Infective Endocarditis

The typical imaging findings on Multi-detector Computed Tomography (MDCT) primarily involve high-resolution anatomical details of cardiac structures and perivalvular extensions, while Magnetic Resonance Imaging (MRI), especially cerebral MRI, is crucial for detecting embolic complications related to infective endocarditis (IE).

Multi-detector Computed Tomography (MDCT) Findings

MDCT (or cardiac CT) offers increased spatial resolution compared to echocardiography and is unaffected by acoustic shadowing, making it highly valuable, especially for prosthetic valves.

Key Cardiac and Perivalvular Findings:

• Perivalvular Lesions: MDCT excels at evaluating the extension of perivalvular lesions. Typical findings include detection of abscesses, fistulas, pseudoaneurysms, and the extension of infection into the cardiac skeleton.

  • In comparison to Transesophageal Echocardiography (TEE), MDCT has been found to be superior in the identification of abscesses and pseudoaneurysms and provides more accurate anatomical information.

• Aortic Root and Tricuspid Valve: MDCT allows evaluation of the aortic root and coronary arteries. It facilitates effective imaging of the tricuspid annulus and leaflets.

• Calcification: MDCT permits the evaluation of annular and leaflet bulky calcium.

• Vegetations: MDCT can detect vegetations, reporting a high sensitivity (96%) and specificity (99%) for this finding, although small vegetations (less than 4 mm) are more commonly missed by CT compared to TEE.

• Surgical Planning: Cardiac CT is valuable in surgical planning, offering a noninvasive assessment for coronary artery disease.

• Extracardiac Structures: MDCT enables the evaluation of extracardiac structures. It can also detect primary or IE-related pneumonic diseases such as abscesses or necrotic deposits.

Magnetic Resonance Imaging (MRI) Findings

MRI's primary application in IE management is the detection of cerebral embolic events. Cerebral MRI is the most sensitive technique to detect cerebral emboli. Its findings are crucial, as neurologic complications are common in IE, affecting up to 55% of patients, often without symptoms.

Typical Findings on Brain MRI (Pooled Frequencies):

In patients with suspected or confirmed IE, relevant abnormalities are commonly shown on brain MRI. The following findings were reported in a systematic review and meta-analysis of 21 studies evaluating 2,133 patients:

• Acute Ischemic Lesions: This was the most frequent finding, with a pooled frequency of 61.9% (95% CI, 50.7–71.9%). These are defined as hyperintense lesions on T2-weighted imaging with corresponding restricted diffusion on DWI (Diffusion-Weighted Imaging).

• Cerebral Microbleeds: Pooled frequency of 52.9% (95% CI, 41.6–63.9%). These appear as rounded foci 10 mm or less in diameter on T2*-weighted gradient-recalled echo (GRE) or susceptibility-weighted imaging (SWI).

• Hemorrhagic Lesions: Pooled frequency of 24.7% (95% CI, 15.1–37.9%). This category includes acute or chronic subarachnoid hemorrhage, intracerebral hemorrhage, or hemorrhagic transformation of ischemic stroke.

• Brain Abscess or Meningitis: Pooled frequency of 9.5% (95% CI, 5.6–15.6%).

• Intracranial Mycotic Aneurysm (on MRA): Pooled frequency of 6.2% (95% CI, 4.0–9.4%).

Clinical Significance:

The detection of these lesions is important because findings on cerebral MRI can influence clinical decisions, including upgrading the diagnostic classification of IE and modifying therapeutic or surgical plans. For instance, MRI findings led to the modification of the therapeutic plan in 12.8% (95% CI, 6.5–23.7%) and the surgical plan in 14.2% (95% CI, 8.2–23.4%) of cases evaluated in six and five studies, respectively.

MRI protocols for suspected IE often include DWI, SWI, full-coverage time-of-flight imaging, contrast-enhanced MRA, and 3D contrast-enhanced T1-weighted imaging along with axial T1- and T2-weighted and FLAIR sequences.

The principal agents preferred by authors, as they cover methicillin-resistant S aureus (MRSA), methicillin-sensitive S aureus (MSSA), streptococci, and most enterococci, are Vancomycin or Daptomycin.

Agent

Rationale

Vancomycin (IV)

This is the principal agent most authors use, as it has the most evidence and provides coverage for the key organisms, including MRSA, and covers coagulase-negative staphylococci in prosthetic valve cases.

Daptomycin (IV)

Daptomycin offers a similar spectrum of activity to vancomycin and may provide advantages in pharmacokinetics. It is an acceptable alternative to vancomycin, especially for MRSA.

