Bicuspid aortic valve (BAV) is the most common congenital cardiac malformation, and the historical nomenclature for it was a mess — Sievers types, clock-face descriptions, and a dozen competing schemes that used numbers and letters instead of anatomy. The 2021 International Consensus replaced all of it with a plain-language, imaging-based system built around three types and their specific phenotypes.
Key reference: Michelena HI, Della Corte A, Evangelista A, et al. International consensus statement on nomenclature and classification of the congenital bicuspid aortic valve and its aortopathy, for clinical, surgical, interventional and research purposes. Eur J Cardiothorac Surg. 2021;60(3):448–76. DOI: 10.1093/ejcts/ezab038 — full PDF
1 The three BAV types
Everything in the consensus starts here. Each type is defined by how many aortic sinuses are present and how the cusps relate to them — not by a number code.
| Type | Prevalence | Sinuses | Cusps | Commissures | Raphe |
|---|---|---|---|---|---|
| Fused BAV | 90–95% | 3 | 2 (usually different size/shape) | 2 | Common — visible or not |
| 2-sinus BAV | 5–7% | 2 | 2 (roughly equal size/shape) | 2 | Never |
| Partial-fusion BAV (forme fruste) | Unknown | 3 | 3 (usually symmetric) | 3 “apparent” — one fused < 50% | Small mini-raphe |
The single most useful discriminator on CT is the sinus count. Three sinuses with two functional cusps = fused type. Two sinuses = 2-sinus type. Count sinuses on a true short-axis, systolic-phase reconstruction.
2 Fused BAV — the three phenotypes
The fused type accounts for the overwhelming majority of BAV. Two of the three cusps are fused or joined within three distinguishable aortic sinuses, producing two functional cusps: one conjoined and one non-fused. These are usually different in size and shape, and the non-fused sinus and cusp commonly show eccentric dominance — it is larger than the two fused sinuses, at any age.
Name the phenotype by which two cusps are fused:
| Phenotype | Prevalence | Systolic commissure position (clock-face) | Notes |
|---|---|---|---|
| Right–left cusp fusion (R-L) | 70–80% | 4 and 10 o’clock (or 5 and 11) | Most common phenotype across American, European, and Asian populations, and across all aortic phenotypes |
| Right–non cusp fusion (R-N) | 20–30% | 1 and 7 o’clock (or 12 and 6) | Next most common; more prevalent in Asian populations |
| Left–non cusp fusion (L-N) | 3–6% | 2 and 8 o’clock (or 3 and 9) | Least common; also more prevalent in Asian populations |
| Indeterminate cusp fusion | — | — | Three sinuses and two fused cusps are identifiable, but the specific fusion cannot be discerned |
Anatomic landmarks are what let you assign the phenotype — the clock face alone can overlap between positions. On a base-of-the-heart short axis:
- Right coronary cusp (R) — anterior, positioned between the tricuspid and pulmonic valve insertions
- Left coronary cusp (L) — posterior-lateral, related to the left atrium
- Non-coronary cusp (N) — most posterior, related to the interatrial septum
Confirming the origin of the left and right coronary arteries is often the fastest way to settle an ambiguous case.
3 Clinical associations of the fused phenotypes
The phenotypes are not interchangeable — they carry different valve and aortic natural histories.
| Phenotype | Valve dysfunction | Aortopathy pattern | Other associations |
|---|---|---|---|
| R-L fusion | AR more common; male preponderance | Associated with the root phenotype; greater wall shear stress on root/proximal aorta | Strongly associated with aortic coarctation in children; more common in Turner syndrome and Shone complex |
| R-N fusion | Higher prevalence of AS in adults; independently predicts AR progression; more rapid AS and AR progression in children/adolescents | Associated with dilatation of the ascending aorta and arch; posteriorly directed flow jet on 4D flow | More common in Down syndrome |
| L-N fusion | Least studied | — | Highest prevalence in Asian populations |
These associations are statistical, not deterministic. R-L fusion BAV can be associated with either aortic phenotype.
