International Consensus Statement on Nomenclature and Classification of the Congenital Bicuspid Aortic Valve and Its Aortopathy, for Clinical, Surgical, Interventional and Research Purposes

Abstract

This International Consensus Classification and Nomenclature for the congenital bicuspid aortic valve condition recognizes 3 types of bicuspid valves: 1. The fused type (right-left cusp fusion, right-non-coronary cusp fusion and left-non-coronary cusp fusion phenotypes); 2. The 2-sinus type (latero-lateral and antero-posterior phenotypes); and 3. The partial-fusion (forme fruste) type. The presence of raphe and the symmetry of the fused type phenotypes are critical aspects to describe. The International Consensus also recognizes 3 types of bicuspid valve-associated aortopathy: 1. The ascending phenotype; 2. The root phenotype; and 3. Extended phenotypes. © 2021 Jointly between the RSNA, the European Association for Cardio-Thoracic Surgery, The Society of Thoracic Surgeons, and the American Association for Thoracic Surgery. The articles are identical except for minor stylistic and spelling differences in keeping with each journal's style. All rights reserved. Keywords: Bicuspid Aortic Valve, Aortopathy, Nomenclature, Classification.

Keywords: Aortopathy; Bicuspid Aortic Valve; Classification; Nomenclature.

Figure 1:

Nosology of the congenital BAV condition. (Left) Anatomically and prognostically complex presentations of the BAV valvulo-aortopathy are those associated with syndromes, left-sided obstructions, significant aortic coarctation, early/accelerated valve dysfunction (stenosis or regurgitation) and/or early aortopathy, manifested as thoracic aorta dilatation. These conditions are more commonly diagnosed in childhood, adolescence and young adulthood. (Middle) The anatomically and prognostically typical valvulo-aortopathy is usually diagnosed in young and middle-aged adults, although it may be diagnosed in children as well and comprises various degrees of progressive valvular dysfunction with a high cumulative incidence of aortopathy over the long run, manifested as thoracic aortic dilatation, without major associated conditions. Complex- and typical-presentation forms are susceptible to development of infective endocarditis and aortic dissection, although dissection is rare in the paediatric population and adults without aortic dilatation. (Right) The undiagnosed or uncomplicated form is rarely diagnosed in the patient’s lifetime (without any BAV-related complications, some are diagnosed post-mortem) or is diagnosed during the patient’s lifetime but does not cause complications requiring treatment. Therefore, it is a retrospective definition. Modified from Michelena et al [10] with permission from Elsevier. BAV: bicuspid aortic valve.

Figure 2:

Diagnosis of congenital bicuspid aortic valve by transthoracic echocardiography and pathological manifestations. (A) Parasternal short-axis aortic valve systolic still image demonstrating the existence of only 2 commissures (asterisks) delimiting only 2 cusps (see Video 1). (B) Parasternal long-axis systolic still shows systolic doming of the fused (conjoined) cusp (arrow), common for right-left coronary cusp fusion (see Video 2). (C) Pathological congenital bicuspid aortic valve specimen shows the area of the raphe (dashed line) from the left ventricular perspective, forming an obtuse angle between the fused cusps. (D) Ventricular side of a tricuspid aortic valve with acquired rheumatic fusion shows the cleavage plane with acute angle (yellow arrow). LV: left ventricle.

Figure 3:

The aortic root complex. (A) Schematic drawing of the aortic root: The blue line indicates the virtual basal ring (aortic annulus); the yellow line depicts the ventriculo-aortic junction (whose non-planar nature is emphasized schematically) [48]; the red lines show the crown-shaped attachments of the cusps to the wall of the aortic sinuses [note the different height of the underdeveloped commissure (asterisk) under the raphe compared to the other 2 true commissures]; and the brown line depicts the STJ. (B) All the above boundaries and structures are shown (same colours as above) in an anatomical specimen of a normal aortic root and tricuspid aortic valve. (C) Echocardiographic view of the aortic root: the levels of the aortic annulus, ventriculo-aortic junction and STJ are shown (same colours as above). It is important to recognize that it is the measurement of the virtual annulus, sinuses and STJ that have clinical and practical implications for the patient with BAV. LCO: left coronary orifice (green pin and arrow); RCO: right coronary orifice (blue pin and arrow); STJ: sinotubular junction.

Figure 4:

Types and specific phenotypes of the congenital BAV. There are 3 major types of BAVs and each type has specific phenotypes: fused BAV (right-left cusp fusion, right non-cusp fusion, left non-cusp fusion and indeterminate phenotypes); 2-sinus BAV (laterolateral and anteroposterior phenotypes) and partial-fusion BAV or forme fruste BAV (small raphe, single phenotype). Symmetrical or asymmetrical refers to the angle of the commissures of the non-fused cusp (see Fig. 9). BAV: bicuspid aortic valve.

