Understanding Endocarditis: A Rare but Dangerous Heart Condition

Endocarditis is an inflammation of the endocardium, which is the inner lining covering the heart’s chambers and valves. This condition occurs when germs—most commonly bacteria, but sometimes fungi—manage to enter the bloodstream and travel to the heart. Once there, these organisms attach to damaged areas of the heart tissue and begin to multiply, forming clumps called vegetations that can cause serious damage.^[1][2]

Although the heart is naturally well protected against infection, certain circumstances can make it easier for bacteria or fungi to bypass the immune system and establish an infection. The vegetations that form in endocarditis consist of infecting organisms, fibrin (a protein involved in blood clotting), and platelets. As inflammation continues, these vegetations break down the surrounding heart tissue, potentially causing severe damage to the heart valves.^[2]

There are two main types of endocarditis. Infective endocarditis, the most common form, happens when germs attach to damaged heart tissue. The rarer form, called non-infective endocarditis, involves sterile vegetations that aren’t caused by infection but are linked to conditions that make blood clot too easily, such as lupus or antiphospholipid syndrome.^[2]

Without prompt treatment, endocarditis can be fatal. With quick and aggressive treatment, however, many people survive. The condition requires several weeks of antibiotic therapy and sometimes surgery to repair or replace damaged heart valves.^[2]

Epidemiology: How Common Is Endocarditis?

Endocarditis is a rare condition in most developed countries. In the United States, approximately 5 to 7.9 cases occur per 100,000 people each year.^[14] In England, endocarditis remains rare even among those at higher risk.^[3] Each year in the United States, about 34,000 patients are admitted to hospitals specifically for infective endocarditis.^[21]

Despite being uncommon, endocarditis is the fourth most common life-threatening infection after sepsis, pneumonia, and intra-abdominal abscess. The estimated inpatient mortality rate ranges between 15 and 30 percent, making it a serious condition that requires immediate medical attention.^[13]

The condition affects men more frequently than women. Studies consistently show that twice as many men are affected as women.^[3][22] Age is also a significant factor—endocarditis is more common in older adults, with a median age of affected patients being around 57.9 years. However, cases have been recorded in children, particularly those born with congenital heart disease.^[2][3]

Interestingly, rates of endocarditis are actually increasing, but this is largely because of advances in medical care rather than new risk factors. There is a growing number of people receiving valve replacement surgery or surgery to repair congenital heart disease, and these procedures create more opportunities for infection to develop. Healthcare-associated infection has become increasingly common, now representing about 30 percent of all endocarditis cases.^[3][13]

From 2000 to 2005, an international study of 2,781 consecutive cases found that 72.1 percent had endocarditis of the native valve, meaning they didn’t have artificial valves. Common risk factors identified in that study included hemodialysis (7.9 percent of cases), intravenous drug use (9.8 percent), degenerative valvular disease with mitral regurgitation (43.4 percent) or aortic regurgitation (26.3 percent), and rheumatic heart disease (3.3 percent).^[14]

Causes of Endocarditis

The vast majority of endocarditis cases are caused by bacterial infections. When bacteria enter the bloodstream, they can travel to the heart and attach to damaged or abnormal areas of heart tissue. In rare cases, fungi or other germs cause the infection.^[1][4]

The bacteria that cause endocarditis typically come from other parts of the body, such as the mouth, skin, or respiratory system. They enter the bloodstream through various routes and then make their way to the heart. Once there, they attach to damaged heart valves or other areas of compromised heart tissue and begin to multiply.^[2][11]

Healthy heart tissue is normally very resistant to infection. However, when heart tissue is already damaged or abnormal, it becomes much easier for bacteria to attach and grow. The bacteria produce enzymes that destroy the surrounding heart tissue, creating the vegetations characteristic of endocarditis.^[2]

Common ways bacteria can enter the bloodstream include through injuries such as cuts or scrapes on the skin, dental work, certain surgical procedures, or the use of unclean needles. Bacteria can also enter through existing infections elsewhere in the body, such as urinary tract infections, gum infections, or infections of the respiratory system.^[4][9]

The most frequently identified pathogens in endocarditis have changed over time. While streptococcus viridans was the most common organism identified in the 1960s, Staphylococcus aureus is now the most frequently identified pathogen. This shift is partly due to increased rates of intravenous drug abuse and healthcare-associated infections. Other common blood culture isolates include viridans Streptococcus, enterococci, and coagulase-negative staphylococci.^[13][14]

Risk Factors: Who Is at Higher Risk?

