Infective Endocarditis
Last updated 15th May 2019 - Tom Heaton
Endocarditis refers to inflammation of the endocardium, the inner lining of the heart.
It is most commonly caused by infection, usually bacterial.
There are other causes which won’t be focused on much here.
It is the valves of the heart which are most commonly affected.
This is a good quick introductory video from the Osmosis team: https://www.youtube.com/watch?v=CdTCdHK77Zw
It is most commonly caused by infection, usually bacterial.
There are other causes which won’t be focused on much here.
It is the valves of the heart which are most commonly affected.
This is a good quick introductory video from the Osmosis team: https://www.youtube.com/watch?v=CdTCdHK77Zw
Pathophysiology
The process starts with the development of a non-infective thrombus formation prior to the infective component.
This formation occurs at locations in the heart where there is low pressure.
This is usually at the valves because of the venturi effect (the energy is in the form of kinetic energy rather than potential energy due to the narrowing).
This process can be acute or subacute in onset.
As can therefore be well appreciate, there are a number of conditions that will promote this environment and so increase the risk of IE.
Risk factors include
Structural:
However, some structural heart disease does not impart an increased risk:
The valves that are most commonly involved, in descending order are:
Right sided IE only makes up about 10% of cases.
The infection results in tissue destruction and the formation of vegetations.
Whilst the problem is related to the heart, the location results in significant haematological exposure and so systemic effects.
This formation occurs at locations in the heart where there is low pressure.
This is usually at the valves because of the venturi effect (the energy is in the form of kinetic energy rather than potential energy due to the narrowing).
This process can be acute or subacute in onset.
As can therefore be well appreciate, there are a number of conditions that will promote this environment and so increase the risk of IE.
Risk factors include
Structural:
- Valvular heart disease
- Valve replacement
- Previous IE
- Hypertrophic cardiomyopathy
- Structural congenital heart disease
- IVDU
- Invasive procedures e.g. vascular, dental
- HIV
However, some structural heart disease does not impart an increased risk:
- Isolate ASD
- Fully repaired VSD
- Fully repaired PDA
- Endothelialised closure devices
The valves that are most commonly involved, in descending order are:
- Mitral
- Aortic
- Tricuspid
- Pulmonary (rare)
Right sided IE only makes up about 10% of cases.
The infection results in tissue destruction and the formation of vegetations.
Whilst the problem is related to the heart, the location results in significant haematological exposure and so systemic effects.
Pathogens
The most common organisms are:
There may also be a fungal pathogen (usually candida or aspergillus species).
Staph. Aureus is the most common cause overall and has a high mortality rate.
It is particularly related to IVDU and prosthetic valves.
Coagulase negative Staph. causes a subacute disease similar to Strep. viridans.
Strep. viridans is another common pathogen, usually causing a subacute picture.
Many of the other strep. pathogens cause quite an acute and severe clinical picture.
Group A, C, and G are associated with a high mortality.
The HACEK group are gram negatives with a slowly progressing picture but which are actually a fairly rare cause of IE.
There are a number of rarer organisms that may cause blood culture negative IE:
- Staph. Aureus
- Coagulase negative Staph.
- Streptococci
- Viridans
- Intermedius
- Group A, B, C, D, G
- Viridans
- Pseudomonas
- Enterococci
- HACEK organisms:
- Haemophilus - parainfluenzae, paraphrophilus
- Actinobacillus actinomycetemcomitans
- Cardiobacterium hominis
- Eikenella corrodens
- Kingella kingae
There may also be a fungal pathogen (usually candida or aspergillus species).
Staph. Aureus is the most common cause overall and has a high mortality rate.
It is particularly related to IVDU and prosthetic valves.
Coagulase negative Staph. causes a subacute disease similar to Strep. viridans.
Strep. viridans is another common pathogen, usually causing a subacute picture.
Many of the other strep. pathogens cause quite an acute and severe clinical picture.
Group A, C, and G are associated with a high mortality.
The HACEK group are gram negatives with a slowly progressing picture but which are actually a fairly rare cause of IE.
There are a number of rarer organisms that may cause blood culture negative IE:
- Coxiella
- Legionella
- Chlamydia
- Brucella
- Bartonella
Presentation
This can be highly variable and it is recognised that a high degree of suspicion is often needed to detect and diagnose it.
