**1. Introduction**

The term *infective endocarditis* (IE) denotes infection of the endocardial surface of the heart. Infection involves heart valves most commonly but may occur within a septal defect, chordae tendinae, or in the mural endocardium. Infections of arteriovenous shunts, arterioarterial shunts (patent ductus arteriosus), or coarctation of the aorta are clinically and pathologically similar to IE. The characteristic lesion of the IE, the vegetation, is a variably sized mass with inflammatory cells, platelets, fibrin, and abundant immerse microorganisms. The term *infective endocarditis,* first used by Thayer and later popularized by Lerner and Weinstein,is preferable to the former term bacterial endocarditis, because chlamydiae, rickettsiae, mycoplasmas, fungi, and perhaps even viruses may be responsible for the syndrome [1].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Diagnostic criteria for IE were published in 1982 by von Reyn and colleagues (The Beth Israel criteria), but these criteria did not use echocardiographic findings in the case definitions [2]. Including the central role of echocardiography in the evaluation of suspected IE, new case definitions and diagnostic criteria (The Duke criteria) were proposed in 1994 [3], modified in 2000, and widely used since then (**Table 1**) [4]. Echocardiography utility in the diagnosis of IE is clearly recognized [5], transesophageal imaging has superior sensitivity and specificity, is cost-effective, and is recommended when transthoracic approach is negative and a high clinical suspicion is present. The utility of both modalities is diminished when used indiscriminately [6, 7]. Advances in imaging technology have had minimal impact at the day-to-day clinical level; the role of three-dimensional (3D) echocardiography and other modes of clinical imaging (magnetic resonance imaging, computed tomography, and technetium scintigraphy) are yet to be formally evaluated [8].

#### **Definition of infective endocarditis (IE) according to modified Duke criteria**

#### **Definite infective endocarditis**

#### *Pathologic criteria*


#### *Clinical criteria*


#### **Possible infective endocarditis**


#### **Rejected**


#### **Major criteria**

#### *Blood culture positive for IE*

**• Typical microorganisms consistent with IE from two separate blood cultures: viridans** *Streptococci, Streptococcus bovis***, HACEK group,** *Staphylococcus aureus; or*


#### *Evidence of endocardial involvement*

	- **Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant jets, or on implanted material in the absence of an alternative anatomic explanation;** *or*
	- **Abscess;** *or*
	- **New partial dehiscence of prosthetic valve New valvular regurgitation (worsening or changing of preexisting murmur not sufficient)**

#### **Minor criteria**

Diagnostic criteria for IE were published in 1982 by von Reyn and colleagues (The Beth Israel criteria), but these criteria did not use echocardiographic findings in the case definitions [2]. Including the central role of echocardiography in the evaluation of suspected IE, new case definitions and diagnostic criteria (The Duke criteria) were proposed in 1994 [3], modified in 2000, and widely used since then (**Table 1**) [4]. Echocardiography utility in the diagnosis of IE is clearly recognized [5], transesophageal imaging has superior sensitivity and specificity, is cost-effective, and is recommended when transthoracic approach is negative and a high clinical suspicion is present. The utility of both modalities is diminished when used indiscriminately [6, 7]. Advances in imaging technology have had minimal impact at the day-to-day clinical level; the role of three-dimensional (3D) echocardiography and other modes of clinical imaging (magnetic resonance imaging, computed tomography, and technetium scintigraphy) are yet

**• Microorganisms demonstrated by culture or histologic examination of a vegetation, a vegetation that has**

**• Pathologic lesions; vegetation or intracardiac abscess confirmed by histologic examination showing active**

to be formally evaluated [8].

36 Contemporary Challenges in Endocarditis

**Definite infective endocarditis**

*Pathologic criteria*

**endocarditis** *Clinical criteria*

**• Two major criteria;** *or*

**• Five minor criteria**

**• Three minor criteria**

**Rejected**

**Major criteria**

*Blood culture positive for IE*

**Possible infective endocarditis**

**Definition of infective endocarditis (IE) according to modified Duke criteria**

**embolized, or an intracardiac abscess specimen;** *or*

**• One major criterion and three minor criteria;** *or*

**• One major criterion and one minor criterion;** *or*

**• Does not meet criteria for possible IE, as above**

*bovis***, HACEK group,** *Staphylococcus aureus; or*

**• Firm alternate diagnosis explaining evidence of IE;** *or*

**• Resolution of IE syndrome with antibiotic therapy for ≤4 days;** *or*

**• No pathologic evidence of IE at surgery or autopsy, with antibiotic therapy for ≤4 days;** *or*

**• Typical microorganisms consistent with IE from two separate blood cultures: viridans** *Streptococci, Streptococcus*


TEE, transesophageal echocardiography; TTE, transthoracic echocardiography. Modified from [4].

**Table 1.** HACEK, *Hemophilus* spp., *Aggregatibacter* spp., *Cardiobacterium hominis, Eikenella corrodens*, and *Kingella* spp.

The challenges associated with IE are of increasing importance. The patients affected are older and sicker than those in the past, often with many comorbidities [9]. *Staphylococcus aureus* has surpassed penicillin-sensitive *Streptococci* as the most common cause in many high-income countries [10]. The population at risk is growing and health-care-associated *Staphylococcal bacteremia*, a conditioning of IE, is a major problem around the world [11].

In the last 30 years, the overall incidence of IE has remained between two and six per 100,000 individuals per year in the general population [12–14], whereas associated mortality has remained between 10 and 30% depending on the type of pathogen [15], the site of infection (native or prosthetic valve), and the underlying condition [16]. This quiescent trends in mortality and incidence are due to a continuing evolution of epidemiological features and risk factors rather to a lack of medical progress. The variability of disease presentation and course represents a challenge for the physician [8]. Even though clinical practices are clearly explained by international guides, they are derived mainly from observational cohort studies rather than randomized trials [17, 18]. Chronic rheumatic heart disease was considered a primary risk factor for IE until the widespread introduction of antibiotics; nevertheless, this finding prevails for low-income countries [14]. Current behavior in industrialized countries portraits different risk groups including prosthetic valve recipients, intravenous (IV) drug users, individuals with intravenous catheters, patients undergoing hemodialysis, and elderly people with degenerative valve lesions. Oral *Streptococci* are the main cause of IE in the general population [14, 19, 20], whereas *S. aureus* and coagulase-negative *Staphylococci* (e.g., *S. epidermidis*) are more frequently found in intravenous drug users, individuals with prosthetic-valve IE and in those with health-care-related IE [12, 21–23] and group *D Streptococci* (e.g. *S. gallolyticus*) are increasingly prevalent in elderly patients [12, 14, 19, 24, 25]. Patients with IE require opportune diagnosis and prompt response from a multidisciplinary group including cardiologists, cardiac surgeons, infectious disease specialists, and radiologists. The logistics of high-level patient care remains difficult even in developed countries and is frequently unobtainable in low-income countries.
