Infective Endocarditis - Infectious Diseases of the Heart

INFECTIVE ENDOCARDITIS

Infective endocarditis is an infection of the valves and endothe-lial surface of the heart. Endocarditis usually develops in people with cardiac structural defects (eg, valve disorders). Infective en-docarditis is more common in older people, probably because of decreased immunologic response to infection and the meta-bolic alterations associated with aging. There is a high incidence of staphylococcal endocarditis among IV/injection drug users who most commonly have infections of the right heart valves (Bayer et al., 1998; Braunwald, 2001).

The incidence of infective endocarditis remained steady at about 4.2 cases per 100,000 patients in the years from 1950 to the mid-1980s (Braunwald et al., 2001). The incidence then in-creased, partially attributed to increased IV/injection drug abuse (Braunwald et al., 2001). In 1998, a total of 2212 deaths were attributed to infective endocarditis (American Heart Association, 2001). Invasive procedures, particularly those involving mucosal surfaces, can cause a bacteremia. The bacteremia rarely lasts for more than 15 minutes (Dajani et al., 1997). If a person has some anatomic cardiac defect, bacteremia can cause bacterial endo-carditis (Dajani et al., 1997). The combination of the invasive procedure, the particular bacteria introduced into the bloodstream, and the cardiac defect may result in infective endocarditis.

Pathophysiology

Infective endocarditis is most often caused by direct invasion of the endocardium by a microbe (eg, streptococci, enterococci, pneumococci, staphylococci). The infection usually causes de-formity of the valve leaflets, but it may affect other cardiac structures such as the chordae tendineae. Other causative micro-organisms include fungi and rickettsiae. Patients at higher risk for infective endocarditis are those with prosthetic heart valves, a his-tory of endocarditis, complex cyanotic congenital malformations, and systemic or pulmonary shunts or conduits that were surgically constructed (eg, saphenous vein grafts, internal mammary artery grafts). At high risk are patients with rheumatic heart disease or mitral valve prolapse and those who have prosthetic heart valves (Chart 29-2).

Hospital-acquired endocarditis occurs most often in patients with debilitating disease, those with indwelling catheters, and those receiving prolonged intravenous or antibiotic therapy. Patients receiving immunosuppressive medications or cortico-steroids may develop fungal endocarditis.

A diagnosis of acute infective endocarditis is made when the onset of infection and resulting valvular destruction is rapid, oc-curring within days to weeks. The onset of infection may take 2 weeks to months, diagnosed as subacute infective endocarditis (Braunwald et al., 2001).

Clinical Manifestations

Usually, the onset of infective endocarditis is insidious. The signs and symptoms develop from the toxic effect of the infection, from destruction of the heart valves, and from embolization of fragments of vegetative growths on the heart. The occurrence of peripheral emboli is not experienced by patients with right heart valve infective endocarditis (Bayer et al., 1998; Braunwald, 2001). The patient exhibits signs and symptoms similar to those described in rheumatic endocarditis (see previous discussion).

Assessment and Diagnostic Findings

The general manifestations, which may be mistaken for influenza, include vague complaints of malaise, anorexia, weight loss, cough, and back and joint pain. Fever is intermittent and may be absent in patients who are receiving antibiotics or corticosteroids or in those who are elderly or have heart failure or renal failure. Splinter hemorrhages (ie, reddish-brown lines and streaks) may be seen under the fingernails and toenails, and petechiae may appear in the conjunctiva and mucous membranes. Small, painful nodules (Osler’s nodes) may be present in the pads of fingers or toes. Hemorrhages with pale centers (Roth’s spots) that may be seen in the fundi of the eyes are caused by emboli in the nerve fiber layer of the eye.

The cardiac manifestations include heart murmurs, which may be absent initially. Progressive changes in murmurs over time may be encountered and indicate valvular damage from veg-etations or perforation of the valve or the chordae tendineae. Enlargement of the heart or evidence of heart failure is also found.