Figure 5:

Schematic transthoracic echocardiography-based short-axis, base-of-the-heart anatomical landmarks and clock face for bicuspid aortic valve diagnosis and phenotyping. (Left panel) Schematic of the normal tricuspid aortic valve in the echocardiographic parasternal short-axis view, applicable to similar views obtained with cardiac computed tomography and cardiac magnetic resonance. The right coronary cusp (small R) is anterior and positioned between the TV and PV insertions. The left coronary cusp (small L) is posterior-lateral and related to the LA, whereas the non-coronary cusp (small N) is the most posterior and related to the IAS. Note the origin of the coronary arteries at the right and left cusps. These landmark anatomical relations of each cusp relative to adjacent structures are critical in determining which 2 cusps are fused. Modified from Michelena et al [10] with permission from Elsevier. (Right panel) The annular circumference of the aortic valve can be visualized like the face of a clock. Fused bicuspid valves with right-left cusp fusion usually have commissures at 4 and 10 or 5 and 11 o’clock (see Figs 6 and 7), and the anatomy relative to adjacent structures suggests right-left cusp fusion. In right non-coronary cusp fusion, the commissures are usually at 1 and 7 or 12 and 6 o’clock (see Figs 6 and 7); the anatomy relative to adjacent structures suggests right non-cusp fusion. In left non-coronary cusp fusion, usually 2 and 8 or 9 and 3 o’clock (see Figs 6 and 7) and the anatomy relative to adjacent structures suggest left non-fusion. It is important to note that there can be overlap between the clock positions; thus, it is critical to know the landmark anatomical relations of each cusp. Identification of the raphe can be invaluable in determining the conjoined cusp. Identification of the origin of the left and right coronary arteries (left panel) may also be invaluable. IAS: interatrial septum; LA: left atrium; large L: left side of the patient; large R: right side of the patient; P: posterior aspect of the heart; PA: pulmonary artery; PV: pulmonary valve; RA: right atrium; RVOT: right ventricular outflow tract; TV: tricuspid valve. Modified from Michelena et al [10] with permission from Elsevier.

Figure 6:

Schematic of fused BAV phenotypes as seen by parasternal short-axis transthoracic echocardiography. Applicable to similar tomographic views by cardiac computed tomography and cardiac magnetic resonance, the figure demonstrates the 3 fused BAV phenotypes as zoomed views of the base of the heart (black square) for anatomical landmark correlation. Note that all fused BAVs have 3 distinguishable aortic sinuses. Note the oval (American football shape) systolic opening of these 3 valves as opposed to the triangular opening of a tricuspid aortic valve. (1) Right-left cusp fusion (most common) with visible raphe, 2 different size/shape functional cusps [the non-fused cusp (non-coronary) is commonly of larger ‘compensatory’ size than the others]. (2) Right non-cusp fusion with visible raphe, 2 different size/shape functional cusps [the non-fused cusp (left) is larger than the others]. (3) Left non-cusp fusion with a visible raphe (least common), 2 different size/shape functional cusps [the non-fused cusp (right) is larger than the others]. It is important to note that these short-axis imaging views do not correspond to the surgeon’s intraoperative view. Note how, in diastole, the commissural angle of the non-fused cusp of these 3 asymmetrical BAVs is <170-180° (see Fig. 9); in systole, the right-left commissures are at 10 and 4 o’clock (1: yellow arrows), right non-commissures at 1 and 7 o’clock (2: yellow arrows) and left-non-commissures at 2 and 8 o’clock (3: yellow arrows) (see Fig. 7). These 3 fused phenotypes may not have a visible raphe and may also have symmetrical non-fused cusp angle (see Fig. 8). BAV: bicuspid aortic valve; IAS: interatrial septum; LC: left cusp; NC: non-coronary cusp; RC: right cusp; RV: right ventricle; TV: tricuspid valve. Modified from Michelena et al [10] with permission from Elsevier.

Figure 7:

Diastolic and systolic transthoracic echocardiography parasternal short-axis still images of the 3 phenotypes of fused bicuspid aortic valve (BAV). Applicable to similar tomographic views obtained with cardiac computed tomography and cardiac magnetic resonance. (A) Right-left cusp fusion BAV within 3 distinguishable aortic sinuses, with raphe (arrow) in diastole and (B) typical systolic opening with commissures marked as the clock face (arrows) (see Video 1). (C) Right non-cusp fusion BAV within 3 distinguishable aortic sinuses, with raphe (arrow) in diastole and (D) typical systolic opening with commissures marked as the clock face (arrows) (see Video 3). (E) Left non-cusp fusion BAV within 3 distinguishable aortic sinuses, with raphe (arrow) in diastole and (F) typical systolic opening with commissures marked as the clock face (arrows) (see Video 4). Modified from Michelena et al [6] with permission from Elsevier. L: left coronary cusp; N: non-coronary cusp; R: right coronary cusp.

