A 68-year-old woman presents to the provider for headaches and pain with chewing. She has a history of hypertension that is well controlled with lisinopril. She denies any tobacco use. Her blood pressure is 128/84 mm Hg, her pulse is 86/min, and her respiratory rate is 12/min. Physical exam reveals a tender and prominent left temporal artery. A biopsy of the temporal artery shows granulomatous inflammation. What is a serious complication of this patient’s condition if left untreated?