A 65-year-old man with a history of atrial fibrillation presents to his PCPs office 2 months after suffering from a myocardial infarction

A 65-year-old man with a history of atrial fibrillation presents to his PCP’s office 2 months after suffering from a myocardial infarction.  He declined anticoagulation due to fear he would bleed to death. He has had sudden-onset, moderately severe diffuse abdominal pain that began 18 hours ago. He has been vomiting, and he has had several episodes of diarrhea, the last of which was bloody. He has a fever of 100.9 ˚ F. CBC reveals WBC of 15,000/mm3.

Question:

What is the most likely mechanism behind his current symptoms?