Approach Considerations
Laboratory Studies
Complete blood cell count
Hemolysis may cause anemia; in this case, microscopic evidence of hemolysis should be present. A sudden increase in hemolysis may signal a perivalvular leak. [22]
A hematocrit lower than 34% is present in 74% of patients with prosthetic valve endocarditis (PVE); this is the most common hematologic finding.
A white blood cell (WBC) count lower than 12,000/μL is present in as many as 54% of patients with PVE.
Blood urea nitrogen/creatinine levels
Glomerulonephritis and acute renal failure may complicate PVE.
Urinalysis
Hematuria is present in 57% of patients with PVE.
Blood cultures
Multiple blood cultures should be taken, and they should be held for 3 weeks. Blood culture results are positive in multiple samples in 97% of patients with PVE.
Prothrombin time (PT)/international normalized ratio (INR)
Recommendations vary regarding the target INR. The following information is offered as a general guideline, but remember that therapy must be individualized.
Bioprosthetic valves
INR of 2-3 for 3 months following implantation; anticoagulation may then be discontinued unless the patient has another indication, such as atrial fibrillation or the development of prosthetic valve thrombosis.
Mechanical valves
Aortic valve INR is 2-3; mitral valve INR is 2.5-3.5. Patients with atrial fibrillation should be kept at the higher end of these ranges. [4] In patients with low hemorrhage risk, low-dose aspirin is recommended in addition to warfarin. [4]
Nontherapeutic values should raise the suspicion of valve thrombosis or systemic embolization.
Procedures
Certain procedures may cause bacteremia and thereby raise the risk of prosthetic valve endocarditis (PVE). Emergency physicians and other clinicians must be up to date with the latest prophylaxis guidelines. See Prevention.
Chest Radiography
An overpenetrated anteroposterior chest radiograph helps to delineate the valvular morphology and whether or not the valve and occluder are intact. In more clinically stable patients, a lateral chest film helps identify the valve position and type.
The following sections contain descriptions of the radiographic appearance of the more commonly seen valves.
Starr-Edwards caged ball valve
The base ring is radiopaque, as is the cage.
There are three struts for the aortic valve, and there are four struts for the mitral or tricuspid valve
The silastic ball is impregnated with barium that is mildly radiopaque (but not in all models).
Bjork-Shiley tilting disc valve
Although the Bjork-Shiley tilting disc valve has been discontinued, many patients still have these valves implanted.
The base ring and struts are radiopaque. Two U-shaped struts project into the base ring.
The edge of the occluder disc is also radiopaque.
Medtronic-Hall tilting disc valve
The base ring is radiopaque.
Three small radiopaque struts and one large hook-shaped strut project into the base ring.
The occluder disc is mildly opaque, but it often cannot be seen.
Alliance Monostrut valve
The occluder has a radiopaque rim; the base ring and two struts are radiopaque.
St. Jude medical bileaflet valve
The mildly radiopaque leaflets are best seen when viewed on end. They appear as radiopaque lines when the leaflets are fully open.
The base ring is not visualized on most models. The valve may not be visualized on some radiographs.
CarboMedics bileaflet valve
The valve housing and leaflets are radiopaque and easily visible.
Carpentier-Edwards porcine valve
The tall serpiginous wire support is the only visualized portion.
Hancock porcine valve
The radiopaque base ring is the only visible part in some models.
Other models have radiopaque stent markers with or without a visible base ring.
Ionescu-Shiley bovine pericardial valve
The base ring and wide fenestrated stents are one piece.
Echocardiography
Two-dimensional (2D) transthoracic echocardiography (TTE) is the examination of choice as a first-line imaging study when assessing prosthetic heart valves. [11] Its ease of use and ability to assess ventricular function and size as well as pulmonary pressures make it an effective first-line imaging study. TTE is also the image of choice when assessing valvular abnormalities with Doppler signal recordings; it is able to demonstrate perivalvular leaks, vegetations, and inadequate valve/occluder movement. TTE with Doppler can also detect the presence of acute valvular regurgitation and grade its severity.
Drawbacks with TTE include limited windows, which can be further affected by body habitus, dependency on angles for Doppler accuracy, and acoustic shadowing from the prosthetic valve. [23] Acoustic shadowing originating from the components of the prosthetic valve can severely limit the image of the valve itself as well as any pathologic process such as regurgitant streams, vegetations, and thrombosis. This is especially true with valves in the mitral position.