Figure 8:

Fused-type right-left cusp fusion without visible raphe and symmetrical non-fused cusp commissural angle. (A) Diastolic transthoracic echocardiography short-axis still frame shows right-left cusp fusion without visible raphe (uncommon) and 180° angle of the non-fused cusp commissures, yet the sizes and shapes of the 2 functional cusps are different, the conjoined cusp is smaller than the predominant non-fused non-coronary cusp (N) and there are 3 aortic sinuses. (B) Systolic transthoracic echocardiography short-axis still frame confirms the absence of a visible raphe and the 180° commissural angle (Video 5). L: left coronary cusp; N: noncoronary cusp; R: right coronary cusp; RVOT: right ventricular outflow tract.

Figure 9:

Schematic of the transthoracic echocardiographic evaluation of fused BAV symmetry in the parasternal short axis. Applicable to similar tomographic views obtained from cardiac computed tomography and cardiac magnetic resonance, the figure demonstrates different commissural angles of the non-fused cusps (applicable to the 3 fused BAV phenotypes, although only right-left cusp fusion is shown) that define symmetry. (Left panel) Symmetrical (angle 160-180°) right-left cusp fusion BAV with raphe, where the 2 functional cusps are almost the same size/shape (the non-fused cusp is a little larger) and the commissural angle of the non-fused cusp is about 170°. (Middle panel) Asymmetrical (angle 140-159°) right-left fusion BAV with a raphe, and the commissural angle of the non-fused cusp is about 150°. (Right panel) Very asymmetrical (angle 120-139°) right-left fusion BAV shows retraction of the conjoined cusp at the raphe area and the commissural angle of the non-fused cusp is about 130°. Note that retraction is more prominent as the angle decreases and that this may cause aortic regurgitation. Modified from Michelena et al [10] with permission from Elsevier. BAV: bicuspid aortic valve.

Figure 10:

Transesophageal echocardiographic measurement of the commissural angle of the non-fused cusp prior to valve repair. Applicable to similar tomographic views obtained using cardiac computed tomography and cardiac magnetic resonance, after careful visualization of the systolic and diastolic motion (Video 6) of this regurgitant fused-type right-left cusp fusion bicuspid aortic valve, the non-fused commissures are identified, and a line is drawn from the position of the commissures to the centre of the valve in diastole (left). The angle of the non-fused cusp (N) is then carefully measured at approximately 162° on the protractor to the right, suggesting a good chance for repair. Modified from Michelena et al [6] with permission from Elsevier.

Figure 11:

Schematic of the 2-sinus BAV phenotypes as seen by the transthoracic echocardiogram parasternal short axis. Applicable to similar tomographic views obtained from cardiac computed tomography and cardiac magnetic resonance, the figure demonstrates 2-sinus BAV phenotypes as zoomed views of the base of the heart for anatomical landmark correlation. (Left panels) (1) 2-sinus laterolateral BAV with only 2 distinguishable aortic sinuses in diastole and 2 cusps of roughly same size and shape, each occupying 180° of the circumference, with a 180° angle of the commissures. Note that although it is possible to suspect right non-fusion, the landmark anatomical relations are not clear because both the normal geographic ‘left’ and ‘non-coronary’ cusps occupy portions of the normal geographic location of the ‘non-coronary’ cusp, and the posterior commissural line is almost aligned with the interatrial septum, bisecting the geographical location of the normal non-coronary cusp (Figs 5 and 12). The 2-sinus BAV laterolateral phenotype has 1 coronary artery arising from each sinus. (Right panel) (2.A) A 2-sinus anteroposterior BAV with only 2 distinguishable aortic sinuses in diastole and 2 cusps of roughly same size and shape each occupying 180° of the circumference, with a 180° angle of the commissures. Note that although it is possible to suspect right-left fusion, the landmark anatomical relations are not clear because the commissural line actually bisects the normal geographical location of the left cusp, such that both anterior and posterior functional cusps appear to have a ‘piece’ of the left cusp (see Figs 5 and 12). (2.B) A 2-sinus anteroposterior BAV that resembles a fused right-left fusion but without a raphe, with only 2 distinguishable aortic sinuses in diastole and 2 same size/shape cusps each occupying 180° of the circumference. The 2-sinus anteroposterior BAV may have coronary arteries arising from each cusp (2.A) or from the anterior cusp (2.B). Modified from Michelena et al [10] with permission from Elsevier. A: anterior cusp; BAV: bicuspid aortic valve; L: lateral cusp; P: posterior cusp.

