Fig. 1.1
Parasternal long (left, a) and short (right, b) axis transthoracic echocardiographic view of a normal aortic valve in systole. In the parasternal long axis, the leaflet closest to the right ventricle is the right leaflet while the leaflet closest to the mitral valve is either the left or non-coronary cusp depending on the angle. In the short axis view, the interatrial septum points to the non-leaflet and the right is closest to the right ventricle RV right ventricle, LV left ventricle, AC aortic valve cusp, A aorta, ML mitral valve leaflets, LA left atrium, N non-coronary cusp, L left coronary cusp, R right coronary cusp
Fig. 1.2
Long (left, a) and short (right, b) axis cardiac CT angiographic view of the aortic valve in diastole. N non-coronary cusp, L left coronary cusp, R right coronary cusp
The nomenclature of the aortic valve apparatus includes three rings: basal, ventriculo-aortic junction, and sinotubular junction (Fig. 1.3a, b) [5].
Fig. 1.3
(a, top). Anatomical specimen of the aortic root with leaflets removed showing location of three virtual rings relative to the crown-like hinges of the leaflets (From Piazza et al. [5] with permission). (b, bottom) reveals a diagram representing the three circular anatomic rings of aortic root (Modified from Piazza et al. [5] with permission)
(A)
The basal ring comprises of the bottom of the sinuses formed by the semi-lunar leaflets and membranous septum.
(B)
The ventriculo–aortic junction is an anatomic ring where the membranous septum connects to the aortic wall at the bases of the right and left coronary sinuses while the aortic wall connects to the fibrous continuity of the anterior leaflet of the mitral valve at the base of the non-coronary sinus. The interleaftlet trigones between the semilunar leaflets and the membranous ventricular attachment are made of fibrous tissue.
(C)
The ring of the sinotubular junction is formed by the attachment of the sinuses to the ascending aorta.
Prevalance and Epidemiology of Aortic Stenosis
The Euro Heart study on valvular heart disease revealed that aortic stenosis was the most common valve disease in a population of 4,910 patients greater than 65 years of age (43.1 % of patients) and degenerative pathology accounted for almost 82 % of the cases [5].
In the US study of 1,797 patients older than 60 years, aortic stenosis was the second most common disease after mitral regurgitation. There appears to be a trend towards a higher prevalance of AS in men which becomes significant after adjusting for age [6]. Osnabrugge et al. pooled data from seven studies of elderly (>75 years) patients with severe aortic stenosis to determine the prevalence of aortic stenosis in Europe and North America and to estimate the potential surgical and transcatheter procedures [7]. The prevalence of mild to severe aortic stenosis was 2.4 % (2.7 million North Americans, 4.9 million Europeans) while severe aortic stenosis was 3.4 %. Three quarters of the patients with severe AS were symptomatic which corresponds to 540,000 North Americans and one million Europeans. The prevelance of AS, expectedly, increases with age and it is four times more common over the age of 65 (1.3 % vs 0.32 %) [6, 7].
In a survey of patients with severe AS at a single center, only half of patients with AS underwent AVR, 75 % of which were symptomatic despite a predicted mortality of <10 %, and fewer than one third were even referred to a surgeon [8].
Causes of Aortic Stenosis
As mentioned above, AS may occur at the level of, beneath, or above the level of the AV. The most common cause is valvular AS and its main causes are congenital, calcific, and rheumatic. Para–valvular obstruction (supra, and sub valvular aortic stenosis) can occur through membranes, muscular hypertrophy, or iatrogenically following surgical procedures.
Valvular Aortic Stenosis
Valvular aortic stenosis is by far the most common form of aortic stenosis and rheumatic heart disease remains the most common cause of valvular aortic stenosis worldwide especially in developing nations [9].
Calcific aortic stenosis is the most common form of valvular aortic stenosis in industrialized countries. It is primarily a disease of the elderly with increasing in prevalence with age. Superimposed calcification of congenital aortic stenosis is the second most common form of aortic stenosis in industrialized nations and commonly presents after the age of 50. Half of the adults with aortic stenosis have underlying bicuspid stenosis [10] and it is the most common cause of aortic stenosis before the age of 65. Other uncommon forms of aortic stenosis in the industrialized world is radiation and drug-induced aortic valve disease. Childhood aortic stenosis from either homozygous type II hyperlipoproteinemia, ochronosis with alkaptonuria, and Paget’s disease [9] is exceedingly rare.
