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Abstract

The aortic arch and its branches form during the third week of embryogenesis, which involves a complex process. Abnormalities of the arch branching pattern arise by persistence of segments of arches that normally disappear or the disappearance of segments of arches that normally remain, or both [1]. The most common human aortic arch branching pattern has the innominate artery, the left common carotid artery and the left subclavian artery all as separate branches (Fig. 1). The most common variant branching pattern involves the left common carotid artery arising in a common origin with the innominate artery (Fig. 2), and the next most common the similar left common carotid artery originating from the innominate artery itself (Fig. 3). A true bovine arch involves a single common brachiocephalic trunk arising from the arch which then splits into the right subclavian artery, a bicarotid trunk and a left subclavian artery (Fig. 4), and is actually extremely uncommon in humans [2]. Originally the variations of the arch branching patterns were made by post-mortem studies [3], but, more recently large imaging studies have been performed [4,5] confirming that approximately 70% of people have a normal branching pattern with 20% having a common origin of the innominate artery and left common carotid artery (as in Fig. 2) [4,5], but these studies were performed without reference to the anatomy of the aortic valve (bicuspid versus tricuspid). Bicuspid aortic valve (BAV) is the commonest congenital cardiac malformation with 1–2% of the population being affected [6], and is associated with other cardiac anomalies, especially coarctation [6]. BAV is also associated with dilatation of the ascending aorta which is thought to be related to intrinsic pathological properties of the aortic wall and altered flow dynamics through the abnormal valve [7,8], with increased risk of aortic dissection compared to tricuspid aortic valve (TAV) patients [9,10]. As BAV is a common congenital anomaly and the variants of the aortic branching pattern are developmental in origin we decided to see if the frequency of arch variants in BAV and TAV patients differed, as this has not previously been looked at. We examined Computerised Tomographic aortograms (CT) and echocardiograms of BAV and TAV patients to assess the aortic arch branching pattern and any possible association with the valve morphology.

Materials and Methods

An established BAV patient database at the Heart Hospital, Doha, Qatar was used to retrieve patients. All BAV patients with CT scans of the aorta were examined. During the same period (September 2011–2014) 200 CT aortograms were performed in the Radiology department of the Heart Hospital and from these TAV patients were selected for comparison. Basic demographic data were collected for all the patients. This study was approved by the Institutional Review Board with waiver of consent as all tests had been preformed previously. Aortic images, obtained with Multidetector CT aortic angiography (MDCT) using dual source 128 multi slice CT, were further processed by the reporting consultant radiologist for three-dimensional reconstructions to obtain volume rendered images and maximum intensity projections for assessment of the aortic arch branching variation. Echocardiograms of both the BAV and TAV patients were examined to confirm valve anatomy, (images assessed by an echocardiography trained cardiologist, not just reading reports).

Results

Results of the 129 BAV patients in the BAV database 28 had ‘readable’ (branch pattern could be clearly discerned) CT scans. Fifty-seven (double the number of BAV patients) CT aortograms were selected from the radiology archive (first 57 that were ‘readable’ from September 2011 that had also undergone echocardiography). The sex and ethnic distributions are shown in Tables 1 and 2. Eighty-five patients’ images were assessed with 28 BAV and 57 TAV. All 85 patients had their echocardiographic images re-examined to verify BAV or TAV morphology. For BAV the aortic branching patterns were: 86% normal (24/28) and 14% abnormal branching patterns (4/28), and for TAV: 70% normal (40/57) and 30% abnormal branching patterns (17/57). The BAV patients abnormal patterns were all the left common carotid artery common origin with innominate artery (as in Fig. 2), whereas the TAV patients had 16 of the type left common carotid artery common origin with innominate artery (as in Fig. 2) and one left common carotid arising from the innominate artery (as in Fig. 3). There were no true bovine variants in our group. Other anomalies found in our group include 1 coarctation (BAV patient) and 1 dissection (BAV patient). The valve morphology was discernable in 42 (49%) of the 85 CT scans.

Discussion/Conclusions

Bicuspid aortic valve has previously been quoted as having a related aortopathy, but is this embryological or functional (related to intrinsic wall properties) in origin? [7,8]. If in fact BAV patients have fewer arch variations it may support the idea that the aortopathy is related to functional changes in the wall rather than embryological origins (excluding coarctation). In our group it does not appear to affect the embryological development of the branches of the aortic arch and we actually appear to have fewer arch variants in the BAV group. Although this is a small study our TAV group had similar percentages of normal (70%) and abnormal (30%) arch variants as the reported literature [1,2,4,5]. Our BAV group is small and we will expand it further in the future but the results at this stage suggest no increase, in fact a possible decrease in arch variants compared to the TAV patients. Despite this it would not be possible to exclude an embryologically based pathological change to the aorta in BAV patients. Some racial variations have been reported but these studies were done many years ago and involved post-mortem analysis [3], and suggested that arch branching variants were more common in African Americans (about 50%) [3], but these studies would be difficult to repeat due to widespread racial mixing nowadays and could only be looked at in isolated communities with a single racial group. In Qatar 60% of the population is originally from the Asian Indian Subcontinent so there may in fact be a greater prevalence of Bicuspid valves in the MENA region patients and also Arch Variants appear to be more common in the MENA region patients. The two large radiological studies that have looked at the aortic arch anatomy showed that approximately 70% of patients had normal configuration of the arch vessels and 20% had a common origin of the innominate artery and left common carotid artery [7,8], but these studies were performed without reference to the anatomy of the aortic valve. This is the first study in the literature to look at the arch branching variants when consideration of the aortic valve morphology (BAV versus TAV) is taken into account. Although there is little physiological significance in the majority of patients, these variations may have an impact if endovascular or surgical procedures are planned in the region of the arch. BAV patients have been shown to have ascending and arch dilatation [7–11] and are more likely to require intervention than TAV patients (due to concomitant valve dysfunction), so knowing the arch anatomy will become more important. We will continue to expand our numbers as this is a relatively small study.

