Myocardial Abscess Workup

Routine blood tests

Complete blood cell count findings (ie, hematologic parameters) commonly are abnormal.

Anemia with normochromic, normocytic red cell indices is present. A low serum iron level is also observed. A low serum iron-binding capacity is observed in 70-90% of patients.

Anemia worsens with increased duration of illness.

In subacute endocarditis, the white blood cell count usually is normal. In contrast, a leukocytosis with increased segmented granulocytes is common in acute endocarditis and myocardial abscess.

Thrombocytopenia only rarely occurs.

A metabolic chemistry panel should be obtained.

Erythrocyte sedimentation rate

The erythrocyte sedimentation rate (ESR) is elevated (on average, to approximately 55 mm/h) in almost all patients with endocarditis and myocardial abscess. The exceptions to this are patients with CHF, renal failure, or disseminated intravascular coagulation.

Although the results are nonspecific, the absence of an increased ESR, other than in the selected circumstances preciously mentioned, is evidence against a diagnosis of endocardial or myocardial infection or abscess.

C-reactive Protein

An elevated CRP also can be seen with myocardial abscess. Similar to ESR, the results are non-specific but can be used to trend response to therapy over time. 

Blood cultures

Blood cultures are the crucial laboratory tests for confirming the diagnosis of the underlying endocarditis. They should be repeated until bacteremia resolves. 

Urinalysis

Urinalysis results often are abnormal, even when renal function remains normal.

Proteinuria and microscopic hematuria are noted in 50% of patients.

Urinalysis plays a standard role in the evaluation of azotemia, which is frequently associated with myocardial abscess.

Other tests

Perform these as needed for the assessment of the primary source of bacteremia.

In the past, most cases of myocardial abscess were found during autopsy; however, detection of myocardial abscess now can be achieved antemortem using multiple noninvasive imaging modalities, including transthoracic echocardiography (TTE), transesophageal echocardiography (TEE), indium-111 (¹¹¹In) radionuclide scintigraphy, computed tomography (CT) scan, and magnetic resonance imaging (MRI).

Transthoracic echocardiography

Transthoracic echocardiography TTE helps evaluate patients in whom endocarditis or myocardial abscess is suggested clinically. ^[13]  An echocardiographic evaluation in all patients suspected of having an intracardiac or pericardial infection, including those with negative blood culture findings, should be performed. Findings frequently allow the morphologic confirmation of infection and aid in making decisions regarding management. 

TTE has a sensitivity of 23% and specificity of 98.6%, and is the first-line imaging modality in these patients. 

According to Ellis et al (1985), the following 5 criteria are 86% sensitive and 88% specific for myocardial abscess: ^[14]

• Evidence of prosthetic valve rocking

• Aneurysmal dilatation of the sinus of Valsalva

• Posterior aortic root thickness greater than 10 mm

• Perivalvular density in the septum of greater than 14 mm

• The presence of "echo-free space" - Very specific but found relatively infrequently.

Walker et al report a rare case of a myocardial abscess in valvular endocarditis that was difficult to assess with 2-dimensional TTE; however, real-time 3-dimensional (3D) contrast TTE allowed visualization of the full extent of the defect and its precise anatomical location, prior to successful surgical resection. ^[15]  3D echocardiography results in improved spatial resolution of the cardiac structures, allowing for better images of abscess and other complications such as vegetations and valvular deformities.  ^[13]

Transesophageal echocardiography

Although many patients with NVE involving the aortic or mitral valve can be adequately assessed using transthoracic echocardiography (TTE), TEE with color flow and continuous pulsed Doppler is the state-of-the-art technique. Doppler and color-flow Doppler or contrast 2-dimensional echocardiography helps optimally define fistulas and abscess pockets and extensions. 

TEE is far more sensitive than transthoracic (TTE) to detect myocardial abscess. TEE has a sensitivity of 87% and specificity of 94.6%. Patients in whom an abscess is suggested but which has not been detected using TEE should undergo MRI, including magnetic resonance angiography. 

Scintigraphy

Indium-111 leukocyte scintigraphy is especially useful in prosthetic valve endocarditis, in which echocardiography shows too much scatter and thus limits interpretation.

A few milliliters of venous blood is drawn and mixed with an anticoagulant solution. The white blood cells are separated and labeled with radioactive isotope¹¹¹, centrifuged, resuspended in isotonic sodium chloride solution, and then reinjected into the patient. Images are then obtained with a gamma-ray camera within 16-24 hours. The viable radioactive leukocytes potentially accumulate in the areas of inflammation or abscess. Obtain oblique views to avoid overshadowing by sternal accumulation.

The need for radioactive isotope¹¹¹ in scintigraphy is very low if TEE is used.

MRI

This is a good modality for helping delineate myocardial abscess. However, the portability and excellent resolution of echocardiography make it more practical than MRI.

Computed tomography scan

Use of computed tomography (CT) scan is not routine. However, cardiac CT may play an increasing role in the diagnosis of infective endocarditis, and thus, in helping delineate myocardial abscesses. Two studies indicate that cardiac CT was superior to TEE in the detection of abscess and pseudoaneurysms, and felt this to be due to superior spatial resolution, leading to more accurate anatomical information. ^{[16, 17]}

Intraoperative echocardiography

Although invasive, small abscesses can be detected in the operating room by means of intraoperative echocardiography, which may enable the operating surgeon to drain the abscess effectively.

Electrocardiography

New-onset and persistent electrocardiographic conduction abnormalities may be observed. These can present as first-degree atrioventricular block, second-degree atrioventricular block, third-degree atrioventricular block, or bundle branch and fasicular blocks. ^[18] The development of a pericardial friction rub or the presence of a pericardial effusion is suggestive of the development of a valve ring abscess.  ^[12]

Although not a sensitive indicator of perivalvular infection or abscess (28%), these findings are relatively specific (85-90%). 

Tests of immune system stimulation

Tests results may show disease activity, but the tests are costly and not very efficient for diagnosis or monitoring response to therapy.

These may include testing of circulating immune complexes, rheumatoid factor, quantitative immune globulin, cryoglobulins, and C-reactive protein.

Serologic tests

Serologic test findings are used to evaluate cardiac sepsis in which blood culture findings are negative.

Tests to detect antibodies to ribitol teichoic acids from staphylococci may help distinguish uncomplicated Staphylococcus aureus bacteremia from that associated with cardiac involvement.

These tests have not been used in clinical applications because of their lack of adequate specificity or predictive value.

Cardiac catheterization may add very little to the imaging studies and is not recommended unless coronary angiography is needed for patients undergoing valve surgery who also may have significant coronary artery disease.

Biopsy and histologic assessment is not a part of the diagnostic workup of myocardial abscess. However, surgically removed valves and autopsy findings from fatal cases reveal certain gross and microscopic features. 

The infection in native valves and mechanical prostheses that leads to development of myocardial abscess tends to extend beyond the valve ring into the annulus and periannular tissue and into the mitral-aortic intravalvular fibrosa, resulting in ring abscesses, septal abscesses, fistulous tracts, and dehiscence of the prosthesis with hemodynamically significant paravalvular regurgitation.

Myocardial abscess histology findings demonstrate damaged cardiac tissue with degraded collagen and polymorphonuclear predominance.