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 the PV from IE occurrence. Second, valvular abnormalities are rare in the 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]. The most common pathogenic microorganism in North America is Staphylococcus aureus [3, 4], 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 with bacteremia 4 days after his first fever and went on antibiotic therapy. The blood culture results were obtained on the 7th day, and antibiotics were adjusted according to these results. On the 12th day, vegetation was discovered and measured 14*13 mm and 11*16 mm in size, while 1 day later, the whole vegetation measurement was 43.8*19.9 mm. Then, the patient was transferred to the ICU for pulmonary embolism on the 16th day. Most embolism events occur within 2–4 weeks of antibiotic therapy [5]. In this case, pulmonary embolism occurred in less than 2 weeks. IE due to Staphylococcus spp. was found to be an independent predictor of worse in-hospital outcomes [6], and Staphylococcus spp. was an independent predictor of in-hospital mortality, which has been confirmed to be associated with worse prognosis [3, 7, 8]. This may be one of the reasons for the rapid decline in our patient’s statues. Furthermore, except for the first blood culture, the repeated cultures remained negative as the situation deteriorated rapidly, which made the treatment more complicated.
As the AHA (American Heart Association) guidelines [9] recommend, both TTE (transthoracic echocardiography) and TEE (transesophageal echocardiography) are indispensable in many patients with IE during initial evaluation and subsequent follow-up, and they provide complementary information. It is estimated that the sensitivity and specificity of TTE are 30–63% and 91–100%, respectively, and those of TEE are 87–100% and 91–100%, respectively [10] Even if our patient’s blood culture remained negative, TTE would provided additional information to evaluate the severity of IE. Robbins et al. found that vegetation size could predict the response to medication alone [11] The response to medication of vegetations < 10 mm was 100% versus 63% in vegetaion > 10 mm, and surgery was unavoidable for the remaining patients. In their assumption, as bacterial colonies deepen, their metabolism and proliferation become slower, leading to certain antibiotics being less effective. All this evidence indicates that our patient might benefit more from surgery than from conservative treatment alone.
However, it seems that surgery is not the optimal treatment for right-sided IE. The AHA guidelines [9] recommend that right-sided IE should be treated as conservatively as possible, and nonrandomized trial data from a single center experience [12] and international collaboration [13] support that early valve surgery may not be beneficial for all primary patients with primary IE caused by Staphylococcus aureus. Even the ESC (European Society of Cardiology) guidelines do not explain the role of surgery in pulmonary valve infection [14]. This unclear attitude may be due to the rarity of occurrence and invasiveness of right-sided IE [15] However, embolization, valve destruction, and large vegetation were indicated in our patient, and the general situation deteriorated in a short time. The role of surgery at an early stage in patients with such a rapid course and multiple complications, might need to be reconsidered. As Witten JC et al. found in a 13-year retrospective study of right-sided IE [4] if surgery was performed at an early stage, the surgical risk was low. Otherwise, with the burden of septic pulmonary embolism, the risk increases, and the opportunity for intervention may narrow as pulmonary complications result in a rapid decline in patient status, which is similar to our patient. Recurrent IE was is infrequent in their study (the greatest occurrence was found in injection drug users). Even if pulmanory IE only accounts for 5% of cases, it provides clues to support IPE surgery in the early course. Given the 15-year single-center experience from Liekiene D et al. [16], removal of vegetaion by preserving the valve is the most beneficial at the early stage of IPE [16, 17]. However, as surgery is not commonly recommended at an early stage, pulmonary cusps are damaged when surgeons see the patients. In this case, the most common method is pulmonary valve replacement. Moreover, the most significant point from their study is that surgery performed earlier may make the surgery less radical, and early surgery may improve patient outcomes, which is worth learning in cases such as our patient.
Postoperative results are generally favorable, as two of the largest case series reported that none of the nine cases had repeated vegetation [17, 18] The bioprosthetic valve of our patient functioned well and stably after 3 months of follow-up. As with some reports supporting early surgical interventions, it may be viable to combine medical and surgical approaches in IE patients upon admission.