Calcific Aortic Valve Stenosis
The prevailing mechanism causing calcification is thought to be secondary to lipid accumulation, inflammation and proliferative cellular and extracellular changes (Fig. 1.4). Calcification leads to leaflet immobility and obstruction without commissure fusion (Fig. 1.5a, b). Atherosclerosis and calcific aortic stenosis share similar pathophysiologic features in that risk factors include hypertension, smoking, elevated LDL cholesterol [9]. However, various studies examining the role of statin therapy for delaying the progression of valvular aortic stenosis have been unsuccessful in documenting a preventative or therapeutic role for statin in patients with AS [11].
Fig. 1.4
Potential pathway depicting calcific valvular aortic stenosis pathophysiology. 1. T–lymphocytes and macrophages infiltrate the endothelium and release cytokines, which act on valvular fibroblasts to promote cellular proliferations and extracellular matrix remodeling. 2. A subset of valvular fibroblasts within the fibrosa layer differentiates into myofibroblasts, which possesses characteristics of smooth muscle cells. 3. LDL particles taken into the subendothelial layer are oxidized an taken up by macrophages that become foam cells. 4. ACE is co-localized with APoB and facilitates the conversion of angiotensin II, which acts on angiotensin 1 receptors, expressed on valve myofibroblasts. 5. A subset of myofibroblast differentiates into an osteoblast phenotype that can promote calcium nodule and bone formation (From Libby et al. [10] with permission)
Fig. 1.5
Parasternal long (top left, a) and short (top right, b) axis transesophageal echocardiography showing reduced excursion aortic leaflets due to severe aortic stenosis. Cardiac CT angiography (bottom left, c) and surgical field (bottom right, d) demonstrating severe aortic stenosis
Congenital Aortic Valve Stenosis
Congenital aortic stenosis may be unicuspid or bicuspid (Fig. 1.6) with fusion of one or more commissures, and less commonly quadricuspid with a four leaflet aortic valve. Infants do not survive the severe obstruction caused from rare congenital unicuspid or quadricuspid valves unless surgically corrected. Bicuspid aortic valve disease is more common and occurs in 0.5–2 % of the population and in 66 % of all valves excised surgically for aortic stenosis with almost a double prevalence in males compared to women [9, 12]. However, only 1 in 50 children will develop significant obstruction by adolescence [13]. Patients may also present with aortic regurgitation with or without aortic stenosis [14, 15].
Fig. 1.6
Congenital unicuspid (a) and bicuspid valves (b) noted on echocardiography. The right cusp and non-coronary cusps are fused. (c) Demonstrates a calcified bicuspid aortic valve noted on CTA
Bicuspid aortic valve (BAV) usually occurs from fusion of the right and left aortic cusps (70 %) and maybe associated with other forms of congenital heart disease including coarctation of the aorta (50–80 %), interruption of the aorta (36 %) and isolated ventricular septal defect (20 %) [16, 17]. Patients with either aortic coarctation or Turner syndrome should be screened for the presence of BAV as the incidence approaches 50 % and 10–12 %, respectively [18, 19]. Systolic doming of the aortic valve leaflets is demonstrated in the long axis of the AV on various imaging modalities as echocardiography and MRI. While a classic “fish mouth” appearance is noted in the short axis view during diastole, with the corresponding fused leaflets appearing as one as demonstrated in Fig. 1.6 [20]. Extensive hypertrophy and supernormal ejection performance are the rule with congenital aortic stenosis and systolic dysfunction is uncommon unless severe stenosis is present at birth. However, sudden cardiac death is more common in infants and children than in adults [8].
BAV maybe also associated with aortopathy and patients are at an increased risk of aortic dissection, dilatation and aneurysm formation due to medial tissue changings including loss of elastic fibers, altered smooth muscle cell alignment, and cystic medial necrosis [21]. Multiple studies have shown familial clustering but the exact genetic mechanisms are still under investigation. Inheritance is likely multifactorial and in some instances autosomal dominant inheritance with incomplete penetrance [9, 14, 22].
Rheumatic Aortic Valve Stenosis
Rheumatic aortic stenosis is rare due to the decline in rheumatic fever and is primarily associated with rheumatic mitral stenosis. Unlike calcific aortic stenosis, there is fusion of both the leaflets and commissures creating an immobile small triangular or round opening with eversion of leaflet tips. Calcific nodules can form on the leaflets and commissures creating a fixed opening that may lead to both aortic stenosis and aortic regurgitation (Fig. 1.7) [9, 15].
Fig. 1.7
Rheumatic aortic stenosis noted on a surgical specimen (left, a) and on echocardiography (right, b). Note the thickening and eversion of leaflet tips
Para-valvular Aortic Stenosis
Supra Valvular Aortic Stenosis
Supra valvular aortic stenosis is exceedingly rare and may present either in isolation or as a part of congenital syndromes as autosomal dominant William’s Syndrome or familial non-Williams supra valvular aortic stenosis. It may occur in the form of membranes, muscular ridges, or tunneling of the ascending aorta for variable distances (Fig. 1.8). The coronary arteries are proximal to the stenosis and are subjected to high systolic and limited diastolic flow and can have atretic ostia, ectasia, or aneurysms [23]. It has also been reported after arterial switch operation.
