When is extra-anatomical bypass for the left subclavian artery required to prevent ischaemia after thoracic endovascular stent grafting?

Introduction: Thoracic endovascular aortic repair (TEVAR) has become an accepted treatment for thoracic aortic disease. However, the principal complications relate to coverage of the thoracic aortic wall and deliberate occlusion of aortic branches over a potentially long segment. Complications include risk of stroke, spinal cord ischaemia (SCI) and arterial insufficiency to the left arm (left arm ischaemia (LAI)).