4 DISCUSSION
Usually, IE is insidious in onset, variable in symptoms, and critical with rapid progression and high mortality (> 30%)4, making diagnosis and treatment challenging and prone to underdiagnosis, late diagnosis, or misdiagnosis. Echocardiography can clarify the attachment site, size, and shape of the vegetation and the structural changes of the heart and cardiac hemodynamic changes caused by various complications5. The key is how to diagnose vegetation, which requires understanding the mechanisms underlying IE occurrence. Three conditions must be met for bacterial IE to occur: the presence of valve thrombus, bacteria in the circulation, and bacterial growth on the valve1. High-velocity blood flow damage to the contact surfaces can lead to thrombosis, promoting vegetation occurrence.
Compared to left heart endocarditis, right heart system endocarditis shows fevers of unknown origin, bacteremia, and other infection symptoms and complications caused by right heart system function damage6. In the first case, various tests suggested infection, and the ultrasound findings of ventricular septal defect (prerequisite) and perforated leaflet regurgitation (complication) allowed a relatively easy diagnosis of the mass as vegetation. In the second case, it was not easy to distinguish thrombus from infective vegetation. On the one hand, the patient had congenital heart disease, a high fever, a high infection index, and evidence pointing to infective endocarditis, but the blood culture was negative many times. On the other hand, the patient had whole-body edema, long-term bed rest, increased blood coagulation function, and the risk of thrombus, representing a contradiction between the two diagnoses.
The following aspects can distinguish thrombus and vegetation: (1) Mass nature: the surface of the thrombus is smooth, and the internal echo is often uneven due to different formation times; the old thrombus is closely combined with the vascular endothelium and does not fall off easily; the texture of infectious vegetation is relatively fragile and easy to rupture and spread, causing infarction and multiple emboli in small abscesses. (2) Clinical manifestations: the thrombus often has high-risk factors for thrombosis, such as atrial fibrillation and myocardial infarction; infectious vegetation has typical clinical manifestations and signs of infective endocarditis, and the blood culture is positive. Here, the blood cultures were negative many times for the two patients, which was related to the use of antibiotics. (3) Attachment site: the thrombus is often attached to the blood stasis site, such as the left atrial appendage and apical part, and its activity is relatively limited; vegetations are often attached to the valvular blood flow scouring site, with a large activity range, and infection can spread to adjacent tissues. It often causes erosive damage, such as valvular ulcer perforation and valve annulus abscess.