4 Symmetry of the fused type
Symmetry is defined by the commissural angle of the non-fused cusp — measured in the short axis, from the position of the two commissures to the centre of the valve. This is a critical pre-repair measurement and is one of the main things the Sievers classification could not express.
| Symmetry | Non-fused cusp commissural angle | Repair implications |
|---|---|---|
| Symmetrical | 160–180° | Single, straight coaptation line — repair is most reproducible |
| Asymmetrical | 140–159° | Less symmetric; more technically challenging to “bicuspidize” |
| Very asymmetrical | 120–139° | Closely resembles a tricuspid valve; surgeon may treat it as tricuspid instead |
As the angle decreases, retraction of the free edge of the fused cusp at the raphe level becomes more prominent — a contributor to regurgitation. This retraction is best appreciated by direct surgical visualization or gross pathologic inspection, and is not reliably assessed by imaging.
5 2-sinus BAV — the two phenotypes
The 2-sinus BAV is uncommon (5–7%) and represents the most severe expression of the embryological defect — it is anatomically closest to perfect “bicuspidity”. Two cusps, roughly equal in size and shape, each occupying 180° of the annular circumference, formed within only two aortic sinuses. There is no raphe and the commissural angle is 180°.
Name the phenotype by the orientation of the commissural line in the short-axis base-of-the-heart plane:
| Phenotype | Frequency | Commissural line orientation | Coronary origins |
|---|---|---|---|
| Latero-lateral (side-to-side) | Most common | Bisects the normal geographic position of the non-coronary cusp | One coronary artery arising from each cusp |
| Antero-posterior (front-and-back) | Least common | Bisects the interatrial septum, splitting the normal geographic location of the left cusp | One from each cusp, or both arising from the anterior cusp |
Why these are easy to misname. In the latero-lateral phenotype the two functional cusps each occupy part of the normal “left” and “non-coronary” geography, so it superficially suggests right–non fusion — but the landmark relations don’t hold up. The antero-posterior phenotype resembles a right–left fusion without a raphe. The sinus count is what settles it.
If you suspect only two sinuses but cannot be certain, the consensus explicitly sanctions reporting “possible” or “probable” 2-sinus BAV rather than forcing a call. There is a genuine lack of clinical and prognostic data for this type, and the consensus asks that research be directed toward it.
6 Partial-fusion BAV (forme fruste)
A newly recognized type whose prevalence is unknown. In diastole it looks like a normal tricuspid aortic valve — three symmetrical cusps with 120° commissural angles. The abnormality is revealed in systole: the opening appears triangular, but there is fusion of less than 50% at the base of one commissure, forming a small mini-raphe.
- Most commonly described intraoperatively in patients undergoing surgery for aorta dilatation
- Suspected on TTE/TEE, confirmed by 3D TEE, CMR, or CCT; definitive confirmation is usually surgical or pathological
- Alters aortic flow patterns — increased flow eccentricity and vortices — which may explain the apparently high prevalence of aortic dilatation in these patients
7 The BAV anatomical spectrum
The consensus frames the phenotypes as a continuum of increasing “bicuspidity”, tracking the severity of the underlying embryological defect. From mildest to most severe:
Partial-fusion → very asymmetric fused → asymmetric fused → symmetric fused (with raphe) → symmetric fused (no raphe) → 2-sinus antero-posterior → 2-sinus latero-lateral
Across this spectrum, the non-fused cusp commissural angle increases and the two cusps become progressively more similar in size and shape.
8 The raphe
A raphe is a congenital fibrous ridge between the fused cusps. It is present in approximately 70% of fused BAV — but not always, and its absence does not exclude the fused type.
