Aortic Regurgitation
Aortic regurgitation can arise from either pathological abnormality of the aortic valve leaflets (congenital, degenerative, or infectious) or primary dilatation of the aortic root and ascending thoracic aorta. Identifying the etiology and severity of aortic regurgitation is crucial for decision making regarding the choice and the timing of aortic valve intervention. Therefore, it is important to assess the aortic valve apparatus, ascending aorta, and left ventricle to decide on the type of intervention needed. Similar to aortic stenosis, transthoracic echocardiography is usually sufficient to diagnosis and assess the severity of aortic regurgitation. Once a significant aortic regurgitation is identified by Doppler echocardiography assessing the aortic regurgitation severity, etiology, aortic root dimensions, and left ventricular size and function is essential for comprehensive evaluation. However, both qualitative and quantitative Doppler assessment of aortic regurgitation including pressure half time, vena contracta width, proximal isovelocity surface area, regurgitant volume and fraction suffer several limitations due hemodynamic changes, eccentric jets and inherited geometric assumption that the regurgitant orifice is circular, which is not the case in most cases. Adding TEE and 3D echocardiography can provide more detailed assessment of the aortic regurgitation and aortic valve morphology and function. 3D echocardiography can reliably identify the mechanism of aortic regurgitation and with the complementary use of 3D color mode provides important diagnostic information about the regurgitant jets size, location, and severity. In addition, full-volume 3D mode can be very useful for accurate quantification of the left ventricular size and function, an important echocardiographic criterion for surgical referral in patients with severe chronic aortic regurgitation.
The recent advances in 3D technology allows for volumetric assessment of the regurgitant volume by measuring the left and right ventricular stroke volumes with strong correlation with other cardiac imaging modalities.In the setting of good 2D image quality, the use of 3D stroke volume measurements eliminate the interobserver variation, geometric assumption of the LVOT size and ventricular foreshortening.
Another unique advantage of 3D over standard 2D echocardiography is the ability to measure the vena contracta area (VCA). Adding 3D color Doppler to live 3D of the aortic valve allows visualization of the regurgitant jet. In a multiplanar reconstruction model, 3D color dataset can be cropped from either the aortic or left ventricular perspective to the level of the narrowest regurgitant jet (vena contracta) in a perpendicular plane to measure the VCA in early diastole (Figure 4, Movie 3).24 The VCA can be multiplied by the velocity time integral of the aortic regurgitant jet to calculate the regurgitant volume. 3D measurement of VCA is simple and correlates very well with MRI method.25 Noteworthy, the incremental value of 3D echocardiography is invaluable in the evaluation of patients with prosthetic aortic valve regurgitation. The use of color 3D TEE allows for accurate assessment of paravalvular regurgitation site, size, and severity. In addition, live 3D TEE is used to guide percutaneous paravalvular leak closure (Figure 5, Movie 4).