Summary
Background
As current multidetector computed tomography (MDCT) measurements underestimate the size of the aortic annulus ahead of transcatheter aortic valve implantation (TAVI), a strategy of approximate annulus area oversizing has been adopted recently.
Aims
To measure the aortic annulus using a novel complementary intravalvular MDCT slice.
Methods
Fifty-five patients with severe aortic stenosis were selected for MDCT ahead of and 1 month after CoreValve ® TAVI. Two MDCT slices were analysed and compared: the current standard virtual basal ring (VBR) at the nadir of the aortic cusps; and a novel slice, defined as the basal (lowest) complete commissural coaptation (BCCC) plane.
Results
BCCC is an intravalvular plane lying 5.2 ± 0.8 mm above the VBR. The BCCC annulus is almost circular, unlike the VBR (mean eccentricity index 0.09 ± 0.04 vs 0.3 ± 0.1, respectively). The mean BCCC annulus diameter was 26.6 ± 2.3 mm, 16% larger than that of the VBR (23.9 ± 2.2 mm; P < 0.001). The BCCC annulus area proved coherent with the orifice area measured after TAVI on the projection of the same slice (i.e. systematically equal to or greater than the latter [mean difference, +2.3 ± 1.4 mm]), in contrast to the wider scatter found for the VBR (–1.3 ± 2.0 mm). Once the sclerotic calcified valves have been pushed back by the implant, the aortic orifice after TAVI will inevitably be equal to or less than the diameter of the virtually unvalved annulus before TAVI.
Conclusion
Based on the present results, we recommend including a BCCC slice to complete aortic annulus sizing, in order to optimize implant calibration.
Résumé
Contexte
Les mesures scannographiques sous-estimant le diamètre de l’anneau aortique, une stratégie approximative de surtaillage des prothèses aortiques percutanées a récemment été adoptée.
Objectif
Cette étude propose une nouvelle mesure scannographique intravalvulaire de l’anneau aortique.
Méthodes
Un scanner aortique avant et à un mois d’un remplacement valvulaire aortique percutané par CoreValve ® a été réalisé chez 55 patients avec un rétrécissement aortique serré. Deux plans de coupe scannographique ont été analysés et comparés : le communément admis « virtual basal ring » (VBR) au nadir des cusps aortiques ; et le nouveau « Basal complete commissural coaptation » (BCCC), plan le plus bas de coaptation centrale des feuillets valvulaires aortiques.
Résultats
BCCC est un plan intravalvulaire situé à 5,2 ± 0,8 mm en dessus du VBR. L’anneau BCCC est circulaire contrairement au VBR (0,09 ± 0,04 vs 0,3 ± 0,1). Le diamètre moyen de l’anneau BCCC était de 26,6 ± 2,3 mm, supérieur de 16 % au VBR (23,9 ± 2,2 mm ; p < 0,001). Comparativement à la mesure de l’orifice de la prothèse implantée, la mesure de l’anneau BCCC est cohérente car systématiquement égale ou plus grande (différence moyenne, +2,3 ± 1,4 mm), contrairement à l’anneau VBR (–1,3 ± 2,0 mm). Le diamètre annulaire natif est, logiquement, systématiquement supérieur au diamètre de la prothèse implantée dans la valve en refoulant, en périphérie, le matériel valvulaire scléreux et calcifié.
Conclusions
Nos résultats nous incitent à utiliser le plan de coupe du basal complète commissural coaptation pour la détermination précise des dimensions de l’anneau aortique, dans l’optique de la calibration de la prothèse percutanée.
Background
The means of measuring the aortic annulus to optimize sizing and transcatheter aortic valve implantation (TAVI) techniques have been improving for a number of years, but still create problems.
Historically, the aortic annulus was first measured on transthoracic echocardiography (TTE) or transoesophageal echocardiography, but multidetector computed tomography (MDCT) rapidly became the preferred option, as it provides multiplanar three-dimensional analysis . TTE and transoesophageal echocardiography systematically underestimate annulus diameter by a mean of 2 mm (range 1.3–2.4 mm) compared with MDCT . This underestimation is caused by off-axis echocardiographic cross-sections inducing variability in measurement . These significant differences lead to a change in choice of bioprosthesis in 44% of cases .
The definition of the aortic annulus as measured on MDCT is itself indeterminate and even measurements taken from the virtual basal ring (VBR) vary greatly . In five large cohort studies (comprising 53, 60, 71, 80 and 109 patients awaiting TAVI, respectively), the mean VBR diameter – reputed to be highly reproducible – ranged from 22.8 mm to 24.5 mm. Prosthesis/annulus discrepancy can lead to complications, most commonly mismatch or paravalvular aortic regurgitation , with a potentially severe effect on morbidity and mortality.
