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Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant
Eur J Vasc Endovasc Surg (xxxx) xxx, xxx
Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant Massimiliano M. Marrocco-Trischitta a,b,*, Moad Alaidroos Paolo Righini b, Mattia Glauber f, Giovanni Nano b,g
a,c
, Rodrigo M. Romarowski d, Francesco Secchi
e,g
,
a
Clinical Research Unit, IRCCS e Policlinico San Donato, Milan, Italy Vascular Surgery Unit, IRCCS e Policlinico San Donato, Milan, Italy c Vascular Surgery Unit, Policlinico San Marco, Zingonia, Italy d 3D and Computer Simulation Laboratory, IRCCS e Policlinico San Donato, Milan, Italy e Division of Radiology, IRCCS e Policlinico San Donato, Milan, Italy f Minimally Invasive Cardiac Surgery Unit, Istituto Clinico Sant’Ambrogio, Milan, Italy g Department of “Scienze Biomediche per la Salute”, University of Milan, Italy b
WHAT THIS PAPER ADDS This work shows that the “bovine” aortic arch is associated with a consistent geometric pattern, which identifies hostile proximal landing zones for endograft deployment, namely Zone 3 and Zone 0 in Type I arch. The results suggest that the “bovine” aortic arch mandates a specific amendment to thoracic endovascular aortic repair planning. Further biomechanical studies are warranted to disclose the potential causative relationship between the described peculiar geometric features and the risk of developing thoracic aortic pathologies in patients with this anatomical variant. Objectives: The aim was to investigate whether the “bovine” aortic arch (i.e. arch variant with a common origin of the innominate and left carotid artery (CILCA)) is associated with a consistent geometric configuration of proximal landing zones for thoracic endovascular aortic repair (TEVAR). Methods: Anonymised thoracic computed tomography (CT) scans of healthy aortas were reviewed to retrieve 100 cases of CILCA. Suitable cases were stratified according to type 1 and 2 CILCA, and also based on type of arch (I, II, and III). Further processing allowed calculation of angulation and tortuosity of the proximal landing zones. Centre lumen line lengths of each proximal landing zone were measured in a view perpendicular to the centre line. All geometric features were compared with those measured in healthy patients with a standard arch configuration (n ¼ 60). Two senior authors independently evaluated the CT scans, and intraand interobserver repeatability were assessed. Results: The 100 selected patients (63% male) were 71.4 7.7 years old. Type 1 CILCA (62/100) was more prevalent than type 2 CILCA (38/100), and the two groups were comparable in age (p ¼ .11). Zone 3 presented a severe angulation (i.e. > 60 ), which was greater than in Zone 2 (p < .001), and a consistently greater tortuosity than Zone 2 (p ¼ .003). This pattern did not differ between type 1 and type 2 CILCA. A greater tortuosity was also observed in Zone 0, which was related to increased elongation of the ascending aorta (i.e. Zone 0), than the standard configuration. The CILCA had an overall greater elongation, and Zone 2 also was specifically longer. When stratifying by type of arch, reversely from Type III to Type I, the CILCA presented a gradual flattening of its transverse tract, which entailed a consistent progressive elongation (p ¼ .03) and kinking of the ascending aorta, with a significant increase of Zone 0 angulation to even a severe degree (p ¼ .001). Also, from Type III to Type I, Zone 2 presented a progressively shorter length (p ¼ .004), which was associated with increased tortuosity (p < .05). Mean intra- and interobserver differences for angulation measurements were 1.4 6.8 (p ¼ .17) and 2.0 10.1 (p ¼ .19), respectively. Conclusions: CILCA presents a consistent and peculiar geometric pattern compared with standard arch configuration, which provides relevant information for TEVAR planning, and may have prognostic implications. Keywords: Aortic angulation, Aortic elongation, Aortic tortuosity, Bovine arch, Proximal landing zones, Thoracic endovascular aortic repair Article history: Received 20 June 2019, Accepted 12 November 2019, Available online XXX Ó 2019 European Society for Vascular Surgery. Published by Elsevier B.V. All rights reserved.
* Corresponding author. Clinical Research Unit, IRCCS - Policlinico San Donato, Via Morandi 30, 20097 San Donato Milanese, Milan, Italy. E-mail address: [email protected] (Massimiliano M. Marrocco-Trischitta). 1078-5884/Ó 2019 European Society for Vascular Surgery. Published by Elsevier B.V. All rights reserved. https://doi.org/10.1016/j.ejvs.2019.11.019
Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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INTRODUCTION The so called “bovine” aortic arch is characterised by the presence of a common origin of the innominate and left carotid artery (CILCA), or, less frequently, by the origin of the left carotid directly from the innominate artery (i.e. type 2 CILCA)1 (Fig. 1). Recent guidelines and recommendations2,3 have suggested abandoning the use of the misnomer bovine, and adopting a more descriptive terminology. Accordingly, in the present work, for brevity and practical reasons, we used the acronym CILCA, which was previously employed in a meta-analysis on this topic.4 The CILCA is the second most common arch configuration, and its prevalence in the general population is 13.6%, with relevant differences among ethnic groups.5 Notably, however, the real prevalence of the CILCA is probably underestimated, because its presence is largely unreported6,7 due to the presumed clinical irrelevance of this anatomical variant. In fact, the peculiar anatomical features associated with the CILCA mandate specific management strategies and pre-operative planning in both surgical and endovascular procedures involving the aortic arch, including type A aortic dissection repair8 and carotid stenting.9 There is evidence in the literature that the CILCA represents a potential determinant of the onset of thoracic aortic disease,4 and this entails a relevant prevalence of this anatomical variant among patients requiring thoracic endovascular aortic repair (TEVAR). Nevertheless, despite the apparent need for specific studies on the impact of the CILCA configuration on TEVAR planning, this issue has never been addressed specifically. Severe angulation and tortuosity of proximal landing zones for endovascular aortic repair represent recognised determinants of post-operative endograft performance,10e 13 even though there is no consensus on their definition and on clinically significant threshold values, either in guidelines11,14,15 or in current instructions for use of commercially available endografts.16 Also, these relevant anatomical features are associated with high displacement forces that further increase the risk of endograft failure.17
Previous studies showed that consistent geometric16 and haemodynamic patterns17 can be predicted in specific aortic arch configurations. These analyses allow the identification of landing zones that present consistent unfavourable biomechanical features compared with the adjacent ones, and therefore can be regarded as hostile for endograft deployment.18 The aim of the present study was to investigate the angulation and tortuosity of proximal landing zones for TEVAR in CILCA configuration (i.e. Zone 0, 2, and 3) (Fig. 2), and assess whether this anatomical variant is associated with a consistent geometric pattern, which may provide useful insights for assessing TEVAR feasibility and planning. METHODS A retrospective review of anonymised thoracic CT angiography scans performed at our institution in 2016 was conducted to retrieve 100 cases of CILCA. A control group of subjects with standard arch configuration was also retrieved. This cohort has already been described in a previous work.16 The present study was conceived as a proof of concept geometric analysis, and therefore the search included subjects with a healthy aortic arch undergoing diagnostic evaluation for various clinical reasons. Only thin cut (1.0 mm or 1.5 mm) CTs of patients with visible origins of the supra-aortic branches were considered. Exclusion criteria for both groups were age <60 years, diameter of the thoracic aorta >40 mm, radius of arch curvature <20 mm, previous aortic surgery, and presence of radiological signs of aortic pathology, including dissection, intramural haematoma, or penetrating aortic ulcer. Regarding exclusion criteria, pathological and ectatic aortas were excluded to eliminate potential confounding variables for the assessment of a consistent geometric pattern. Aortas with radius of curvature <20 mm were excluded because the latter represents a contraindication to TEVAR according to manufacturers’ instructions for use of stent grafts, and defines a steep aortic arch angulation that
Figure 1. Anatomical configurations of the CILCA aortic arch (arch variant with a common origin of the innominate and left carotid artery): type 1 (A) and type 2 (B). Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Figure 2. Ishimaru’s proximal landing zones in the bovine arch variant (A) and in the standard arch configuration (B).