Acknowledgement

Mr Mohammed Abdulsamad for diagrams. Conflicts of interest, disclosures: none declared by any author.

Table 1: Sex and Ethnicity for tricuspid valves. Tricuspid Male Female Ethnicity Numbers Normal (n = 40) 36 4 Africa 0 Asian Indian Subcontinent 15 Asian Oriental 3 Caucasian 3 MENA Region 19 Arch Variant (n = 17) 15 2 Africa 1 Asian Indian Subcontinent 5 Asian Oriental 2 Caucasian 0 MENA Region 9

Table 2: Sex and Ethnicity for bicuspid valves. Bicuspid Male Female Ethnicity Numbers Normal (n = 24) 24 0 Africa 1 Asian Indian Subcontinent 7 Asian Oriental 3 MENA Region 13 Arch Variant (n = 4) 4 0 Africa Asian Indian Subcontinent 2 Asian Oriental MENA Region 2

References

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[2] Layton KF, Kallmes DF, Cloft HJ, Lindell EP, Cox VS. Bovine aortic arch variant in humans: clarification of a common misnomer. American Journal of Neuroradiol 2006;27:1541–42.

[3] De Garis CF, Black IH, Riemenschneider EA. Patterns of the aortic arch in American white and negro stocks, with comparative notes on certain other mammals. J Anat 1933;67:599–618.

[4] Jakanani GC, Adair W. Frequency of variations in aortic arch anatomy depicted on multidetector CT. Clinical Radiology 2010;65:481–487.

[5] Shakeri A, Pourisa M, Deldar A, Goldust M. Anatomic variations of aortic arch branches and relationship with diameter of aortic arch by 64-row CT angiography. Pak J Biol Sci 2013;16(10):496–500.

[6] Nistri S, Basso C, Marzari C, Mormino P, Thiene G. Frequency of bicuspid aortic valve in young male conscripts by echocardiogram. Am J Cardiology. 2005;96(5):718–721.

[7] Mahadevia R, Barker AJ, Schnell S, Entezari P, Kansal P, Fedak PW, Malaisrie SC, McCarthy P, Collins J, Carr J, Markl M. Bicuspid aortic cusp fusion morphology alters aortic three-dimensional outflow patterns, wall shear stress, and expression or aortopathy. Circ 2014;129(6):673–82.

[8] Phillippi JA, Green BR, Eskay MA, Kotlarczyk MP, Hill MR, Robertson AM, Watkins SC, Vorp DA, Gleason TG. Mechanism of aortic medial matrix remodeling is distinct in patients with bicuspid aortic valveJ Thorac Cardiovasc Surg 2014;147(3):1056–64.

[9] Michelena HI, Khanna AD, Mahoney D, Margaryan E, Topilsky Y, Suri RM, Eidem B, Edwards WD, Sundt TM 3rd, Enriquez-Sarano M. Incidence of aortic complications in patients with bicuspid aortic valves. JAMA 2011;306(10):1104–12.

[10] Eleid MF, Forde I, Edwards WD, Maleszewski JJ, Suri RM, Schaff HV, Enriquez-Sarano M, Michelena HI. Type A aortic dissection in patients with bicuspid aortic valves: clinical and pathological comparison with tricuspid aortic valves. Heart 2013;99(22):1668–74.

[11] Fazel SS, Mallidi HR, Lee RS, Sheehan MP, Laing D, Fleischman D, Herfkens R, Mitchell RS, Miller DC. The aortopathy of bicuspid aortic valve disease has distinctive patterns and usually involves the transverse aortic arch. The Journal of Thoracic and Cardiovascular Surgery 2008;135:901–7.

Figure Legends

Figure 1: the most common human aortic arch branching pattern with the innominate artery (IA), the left common carotid artery (LCA) and the left subclavian artery (LSA) arising as separate branches from the arch. Other branches shown are right subclavian artery (RSA), right common carotid artery (RCA), right vertebral artery (RVA) and left vertebral artery (LVA).

Figure 2: the left common carotid artery arising from a common origin with the innominate artery. Incidental finding on the central image - left vertebral artery arising from the arch, directly after the common origin vessel.

Figure 3: the left common carotid artery originating from the innominate artery itself.

Figure 4: the true bovine arch involving a single common brachiocephalic trunk arising from the arch which then splits into the right subclavian, a bicarotid trunk and a left subclavian artery.

Table 1: Sex and Ethnicity for tricuspid valves.

Table 2: Sex and Ethnicity for bicuspid valves.

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2016-03-21
2020-04-08
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