Prevention of Endocarditis

Antibiotic prophylaxis aims to reduce the incidence of infective endocarditis (IE).¹ A major shift in advice has emerged, culminating in new NICE guidance.² This challenges the efficacy of previous recommendations and to some extent the rationale for antibiotic prophylaxis. Measures to prevent IE need to go beyond antibiotic prophylaxis and the risks of antibiotic prophylaxis need to be considered. The new recommendations may prompt patient concern. Ultimately the recommendations should lead to safer, better preventive measures which are ultimately easier to follow. There may be some confusion until the recommendations are fully understood and accepted.

Infective endocarditis is a serious condition and often difficult to diagnose. This can be appreciated from the linked article on Infective Endocarditis.

Antibiotic prophylaxis for infective endocarditis has traditionally been thought to work at one of three steps in the pathogenic process:

• Killing the pathogen in the bloodstream before it can adhere to the heart valve.
• Preventing adherence of bacteria to the thrombus forming on the valve.
• Eradicating organisms that do attach to the thrombus.

However, as we shall see, the conventional wisdom of successive expert recommendations has been challenged by lack of evidence of efficacy for antibiotic prophylaxis.

• Guidelines for use of antibiotic prophylaxis of infective endocarditis have been developed often with international consensus.⁴ It should be remembered that:
  • They are unproven by randomised controlled trials.¹
  • Even when guidelines are followed appropriately they may fail to prevent infective endocarditis.³
  • The guidelines exist to guide and inform, but may occasionally be modified to fit particular circumstances.³
  • Recent guidelines by the British Society for Antimicrobial Chemotherapy⁵ and the American Heart Association have challenged existing dogma by highlighting the prevalence of bacteraemias that arise from everyday activities such as toothbrushing, the lack of association between episodes of IE and prior interventional procedures, and the lack of efficacy of antibiotic prophylaxis regimens.
• The scope for prevention is limited:
  • Only 15-20% of cases of infective endocarditis result from the bacteraemia produced by an invasive procedure.
  • Only half of patients developing infective endocarditis after invasive procedures were identified beforehand as candidates for antibiotic prophylaxis.
  • This means that only 10% of all cases of infective endocarditis can be prevented by prophylactic antibiotics.

Against this background NICE guidelines have recently been produced.² They have prompted a major shift in clinical practice.

These recommendations are described as 'a paradigm shift from current accepted practice'.² The guidance acknowledges that patients with pre-existing cardiac lesions are at risk of developing IE. However, NICE concluded that clinical and cost-effectiveness evidence supported the recommendation that at-risk patients undergoing interventional procedures should no longer be given antibiotic prophylaxis against IE. Further, NICE considers that there is evidence to suggest that current antibiotic prophylaxis regimens might result in a net loss of life. It should be emphasised that antibiotic therapy is still thought necessary 'to treat active or potential infections'.²

It is still useful to consider which patients are at greatest risk of IE. However the evidence does not support in practice a recommendation for antibiotic prophylaxis on such an assessment. These factors may still be used to identify patients with active infection requiring treatment.
Previous guidelines were devised empirically. A number of important factors were considered including:

• Identification of at-risk patients. Patients at high, moderate and low risk of infective endocarditis can be identified:
  • Highest risk patients include:
    • Those with all types of prosthetic valve
    • Previous infective endocarditis
    • Surgically produced systemic or pulmonary shunts
    • Congenital cyanotic heart disease
  • Moderate risk patients are:
    • Congenital cardiac conditions (other than cyanotic) but excluding isolated atrial septal defects (ASD) and surgical repairs of ASD or patent ductus arteriosus over 6 months ago
    • Bicuspid aortic valves
    • Acquired valve disease including rheumatic heart disease, mitral stenosis and calcific aortic stenosis
    • Hypertrophic cardiomyopathy
    • Mitral valve prolapse with regurgitation and with or without thickened leaflets
  • Low risk patients include:
    • Mitral valve prolapse without significant regurgitation
    • Implanted pacemakers, defibrillators and coronary stents
    • Innocent murmurs (except elderly patients where this may represent an at risk calcified leaflet)
• Different procedures carry different risk and type of bacteraemia (and in theory subsequent infective endocarditis):
  • High/moderate risk procedures include invasive respiratory tract manipulation (for example tonsillectomy and rigid bronchoscopy), gastrointestinal surgery, biliary surgery, urological surgery (including prostate surgery, cystoscopy and even urethral dilatation).¹
  • Low risk procedures not requiring prophylaxis include:
    • Most gynaecological procedures ranging from hysterectomy to insertion and removal of intrauterine devices where there is no infection
    • Vaginal deliveries and caesarean section
    • Cardiac catheterisations and angioplasties
    • Endoscopy with or without biopsy (note that ERPC with biliary obstruction, dilatation of oesophageal strictures, and injection of varices are moderate risk procedures)
• The perceived level of risk determined the appropriate antibiotic or combination of antibiotics used (including the appropriate time and dose).

Prophylaxis for dental procedures

Detailed prophylactic antibiotic regimens were recommended in the past.^1,4 However, even for high risk patients, prophylaxis for all dental procedures involving dento-gingival manipulation or endontics is no longer routinely recommended. Streptococci are in theory the most likely organisms. However, it has recently been concluded that there is no evidence to support the use of antibiotics to prevent endocarditis in dental procedures.¹ There may be reluctance to give up prophylaxis and definitive trials balancing risk and benefit are unlikely to be forthcoming. There may be concern in patients at high risk of endocarditis (previous endocarditis, cardiac valve replacements, surgical systemic or pulmonary shunts). Even the use of chlorhexidine mouthwashes is no longer recommended.

Endocarditis prophylaxis for non-dental procedures

This was considered the most important form of prophylaxis and a cautious approach was taken.¹ Enterococci, streptococci and staphylococci are the most prominent organisms. All patients at risk (high and medium) were recommended to have prophylaxis.¹ Different procedures were looked at to see what percentage of different procedures were associated with bacteraemia. Consideration was also given to anecdotal evidence about which procedures were associated with endocarditis.¹ This enabled possible high risk procedures (see above) to be identified. Routine prophylaxis is now no longer recommended and antibiotics would only be given to treat active infection (of whatever type) whilst awaiting (or with) microbiological advice.

Good oral hygiene is very important and good dental care should be facilitated. Patients with a cardiac anomaly putting them at risk of endocarditis (high and moderate risk patients above) should be referred for dental assessment. Any interventions should be performed at least 14 days before cardiac surgery to allow mucosal healing. If cardiac surgery is performed as an emergency before dental assessment can be made, the assessment should be made at the earliest opportunity after surgery. Elective dental procedures should be delayed for 3 months post-surgery.

General measures and health education have enormous potential to prevent infective endocarditis. For example:

• Education of patients to inform doctors and health care workers of any underlying diagnosis/IE risk.
• Since gingivitis is the commonest cause of spontaneous bacteraemia, meticulous oral hygiene is important. Similarly, attention to skin hygiene is important in prevention.
• Many cases of hospital-acquired infection can be prevented by better asepsis during handling and insertion of vascular catheters, and prompt removal if infected. Poor hospital hygiene has been blamed for the rise in MRSA.
• Needle-exchange programmes, education, and addiction treatment for drug-abusers.