The VBR is the current standard MDCT measurement plane for the aortic annulus, but there have been several reports of underestimation, leading to a recommendation to oversize the bioprosthesis systematically by 10–25% . Recently, Binder et al. , in a large prospective multicentre controlled trial, confirmed that an MDCT annular area sizing algorithm allowing for 5–10% (maximum 20%) oversizing significantly reduced paravalvular aortic regurgitation rates after TAVI. Implant choice is becoming increasingly moot, given the multiplicity of sizes offered by each manufacturer and the advent of new types of bioprosthesis. Some authors are already anticipating future progress by developing implants that do not exceed the height of the native valves, thereby avoiding any contact with adjacent tissue and structures, such as the left ventricular outflow track and septum or anterior mitral leaflet, coronary ostia and ascending aorta. This trend makes an intra-annular measurement of the aortic valve all the more valuable.
The present study sought to define a novel MDCT slice that would be intravalvular, reproducible and coherent with annular measurements taken 1 month after TAVI: an optimal estimation of (virtually unvalved) aortic annulus diameter will inevitably be equal to or greater than that measured after valve implantation in the native valve.
Methods
Subjects
Overall, 102 consecutive patients treated exclusively with the CoreValve ® aortic implant (Medtronic CV, Irvine, CA, USA) between September 2011 and March 2014 were included for analysis. Aortic stenosis secondary to bicuspid aortic valve disease was an exclusion criterion. Fifty-five subjects were selected retrospectively as having undergone aortic computed tomography before and 1 month after TAVI. Subjects implanted for severe aortic insufficiency ( n = 4) or prior bioprosthesis malfunction ( n = 2) or having previously undergone aortic valvuloplasty ( n = 4) were excluded. Twenty-four subjects were excluded for excessive artefacts (respiration, movement, non-optimal injection) and 13 lacked computed tomography scans after TAVI (including five early deaths). Twenty subjects aged < 45 years with MDCT angiography for atypical chest pain without aortic valve pathology were analysed as controls. The study was performed according to French regulations and was approved by a local ethics committee.
Transthoracic echocardiography protocol
The aortic annulus diameter was measured during systole, within the aortic sigmoid insertion points, on a zoom image in a parasternal long axis window, with the patient in left lateral decubitus .
MDCT protocol before and after TAVI
MDCT comprised an electrocardiogram-gated whole-aorta scan . One month after TAVI, implant position and deployment were checked on a second electrocardiogram-gated thoracic aorta scan with iodized contrast agent injection. All acquisitions were performed on a Philips 64-row scanner (Brilliance CT, Philips Healthcare, Cleveland, OH, USA). Eighty millilitres of Iomeron ® 400 iodized contrast agent (Bracco, Courcouronnes, Paris, France) were injected at 3 mL/s, followed by 40 mL isotonic saline at the same rate, by the peripheral venous route. Acquisition triggering after contrast agent injection was controlled by bolus tracking; the region of interest was situated on the descending aorta, with automatic triggering at 150 HU. Scan direction was craniocaudal during a single apnoea. The acquisition variables were: tube voltage, 120 kV; current, 650–800 mA, according to body surface area; collimation, 64 × 0.625 mm; tube rotation time, 400 ms/revolution; pitch factor, 0.3; field of view, 350 mm; and radiation dose, 1500–2000 mGy/cm. Given the patients’ valvular pathology, beta-blockers were not used to slow heart rate.
Computed tomography reconstruction
Only the 75% cardiac cycle phase was conserved, with a slice thickness of 1.4 mm, to optimize image quality without kinetic blur , as no significant difference between systolic and diastolic images has been proven . Images were transferred to a workstation and analysed on OsiriX DICOM Viewer software (OsiriX Foundation, Geneva, Switzerland) by two experienced operators. Multiplanar reconstruction was used to optimize measurement along the aortic valve anatomy.
Selection of MDCT slice planes
Multiplanar reconstruction of the aortic root allowed study of specific slice planes ( Fig. 1 ). In light of the literature, the following planes were selected for analysis: aortic leaflets basal attachment plane (ALBAP) , at the nadir of the aortic cusps; VBR, directly under the zenith of the left ventricular outflow track ; ascending aorta, 4 cm above the ALBAP; and sinotubular junction (upper limit of commissures), corresponding to the transition between the sinuses of Valsalva and the tubular aorta .
In addition to these standard planes, we further defined two novel planes, referred to as: the upper complete commissural coaptation plane, the uppermost plane of central commissure coaptation (upper limit of valve tightness); and the basal complete commissural coaptation (BCCC) plane, the lowest plane of central commissure coaptation (lower limit of valve tightness). Attention was focused more particularly on the BCCC plane, as it is critical for implant anchorage; the three fibrous commissural insertions and calcific masses that tend to concentrate here exert the greatest mechanical stress on the deployed stent .
We further defined a TTE-like plane, reconstructed from an oblique sagittal slice by modifying the slice plane coronally to achieve perfect aortic sigmoid symmetry and thereby reproduce the conditions for echocardiographic measurement of the aortic annulus in a parasternal long axis window.