While endocarditis is rare in the general population, certain factors significantly increase a person’s risk of developing this condition. The most significant risk factors involve conditions that affect blood flow through the heart or that allow bacteria easier access to the bloodstream.^[5]

People with existing heart problems are at considerably higher risk. This includes those with artificial (prosthetic) heart valves, which provide extra surface area for bacteria to attach and form vegetations. Individuals with structural or congenital heart disease, damaged heart valves, heart valve disease, or hypertrophic cardiomyopathy (where the heart muscle cells have enlarged) are also more vulnerable.^[1][3]

Having had endocarditis before significantly raises the risk of getting it again, as the condition can leave lasting damage to heart tissue that makes future infections more likely. People with implanted heart devices such as pacemakers, implantable cardioverter-defibrillators (ICDs), or hemodialysis access points also face increased risk.^[2][5]

Intravenous drug use is a major risk factor, as unclean needles can carry bacteria directly into the bloodstream. People who inject illegal drugs are much more likely to develop endocarditis.^[3][9]

Poor dental health and gum disease create opportunities for bacteria from the mouth to enter the bloodstream. Not taking care of teeth and gums makes it easier for germs to get into the bloodstream through the gums and mouth. Recent dental procedures can also temporarily increase risk.^[9]

Other factors that increase susceptibility include diabetes, conditions that weaken the immune system, long-term central venous lines (tubes that stay in a large vein for weeks or months for medical treatment), and having recently undergone invasive procedures such as wound care or surgery.^[2][4]

Age-related changes to the heart valves, such as mitral valve prolapse or calcium deposits in the aortic valve, can create places for germs to attach. This explains why older adults have a higher risk than younger people.^[9]

Importantly, not all heart problems put you at higher risk for endocarditis. People who have had bypass surgery for heart disease, rheumatic fever without heart valve damage, a heart attack without other complications, mitral valve prolapse without regurgitation or unusually thickened valve leaflets, or a coronary artery stent do not have increased risk of endocarditis.^[5]

Symptoms: Recognizing the Warning Signs

The symptoms of endocarditis can vary widely from person to person, and they may be severe or very mild. They can start suddenly or develop slowly over weeks or even months. This variability depends on the type of germs causing the infection and whether there are other heart problems present.^[1][22]

Endocarditis can be acute, beginning suddenly with a high fever and fast heart rate and becoming life-threatening within days. Or it can be subacute, developing gradually over weeks or several months.^[2]

The most common symptoms of endocarditis often resemble flu-like illness. These include fever (often above 100°F or 38.4°C), chills, night sweats (heavy sweating during sleep), and fatigue. Many people also experience aching joints and muscles, headaches, cough, and sore throat.^[1][2][22]

Heart-related symptoms include chest pain, particularly when breathing, shortness of breath, a fast or irregular heart rate, and a new or changed heart murmur (an unusual whooshing sound heard between heartbeats). Swelling in the feet, legs, or abdomen may also occur.^[1][2]

Some people experience loss of appetite and unexplained weight loss. Tenderness under the left rib cage, where the spleen is located, can indicate an enlarged spleen, which sometimes occurs with endocarditis.^[1][6]

Less common but distinctive symptoms involve changes to the skin and extremities. These can include blood in the urine, painless flat red, purple, or brown spots on the soles of the feet or palms of the hands (called Janeway lesions), painful red or purple bumps on the tips of the fingers or toes (Osler nodes), tiny purple, red, or brown round spots on the skin (petechiae), unusual dark lines under the fingernails, or broken blood vessels visible on the skin.^[1][2][6]

It’s important to note that non-infective endocarditis typically doesn’t cause symptoms. People with this rare form usually don’t know they have it until they get heart imaging tests for other reasons.^[2]