The trajectory can be very acute, such as from a septic picture or rapid valvular compromise, through to a slower onset of more general systemic disturbance.
In general, the effect of the disease can be broken down to:
Systemic features
These are very common.
A severe septic shock picture may also occur.
Localised Valvular
Embolic Phenomenon
The trajectory can be very acute, such as from a septic picture or rapid valvular compromise, through to a slower onset of more general systemic disturbance.
In general, the effect of the disease can be broken down to:
- Systemic inflammatory/immune
- Localised valvular
- Embolic phenomenon
Systemic features
These are very common.
- Fever
- Malaise
- Poor appetite
- Weight loss
- Night sweats
A severe septic shock picture may also occur.
Localised Valvular
- Murmur
- Congestive cardiac failure
Embolic Phenomenon
- Stroke
- Septic PE
- Other end organ infarction e.g. spleen
Examination
There are a number of clinical findings that can arise from IE that are worth knowing.
However, it is important to bear in mind that these features are fairly rare.
Soft tissue
CVS
Abdo/renal
CNS
A good mnemonic for remembering the features is FROM JANE:
However, it is important to bear in mind that these features are fairly rare.
Soft tissue
- Osler’s nodes - painful, purple/red nodules (oww! for Osler)
- Janeway’s lesions - painless macular lesions, usual thenar or hypothenar eminence
- Roth spots - retinal haemorrhages
- Splinter haemorrhages - nail bed haemorrhages
- Petechiae e.g. conjunctivae, chest wall
- Arthritis
- Rash
CVS
- Murmur
- Very common finding
- Aortic regurgitation most common
Abdo/renal
- Splenomegaly
- Haematuria - glomerulonephritis
CNS
- Stroke
A good mnemonic for remembering the features is FROM JANE:
- Fever
- Roth spots
- Osler nodes
- Murmur
- Janeway lesions
- Anaemia
- Nail bed haemorrhages
- Emboli
Investigation
Part of these may be part of a general investigative process whilst others may be more specifically directed at confirming endocarditis as a diagnosis.
Bloods
ECG
Changes may include:
Blood cultures
These are a key part of the diagnostic criteria.
As such, a careful approach to culture should be taken:
Echo
Transthoracic echo (TTE) is an important initial investigation and should be undertaken with 24h.
It has a sensitivity of about 60%.
Transoesophageal echo (TOE) is more sensitive (90-99%) and with a 90% specificity and so should be undertaken in the case of an inconclusive or negative TTE.
In cases of high clinical suspicion but negative echo, a repeat exam should be undertaken after a week.
Echo findings of IE may include:
Bloods
- FBC - may show anaemia, raised WBC
- U&E
- CRP
ECG
Changes may include:
- Widened PR
- T wave inversion
- P mitrale
Blood cultures
These are a key part of the diagnostic criteria.
As such, a careful approach to culture should be taken:
- Meticulous ANTT to avoid contamination
- Before antibiotic administration when clinically able (i.e. stable enough)
- Spaced in time - 3 sets with 6 hour gaps
- In severely ill patients this can be reduced to 2 separate sets within an hour.
Echo
Transthoracic echo (TTE) is an important initial investigation and should be undertaken with 24h.
It has a sensitivity of about 60%.
Transoesophageal echo (TOE) is more sensitive (90-99%) and with a 90% specificity and so should be undertaken in the case of an inconclusive or negative TTE.
In cases of high clinical suspicion but negative echo, a repeat exam should be undertaken after a week.
Echo findings of IE may include:
- Oscillating intracardiac mass associated with a valve or supporting structure
- Abscess
- Prosthetic valve dehiscence
- New valvular regurgitation
Diagnosis
To help with the clinical variability of presentation, scoring systems have been developed to aid confidence in the diagnosis.
Probably the most familiar is the Duke criteria - https://www.mdcalc.com/duke-criteria-infective-endocarditis
This uses a combination of major and minor criteria.
Major
Minor
These can be brought together to create a risk category:
An additional part of the Duke criteria is the pathological criteria.