The central nervous system manifestations include headache, temporary or transient cerebral ischemia, and strokes, which may be caused by emboli to the cerebral arteries. Embolization may be a presenting symptom; it may occur at any time and may involve other organ systems. Embolic phenomena may occur, as discussed in the previous section on rheumatic endocarditis.

Although the described characteristics may indicate infective endocarditis, the signs and symptoms may indicate other diseasesas well. A definitive diagnosis is made when a microorganism is found in two separate blood cultures, in a vegetation, or in an ab-scess. Three sets of blood cultures (with each set including one aerobic and one anaerobic culture) should be obtained before ad-ministration of any antimicrobial agents. Negative blood cultures do not totally rule out the diagnosis of infective endocarditis. An echocardiogram may assist in the diagnosis by demonstrating a moving mass on the valve, prosthetic valve, or supporting struc-tures and by identification of vegetations, abscesses, new pros-thetic valve dehiscence, or new regurgitation (Braunwald et al., 2001). An echocardiogram may also demonstrate the develop-ment of heart failure.

Prevention

Although rare, bacterial endocarditis may be life-threatening. A key strategy is primary prevention in high-risk patients (ie, those with rheumatic heart disease, mitral valve prolapse, or prosthetic heart valves). Antibiotic prophylaxis is recommended for high-risk patients immediately before and sometimes after the following procedures:

·      Dental procedures that induce gingival or mucosal bleed-ing, including professional cleaning and placement of orthodontic bands (not brackets)

·      Tonsillectomy or adenoidectomy

·      Surgical procedures that involve intestinal or respiratory mucosa

·      Bronchoscopy with a rigid bronchoscope

·       Sclerotherapy for esophageal varices

·       Esophageal dilation

·       Gallbladder surgery

·       Cystoscopy

·       Urethral dilation

·       Urethral catheterization if urinary tract infection is present

·       Urinary tract surgery if urinary tract infection is present

·       Prostatic surgery

·       Incision and drainage of infected tissue

·       Vaginal hysterectomy

·       Vaginal delivery

The type of antibiotic used for prophylaxis varies with the type of procedure and the degree of risk. The patient is usually in-structed to take 2 g of amoxicillin (Amoxil) 1 hour before dental, oral, respiratory, or esophageal procedures. If the patient is aller-gic to penicillin (eg, ampicillin [Omnipen, Polycillin], carbenicillin [Geocillin], cloxacillin [Cloxapen], methicillin [Staphcillin], nafcillin [Nafcil, Unipen], oxacillin [Prostaphlin, Bactocill], penicillin G [Bicillin, Permapen]), clindamycin (Cleocin), ceph-alexin (Keflex), cefadroxil (Duricef), azithromycin (Zithromax), or clarithromycin (Biaxin) may be used. Recommendations for gastrointestinal or genitourinary procedures are ampicillin and gentamicin (Garamycin) for high-risk patients, amoxicillin or am-picillin for moderate-risk patients, and substituting vancomycin (Vancocin) only for patients allergic to ampicillin or amoxicillin.

The severity of oral inflammation and infection is a significant factor in the incidence and degree of bacteremia. Poor dental hy-giene can lead to bacteremia, particularly in the setting of a den-tal procedure. Regular personal and professional oral health care and rinsing with an antiseptic mouthwash for 30 seconds before dental procedures may assist in reducing the risk of bacteremia. Increased vigilance is also needed in patients with intravenous catheters. To minimize the risk of infection, nurses must ensure that meticulous hand hygiene, site preparation, and the use ofaseptic technique occur during the insertion and maintenance procedures (Schmid, 2000). All catheters are removed as soon as they are no longer needed or no longer function.

