Infective Endocarditis


Although relatively uncommon, infective endocarditis ( IE ) is of great importance for several reasons:

At present this page merely covers a few aspects of diagnosis and prophylaxis. More information will follow. Note that we use the more general term "Infective Endocarditis" rather than the quaint, old- fashioned "Subacute bacterial endocarditis".

Diagnosis of Infective Endocarditis

Infective endocarditis should be suspected in anyone who has a heart valve lesion (as indicated by a significant murmur) and fever. The fever is not usually marked. Rarely, it may be absent - more often, it is missed. Also note that murmurs may be absent in IV drug abusers or others with right-sided infective endocarditis, so in these patients one must be even more alert! This is particularly relevant to patients in ICU, where IE is often missed until florid.

Thorough clinical assessment is vital. Apart from the above two sentinel findings, one should particularly look for:

"Classical" features of IE such as clubbing, Osler's nodes (tender lesions on the pulps of the fingers), Roth's spots (fundal haemorrhages with whitish centers), and splenomegaly are relatively infrequent findings, and their absence means little. Subungual splinter haemorrhages are unfortunately rather common in normal individuals, where they are usually related to trauma - those seen with IE are said to be more proximally located and less obviously "traumatic". Vague musculoskeletal complaints are common - these include arthralgias in about a sixth of patients, and myalgias. As a consequence of severe valve involvement patients are often in heart failure. Another much-neglected finding is central nervous system disease, with mycotic aneurysms of the cerebral circulation a fairly frequent occurrence (often presenting when they leak), as well as embolic stroke.

The cornerstone of diagnosis is growing the offending organism on blood culture. This is vital. Adequate volumes of blood must be obtained (for example 3 x 20ml). There is little evidence that taking these cultures at different times or different sites is better than taking them at the same time from one site, but pickup is probably improved by taking samples from the patient while his/her temperature is on the rise! DO NOT start antibiotics before adequate cultures have been taken! One can even make a case for waiting for cuture results and then reculturing if no organism is found, provided the clinical condition of the patient justifies this!? Cultures should be taken by direct needle stab of a peripheral vein, and not from venous or arterial lines.

If cultures are negative:

Echocardiography is invaluable in detecting the presence of vegetations on the valves, as well as providing evidence about the nature and severity of the valve lesions. As important as defining the valvular vegetations is examination for perivalvular infection. If there is a strong clinical suspicion of infective endocarditis, trans-thoracic echo cannot rule out IE: a trans-oesophageal echocardiogram should be obtained.

The Duke criteria have supplanted previous diagnostic criteria:

Major Criteria are:

Minor criteria include:

{ It's probably worthwhile looking at the original article where this rather complex set of criteria was proposed. See [Durack D Lukes A Bright D, Am J Med Mar 1994 (96) 211-9pp]. Note that a "persistently positive blood culture" is where two cultures over 12 hours apart contain the same micro- organism, OR all of 3 OR the majority of 4(+) cultures taken at least an hour apart contain the organism. This all seems rather complex, doesn't it? Very Americain}.

Causative Organisms

These vary, depending on:

Common organisms include:

Less common are gram negative bacilli, Candida spp., Corynebacteria, HACEK group organisms {Haemophilus aphrophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella, Kingella} and so on.

Prophylaxis of Infective Endocarditis

This is still a controversial topic, with many conflicting sets of recommendations. We can however extract a few general rules:

  1. Although most infective endocarditis is NOT related to procedures performed by doctors/dentists, prophylaxis is said by some over 50% effective when properly administered. (But see Note 1). If not given to patients at substantial risk of endocarditis, or incorrectly administered, endocarditis may occur, and this may be difficult do defend medico-legally;
  2. Dental procedures may be the most important risk factor. Bacteraemia occurs with periodontal work, scaling etc. (Even when you bite hard on your teeth). Maintenance of good dental hygiene in patients at risk is thus very important.
  3. Administration of prophylactic antibiotics is not benign: the risk of adverse reactions and cost should be weighed up against the risk of endocarditis. Risk varies widely, depending on the patient.
High risk cases include: The incidence of IE in patients after surgical repair of congenital defects is explored in a JAMA article from 1998 [Morris &c, JAMA Feb 1998 (279.8) 599-603pp] The bottom line is that it is common, for example over a 25 year period, 13.3% of those who had surgery for valvular aortic stenosis developed IE, with lesser incidences for Fallot's, VSD, coarctation and primum ASD. IE was NOT however seen in children after repair of secundum ASD, PDA or pulmonic stenosis!

