Infective endocarditis

Infective endocarditis
Classification and external resources
A mitral valve vegetation caused by bacterial endocarditis.
ICD-10	I33
ICD-9	421.0-421.1

Infective endocarditis is a form of endocarditis, or inflammation, of the inner tissue of the heart, such as its valves, caused by infectious agents. The agents are usually bacterial, but other organisms can also be responsible.

The valves of the heart do not receive any dedicated blood supply. As a result, defensive immune mechanisms (such as white blood cells) cannot directly reach the valves via the bloodstream. If an organism (such as bacteria) attaches to a valve surface and forms a vegetation, the host immune response is blunted. The lack of blood supply to the valves also has implications on treatment, since drugs also have difficulty reaching the infected valve.

Normally, blood flows smoothly through these valves. If they have been damaged - from rheumatic fever, for example - the risk of bacterial attachment is increased.

Classification

By duration

Historically, infective endocarditis has been clinically divided into acute and subacute presentations (because untreated patients tended to live longer with the subacute as opposed to the acute form). This classifies both the rate of progression and severity of disease.

• Subacute bacterial endocarditis (SBE) is often due to streptococci of low virulence and mild to moderate illness which progresses slowly over weeks and months and has low propensity to hematogenously seed extracardiac sites.
• Acute bacterial endocarditis (ABE) is a fulminant illness over days to weeks, and is more likely due to Staphylococcus aureus which has much greater virulence, or disease-producing capacity and frequently causes metastatic infection.

This classification is now discouraged, because the ascribed associations (in terms of organism and prognosis) were not strong enough to be relied upon clinically. The terms short incubation (meaning less than about six weeks), and long incubation (greater than about six weeks) are preferred.

By culture results

Infective endocarditis may also be classified as culture-positive or culture-negative.

Culture-negative endocarditis can be due to micro-organisms that require a longer period of time to be identified in the laboratory, such organisms are said to be fastidious because they have demanding growth requirements, or due to absence of an organism as in marantic endocarditis. Some pathogens responsible for culture-negative endocarditis include Aspergillus species, Brucella species, Coxiella burnetii, Chlamydia species, and HACEK bacteria. Another possible reason for culture negativity, even with the more typical pathogens, is prior antibiotic treatment.

By heart side

Endocarditis can also be classified by the side of the heart affected:

• Patients who inject narcotics or other drugs intravenously may introduce infection which will travel to the right side of the heart classically affecting the tricuspid valve, and most often caused by S. aureus.
• In other patients without a history of intravenous exposure, endocarditis is more frequently left-sided.

By infection type

Another form of endocarditis is nosocomial endocarditis which is when the patient is diagnosed with endocarditis and has had hospital care one month prior to the incident and is usually secondary to IV catheters, Total parenteral nutrition lines, pacemakers, etc.

By valve type

Finally, the distinction between native-valve endocarditis and prosthetic-valve endocarditis is clinically important. Prosthetic valve endocarditis can be early (< 60 days of valvular surgery) or late (> 60 days of valvular surgery).

• Early prosthetic valve endocarditis is usually due to intraoperative contamination or a postoperative bacterial contamination which is usually nosocomial in nature.
• Late prosthetic valve endocarditis is usually due to community acquired microorganisms.

Signs and symptoms

• Fever, i.e. fever of unknown origin occurs in 97% of people; malaise and endurance fatigue in 90% of people.
• A new or changing heart murmur, weight loss, and coughing occurs in 35% of people.
• Vascular phenomena: septic embolism (causing thromboembolic problems such as stroke in the parietal lobe of the brain or gangrene of fingers), Janeway lesions (painless hemorrhagic cutaneous lesions on the palms and soles), intracranial hemorrhage, conjunctival hemorrhage, splinter hemorrhages, renal infarcts, and splenic infarcts.
• Immunologic phenomena: Glomerulonephritis which allows for blood and albumin to enter the urine, Osler's nodes (painful subcutaneous lesions in the distal fingers), Roth's spots on the retina, positive serum rheumatoid factor
• Other signs may include; night sweats, rigors, anemia, splenomegaly, clubbing

A common mnemonic for the signs and symptoms of endocarditis is FROM JANE:

• Fever
• Roth spots
• Osler's nodes
• Murmur
• Janeway lesions
• Anemia
• Nail-bed (splinter) hemorrhages
• Emboli

Cause

In a healthy individual, a bacteremia (where bacteria get into the blood stream through a minor cut or wound) would normally be cleared quickly with no adverse consequences. If a heart valve is damaged and covered with a piece of a blood clot, the valve provides a place for the bacteria to attach themselves and an infection can be established.

