Download Infective Endocarditis

Endocarditis
Endocarditis
Chapter 3
Infective Endocarditis: Imaging to
Improve Detection Rates
Abdelhai Abdelqader1*, Chanukya Dahagam1,
Aditya Goud1, Ramez Jabaji1, Gabriel Soudry2 and
Sriram Padmanabhan3
Department of Internal Medicine, MedStar Franklin
Square Hospital Center, USA
2
Department of Nuclear Medicine, MedStar Franklin
Square Hospital Center, USA
3
Department of Cardiology, MedStar Franklin Square
Hospital Center, USA
Copyright: © 2016 Abdelhai Abdelqader, et al.
This article is distributed under the terms of the Creative
Commons Attribution 4.0 International License
(http://creativecommons.org/licenses/by/4.0/), which
permits unrestricted use, distribution, and reproduction
in any medium, provided you give appropriate credit to
the original author(s) and the source.
1
Corresponding Author: Abdelhai Abdelqader, 9000
Franklin Square Drive, Baltimore, MD 21237, USA, Tel:
443-777-6346; Fax: 443-777-8155; Email: [email protected]
*
First Published September 10, 2016
All authors contributed equally to the creation of this
manuscript. A Abdelqader is the article guarantor.
Informed Consent: Informed consent was obtained from
the patient for educational use of the below mentioned
data and no personal patient information has been disclosed.
2
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Introduction
Infective endocarditis (IE) is an infection of the endocardium, but can involve any structure of the heart including prosthetic valves and implanted devices [1-4]. IE
is a fatal disease with an in-hospital mortality rate up to
26% with half of patients having surgery during their hospital stay [1-4]. Echocardiography has played a key role
in diagnosing IE, evaluating response to treatment, and
predicting prognosis, however, has its own limitations.
The limited anatomical information provided and lack of
molecular activity monitoring has brought into question
the use of other imaging modalities. Our aim is to discuss
the roles of current imaging modalities can have in the
diagnosis of IE.
Imaging Modalities
Echocardiogram is an essential imaging technique in
diagnosing and managing IE. Echocardiography provides
prognostic evaluation, follow-up during therapy and usewww.avidscience.com
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ful in the perioperative period. Before and during surgery,
transesophageal echocardiography (TEE) plays a crucial
role [5]. Our aims of this review is to discuss the supplementary role in the diagnosis and possibly follow up care
in IE with the use of multislice computerized tomography
(CT), magnetic resonance imaging (MRI) and nuclear imaging.
Echocardiography
Echocardiography is the image test of choice to diagnose IE and plays a major role in the management and
the follow up care in these patients. Echocardiography
must be done without delay when IE is suspected. The
diagnosis currently relies on clinical, microbiological and
morphological criteria included in the modified Duke
classification [5]. A strong understanding of the cardiothoracic anatomy is essential for understanding and analyzing echocardiographic findings. The initial test is a
transthoracic echocardiography (TTE), that if negative in
low-risk patients the IE is unlikely diagnosis. TTE is superior to TEE for detecting anterior cardiac abscesses and
for assessing valvular function (Figure 1). If TTE is negative and high suspicion for IE exists, it should be followed
up by TEE. A TEE should be done when a TTE is nondiagnostic, e.g. operator expertise, intracardiac device,
distorted intra-thoracic or chest wall anatomy.
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Figure 1: TTE of a patient with mitral valve IE due to Staphylococcus aureus with showing dynamic flow from the peri-valvular abscess
seen at the center.
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Figure 3: TEE of a large anterior mitral valve with IE.
Figure 2: TTE of mitral valve IE due to Staphylococcus
aureus.
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Major echocardiographic findings in diagnosing IE
include vegetation, abscess or pseudoaneurysm and new
dehiscence of a prosthetic valve [2,6,7]. With TEE, the
diagnosis may remain very challenging in the setting of
intracardiac device, pre-existing mitral valve prolapsed
or degenerative calcified valves, prosthetic valves, vegetations <2 mm, or even non-vegetant IE (Figure 2). Threedimensional (3D) TEE superior to two-dimensional TEE
in being able to identify and localize vegetations to better
estimate risk of embolism as well as identifying complications such as abscesses, perforationsor ruptured chordate [8] (Figure 3). This is often used in many centers and
is a reasonable technique that can complement standard
echocardiography.
In addition to diagnosis, echocardiography identifies
prognostic signs that directly impact management of IE.
The three most frequent and severe complications of IE are
heart failure, perivalvular extension and embolic events.