Transesophageal echocardiography (TEE) has emerged as the imaging study of choice to further evaluate a patient with prosthetic heart valves after initial assessment with TTE, particularly when there is a suspicion for prosthetic valve complications. Its advantages relative to TTEs include higher resolution, better visualization of the atrial side of prosthetic mitral valves and the posterior aspect of the prosthetic aortic valve, and better evaluation of any periannular complications. TEE has similar drawbacks as TTE, with imaging limited by acoustic shadowing of the prosthetic valve and dependency on angles for Doppler accuracy. [23]
Cinefluorography
Cinefluorography is an easy and noninvasive imaging study that uses fluoroscopy to evaluate mechanical prosthetic heart valves. Its ease of use paired with its ability to evaluate prosthetic heart valves function and to detect calcium on the leaflets make it another imaging study that can be used in prosthetic valve assessment. What cinefluorography fails to do is provide any assessment on hemodynamics as well as the etiologies for the prosthetic valve dysfunction. [23]
Electrocardiography
An atrioventricular (AV) block may indicate the presence of a myocardial abscess. A fever and new AV block is considered prosthetic valve endocarditis (PVE) until proven otherwise.
AV block may also complicate transcatheter aortic valve implantation (TAVI), although this usually occurs early in the postoperative period.
Atrial fibrillation is common in mitral valve replacement and may cause hemodynamic compromise.
Computed Tomography Scanning
In the current era of transcatheter device therapy, the prevalence of prosthetic aortic valves and their associated complications is increasing.
Although echocardiography remains the first-line imaging investigation for the assessment of prosthetic valve complications, it often fails to identify the underlying mechanism of prosthesis failure. Cardiac computed tomography (CT) scanning provides better anatomical delineation and excellent isotropic spatial resolution but no hemodynamic assessment.
Cardiac CT scanning, although not typically used for routine evaluation of prosthetic valves, can provide information when valvular dysfunction or other complications are suspected. Unlike transthoracic echocardiography (TTE), it is not limited by body habitus and has excellent spatial imaging. It is great for aortic pathologies, has a high sensitivity to detect calcifications, and allows for the detection and differentiation of thrombi. Limitations of the cardiac CT scan include radiation exposure, contrast exposure, and disrupted images from metallic artifacts. Patients with renal disease or contrast allergies are typically unable to have this study. [23]
Relatively recently, cardiac CT imaging has emerged as an imaging technique capable of providing high isotropic spatial resolution of the prosthetic valve, and its utility can provide important complementary diagnostic information. Retrospective gating may be used to visualize leaflet excursion throughout the cardiac cycle. Valvular and nonvalvular complications can be readily assessed (eg, pseudoaneurysm, valvular thrombus, pannus formations, patient prosthesis mismatch, valve dysfunction). Moreover, differentiation of pannus versus thrombus can be discriminated by Hounsfield units (HU), with a thrombus having less than 90 HU and a pannus having over 145 HU. [24]
Magnetic Resonance Imaging
Cardiac magnetic resonance imaging (CMRI) can be used in patients with prosthetic heart valves when trying to rule out concomitant aortic pathology. It allows for visualization of the aortic valve even without contrast medium. There is no radiation associated with this study, and it allows for better characterization of the myocardium as well as for volumetric and flow assessments. There remain limited data on its use in assessing prosthetic valves, however, and imaging can be hampered by artifacts from metallic objects. [23]
CMRI in the evaluation of valvular prosthesis is limited. The data are not as comprehensive as that of echocardiography and cardiac computed tomography scanning. The presence of a metallic stent scaffold and metallic leaflets limit leaflet visualization due to susceptibility artifact.
Quantitative assessment of regurgitation by phase velocity mapping can offer another layer of assessment in addition to that of echocardiography. Recent guidelines identify specific indications for appropriate use of CMRI in evaluation of patients. CMRI is a class I indication for patients with moderate to severe aortic regurgitation who have poor echocardiographic images for left ventricular function, volume, and severity assessment. Remodeling secondary to chronic valve dysfunction can be assessed via chamber size, function, and myocardial tissue characterization. [23]
Nuclear Imaging
Nuclear imaging modalities are not often used for assessing prosthetic valves as data are limited for their use except in the setting of infective endocarditis. Positron emission tomography (PET) scanning using fluorodeoxyglucose (FDG) uptake can suggest infectious or metabolic activity. [23]
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Prosthetic Heart Valves. Medtronic Hall mitral valve. Reproduced with permission from Medtronic, Inc.
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Prosthetic Heart Valves. The Hancock M.O. II aortic bioprosthesis (porcine). Reproduced with permission from Medtronic, Inc.
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Prosthetic Heart Valves. Starr-Edwards Silastic ball valve mitral Model 6120. Reproduced with permission from Baxter International, Inc.
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Prosthetic Heart Valves. Carpentier-Edwards Duralex mitral bioprosthesis (porcine). Reproduced with permission from Baxter International, Inc.
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Prosthetic Heart Valves. Carpentier-Edwards Perimount pericardial aortic bioprosthesis. Reproduced with permission from Baxter International, Inc.
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Prosthetic Heart Valves. St. Jude Medical mechanical heart valve. Photograph courtesy of St. Jude Medical, Inc. All rights reserved. St. Jude Medical is a registered trademark of St. Jude Medical, Inc.
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Prosthetic Heart Valves. Edwards Sapien transcatheter aortic valve.
