Which condition is NOT a known complication of acute myocardial infarction (MI)?

Acute myocardial infarction (MI) can lead to several serious complications due to the loss of blood supply to the heart and subsequent damage to the myocardial tissue. Among the complications that are commonly associated with MI are papillary muscle rupture, arrhythmias, and pericarditis.

Papillary muscle rupture can occur as a result of ischemic damage to the heart muscle, leading to acute mitral regurgitation, which can be life-threatening if not addressed promptly. Arrhythmias are also frequently seen following an MI due to the disruption of the heart's electrical conduction system caused by the necrotic tissue. Lastly, pericarditis can develop post-MI as a result of inflammation in the pericardium (the heart's outer layer), known as post-myocardial infarction pericarditis, which can lead to chest pain and other symptoms.

In contrast, pneumothorax, which is the presence of air in the pleural space, is not associated with the complications of an acute MI. It is typically related to lung injuries or other thoracic conditions rather than a cardiac event. Therefore, the condition that is not a known complication of acute myocardial infarction is pneumothorax.