Patients with valvular dysfunction, other congenital cardiac malformations, mitral valve prolapse WITH mitral regurgitation, and possibly those with hypertrophic cardiomyopathy present a lower risk, but should still generally receive prophylaxis.

Prophylaxis should be administered for:

Antibiotics can be given either orally or parenterally. As with all prophylaxis, the antibiotic should be in the blood when the bug hits the blood. We therefore generally give these agents:

Table VII in the article by Stamboulian & Carbone neatly summarises American Heart Association and European recommendations. Briefly:

Procedure Usual Rx Penicillin Allergy
Dental, Upper respiratory tract amoxicillin 2g PO, OR
ampicillin IV / IM
Replace ampicillin with ONE of:
clindamycin 600mg PO / IV
clarithromycin 500mg PO
azithromycin 500mg PO
? roxithromycin 300mg PO
Genitourinary ampicillin 2g IV / IM
AND gentamicin 1.5mg/kg
(maximum 120mg)
Replace ampicillin with:
Vancomycin 1g IV 1 hour before procedure,
OR teicoplanin 400mg IV.
STILL give the gentamicin.
In addition, some authorities recommend a a follow-up dose of 1g amoxicillin or ampicillin, SIX HOURS after the genitourinary procedure!

Paediatric doses are: ampicillin 50mg/kg, azithromycin/clarithromycin 15mg/kg, clindamycin 20mg/kg and teicoplanin 6mg/kg.

In other words, for dental and URT procedures, give ampicillin or amoxicillin, unless penicillin allergic. For genitourinary procedures, give ampicillin parenterally and add aminoglycoside. With penicillin allergy, give clindamycin or one of a variety of other agents for the dental work, or replace the penicillin with vancomycin for genitourinary work. The possible second dose of ampi/amoxicillin seems peculiar to us.

Note that the above are guidelines . Therapy may need to be tailored to the special patient. Physicians performing lower gastrointestinal procedures should probably follow the guidelines for genitourinary procedures, and many would argue that this holds good for upper GIT procedures as well.

Little appears to have been written about prophylaxis in patients who have already been in hospital for some length of time. This is a pity, as such patients will most likely be colonised by the local (often multiresistant) flora, so more aggressive prophylaxis might be indicated.

Why not use the URT regimen with upper GIT endoscopy, unless there is severe disease with probable colonisation by more aggressive organisms? When in doubt, best stick to the "rules". Several surveys have shown low compliance by doctors with established guidelines. Do NOT trust your patient to take the antibiotics 1 hour before the procedure if you prescribe an oral regimen. Make sure they take it! Patients should also ideally carry an "endocarditis risk" card! There is little/no evidence to support prophylaxis for insertion of tympanostomy tubes, endotracheal tube insertion, flexible bronchoscopy, cardiac catheterisation, urethral catheterisation in the absence of infection, therapeutic abortion, laparoscopy and sterilisation.

Further notes:


Note 1
Thanks to Steve Shanahan for the following references (2006), which cast doubt on the value of antibiotic prophylaxis for infective endocarditis in some circumstances:
Older references

  1. Drugs Nov 1997 54(5) 730-44pp
    Stamboulian D & Carbone E
    A fairly good recent article on recognition, management and prophylaxis. Much of the above is based on this article.

  2. Br J Hosp Med Oct 1995 54(7) 341-7pp
    Prasad A & Fraser A
    Notes on British recommendations.

  3. JAMA 1997 277(22) 1794-801pp
    Dajani A et al
    Contains the American Heart Association recommendations.

  4. Eur Heart J 1995 16SB 126-31pp
    Leport C et al
    This is a European Consensus report from the International Society for Chemotherapy.

  5. N Engl J Med Jan 1995 332(1) 38-44pp
    Durack D
    Yet another review on the prevention of IE, from the UK.

  6. Lancet 1990 335 88-9
    Simmons N
    These are the older British recommendations. Fairly straightforward, easy to use, and things haven't really changed that much (although now Erythromycin is less popular).