could alter the measurements of landing zones angulation.16 Suitable cases were stratified according to type 1 and 2 CILCA1 (Fig. 1) and also stratified based on the Aortic Arch Classification in Type I, II and III, according to the Modified Arch Landing Areas Nomenclature (MALAN)16 (Fig. 3). Further processing, based on 3D multiplanar reconstruction, was performed as previously described in detail16 with 3Mensio Vascular software 8.0Ò (3Mensio Medical Imaging B.V., Bilthoven, The Netherlands), which provides specific functions for automatic measurements. Proximal landing zones angulation was determined using the centre lumen line “tangent angle” function, which calculates the angle between tangent lines drawn for any two points along the centre lumen line (Fig. 4). Specifically, we considered the angle between the flow axis of each proximal landing zone and the hypothetical body of the lesion to treat, equivalent to the b angle defined by the Society for Vascular Surgery reporting standards for endovascular repair of the abdominal aorta (EVAR).19 b angles were calculated by selecting the most proximal point of each proximal landing zone, and a point at 40 mm distance along the centre lumen line.16 The more proximal 20 mm of such a distance accounted for the proximal neck for theoretical endograft deployment. The more distal 20 mm accounted for the hypothetical body of the lesion to treat. For Zone 0, the proximal point was chosen at the level of the top of the pulmonary trunk. Angulations were classified into mild (<40 ), moderate (40e60 ), or severe (>60 ).16 The aortic arch tortuosity index was calculated by placing two markers (AeB) in axial view at the mid-luminal point of the ascending and descending aorta at the height of the bifurcation of the pulmonary trunk. The index was defined as the shortest distance between A and B divided by the centre lumen line distance between A and B.20 Tortuosity angle of each landing zone was measured using the “tortuosity angle function”, which is calculated between two line elements that are defined by three control
points located on the centreline (Fig. 4). According to the manufacturer, the first point is the start of the first line element, the second point is the end of the first line element and the start of the second line element, and the third point is the end of the second line element. The distance between the points was automatically set by the software at 15 mm. Proximal landing zones with greater angulation and tortuosity than the adjacent ones were identified as geometrically hostile for endograft deployment.18 Centre lumen line lengths of each landing zone were measured in a view perpendicular to the centre lumen line. Zone 0 was measured starting from level of the top of the pulmonary artery bifurcation. Two investigators independently evaluated the CT scans. Measurements were repeated for 15 (15%) scans, randomly selected from the study group, to assess intra- and interobserver repeatability using BlandeAltman plots. The study was approved by the local ethics committee, and the need for informed patient consent was waived because of the retrospective nature of the analysis and the use of anonymised data. Statistical analysis Data were analysed with SPSS software v. 22 (SPSS Inc, Chicago, IL, USA). The normality of each sample was tested with the ShapiroeWilk test. Comparisons between age groups and types of CILCA (type 1 vs. type 2) were made with the unpaired t test for normally distributed samples, and with the ManneWhitney U test for non-normally distributed data. Comparisons between zones of different Types of arch were made with one way analysis of variance or the KruskaleWallis test for normally and non-normally distributed samples respectively. The JonkheereeTerpstra test was used to verify the hypothesis that angulation and tortuosity increase across landing zones based on the type of arch, as previously described in the standard aortic arch.16 Continuous variables were reported as mean and
Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Type I
Type II
2 diameter of CCA
Zone 0
0/I
MALAN
>2 diameter of CCA
0/II
2 diameter of CCA
Zone 1
2 diameter of CCA
Zone 2
2/I
MALAN
2/II
3/I
MALAN
1/III
>2 diameter of CCA
2 diameter of CCA
Zone 3
0/III
>2 diameter of CCA
1/II
1/I
MALAN
Type III
2/III
>2 diameter of CCA
3/II
3/III
Figure 3. The Modified Arch Landing Areas Nomenclature (MALAN), which comprises proximal landing zones according to Ishimaru’s Aortic Arch Map, and types of arch according to the Aortic Arch Classification. CCA ¼ common carotid artery. (This picture was previously published in an article by the present authors in the Journal of Vascular Surgery16).
A
B Angle = 14° Arm Length: 15mm
Zone 2
Zone 2
Angle = 56° Distance Between handles: 40mm
Figure 4. (A) b angles of proximal landing zone (defined as a by 3Mensio Vascular software 8.0Ò). (B) Tortuosity angle of proximal landing zone (see Methods for details). Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Table 1. Angulation (b angle) in proximal landing zones of all CILCA arches, and stratified by type 1 and type 2 CILCA Proximal landing zone
All CILCA (n [ 100) Mean (95% CI)
Type 1 CILCA (n ¼ 62) Mean (95% CI)
Type 2 CILCA (n ¼ 38) Mean (95% CI)
p value
Zone 0 Zone 2 Zone 3 p value
52.3 (50.0e54.6) 51.6 (48.8e54.4) 63.1 (60.7e65.5) <.001
52.0 (49.0e55.0) 52.2 (48.3e56.0) 63.4 (60.5e66.4) <.001
52.8 (49.1e56.6) 50.7 (46.4e54.9) 62.6 (58.3e66.9) <.001
.73* .98* .87*
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. * Type 1 vs. type 2 CILCA.
95% confidence intervals. Statistical significance was assumed at p < .05.
RESULTS Overall, 1 036 CTs were reviewed to retrieve 128 CILCA arch cases. The prevalence observed (i.e. 12.35%) was consistent with the literature. After applying the inclusion and exclusion criteria, the 100 selected patients (63% male) were 71.4 7.7 years old. The control group of subjects with standard arch configuration (70% male) was 71 8 years old. It listed 60 cases, 20 for each type of arch (I to III). The three subgroups were comparable in age (78.8 8.5 years, 75.2 8.5, and 75.4 9.5 respectively; p ¼ .29). Type 1 CILCA (62/100) was more prevalent than type 2 CILCA (38/100) in the study cohort, and the two groups were comparable in age (70.4 7.3 years old and 73.0 8.3 years old respectively, p ¼ .11). Types of arch were equally distributed in the study group (Type I, n ¼ 31; Type II, n ¼ 32; Type III, n ¼ 37), and three groups did not significantly differ in terms of age (Type I, 71.3 8.6 years, Type II, 70.8 7.2 years, and Type III 72.0 7.6 years; p ¼ .70). Proximal landing zone angulations of the whole study group are reported in Table 1. In terms of absolute values, both Zone 0 and Zone 2 had a moderate degree of angulation, whereas Zone 3 presented a severe angulation. When comparing different landing zones, Zone 3 presented a much greater angulation than Zone 2 (p < .001) and Zone 0 (p < .001), whereas there was no difference between Zone 2 and Zone 0 (p ¼ 1.0). The same pattern was found after stratification in Type 1 and Type 2 CILCA arch (Table 1).
