The role of 3D transesophageal echocardiography in native mitral valve endocarditis – A case report and review of the literature

1. Introduction

In recent decades, Staphylococcus aureus (S. aureus) and Streptococci have been the most commonly isolated microorganisms responsible for infective endocarditis (IE).^1,2 S. aureus IE is particularly severe, with higher rates of mortality and morbidity compared to other pathogens. Morbidity often involves frequent embolic events,^3,4 sepsis,^5,6 and the need for early surgical intervention.^3,4 The aggressive nature of S. aureus IE is also associated with more destructive IE lesions, such as abscesses, perforations, and fistulas, even in cases of native valve endocarditis.^7–9 Recent studies have shown that S. aureus IE typically arises in patients with vulnerable clinical conditions, including chronic renal failure, hemodialysis, long-term diabetes, alcoholism, cancer, hematological malignancies, immunosuppression, and drug addiction.^5,10–12 The aim of this paper is to present a case of IE caused by S. aureus, with a focus on diagnostic and therapeutic modalities.

2. Case presentation

The patient, a 61-year-old male, was transferred from a regional hospital to a tertiary care center, specifically to the intensive care unit (ICU), due to the sudden onset of respiratory failure requiring mechanical ventilation, a decline in consciousness leading to coma, and acute multisystem dysfunction. He had a 20-year history of diabetes mellitus and arterial hypertension. In the two months prior to his admission, he developed gangrene in the third toe of his left foot, which was treated conservatively. Upon admission, the patient was diagnosed with sepsis and multiorgan dysfunction. Three blood cultures were positive for S. aureus, while Acinetobacter was identified in his sputum. A wound culture also revealed S. aureus. A computed tomography (CT) scan of the head confirmed multiple ischemic strokes, with three significant areas of subacute ischemia. Pulmonary multi-slice CT angiography revealed multi-segmental pulmonary embolism and acute respiratory distress syndrome (ARDS). An abdominal CT scan confirmed splenomegaly, consistent with the septic state. Given the patient's septic condition, the isolation of S. aureus, evidence of multi-system embolization, and the newly detected heart murmur on auscultation, a transesophageal echocardiogram (TOE) was performed.

Initial imaging with 2D transesophageal echocardiography (TOE) revealed a saccular formation on the P2 segment of the posterior mitral leaflet (Figure 1). This was associated with a transvalvular mitral regurgitation jet detected by 2D color Doppler, presenting as a central jet along the coaptation line. Further assessment using 3D TOE—with Zoom, 3D Live, and Full Volume modes, as well as tissue rendering in 3D—enabled direct “en face” visualization of the mitral valve (Figures 2–3). This clearly demonstrated a perforation in the P2 segment of the posterior mitral leaflet, resulting in transvalvular mitral insufficiency and an eccentric jet along the coaptation line. The patient was evaluated by the Endocarditis team in concordance with recent guidelines, but due to rapid multi-organ dysfunction and an unfavorable risk-benefit profile, surgical intervention was deemed unfeasible. During the second week of the ICU stay, the patient's level of consciousness further declined to a Glasgow Coma Scale score of 4. This deterioration was accompanied by rapid worsening of renal function, leading to anuria and hypotension. Despite all intensive care measures, the patient passed away on the 18th day of ICU treatment.