Heart failure is a major indication for emergent (within 24
hours) or urgent (few days) surgery [2]. TEE is excellent
at identifying acute valvular regurgitation, valve obstruction or intracardiac fistula. TTE can demonstrate hemodynamic changes such as increased left and right diastolic
pressures, pulmonary arterial pressures and ventricular
dysfunction. Perivalvular extensions can be a precursor
to heart failure via fistula or prosthetic valve dehiscence,
complete heart block and persistent infection. In general,
perivalvular extension is best seen with TEE, while TTE
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is best to demonstrate anterior abscess of the aortic annulus [9]. Embolic events are common and symptomatic
in 25% of cases with half incidentally found [10,11]. The
risk of embolization is related to vegetation size. There is
strong evidence that early surgery helps reduces embolic
risk. When a vegetation is > 10mm there is high risk for
embolization and when associated with complications
(heart failure, infection refractory to therapy, abscess or
prosthetic valve) or simply vegetation > 15mm it needs
urgent surgery. If possible, valves should be surgically repaired especially mitral valves [2].
One of the challenges in managing IE is improving
the diagnosis of IE to start treatment at an early stage
[12]. The sensitivity of diagnosing vegetations in native
and prosthetic valves for TTE is 70% and 50%, respectively and with TEE is 96% and 92%, respectively [6,7]. A
negative echocardiography is observed in 15% of IE cases.
False negatives that occur with echocardiography include
intracardiac devices, valvular prosthesis, pre-existing severe valvular disease, very small vegetations, abscess or
lack of vegetations. Identifying these lesions early in the
disease can be difficult [13]. Conversely, false positive
with echocardiography include thrombi that mimic vegetations, prolapsed cusp, intracardiac tumors, myxomatous changes, Lambl’s excresences or strands [13]. Hence,
results can be misleading, even in the hands of an experienced person. We will now explore other imaging modalities that may improve the diagnosis of IE for earlier
appropriate therapy.
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Multislice Computed Tomography
Multislice CT (MSCT) is a non-invasive test that
provides detailed demonstration of not only coronary
anatomy, but valvular and perivalvular damage through
high temporal and spatial resolution and multiplanar reconstruction [14]. In identifying valvular and perivalvular
damage, ECG-gated 64-slice CT (the minimum slices) has
a reported sensitivity of 97%, specificity of 88% and negative predictive value (NPV) 88% compared to TEE [15].
Although MSCT misses small leaflet perforations, it
is able to detect vegetations in prosthetic valve IE. MSCT
can detect abscesses and pseudoaneurysms as accurate as
TEE and superior in providing information on extent and
consequences of any perivalvular extension, anatomy of
abscesses, pseudoaneurysms, and fistulae [13,15]. Cardioembolic events can occur throughout the body, but
most frequently the brain and spleen. For cerebral emboli,
MRI is certainly superior, however, in critically ill patients
MSCT serves a sensitive non-invasive diagnostic tool. If
MSCT is negative for IE or IE complications, but clinical suspicion remains high the test is readily available to
repeat. Splenic infarcts appear as triangular hypodensities
on contrast CT, but are nonspecific for IE.
The use of contrast offers high sensitivity and specificity in detecting systemic abscesses, but differentiation
from infarct is a challenge. Administering intravenous
contrast in a patient receiving potentially nephrotoxic an10
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tibiotics and possible septic renal emboli should be done
on case-by-case situation. Comparing MSCT to TEE, we
are able to extract more information in a shorter time, but
their utility remains case dependent (Table 1). The major
limitations of MSCT are potential artifacts from metal
and lack of hemodynamic assessment.
Table 1: Comparing MSCT to TEE.
Hemodynamics
Vegetations and perforations
TEE
Accurate for evaluating
hemodynamics
Can be inaccurate in very
severe acute lesions
Excellent to detecting small
vegetations and perforations
Difficult to identify in PVE or
calcified valves
Difficult to identify leaflet
perforation in AV IE
CT
Limited due to static image
Difficult to demonstrate
vegetations <2 mm
Preferred method to demonstrate prosthetic valve
vegetations
Well demonstrates valular
and perivalvular extension
Difficult to demonstrate
leaflet perforations
Abscesses
Difficult to identify in
early IE
Very operator dependent
Fistulae
Coronary anatomy
Excellent demonstration of
abscesses, aneurysms, and
pseudoaneurysms
Visualize mediastinal
structures
Can be combined with PET
Excellent visualization
Well visualized, but operator
dependent
Can demonstrate stenosis of
ostial coronary artery
Excellent visualization of
coronary artery anatomy
Wall motion abnormalities
suggestive of ischemia or
infarction
Possible avoidance of
pre-operative cardiac catherization in high-risk cases
RCA may be difficult to
visualize in presence of AVR
Extra-cardiac signs
An enlarged aortic root may
prevent visualization of anomalous coronary arteries
Ascending aorta well demonstrated
Extra-cardiac shunts poorly
seen
Peripheral embolization not
well seen
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Excellent demonstration of
neurologic, pulmonary, and
systemic embolizations and
abscesses
Extra-cardiac shunts well
seen, but may not indicate
infection
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Magnetic Resonance Imaging
Several studies have investigated the role of MRI in
IE diagnosis and management and have made remarkable
findings. Yet, the most plausible role of MRI in IE is detecting cerebral complications of embolic IE. MRI of the brain
during acute IE has reported lesions in about 60% of cases
[10,11,16]. Most cardioembolic strokes were ischemic,
often with small infarcts than large infarcts. Studies have
suggested< 10% of patients have lesions associated with
parenchymal or subarachnoid hemorrhages, abscesses or
mycotic aneurysms [10,11,16,17].
