Introduction

Endocarditis (also known as infectious endocarditis, bacterial endocarditis, or infective endocarditis (IE)) is a medical condition in which the innermost lining of the heart muscle (called the endocardium) and/or heart valves become infected and inflamed.

The human heart is made up of four chambers: the right atrium, the left atrium, the right ventricle, and the left ventricle. These chambers are separated by different valves, which help maintain appropriate blood pressure and ensure that blood flows in the correct direction through the heart and body.¹

Like other organs, the heart is made up of (and surrounded by) multiple layers of tissue, which support its function.¹ In endocarditis, the inner lining of the heart and heart valves become infected. This significantly impacts the strength and efficiency of the cardiac (heart) muscle, which can lead to life-threatening complications.^2,3

Normally, the heart pumps blood to the body via the lungs. This detour is vital, as the lungs oxygenate our blood and ensure it contains enough oxygen to support respiration in our body’s cells. Endocarditis negatively affects the flow of blood through the lungs and, by extension, the flow of oxygenated blood to our body’s cells and tissues.^4,5,6 However, symptoms associated with endocarditis can affect the whole body and include chills, tiredness, pain in various body parts, weight loss, red spots under the nails, on the palms of your hands, or the soles of your feet, and shortness of breath.^7,8

Whilst the majority of endocarditis cases are triggered by infections, there have been some exceptional cases where endocarditis has occurred without any infection.⁴ Regardless, many factors can influence your risk of endocarditis, including oral hygiene, exposure to or use of unsterile needles, and pre-existing heart conditions. Furthermore, individuals assigned male at birth (AMAB) are typically at a slightly increased risk.^4,5 It’s important to understand how to minimise your risk of endocarditis, as it can cause clusters of infectious cells to form and spread around the body - which can increase your risk of other conditions later on.

Causes of endocarditis

The most common cause of endocarditis is bacterial infection. Many kinds of bacteria are found in our mouths, throats, and digestive systems. Any of these usually harmless bacteria can become a problem if they enter the bloodstream. Once in the blood, bacteria can travel to and attack the inner lining of the heart (the endocardium) or the heart valves, triggering the inflammation associated with endocarditis.^2,3

Unfortunately, it is extremely difficult for our bodies to fight off infections in the heart valves. This is because blood is not directly supplied to the heart valves - meaning that the white blood cells responsible for identifying and attacking invading bacteria are unable to reach the valves. As such, the immune system cannot easily clear infections in the valves - making it easy for bacteria to establish themselves.⁵

Several risk factors can affect your risk of bacterial infection and endocarditis. We will discuss some of these now.

Poor oral hygiene

Poor oral hygiene - which includes not brushing the teeth and tongue regularly, not flossing, and not chewing food properly - significantly impacts the condition of your teeth and gums. Poor oral health encourages bacterial growth, significantly increasing the risk of bacteria getting into the bloodstream and causing infection elsewhere.^8,10

Previous infection(s)

Anyone suffering from an infectious disease is at an increased risk of endocarditis compared to a healthy individual. Although many kinds of bacteria can cause endocarditis, infections of organs in the digestive tract (e.g. the mouth, gums, throat, or stomach) are most commonly responsible for endocarditis.^6,10

Medical devices

Medical devices (such as pacemakers, catheters, and cannulas) are used in medical procedures to diagnose, treat and/or manage a range of conditions. When these devices are inserted into the body, they can directly or indirectly increase our risk of bacterial infection, especially if they are not sterilised properly beforehand.^5,10

Drug abuse

Individuals who regularly inject drugs or other illicit substances into their veins are at an increased risk of developing endocarditis. This is due to the frequent use of non-sterile and/or reused needles, which often carry bacteria that can be injected into the bloodstream and cause infection.^9,10,11

Cardiac valve issues

Several conditions that affect the heart valves can increase your risk of developing endocarditis.^8,12,13 Normally, the heart valves ensure the one-way flow and pressure of the blood is maintained. However, some conditions can change the physical aspects of the valves, such as their size. These problems can disrupt the unidirectional flow of blood through the heart, decrease the volume of blood that can pass through an open valve at any one time, or otherwise impact a valve’s functionality.

These conditions are either present at birth (known as congenital heart disease) or develop throughout life (known as acquired heart disease).^9,14

Acquired heart disease may be a result of other conditions. For example, a heart attack can cause some heart muscle to die, affecting the arrangement of the remaining tissue. This, in turn, can make the valves less functional.⁷ Similarly, hypertension (high blood pressure), if left untreated, can put excessive strain on the heart muscle and valves - negatively impacting their function and increasing the risk of bacterial infection and endocarditis.¹⁰

Artificial valve

Sometimes, dysfunctional valves must be replaced with artificial valves in a surgical procedure. Whilst the risk of infection is incredibly low, there is a small chance that bacteria enter the bloodstream during the procedure - either from the air, surgical tools, or the replacement valve itself.^10,12

Weak immune system

There are many conditions and medications which can weaken our immune systems, including human immunodeficiency virus (HIV), autoimmune disorders, organ transplant medications, and chemotherapy, to name a few.

Rheumatic heart disease is an autoimmune condition which causes the heart to become inflamed, increasing the patient’s risk of endocarditis. Thanks to antibiotics, this condition is rare and easily managed today. However, it can still cause problems for elderly patients.⁴

Vegetation

Whilst most cases of endocarditis are triggered by infection, some (referred to as non-infective endocarditis) are not. Non-infective endocarditis occurs when protein molecules and/or blood cells attach to the inner lining of the heart or heart valves. Over time, these aggregates can form a lesion or mass, which is known as vegetation.

Similar masses appear in a medical condition called SLE (systemic lupus erythematosus), in which any inflamed tissue in the body can detach from its normal anchor and travel to other parts of the body in the blood. If a detached mass settles on the walls or valves of the heart, it can trigger non-infective endocarditis.⁴

Symptoms of endocarditis

Symptoms of infective endocarditis include:^6,7,11,15,16

• Cardiac murmur (an abnormal heart sound that a doctor can hear using a stethoscope). Cardiac murmurs are seen in approximately two-thirds of endocarditis patients. 
• A persistent fever
• Chills
• Shortness of breath, even at rest
• Night sweats
• Chest pain
• Swelling in the legs, feet and abdomen
• Increased heart rate
• Loss of appetite
• Weight loss
• Red-coloured urine
• Small red spots under the fingernails
• Red spots on the palm of the hand and soles of feet (these might not be visible in darker-skinned individuals)
• Red and painful lumps or nodules on the toes and fingers

Non-infective endocarditis does not typically cause any symptoms, but patients may experience shortness of breath and increased heart rate.⁹

Summary

Endocarditis is a medical condition in which the inner lining and valves of the heart become infected and inflamed. This is triggered by the settlement of bacteria, inflamed tissues, proteins, or cells on the valves or inner lining of the heart. There are several factors which can increase the chance of causative bacteria entering the bloodstream, such as poor oral hygiene, the abuse of intravenous drugs, previous infections and weak immunity. Common symptoms of endocarditis are change in the heart sound, high fever, increased heart rate, shortness of breath and small red spots on the hands and feet. As with all heart conditions, it is recommended that you speak to a doctor immediately if you suspect you have endocarditis.