- A raphe may be present but not initially visible on echocardiography, and may become visible years later
- CCT identifies raphe calcification readily by its attenuation — dense, usually > 130 HU
- On echo, significant raphe calcification can be identified (highly echogenic, casting a shadow), but less-severe raphe calcification cannot be reliably distinguished from raphe fibrosis
- The presence of a raphe is associated with progression of valvular dysfunction (particularly AS) and with future valvular surgery
Congenital vs. acquired fusion. A fibrotic, calcified, or rheumatic tricuspid valve can present with acquired fusion that mimics BAV. Two features separate them:
| Feature | Congenital fusion | Acquired (rheumatic) fusion |
|---|---|---|
| Angle between fused cusps | Obtuse | Acute |
| Cleavage plane on ventricular aspect | Absent | Present |
The pseudocommissure — the attachment of the raphe at the aortic wall — sits lower within the root than the true commissures, which is how a surgeon confirms congenital bicuspidity intraoperatively.
9 BAV aortopathy phenotypes
BAV is a valvulo-aortopathy — the aorta must be phenotyped alongside the valve. There are three aortic dilatation phenotypes:
| Phenotype | Prevalence | Pattern | Clinical note |
|---|---|---|---|
| Ascending phenotype | ~70% | Dilatation preferentially in the tubular ascending aorta beyond the STJ | Typically the older patient, male or female, with aortic valve sclerosis/stenosis |
| Root phenotype | ~20% | Dilatation preferentially at the root (sinuses of Valsalva), possibly involving the ventriculo-aortic junction/annulus | Typically the younger male patient with mild-to-severe AR; associated with greater rates of acute dissection after simple AVR |
| Extended phenotype | Variable | Root plus ascending, or ascending plus arch | May evolve from either pattern on follow-up |
The root and ascending phenotypes are not mutually exclusive — a root phenotype may have mild ascending dilatation, and vice versa. Name the phenotype by where dilatation predominates.
Growth rates for the tubular ascending tract run 0.2–2.3 mm/year, usually 0.4–0.6 mm/year. A small percentage of patients grow faster. The root phenotype is independently associated with faster ascending growth, so “cross-over” to an extended phenotype is a recognized evolution — progressive STJ effacement may be the first sign.
10 Defining aortic dilatation
For adults with typical valvulo-aortopathy, the consensus uses simple absolute-diameter partitions:
| Severity | Root or ascending diameter |
|---|---|
| Mild | Between the age-, body-size- and sex-specific ULN and 45 mm |
| Moderate | 46–50 to 54 mm |
| Severe | ≥ 55 mm — elective surgical cut-off |
| Severe (with risk factors) | > 50 mm if any risk factor is present |
Risk factors that increase the likelihood of aortic complications:
- Root phenotype
- Severe BAV regurgitation
- Uncontrolled hypertension
- Personal history of coarctation
- Family history of aortic dissection or early unexplained sudden cardiac death
- Aortic diameter increase > 3 mm/year
In children, adolescents, and young adults, use z-scores rather than absolute diameters — dilatation is identified at a z-score > +2.0 (97.7th percentile).
Measurement caveat. In adults with BAV, TTE systematically underestimates the aortic root compared to CCT because the sinuses are asymmetric. CCT/CMR should be used for the root when it is enlarged (> 45 mm) or asymmetric. Adult TTE diastolic leading-edge-to-leading-edge is generally equivalent to diastolic inner-to-inner wall CCT/CMR for the ascending aorta. Always compare like with like across serial studies — same modality, same anatomical location, same method.
11 CT acquisition & technique
Cardiac CT provides unparalleled visualization of the aortic valve, root complex, and ascending aorta, and has become the gold standard for pre-TAVR BAV evaluation.
The single most important technical point: evaluating the aortic valve requires systolic phase imaging, best achieved with retrospective ECG synchronization.
Routine coronary CTA is often acquired in diastole only. On a diastolic-only dataset, partial or complete cusp fusion can be overlooked and the valve mistaken for tricuspid. You are unlikely to make this mistake only if the tricuspid valve is symmetrical with no leaflet thickening or asymmetrical calcification.
| Parameter | Recommendation |
|---|---|
| Synchronization | Retrospective ECG gating; full multiphase dataset |
| Phase targeting | Identify the absolute delay after the R peak in milliseconds — more reliable than preselected R-R percentages |
| Tube modulation | Turn off during systole to reduce noise in the critical phase |
| Contrast | 50–100 mL at 4–6 mL/s |
| Slice thickness | Thin slices, < 1 mm, multiphasic reconstruction |
| Reformatting | Double-oblique views to define annulus, sinuses, and STJ; manual or semiautomated |
Because of high spatial resolution, reduced radiation dose with newer scanners, and the ability to simultaneously clear the coronaries, CCT often avoids the need for separate coronary angiography in these typically younger patients.