Fig. 1.8
Supravalvular obstruction noted on parasternal long (top left, a) and suprasternal (top right, b) echocardiographic images (red arrows). Also noted on angiography (bottom left, c) and surgical specimen (bottom right, d) (black arrows)
Associated features of patients with William’s Syndrome include:
(a)
Other cardiovascular abnormalities: aortic valve stenosis, pulmonary stenosis, renal artery stenosis, and hypertension, sub valvular aortic stenosis, parachute mitral valve, bicuspid aortic valve, ventricular septal defect, and circle of Willis aneurysms.
(b)
Elfin features: these include puffy eyes, star like pattern in the iris, short nose with broad nasal tip, full cheeks and lips, small chin, wide mouth, and small widely spaced teeth.
(c)
Short stature, long neck, sloping shoulder, limited joint mobility, low muscle tone, and spine curvature, hyperacusis, strabismus, and poor growth
(d)
Hypercalcemia, chronic ear infections, gastric reflux, and hernias
(e)
Developmental delays, self mutilation, anxiety, phobias
Surgical correction is indicated in patients with a mean Doppler gradient of 50 mmHg and/or a peak Doppler gradient of 70 mmHg, symptoms of angina, dyspnea, or syncope, in the presence of LVH, and in case of the desire of pregnancy or greater exercise [23].
It is performed by either a single patch through a single sinus incision (McGoon), inverted Y patch requiring double sinus incision (Doty), and the Brom and Myers techniques with either a three patch or direct three sinus incision, respectively. The latter is the most recent approach to surgical correction [23].
Sub Valvular Aortic Stenosis
Sub valvular aortic stenosis may occur due to a multitude of etiologies:
1.
Fixed congenital: Fixed congenital sub valvular aortic stenosis is more common than the supra valvular form (Fig. 1.9). It may occur as a part of a familial syndrome as Shone’s complex or occur in isolation with a 2:1 male predominance. Sub aortic membranes, muscular ridges, and tunnels can also account for the obstruction and can extend to the mitral valve anterior leaflet. It may occur with ventricular and atrioventricular septal defects and conotruncal abnormalities. Accessory mitral valve tissue or anomalous chords may also cause a fixed sub valvular obstruction [23]. Associated features of Shone’s complex include: coarctation of the aorta, parachute mitral valve, supravalvar mitral membrane, bicuspid aortic valve, and valvular aortic stenosis.
Fig. 1.9
Subaortic membrane: on TEE (top left, a) long axis, short axis (top right, b). Doppler across the LVOT revealing aortic stenosis and regurgitation (bottom left, c). Bottom right (d) image demonstrated surgical excision of a subaortic membrane
Damage to the aortic valve from the eccentric high velocity jet may lead to aortic valve regurgitation further increasing the hemodynamic burden on the left ventricle and is present in 50 % of cases. Moreover, a dynamic element of obstruction may also co-exist from left ventricular hypertrophy, and in contrast to valvular aortic stenosis, no ejection click is noted.
Surgical intervention is indicated in patients with a peak Doppler gradient >50 mmHg, mean Doppler gradient >30 mmHg, or catheter peak-to-peak gradient >50 mmHg. Similar to patients with supravalvular obstruction, the presence of symptoms of angina, dyspnea, or syncope, or in the presence of LV systolic dysfunction or significant aortic valve regurgitation or the patient desires to become pregnant or to participate in active sports may be considered for surgery with lesser gradients. In patients with a lesser degree of obstruction, an exercise challenge may unmask higher gradients not noted on rest [23]. The presence of LV systolic dysfunction or a ventricular septal defect proximal to the subvalvular obstruction may result in underestimation of obstruction [23].
Surgical repair of the discrete membranous form usually involves circumferential resection of the fibrous ring and some degree of resection of the muscular base along the left septal surface. Injury to the aortic or mitral valves, complete heart block, or creation of a ventricular septal defect may occur as the result of surgery. Patients with associated aortic regurgitation often undergo valve repair at the time of subaortic resection. Fibromuscular or tunnel-type subvalvular obstruction is more difficult to palliate surgically and usually involves a more aggressive septal resection and sometimes mitral valve replacement. Patients with subvalvular obstruction due to severe long-segment LVOT obstruction may require a Konno procedure, which involves an extensive patch augmentation of the LV outflow area to the aortic annulus.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
