Internal Medicine Boards Disease Profile: Infective Endocarditis
Everything you need to know about Infective Endocarditis, as relevant for the Internal Medicine boards, shelf exam and USMLE Step 3
Infective endocarditis (IE) is a condition in which bacteria or fungus attach to the inside of the endocardial surface of the heart. When this attachment is with a heart valve, it is referred to as a vegetation. Initially streptococcal infections used to be the predominant cause of IE; however, staph infections are now considered the main etiology of native and prosthetic valves. Despite advancements in the diagnosis and therapy for endocarditis, mortality rate in the hospital remains as high as 20 percent
MAIN CAUSES
The main organisms that cause IE include Streptococcus pyogenes, Streptococcus bovis (if this organism is present, colonoscopy must be performed to rule out colon cancer), coagulase negative staph (e.g. Staph epidermidis), Staph aureus, Enterococcus faecalis, fungal infections, and HACEK organisms. HACEK organisms stand for Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella. HACEK organisms should be suspected if the blood cultures are negative but there is high concern IE based on history, physical, and risk factors.
RISK FACTORS
- Age greater than 60: more than 50 percent of the cases of IE occur in individuals greater than 60
- Males greater than Females in a ratio of 9:1
- Being an IV drug user predisposes individuals to bloodstream infections that can disseminate and cause valve vegetation
- Poor dentition or dental infections
- Valvular heart disease
- Congenital heart disease
- Prosthetic heart valve
- History of Infective Endocarditis
- Patients who have chronic intravenous devices
- Chronic hemodialysis
- Patients infected with HIV
DIAGNOSIS
IE should be suspected in any individual with the above risk factors, new or increasing intensity murmur and the signs or symptoms of infection or bacteremia. It is important to obtain at least three sets of blood cultures from three different venipuncture sites. These should be obtained before antibiotics are administered to decrease the chances of false negative results.
The mainstay of diagnosis remains echocardiography. Transthoracic echocardiography has less than 50-80% sensitivity for detecting endocardial involvement. Transesophageal echocardiography, on the other hand, has a very high sensitivity and specificity for diagnosing IE. It is also useful in determining if a patient has complications of endocarditis (like abscess or fistula formation).
CLINICAL FINDINGS
As mentioned above, having a new onset murmur or an increase in intensity in a previous murmur with signs of infection or bacteremia provides a major clue clinically that a patient has infective endocarditis. Other clinical findings that suggest infective endocarditis are weight loss, splenomegaly, and skin lesions. Some of the more common skin lesions associated with IE are Osler Nodes and Janeway Lesions.
Osler nodes are painful nodules that are present on the tips of the fingers and toes. Janeway lesions, on the other hand, are small, erythematous macules or nodules that are painless and can be found on the palms and soles. Roth spots (retinal hemorrhages) are an example of a fundoscopic finding that can be seen in patients with IE.
TREATMENT
Treatment for IE should be aimed at the specific organism that is growing in the blood as 90 percent of the patients who have IE will have positive blood cultures. In addition, duration of treatment depends on whether the patient has native valve endocarditis or prosthetic valve endocarditis. With native valve endocarditis, the duration of treatment is usually four weeks; whereas, for prosthetic valve endocarditis, the duration of treatment is usually six weeks. Using IV antibiotics are preferred over PO antibiotics when treating for IE.
If the patient has streptococcus isolated from the blood, mainstay of treatment is with penicillin combined with gentamycin for 4 weeks. Another alternative is IV Ceftriaxone combined with gentamycin. Patients who are allergic to penicillin can be treated with Vancomycin.
Patients with staph infections (MSSA) and native valve endocarditis can be treated with Nafcillin or Oxacillin with Gentamycin for about 4 weeks. If the patient has MRSA, Vancomycin is substituted for Nafcillin or Oxacillin.
Patients who have prosthetic valves and staph infections should be treated with Oxacillin or Nafcillin +Gentamycin +Rifampin X 6 weeks if MSSA. If the patient has MRSA infection, then Vancomycin should be substituted but Gentamycin and Rifampin should be used for 6 weeks.
If a patient has HACEK infection, Ceftriaxone 2 grams (IV or IM) is recommended for 4 weeks.
INDICATIONS FOR SURGERY IN INFECTIVE ENDOCARDITIS
- Severe Congestive Heart Failure
- Positive blood cultures even after seven days of aggressive antibiotics treatment
- Persistent embolic events
- Valve abscess formation
- Fungal infection
- Vegetations greater than 1 cm in diameter
You can see all the previous ABIM Exam disease of the week blog posts at the Knowmedge Blog. You can find also additional topics and questions directly from the Knowmedge Internal Medicine ABIM Board Exam Review Questions QVault.
