Endocarditis is an infection of the heart’s inner lining, the endocardium. However, in some cases, endocarditis may also be non-infective.

In non-infective endocarditis or nonbacterial thrombic endocarditis (NBTE), sterile clots form on cardiac valves and nearby endocardium as a result of trauma, vasculitis or a hypercoagulable state such as pregnancy. This condition usually affects valves that have not previously been damaged.

In infective endocarditis, the bacteria that have entered the bloodstream travel to the heart and become established in damaged heart valves, where they form vegetations or tiny growths in the valves. In non-infective endocarditis, small and sterile vegetations tend to aggregate and cluster along the edges of the valves or cusps. This form of endocarditis is also called marantic endocarditis. In infective endocarditis, the body’s response is inflammation, whereas NBTE does not cause an inflammatory response.

The most common cause of NBTE is a hypercoagulable state or the increased propensity of blood to coagulate in certain disease conditions. This is caused by an increase or imbalance in blood coagulation factors and enzymes and may occur in systemic wide bacterial infection or pregnancy. Patients with certain cancers and in particular, mucinous adenocarcinoma, are at an increased risk of developing NBTE.  

By itself, NBTE does not pose any particular health risk, but fragments of vegetation may break off and move towards the brain or heart, causing an embolism. In addition, the vegetation can provide a point of accumulation for bacteria and lead to the infective form of the condition, endocarditis.

Libman-Sacks endocarditis is another form of non-infective endocarditis, seen in patients with lupus erythematosus. This condition is thought to be caused by immune complexes depositing and forming small vegetations that then trigger inflammation (unlike in NBTE). In Libman-Sacks endocarditis, the deposits do not seem to form in a particular place and may accumulate under the surface of valves or even on the endocardium.