Q. A 70-year-old Hispanic male undergoes a left-side total hip replacement. Due to his age and a history of a small, right-side interatrial septum aneurysm, he is held for post-operative monitoring. On his third hospital day, he develops chest pain, tachycardia, dyspnea, and a low-grade fever. The man goes into cardiac arrest and efforts to resuscitate him are unsuccessful. An autopsy reveals a massive pulmonary embolus. Which of the following would most likely predispose the patient to this event?