Figure 12:

Diastolic and systolic short-axis still images of the 2-sinus bicuspid aortic valve phenotypes obtained from transthoracic echocardiographic and diastolic still images from electrocardiographic-gated cardiac computed tomography. (A) A 2-sinus laterolateral bicuspid aortic valve in systole, with the commissural line bisecting the normal geographic position of the non-coronary cusp (B and C), with only 2 distinguishable aortic sinuses in diastole (B), and roughly equal size/shape cusps occupying 180° of the circumference, reproducible on an equivalent tomography cut as seen with cardiac computed tomography (C). Note the coronary arteries arising, 1 from each cusp (D). See Videos 7 and 8 for the transthoracic and transoesophageal short axes of this valve. (E) A 2-sinus anteroposterior bicuspid aortic valve in systole, with the commissural line bisecting the left-coronary cusp geographic position (F) (diastolic still frame), with only 2 distinguishable aortic sinuses and roughly equal size/shape cusps occupying 180° of the circumference, reproducible on an equivalent tomographic cut as seen with cardiac computed tomography (G). Note the coronary arteries arising, 1 from each cusp in this particular example (H). See Videos 9 and 10 for the transthoracic and transoesophageal short axes of this valve, respectively. A: anterior cusp; L: lateral cusp; LA: left atrium; LCA: left coronary artery; P: posterior cusp; RA: right atrium; RCA: right coronary artery; RV: right ventricle.

Figure 13:

A 2-sinus anteroposterior bicuspid aortic valve evaluated by electrocardiographic-gated cardiac magnetic resonance. (A) A diastolic still frame depicts a 2-sinus bicuspid aortic valve with roughly similar size/shape cusps and sinuses, clearly suggestive of a 2-sinus bicuspid aortic valve in the systolic frame. (B). In this case, both coronary arteries arise from the anterior cusp (C), see Fig 11. A: anterior cusp; LCA: left coronary artery; P: posterior cusp; RA: right atrium; RCA: right coronary artery; RV: right ventricle.

Figure 14:

Schematic of the partial-fusion BAV phenotype as seen from the transthoracic echocardiogram parasternal short-axis view. (Left panel) The imaging appearance in diastole of the partial-fusion or forme fruste BAV is that of a tricuspid aortic valve. (Right panel) The imaging diagnosis is usually made in systole. Although the opening appears triangular, there is a small fusion of the right and left cusps with a ‘mini-raphe’. These can be suspected by transthoracic or transoesophageal echocardiogram, and confirmed by a 3-dimensional transoesophageal echocardiogram, cardiac magnetic resonance or cardiac computed tomography. Definitive confirmation is usually made by surgical inspection or pathological analysis. Modified from Michelena et al [10] with permission from Elsevier. BAV: bicuspid aortic valve.

Figure 15:

Systolic transoesophageal echocardiogram still images and intraoperative photograph of a partial-fusion bicuspid aortic valve. (A) Intraoperative 2-dimensional transoesophageal echocardiogram shows a triangular systolic opening with a suspected small fusion between the right (R) and left (L) cusps (red arrow) (Video 11). (B) The 2-dimensional transoesophageal long axis demonstrates no evidence of systolic doming with asymmetrical dilatation of the non-coronary sinus (arrows), which was accompanied by significant dilatation of the ascending aorta in this patient. (C) 3-Dimensional transoesophageal systolic short axis demonstrates a small raphe (arrows) between the right and left coronary cusps with 2 other normal commissures (asterisks) (Video 12). (D) Explanted valve shows the small raphe between the right and left cusps (arrow). N: non-coronary cusp.

Figure 16:

Schematic of the BAV anatomical spectrum using the most common right-left cusp fusion as the example. From left to right, note the partial-fusion BAV resembling a tricuspid aortic valve, likely associated with a mild embryological defect, then spanning a continuum of increasing non-fused cusp commissural angles and increasing cusp size/shape similarity, ending with the 2-sinus BAV phenotypes that represent almost perfect ‘bicuspidity’ and are likely associated with the most severe embryological defects. Modified from Michelena et al [10] with permission from Elsevier. BAV: bicuspid aortic valve.