Linezolid (IV)

May be used as an alternative if vancomycin and daptomycin are precluded (e.g., due to allergy or resistance concerns) or where challenges exist in maintaining IV access.

2. Secondary/Adjunctive Agents

Secondary agents, often β-lactams, are added to achieve broader coverage or synergistic effects:

Agent

Rationale

Ceftriaxone (IV)

Provides superior coverage for streptococcal species and HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella). It covers Gram-negative and Gram-positive organisms.

Cefazolin (IV)

Used if MSSA is suspected or when coverage is needed in combination with a primary agent, as it is synergistic for MRSA when used with vancomycin or daptomycin. Many authors prefer cefazolin over anti-staphylococcal penicillins due to decreased toxicity for MSSA.

Cefepime, Piperacillin-tazobactam, Carbapenems (IV)

These are considered, particularly for early prosthetic valve endocarditis (PVE, defined as <3 months after surgery), where the choice is driven by the local microbiology of nosocomial Gram-negative infections and potential pseudomonal coverage. Carbapenems offer the broadest coverage but should be reserved for resistant bacteria.

Empirical Dosing Summary - RENAL DOSING NOT CONSIDERED

Vancomycin (IV)

Loading Dose (Normal Kidney Function)

25 to 30 mg/kg IV (maximum dose, 3 grams)

Vancomycin (IV)

Maintenance Dose (Normal Kidney Function)

15 to 20 mg/kg IV every 8 to 12 hours

Vancomycin (IV)

Target Activity/Trough Level

Goal trough levels are 15 to 20 mg/L

Daptomycin (IV)

Suspected MRSA (S. aureus)

Suggested total daily dosing is 8–10 mg/kg

Daptomycin (IV)

Suspected Enterococcus spp.

Suggested total daily dosing is 10–12 mg/kg

Cefepime (IV)

Empirical coverage (AHA/ESC)

2 g every 8 hours

Empiric Need to Cover the CSF/Brain

The decision to ensure specific, high-level coverage of the central nervous system (CNS) is highly relevant in IE because neurologic complications are the most common extracardiac complications, affecting up to 55% of patients. These complications include ischemic or hemorrhagic stroke, brain abscess, meningitis, and intracranial mycotic aneurysms.

However, the sources do not explicitly recommend initiating therapy with special CNS penetration empirically (before confirmation of CNS involvement).

Instead, the evidence suggests that imaging (specifically Cerebral MRI) is used to detect these embolic events.

• CNS Involvement Triggers Therapeutic Modification: When CNS complications are detected via imaging, this significantly influences treatment and surgical planning. For instance, modification of the therapeutic plan based on MRI findings has included the addition of a high cerebral diffusion antibiotic in one case.

• Antibiotic Selection: While the core empirical regimens target the endocarditis organisms, drugs like ceftriaxone (frequently chosen as a secondary agent empirically for its superior coverage of Streptococci and HACEK organisms) typically possess good CNS penetration, which may offer incidental coverage of potential neurological infections.

• Need for Imaging and Consultation: Patients presenting with neurologic symptoms should receive Cerebral MRI. If an embolic stroke or intracranial bleeding is found, a neurologist and/or neurosurgeon should be consulted, as the timing of cardiac surgery may be delayed (up to 4 weeks for hemorrhagic stroke) due to the risk of expanding the stroke or causing hemorrhagic conversion during the operation.

Thus, while neurologic risk is extremely high, the empirical antimicrobial regimen focuses first on eradicating the primary source (the cardiac infection), and specific adjustment for CNS penetration is often a reaction to confirmed neurological involvement rather than a uniform empirical requirement, although selecting agents like ceftriaxone provides favorable characteristics.

1.McDonald, E. G. et al. Guidelines for Diagnosis and Management of Infective Endocarditis in Adults. JAMA Netw. Open 6, e2326366 (2023).

2.Hubers, S. A., DeSimone, D. C., Gersh, B. J. & Anavekar, N. S. Infective Endocarditis: A Contemporary Review. Mayo Clin. Proc. 95, 982–997 (2020).

3.Brien, L., Tierney, C. & Thompson-Brazill, K. Current Diagnosis and Management of Infective Endocarditis in Adults. J. Nurse Pr. 21, 105494 (2025).

4.Ahn, Y. et al. Impact of Brain MRI on the Diagnosis of Infective Endocarditis and Treatment Decisions: Systematic Review and Meta-Analysis. Am. J. Roentgenol. 218, 958–968 (2022).

5.Singh, S. S. A. et al. A narrative review of diagnosis of infective endocarditis—imaging methods and comparison. Ann. Transl. Med. 8, 1621–1621 (2020).