A patient is diagnosed with aortic regurgitation and presents with fatigue and palpitations. What is the priority diagnostic test?

Aortic regurgitation is a valvular heart disorder characterized by incompetent aortic valve closure, leading to diastolic backflow of blood from the aorta into the left ventricle. This causes volume overload, left ventricular dilation, reduced forward cardiac output, and symptoms such as fatigue and palpitations. Rationale: A. A 12-lead ECG may show left ventricular hypertrophy or arrhythmias, but it does not directly evaluate valve structure or severity of regurgitation. It provides indirect information and is not the most definitive test for valvular dysfunction. B. Chest X-ray may show cardiomegaly or pulmonary congestion in advanced disease, but it lacks specificity for valvular pathology. It cannot assess regurgitant flow or valve anatomy. This does not directly evaluate aortic valve competence. C. Echocardiogram is the gold standard diagnostic test for aortic regurgitation. It visualizes valve structure, measures regurgitant volume, and assesses left ventricular size and function. This directly confirms severity of valvular insufficiency and guides management. D. Cardiac catheterization is invasive and typically reserved for preoperative evaluation or when noninvasive imaging is inconclusive. It is not the initial diagnostic test of choice. It does not replace echocardiography for assessing valvular function.