Figure 17:

Surgical and pathological demonstration of the bicuspid aortic valve anatomical spectrum according to non-fused cusp commissural angles and cusp size/ shape. (Top) Intraoperative photographs demonstrate the bicuspid aortic valve phenotypic spectrum. (Bottom) Photographs of the pathological specimens demonstrate the bicuspid aortic valve phenotypic spectrum.

Figure 18:

Nomograms based on transthoracic echocardiographic long-axis end-diastolic leading-edge-to-leading-edge measurements. Graphs display the ULN in millimetres (mm) for the root (SoV) and AA diameters as a function of body surface area (Dubois and Dubois formula) and age for both sexes. Modified from Campens et al [78] with permission from Elsevier. AA: ascending aorta; ULN: upper limit of normal.

Figure 19:

BAV aortopathy phenotypes. On the left is a normal aorta. (Top) The most common phenotype (approximately 70%), the ascending phenotype, is preferential dilatation of the tubular ascending aorta. (Middle) The root phenotype involves preferential dilatation of the root, seen in approximately 20% of patients with bicuspid aortic valve with aortopathy. (Bottom) The extended phenotype shows dilatation of the root, the ascending aorta and the arch. The most common extended phenotypes are root plus ascending aorta and ascending aorta plus arch. BAV: bicuspid aortic valve.

Figure 20:

Critical imaging evaluation of the congenital BAV condition. BAV: bicuspid aortic valve; CCT: cardiac computed tomography; CMR: cardiac magnetic resonance.

Figure 21:

Schematic of surgical bicuspid aortic valve repair for aortic regurgitation. (A) Fused bicuspid aortic valve with the fused or conjoined cusp having prolapse (P). (B) Central plication sutures are applied to correct the prolapse of the fused cusp (black arrows). The sutures are best placed in the central portion of the cusp. The circumference of the fused sinus has been reduced through plication of the aortic wall, thus bringing the commissures into a more symmetrical configuration (‘bicuspidization’) (red arrows). (C) Suture annuloplasty placed at the basal level of the root, i.e. the functional (virtual) aortic annulus. (D) Alternatively, an external band annuloplasty may be used to stabilize the annulus (bottom arrow). A second band or ring has been placed at the sinotubular junction (top arrow), which would not be needed if the tubular ascending aorta needed replacement, because the proximal anastomosis of the ascending graft would stabilize the sinotubular junction. Modified from Pavel Zacek, MD, PhD, with permission.

Figure 22:

Repair-oriented bicuspid aortic valve classification according to commissural orientation. Commissural orientation optimal for repair is shown in the symmetrical type; the asymmetrical bicuspid aortic valve benefits from increasing its commissural angle; the very asymmetrical type should likely be best treated as a tricuspid aortic valve (see also Fig. 9). Note how the height of the fused commissure increases as the asymmetry increases and looks more like a tricuspid aortic valve. Note that the annulus tends to be more circular in symmetrical bicuspid aortic valve and becomes more elliptic with increasing bicuspid aortic valve asymmetry. From Pavel Zacek, MD, PhD, with permission.

Figure 23:

Cardiac magnetic resonance 4-dimensional flow. Systolic streamlines in a healthy volunteer (left), in a right-left cusp fusion (RL) patient with BAV (middle) and in a right non-cusp fusion (RN) patient (right). Neither the patients nor the volunteer had aortic valve stenosis, and neither had aortic surgery. Notice the difference in the flow direction: In right-left cusp fusion, flow impinges on the outer curvature of the proximal ascending aorta (arrows), including the root. In right non-cusp fusion, flow is posteriorly directed in the proximal aorta (arrowhead) and impinges on the outer wall in the distal ascending aorta (arrows) [Videos 13 (normal), 14 (right-left fusion) and 15 (right non-fusion)]. Visualization of the streamlines was obtained with CVI42, Circle Cardiovascular Imaging Inc., Calgary, Alberta, Canada by Andrea Guala, PhD, Vall d’Hebron Hospital. BAV: bicuspid aortic valve; L: left cusp; N: non-cusp; R: right cusp.

Figure 24:

Cardiac computed tomography pre-transcatheter aortic valve replacement bicuspid aortic valve morphologies. Various aortic valve morphologies on volume-rendered computed tomography for bicuspid aortic valve stenosis (A through F) are shown. The bicuspid aortic valve is categorized as no raphe type (A and B) and raphe type (C through F). Raphe type is further categorized as non-calcified raphe type (C and D) and calcified raphe type (E and F). Arrowheads indicate non-calcified raphe and arrows indicate calcified raphe. Upper panels represent aortic valve with mild leaflet calcification and lower panels represent aortic valves with excess leaflet calcification. Modified from Yoon et al [128] with permission from Elsevier.