Valve Characteristics and Imaging Modality

We analyzed in vitro 53 new and unused aortic bioprosthesis in the most commonly used available sizes: Perimount ( n = 7), Magna ( n = 1), Carpentier Edwards standard ( n = 7), Mosaic ( n = 5), Biocor ( n = 5), Biocor Supra ( n = 5), Aspire ( n = 5), Soprano ( n = 3), Trifecta ( n = 6), Hancock ( n = 5), and Mitroflow ( n = 4). In total, we performed 2,332 two-dimensional (2D) and three-dimensional (3D) TEE in vitro measurements using both Philips iE33 (Philips Medical Systems, Best, The Netherlands) and GE Vivid E9 (GE Healthcare, Little Chalfont, United Kingdom) systems with a range of system settings. TEE in vitro was performed for each aortic bioprosthesis. An iE33 echocardiographic system with an X7-2t Live 3D transesophageal echocardiographic transducer with 2- to 7-MHz operating frequency and a Vivid E9 6 TC multiplane phased-array transesophageal echocardiographic transducer with a 3- to 8-MHz operating frequency probe were used. Both systems enable real-time 3D TEE, as well as simultaneous imaging in two orthogonal planes (Live xPlane [Philips] and Multi-D [GE]) and conventional 2D multiplane TEE.

Methodology

A metal bowl lined with a soft, thick cloth to minimize reverberation artifacts was filled with water and stood for 24 hours to allow degasification. A purpose-built frame was attached to the bowl and supported the transesophageal echocardiographic probe so that the transducer surface was under the water facing downward and approximately 5 cm above the valves that were placed on the cloth at the bottom of the bowl ( Figure 1 ). This essentially provided an in vitro simulation of midesophageal imaging of an aortic bioprosthesis. On the Philips iE33 system, Live xPlane imaging was used to obtain two orthogonal 2D views of the valves. We performed the measurements using simultaneous orthogonal planes because we believe that most operators would use this mode to check the orientation of the 2D scan planes relative to the prosthetic valve sewing ring plane. The 2D line density is the same as nonsimultaneous imaging. In all cases, the frame rate was >30 Hz, which we believe is quite adequate, assuming the patient is not tachycardic. The planes were adjusted to intersect the midpoint of the valve. Therefore, measurements were made from the edge of the strongest (brightest) and most consistent echo signal, ignoring the softer (darker) signals inside the valve ring. Images were acquired using three different system settings, resolution, general, and penetration, maintaining overall gain power at 60%. These settings are equivalent to high, medium, and low fundamental. Three-dimensional mode data sets were acquired using the 3D zoom modality in fundamental mode with the overall gain power maintained at 50% for penetration, general, and resolution modes. A second 3D data set was obtained for each valve using resolution mode, with overall gain at 60% and a high volume rate, to determine the impact of lowering line density and hence spatial resolution. All 3D and four-dimensional zoom data sets were obtained in single-beat mode to replicate the in vivo situation in which this would be used to avoid stitching artifacts.

Experimental setup of water tank. This is an image of the in vitro setup with a transesophageal echocardiographic probe suspended above a BV in a water tank lined with toweling to minimize reverberation artifacts.

All valves were also imaged with a GE Vivid E9 BT12 machine. Multi-D was used and is comparable with Live xPlane imaging on the Philips system. We acquired images using three different frequencies, 8, 6, and 4 MHz, which are comparable with the Philips resolution, general, and penetration modes, maintaining overall gain power at −20 dB. We also used the four-dimensional zoom modality. Initially, data sets were obtained using frequencies of 8, 6, and 4 MHz, with a low volume rate. Then we acquired further images using a frequency of 8 MHz with a high frame rate, which again lowers the line density and, potentially, the spatial resolution.

The internal surface of the valve sewing ring was determined to be the most appropriate and likely landing zone for a VIV implant. The valve sewing ring is the narrowest internal dimension of the valve and is the point chosen by all operators performing this procedure to be the best landing zone for the implant. It is relatively easy to visualize this point on TEE and is analogous to the virtual aortic annulus used as a landing zone during TAVR procedures. Therefore, 2D echocardiographic ID measurements were made for the Philips iE33 machine in Live xPlane at the level of the sewing ring using Xcelera software (R3.2L1 SP2 3.2.1.712-2011) ( Figure 2 ); 3D echocardiographic ID measurements, made at the same level, were generated using the manufacturer’s software (QLAB version 9-3DQ) ( Figure 3 ). Multiplane reconstruction from the 3D data sets was used to facilitate geometrically oriented measurements of the internal dimensions of the sewing rings using three orthogonal and perpendicular axes. Equivalent 2D and 3D echocardiographic ID measurements were also made at the same level of the sewing ring using analysis software on the GE Vivid E9 (version 112.2013) ( Figures 4 and 5 ). Two experienced operators performed the ID measurements on the iE33, and a third experienced operator performed the ID measurements on the Vivid E9. All 2D and 3D echocardiographic measurements of the anatomic ID were compared with the MID and the TID. MID was derived from the published information supplied by the valve companies, and TID was obtained by using Hegar dilators, which is a standard surgical sizing technique ( Table 1 ). Hegar dilators are adjustable and were used in increments of 0.5 mm. Multiple measurements were taken. There is no other practical way to measure TID, as other methods have greater margins of error.

