Infective Endocarditis

The transcript of a MedTutor online class on infective endocarditis

Q1. How do bacteria and other organisms cause infective endocarditis?

Student: Infective endocarditis begins with a minor injury of the endothelium, which forms a microthrombi that serves as a focus for bacteria or fungi to colonize. Certain bacteria also have the propensity to lodge and adhere to the endothelium wall… like Streptococci sp. WIth that being said, damage to the endothelium is more common in valves that are structurally abnormal or where there is turbulent flow (i.e. the mitral or aortic valve).

Student: Infectiveendocarditis occurs when there is a turbulence or trauma to the endothelial surface (more commonly valves) of the heart. When there is bacteremia, it will then seed the bacteria to the area invading the endothelial causing tissue destruction forming vegetations which includes bacteria and platelet/fibrin.

Student: Acute endocarditis occurs on normal valve in the presence of bacteremia in patients at risk e.g those with debilitating illness, immunocompromised, chronic alcoholics. Toxic agents cause valvular damage predisposing the valves to thrombus formation and infection. Subacute endocarditis often occurs on abnormal valves such as those with calcific lesions, rheumatic heart disease, etc. Endothelial damage due to turbulent flow or trauma results in foci of sterile platelet and fibrin thrombi which are colonized by circulating bacteria

Student: Bacteraemia delivers the offending organisms to the endothelial surface of the valves (previously damaged by trauma or turbulence, and have sterile fibrin-platelet vegetations). The organisms then adhere and invade the valvular leaflets.

Moderator: For Infective endocarditis (IE) to occur, normally there needs to be either a damaged heart valve or damage to the endocardium through trauma or turbulence. When this is present, sterile platelet-thrombi settle on these surfaces. IE results when bacteremia seeds these platelet-thrombi. In intravenous drug users, IE can occur without preexisting damage to the heart. The explanation here, I think, is that virulent bacteria when present in large numbers are capable of seeding the endocardium of normal hearts.


Q2. In what clinical situation will you suspect infective endocarditis? I am not asking about the signs and symptoms of IE but rather about the clinical situation where you should think of IE and then look for the diagnostic clinical signs.

Student: IE should be suspected in a febrile patient with underlying rheumatic heart disease, congenital heart disease or prosthetic heart valves as well as in those who have a history of self-injecting intravenous drugs and those with invasive procedures (e.g. cardiac catheterization) done recently. A previous history of infective endocarditis should be viewed as a significant risk factor in a febrile patient.

Moderator: IE should be suspected in two clinical situations: Whenever a patient has fever and a cardiac murmur and Whenever the diagnosis is PUO.
The diagnosis of IE becomes more likely when there are clinical clues like spleenomegaly, features of vasculitis and microemboli like splinter hemorrhages, Osler's nodes and microscopic hematuria. Confirm the diagnosis by doing blood cultures (three blood cultures from different sites within one hour) and echocardiography.


Q3. What are the situations where blood cultures are likely to be reported as 'negative' in the presence of IE?

Student: Prior use of antibiotics is the most common cause of false-negative blood culture results. Prior antibiotic therapy can suppress bacterial growth within the vegetation, but it is not sufficient to completely eliminate the valvular infection. Culture-negative IE can have non-infectious causes (e.g. vasculitis), or may be caused by fastidious organisms or fungi. Other causes include blood volume that is inadequate to produce a blood to broth ratio of 1:10.

Student: The blood culture are likely to be negative in patient who is already started with antibiotic. Blood culture should be taken prior to any antibiotic treatment. Another reason that the blood culture can be negative is that the patient has Libman-Sacks endocarditis. Libman-Sacks endocarditis is a non-bacterial endocarditis that is associated with SLE.

Student: Since patients with IE may have PUO, they may have previous antibiotic use, which cause negative blood cultures. Infective endocarditis of non-infective cause e.g. vasculitis may also have negative blood cultures. Also, it may occur in those caused by bacteria like Chlamydia, Coxiella, Abiotrophia, Legionella and HACEK group, and fungi like Candida, Histoplasma and Aspergillus.

