Why was this patient at risk for developing pericarditis?

A patient who is 4 days post–coronary artery bypass surgery reports she is having new chest pain that is “different from my angina pain.” The pain’s onset was 5 or 6 hours ago upon first waking up in the morning. The patient has a new pericardial friction rub and a low-grade fever of 100.5°F. The patient is diagnosed with acute pericarditis.

a.            Why was this patient at risk for developing pericarditis?

b.            Why is this patient now at risk for cardiac tamponade?

c.             What are the signs or symptoms that would be indicative of cardiac tamponade in this patient? What is the underlying pathophysiology of these signs and symptoms?