Septaly Oriented Mild Aortic Regurgitant Jets Negatively Influence Left Ventricular Blood Flow-Insights From 4D Flow MRI Animal Study

Abstract

Objectives: Paravalvular leakage (PVL) and eccentric aortic regurgitation remain a major clinical concern in patients receiving transcatheter aortic valve replacement (TAVR), and regurgitant volume remains the main readout parameter in clinical assessment. In this work we investigate the effect of jet origin and trajectory of mild aortic regurgitation on left ventricular hemodynamics in a porcine model. Methods: A pig model of mild aortic regurgitation/PVL was established by transcatheter piercing and dilating the non-coronary (NCC) or right coronary cusp (RCC) of the aortic valve close to the valve annulus. The interaction between regurgitant blood and LV hemodynamics was assessed by 4D flow cardiovascular MRI. Results: Six RCC, six NCC, and two control animals were included in the study and with one dropout in the NCC group, the success rate of model creation was 93%. Regurgitant jets originating from NCC were directed along the ventricular side of the anterior mitral leaflet and integrated well into the diastolic vortex forming in the left ventricular outflow tract. However, jets from the RCC were orientated along the septum colliding with flow within the vortex, and progressing down to the apex. As a consequence, the presence as well as the area of the vortex was reduced at the site of impact compared to the NCC group. Impairment of vortex formation was localized to the area of impact and not the entire vortex ring. Blood from the NCC jet was largely ejected during the following systole, whereas ejection of large portion of RCC blood was protracted. Conclusions: Even for mild regurgitation, origin and trajectory of the regurgitant jet does cause a different effect on LV hemodynamics. Septaly oriented jets originating from RCC collide with the diastolic vortex, reduce its size, and reach the apical region of the left ventricle where blood resides extendedly. Hence, RCC jets display hemodynamic features which may have a potential negative impact on the long-term burden to the heart.

Keywords: 4D flow MRI; aortic regurgitation; intraventricular hemodynamics; mild regurgitation; paravalvular leakage; translational large animal model; vortex formation.

Figure 1

Pierce and dilate technique used to create the model of mild eccentric aortic regurgitation/para valvular leakage (AO, aorta; LA, left atrium; LV, left ventricle). (A1) Coronary guide wire (orange arrow) is used to pierce the leaflet/annulus at the hinge point. (A2) Standard PTCA 5 mm balloon (green arrow) is positioned across the defect and inflated. (B1,B2) Aortic regurgitant jet (blue arrows) originating from NCC and RCC region, respectively. (C) Defect of the aortic valve at the hinge point of the leaflet.

Figure 2

Schematic representation of different observation planes annotated as 10–2 h and example images for vortex cross sectional area estimation. Dashed white lines represent outline of anatomical structures of interest. AO, Aorta; LA, Left Atrium; LV, Left Ventricle; RV, Right Ventricle. Anterior cross section of the vortex is delineated in red and the posterior in orange.

Figure 3

Streamline tracing of blood flow for NCC and RCC paravalvular leakage. Mitral inflow in blue and aortic regurgitant jet in red. The time points correspond to ejection (TP0), E-wave acceleration (TP1) peak E-wave (TP2) E-wave deceleration (TP3), diastasis (TP4), A-wave acceleration (TP5), peak A-wave (TP6), A-wave deceleration phase (TP7). The mitral and aortic streamlines are color coded according to the flow velocities. The regurgitant jet is depicted in red. The NCC jet integrated into the anterior vortex and the mitral inflow jet, while the RCC jet is directed along the septum and collides with the anterior vortex during filling.

Figure 4

Cross-sectional area of the anterior vortex for different long axis cut planes (according to Figure 2) for NCC (red circles), RCC (blue stars), and control (grey triangles) animals.

Figure 5

Particle tracking of NCC and RCC regurgitant jets to illustrate residence time of regurgitant blood (left). Particles originating from mitral valve inflow are colored in blue and particles from the regurgitant jet red. Ratios of direct and retained flow of the regurgitant blood volume are shown on the right. Direct flow is the part of diastolic inflowing blood volume that is ejected in the next systole, whereas retained flow represents the diastolic inflow volume that resides in the ventricle for more than 1 heart beat.