In the control group, angulation did not differ between adjacent proximal landing zones, even though it progressively increased towards the distal arch (p < .001) (Table S1). After stratification based on the type of arch, angulation progressively increased across landing zones from Type I to Type III arch (p < .001) (Table S2).16 Of note, in standard Type III arch, Zone 3 had a severe and a consistently greater angulation than Zone 2 (p ¼ .02), which reflects the pattern observed in the whole CILCA group (Table 1). By contrast, angulations of CILCA landing zones after stratification based on the Type of arch (Table 2) presented a different trend. Zone 3 and Zone 2 angulation pattern did not differ between types of arch, with Zone 3 being consistently associated with a severe and much greater angulation than Zone 2. A novel and peculiar pattern was instead found in Zone 0, where angulation was moderatee severe in Type I CILCA arch, and gradually and significantly decreased in Type II and Type III CILCA arch (p < .001). The tortuosity index in CILCA arch was 1.55 (1.51e1.59), and it was greater than that measured in standard arch configuration (1.49 (1.44e1.53), p ¼ .02). Tortuosity angles of proximal landing zones of the whole study group are reported in Table 3. Tortuosity was greater in Zone 3 and Zone 0, whereas it was consistently and significantly lower in the transverse aortic tract, namely in Zone 2 (Zone 3 vs. Zone 2 p ¼ .003; Zone 0 vs. Zone 2 p < .001). The same pattern was observed when Type 1 and Type 2 CILCA were separately considered. In the control group, tortuosity angles did not differ between adjacent proximal landing zones (Table S1). After stratification based on the type of arch, landing zones
Table 2. Angulation (b angle) in proximal landing zones of 100 individuals with CILCA arch stratified by the type of arch (i.e. Modified Arch Landing Areas Nomenclature) Proximal landing zone
Type I (n [ 31) Mean (95% CI)
Type II (n [ 32) Mean (95% CI)
Type III (n [ 37) Mean (95% CI)
p value
Zone 0 Zone 2 Zone 3 p value
57.6 (53.7e61.5) 51.4 (46.1e56.7) 59.4 (55.2e63.7) <.05
53.5 (49.5e57.5) 50.1 (44.9e55.4) 62.2 (58.3e66.2) <.001
46.9 (43.4e50.4) 53.0 (48.3e57.7) 66.9 (62.8e71.1) <.001
.001 .69 .03
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Table 3. Tortuosity angle in proximal landing zones of all CILCA arches, and stratified by type 1 and type 2 CILCA Proximal landing zone
All CILCA (n [ 100) Mean (95% CI)
Type 1 CILCA (n [ 62) Mean (95% CI)
Type 2 CILCA (n [ 38) Mean (95% CI)
p value
Zone 0 Zone 2 Zone 3 p value
24.5 (23.4e25.5) 16.4 (15.3e17.6) 20.3 (18.8e21.7) <.001
24.0 (22.7e25.2) 17.1 (15.6e18.7) 20.7 (18.6e22.7) <.001
25.3 (23.5e27.1) 15.3 (13.5e17.2) 19.6 (17.5e21.7) <.001
.12* .14* .81*
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. * Type 1 vs. type 2 CILCA.
tortuosity progressively increased from Type I to Type III arch (p ¼ .03) (Table S3).16 Also, in standard Type III arch, Zone 3 had a greater angulation than Zone 2 (p ¼ .02), which again is consistent with the pattern observed in the whole CILCA group (Table 1). In the CILCA arch, after stratification based on types of arch (Table 4), a greater tortuosity was observed in Zone 0 regardless the type of arch, whereas in Zone 2 tortuosity gradually and consistently decreased in Type II and Type III CILCA arch (p < .05). Centre lumen line lengths are reported in Table S4, and did not differ in type 1 and type 2 CILCA. When compared with those measured in subjects with standard arch configuration, the cumulative length (CILCA Z0þZ2 vs. standard arch Z0þZ1þZ2) was much greater in CILCA (67.0 mm (64.5e69.6) vs. 60.2 mm (57.4e63.0), p < .001). Zone 0 was also significantly longer in CILCA (46.3 mm (44.5e48.2) vs. 34.5 (32.5e36.5), p < .001). Zone two as well had a greater length in CILCA than the standard arch (20.7 mm (19.0e22.4) vs. 16.6 mm (15.5e17.7), p < .001). When stratified based on the Type of arch (Table 5), in reverse from Type III to Type I, Zone 0 gradually increased in length (p ¼ .03), whereas Zone 2 appeared gradually shortened (p ¼ .004). Mean intra- and interobserver differences for b angle measurements were 1.4 6.8 (p ¼ .17) and 2.0 10.1 (p ¼ .19), respectively. DISCUSSION This work has shown that the CILCA arch variant presents a consistent and peculiar geometric pattern of proximal
landing zones for TEVAR compared with the standard arch configuration, and that this pattern does not differ between type 1 and type 2 CILCA arch (Fig. 1). Specifically, the results indicate that Zone 3 in CILCA is associated with a severe angulation (i.e. > 60 ),18 whereas Zone 2 presents a much lesser angulation compared with Zone 3, and a consistent moderate degree of angulation (i.e. 40 e60 ).16 Zone 3 appears also associated with a consistently greater tortuosity than Zone 2. Interestingly, in CILCA arch, a greater tortuosity is also observed in Zone 0, and this finding appears related to increased elongation of the ascending aorta. From the comparison between CILCA and standard arch configuration, it becomes apparent that, because of the common origin of the left carotid and innominate artery, the take off of the common trunk is shifted distally towards the top of the arch. In this respect, Zone 0 in CILCA arch is on average 1 cm longer than Zone 0 in the standard configuration. Notably also, Zone 2 as well is specifically longer in CILCA, and this anatomical variant has an overall greater elongation than the standard arch configuration. From a clinical standpoint, these findings suggest that Zone 3 in CILCA arch should be regarded as unfavourable for endograft deployment, and that Zone 2 represents the preferred proximal landing zone for the treatment of pathologies of the distal arch, possibly after prophylactic rerouting of the left subclavian artery (LSA) by either surgical or endovascular means.3 This is also the case because the presence of severe angulation requires a longer proximal landing zone to obtain an adequate sealing and fixation.10 In this respect, an acceptable length is often unavailable in Zone 3 due to the anatomical limitation of
Table 4. Tortuosity angle in proximal landing zones of 100 individuals with CILCA arch stratified by the Type of arch (i.e. Modified Arch Landing Areas Nomenclature) Proximal landing zone
Type I (n ¼ 31)
Type II (n ¼ 32)
Type III (n ¼ 37)
p value
Zone 0 Zone 2 Zone 3 p value
25.6 (23.7e27.4) 18.0 (15.6e20.4) 19.0 (16.9e21.2) <.001
24.9 (23.4e26.5) 17.1 (14.9e19.3) 19.3 (16.5e22.0) <.001
23.1 (21.1e25.1) 14.6 (13.0e16.2) 22.1 (19.4e24.9) <.001
.13 <.05 .14
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Table 5. Centreline length in proximal landing zones of 100 individuals with CILCA arch stratified by the type of arch (i.e. Modified Arch Landing Areas Nomenclature) Proximal landing zone
Type I (n [ 31)
Type II (n [ 32)
Type III (n [ 37)
p value
Zone 0 Zone 2
49.3 (46.3e52.3) 17.7 (15.9e19.5)
46.9 (43.5e50.2) 20.5 (17.7e23.3)
43.4 (40.2e46.7) 23.4 (19.9e26.9)
.034 .004
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. Data are presented as mean and 95% confidence interval. Values are lengths in mm.