3. Discussion

S. aureus is an opportunistic pathogen that typically colonizes the human anterior nares and is one of the leading causes of life-threatening bloodstream infections such as sepsis and endocarditis.^1,2,5,6,13 It is also a primary cause of skin and soft tissue infections. Although local skin infections are often self-limiting, they can frequently serve as an entry point for the pathogen to invade deeper tissues and the bloodstream.^13–21 In the case of our patient, a skin infection due to gangrene—coupled with a long-standing history of diabetes mellitus served as the entry point for S. aureus into the bloodstream. The virulence of S. aureus is attributed to a variety of complex factors, including its capsule and cell wall structure, the production of extracellular invasive enzymes and toxins that facilitate tissue invasion, its ability to persist intracellularly within phagocytes, the unique host-pathogen interactions, and its capacity to develop resistance to antimicrobials.^5,13–16 Due to its high virulence, S. aureus IE is often characterized by a rapid clinical progression, destructive cardiac lesions, and a high incidence of embolic events that lead to neurological complications.^17,18 Our patient initially presented with several embolic complications, including multi-segmental pulmonary embolism and multiple ischemic strokes, with three notable zones of subacute ischemia. These complications resulted in ARDS and a progressive decline in consciousness, eventually leading to coma. Previous studies have indicated that neurological manifestations, ranging from transient ischemic attacks (TIA) to coma, are frequently among the first clinical signs of S. aureus IE.^17–19 Although pulmonary embolism is more commonly associated with right-sided S. aureus IE, there have been case reports and studies, such as the one by Miro et al., ⁵ that describe its occurrence in left-sided IE as well.^20–23 All embolic events significantly increase mortality in these patients.^{3,4,8,9,24–29} S. aureus IE often causes complex and destructive lesions in cardiac structures, largely due to the tissue-damaging effects of its invasive enzymes.

The development of high quality real-time three-dimensional trans-esophageal echocardiography increased diagnostic accuracy of TOE in visualization of the mitral valve. It is particularly effective in patients with obesity, chest deformities, emphysema, or those receiving mechanical ventilation. Particularly, 3D-TOE permits direct visualization of the mitral anterior and posterior leaflet in “zoom” mode.^30,31 Leaflet perforation is more common in the mitral valve than in the aortic valve. 3D TOE is the only echocardiographic modality capable of providing multiplanar reconstruction of these complex entire cardiac structures and enabling direct visualization of leaflet destruction with perforation.^28–33 It improves our ability to identify, morphologically characterize, and measure endocarditis lesions by visualizing them in a numerous of planes. Volume rendering enable us 3D views with high realism of a structure of interest, facilitating our understanding of their spatial relationships within the other cardiac structures. Techniques such as transillumination and transparency enhance the sense of three dimensionality.^29–31

In our case, 3D TOE was essential for diagnosing a perforation of the P2 segment of the posterior mitral leaflet, leading to transvalvular mitral regurgitation. This finding aligns with the conclusions of several authors,^24,25,29,33 who have previously noted the superiority of 3D TOE in visualizing mitral valve perforations. The superiority of 3D TOE could be explained with its ability to provide anatomical views directly facing the leaflets, allowing for accurate characterization of the shape and location of valvular perforations, which are critical for preoperative planning.

After completing the necessary diagnostic procedures, the Endocarditis team assessed the patient. However, due to the presence of multiple embolic complications and multi-organ failure, surgery was deemed too high-risk. Numerous studies examining the course of S. aureus IE have found that not performing surgery is associated with poorer outcomes.^9,14,27 These studies often report that patients who were not candidates for surgery were typically older, had multiple comorbidities, presented with embolic complications and heart failure and had an unacceptable risk-to-benefit ratio for surgery.

4. Conclusion

S. aureus IE progresses rapidly and is associated with a malignant clinical course, often leading to severe multisystemic embolic complications and multi-organ failure. The cardiac infection caused by S. aureus is highly virulent, frequently resulting in complex, destructive tissue lesions, such as the perforation observed in this case. Unfortunately, for a small subset of patients, the severity of multi-organ failure renders surgery an unviable option due to the unfavorable risk-to-benefit ratio.

Our study also emphases the superior diagnostic capabilities of 3D TOE for assessing these complex lesions due to its powerful spatial reconstruction of mitral leaflets from a surgical perspective. Furthermore, full-volume acquisition provides wide angle images with a higher temporal resolution, what increase ability to discriminate small structures, recent 3D modalities such as transillumination and transparency enhance the sense of three dimensionality. All these advantages enable us accurate characterization of the shape and location of valvular perforations, which are critical for preoperative planning. OPEN IN VIEWER

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Figure 2.

3D TOE improved with transillumination and transparency - visualization of perforation on P2 segment of posterior mitral leaflet.

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Figure 3.

3D TOE - visualization of mitral valve with mitral regurgitation.