Echocardiography
Accurate and adequate imaging prior to a TAVR procedure ensures safe and effective device deployment, giving the patient the highest likelihood for long-term benefit. The majority of patients will undergo transesophageal echocardiography TTE as an initial evaluation for symptoms of AS that might include shortness of breath, fatigue, and chest discomfort. Echocardiographic assessment of the aortic root and surrounding structures gives the care team a general sense for the anatomy and function of the aortic valvular complex, extent and location of surrounding calcification, severity of aortic valve stenosis, and assessment of ventricular function
A normal aortic valve area (AVA) is 3 to 4 cm2. Aortic valve stenosis becomes severe when the area is reduced to about 25% of normal (example provided in Fig. 1). The American Society of Echocardiography (ASE) defines severe AS as a peak transaortic valve blood flow velocity greater than 4 m/s, a mean transaortic valve pressure gradient greater than 40 mm Hg, or AVA less than 1 cm2 in the presence of normal left ventricular function (example provided in Fig. 2). Using echocardiography, the continuity equation is used to calculate the effective AVA by measuring the aortic and left ventricular outflow tract (LVOT) velocity-time integrals and LVOT cross-sectional area. The continuity equation is based on the principle that the left ventricular stroke volume ejected through the LVOT is equal to the stroke volume ejected through the aortic valve, and by knowing the cross-sectional area of the LVOT, can be used to calculate the cross-sectional area of the aortic valve. The AVA can be indexed to body surface area (BSA), but this becomes problematic and inaccurate with obese patients. A dimensionless index (DI) is the ratio of the velocity of blood flow in the LVOT to the velocity of blood flow across the aortic valve. When this ratio becomes less than 0.25, the aortic valve stenosis is considered severe.