the origin of LSA. Zone 2 in CILCA, by contrast, not only presents a significantly lesser degree of angulation and tortuosity, but also offers a longer neck for endograft deployment. In this work, we also investigated whether the recently introduced MALAN nomenclature16 (Fig. 3), which merges the Ishimaru’s map21 and the Aortic Arch Classification in Type I, II, and III could be applied to the CILCA variant. Interestingly, in contrast to what is observed in the standard anatomical pattern of the aortic arch,18 the CILCA Type II and Type III configurations are not associated with a progressively less favourable anatomy for TEVAR than Type I, but quite the contrary. In reverse, from Type III to Type I (Fig. 5), the CILCA presents a gradual flattening of the transverse tract of the aortic arch, which eventually provides a “cubic shape”22 to the whole arch. This entails a consistent progressive elongation (Table 5) and kinking of the ascending aorta, with a significant increase of Zone 0 angulation to even a severe degree (Table 2). Notably also, from Type III to Type I, Zone 2 presents a progressively shorter length (Table 5), which is consistently associated with an increased tortuosity (Table 4). These findings provide valuable insights also into the increased risk of developing thoracic aortic aneurysm and dissection in subjects with CILCA arch.4 The pathophysiological mechanism underlying this phenomenon remains to be established.23 Previous studies however, suggested a potential causative role for specific geometric features, including aortic angulation,24,25 tortuosity,26,27 and elongation,28e30 and the inherent detrimental haemodynamic effects on the aortic wall respectively.31e36
In CILCA arch, it is anticipated that the presence of these anatomical features, and particularly in Zone 3 and in Zone 0, entails a local adverse biomechanical environment, which may cause a failure of aortic wall properties in that area. In this respect, it is noteworthy that Zone 3 identifies the aortic tract within 2 cm of the LSA, which represents the most common site for proximal entry tear in Type B dissections.11 Also, Zone 0 comprises the areas where the entry tear in Type A dissections most frequently occurs (i.e. just above the sinotubular junction and just proximal to the origin of the innominate artery).24 Finally, the work showed that the geometric pattern of the CILCA arch resembles that of the Type III standard arch. Interestingly, both configurations have a high prevalence in patients with Type B aortic dissection,31,37 and these observations further support the relevance of specific geometric features as potential anatomical risk factors for the onset of aortic disease. Some limitations of the study are recognised, including the use of a hypothetical body of the lesion to treat for the calculation of proximal landing zone angulation and tortuosity, which is related to the use of healthy aortas.16 Also, methods and angle grades previously validated for EVAR19 were employed, and used for TEVAR cases only in preliminary studies.16,18 Finally, the reported data need to be validated in patients with aortic arch pathologies. Nevertheless, the analyses were based on centreline measurements, which are less likely to be affected by the modification of the aortic wall induced by the onset of pathological derangements. In this respect, previous studies in the standard arch configuration demonstrated that the
Figure 5. Three dimensional computed tomography based surface reconstruction of CILCA aortic arches (arch variant with a common origin of the innominate and left carotid artery) stratified based on Type of arch. (A) Type I arch, (B) Type II arch and (C) Type III arch. Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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methods16 reported here reliably and consistently predict the geometric pattern observed in diseased aortas even when performed in healthy aortas.18 Hence, the work provides robust evidence to further investigate the geometric as also the haemodynamic pattern potentially associated with the CILCA arch, as suggested by preliminary results from the literature.31 CONCLUSIONS CILCA arch is associated with a consistent geometric configuration, which provides relevant information to improve the decision making process for TEVAR, even though patient specific pre-operative planning remains essential. Also, the findings suggest a potential role for the described anatomical pattern in the development of thoracic aortic pathologies in patients with CILCA variant,4 which warrants further specific biomechanical studies.
Massimiliano M. Marrocco-Trischitta et al.
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CONFLICTS OF INTEREST None. FUNDING This work was supported in part by “Ricerca Corrente” grants from IRCCS -Policlinico San Donato, San Donato Milanese, Milan, Italy.
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ACKNOWLEDGEMENTS An abstract of this manuscript has been accepted for fasttrack presentation at the Annual Meeting of the European Society for Vascular Surgery, Hamburg, 24e27. September 2019.
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APPENDIX A. SUPPLEMENTARY DATA Supplementary data to this article can be found online at https://doi.org/10.1016/j.ejvs.2019.11.019.
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REFERENCES 1 Moorehead PA, Kim AH, Miller CP, Kashyap TV, Kendrick DE, Kashyap VS. Prevalence of bovine aortic arch configuration in adult patients with and without thoracic aortic pathology. Ann Vasc Surg 2016;30:132e7. 2 Rylski B, Pacini D, Beyersdorf F, Quintana E, Schachner T, Tsagakis K, et al. Standards of reporting in open and endovascular aortic surgery (STORAGE guidelines). Eur J Cardiothorac Surg 2019;56:10e20. 3 Czerny M, Schmidli J, Adler S, van den Berg J, Bertoglio L, Carrel T, et al. Current options and recommendations for the treatment of thoracic aortic pathologies involving the aortic arch: an expert consensus document of the European Association for Cardio-Thoracic Surgery (EACTS) and the European Society for Vascular Surgery (ESVS). Eur J Vasc Endovasc Surg 2019;57:165e 98. 4 Marrocco-Trischitta MM, Alaidroos M, Romarowski RM, Milani V, Ambrogi F, Secchi F, et al. Aortic arch variant with a common origin of the innominate and left carotid artery as a determinant of thoracic aortic disease: a systematic review and meta-analysis. Eur J Cardiothorac Surg 2019 Oct 16. https://doi.org/10.1093/ ejcts/ezz277. pii: ezz277. [Epub ahead of print]. 5 Popieluszko P, Henry BM, Sanna B, Hsieh WC, Saganiak K, Pekala PA, et al. A systematic review and meta-analysis of Î
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Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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tortuosity of the thoracic aorta on computed tomography. J Vasc Surg 2018;68:1183e92. Ishimaru S. Endografting of the aortic arch. J Endovasc Ther 2004;11(Suppl. 2):II62e71. Schnell S, Smith DA, Barker AJ, Entezari P, Honarmand AR, Carr ML, et al. Altered aortic shape in bicuspid aortic valve relatives influences blood flow patterns. Eur Heart J Cardiovasc Imaging 2016;17:1239e47. Wanamaker KM, Amadi CC, Mueller JS, Moraca RJ. Incidence of aortic arch anomalies in patients with thoracic aortic dissections. J Card Surg 2013;28:151e4. Poullis MP, Warwick R, Oo A, Poole RJ. Ascending aortic curvature as an independent risk factor for type A dissection, and ascending aortic aneurysm formation: a mathematical model. Eur J Cardiothorac Surg 2008;33:995e1001. Nathan DP, Xu C, Gorman 3rd JH, Fairman RM, Bavaria JE, Gorman RC, et al. Pathogenesis of acute aortic dissection: a finite element stress analysis. Ann Thorac Surg 2011;91:458e63. Franken R, El Morabit A, de Waard V, Timmermans J, Scholte AJ, van den Berg MP, et al. Increased aortic tortuosity indicates a more severe aortic phenotype in adults with Marfan syndrome. Int J Cardiol 2015;194:7e12. Shirali AS, Bischoff MS, Lin HM, Oyfe I, Lookstein R, Griepp RB, et al. Predicting the risk for acute type B aortic dissection in hypertensive patients using anatomical variables. JACC Cardiovasc Imaging 2013;6:349e57. Krüger T, Oikonomou A, Schibilsky D, Lescan M, Bregel K, Vöhringer L, et al. Aortic elongation and the risk for dissection: the Tübingen Aortic Pathoanatomy (TAIPAN) project. Eur J Cardiothorac Surg 2017;51:1119e26. Heuts S, Adriaans BP, Gerretsen S, Natour E, Vos R, Cheriex EC, et al. Aortic elongation part II: the risk of acute type A aortic dissection. Heart 2018;104:1778e82.