12 Pre-TAVR raphe & calcification morphology
For TAVR planning, BAV stenosis is further categorized on volume-rendered CT by raphe type and cusp calcium burden — a 2 × 3 framework:
| No raphe | Non-calcified raphe | Calcified raphe | |
|---|---|---|---|
| Mild cusp calcification | Lowest-risk morphology | Intermediate | Intermediate |
| Excess cusp calcification | Intermediate | Intermediate | Highest-risk morphology |
Calcified raphe combined with excess leaflet calcification is the morphology most associated with procedural difficulty and adverse TAVR outcomes. → See TAVR planning and CT aortic valve calcification.
13 What to put in the report
The consensus reduces to three things that must be described in every BAV patient:
1. Type and specific phenotype (plus valvular function)
- Fused BAV → right–left / right–non / left–non / indeterminate
- 2-sinus BAV → latero-lateral / antero-posterior
- Partial-fusion BAV (forme fruste)
2. Raphe and symmetry
- Raphe: visible or not visible; calcified or not calcified
- Cusp size/shape: different or roughly equal
- Symmetry (non-fused cusp angle): symmetric (160–180°) / asymmetric (140–159°) / very asymmetric (120–139°)
3. Aortopathy and coarctation
- Dilatation present → ascending / root / extended phenotype, with diameters
- Dilatation absent
- Aortic coarctation → present (with severity) or absent
Sample phrasing: “Fused bicuspid aortic valve, right–left cusp fusion phenotype, with a visible calcified raphe. Non-fused cusp commissural angle 155° (asymmetric). Ascending aortopathy phenotype with a maximal ascending aortic diameter of 47 mm; root 38 mm. No coarctation.”
14 Why this replaced the Sievers classification
| Sievers limitation | International Consensus |
|---|---|
| Not language-intuitive — Types 0, 1, 2 | Language-intuitive — fused, 2-sinus, partial-fusion |
| Type 0 does not differentiate a fused BAV with no raphe from a true 2-sinus BAV | Fused types may or may not have a raphe; 2-sinus types never do |
| No pre-repair symmetry assessment | Fused types require symmetry assessment for surgical planning |
| Does not recognize partial fusion (forme fruste) | Recognizes partial-fusion BAV |
| No aortopathy phenotypes | Root, ascending, and extended aortic phenotypes |
| Sievers “type 2” is not a BAV — it is a unicuspid valve | Unicuspid aortic valves are excluded |
| Derived from anatomical pathology only | Built from imaging, anatomical pathology, surgical-functional pathology, and clinical associations |
15 Clinical context worth knowing
- AVR risk: community risk of aortic valve replacement 25 years after BAV diagnosis is greater than 50%, strongly driven by AS
- Up to 20% of patients ≥ 80 years old undergoing AVR have a congenital BAV
- AR in BAV is considerably less common than AS (30% vs 70%) and is more frequent in men
- Aortic dilatation is reported in 40–70% of BAV depending on population and definition; ~25% reach ≥ 45 mm at 25 years, and > 20% undergo surgery for aortic repair
- Coarctation occurs in 7–10% of adults with BAV; conversely, BAV is present in 50–60% of patients with coarctation
- Endocarditis: ~2% in contemporary cohorts; ~14 cases per 10,000 patient-years — 11× the general population
- Dissection: ~3 cases per 10,000 patient-years — 8× the general population — rising to 0.5% with diameters ≥ 45 mm, but generally < 1%
- Mitral valve prolapse affects 2–3% of BAV patients — no different from the general population