Infectious endocarditis (IE)

  Introduction:

        Infective endocarditis (IE) is a microbial infection of a heart valve (native or prosthetic) or the endocardium, leading to tissue destruction and formation of vegetation. Caused mainly due to streptococcal and staphylococcal infection in the heart valves.

Etiological statistics:

üThe incidence of IE is 1.7–7.2 cases per 100 000 person-years.

üThe female to male ratio is 1:2.

üWhenever blood-culture-negative IE is suspected, other organisms such as Coxiella burnetti, Legionella spp., Brucella spp., Bartonella spp., and Chlamydiae spp. must be considered.

Development of Aschoff nodules in IE:

  The cardiac manifestations are in the form of focal inflammatory involvement of the interstitial tissue of all the three layers of the heart, the so-called pancarditis. The feature of pancarditis in RF is the presence of distinctive Aschoff nodules or Aschoff bodies. The Aschoff nodules are spheroidal or fusiform distinct tiny structures, 1-2 mm in size.

Fully-developed Aschoff bodies occurs through 3 stages:

1. Early (exudative or degenerative) stage
2. Intermediate (proliferative or granulomatous) stage
3. Late (healing or fibrous) stage 

Early (exudative or degenerative) stage:

üThe earliest sign of injury in the heart is about 4th week of illness.

üEdema of the connective tissue and increase in acid mucopolysaccharide in the ground substance.

üThe collagen fibers are fragmented. This change is referred to as fibrinoid degeneration.

Intermediate stage:

üThis stage is apparent in the 4th to 13th week of illness.

üThe early stage of fibrinoid change is followed by proliferation of cells that includes infiltration by lymphocytes (mostly T cells), plasma cells, a few neutrophils and the characteristic cardiac histiocytes (Anitschkow cells) at the margin of the lesion.

üThese cardiac histiocytes become multinucleate cells containing 1 to 4 nuclei and are called Aschoff cells.

Late (healing or fibrous) stage:

üThe stage of healing occurs about 12 to 16 weeks after the illness.

üThe nodule becomes oval or fusiform in shape, about 200 µm wide and 600 µm long.

üThe Anitschkow cells in the nodule become spindle-shaped with diminished cytoplasm

These cells tend to be arranged in a palisaded manner.

IE develops in heart, in a manner of layer by layer associated with rheumatic heart disease (RHD).

1. Rheumatic endocarditis
  - Rheumatic valvulitis
2. Rheumatic myocarditis

3. Rheumatic pericarditis

 

But for a look, rheumatic endocarditis is the only pathologic condition that associate with infectious endocarditis.

Development of IE Associated with Rheumatic endocarditis:

üIE originates where the endothelium is damaged by high blood velocity or mechanical damage and on foreign bodies in the circulation.

üA sterile thrombotic vegetation (non-bacterial thrombotic endocarditis) is formed, which facilitates bacterial adherence during transient bacteremia.

üNormally 1 to 3 mm in diameter. Mainly along the line of closure of the leaflets and cusps.

üPlatelets and fibrin deposits at the injury site provide an adherent surface for the formation of vegetations.

üThe vegetations may produce the secondary effects of endocarditis such as tissue destruction, generalized and difficult to eradicate sepsis, and septic emboli and abscesses.

üGram-positive bacteria are particularly resistant to the patient’s bactericidal activity (i.e. Complement), which facilitates the adhesion and formation of vegetation.

  The approximate frequency of deformity of various valves:

üMitral alone = 37% cases.

üMitral + aortic = 27% cases.

üMitral + aortic + tricuspid = 22% cases.

üMitral + tricuspid = 11% cases.

üAortic alone = 2%.

üMitral + aortic + tricuspid + pulmonary = less than 1% cases.

According to the data, the mitral valve is almost always involved in RHD and IE.

Gross appearance of chronic healed mitral valve in  RHD and IE is characteristically ‘fish mouth’ or ‘buttonhole’ stenosis. 

Diagnosis of IE:

üClinical features
üMicrobiological analysis

üEchocardiography

Clinical features:

üWeight loss and night sweats are frequently described (up to 96% of cases).

üA new or a different heart murmur (48% and 20%, respectively).

üWhen the left heart is affected, vegetations most often develop on the ventricular aspect of the aortic valve and the atrial surface of the mitral valve,  this explains why peripheral embolism is common.

üUp to 30% of the patients have renal or splenic infarction at the time of diagnosis.

Microbiological analysis:

      Blood cultures are positive in about 80% of cases, but maybe negative in cases of intracellular or fastidious pathogens or after previous antibiotic treatment.

Echocardiography:

üA transthoracic echocardiogram (TTE) should be performed promptly.

üTransoesophageal echocardiography (TOE) offers better image quality and the overall sensitivity for IE is 90–100%.

Three echocardiographic findings are the major criteria for the diagnosis of IE.

(i) vegetation,
(ii) Peri annular abscess;

(iii) new dehiscence of a valvular prosthesis.

Vegetation size and mobility is important.

If the vegetations are small or have already embolized, echocardiography can produce false-negative results in about 15% of cases.

Treatment for IE:

Surgical Importance:

        Antimicrobial therapy can offer a curative treatment in only 50% of patients.

        The surgical aim is valve repair, but most patients require valve replacement. Patients with IE and large vegetations, intracardiac abscess (9–14%), or persisting infection (9–11%) almost always need surge. The current IE perioperative mortality is 5–15%. The most frequent postoperative complications are persistent septic shock, coagulopathy, acute renal failure, stroke, refractory heart failure, and conduction abnormalities.

Conclusion:

        Epidemiology of IE makes the diagnosis a challenge, and traditional diagnostic criteria are insufficient. Despite modern medical and surgical therapy, IE is still associated with a high rate of complications and increased mortality. Early surgery is becoming more common and TOE should be used for all patients.