The degree of holodiastolic flow reversal in the aortic arch, in comparison with the forward systolic flow, provides a quick semiquantita- tive estimate of regurgitant fraction. Acute severe AR caused by aortic dissection is a surgical emergency. CT imaging is the primary approach for diagnosis of acute aortic dissection because it is highly accurate and continuously available at most medical centers. MRI is rarely used in the acute setting because of pa- tient instability. TEE may be used when CT imaging is unavailable and is helpful in intraoperative assess- ment of aortic valve function before and after the surgical intervention. The sensitivity and specificity of TTE for diagnosis of Type A3 aortic dissection are only 60% to 80%, whereas TEE has a sensitivity of 98% to 100% and a specificity of 95% to 100%. Angiog- raphy should be considered only when the diagno- sis cannot be determined by noninvasive imaging or when the differential diagnosis is an acute coronary syndrome. 4.1.2. Intervention for Acute AR In patients with acute severe AR resulting from IE or aortic dissection, medical therapy to reduce LV afterload may allow temporary stabilization, but surgery should not be delayed, especially if there is hypotension, pulmonary edema, or evidence of Intra-aortic balloon counterpulsation is contraindicated in patients with acute severe AR.5 Beta blockers are often used in treating aortic dis- section. However, these agents should be used very cautiously, if at all, for other causes of acute AR be- cause they will block the compensatory tachycardia and could precipitate a marked reduction in blood pressure. 4.2. Stages of Chronic AR The most common causes of chronic severe AR in the United States and other high-income countries are BAV disease and primary diseases of the ascend- ing aorta or the sinuses of Valsalva. 