Because symptoms can be unclear and easily confused with other illnesses, endocarditis should be suspected in anyone with unexplained fevers, especially if they have risk factors such as heart valve disease, artificial heart valves, or a history of intravenous drug use.^[1][3]

Prevention: Protecting Yourself from Endocarditis

Prevention strategies for endocarditis focus on reducing opportunities for bacteria to enter the bloodstream and maintaining good overall health, especially for those at higher risk.^[5]

Good dental and oral hygiene is one of the most important preventive measures. Practicing daily dental hygiene by brushing and flossing teeth regularly and visiting a dentist at least twice a year can significantly reduce the risk of bacteria from the mouth entering the bloodstream. If you have risk factors for endocarditis, make sure your dentist knows about your condition.^[5][9]

People who have been successfully treated for endocarditis in the past, those with artificial heart valves, those who have had heart valve repair, those with certain types of congenital heart defects, and those with heart valve problems after a heart transplant may need to take antibiotics before certain dental procedures or surgeries. This antibiotic prophylaxis helps prevent bacteria from establishing an infection in the heart. Always inform your healthcare providers about your endocarditis history or risk factors.^[5][10]

Avoiding intravenous drug use is crucial, as unclean needles are a major source of bloodstream infections. For those with long-term intravenous access for medical treatments, proper care and hygiene of these access points is essential.^[9]

Managing underlying health conditions, particularly heart conditions and diabetes, can help reduce risk. Maintaining a strong immune system through healthy lifestyle choices also provides protection.^[2]

If you have had endocarditis before, it’s important to carry a card in your wallet stating that you need preventive antibiotics before certain procedures. Your doctor can provide this card, and you should show it to all healthcare providers you see.^[5]

Pathophysiology: How Endocarditis Affects the Heart

Understanding how endocarditis damages the heart helps explain why this condition is so serious and why treatment must be aggressive. The disease process involves several interconnected mechanisms that progressively harm heart tissue.^[2]

The development of endocarditis requires two key elements: bacteria or fungi present in the bloodstream, and an area of damaged or abnormal heart tissue where these organisms can attach. Healthy endocardium—the inner lining of the heart—is normally very resistant to infection. However, mechanical and biomechanical abnormalities, such as those created by prosthetic heart valves or damaged natural valves, provide surfaces where platelets can adhere and blood clots (thrombi) can form. These sites then provide additional surface area where bacteria or fungi can attach and establish colonies.^[14]

Once bacteria attach to damaged heart tissue, they multiply and become embedded within layers of fibrin and platelets, forming vegetations. These vegetations are densely packed structures that create a mechanical barrier. This barrier is one reason why treating endocarditis is so challenging—it limits how well antibiotics can penetrate to reach the bacteria, and the bacteria within are somewhat protected from the body’s immune system.^[13]

As the bacteria continue to grow, they produce enzymes that actively destroy the surrounding heart tissue. The vegetations themselves also cause damage by interfering with normal valve function. As inflammation continues, the vegetations break down heart tissue, particularly affecting the heart valves. This can lead to valvular structural and functional problems, including valve insufficiency where the valve doesn’t close properly, allowing blood to flow backward.^[2][11]

Pieces of the vegetations can break off and travel through the bloodstream to other parts of the body. These fragments, called emboli, can block blood vessels in the brain (causing stroke), lungs, kidneys, spleen, or other organs. This can lead to additional infections in those organs or cause tissue damage by cutting off blood supply.^[4][9]

The infection can also extend beyond the valves into the heart muscle itself, potentially forming abscesses (collections of pus). In cases involving prosthetic valves, the infection may cause perivalvular invasion, extending into nearby tissue and potentially affecting the heart’s electrical conduction system, which can lead to heart block or other rhythm problems.^[3][14]

The combination of valve damage, tissue destruction, emboli formation, and potential spread of infection explains why endocarditis can lead to serious complications such as heart failure (where the heart cannot pump blood effectively), stroke, kidney damage, and sepsis (an overwhelming body-wide response to infection).^[9]

Without treatment, the progressive destruction of heart tissue makes endocarditis fatal. Even with treatment, approximately 50 percent of patients will require some form of surgical intervention to repair or replace damaged valves or to drain abscesses.^[2]