**7. Right‐sided endocarditis and septic pulmonary embolism**

tions (e.g., pseudoaneurysm or a large infarction) should prompt the consideration of splenectomy [84–87]. Likewise, refractory pain may also constitute a surgical indication (or be a clinical warning sign of one of the above complications) [80, 87, 88]. The decision to operate in the setting of therapeutic uncertainty should be considered in the context of the simultaneous presence of any other relative indications, risks, and benefits. The diagnosis of splenic infarct is not a contraindication for a cardiac operation when such intervention is indicated. The situation is not as clear in the presence of a splenic abscess. In most cases, it is preferable to perform splenectomy prior to valve surgery in order to prevent re-infection of the valve prosthesis or annuloplasty ring [58, 89]. Combined cardiac procedure and splenectomy has

Septic embolization to the mesenteric vessels is a serious, potentially life-threatening complication of IE [4]. Small valvular vegetations can break off, enter the circulation, and become lodged in the mesentric arteries, endangering blood supply to the small intestine and colon [91, 92]. Compared to other organ systems affected by metastatic or embolic events of IE, mesenteric embolization is relatively rare, constituting approximately 3% of SE [2]. However, general surgeons must consider this entity on their differential list of causes leading to acute bowel ischemia. In terms of vascular distribution, the inferior mesenteric artery (IMA) involvement is much less common than SE to the superior mesenteric artery (SMA, approximately 3% versus <1%, respectively) [93]. Clinical indications for operative abdominal intervention following mesenteric SE are similar to those for other acute abdominal emergen-

Septic embolism involving the mesenteric vessels can also be associated with mycotic aneurysms [96]. Pathophysiology involves embolization of small valvular vegetation fragments to the arterial vasa vasorum or the intraluminal space with subsequent extension of the infection through the intima and outward through the media of the vessel wall [58, 97]. This process gradually weakens the arterial wall, resulting in pathologic dilation and pseudoaneurysm formation [58]. Depending on the anatomic characteristics of the pseudoaneurysm, and the presence versus absence of associated distal embolization/thrombosis, management may include resection or vascular bypass of the lesion [98]. Inherent to the nature of pseudoaneurysms secondary to SE, high complication rate and/or mortality may be encountered [98].

In one unusual case, *Streptococcus bovis* endocarditis was reported to be associated with SE to the superior mesenteric artery (SMA) resulting in a mycotic aneurysm. Computed tomography (CT) imaging demonstrated a saccular aneurysm of the SMA and follow-up angiography showed evidence of SE to the left femoral artery [99]. A duplex ultrasound further characterized the femoral artery lesion as an intravascular mass at the left femoral artery bifurcation. Echocardiography confirmed mitral valvular vegetations. The patient underwent surgical resection of the mesenteric aneurysm, embolectomy of the femoral artery, as well as mitral

been reported with good outcomes [90].

152 Contemporary Challenges in Endocarditis

**6. Septic emboli to mesenteric vasculature**

cies and have been discussed elsewhere [94, 95].

valve replacement procedure [99].

Right-sided IE (**Figure 5**) usually manifests as persistent fevers, bacteremia, and multiple septic pulmonary emboli (SPE, **Figure 6**). Isolated pulmonary valve endocarditis accounts for only about 2% of IE cases [101]. Due to its rarity, SPE is often difficult to diagnose due to its nonspecific presentation. In addition to the signs and symptoms of IE, SPE may cause pleuritic chest pain, cough, and/or hemoptysis [102] and may be complicated by pulmonary infarction, abscess, pneumothorax, pulmonary infiltrates, and purulent pulmonary effusion [103–105]. Although rare, right-sided heart failure due to increased pulmonary arterial pressure or severe right-sided valvular regurgitation/obstruction may occur. Historically, SPE was associated with intravenous drug use [106]. However, today the most common clinical risk factors include indwelling intravascular catheters, intravascular devices, and noncardiac sources of sepsis, especially in hospitalized patients [107–110].

**Figure 5.** Echocardiographic images of tricuspid valve endocarditis characterized by the presence of a large vegetation (arrows).

**Figure 6.** Septic pulmonary emboli associated with tricuspid valve endocarditis due to methicillin-resistant Staphylococcus aureus. Source: Stawicki et al. [2]. Used under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Regarding diagnostic modalities used in the setting of suspected SPE, chest radiography is nonspecific and usually shows poorly marginated peripheral lung nodules, possibly with cavitary features [25]. Computed tomography provides much better image granularity and usually demonstrates bilateral nodules or multifocal infiltrates, often involving peripheral lung zones and associated cavitary lesions [102]. These features, in conjunction with extrapulmonary infection, should raise suspicion of SPE as the underlying cause. The "feeding vessel" sign, or the finding of a vessel which projects into a peripheral lung lesion, is fairly specific for SPE [111, 112]. Patients with SPE and suspected IE should undergo echocardiography to rule out valvular infection and to assess for any associated cardiac complications [113, 114]. TEE is preferred over TTE due to better image resolution and improved diagnostic accuracy for detecting small vegetations, abscesses, and leaflet perforations up to 5 mm in size [113, 114].

A conservative approach is recommended in most patients with right-sided IE because significant majority of the cases will resolve with antimicrobial therapy alone [115, 116]. The role of surgery remains unclear because the presence of SPE and/or recurrent SPE is not an absolute indication for operative intervention. Surgery is usually indicated in cases of persistent sepsis, lack of response to appropriate antimicrobial therapy, right heart failure secondary to severe tricuspid regurgitation, and persistent large vegetation [50, 58, 117, 118]. Thoracoscopy or thoracotomy may be required in complicated cases of SPE (e.g., empyema, pulmonary abscess) [102, 106].
