causes should be conducted. (See 'Approach to further evaluation' above.)
●The choice between TEE and MDCT as the next imaging test after TTE is made based upon availability, prior test results, patient characteristics, mechanical valve location, and clinician experience. (See 'Choice between TEE or MDCT' above.)
●For patients with new mechanical valve obstruction causing moderate to severe symptoms (New York Heart Association [NYHA] functional class III or IV), urgent multimodality imaging is performed to assess the prosthetic transvalvular gradient, leaflet motion, and the cause of the obstruction (thrombus versus pannus), and urgent referral to a Heart Valve Team is indicated to guide the choice among valve surgery, fibrinolytic therapy (if thrombus is suspected), and palliative care. (See 'If moderate to severe symptoms' above.)
●For patients with mechanical valve obstruction causing no or mild symptoms (NYHA functional class I or II), the situation is less urgent, and evaluation is performed to identify the likely cause of the obstruction. (See 'If no or mild symptoms' above.)
●For patients with suspected mechanical valve thrombosis with no significant obstruction, imaging is performed to confirm whether or not thrombus is present. (See 'For valve thrombosis without obstruction' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff would like to thank Dr. Catherine M. Otto for her contributions as section editor to previous versions of this topic review.
