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Infective Endocarditis

In This Article

Introduction

This is a condition caused by infection of the endocardium by bacteria, or rarely, fungus. It most commonly affects the heart valves (natural or prosthetic), but can occur anywhere along the lining of the heart or blood vessels.
It will most commonly occur at sites of previous damage, however, particularly virulent organisms (such as staphylococcus aureus and streptococcus pneumoniae) can infect previously normal areas of tissue; for example, Staph. Aureus will commonly infect the tricuspid valve in IV drug users.
 
In can present acutely or, more commonly, subacutely, where the symptoms may be more indolent and non-specific.
 
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Epidemiology

50% of all cases of infective endocarditis will occur on normal valves. This type of infection tends to follow and acute course.
50% of infections occur on abnormal tissue, and these infections will tend to follow a sub-acute course.
The incidence in the UK is 4-7 per 100 000, although this is higher in the developing world

  • The disease is rare before the age of 55 in the UK
    • 4-7 per 100 000 in general population
    • 15 per 100 000 in the over 55’s

Without treatment, the mortality is close to 100%!

 
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Risk Factors

Valvular damage

  • Previous Rheumatic heart disease (rare in the western world)
  • Age related valvular degeneration
  • Prosthetic valve (both mechanical and bioprostheses)

IV drug use

  • More chance of multiple organisms with IV drugs users. IV drug users are usually affected at the tri-cuspid valve, and the right side of the heart. Often the endocarditis is less clinically severe in IV drug users
 
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Pathophysiology

Endocardial damage leads to the formation of thrombi at the damaged site. The thrombus is made mainly of platelets and fibrin. Initially these thrombi are sterile, and are sometimes called ‘sterile vegetations’. In normal circumstances, they usually heal within 24 hours.
 
The endocardial damage tends to occur around damaged valves, as aberrant jets of blood around these valves cause increased shearing forces in the endocardium, leading to endocardial damage. Also, the valve cusps themselves are avascular, and thus normal immune responses in this region are impaired.
 
These thrombi (and therefore IE) tend to occur at sites of high hemodynamic pressure, due to the increased shearing forces in these areas. Valves are also more likely to become fibrosed in areas of high pressure. Infections are not common at areas of low pressure, and thus IS most commonly occurs on the left side of the heart.
 
Transient bacteraemia exists in all individuals at some time. Common sources of bacteria include oral fauna, and genitourinary tract lesions. Therefore, poor oral hygiene and UTI’s are also risk factors.
 
Bacteria are able to colonise the thrombi, leading to infective endocarditis.
 
So essentially you require two factors:
  1. The presence of organisms in the blood - Many things can cause this. Common mechanisms include poor dental hygiene, IV drug use, soft tissue infection, and iatrogenic causes (including dental treatment, cannulae, cardiac surgery, and pacemakers).
  2. Abnormal / unusual endocardial tissue (most often the valve cusps themselves)
 
Once a thrombus has been colonised by bacteria, we call it a ‘vegetation’. These can become large enough to form an obstruction, or they may also break off to form emboli.
The emboli can affect pretty much any organ in the body (i.e. anything with a blood supply), but commonly affect structures that are highly vascularised, e.g. CNS, lungs, spleen, kidneys, liver. Therefore, common complications include e.g. splenic infarcts, PE. In sub-acute IE in particular,
 
IE is particularly hard to treat with antibiotics, because the platelets and fibrin in the vegetation prevent antibiotic agent, and white blood cells from being in direct contact with the bacteria.
  • Aortic and mitral valves are more commonly affected – because these exist in a higher pressure system than the tricuspid and pulmonary valves.
  • Right sided infection is more common in drug users – although the mechanism for this is poorly understood.
 
Also note that there are many rare causatory organisms (such as Haemophillus types), and that 5-10% of cases of infective endocarditis will be culture negative – because the causatory organism will not be able to be grown on normal blood cultures. In such cases, previous antibiotic therapy may be a factor – and this will need to be elicited in the history.
 
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Signs and Symptoms

If the patient has a new murmur AND a fever – then it is endocarditis until proven otherwise
It can present as an acute infection, but more commonly presents sub-acutely with an insidious course. In this instance it is sometimes referred to as Sub-acute bacterial endocarditis (SBE)
 
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Acute Presentation

Fever + new heart murmur (90%)
Petechiae (50%)

  • These are red/purple spots of 1-2mm diameter. They often form at sites of trauma, and in this instance they will usually disappear within a couple of days. Extreme bouts of vomiting, coughing or crying can also produce them around the eyes. They may also be a sign of a low platelet count (thrombocytopaenia).
  • In children they also may occur as a result of viral infection
  • They can be a sign of malignancy
  • Basically – lots of things can cause them!
  • They are non-blanching and essentially caused by bleeding under the skin.

Cardiac / renal failure can develop rapidly (50-70%)

  • Haematuria secondary to renal failure present in about 70% of patients

Rigors
Night sweats
Splinter haemorrhages (10-20%)

  • Red lines that run vertically along the nails. A non-specific sign, often associated with rheumatologic conditions as well as IE. In the case of IE, they are caused by small emboli.

Nail fold infarcts (5-10%)
Roth spots (5%)
Embolic incidents

Malaise (90%)

 
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Sub-acute presentation

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