Student: Blood cultures are likely to be negative if the patient has received prior antibiotic treatment; the antibiotics inhibit bacteremia but does not affect the vegetations. Endocarditis due to fungi such as Aspergillus and Candida and also the …HACEK group of organisms may also lead to a negative result as their slow and fastidious growth makes them difficult to be cultured. Other organisms such as Coxiella burnetii, Bartonella sp may also contribute to negative cultures. With negative cultures non-bacterial thrombotic endocarditis such as Libmann-Sacks endocarditis should be considered as well.

Moderator: The answer by the last student has explained it very well


Q4. Imagine yourself faced with a situation where you strongly suspect IE in a young man of 25 years age. You have sent the blood for cultures and will need to wait for 72 hours before receiving the results. Will you start antibiotics before seeing the culture reports? Or will you wait till the culture reports are in your hand?

Student: In that situation, the patient should be started on empirical antibiotic therapy. Knowing that Staphylococcus being the most common organism causing infective endocarditis, penicillin should be given preferably via intravenous route.

Moderator: You can start antibiotics empirically when the clinical suspicion is very strong and before culture reports are received. The choice of empirical antibiotics will depend on what organism you suspect to be the cause of the IE. If you are not sure, it is best to cover for these three organisms: Staphylococci and Streptococci and Enterococci fecalis. The best choice will be the combination of a beta lactamase resistant penicillin (Cloxacillin or better still, Nafcillin) plus Gentamycin. For those who are sensitive to penicillin, Vancomycin is used. If you are quite sure that the organism is not Staphylococci, then the combination of Benzylpenicillin and Gentamycin is adequate. The antibiotics can be appropriately changed after culture reports are obtained. If the blood culture does not grow any organism, you will have to use clinical parameters to guide you as to whether to continue these same antibiotics or not. When you suspect that, because of a negative culture report, the organisms may belong to the HACEK group of bacteria, it is better to change from penicillin to Ceftriaxone.


Q5. A patient with a known valvular heart disease is scheduled for a surgical procedure. Does this patient need prophylactic antibiotics before the surgical procedure to prevent IE? Will the type of surgical procedure influence the decision to give prophylactic antibiotics?

Student: Previous guidelines from the American Heart Association divided patients into high, moderate and low risk groups, and prophylaxis was recommended for the high and moderate-risk groups. Following those guidelines, this patient would have bee…n at moderate risk and would require antibiotics. However in the 2007 AHA guidelines, prophylaxis is only recommended for conditions with the highest risk of adverse outcome from endocarditis, i.e. a history of previous IE, prosthetic valves or material used in valve repair, cardiac transplant patients who develop valvulopathy and certain types of congenital heart disease. This means that this patient does not require IE prophylaxis.
In patients whom prophylaxis is recommended, the type of procedure should be accounted for as not all procedures will require prophylaxis. Invasive procedures which involve oral mucosa and respiratory tissues will require prophylaxis, whereas antibiotics are no longer recommended for gastrointestinal or genitourinary procedures.

Student: Prophylaxis antibiotic in the prevention of IE in patient with valvular heart diseases was previously recommended for all dental, GI and GU procedures. This is base on the risk of bacterimia in these procedures. Dental procedure has high ri…sk of streptococci bacterimia. GI and GU procedures has high risk of enterococci bacterimia. Thus it has been many years that antibiotic prophylaxis was given in these procedures.

