Abstract
Echocardiography plays an important role in the diagnosis and management of aortic valve disease with the introduction of transcatheter aortic valve replacement greatly expanding its role in guiding treatment. Both transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) and, increasingly, three-dimensional techniques are essential tools. This chapter covers the use of echocardiography in the comprehensive evaluation of the aortic valve, with the objectives of assessing the nature, severity and etiology of valve dysfunction (stenosis and/or regurgitation), the anatomic changes responsible for this dysfunction, and, where possible, the disease process that has resulted in these anatomic changes. Importantly, echo also provides important information concerning secondary changes in cardiac anatomy and function, notably those of the left ventricle.
Keywords
aortic regurgitation, aortic stenosis, aortic valve, echocardiography, Doppler echocardiography, transesophageal echocardiography
Introduction
Aortic valve (AV) disease is the most common valve disease in developed countries. Aortic stenosis (AS), which is most often due to calcification and degeneration of congenitally normal tricuspid valves, affects approximately 1.5 million people in the United States with a prevalence that increases with age. While hemodynamically significant AS (moderate or severe) is unusual before the age of 65, in those aged 65–74 the prevalence is approximately 1%, increasing to 3%–5% of those over the age of 75. Aortic sclerosis, arguably a precursor to AS, is even more common, affecting 40% of those over the age of 75, and, while not hemodynamically significant, it is associated with an increased risk of stroke, myocardial infarction, and death, even with adjustment for traditional cardiovascular risk factors.
In those under the age of 70, AS is most typically based on a bicuspid AV, often with superimposed calcific changes. Bicuspid AV is one of the most common forms of congenital heart disease, affecting 0.5%–0.8% of the population, and occurring more commonly in men. Rheumatic valve disease is a less common cause of AS and there are rare cases of AS due to endocarditis, Fabry disease, lupus, ochronosis, hyperuricemia, and Paget’s disease.
Aortic regurgitation (AR) may be due to a primary valvular problem or loss of support as a result of aortic root or annular dilatation. A less common cause is aortic dissection with prolapse of the intimal flap. The most common valvular abnormality is bicuspid AV with less common causes being endocarditis, rheumatic disease, aortic sclerosis, connective tissue disease, anorectic drug toxicity, radiation, antiphospholipid syndrome, subaortic stenosis, ventricular septal defect, and systemic inflammatory disorders. Moderate to severe AR has a reported prevalence of 0.5% in the US population.
Echocardiography plays an important role in the diagnosis and management of AV disease with the introduction of transcatheter AV replacement greatly expanding its role in guiding treatment. Both transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) and, increasingly, three-dimensional (3D) techniques are essential tools. This chapter covers the use of echocardiography in the comprehensive evaluation of the AV, with the objectives of assessing the nature, severity and etiology of valve dysfunction (stenosis and/or regurgitation), the anatomic changes responsible for this dysfunction, and, where possible, the disease process that has resulted in these anatomic changes. Importantly, echo also provides important information concerning secondary changes in cardiac anatomy and function, notably those of the left ventricle.
Introduction
Aortic valve (AV) disease is the most common valve disease in developed countries. Aortic stenosis (AS), which is most often due to calcification and degeneration of congenitally normal tricuspid valves, affects approximately 1.5 million people in the United States with a prevalence that increases with age. While hemodynamically significant AS (moderate or severe) is unusual before the age of 65, in those aged 65–74 the prevalence is approximately 1%, increasing to 3%–5% of those over the age of 75. Aortic sclerosis, arguably a precursor to AS, is even more common, affecting 40% of those over the age of 75, and, while not hemodynamically significant, it is associated with an increased risk of stroke, myocardial infarction, and death, even with adjustment for traditional cardiovascular risk factors.
In those under the age of 70, AS is most typically based on a bicuspid AV, often with superimposed calcific changes. Bicuspid AV is one of the most common forms of congenital heart disease, affecting 0.5%–0.8% of the population, and occurring more commonly in men. Rheumatic valve disease is a less common cause of AS and there are rare cases of AS due to endocarditis, Fabry disease, lupus, ochronosis, hyperuricemia, and Paget’s disease.
Aortic regurgitation (AR) may be due to a primary valvular problem or loss of support as a result of aortic root or annular dilatation. A less common cause is aortic dissection with prolapse of the intimal flap. The most common valvular abnormality is bicuspid AV with less common causes being endocarditis, rheumatic disease, aortic sclerosis, connective tissue disease, anorectic drug toxicity, radiation, antiphospholipid syndrome, subaortic stenosis, ventricular septal defect, and systemic inflammatory disorders. Moderate to severe AR has a reported prevalence of 0.5% in the US population.
Echocardiography plays an important role in the diagnosis and management of AV disease with the introduction of transcatheter AV replacement greatly expanding its role in guiding treatment. Both transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) and, increasingly, three-dimensional (3D) techniques are essential tools. This chapter covers the use of echocardiography in the comprehensive evaluation of the AV, with the objectives of assessing the nature, severity and etiology of valve dysfunction (stenosis and/or regurgitation), the anatomic changes responsible for this dysfunction, and, where possible, the disease process that has resulted in these anatomic changes. Importantly, echo also provides important information concerning secondary changes in cardiac anatomy and function, notably those of the left ventricle.
