Figure 2. Diagram of systemic thoracic (A and B), thoracoabdominal (B), and abdominal (C and D) collateral pathways in cases of aortic stenosis. In A, the thoracoacromial and descending scapular arteries (arising from the subclavian arteries) supply the poststenotic descending thoracic aorta with retrograde flow via the intercostal arteries. In B, the internal mammary arteries (arising from the subclavian arteries) connect both with the descending thoracic aorta via the intercostal arteries and with the external iliac arteries via the superior and inferior abdominal epigastric arteries. In C, the inferior intercostal arteries supply the external iliac arteries through the superficial and deep iliac circumflex arteries. In D, the lumbar arteries supply the internal iliac arteries via the inferior gluteal arteries.