Finally, for the multiplanar reconstruction 1 month after TAVI, we defined the post-TAVI BCCC plane, using the distance from the sinotubular junction to the BCCC plane as determined before TAVI: this distance was projected onto the contrast-enhanced scan taken 1 month after TAVI, to obtain the slice plane.
Measurements
Having determined the BCCC plane, we used the three points of aortic valve commissural insertion to trace a deformable circle circumscribing an almost equilateral triangle ( Fig. 2 ). The mean diameter of the BCCC aortic annulus was calculated from the circle and the mean of the sides ( S ) of the triangle as D = 2√( A /π), where A is the measured area and D = 2 S × sin 30°/sin 120° ≈ 1.155 S . In our study, the size of valve prosthesis was chosen according to this BCCC aortic annulus diameter.
Other measurements were based on the standard definitions found in the literature. On VBR axial slices, the diameters D max and D min and the diameter calculated from the area as determined by manual planimetry were assessed. The cusp-commissure distance was assessed as the mean of the three distances between the respective commissure insertions and the facing sinus of Valsalva. The diameters of the ascending aorta, sinotubular junction and sinus of Valsalva were measured on coronal slices . Valsalva sinus height was measured between the ALBAP and the sinotubular junction . The heights of the left and right coronaries were measured, respectively, on oblique coronal and sagittal slices between the lower end of the ostium and the ALBAP .
The eccentricity index was calculated as [1 – ( D min / D max )], an index > 0.1 defining an elliptic annulus .
The diameter on TTE-like slices was measured between the two aortic sigmoid insertions.
After TAVI, planimetric analysis of the outer edge of the stent struts was performed manually on axial BCCC slices to calculate the mean diameter corresponding to the maximum aortic orifice expansion caused by implantation; diameters D max and D min were measured perpendicularly.
Transcatheter aortic valve implantation sizing in our institution
The size of valve prosthesis is chosen according to the BCCC annulus diameter and the manufacturers’ guidelines (Medtronic CV, Irvine, CA, USA); the VBR and echocardiographic measurements are not taken into account.
Statistical analysis
Categorical variables are expressed as percentages and were compared using the Chi 2 test or Fisher’s exact test, as appropriate, with Bonferroni adjustment. Continuous variables are expressed as means ± standard deviations or medians with ranges and were compared between groups using the Mann–Whitney test, with Bonferroni adjustment. Measurement techniques were compared using Bland–Altman plots. Intra- and interobserver agreement was evaluated by calculating intraclass correlation coefficients. Statistical analysis was performed with SPSS 18.0 software (SPSS Inc. Chicago, IL, USA).
Results
Characteristics of the healthy control population
The 20 control subjects had a mean age of 36 ± 6 years (range, 22–44 years) and a mean body surface area of 2.0 ± 0.2 m 2 . Four of the 20 control subjects were women. Table 1 presents aortic root data.
| Mean ± SD | Median | Minimum | Maximum | ICC | |
|---|---|---|---|---|---|
| Ascending aorta | |||||
| Diameter (mm) | 27.7 ± 3.5 | 27.4 | 22.4 | 38.0 | 0.96 |
| Sinotubular junction | |||||
| Diameter (mm) | 26.8 ± 2.7 | 26.5 | 23.6 | 34.7 | 0.97 |
| Coronary arteries | |||||
| Height of the left coronary artery (mm) | 14.1 ± 2.7 | 13.6 | 10.7 | 21.9 | 0.96 |
| Height of the right coronary artery (mm) | 15.1 ± 2.9 | 14.5 | 10.2 | 20.5 | 0.76 |
| Sinus of Valsalva | |||||
| Diameter (mm) | 33.2 ± 3.8 | 32.1 | 29 | 43.7 | 0.95 |
| Height (mm) | 19.0 ± 1.3 | 18.8 | 17.8 | 22.1 | |
| Basal complete commissural coaptation | |||||
| Calculated average annulus diameter (mm) | 26.4 ± 3.2 | 25.1 | 22.2 | 33.9 | 0.97 |
| Diameter calculated from the side of the triangle (mm) | 26.5 ± 3.3 | 25.3 | 22.1 | 33.9 | 0.89 |
| Eccentricity | 0.08 ± 0.03 | 0.08 | 0.03 | 0.15 | |
| Height between BCCC and VBR (mm) | 5.2 ± 0.8 | 5.1 | 3.7 | 6.5 | |
| Virtual basal ring | |||||
| Short axis (mm) | 20.9 ± 2.2 | 20.7 | 17.4 | 24.2 | 0.85 |
| Long axis (mm) | 28.1 ± 2.8 | 27.9 | 23.2 | 32.5 | 0.91 |
| Calculated average annulus diameter (mm) | 24.9 ± 2.5 | 24.4 | 21.1 | 29.4 | 0.96 |
| Eccentricity | 0.25 ± 0.04 | 0.26 | 0.16 | 0.33 | |
| TTE-like diameter (mm) | 22.8 ± 3.0 | 23.1 | 17.4 | 27.7 | 0.78 |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
