Cardiac Imaging

What Is the Best Initial Imaging Test for Suspected Infective Endocarditis?

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What Is the Best Initial Imaging Test for Suspected Infective Endocarditis?

A 42-year-old man with a history of intravenous drug use presents to the emergency department with a week of fevers, chills, and malaise. On exam, he is febrile to 39.1°C and has a new 2/6 holosystolic murmur at the apex. Blood cultures are drawn, and you are faced with a classic presentation for infective endocarditis (IE). The immediate clinical question is which imaging study to order first to visualize the heart valves and confirm the diagnosis. This article details the ACR-guided workflow for this specific scenario, explaining why one test stands out as the initial step. According to the ACR Appropriateness Criteria, a **US echocardiography transthoracic resting** study is *Usually Appropriate* for the initial imaging of suspected infective endocarditis.

Who Fits This Clinical Scenario for Initial Endocarditis Imaging?

This guidance applies specifically to patients for whom there is a new clinical suspicion of infective endocarditis, and no definitive cardiac imaging has yet been performed. These are typically patients presenting with signs and symptoms that raise concern for IE based on the modified Duke criteria, such as persistent fever, positive blood cultures (especially with typical organisms like *Staphylococcus aureus* or *Streptococcus viridans*), a new or changing heart murmur, or evidence of embolic phenomena. The patient may have predisposing factors, including a history of intravenous drug use, a prosthetic heart valve, structural heart disease, or a recent invasive procedure.

This workflow is intended for the *initial diagnostic phase*. It is crucial to distinguish this from other clinical situations. This guidance does **not** apply to:

  • Patients with a confirmed diagnosis of IE: Once IE is diagnosed, subsequent imaging is performed to guide management, assess for complications, or for preoperative planning. This falls under a different clinical scenario: “Known or suspected infective endocarditis. Additional imaging to direct patient management or treatment.”
  • Patients with non-specific fever: If a patient has a fever without other localizing signs or risk factors pointing toward an endovascular source of infection, the diagnostic algorithm is much broader, and cardiac imaging may not be the appropriate first step.
  • Asymptomatic screening: This guidance is not for screening asymptomatic patients, even those with underlying valvular disease.

What Diagnoses Are You Working Up with Initial Imaging for Suspected Endocarditis?

When ordering the initial imaging study for suspected IE, you are primarily investigating for direct evidence of endocardial infection, but the differential diagnosis includes several critical mimics and complications.

**Infective Endocarditis (IE):** This is the primary diagnosis of concern. Imaging aims to identify the hallmark lesions of IE: vegetations (infected masses of platelets, fibrin, and microorganisms on a valve or endocardial surface), abscesses (contained areas of necrosis, often perivalvular), or new valvular regurgitation caused by leaflet destruction or perforation. Identifying any of these provides a major criterion for diagnosis under the modified Duke criteria.

**Nonbacterial Thrombotic Endocarditis (NBTE):** Also known as marantic endocarditis, this condition involves the formation of sterile vegetations on heart valves. It is most commonly associated with advanced malignancy or systemic inflammatory conditions like systemic lupus erythematosus. These vegetations can be indistinguishable from infectious ones on imaging alone and can also embolize, causing similar systemic effects.

**Cardiac Abscess:** While often a devastating complication of IE, a perivalvular or myocardial abscess can sometimes be the most prominent or only initial finding. It represents a more advanced and aggressive disease process that often requires urgent surgical intervention.

**Primary Valvular Dysfunction:** A new murmur and signs of heart failure can also result from an acute, non-infectious valvular problem, such as a ruptured chorda tendinea in the setting of myxomatous mitral valve disease. While fever would be atypical unless there is a concurrent process, imaging is essential to differentiate structural failure from infection-driven destruction.

Why Is a Transthoracic Echocardiogram the Recommended First Study for Suspected IE?

