EVR (Electromagnetic Valve Replacement) is a self-expanding transcatheter aortic bioprosthesis. It is designed to provide patients with long-term aortic valve regurgitation relief and prevent more severe aortic regurgitation. Its new design features an extended sealing skirt, lower implantation depth, and smaller insertion profile. These factors are expected to increase its success and decrease complications. Compared to the CV TAVI system, EVR has a shorter insertion length and smaller diameter, making it easier to place in challenging anatomical locations such as the left ventricular outflow tract. It also has a lower incidence of vascular complications.
The device is primarily composed of an electromagnetic solenoid assembly. It includes a passageway, which communicates with the atmosphere, and a chamber containing an armature and a magnetic pole piece. A control vacuum signal is generated inside the chamber, and a damping orifice is placed between the chamber and the atmosphere. A preload spring urges the armature towards a “closed” valve position.
The electromagnetic solenoid assembly is encased in a valve housing. The lower connecting flange 78 of the solenoid assembly is retained in the external cavity 80 of the upper valve housing 26. In order to keep the pressure within the chamber to a minimum, an electric vacuum regulator valve is installed. The preload of the biasing spring in this valve is sensitive and requires calibration. In addition, the inherent preload variations in production spring components are eliminated.
The electromagnetic solenoid assembly includes an EVR chamber 82, a bobbin 30, and an air inlet 38. The bobbin has a central bore 36, which communicates with the air inlet. The evr valve bobbin is constructed of a non-magnetic nylon tape. Its axial length is the same as the valve. When the bobbin is assembled, the armature and the air inlet are located at the center of the valve, and the primary air gap is the working air gap between the armature and the bobbin. The EVR valve is secured to the upper valve housing of the vacuum regulator valve 14.
The primary air gap in the EVR valve is the axial distance between the armature and the bobbin. This axial distance is similar to that of the bobbin in the CV TAVI system, but the EVR’s insertion profile is slightly smaller, which is important for transfemoral access. In CV patients, the armature is also deep, which may contribute to the fact that the EVR valve does not deploy supra-annularly.
The EVR valve is also available with a built-in re-capture function, allowing the device to be deployed into the left ventricular outflow tract at an intended position 3-5 mm below the native annulus. The EVR has a reduced rate of mild paravalvular regurgitation, and the EVR has a lower incidence of vascular complications. It has a smaller insertion and postdilation profile, as well. This may be beneficial to patients with challenging iliofemoral anatomy.
While a large-scale clinical study is needed to determine the effectiveness of the EVR valve, preliminary results indicate that the bioprosthesis has a high clinical success and low risk of vascular complications. Its long-term clinical outcomes are excellent.