The presence of just one of these confirms the diagnosis:
Probably the most familiar is the Duke criteria - https://www.mdcalc.com/duke-criteria-infective-endocarditis
This uses a combination of major and minor criteria.
Major
- Blood culture positive
- Two separate positive cultures
- A organism that causes IE
- Echo evidence of endocardial involvement
Minor
- Predisposition - predisposing heart condition or IVDU
- Fever
- Vascular phenomenon
- Immunologic phenomenon
- Microbiologic evidence (not meeting major criteria)
- Echo evidence (not meeting major criteria) - added in the modified Duke
These can be brought together to create a risk category:
- Definite
- 2 major
- 1 major and 3 minor
- 5 minor
- Possible
- 1 major and 1 minor
- 3 minor
An additional part of the Duke criteria is the pathological criteria.
The presence of just one of these confirms the diagnosis:
- Microorganisms in a vegetation
- Histological examination of a lesion
Management
The components of management can be seen as:
Antibiotics
These remain the key part of IE treatment.
Due to the nature of difficulty getting adequate antibiotic exposure to the bacteria (e.g. due to biofilm development) they are generally given IV and for a prolonged course.
The antibiotic choice and duration will be guided by:
Surgery
A surgical opinion is recommended in all patients with an infected prosthetic valve, and they may need to advise in cases of native valve disease.
Their main involvement will be in cases where there has been a degree of valvular/structural damage from the infection that surgical intervention is needed e.g. valve replacement.
This is clearly challenging given problems of performing surgery at a sight of infection.
Indications for surgery may include:
- Resuscitation (if needed)
- Antibiotics
- Supportive care
- Surgery (if indicated)
Antibiotics
These remain the key part of IE treatment.
Due to the nature of difficulty getting adequate antibiotic exposure to the bacteria (e.g. due to biofilm development) they are generally given IV and for a prolonged course.
The antibiotic choice and duration will be guided by:
- Causative pathogen
- Nature of valve (native vs artificial)
- Degree of systemic illness
Surgery
A surgical opinion is recommended in all patients with an infected prosthetic valve, and they may need to advise in cases of native valve disease.
Their main involvement will be in cases where there has been a degree of valvular/structural damage from the infection that surgical intervention is needed e.g. valve replacement.
This is clearly challenging given problems of performing surgery at a sight of infection.
Indications for surgery may include:
- Heart failure
- CVS failure relating to valvular compromise e.g. severe AR
- Severe infection
- Abscess
- Inadequate response to antimicrobial therapy
- Prevention of embolism
- Large vegetations with embolic phenomenon (left side of heart)
- Very large vegetations
Prognosis/Complications
Complications include;
Valve destruction leading to heart failure occurs in about half of patients.
This is a trigger for surgical intervention as untreated failure carries a significant mortality (80%).
Stroke can complicate between 20-40% of cases of left sided IE.
It is a major contributor to morbidity and mortality.
A vegetation larger than 10mm is a major risk factor.
Perioperative mortality for urgent/emergent surgical intervention is high (5-15%).
In stable patients this approaches the normal risk for valve surgery.
- Heart failure
- Stroke
Valve destruction leading to heart failure occurs in about half of patients.
This is a trigger for surgical intervention as untreated failure carries a significant mortality (80%).
Stroke can complicate between 20-40% of cases of left sided IE.
It is a major contributor to morbidity and mortality.
A vegetation larger than 10mm is a major risk factor.
Perioperative mortality for urgent/emergent surgical intervention is high (5-15%).
In stable patients this approaches the normal risk for valve surgery.
Links & References
- Osmosis. Clinician’s corner: endocarditis. 2019. https://www.youtube.com/watch?v=CdTCdHK77Zw
- Nickson, C. Infective endocarditis. LITFL. 2019. https://litfl.com/infective-endocarditis/
- Tidy, C. Infective endocarditis. Patient.info. 2015. https://patient.info/doctor/infective-endocarditis-pro
- Aryal, P. Duke criteria for infective endocarditis. MDCALC. https://www.mdcalc.com/duke-criteria-infective-endocarditis
- Martinez, G. Valchanov, K. Infective endocarditis. CEACCP. 2012. 12(3):134-139. https://academic.oup.com/bjaed/article/12/3/134/258704
