Infective Endocarditis – Pathophysiology, Criteria & Treatment
Infective endocarditis (IE) is a serious form of heart disease where there is an infection of the endocardium (the inner aspect of the heart chambers) by microorganisms.
This condition needs to be identified quickly and treated aggressively to save the patient from death or serious heart complications.
These structures or areas of the endocardium may get involved either alone or in combination;
- Heart valves (native)
- Heart valves (prosthetic)
- Mural endocardium
- Intra-cardiac devices
The heart valves are structures that serve as one way gates between the two chambers of the heart on right or left side, also between the ventricles and pulmonary artery or aorta.
Native heart valves are the valves a person was born with and prosthetic ones are the artificial valves.
Mural endocardium is the thin structure that lines the inner surface of the heart. Examples of intra-cardiac devices include implanted defibrillator, transvenous pacemaker lead etc.
What organisms cause IE?
The organisms mostly responsible for IE are
- Bacteria &
Most of the IE is caused by bacteria; and many different types of bacteria are involved with the IE and few of the common ones are;
- HACEK organisms
- Pseudomonas etc.
What situations predispose these infections?
- Prior damage to the endocardium, such as
- Rheumatic heart disease
- Congenital heart diseases etc
- Recent surgical interventions related with the heart
- IVDA (Intravenous drug abuse) etc.
The normal intact endocardium is highly resistant to infection however the above mentioned situations promote the invasion of the pathogens to the endocardial structures including the valves.
Initially there a development of what we call as NBTE (nonbacterial thrombotic endocarditis) which is a sterile clot or thrombus like structure that attaches to these damaged areas.
When there is an invasion of microorganisms into the blood stream and as they move across these NBTE structures these organisms may attach themselves to NBTE and such NBTE is called as vegetations as they contain the pathogens. These vegetations are the hallmark features of IE.
The microorganisms in the vegetations divide and grow in number and initiate an inflammatory response and this will produce additional damage to the already compromised structures. Patients usually develop new murmurs related with this new damage.
This will put extra burden on the heart muscle and in severe cases will result in heart failure (HF).
Also the vegetations can break from the endocardium and enter the arterial circulation and reach other organs like brain. They may block the arterial branches and can result in conditions like stroke.
Sometimes the blockage of arteries by infected vegetations may result in damage to the arterial walls and may result in what is called as mycotic aneurysms. They may rupture causing bleeding in to the organ especially the brain.
Infective especially the bacterial endocarditis is traditionally classified as acute & sub acute bacterial endocarditis (SABE) based on the evolution of clinical manifestations.
The more virulent organisms cause more severe damage to the valves and results in earlier onset of clinical manifestation and rapid progression of the disease process. SABE presents & progresses somewhat slowly.
Generally patients present with these manifestations including (not all patients);
- Sweating & chills
- Loss appetite and loss of weight
- Malaise (ill feeling)
- Joint & muscle pain
- Heart murmurs
- Osler’s nodes, subungual hemorrhages, spleen enlargement etc
- Manifestation related to the complications (e.g. stroke, seizures)
Duke criteria, a set of clinical criterias used in diagnosing IE, are employed to arrive at the diagnosis with reasonable accuracy and the clinical, blood tests and echocardiograpic findings are used here.
There are two major & five minor criteria.
The major criteria include;
- Positive blood culture
- Proof that endocardium is indeed involved
- Abnormal echocardiogram
- Evidence for the involvement of a new murmur
Minor criteria include;
- Predisposing conditions (preexisting heart problems, intravenous illicit drug abuse)
- Presence of fever (temp equal or more than 38.0 degrees)
- Vascular manifestations
- Immunological manifestations
- A positive blood culture or serological proof of active infection
A clinical diagnosis of definite IE is made if one of the following is fulfilled;
- Two major criteria
- One major + three minor criteria
- Five minor criteria
Possible IE if one of the following is fulfilled;
- One major + one minor criterion
- Three minor criteria
The blood culture, if comes positive will assist with the diagnosis as well as with choosing the appropriate antibiotics through culture sensitivity.
The echocardiogram uses ultrasound technique to visualize the heart chambers, valves, blood flow etc of the heart. The endocarditic vegetations may be seen.
Generally TTE (trans-thoracic echo) is performed however TEE (trans-esophageal) is more sensitive for smaller vegetations.
The management of IE includes the following;
- Empirical antibiotic treatment
- Specific antibiotic treatment
- Symptomatic treatment
- Treatment of complications
- Surgical treatment etc.
Initially if the exact causative organism is not known then a combinational empirical antibiotic course is initiated. If the culture grows & identifies the pathogen then only specific antibiotics can be tried based on antibiotic sensitivity information.
The initial antibiotics generally used include:
- 3rd or 4th generation intravenous cephalosporins
- Gentamicin etc.
Fungal endocarditis is much rare as compared to the bacterial one and amphotericin antibiotic is the mainstay of treatment.
Surgical treatment is employed if medical management fails and includes procedures like removal of the infected valve etc.
Infective endocarditis (IE) is a life threatening illness involving the heart so the diagnosis & treatment both need to be achieved at the earliest.