Compared to CT, MRI is a more sensitive test that can
better characterize cerebrallesions in patients with IE, but
its impact on IE diagnosis is reflected in adding one minor
Duke criterion in patients with cerebral lesions without
clinically evident neurologic deficits [11]. A prospective
study by Duval et al. reported MRI brain upgraded the
diagnosis of IE in a fourth of patients who presented with
suspected IE, leading to an earlier diagnosis [10]. This
study excluded microhemorrhages since they are nonspecific for IE-related cardioembolism [10,19]. Abdominal
MRI detects a third of patients with lesions, often ischemic, but has no impact on diagnosis of IE compared to brain
MRI [16,20].
Cardiac MRI has been shown to detect contrast enhancement in the late phase for irreversible myocardial
damage and fibrosis. IE can result in myocarditis or coronary artery embolization leading to myocardial damage
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and fibrosis. These can be detected with delayed phase
enhancement MRI [21]. Delayed contrast enhancement
MRI on the paravlavular tissues has been shown to detect
paravalvular extension, a predictor for further complications such as paravalvular abscess, endothelial erosion,
mycotic aneurysm, intracardiac fistula [21].
Unfortunately, limitations to cardiac MRI include
artifacts due to prosthetic valves. This limits diagnostic
information and lower spatial resolution, but is a nonionizing study. Given the information cardiac MRI provides despite its limitations, it may have a role in IE, albeit
limited.
Nuclear Imaging
In an effort to accelerate the diagnostic phase if IE,
focus has shifted from anatomical to functional at the
molecular level. The most recently studied new nuclear
imaging tool for use in IE has been positron emission tomography (PET-CT). The predominant utility in using
this modality is to increase detection of IE in those with
unclear diagnosis when using modified Duke criteria, peripheral emboli and inflammatory disease [22].
PET/CT uses 18 fluorodeoxyglucose (18F-FDG) that is
injected and taken up in vivo by metabolically active cells.
Images are taken approximately one hour after injection.
The radioactive tracer, 18F-FDG, is taken up by inflammatory cells, which aggregate at sites of active infection [21].
Cases have been reported where PET/CT has detected
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periprosthetic valve abscesses, while the initial echocardiography was negative. In following patients diagnosed
with IE, PET/CT has revealed clinically silent cardioembolic events in a third of cases [23,24].
For PET/CT, cerebral septic emboli may be obscured
as this tracer has high physiological uptake in the brain.
Metastatic infections (generally <5 mm), may be below the threshold of detectability for PET/CT scanners
[23,24]. For patients with recent implantation of the prosthetic valve, postoperative inflammation results in usually
low grade tracer uptake of variable duration. FDG PETCT may also provide adequate differentiation between
post-operative inflammation and active infection in patients with cardiovascular implantable electronic devices
[23,25].
Additionally, a number of other conditions can imitate 18F-FDG uptake seen in IE, such as active thrombi,
soft atherosclerotic plaques, vasculitis, primary cardiac
tumors or cardiac metastasis from non-cardiac tumor,
post-surgical inflammation, and foreign body reactions
[23]. There is increasing interest in using PET/CT in established IE to monitor antibiotic responses, but currently
there is insufficient data to make any recommendations.
There is limited data exploring PET/CT in IE with native
valves, impact of hyperglycemia, and cost analysis.
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Conclusion
In summary, review of recent data, the United States
Task Force proposes three additions to the diagnostic criteria [18]:
1. Identifying paravalvular lesions by cardiac CT to
be considered a major criterion.
2. When IE is not clear on a prosthetic valve, abnormal nuclear uptake around the valve site by 18FFDG PET CT if implanted >3 months or cardiac
MRI should be considered a major criterion.
3. Identifying recent silent embolic events or infectious aneurysms by imaging only should be considered minor criterion.
Echocardiography serves a major role in diagnosis
and management of IE. Recent data suggests other imaging tools, namely MSCT, cerebral MRI and 18F-FDP PET
CT can be used to improve detection rate of silent vascular phenomena and endocardial lesions in IE. In combination, these imaging tools may have use for diagnosis,
follow up and diagnostically challenging cases of IE.
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