Explaining what infective endocarditis (IE) is requires a little translation of the name; endo- means inside, -card- refers to the heart (like 'cardiac') and the -itis bit signifies a process of inflammation. Combining all three gives you an inflammation of the inside of the heart, which is caused by an infection.
Essentially what happens is that the bacteria involved can collect on one of the four valves inside the heart which normally keep the blood flowing in the right direction, and grow into vegetations which damage the valve and interfere with the normal flow of blood. They are able to maintain their presence in the bloodstream because the heart valves are an especially difficult place for the body's immune system to reach in order to fight off the infection.
The condition, which can occur in just about anyone, is more common in those people who have damaged or replacement heart valves and is particularly serious when it affects intra-venous (IV) drug users.
Signs, Symptoms and Complications
IE's signs and symptoms are similar to those of many infections: a fever, tiredness and a general feeling of sickness, as well as some heart specific conditions like the development of a murmur, bleeding from tiny blood vessels under the nails (known as splinter haemorrhages), and odd lumps and bumps in the hands.
The major complications fall under two categories - local and distant. Local complications involve permanent damage to the valve affected which requires surgical repair or replacement to restore its function. Distant complications occur when parts of the vegetation break off and travel in the arteries to other sites around the body, for instance causing a stroke if the fragment becomes lodged in the blood vessels supplying the brain, cutting off the supply and causing damage to the brain tissue.
Risks, Bugs and Drug Users
There are a number of reasons why certain groups might be more commonly or more seriously affected. The chances of getting endocarditis are principally determined by how easily the bacteria can gain entry to the body and how easy it is for them to grow on the heart valves. Replacement valves, or those damaged as a result of previous IE or other diseases, are inherently more susceptible to infection than healthy valves because of the turbulent flow of blood around them being a better environment for bacteria. This means there is a higher risk of contracting the condition for people with these problems and they are often advised to take preventative antibiotics whenever they cut themselves or have things like dental surgery done which might introduce infection.
There is also a variation in which families of bacteria are causing the problem. People not in one of the above groups tend to be infected by a bug known as streptococcus viridans which is thankfully less aggressive than the others: staphylococcus epidermidis1, which characteristically infects patients with replacement heart valves, and staphylococcus aureus2 which is the characteristic infection in IV drug users. There are other bugs but they are relatively rare and tend only to cause problems in people with a damaged immune system, such as with AIDS.
IV Drug Users Are Particularly Seriously Affected
This is not only because of the reasons mentioned above. Infection of these people occurs via a similar route as the transmission of HIV and hepatitis - the repeated insertion of needles into the bloodstream. In contrast to the other two conditions however, endocarditis is not preventable by avoiding needle sharing as it is not transmitted directly from person to person.
Drug users are also affected on the right side of the heart - which pumps blood to the lungs - in contrast to the other forms of endocarditis, which normally affect the valves on the left side - which pumps blood around the rest of the body. This makes little difference to the complications since a piece of the vegetation breaking off and lodging in the lungs (a pulmonary embolism, see the Entry on A592715 for a more comprehensive description) from the right side of the heart can be just as rapidly fatal as one which lodges in the brain from the left side as described earlier.
The difference comes in terms of treatment. Left-sided valves can be relatively easily replaced surgically, but replacing a right-sided valve is a more difficult operation with lower success rates, and because of this, does not tend to be attempted. This means that the affected person, even if treated successfully with antibiotics, can still be left with a permanently damaged valve and will be more prone to heart problems, including further attacks of endocarditis, in later life.
Despite all of these serious problems with the condition, IE is still very treatable as long as it is recognised early. The first line of defence is a combination of antibiotics given intra-venously3, in a course which normally lasts for six weeks and necessitates a long hospital admission. Success is determined by ultrasound scanning to assess the size of the vegetations as well as the observed reduction in the person's symptoms. If the damage to the valve is significant, the person may be considered for surgery (to left-sided valves).
In general, although replacement valves bring their own set of problems, the long-term outlook for IE is relatively good as long as the diagnosis is made promptly and the condition is appropriately treated.