9 30 Lescan M, Veseli K, Oikonomou A, Walker T, Lausberg H, Blumenstock G, et al. Aortic elongation and stanford B dissection: the tübingen aortic pathoanatomy (TAIPAN) project. Eur J Vasc Endovasc Surg 2017;54:164e9. 31 Shalhub S, Schäfer M, Hatsukami TS, Sweet MP, Reynolds JJ, Bolster FA, et al. Association of variant arch anatomy with type B aortic dissection and hemodynamic mechanisms. J Vasc Surg 2018;68:1640e8. 32 Ou P, Celermajer DS, Raisky O, Jolivet O, Buyens F, Herment A, et al. Angular (Gothic) aortic arch leads to enhanced systolic wave reflection, central aortic stiffness, and increased left ventricular mass late after aortic coarctation repair: evaluation with magnetic resonance flow mapping. J Thorac Cardiovasc Surg 2008;135:62e 8. 33 Jackson ZS, Dajnowiec D, Gotlieb AI, Langille BL. Partial offloading of longitudinal tension induces arterial tortuosity. Arterioscler Thromb Vasc Biol 2005;25:957e62. 34 Chi Q, He Y, Luan Y, Qin K, Mu L. Numerical analysis of wall shear stress in ascending aorta before tearing in type A aortic dissection. Comput Biol Med 2017;89:236e47. 35 Adriaans BP, Heuts S, Gerretsen S, Cheriex EC, Vos R, Natour E, et al. Aortic elongation part I: the normal aortic ageing process. Heart 2018;104:1772e7. 36 Akin I, Nienaber CA. Age-dependent aortic elongation: a new predictor for type A aortic dissection? Heart 2018;104:1729e30. 37 Marrocco-Trischitta MM, Rylski B, Schofer F, Secchi F, Piffaretti G, de Beaufort H, et al. Prevalence of type III arch configuration in patients with type B aortic dissection. Eur J Cardiothorac Surg 2019 Apr 30. https://doi.org/10.1093/ejcts/ ezz137. pii: ezz137 [Epub ahead of print].
Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant Massimiliano M. Marrocco-Trischitta a,b,*, Moad Alaidroos Paolo Righini b, Mattia Glauber f, Giovanni Nano b,g
a,c
, Rodrigo M. Romarowski d, Francesco Secchi
e,g
,
a
Clinical Research Unit, IRCCS e Policlinico San Donato, Milan, Italy Vascular Surgery Unit, IRCCS e Policlinico San Donato, Milan, Italy c Vascular Surgery Unit, Policlinico San Marco, Zingonia, Italy d 3D and Computer Simulation Laboratory, IRCCS e Policlinico San Donato, Milan, Italy e Division of Radiology, IRCCS e Policlinico San Donato, Milan, Italy f Minimally Invasive Cardiac Surgery Unit, Istituto Clinico Sant’Ambrogio, Milan, Italy g Department of “Scienze Biomediche per la Salute”, University of Milan, Italy b
WHAT THIS PAPER ADDS This work shows that the “bovine” aortic arch is associated with a consistent geometric pattern, which identifies hostile proximal landing zones for endograft deployment, namely Zone 3 and Zone 0 in Type I arch. The results suggest that the “bovine” aortic arch mandates a specific amendment to thoracic endovascular aortic repair planning. Further biomechanical studies are warranted to disclose the potential causative relationship between the described peculiar geometric features and the risk of developing thoracic aortic pathologies in patients with this anatomical variant. Objectives: The aim was to investigate whether the “bovine” aortic arch (i.e. arch variant with a common origin of the innominate and left carotid artery (CILCA)) is associated with a consistent geometric configuration of proximal landing zones for thoracic endovascular aortic repair (TEVAR). Methods: Anonymised thoracic computed tomography (CT) scans of healthy aortas were reviewed to retrieve 100 cases of CILCA. Suitable cases were stratified according to type 1 and 2 CILCA, and also based on type of arch (I, II, and III). Further processing allowed calculation of angulation and tortuosity of the proximal landing zones. Centre lumen line lengths of each proximal landing zone were measured in a view perpendicular to the centre line. All geometric features were compared with those measured in healthy patients with a standard arch configuration (n ¼ 60). Two senior authors independently evaluated the CT scans, and intraand interobserver repeatability were assessed. Results: The 100 selected patients (63% male) were 71.4 7.7 years old. Type 1 CILCA (62/100) was more prevalent than type 2 CILCA (38/100), and the two groups were comparable in age (p ¼ .11). Zone 3 presented a severe angulation (i.e. > 60 ), which was greater than in Zone 2 (p < .001), and a consistently greater tortuosity than Zone 2 (p ¼ .003). This pattern did not differ between type 1 and type 2 CILCA. A greater tortuosity was also observed in Zone 0, which was related to increased elongation of the ascending aorta (i.e. Zone 0), than the standard configuration. The CILCA had an overall greater elongation, and Zone 2 also was specifically longer. When stratifying by type of arch, reversely from Type III to Type I, the CILCA presented a gradual flattening of its transverse tract, which entailed a consistent progressive elongation (p ¼ .03) and kinking of the ascending aorta, with a significant increase of Zone 0 angulation to even a severe degree (p ¼ .001). Also, from Type III to Type I, Zone 2 presented a progressively shorter length (p ¼ .004), which was associated with increased tortuosity (p < .05). Mean intra- and interobserver differences for angulation measurements were 1.4 6.8 (p ¼ .17) and 2.0 10.1 (p ¼ .19), respectively. Conclusions: CILCA presents a consistent and peculiar geometric pattern compared with standard arch configuration, which provides relevant information for TEVAR planning, and may have prognostic implications. Keywords: Aortic angulation, Aortic elongation, Aortic tortuosity, Bovine arch, Proximal landing zones, Thoracic endovascular aortic repair Article history: Received 20 June 2019, Accepted 12 November 2019, Available online XXX Ó 2019 European Society for Vascular Surgery. Published by Elsevier B.V. All rights reserved.
