Right-sided IE, especially IPE is rare, occurring ten times less frequently than tricuspid valve endocarditis[1]. A structurally normal pulmonary valve is hardly affected alone. The first possible reason is that the lower pressure gradient through the pulmonary valve results in less shear stress than other valves. This leads to less valvular damage and protects PV from IE occurrence. Secondly, valvular abnormalities are rare in PV.
In a prospective cohort study, the main pathogenic microorganism isolated from blood culture was gram's bacteria (83%), of which Staphylococcus aureus accounted for 31% [3]. And the most common pathogenic microorganism in north America is Staphylococcus aureus [3], which is consistent with the patient’s history and blood culture.
In the review of our patient, a rapidly progressive course was observed. The patient was diagnosed as bacteremia 4 days after his first fever and went on antibiotic therapy. The blood culture result came out on the 7th day and antibiotics were adjusted according to it. On the 12th day, vegetations were discovered and measured 14*13 mm,11*16 mm, while one day later, the whole vegetation measurement was 43.8*19.9 mm. Then the patient was transferred to ICU for pulmonary embolism on the 16th day. Most embolism events occurred in 2–4 week of antibiotic therapy[4]. While in this case, pulmonary embolism occurred in less than 2 weeks. Furthermore, except for the first blood culture, the repeated ones later stayed negative as situation deteriorated rapidly, which makes the treatment more complicated.
It seems that surgery is not the optimal treatment for right-sided IE. AHA(American Heart Association) guidelines[5] recommended that right-sided IE should be treated as conservatively as possible, and non-randomized trial data from single center experience[6] and international collaboration[7] support that early valve surgery may not be beneficial to all primary patients caused by Staphylococcus aureus. And even the ESC(European Society of Cardiology) guidelines do not explain the role of surgery in pulmonary valve infection[8]. However, our patient indicated embolization, valve destruction, and large vegetation, and general situation deteriorated in a short time. The role of surgery at early stage in patients with such rapid course and multiple complications, might need reconsideration.
As AHA guidelines[5] recommended, both TTE(transthoracic echocardiography) and TEE(transesophageal echocardiography) are indispensable in many patients with IE during initial evaluation and subsequent follow-up and provide complementary information. It is estimated that the sensitivity and specificity of TTE is 30–63% and 91–100%, and those of TEE is 87–100% and 91–100%[9]. Even if our patient’s blood culture stayed negative, TTE provided extra information to evaluate severity of IE. Robbins et al. found that vegetation size can predict the response to medication alone[10]. The response to medication of vegetations < 10 mm is 100% verse 63% in those > 10 mm, and surgery is unavoidable for the rest. In their assumption, as bacterial colonies deepen, their metabolism and proliferation get slower, leading to certain antibiotics less effective. All these evidences indicate that our patient might benefit more from surgery than conservative treatment alone.
A prospective cohort study, early surgery is found to be essential to improve the survival rate of patients with IE.Postoperative results are generally favorable, as two of the largest case series reporting that none of the nine cases had repeated vegetation [11][12]. The bioprosthetic valve of our patient functioned well and stably after 3 months’ follow-up. However, optimal surgical strategy for IPE has not been fully investigated. As some reports supporting early surgical interventions, it may be viable to combine medical and surgical approaches in IE patients on admission.