A 63 yeаr оld wоmeаn cоmes to the office due to а vague feeling of heaviness in her legs, especially when standing for long periods. The patient has worked as a cashier at a department store for the last 20 years and her symptoms are worst at the end of the day. Examination of both lower extremities show dilated, tortous veins at the calvesand ankles bilaterally, with no erythema or edema. Upper examination is unremarkable. This patient's current condition increase the risk for which of the following?