* Corresponding author. Clinical Research Unit, IRCCS - Policlinico San Donato, Via Morandi 30, 20097 San Donato Milanese, Milan, Italy. E-mail address: [email protected] (Massimiliano M. Marrocco-Trischitta). 1078-5884/Ó 2019 European Society for Vascular Surgery. Published by Elsevier B.V. All rights reserved. https://doi.org/10.1016/j.ejvs.2019.11.019
Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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INTRODUCTION The so called “bovine” aortic arch is characterised by the presence of a common origin of the innominate and left carotid artery (CILCA), or, less frequently, by the origin of the left carotid directly from the innominate artery (i.e. type 2 CILCA)1 (Fig. 1). Recent guidelines and recommendations2,3 have suggested abandoning the use of the misnomer bovine, and adopting a more descriptive terminology. Accordingly, in the present work, for brevity and practical reasons, we used the acronym CILCA, which was previously employed in a meta-analysis on this topic.4 The CILCA is the second most common arch configuration, and its prevalence in the general population is 13.6%, with relevant differences among ethnic groups.5 Notably, however, the real prevalence of the CILCA is probably underestimated, because its presence is largely unreported6,7 due to the presumed clinical irrelevance of this anatomical variant. In fact, the peculiar anatomical features associated with the CILCA mandate specific management strategies and pre-operative planning in both surgical and endovascular procedures involving the aortic arch, including type A aortic dissection repair8 and carotid stenting.9 There is evidence in the literature that the CILCA represents a potential determinant of the onset of thoracic aortic disease,4 and this entails a relevant prevalence of this anatomical variant among patients requiring thoracic endovascular aortic repair (TEVAR). Nevertheless, despite the apparent need for specific studies on the impact of the CILCA configuration on TEVAR planning, this issue has never been addressed specifically. Severe angulation and tortuosity of proximal landing zones for endovascular aortic repair represent recognised determinants of post-operative endograft performance,10e 13 even though there is no consensus on their definition and on clinically significant threshold values, either in guidelines11,14,15 or in current instructions for use of commercially available endografts.16 Also, these relevant anatomical features are associated with high displacement forces that further increase the risk of endograft failure.17
Previous studies showed that consistent geometric16 and haemodynamic patterns17 can be predicted in specific aortic arch configurations. These analyses allow the identification of landing zones that present consistent unfavourable biomechanical features compared with the adjacent ones, and therefore can be regarded as hostile for endograft deployment.18 The aim of the present study was to investigate the angulation and tortuosity of proximal landing zones for TEVAR in CILCA configuration (i.e. Zone 0, 2, and 3) (Fig. 2), and assess whether this anatomical variant is associated with a consistent geometric pattern, which may provide useful insights for assessing TEVAR feasibility and planning. METHODS A retrospective review of anonymised thoracic CT angiography scans performed at our institution in 2016 was conducted to retrieve 100 cases of CILCA. A control group of subjects with standard arch configuration was also retrieved. This cohort has already been described in a previous work.16 The present study was conceived as a proof of concept geometric analysis, and therefore the search included subjects with a healthy aortic arch undergoing diagnostic evaluation for various clinical reasons. Only thin cut (1.0 mm or 1.5 mm) CTs of patients with visible origins of the supra-aortic branches were considered. Exclusion criteria for both groups were age <60 years, diameter of the thoracic aorta >40 mm, radius of arch curvature <20 mm, previous aortic surgery, and presence of radiological signs of aortic pathology, including dissection, intramural haematoma, or penetrating aortic ulcer. Regarding exclusion criteria, pathological and ectatic aortas were excluded to eliminate potential confounding variables for the assessment of a consistent geometric pattern. Aortas with radius of curvature <20 mm were excluded because the latter represents a contraindication to TEVAR according to manufacturers’ instructions for use of stent grafts, and defines a steep aortic arch angulation that
Figure 1. Anatomical configurations of the CILCA aortic arch (arch variant with a common origin of the innominate and left carotid artery): type 1 (A) and type 2 (B). Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Figure 2. Ishimaru’s proximal landing zones in the bovine arch variant (A) and in the standard arch configuration (B).
could alter the measurements of landing zones angulation.16 Suitable cases were stratified according to type 1 and 2 CILCA1 (Fig. 1) and also stratified based on the Aortic Arch Classification in Type I, II and III, according to the Modified Arch Landing Areas Nomenclature (MALAN)16 (Fig. 3). Further processing, based on 3D multiplanar reconstruction, was performed as previously described in detail16 with 3Mensio Vascular software 8.0Ò (3Mensio Medical Imaging B.V., Bilthoven, The Netherlands), which provides specific functions for automatic measurements. Proximal landing zones angulation was determined using the centre lumen line “tangent angle” function, which calculates the angle between tangent lines drawn for any two points along the centre lumen line (Fig. 4). Specifically, we considered the angle between the flow axis of each proximal landing zone and the hypothetical body of the lesion to treat, equivalent to the b angle defined by the Society for Vascular Surgery reporting standards for endovascular repair of the abdominal aorta (EVAR).19 b angles were calculated by selecting the most proximal point of each proximal landing zone, and a point at 40 mm distance along the centre lumen line.16 The more proximal 20 mm of such a distance accounted for the proximal neck for theoretical endograft deployment. The more distal 20 mm accounted for the hypothetical body of the lesion to treat. For Zone 0, the proximal point was chosen at the level of the top of the pulmonary trunk. Angulations were classified into mild (<40 ), moderate (40e60 ), or severe (>60 ).16 The aortic arch tortuosity index was calculated by placing two markers (AeB) in axial view at the mid-luminal point of the ascending and descending aorta at the height of the bifurcation of the pulmonary trunk. The index was defined as the shortest distance between A and B divided by the centre lumen line distance between A and B.20 Tortuosity angle of each landing zone was measured using the “tortuosity angle function”, which is calculated between two line elements that are defined by three control
points located on the centreline (Fig. 4). According to the manufacturer, the first point is the start of the first line element, the second point is the end of the first line element and the start of the second line element, and the third point is the end of the second line element. The distance between the points was automatically set by the software at 15 mm. Proximal landing zones with greater angulation and tortuosity than the adjacent ones were identified as geometrically hostile for endograft deployment.18 Centre lumen line lengths of each landing zone were measured in a view perpendicular to the centre lumen line. Zone 0 was measured starting from level of the top of the pulmonary artery bifurcation. Two investigators independently evaluated the CT scans. Measurements were repeated for 15 (15%) scans, randomly selected from the study group, to assess intra- and interobserver repeatability using BlandeAltman plots. The study was approved by the local ethics committee, and the need for informed patient consent was waived because of the retrospective nature of the analysis and the use of anonymised data. Statistical analysis Data were analysed with SPSS software v. 22 (SPSS Inc, Chicago, IL, USA). The normality of each sample was tested with the ShapiroeWilk test. Comparisons between age groups and types of CILCA (type 1 vs. type 2) were made with the unpaired t test for normally distributed samples, and with the ManneWhitney U test for non-normally distributed data. Comparisons between zones of different Types of arch were made with one way analysis of variance or the KruskaleWallis test for normally and non-normally distributed samples respectively. The JonkheereeTerpstra test was used to verify the hypothesis that angulation and tortuosity increase across landing zones based on the type of arch, as previously described in the standard aortic arch.16 Continuous variables were reported as mean and
Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Type I
Type II
2 diameter of CCA
Zone 0
0/I
MALAN
>2 diameter of CCA
0/II
2 diameter of CCA
Zone 1
2 diameter of CCA
Zone 2
2/I
MALAN
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2 diameter of CCA
Zone 3
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>2 diameter of CCA
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Type III
2/III
>2 diameter of CCA
3/II
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Figure 3. The Modified Arch Landing Areas Nomenclature (MALAN), which comprises proximal landing zones according to Ishimaru’s Aortic Arch Map, and types of arch according to the Aortic Arch Classification. CCA ¼ common carotid artery. (This picture was previously published in an article by the present authors in the Journal of Vascular Surgery16).