In the past, bacteremia caused by dental procedures (in most cases due to viridans streptococci, which reside in oral cavity), such as a cleaning or extraction of a tooth was thought to be more clinically significant than it actually was. However, it is important that a dentist or a dental hygienist be told of any heart problems before commencing treatment. Antibiotics are administered to patients with certain heart conditions as a precaution, although this practice has changed in the US, with new American Heart Association guidelines released in 2007, and in the UK as of March 2008 due to new NICE guidelines. Everyday tooth brushing and flossing will similarly cause bacteremia. Although there is little evidence to support antibiotic prophylaxis for dental treatment, the current American Heart Association guidelines are highly accepted by clinicians and patients.

Another group of causes results from a high number of bacteria getting into the bloodstream. Colorectal cancer (mostly Streptococcus bovis), serious urinary tract infections (mostly enterococci), and drug injection (S. aureus) can all introduce large numbers of bacteria. With a large number of bacteria, even a normal heart valve may be infected. A more virulent organism (such as S. aureus, but see below for others) is usually responsible for infecting a normal valve.

Intravenous drug users tend to get their right-sided heart valves infected because the veins that are injected enter the right side of the heart, so they will have injured valves on that side, that the bacteria can bind to. In rheumatic heart disease infection occurs on the aortic and the mitral valves, on the left side of the heart.

Other factors that increase the risk of developing infective endocarditis are low levels of white blood cells, immunodeficiency or immunosuppression, malignancy, diabetes, and alcohol abuse.

Pathogenesis

As previously mentioned, altered blood flow around the valves is a risk factor in obtaining endocarditis. The valves may be damaged congenitally, from surgery, by auto-immune mechanisms, or simply as a consequence of old age. The damaged part of a heart valve becomes covered with a blood clot, a condition known as non-bacterial thrombotic endocarditis (NBTE). Altered blood flow, and thus infective endocarditis, are more likely in high pressure areas. Consequently, ventricular septal defects create more susceptibility than atrial septal defects. Damaged vascular endothelium will also promote platelet and fibrin deposition, upon which bacteria can take hold. Valvular lesions are a major cause of such damage, as are jet lesions resulting from ventricular septal defects or patent ductus arteriosus.

Diagnosis

Vegetation on the tricuspid valve by echocardiography. Arrow denotes the vegetation.

In general, a patient should fulfill the Duke criteria in order to establish the diagnosis of endocarditis.

As the Duke criteria rely heavily on the results of echocardiography, research has addressed when to order an echocardiogram by using signs and symptoms to predict occult endocarditis among patients with intravenous drug abuse and among non drug-abusing patients. Unfortunately, this research is over 20 years old and it is possible that changes in the epidemiology of endocarditis and bacteria such as staphylococci make the following estimates incorrect.

Among patients who do not use intravenous drugs and have a fever in the emergency room, there is a less than 5% chance of occult endocarditis. Mellors in 1987 found no cases of endocarditis nor of staphylococcal bacteremia among 135 febrile patients in the emergency room. The upper confidence interval for 0% of 135 is 5%, so for statistical reasons alone, there is up to a 5% chance of endocarditis among these patients. In contrast, Leibovici found that among 113 non-selected adults admitted to the hospital because of fever there were two cases (1.8% with 95%CI: 0% to 7%) of endocarditis.

Among patients who do use intravenous drugs and have a fever in the emergency room, there is about a 10% to 15% prevalence of endocarditis. This estimate is not substantially changed by whether the doctor believes the patient has a trivial explanation for their fever. Weisse found that 13% of 121 patients had endocarditis. Marantz also found a prevalence of endocarditis of 13% among such patients in the emergency room with fever. Samet found a 6% incidence among 283 such patients, but after excluding patients with initially apparent major illness to explain the fever (including 11 cases of manifest endocarditis), there was a 7% prevalence of endocarditis.