Hancock 25 bioprosthetic aortic valve imaged in vitro. Transesophageal echocardiographic in vitro 2D measurements in resolution mode using a Philips iE33 echocardiographic machine. The left-hand image depicts the equivalent of a midesophageal long-axis view at approximately 120°, whereas the right-hand image is the equivalent transverse image plane at approximately 30°. Sample measurements of the valve internal dimensions are depicted in red, green, and yellow . In the right-hand (short-axis) image, there is some dropout of the valve ring in the medial and lateral aspects due to acoustic shadowing, which frequently occurs in vivo. Therefore, two orthogonal measurements were made at angles at which the ring is more clearly visualized. Because the valve is circular, the precise angle of measurements is not critical, but we recommend that the average of a minimum of two measurements be used.

Hancock 25 bioprosthetic aortic valve imaged in vitro. This is the same valve shown in Figure 1 , imaged using 3D TEE in resolution high-frequency mode imaged with the Philips iE33 echocardiographic machine. A series of multiplane reconstructions were made from the 3D image depicted in the bottom right frame. On the top left (green frame) is a longitudinal plane with measurement (D14 = 2.18 cm). Top right is a transverse (red, short-axis) frame with measurements (D11 = 2.18 cm, D12 = 2.23 cm), and bottom left is a coronal plane (blue) with measurement (D16 = 2.14 cm). Measurements were made from the edge of the strongest (brightest) and most consistent echo signal, ignoring the softer (darker) signals inside the valve ring, and we recommend that an average of all measurements be used to obtain a value for the valve internal dimension.

Trifecta 23 bioprosthetic aortic valve imaged in vitro. Transesophageal echocardiographic in vitro 2D measurements with F6 using a GE Vivid E9 echocardiographic machine. The acquired image sequence is played backward and forward to help identify the appropriate landmarks to use in making measurements. In a single still frame (as displayed), it can be more difficult to be confident about the landmarks, so the replay process is important during measurements.

Trifecta 23 bioprosthetic aortic valve imaged in vitro. Transesophageal echocardiographic in vitro 3D measurements with F4 using a GE Vivid E9 echocardiographic machine. Measurements are made using multiplane reconstructions created to simulate long-axis, short-axis, and coronal planes. As previously described, the entire image sequence is viewed to help identify which landmarks on an individual frame (as displayed) represent the valve ring.

Table 1

Bioprosthetic aortic valves

Valve model and size (mm)	TID (mm)	MID (mm)
Perimount 19	17	18
Perimount 21	19	20
Perimount 23	21	22
Perimount 25	23	24
Perimount 27	25	26
Perimount 29	27	28
Perimount EU 29	27	28
Magna 29	27	28
Mosaic 21	16.5	18.5
Mosaic 23	18.5	20.5
Mosaic 25	20.5	22.5
Mosaic 27	22	24
Mosaic 29	24	26
Carpentier Edwards 19	17	18
Carpentier Edwards 21	19	20
Carpentier Edwards 23	20	22
Carpentier Edwards 25	21	24
Carpentier Edwards 27	23	26
Carpentier Edwards 29	25	28
Carpentier Edwards 31	27	30
Biocor 21	16.5	19
Biocor 23	18.5	21
Biocor 25	20.5	23
Biocor 27	22.5	25
Biocor 29	24.5	27
Biocor Supra 19	16.5	19
Biocor Supra 21	18.5	21
Biocor Supra 23	20.5	23
Biocor Supra 25	22.5	25
Biocor Supra 27	24.5	27
Aspire 20	16.5	18.2
Aspire 21	17.5	19.2
Aspire 23	19	21
Aspire 25	20	23
Aspire 27	22	25
Trifecta 19	16	17
Trifecta 21	18	19
Trifecta 23	20.5	21
Trifecta 25	22	23
Trifecta 27	24	25
Trifecta 29	26	27
Hancock 21	16.5	18.5
Hancock 23	18.5	20.5
Hancock 25	22.5	22.5
Hancock 27	24	24
Hancock 29	26	26
Soprano 20	20	19.8
Soprano 22	22	21.7
Soprano 24	23.5	23.7
Mitroflow 21	17	17.3
Mitroflow 23	19	19
Mitroflow 25	21	21
Mitroflow 27	23	22.9

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