Complications

Even if the patient responds to the therapy, endocarditis can be destructive to the heart and other organs. Heart failure and cerebral vascular complications, such as stroke, may occur before, during, or after therapy. The development of heart failure, which may re-sult from perforation of a valve leaflet, rupture of chordae, blood flow obstruction due to vegetations, or intracardiac shunts from dehiscence of prosthetic valves, indicates a poor prognosis with medical therapy alone and a higher surgical risk (Braunwald et al., 2001). Valvular stenosis or regurgitation, myocardial damage, and mycotic (fungal) aneurysms are potential heart complications. Many other organ complications can result from septic or non-septic emboli, immunologic responses, abscess of the spleen, mycotic aneurysms, and hemodynamic deterioration.

Medical Management

The causative organism may be identified by serial blood cultures. The objective of treatment is to eradicate the invading organism through adequate doses of an appropriate antimicrobial agent.

PHARMACOLOGIC THERAPY

Antibiotic therapy is usually administered parenterally in a con-tinuous intravenous infusion for 2 to 6 weeks. Parenteral therapy is administered in doses that achieve a high serum concentration and for a significant duration to ensure eradication of the dor-mant bacteria within the dense vegetations. This therapy is often delivered in the patient’s home and is monitored by a home care nurse. Serum levels of the selected antibiotic are monitored. If the serum does not demonstrate bactericidal activity, increased dosages of the antibiotic are prescribed, or a different antibiotic is used. Numerous antimicrobial regimens are in use, but penicillin is usually the medication of choice. Blood cultures are taken periodically to monitor the effect of therapy. In fungal endo-carditis, an antifungal agent, such as amphotericin B (Abelect, Amphocin, Fungizone), is the usual treatment.

The patient’s temperature is monitored at regular intervals be-cause the course of the fever is one indication of the effectiveness of treatment. However, febrile reactions also may occur as a re-sult of medication. After adequate antimicrobial therapy is ini-tiated, the infective organism usually disappears. The patient should begin to feel better, regain an appetite, and have less fa-tigue. During this time, patients require psychosocial support be-cause, although they feel well, they may find themselves confined to the hospital or home with restrictive intravenous therapy.

SURGICAL MANAGEMENT

After the patient recovers from the infectious process, seriously damaged valves may need to be replaced. Surgical valve replace-ment greatly improves the prognosis for patients with severe symptoms from damaged heart valves. Aortic or mitral valve ex-cision and replacement are required for patients who develop congestive heart failure despite adequate medical treatment, pa-tients who have more than one serious systemic embolic episode, and patients with uncontrolled infection, recurrent infection, or fungal endocarditis. Many patients who have prosthetic valve en-docarditis (ie, infected prostheses) require valve replacement.

Nursing Management

The nurse monitors the patient’s temperature; the patient may have fever for weeks. Heart sounds are assessed; a new murmur may indicate involvement of the valve leaflets. The nurse monitors for signs and symptoms of systemic embolization, or for patients with right heart endocarditis, the nurse monitors for signs and symptoms of pulmonary infarction and infiltrates. The nurse as-sesses signs and symptoms of organ damage such as stroke (ie, cere-brovascular accident or brain attack), meningitis, heart failure, myocardial infarction, glomerulonephritis, and splenomegaly.

Patient care is directed toward management of infection. The patient is started on antibiotics as soon as blood cultures have been obtained. All invasive lines and wounds should be assessed daily for redness, tenderness, warmth, swelling, drainage, or other signs of infection. Patients and their families are instructed about any activity restrictions, medications, and signs and symptoms of infection. The nurse should instruct the patient and family about the need for prophylactic antibiotics before, and possibly after, dental, respiratory, gastrointestinal, or genitourinary procedures. Home care nurses supervise and monitor intravenous antibiotic therapy delivered in the home setting and educate the patient and family about prevention and health promotion. The nurse pro-vides the patient and family with emotional support and facili-tates coping strategies during the prolonged course of the infection and antibiotic treatment required. If the patient received surgical treatment, the nurse provides postoperative care and instruction.