Infective Endocarditis (IE) carries with it a high risk of morbidity and mortality. Rapid diagnoses, effective treatment, and  prompt recognition of complications are essential to a good outcome for the patient.

   The incidence of IE continues to rise.  There are currently 15,000 to 20,000 newly reported cases of IE a year, and it is now the fourth leading cause of life-threatening infectious disease.

   The most recent diagnostic strategy for IE was proposed by Durack and colleagues from Duke University in 1994 (the Duke criteria).  

     The Duke criteria stratify patients suspected of having IE into 3 categories:

                 -  definite cases identified clinically (echo) or pathologically (IE proven at surgery or autopsy by finding

                        vegetation)

                 -  possible cases - not meeting the criteria for definite IE

                 -  rejected cases - rapid resolution with either no treatment or short term antibiotic therapy, or a firm 

                        alternative diagnosis.

To diagnose IE the Duke criteria requires the presence of: 2 major criteria

                                                                                       1 major criteria and 3 minor criteria

                                                                                       5 minor criteria

   Duke major and minor criteria:

              Major criteria: IE documented by data obtained at the time of surgery or autopsy (finding vegetation) or via well-defined blood culture and electrocardiographic data.

              Minor criteria: Intermittent bacteremia or fungemia, fever, major embolic events, non-embolic vascular phenomena, underlying valvular disease or IVDA (intravenous drug abuse) and echocardiographic abnormalities that fall short of typical valvular vegetation, abscesses, or dehiscence (cut or wound).

ELECTROCARDIOGRAPHY

    Electrocardiography plays a very important role in the diagnoses and management of IE. Vegetation, abscesses, new prosthetic-valve dehiscence, or new regurgitation are all strong indications of IE used with other clinical findings. 

    TTE (transthoracic echocardiography) is rapid, and noninvasive and the overall detection of vegetation is 60%. TTE alone cannot exclude several important aspects of IE, including infection on prosthetic valves, periannular abscess, leaflet perforation and fistulae (an abnormal or surgically made passage).  A negative TTE of even the highest quality should not rule out IE in cases where it is strongly suspected.

    TEE (transesophageal echocardiography can also be done if the clinical picture changes or there is no improvement with therapy, or complications are suspected.  TEE is safe in experienced hands and has a high sensitivity of detecting vegetation. (88% to 100%). A negative TEE does not have enough diagnostic accuracy to rule out vegetative IE.  A negative TEE may be the cause of too small vegetation, embolization of vegetation, or inadequate view to detect small abscesses.  When suspicion of IE is high, a TEE may be redone in 7 to 10 days, which may show previously undetected vegetation or abscesses.

BLOOD TESTING

   Positive blood cultures are a major criterion for IE and a key in identifying the etiologic (science of the cause of the disease) agent and its anti-microbial susceptibility. Continuous bacteremia and a high frequency of positive blood culture are typical of this infections.

   Some cultures come back negative in patients with IE diagnosed by strict diagnostic criteria. Failure to culture the bacteria may be the result from:   inadequate microbiological techniques,  an infection with highly fastidious (fussy) bacteria or nonbacterial microorganisms,  and most important from the administration of anti-microbial agents before cultures are obtained.

   Blood from patients suspected of having IE should be cultured in 3 sets (each set equals 1 aerobic plus 1 anaerobic bottle).  The blood should be diluted at least 1:5 into the broth media, and the lab should be advised that the clinical diagnosis is IE.  When all blood cultures remain negative after 48-72 hours, the lab should incubate these cultures for a prolonged period of 2-3 weeks, microscopically examine and acridine orange-stained aliquot from all bottles (even in absence of growth), and on day 7 day 14, and at the end of incubation period, blindly subculture an aliquot on chocolate agar for further incubation (3-4 weeks) in an atmosphere of increased carbon  dioxide (candle jar).  These steps may facilitate recovery of bacteria.

    Administration of anti-microbial agents to patients with IE before blood cultures, reduces the recovery of bacteria by 35-40%.   IE patients with negative blood cultures after only a few days on antibiotic therapy may have positive cultures after a few days without antibiotics.  The blood cultures of patients who received longer courses oh high dose bactericidal anti-microbials may remain negative for weeks.  Therapy should be delayed if patient does not have a toxic appearance, or no clinical or echocardiographic evidence of sever or progressive valve regurgitation or congestive heart failure.  If the blood culture comes back negative, a delay of 2-4 days allows for additional blood cultures to be obtained without the effect of the antibiotics in the blood.

   In addition to blood cultures and serological essays, culture of valve tissue or vegetation may also reveal the causative organism.

COMPLICATIONS OF IE

   Congestive heart failure (CHF) is a main concern.  This can develop from perforation of the valve leaflet, rupture of infected mitral chordae, valve obstruction from bulky vegetation, or sudden intra-cardiac shunts from fistulous tracts or prosthetic dehiscence.   CHF may also develop as a progressive worsening of valvular insufficiency (regurgitation)  and ventricular dysfunction.

   Embolization is another complication, occurring in 22%-50% of cases of IE.  Emboli often involve major arterial beds, including lungs, coronary arteries, spleen, bowel, and extremities.  Emboli can occur before diagnosis, during treatment, or after the treatment is done, though most emboli occur in the first 2-4 weeks of anti-microbial therapy.

Prediction of who is at the greatest risk  of emboli has proven to be very difficult. It does appear the mitral vegetation has a higher risk of embolic (25%) than aortic vegetation (10%).