https://orcid.org/0000-0001-8926-3752
This editorial refers to ‘Prevalence, multimodality imaging characterization and mid-term prognosis of quadricuspid aortic valves: an analysis of 8 cases, based on 160.004 exams performed during 12 years in a tertiary care hospital’, by A.M. Manuel et al. pp. .
The congenitally malformed aortic valve is the most common congenital cardiac lesion. It is found most frequently in the functionally or anatomically bifoliate arrangement. More rarely, fusion of two of the three zones of apposition between the leaflets produces the so-called unicuspid and unicommissural valve.1 Manuel et al.2 now report their experience of the even rarer variant, the so-called quadricuspid valve. They describe eight cases, detected and interrogated by multi-modality imaging over a 12-year period at their tertiary care hospital. This gave a prevalence of 0.005% of the patients undergoing cardiac imaging during this timeframe at their institution. Of their eight patients, three had severe aortic regurgitation, and underwent repair or replacement of the valve.
First described in 1862,3 multiple systems have been proposed to account for the morphological variability seen in the setting of the valve with four leaflets. Not all the variants in these complicated systems, however, match the features encountered by Manuel et al.,2 nor the preceding accounts they review. Most previous classifications have focused on the sizes of the leaflets, with one system adding information on the sinuses supporting the coronary arteries.2 These features help in understanding the mechanics of deficient coaptation, and in guiding surgical repair, but they merely scratch the surface regarding optimal description of the abnormal root.
The normal aortic root, which supports three leaflets, has two additional components, namely the sinuses, and the oft-neglected interleaflet triangles.1 Each leaflet attaches in semilunar fashion from its nadir at the plane of the virtual basal ring to its zeniths at the sinutubular junction. The abnormal valves, of course, are described on the basis of the number of ‘cusps’. This creates a problem, since ‘cusp’ is currently used indiscriminately to account for either the leaflets or the sinuses.1 We recognize that this word is not going to disappear. When accounting for the anatomy of the roots described in this fashion, we submit that it is better to distinguish between the numbers of leaflets and their supporting sinuses. In this regard, it is recognition of the number of interleaflet triangles that provides the key information.
The so-called ‘bicuspid’ valve, in fact, is usually built on a trifoliate template, with three sinuses, and three interleaflet triangles. It functions in bifoliate fashion because of the fusion between two of its leaflets, with a resulting raphe. And, at the site of the raphe, one of the interleaflet triangles is vestigial, with its apex found well below the sinutubular junction (Figure 1A and B). The variation in height of the vestigial triangle will change the plane of the opening area of the valve to that of the sinutubular junction. Severe hypoplasia, with corresponding significant leaflet fusion, will direct the plane of opening at an increased angle towards the walls of the adjacent sinuses. The unicuspid and unicommissural valve is also built on a trifoliate and trisinuate template. In this setting, however, there is fusion, with concomitant formation of raphes, at two zones of apposition. Hence, there are two vestigial interleaflet triangles. The functional zone of apposition is typically located between the left and non-coronary leaflets (Figure 1C). This most likely reflects the fibrous support of the non-coronary leaflet, with only the two coronary aortic leaflets having partial myocardial basal support.1 Much less frequently, the bicuspid valve can be found in a bifoliate and bisinuate pattern. In this setting, there are only two interleaflet triangles (Figure 1D), both reaching to the plane of the sinutubular junction. The plane of the area of valvar opening is then relatively parallel to the plane of the sinutubular junction.
(A and B) The so-called ‘bicuspid’ aortic valve. The root is trisinuate, with varying fusion between two leaflets producing a raphe. The variation in fusion between the leaflets (red caret) means that the apex of the interleaflet triangle is variably distant from the sinutubular junction (black dots). In (C), the unicuspid, unicommissural valve exhibits a single interleaflet triangle (red caret) between the left and non-coronary leaflets. Less commonly, as shown in (D), the ‘bicuspid’ valve can be found with only two leaflets and two sinuses. Right coronary artery (red arrow); left coronary artery (yellow arrow).