A
B Angle = 14° Arm Length: 15mm
Zone 2
Zone 2
Angle = 56° Distance Between handles: 40mm
Figure 4. (A) b angles of proximal landing zone (defined as a by 3Mensio Vascular software 8.0Ò). (B) Tortuosity angle of proximal landing zone (see Methods for details). Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Table 1. Angulation (b angle) in proximal landing zones of all CILCA arches, and stratified by type 1 and type 2 CILCA Proximal landing zone
All CILCA (n [ 100) Mean (95% CI)
Type 1 CILCA (n ¼ 62) Mean (95% CI)
Type 2 CILCA (n ¼ 38) Mean (95% CI)
p value
Zone 0 Zone 2 Zone 3 p value
52.3 (50.0e54.6) 51.6 (48.8e54.4) 63.1 (60.7e65.5) <.001
52.0 (49.0e55.0) 52.2 (48.3e56.0) 63.4 (60.5e66.4) <.001
52.8 (49.1e56.6) 50.7 (46.4e54.9) 62.6 (58.3e66.9) <.001
.73* .98* .87*
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. * Type 1 vs. type 2 CILCA.
95% confidence intervals. Statistical significance was assumed at p < .05.
RESULTS Overall, 1 036 CTs were reviewed to retrieve 128 CILCA arch cases. The prevalence observed (i.e. 12.35%) was consistent with the literature. After applying the inclusion and exclusion criteria, the 100 selected patients (63% male) were 71.4 7.7 years old. The control group of subjects with standard arch configuration (70% male) was 71 8 years old. It listed 60 cases, 20 for each type of arch (I to III). The three subgroups were comparable in age (78.8 8.5 years, 75.2 8.5, and 75.4 9.5 respectively; p ¼ .29). Type 1 CILCA (62/100) was more prevalent than type 2 CILCA (38/100) in the study cohort, and the two groups were comparable in age (70.4 7.3 years old and 73.0 8.3 years old respectively, p ¼ .11). Types of arch were equally distributed in the study group (Type I, n ¼ 31; Type II, n ¼ 32; Type III, n ¼ 37), and three groups did not significantly differ in terms of age (Type I, 71.3 8.6 years, Type II, 70.8 7.2 years, and Type III 72.0 7.6 years; p ¼ .70). Proximal landing zone angulations of the whole study group are reported in Table 1. In terms of absolute values, both Zone 0 and Zone 2 had a moderate degree of angulation, whereas Zone 3 presented a severe angulation. When comparing different landing zones, Zone 3 presented a much greater angulation than Zone 2 (p < .001) and Zone 0 (p < .001), whereas there was no difference between Zone 2 and Zone 0 (p ¼ 1.0). The same pattern was found after stratification in Type 1 and Type 2 CILCA arch (Table 1).
In the control group, angulation did not differ between adjacent proximal landing zones, even though it progressively increased towards the distal arch (p < .001) (Table S1). After stratification based on the type of arch, angulation progressively increased across landing zones from Type I to Type III arch (p < .001) (Table S2).16 Of note, in standard Type III arch, Zone 3 had a severe and a consistently greater angulation than Zone 2 (p ¼ .02), which reflects the pattern observed in the whole CILCA group (Table 1). By contrast, angulations of CILCA landing zones after stratification based on the Type of arch (Table 2) presented a different trend. Zone 3 and Zone 2 angulation pattern did not differ between types of arch, with Zone 3 being consistently associated with a severe and much greater angulation than Zone 2. A novel and peculiar pattern was instead found in Zone 0, where angulation was moderatee severe in Type I CILCA arch, and gradually and significantly decreased in Type II and Type III CILCA arch (p < .001). The tortuosity index in CILCA arch was 1.55 (1.51e1.59), and it was greater than that measured in standard arch configuration (1.49 (1.44e1.53), p ¼ .02). Tortuosity angles of proximal landing zones of the whole study group are reported in Table 3. Tortuosity was greater in Zone 3 and Zone 0, whereas it was consistently and significantly lower in the transverse aortic tract, namely in Zone 2 (Zone 3 vs. Zone 2 p ¼ .003; Zone 0 vs. Zone 2 p < .001). The same pattern was observed when Type 1 and Type 2 CILCA were separately considered. In the control group, tortuosity angles did not differ between adjacent proximal landing zones (Table S1). After stratification based on the type of arch, landing zones
Table 2. Angulation (b angle) in proximal landing zones of 100 individuals with CILCA arch stratified by the type of arch (i.e. Modified Arch Landing Areas Nomenclature) Proximal landing zone
Type I (n [ 31) Mean (95% CI)
Type II (n [ 32) Mean (95% CI)
Type III (n [ 37) Mean (95% CI)
p value
Zone 0 Zone 2 Zone 3 p value
57.6 (53.7e61.5) 51.4 (46.1e56.7) 59.4 (55.2e63.7) <.05
53.5 (49.5e57.5) 50.1 (44.9e55.4) 62.2 (58.3e66.2) <.001
46.9 (43.4e50.4) 53.0 (48.3e57.7) 66.9 (62.8e71.1) <.001
.001 .69 .03
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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Table 3. Tortuosity angle in proximal landing zones of all CILCA arches, and stratified by type 1 and type 2 CILCA Proximal landing zone
All CILCA (n [ 100) Mean (95% CI)
Type 1 CILCA (n [ 62) Mean (95% CI)
Type 2 CILCA (n [ 38) Mean (95% CI)
p value
Zone 0 Zone 2 Zone 3 p value
24.5 (23.4e25.5) 16.4 (15.3e17.6) 20.3 (18.8e21.7) <.001
24.0 (22.7e25.2) 17.1 (15.6e18.7) 20.7 (18.6e22.7) <.001
25.3 (23.5e27.1) 15.3 (13.5e17.2) 19.6 (17.5e21.7) <.001
.12* .14* .81*
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. * Type 1 vs. type 2 CILCA.