The ACR designates US echocardiography transthoracic resting (TTE) as *Usually Appropriate* because it provides the best balance of diagnostic utility, safety, and accessibility for the initial evaluation of suspected infective endocarditis.

A TTE is a non-invasive ultrasound of the heart performed by placing a probe on the chest wall. Its primary advantage is its ability to rapidly assess key features without risk to the patient. It involves no ionizing radiation (0 mSv) and is readily available in most hospital settings, making it an ideal first-line test. TTE provides excellent visualization of overall left and right ventricular function, can detect moderate-to-large vegetations (typically >5-10 mm), and uses Doppler to accurately quantify the severity of any valvular regurgitation, a key diagnostic and prognostic finding.

While TTE is the recommended starting point, other studies are rated differently for this initial workup for specific reasons:

  • US echocardiography transesophageal (TEE) is rated *May be appropriate (Disagreement)* as an initial test. A TEE involves passing an ultrasound probe into the esophagus, which provides superior images of the heart valves, especially posterior structures and prosthetic valves. It has much higher sensitivity for small vegetations (<5 mm) and perivalvular abscesses. However, it is an invasive procedure requiring sedation and carries a small risk of esophageal injury. For this reason, it is typically reserved as a second-line test when the initial TTE is negative or technically limited, but clinical suspicion for IE remains high.
  • CT heart function and morphology with IV contrast is also rated *Usually Appropriate*. This may seem contradictory, but it serves a complementary, not a primary, role in the initial workup. Cardiac CT is outstanding for visualizing the anatomy *around* the valve, making it superior for detecting perivalvular abscesses, pseudoaneurysms, and fistulae. It is also the modality of choice for screening for septic emboli to the lungs or other organs. However, it is less sensitive than echo for small, mobile vegetations and involves significant radiation (☢☢☢☢ 10-30 mSv) and iodinated contrast. Therefore, the typical workflow begins with TTE to assess the valve leaflets directly, with CT added if complications are suspected.
  • MRI heart function and morphology is rated *Usually not appropriate*. While excellent for assessing myocardial tissue and function, cardiac MRI is less sensitive than echocardiography for detecting the small, mobile vegetations characteristic of IE. It is also more costly, less available, and has longer acquisition times, making it unsuitable as a first-line diagnostic tool in this setting.

What’s the Next Step After a Transthoracic Echocardiogram?

The results of the initial TTE will guide the subsequent diagnostic and management workflow. The decision tree branches based on whether the study is positive, negative, or indeterminate.

**If the TTE is positive:** A definitive finding of a vegetation, abscess, or new severe valvular regurgitation satisfies a major Duke criterion and solidifies the diagnosis of IE. The immediate next steps involve initiating targeted antibiotic therapy based on blood culture results, consulting Cardiology for ongoing management, and often engaging Cardiothoracic Surgery, especially if there are signs of heart failure, large vegetations (>10 mm), or perivalvular extension of infection. Further imaging, such as a TEE for better anatomical definition or a CT scan to screen for embolic events, may be warranted as part of directing patient management.

**If the TTE is negative:** A negative or non-diagnostic TTE does not rule out infective endocarditis, particularly in high-risk patients. If clinical suspicion remains high (e.g., due to persistent *S. aureus* bacteremia, a prosthetic valve, or embolic events of unknown origin), the next step is to proceed to a **transesophageal echocardiogram (TEE)**. TEE offers much higher sensitivity and is the gold standard for ruling out smaller vegetations, prosthetic valve endocarditis, and abscesses that are often missed on TTE.

**If the TTE is indeterminate:** Sometimes, findings can be equivocal, such as a thickened or calcified valve leaflet that could represent a chronic degenerative change or a small, organized vegetation. In these cases of uncertainty, a TEE is the appropriate next step to provide a higher-resolution image and clarify the ambiguous findings.

Common Pitfalls in the Initial Imaging Workup for Endocarditis

Navigating the initial workup for suspected IE requires careful clinical correlation to avoid common errors.

