In patients with IV drug use, vegetation is most commonly found on which heart valve?

In patients who use intravenous (IV) drugs, the tricuspid valve is most commonly affected by infective endocarditis leading to the formation of vegetations. This prevalence is primarily due to the way pathogens enter the bloodstream through contaminated needles or substances. When these pathogens circulate, they often travel through the right side of the heart first, which includes the tricuspid valve.

The tricuspid valve is anatomically positioned in such a way that it is the first valve encountered by blood returning from the systemic circulation, making it more susceptible to infection from bacteria that are introduced into the bloodstream. In contrast, the other heart valves, like the mitral and aortic valves, are associated with left-sided cardiac infections, which are more common in patients with other risk factors, such as pre-existing heart conditions or procedures that directly involve the left heart.

The pulmonic valve can also be involved in endocarditis but is significantly less frequent than the tricuspid valve in the context of IV drug use. Thus, the tricuspid valve being the most commonly affected in this patient population aligns with clinical observations and literature on the subject.