tortuosity progressively increased from Type I to Type III arch (p ¼ .03) (Table S3).16 Also, in standard Type III arch, Zone 3 had a greater angulation than Zone 2 (p ¼ .02), which again is consistent with the pattern observed in the whole CILCA group (Table 1). In the CILCA arch, after stratification based on types of arch (Table 4), a greater tortuosity was observed in Zone 0 regardless the type of arch, whereas in Zone 2 tortuosity gradually and consistently decreased in Type II and Type III CILCA arch (p < .05). Centre lumen line lengths are reported in Table S4, and did not differ in type 1 and type 2 CILCA. When compared with those measured in subjects with standard arch configuration, the cumulative length (CILCA Z0þZ2 vs. standard arch Z0þZ1þZ2) was much greater in CILCA (67.0 mm (64.5e69.6) vs. 60.2 mm (57.4e63.0), p < .001). Zone 0 was also significantly longer in CILCA (46.3 mm (44.5e48.2) vs. 34.5 (32.5e36.5), p < .001). Zone two as well had a greater length in CILCA than the standard arch (20.7 mm (19.0e22.4) vs. 16.6 mm (15.5e17.7), p < .001). When stratified based on the Type of arch (Table 5), in reverse from Type III to Type I, Zone 0 gradually increased in length (p ¼ .03), whereas Zone 2 appeared gradually shortened (p ¼ .004). Mean intra- and interobserver differences for b angle measurements were 1.4 6.8 (p ¼ .17) and 2.0 10.1 (p ¼ .19), respectively. DISCUSSION This work has shown that the CILCA arch variant presents a consistent and peculiar geometric pattern of proximal
landing zones for TEVAR compared with the standard arch configuration, and that this pattern does not differ between type 1 and type 2 CILCA arch (Fig. 1). Specifically, the results indicate that Zone 3 in CILCA is associated with a severe angulation (i.e. > 60 ),18 whereas Zone 2 presents a much lesser angulation compared with Zone 3, and a consistent moderate degree of angulation (i.e. 40 e60 ).16 Zone 3 appears also associated with a consistently greater tortuosity than Zone 2. Interestingly, in CILCA arch, a greater tortuosity is also observed in Zone 0, and this finding appears related to increased elongation of the ascending aorta. From the comparison between CILCA and standard arch configuration, it becomes apparent that, because of the common origin of the left carotid and innominate artery, the take off of the common trunk is shifted distally towards the top of the arch. In this respect, Zone 0 in CILCA arch is on average 1 cm longer than Zone 0 in the standard configuration. Notably also, Zone 2 as well is specifically longer in CILCA, and this anatomical variant has an overall greater elongation than the standard arch configuration. From a clinical standpoint, these findings suggest that Zone 3 in CILCA arch should be regarded as unfavourable for endograft deployment, and that Zone 2 represents the preferred proximal landing zone for the treatment of pathologies of the distal arch, possibly after prophylactic rerouting of the left subclavian artery (LSA) by either surgical or endovascular means.3 This is also the case because the presence of severe angulation requires a longer proximal landing zone to obtain an adequate sealing and fixation.10 In this respect, an acceptable length is often unavailable in Zone 3 due to the anatomical limitation of
Table 4. Tortuosity angle in proximal landing zones of 100 individuals with CILCA arch stratified by the Type of arch (i.e. Modified Arch Landing Areas Nomenclature) Proximal landing zone
Type I (n ¼ 31)
Type II (n ¼ 32)
Type III (n ¼ 37)
p value
Zone 0 Zone 2 Zone 3 p value
25.6 (23.7e27.4) 18.0 (15.6e20.4) 19.0 (16.9e21.2) <.001
24.9 (23.4e26.5) 17.1 (14.9e19.3) 19.3 (16.5e22.0) <.001
23.1 (21.1e25.1) 14.6 (13.0e16.2) 22.1 (19.4e24.9) <.001
.13 <.05 .14
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
PLZ for TEVAR in Bovine Arch Variant
7
Table 5. Centreline length in proximal landing zones of 100 individuals with CILCA arch stratified by the type of arch (i.e. Modified Arch Landing Areas Nomenclature) Proximal landing zone
Type I (n [ 31)
Type II (n [ 32)
Type III (n [ 37)
p value
Zone 0 Zone 2
49.3 (46.3e52.3) 17.7 (15.9e19.5)
46.9 (43.5e50.2) 20.5 (17.7e23.3)
43.4 (40.2e46.7) 23.4 (19.9e26.9)
.034 .004
Data are presented as mean and 95% confidence interval. Values are in degrees. CILCA ¼ arch variant with a common origin of the innominate and left carotid artery. Data are presented as mean and 95% confidence interval. Values are lengths in mm.
the origin of LSA. Zone 2 in CILCA, by contrast, not only presents a significantly lesser degree of angulation and tortuosity, but also offers a longer neck for endograft deployment. In this work, we also investigated whether the recently introduced MALAN nomenclature16 (Fig. 3), which merges the Ishimaru’s map21 and the Aortic Arch Classification in Type I, II, and III could be applied to the CILCA variant. Interestingly, in contrast to what is observed in the standard anatomical pattern of the aortic arch,18 the CILCA Type II and Type III configurations are not associated with a progressively less favourable anatomy for TEVAR than Type I, but quite the contrary. In reverse, from Type III to Type I (Fig. 5), the CILCA presents a gradual flattening of the transverse tract of the aortic arch, which eventually provides a “cubic shape”22 to the whole arch. This entails a consistent progressive elongation (Table 5) and kinking of the ascending aorta, with a significant increase of Zone 0 angulation to even a severe degree (Table 2). Notably also, from Type III to Type I, Zone 2 presents a progressively shorter length (Table 5), which is consistently associated with an increased tortuosity (Table 4). These findings provide valuable insights also into the increased risk of developing thoracic aortic aneurysm and dissection in subjects with CILCA arch.4 The pathophysiological mechanism underlying this phenomenon remains to be established.23 Previous studies however, suggested a potential causative role for specific geometric features, including aortic angulation,24,25 tortuosity,26,27 and elongation,28e30 and the inherent detrimental haemodynamic effects on the aortic wall respectively.31e36
In CILCA arch, it is anticipated that the presence of these anatomical features, and particularly in Zone 3 and in Zone 0, entails a local adverse biomechanical environment, which may cause a failure of aortic wall properties in that area. In this respect, it is noteworthy that Zone 3 identifies the aortic tract within 2 cm of the LSA, which represents the most common site for proximal entry tear in Type B dissections.11 Also, Zone 0 comprises the areas where the entry tear in Type A dissections most frequently occurs (i.e. just above the sinotubular junction and just proximal to the origin of the innominate artery).24 Finally, the work showed that the geometric pattern of the CILCA arch resembles that of the Type III standard arch. Interestingly, both configurations have a high prevalence in patients with Type B aortic dissection,31,37 and these observations further support the relevance of specific geometric features as potential anatomical risk factors for the onset of aortic disease. Some limitations of the study are recognised, including the use of a hypothetical body of the lesion to treat for the calculation of proximal landing zone angulation and tortuosity, which is related to the use of healthy aortas.16 Also, methods and angle grades previously validated for EVAR19 were employed, and used for TEVAR cases only in preliminary studies.16,18 Finally, the reported data need to be validated in patients with aortic arch pathologies. Nevertheless, the analyses were based on centreline measurements, which are less likely to be affected by the modification of the aortic wall induced by the onset of pathological derangements. In this respect, previous studies in the standard arch configuration demonstrated that the
Figure 5. Three dimensional computed tomography based surface reconstruction of CILCA aortic arches (arch variant with a common origin of the innominate and left carotid artery) stratified based on Type of arch. (A) Type I arch, (B) Type II arch and (C) Type III arch. Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019
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methods16 reported here reliably and consistently predict the geometric pattern observed in diseased aortas even when performed in healthy aortas.18 Hence, the work provides robust evidence to further investigate the geometric as also the haemodynamic pattern potentially associated with the CILCA arch, as suggested by preliminary results from the literature.31 CONCLUSIONS CILCA arch is associated with a consistent geometric configuration, which provides relevant information to improve the decision making process for TEVAR, even though patient specific pre-operative planning remains essential. Also, the findings suggest a potential role for the described anatomical pattern in the development of thoracic aortic pathologies in patients with CILCA variant,4 which warrants further specific biomechanical studies.
Massimiliano M. Marrocco-Trischitta et al.
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CONFLICTS OF INTEREST None. FUNDING This work was supported in part by “Ricerca Corrente” grants from IRCCS -Policlinico San Donato, San Donato Milanese, Milan, Italy.
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ACKNOWLEDGEMENTS An abstract of this manuscript has been accepted for fasttrack presentation at the Annual Meeting of the European Society for Vascular Surgery, Hamburg, 24e27. September 2019.
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APPENDIX A. SUPPLEMENTARY DATA Supplementary data to this article can be found online at https://doi.org/10.1016/j.ejvs.2019.11.019.
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Please cite this article as: Marrocco-Trischitta MM et al., Geometric Pattern of Proximal Landing Zones for Thoracic Endovascular Aortic Repair in the Bovine Arch Variant, European Journal of Vascular and Endovascular Surgery, https://doi.org/10.1016/j.ejvs.2019.11.019