Final answer:
Irreversible hypotension and fatality after left heart bypass could be due to hypovolemic shock, hypoxia, obstructive shock, or complications like broken heart syndrome leading to heart failure, lethal arrhythmias, or ventricle rupture.
Step-by-step explanation:
Irreversible hypotension and potential fatality after left heart bypass for the repair of a descending thoracic aortic aneurysm can be caused by several factors. These may include hypovolemic shock due to excessive loss of blood volume, hypoxia from decreased oxygen supply to tissues leading to cardiac muscle or brain tissue death, and obstructive shock from blockage in the vascular system such as a pulmonary embolism. In addition, broken heart syndrome or Takotsubo cardiomyopathy, a condition induced by extreme stress, could contribute to heart failure if the myocardium, particularly in the left ventricle, weakens, potentially causing lethal arrhythmias or ventricle rupture.