The recent guide lines by AHA in year 2007 recommended that antibiotics prophylaxis for any dental procedure was only recommended in patient with highest risk of adverse outcome from IE. These conditions include 1) prosthetic heart valve, 2)previous IE, 3) congenital heart disease such as unrepaired CHD, repaired CHD with residual defect, and first 6 months following repair of CHD, 4) cardiac transplant patient who developed cardiac valvulopathy. This recommendations are based on evidence that daily dental activity has higher risk of developing IE, antibiotic prophylaxis was not able to prevent IE even if it is effective. Antibiotic prophylaxis is also recommended in respiratory, cardiac, skin and MSK procedure in patient with averse outcome from IE. In GI and GU procedures, antibiotic prophylaxis is no longer recommended.

Student: As mentioned by both Wen Chung and Su Ping, prophylactic antibiotics in the prevention of IE in patients with valvular heart disease is no longer universal. It is only appropriate in high-risk patients as the two previous commentators have rightfully pointed out. I have also noted an 'addendum of sorts' in the AHA guidelines which mentioned that elderly patients (commonly afflicted with calcific valvular heart disease) MAY also require prophylactic antibiotics as this conditions are risk factors contributing to IE in the geriatric population… however the AHA have yet to release an official statement/opinion on the matter. I think it's interesting that gingivitis (easily preventable by good oral hygiene habits) is the most common cause of spontaneous bacteraemia which may lead to IE!

Moderator: The answer to this question, based on current guidelines is: No, this patient does not need antibiotic prophylaxis for IE. And, the answer to the second question is: The type of surgical procedure will not influence this decision. However there is something new in the 2008 guidelines from NICE (National Institute of Clinical Excellence) UK that we need to be aware of. This tells us that antibiotic prophylaxis for IE should be given when the surgical procedure is in an area that is already infected.
The 2008 guidelines from NICE also differ from the 2007 American Heart Association guidelines in that the NICE guidelines DO NOT recommend antibiotic prophylaxis even in patients with prosthetic heart valves or a previous history of IE. You can see the summary of these guidelines
in this article

Quote from these guidelines: Adults and children with structural cardiac defects at risk of developing infective endocarditis. Healthcare professionals should regard people with the following cardiac conditions as being at risk of developing infective endocarditis:
1. acquired valvular heart disease with stenosis or regurgitation
2. valve replacement
3. structural congenital heart disease, including surgically corrected or palliated structural conditions, but excluding isolated atrial septal defect, fully repaired ventricular septal defect or fully repaired patent ductus arteriosus, and closure devices that are judged to be endothelialised
4. previous infective endocarditis
5. hypertrophic cardiomyopathy.

Antibiotic prophylaxis against infective endocarditis is not recommended:

1. for people undergoing dental procedures
2. for people undergoing non-dental procedures at the following sites:
a. upper and lower gastrointestinal tract
b. genitourinary tract; this includes urological, gynaecological and obstetric procedures, and childbirth
c. upper and lower respiratory tract; this includes ear, nose and throat procedures and bronchoscopy.

Any episodes of infection in people at risk of infective endocarditis should be investigated and treated promptly to reduce the risk of endocarditis developing. If a person at risk of infective endocarditis is scheduled to undergo a gastrointestinal or genitourinary procedure at a site where there is a suspected infection, the person should receive an antibiotic that covers organisms that can cause infective endocarditis.

As you can see, the practice of Medicine keeps changing, and while we need to be aware of all that is recommended and developing, we need to use our judgement on what is best for our patient. When faced with new information, just remember this: Be not the first by whom the new is tried, nor the last to leave the old aside. And finally, there are two types of antibiotic prophylaxis for patients with rheumatic heart disease. One is the prophylaxis for IE which was discussed above. The other is prophylaxis against rheumatic fever which is the use of penicillin to prevent streptococcal infections. Please understand that antibiotic prophylaxis for rheumatic fever is still recommended for those with Rheumatic heart disease (with certain exceptions).

Student: I was wondering about endocarditis from viral infection, which some journals have mentioned that it has been documented in certain articles (which I failed to access). My question is: is it possible to get endocarditis from viral infection?

Moderator: Viral endocarditis? Hmm. Not sure whether viruses can cause IE

THE END

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