Among patients with staphylococcal bacteremia (SAB), one study found a 29% prevalence of endocarditis in community-acquired SAB versus 5% in nosocomial SAB. However, only 2% of strains were resistant to methicillin and so these numbers may be low in areas of higher resistance.

Echocardiography

The transthoracic echocardiogram has a sensitivity and specificity of approximately 65% and 95% if the echocardiographer believes there is 'probable' or 'almost certain' evidence of endocarditis.

Duke criteria

Established in 1994 by the Duke Endocarditis Society and revised in 2000, the Duke criteria are a collection of major and minor criteria used to establish a diagnosis of endocarditis. A diagnosis can be reached in any of three ways: two major criteria, one major and three minor criteria, or five minor criteria.

Major criteria include:

1. Positive blood culture with typical IE microorganism, defined as one of the following:
   • Typical microorganism consistent with IE from 2 separate blood cultures, as noted below:
     • Viridans-group streptococci, or
     • S. bovis including nutritional variant strains, or
     • HACEK group, or
     • S. aureus, or
     • Community-acquired enterococci, in the absence of a primary focus
   • Microorganisms consistent with IE from persistently positive blood cultures defined as:
     • Two positive cultures of blood samples drawn >12 hours apart, or
     • All of 3 or a majority of 4 separate cultures of blood (with first and last sample drawn 1 hour apart)
     • Coxiella burnetii detected by at least one positive blood culture or antiphase I IgG antibody titer >1:800
2. Evidence of endocardial involvement with positive echocardiogram defined as
   • 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 or new valvular regurgitation (worsening or changing of preexisting murmur not sufficient)

Minor criteria include:

1. Predisposing factor: known cardiac lesion, recreational drug injection
2. Fever >38°C
3. Evidence of embolism: arterial emboli, pulmonary infarcts, Janeway lesions, conjunctival hemorrhage
4. Immunological problems: glomerulonephritis, Osler's nodes
5. Positive blood culture (that doesn't meet a major criterion) or serologic evidence of infection with organism consistent with IE but not satisfying major criterion
6. Positive echocardiogram (that doesn't meet a major criterion) (this criterion has been removed from the modified Duke criteria)

Micro-organisms responsible

Many microorganisms can cause infective endocarditis. These are generally isolated by blood culture, where the patient's blood is removed, and any growth is noted and identified. The term bacterial endocarditis (BE) commonly is used, reflecting the fact that most cases of IE are due to bacteria; however, Infective Endocarditis (IE) has become the preferred term.

Bacterial

Viridans Alpha-hemolytic streptococci, that are present in the mouth will often be the organism isolated if a dental procedure caused the bacteraemia. If the bacteraemia was introduced through the skin, such as contamination in surgery, during catheterisation, or in an IV drug user, S. aureus is common. A third important cause of endocarditis are bacteria of the genus Enterococcus. These bacteria enter the bloodstream as a consequence of abnormalities in the gastrointestinal or urinary tracts. Enterococci are increasingly recognized as causes of nosocomial or hospital-acquired endocarditis. This contrasts with alpha-haemolytic streptococci and S. aureus which are causes of community-acquired endocarditis.

Some organisms, when isolated, give valuable clues to the cause, as they tend to be specific.

