**2. Normal anatomy of the aortic valve apparatus**

The functional unit of a normal aortic root is made up of three aortic sinuses of Valsalva. They are formed by the aortic wall and the aortic valve leaflets, which are attached to the corresponding sinus. This establishes three pocket-like spaces. They are divided by commissural spaces and interleaflet triangles, the so-called trigone [1, 2]. The sum of the zones of the valve leaflets is larger than the cross-sectional region of the aortic root and this in addition to valve leaflet tissue pliability permits for a competent valve closure during the diastolic phase and unhindered valve opening to allow forward flow during the systolic phase of the cardiac cycle. While tricuspid valve leaflets are the most common morphologic structure of the aortic valve, unicuspid, bicuspid, and quadricuspid morphologic variants are also seen, the later in aortic valve or truncal disease states.

## **3. Prevalence**

#### **3.1 Congenital valvar AS**

The incidence of congenital valvar aortic stenosis (AS) is 5–6% of all congenital heart defects (CHDs). Given the prevalence of CHDs in 0.8% of live births [3, 4], the population prevalence of AS is estimated to be 0.5–0.6% (5 to 6 per 1000) of live births. AS's occurrence is more frequent in males than in females.

#### **3.2 Bicuspid aortic valve**

The prevalence of bicuspid aortic valve is generally thought to be 1–2% of population [5, 6]. More recent studies indicated a slightly lower prevalence. A study that reviewed echocardiograms of 24,265 subjects with a gender distribution of 47% males and 53% females revealed a 0.6% prevalence of bicuspid aortic valves [7]. Screening echocardiograms of 1742 teenage athletes with male preponderance (67% male and 33% female) revealed a 0.5% incidence of bicuspid aortic valves [7]. In another study of 2273 competitive athletes, aged 8–60 years, bicuspid aortic valves were present in 2.5% [8], higher than seen in the previous study. An echocardiogram of 1075 neonates revealed a prevalence of 0.46%; there was a higher (0.71%) prevalence in male babies than in female infants (0.19%) [9]. Studies do confirm a high level of accuracy of echocardiography in diagnosing bicuspid aortic valve [10]. Variations from 0.5 to 2.5% in the prevalence of bicuspid aortic valve appear to be related to the types of study cohorts selected in each study.

#### **3.3 Calcific AS**

In a study published in 2013, the prevalence of calcific AS in the elderly has ranged between 2.8 and 4.6% [11]. In a more recent study examining the global epidemiology of valvular heart disease, calcific AS among adults is age-dependent, older the subject, and more frequent, is its prevalence; the highest is in the older adults: 1000 per 100,000 (1%) in 75–79 year-olds and 1400 per 100,000 (1.4%) in 80–85 year-olds [12]. These prevalences are lower than those described in the above study [11]. There was nearly an equal gender distribution [12]. By contrast, rheumatic heart disease is more common in low-income countries with prevalence rates of 400–500 per 100,000 with similar distribution among all adult age groups [12]. The gender distribution of rheumatic heart disease is also similar in all age groups [12].

#### **3.4 Aortic insufficiency**

In the Framingham heart study involving 1696 men and 1893 women aged 54 ± 10 years, the prevalence of aortic insufficiency (AI) was found to be 13% in men and 8.5% in women; the subjects were assessed by echocardiography [13].

#### **3.5 Ascending aortic aneurysm**

The prevalence of ascending aortic aneurysms is 5 per 100,000 patient-years; this is based on population-based studies [14].