  • Stopping the workup after a negative TTE: The most significant pitfall is to prematurely rule out IE based on a negative transthoracic study in a patient with high pre-test probability. The sensitivity of TTE is limited, and a negative result should prompt escalation to TEE if clinical suspicion persists.
  • Underestimating TTE limitations in certain patients: TTE imaging quality can be significantly degraded in patients with obesity, COPD, or chest wall deformities. More importantly, it is notoriously difficult to evaluate prosthetic heart valves with TTE due to acoustic shadowing. In patients with prosthetic valves and suspected IE, many experts advocate for proceeding directly to a TEE.
  • Focusing only on the heart: Infective endocarditis is a systemic disease. While cardiac imaging is central, do not neglect to investigate for the source of infection and the consequences of embolization. This may require CT scans of the head, chest, abdomen, and pelvis depending on the clinical signs.
  • Delaying imaging: In a hemodynamically unstable patient with suspected IE causing acute heart failure, imaging should not be delayed. A point-of-care ultrasound (POCUS) at the bedside can provide rapid, crucial information while arranging for a formal TTE.

If you encounter a patient with hemodynamic instability, evidence of a major embolic event like a stroke, or signs of heart block (suggesting a perivalvular abscess), escalate immediately to a cardiology consultation.

Related ACR Topics and Tools

For a comprehensive overview of imaging across all clinical variants of this condition, please see our parent topic guide. The tools below can assist in navigating appropriateness criteria for related scenarios, understanding imaging protocols, and discussing radiation dose with patients.

Frequently Asked Questions

Why not just order a TEE on everyone with suspected endocarditis to begin with?

While a transesophageal echocardiogram (TEE) is more sensitive than a transthoracic echocardiogram (TTE), it is also an invasive procedure that requires sedation and carries risks like esophageal perforation. The ACR recommends a stepwise approach, starting with the non-invasive TTE. A TEE is reserved for cases where the TTE is negative but clinical suspicion remains high, the TTE is technically inadequate, or in specific high-risk situations like suspected prosthetic valve endocarditis.

My patient has a prosthetic heart valve. Is TTE still the right first test?

This is a key area of clinical nuance. A TTE is still often the first test performed due to its immediate availability. However, its utility is significantly limited for prosthetic valves due to acoustic shadowing. If clinical suspicion for prosthetic valve endocarditis is high, it is very common to proceed directly to a TEE, or to perform a TEE immediately following a non-diagnostic TTE. Some institutions have protocols to expedite TEE in this specific patient population.

When is a cardiac CT a better first choice than an echocardiogram for suspected IE?

A cardiac CT is generally not a better *first* choice for visualizing valvular vegetations. Echocardiography remains superior for that purpose. However, if the primary clinical suspicion is for a perivalvular complication of IE—such as an abscess, pseudoaneurysm, or fistula—cardiac CT is the superior modality. It is often used as a complementary study to an echocardiogram rather than a replacement.

Does a negative TTE and a negative TEE definitively rule out infective endocarditis?

A negative TEE makes the diagnosis of infective endocarditis highly unlikely, as its sensitivity is very high (>90%). However, no test is perfect. In rare cases, vegetations may be too small to detect, may have already embolized, or the infection may be in a location difficult to visualize. If compelling clinical evidence persists (e.g., ongoing bacteremia with a typical organism and no other source), the diagnosis may still be made clinically, and repeat imaging after several days may be considered.

What is the role of a chest radiograph in the initial workup?

A chest radiograph is rated as ‘Usually Appropriate’ by the ACR. While it cannot diagnose endocarditis directly, it is a crucial baseline study. It can reveal cardiomegaly, signs of heart failure (e.g., pulmonary edema), or evidence of septic pulmonary emboli, which are common in right-sided endocarditis. These findings provide important context and can influence management.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 21, 2026