• Pseudomonas species, which are very resilient organisms that thrive in water, may contaminate street drugs that have been contaminated with drinking water. P. aeruginosa can infect a child through foot punctures, and can cause both endocarditis and septic arthritis.
• S. bovis and Clostridium septicum, which are part of the natural flora of the bowel, are associated with colonic malignancies. When they present as the causative agent in endocarditis, it usually call for a concomitant colonoscopy due to worries regarding hematogenous spread of bacteria from the colon due to the neoplasm breaking down the barrier between the gut lumen and the blood vessels which drain the bowel.
• HACEK organisms are a group of bacteria that live on the dental gums, and can be seen with IV drug users who contaminate their needles with saliva. Patients may also have a history of poor dental hygiene, or pre-existing valvular disease.
• Less commonly reported etiological bacteria are responsible for blood culture negative infectious endocartitis. Such bacteria are identified by serology, culture of the excised valve tissue, sputum, pleural fluid, and emboli; and by polymerase chain reaction or and sequencing of bacterial 16S ribosomal RNA. Such bacteria include Streptococcus mitis, Bartonella, Chlamydia psittaci, and Coxiella Propianibacterium are normal skin flora, but have been responsible for deaths, due to the indolent course of this abscess producing infection. Abiotrophia is a separate genus of gram-positive cocci formerly classified as nutritionally variant streptococci. These organisms cause 1% to 2% of all infective endocarditis. Tropheryma whipplei has caused endocarditis without gastrointestinal involvement. Granulicatella elegans is another seldom proven etiology. Citrobacter koseri was found in an immunocompetent adult. Neisseria bacilliformis was found in a patient with a bicuspid aortic valve.

Fungal and viral

Candida albicans, a yeast, is associated with IV drug users and the immunocompromised. Other fungi demonstrated to cause endocarditis are **Histoplasma capsulatum** and **Aspergillus**. Tricosporon asahii is another proven agent.

Viral infections of the heart are usually associated with viral myocarditis or viral pericarditis. The existence of viral endocarditis is disputed, but there is some evidence that it can occur.

Treatment

High dose antibiotics are administered by the intravenous route to maximize diffusion of antibiotic molecules into vegetation(s) from the blood filling the chambers of the heart. This is necessary because neither the heart valves nor the vegetations adherent to them are supplied by blood vessels. Antibiotics are continued for a long time, typically two to six weeks. Specific drug regimens differ depending on the classification of the endocarditis as acute or subacute (acute necessitating treating for S. aureus with oxacillin or vancomycin in addition to gram-negative coverage). Fungal endocarditis requires specific anti-fungal treatment, such as amphotericin B.

In acute endocarditis, due to the fulminant inflammation empirical antibiotic therapy is started immediately after the blood has been drawn for culture. This usually includes oxacillin and gentamicin IV infusions until the culture sensitivity report with the minimum inhibitory concentration comes, when the therapy can be modified to tailor to the microorganism. There should be noted that the routine use of gentamicin to treat Staphylocococcal endocarditis has been questioned, given the lack of evidence to support its use and the high rate of complications.

In subacute endocarditis, antibiotic treatment is based on the microorganism involved, requiring the culture sensitivity report. So immediate therapy is mainly focused on symptomatic treatment.

The most common organism responsible for infective endocarditis are viridans-group streptococci,^{[citation needed]} which are highly sensitive to penicillin. High dose IV crystalline penicillin every 4hrs for 2 weeks is recommended and still remains the drug of choice. Again it is important to note that antibiotic therapy hinges upon the culture sensitivity report.

Another regimen that is followed for endocarditis is the short course treatment which is a 2 week treatment regimen of benzyl penicillin IV which may be sufficient for S. viridans and S. bovis so long as the following conditions are met:

‣ Endocarditis of a native valve, not on a prosthetic valve

‣ An MIC ≤ 0.1 mg/l

‣ No adverse prognostic factors such as heart failure, aortic valve regurgitation, or conduction defects

‣ No evidence of thromboembolism

‣ No vegetations > 5mm in diameter

‣ Clinical response within 7 days

The short course treatment In patients where the blood culture reveals the causative organism, culture sensitivity reports should be followed to treat the patient, in addition to usage of two bactericidal antibiotics for a minimum of two weeks as a combination therapy.

Surgical debridement of infected material and replacement of the valve with a mechanical or bioprosthetic artificial heart valve is necessary in patients who fail to clear micro-organisms from their blood in response to antibiotic therapy, or in patients who develop cardiac failure resulting from destruction of a valve by infection. Other indications to consider surgery include:

‣ Unstable Prosthetic Valve or Obstruction

‣ Recurrent septic emboli, mycotic aneurysm

‣ Large vegetations

‣ Abscess formation

‣ Early closure of mitral valve

‣ Gram negative species

Infective endocarditis is associated with a 25% mortality.

See also

• Dental antibiotic prophylaxis