Flow Changes After Biological and Mechanical Aortic Valve Implantation Measured with VFI

Aortic valve stenosis increases peak systolic velocity (PSV) and flow complexity in the ascending aorta, and is treated with either biological or mechanical implants. Vector flow imaging (VFI) is an angle independent ultrasound method for flow assessment. In contrast to conventional ultrasound, VFI can quantify complex flow patterns, e.g. the flow complexity called vector concentration (VC) in long axis and the secondary rotation (SR) in short axis view. Study aim was to evaluate flow changes only visible with VFI before and after valve implantation in patients with aortic valve stenosis. VFI on a commercial scanner (Pro Focus 2202 Ultra View, BK Medical) with a linear transducer (8670, BK Medical) was applied intraoperatively on the ascending aorta. Four patients scheduled for biological valve implants and 4 patients for mechanical valve implants were scanned before and after surgery. Four patients with normal aortic valve were scanned for comparison. VFI data of the ascending aorta were obtained in long and short axis view during the systolic phase for assessment of VC and SR. VC ranges from 0 to 1 (complex to laminar flow), and SR is measured in Hz. PSV was obtained with conventional spectral Doppler. Before surgery, patients with aortic valve stenosis scheduled for mechanical (PSV: 356.3 (64.3) cmls; SR: 15.3 (7.8) Hz; VC: 0.18 (0.03)) and biological implants (PSV: 350.0 (80.8) cmls; SR: 17.9 (2.6) Hz; VC: 0.26 (0.07)) had more complex flow with higher velocities compared with patients with normal aortic valve (PSV: 124.8 (16. 7) cmls; SR: 2.9 (1.1) Hz; VC: 0.83 (0.09)). After surgery, velocities were lower for mechanical (PSV: 214.5 (47.5) cmls; SR: 5.6 (3.0) Hz) compared with biological implants (PSV: 241.5 (39.1) cmls; SR: 13.2 (1.8) Hz). However, VC was higher for biological (0.68 (0.05)) compared with mechanical implants (0.56 (0.09)) indicating a more laminar and less complex flow despite higher systolic velocities in patients treated with biological implants. The mechanical valve has a larger opening with cusps attached centrally in the lumen opposed to the biological valve, which may explain the differences found. Normal flow was neither found for biological nor mechanical implants. VFI can provide new parameters for flow evaluation and be useful for aortic flow assessment before and after valve implantation and in the development of mechanical valves.