Chapter 197. Infective Endocarditis

1. Does the patient have symptoms consistent with infective endocarditis?

2. What tests and studies are indicated to evaluate infective endocarditis?

3. What infectious etiologies should be considered?

4. What treatments should be considered?

5. What complications should be expected?

Infective endocarditis (IE) is a relatively common infection in the hospital setting, with an inpatient mortality rate of about 18%. The incidence of IE rises linearly with age, from around 1 case per 100,000 person-years among young adults, to over 10 cases per 100,000 person-years among those older than 75 years. The hallmark lesion of IE is the endocardial vegetation. Although the heart valves are affected most commonly, IE also may involve septal defects, mural endocardium, or prosthetic cardiac structures. Vegetations may result in valvular regurgitation or obstruction, myocardial abscess, or mycotic aneurysm. Definitive diagnosis requires identification of the causative organism in blood, cardiac structures, or emboli. Cure requires prolonged antimicrobial treatment and often valve replacement surgery, leading to substantial expense.

Historically, IE was a disease of younger patients with rheumatic heart disease, and mainly involved viridans group streptococci. Over the last decade, however, a new form of the disease, health care–associated IE, has emerged. This new form of IE is distinct in its microbiology (predominantly Staphylococcus aureus) and risk factors (eg, intravenous catheters, hyperalimentation lines, pacemakers, dialysis shunts). It represents about one-third of all IE cases among noninjection drug users with native valve disease.

Risk Factors for IE

Almost any type of structural heart disease may predispose to IE, especially when the defect results in turbulent blood flow. Right-sided IE is primarily an infection of injection drug users and patients with indwelling transvenous pacemakers. In developed countries, the proportion of cases related to rheumatic heart disease has declined to 5% or less in the past 2 decades, while in developing countries, rheumatic heart disease remains the most common predisposing cardiac condition. Congenital bicuspid aortic valve is the underlying lesion in more than 15% of IE cases in patients (especially men) older than 60 years, and is associated with a poor prognosis, despite rapid valve replacement. Degenerative cardiac lesions (eg, calcified mitral annulus, calcific nodular lesions secondary to arteriosclerotic cardiovascular disease, and post–myocardial infarction thrombus) assume the greatest importance in the 30% to 40% of IE patients without any demonstrable underlying valvular disease. Marfan syndrome, when associated with aortic insufficiency, also has been associated with IE. Intravascular infections involving cardiac devices (eg, permanent cardiac pacemakers, defibrillators) also have increased significantly since the 1990s. Injection drug users are at high risk for recurrent and polymicrobial IE.

Mitral and aortic valvular involvement are most common in IE. Distributions of valvular involvement range from 28% to 45% of cases for isolated mitral valve IE, 5% to 36% for isolated aortic valve IE, and 0% to 35% for combined aortic and mitral valves IE. In the absence of injection drug use, the tricuspid valve rarely is involved (0–6% ...