Infected endocarditis typically first affects which valve?

Infected endocarditis most commonly first affects the tricuspid valve, especially in patients with certain risk factors such as intravenous drug use. The tricuspid valve is located on the right side of the heart and is more susceptible to bacterial colonization from bloodborne pathogens, particularly in scenarios where there are frequent injections or other means of introducing bacteria directly into the bloodstream.

When bacteria enter the bloodstream, they can adhere to the valve leaflets, leading to vegetation formation, which is characteristic of infective endocarditis. In the case of individuals with a history of intravenous drug use, the tricuspid valve becomes a primary site of infection due to the introduction of bacteria through non-sterile needles.

While the aortic and mitral valves can also be affected by endocarditis, they are more commonly associated with other underlying conditions, such as rheumatic heart disease or chronic valve disease, rather than with acute infections originating from intravenous drug use. The pulmonary valve is the least commonly affected due to its position and lower prevalence of bacterial insult compared to the right-sided valves.