3D Experimental and Computational Analysis of Eccentric Mitral Regurgitant Jets in a Mock Imaging Heart Chamber.

Mitral valve regurgitation (MR) is a disorder of the heart in which the mitral valve does not close properly. This causes an abnormal leaking of blood backwards from the left ventricle into the left atrium during the systolic contractions of the left ventricle. Noninvasive assessment of MR using echocardiography is an ongoing challenge. In particular, a major problem are eccentric or Coanda regurgitant jets which hug the walls of the left atrium and appear smaller in the color Doppler image of regurgitant flow. This manuscript presents a comprehensive investigation of Coanda regurgitant jets and the associated intracardiac flows by using a combination of experimental and computational approaches. An anatomically correct mock heart chamber connected to a pulsatile flow loop is used to generate the physiologically relevant flow conditions, and the influence of two clinically relevant parameters (orifice aspect ratio and regurgitant volume) on the onset of Coanda effect is studied. A two parameter bifurcation diagram showing transition to Coanda jets is obtained, indicating that: (1) strong wall hugging jets occur in long and narrow orifices with moderate to large regurgitant volumes, and (2) short orifices with moderate to large regurgitant volumes produce strong 3D flow features such as vortex rolls, giving rise to the velocities that are orthogonal to the 2D plane associated with the apical color Doppler views, making them "invisible" to the single plane color Doppler assessment of MR. This is the first work in which the presence of vortex rolls in the left atrium during regurgitation is reported and identified as one of the reasons for under-estimation of regurgitant volume. The results of this work can be used for better design of imaging strategies in noninvasive assessment of MR, and for better understanding of LA remodeling that may be associated with the presence of maladapted vortex dynamics. This introduces a new concept in clinical imaging, which emphasizes that the quality and not only the quantity of regurgitant flow matters in the assessment of severity of mitral valve regurgitation.