Next, valve area is indexed to body size because an apparent small valve area may be only moderate AS in a small patient; an aortic valve area index 0.6 cm2 suggests severe AS. Transaortic stroke volume is calculated by Doppler or 2D imaging. Measurement of a CT calcium score often is helpful. Evaluation for other potential causes of symptoms ensures that symptoms are most likely attributable to valve obstruction. Although the survival rate after TAVI is lower in patients with low-flow severe AS than in patients with normal-flow severe AS, AVR appears beneficial, with an increase in stroke volume and improved survival as compared with 6. Exercise testing may be helpful in clarifying symptom status in patients with severe AS. When symptoms are provoked by exercise test- ing, the patient is considered symptomatic and meets a COR 1 recommendation for AVR; symp- toms are symptoms, whether reported sponta- neously by the patient or provoked on exercise testing. The rate of symptom onset within 1 to 2 years is high (about 60% to 80%) in patients without overt symptoms who demonstrate 1) a fall of 10 mm Hg in systolic blood pressure from baseline to peak exercise or 2) a significant decrease in exercise tolerance as compared with age and sex normal standards. Management of patients with a lack of appropriate rise in BP with exercise is less clear. Decisions about elective AVR in these patients include consid- eration of surgical risk, patient preferences, and clinical factors, such as age and comorbid 7. In patients with very severe AS and an aortic velocity 5.0 m/s or mean pressure gradient 60 mmHg, the rate of symptom onset is approxi- mately 50% at 2 years. 