Endocarditis is an inflammation of the inner lining of the heart, particularly affecting the heart valves. This condition arises when infectious agents, most commonly bacteria, enter the bloodstream and attach themselves to the heart’s endocardium, the delicate tissue lining the heart chambers and valves. The infection can cause serious damage to the heart structures and lead to life-threatening complications if not treated promptly.
The primary cause of endocarditis is the invasion of microorganisms into the bloodstream, a process known as bacteremia. These bacteria or, less commonly, fungi travel through the blood and settle on the heart valves or the inner lining of the heart. The heart valves are especially vulnerable because they have less blood flow compared to other parts of the heart, making it easier for microbes to adhere and multiply there.
Several factors increase the risk of developing endocarditis. One major factor is the presence of abnormal or damaged heart valves. This damage can be due to congenital heart defects, previous heart valve disease, or degenerative changes often seen in older adults. Artificial or prosthetic heart valves also provide surfaces where bacteria can more easily attach. Additionally, people who have had previous episodes of endocarditis are at higher risk of recurrence.
Another important cause is medical procedures that allow bacteria to enter the bloodstream. Dental work, surgeries, or invasive procedures involving the respiratory tract, gastrointestinal tract, or urinary tract can introduce bacteria into the blood. Even routine activities like brushing teeth or flossing can cause transient bacteremia, especially in people with poor dental hygiene or gum disease.
The types of microorganisms causing endocarditis have evolved over time. Historically, streptococci bacteria, often originating from the mouth, were the most common culprits. Today, Staphylococcus aureus has become the leading cause, particularly in hospital settings or among intravenous drug users. Other bacteria such as enterococci and coagulase-negative staphylococci also contribute, along with a group called HACEK organisms, which are less common but can be difficult to detect. Fungal infections, though rare, can also cause endocarditis, especially in immunocompromised individuals.
Sometimes, diagnosing the exact cause of endocarditis is challenging because blood cultures fail to identify the responsible organism. This situation, called culture-negative endocarditis, can occur due to prior antibiotic use, infections with fastidious organisms that require special growth conditions, or intracellular pathogens that evade detection by standard methods.
The process of infection begins when bacteria in the bloodstream adhere to damaged areas of the heart lining or valves. They form clumps called vegetations, which are masses of bacteria, platelets, and fibrin. These vegetations can damage the valves, leading to leakage or obstruction of blood flow. Pieces of the vegetations can break off and travel to other parts of the body, causing embolisms that may result in strokes, organ damage, or other serious complications.
Certain populations are more susceptible to endocarditis. People with congenital heart defects, those with prosthetic heart valves, individuals who use intravenous drugs, and patients with weakened immune systems are at increased risk. Preventive measures, such as antibiotic prophylaxis before dental or certain medical procedures, are recommended for high-risk individuals to reduce the chance of bacteria entering the bloodstream and causing infection.
In summary, endocarditis is caused by microorganisms entering the bloodstream and infecting the heart’s inner lining, especially damaged or artificial heart valves. The main culprits are bacteria like Staphylococcus aureus and streptococci, introduced through medical procedures, intravenous drug use, or even everyday activities in susceptible individuals. The infection leads to the formation of vegetations that damage heart structures and can cause severe complications if untreated.