It is axiomatic that any successful approach towards determining the aetiology of valvar dysfunction, or subsequent surgical repair, must take account of these 3D morphological features.1,4,5 We wonder, therefore, why the features have been neglected when accounting for the rare quadricuspid variant. All the cases described by Manuel et al.,2 along with preceding reports, describe a quadrifoliate valve housed in a quadrisinuate root (Figure 2). Most often, the sinuses which give rise to the coronary arteries are adjacent. This suggests that the intercalated swelling, which gives rise to the non-coronary aortic leaflet and sinus in the trisinuate root, must either have divided or been duplicated during development so as to form the fourth sinus and leaflet. In the rarer circumstance where the coronary arteries arise from opposite sinuses, the inference can be made that one of the major outflow cushions divided or duplicated to produce the fourth sinus and leaflet.6 In five of the eight cases reported by Manuel et al.,2 at least one of the zones of apposition showed a variable degree of fusion, with a resulting raphe. Should we still refer to these variants as being ‘quadricuspid’ when they are not functioning as four-leaflet valves? It is in this setting that description becomes paramount, since even if functioning in trifoliate fashion, the valves are far from normal, often with significant asymmetry between the three functioning leaflets.
The image shows a quadrifoliate aortic valve, with the leaflets housed in a quadrisinuate root. There is no fusion between the leaflets, with each interleaflet triangle reaching to the level of the sinutubular junction. The sinuses giving rise to the coronary orifices are adjacent. There are fenestrations observed in three of the four leaflets.
Two-dimensional imaging of this complex structure can be challenging.7 We agree with Manuel et al.2 that a multi-modality approach is beneficial. While 3D imaging can now be achieved by echocardiography and cardiac magnetic resonance, each with their advantages, because of its superior spatial resolution we prefer computed tomography for pre-surgical planning.8 The value of this technique is shown in relation to both the fourth and sixth patients of Manuel et al.2 The fourth patient is reported to have no fusion, while the sixth is said to have fusion of two zones of apposition. From the supplied 2D videos, we would argue for fusion between the right coronary and accessory leaflet in the fourth patient, and for some degree of fusion between all four zones of apposition, with a central orifice, in the other. Such potential misdiagnosis relates to the through-plane motion of 2D imaging. Multi-planar reformatting and reconstruction serve not only to show the extent of fusion of the zone of apposition, and the resulting raphe, but also the degree of hypoplasia of the corresponding interleaflet triangle, along with its corresponding metric described as the coaptation height (Figure 3). This, and other metrics, now help in understanding aortic valvar dysfunction, and serve to guide surgical repair.4,5
The panels show 2D (A), virtual dissection (B), and a series of endocast images (C) of an individual with a ‘quadricuspid’ aortic root. The endocast shows a hypoplastic interleaflet triangle beneath the site of fusion between the coronary leaflets (red arrow). The interleaflet triangles on either side of the accessory sinus (A) appear more linear in structure, presumably impinged upon by the additional accessory sinus, with their zeniths reaching about two-thirds to the plane of the sinutubular junction (black dotted line), with a smaller degree of fusion between the involved leaflets. The interleaflet triangle between the left (L) and non-coronary sinuses (N) is normal (white arrow) with no fusion between these leaflets. This so-called ‘quadricuspid’ valve is functionally ‘unicuspid’ within a quadrisinuate root. LCA, left coronary artery; R, right coronary sinus; RCA, right coronary artery.
Manuel et al.2 are to be congratulated for emphasizing the significance of this rare entity. We submit, nonetheless, that not only is it necessary to define the sizes of the four leaflets, and the origins of the coronary arteries, but also, as with the bicuspid and unicuspid counterparts, accurately to assess the 3D complexity of the quadrisinuate root. This should include description of the degree of fusion along the zones of apposition between the leaflets, and the corresponding hypoplasia of the interleaflet triangles. Attention to these features will show how the quadrisinuate root is functioning. Only with this degree of precision will we improve our diagnostic descriptions and subsequent surgical repairs.
Acknowledgements
We are thankful to our colleague Dr Yu Izawa from Kobe University Graduate School of Medicine in Kobe, Japan, for supplying the 3D computed tomographic dataset used in Figure 3.
Conflict of interest: none declared.
The opinions expressed in this article are not necessarily those of the Editors of EHJCI, the European Heart Rhythm Association or the European Society of Cardiology.
