Diagnostic Testing: Cardiac Catheterization Diagnostic TTE and Doppler data can be obtained in nearly all patients, but severity of AS may be underes- timated if image quality is poor or if a parallel intercept angle is not obtained between the ultrasound beam and aortic jet. When data from noninvasive testing are non- diagnostic or if there is a discrepancy between clinical and echocardiographic evaluation, cardiac catheteriza- tion for determination of severity of AS can be helpful. Transaortic pressure gradient recordings allow measure- ment of the mean transaortic gradient via simultaneous LV and aortic pressure measurements. Aortic valve area CLINICAL STATEMENTS AND GUIDELINES is calculated with the Gorlin formula by using a Fick or thermodilution cardiac output measurement. See Sec- tion 14.1 for recommendations on coronary angiogra- phy in patients with AS.1,2 3.2.1.5. Diagnostic Testing: Exercise Testing Recommendations for Diagnostic Testing: Exercise Testing in Patients With AS Referenced studies that support the recommendations are summarized in Online Data Supplement 4. COR LOE Recommendations In asymptomatic patients with severe AS (Stage C1), exercise testing is reasonable to assess physiological changes with exercise and to confirm the absence of 3: Harm B-NR In symptomatic patients with severe AS (Stage D1, aortic velocity 4.0 m/s or mean pressure gradient 40 mmHg), exercise testing should not be performed because of the risk of severe Synopsis In a subset of asymptomatic patients with severe AS, exercise testing can provide additional diagnostic and prognostic information, but it should not be performed in symptomatic patients with severe AS. Recommendation-Specific Supportive Text 1. 