Normal Aortic Valve Anatomy and Common Congenital Anomalies
The normal AV consists of three symmetric cusps that are supported by the aortic annulus and extend into the aortic root. The right and left coronary cusps lie within the sinuses of Valsalva that give rise to the corresponding coronary arteries with the remaining cusp termed the noncoronary cusp. The ideal views for assessing AV anatomy are the parasternal short- and long-axis views ( Fig. 29.1 , 
) and their comparable views on transesophageal echocardiography. The short-axis view shows all three cusps that create a triangular-shaped orifice when open and have a Y-shaped appearance when closed. The long axis typically displays the right and noncoronary cusps that flatten against the walls of the aortic root when normally open and meet centrally without prolapse below the plane of the aortic annulus with normal closure. The long-axis view can be angulated to show the right and left coronary cusps. Doppler evaluation employs these views as well as the apical three- and five-chamber, suprasternal and right parasternal views, all of which ensure that Doppler interrogation is parallel to flow.
The most common congenital abnormalities of the AV result from failures of cusp development and include, in order of decreasing frequency, bicuspid, unicuspid, and quadricuspid valves ( Fig. 29.2 , 
). Bicuspid valves can be distinguished based on the position of the coronary arteries to the line of closure. When both coronaries arise on the same side, the commissure is termed horizontal while, with a vertical commissure, the coronaries arise on opposite sides. The newer alternative nomenclature systems reflect which commissures are absent or exist as raphes (vestigial commissures) or the spatial orientation of the commissure (right-left or anterior-posterior). Right-left fusion with a raphe is the most common. A discussion of the clinical implications of bicuspid valve classification is beyond the scope of this chapter.
Because of the inability of bicuspid valves to open fully, the systolic orifice of a bicuspid AV is oval when seen in short axis while the long-axis view demonstrates protrusion of one or both cusp tips into the aortic lumen (doming; see Fig. 29.2 and 
). While classically bicuspid AVs have a single line of closure, many such valves have an echogenic ridge or raphe that represents a vestigial commissure. The closed appearance of such valves may be indistinguishable echocardiographically from a tricuspid valve. Thus, bicuspid AV is an echocardiographic systolic diagnosis. Unicuspid valves typically have circular openings that may be central or asymmetrically positioned, while quadricuspid valves have a cloverleaf-like appearance in systole and cross-like appearance in diastole (see Fig. 29.2 and 
).
Congenital abnormalities of the left ventricular outflow track include subaortic membranes characterized by linear echoes extending from the anterior mitral leaflet to the septum ( Fig. 29.3 , 
) or fibromuscular tunnels in which there is an echogenic ridge extending into the left ventricular outflow track. The presence of subaortic systolic turbulence should prompt a close inspection of the left ventricular outflow tract for evidence of subaortic obstruction that may be best seen in apical or nonstandard parasternal long-axis views. Aortic valvular regurgitation is frequently seen with subaortic membrane reflecting trauma to the valve by the subaortic stenotic jet. Supravalvular AS is a rare phenomenon consisting of a localized or diffuse narrowing of the ascending aorta distal to the sinuses of Valsalva.
Valvular Aortic Stenosis
Although the impeded cusp excursion of the bicuspid or unicuspid AV may alone result in AS, calcium deposition on a congenitally normal tricuspid AV is the most common cause of AS seen in adults. The echocardiographic appearance is one of restricted cusp excursion with irregular nodular cusp thickening ( Fig. 29.4 , 
). While echocardiography can provide a semiquantitative assessment of calcium burden, computed tomography (CT) may be better suited for this purpose.
Quantitation of Aortic Stenosis Severity
Table 29.1 displays a hemodynamic classification of aortic stenotic severity with echocardiography playing a key role. For reference, a normal aortic valve area (AVA) is 3–4 cm 2 . Application of the Bernoulli equation to continuous-wave Doppler interrogation of transvalvular flow provides accurate measures of mean and peak instantaneous gradient. Typically, the simplified form of the equation (ΔP = 4 V 2 ) may be used, but when the left ventricular outflow tract velocity exceeds 1 meter per second, the expanded version, ΔP = 4 (V 2 2 −V 1 2 ) where V 2 is the transaortic velocity and V 1 is left ventricular outflow tract (LVOT) velocity, should be employed.
| Mild | Moderate | Severe | |
|---|---|---|---|
| Mean gradient mm Hg | <20 | 20–39 | ≥40 |
| Aortic valve area cm 2 | >1.5 | 1.1–1.5 | ≤1.0 |
| Peak gradient mm Hg | <36 | 36–63 | ≥64 |
Recognizing the importance of recording Doppler signals parallel to flow, aortic gradients are best recorded using the apical five- or three-chamber, suprasternal notch and right parasternal windows with the highest velocities most commonly achieved using the right parasternal view ( Fig. 29.5 ). The smaller footprint provided by the nonimaging Pedoff probe makes it essential for the optimal assessment of patients with AS. When transesophageal echo is used, velocities are recorded using the deep transgastric views. Contrast may be helpful in enhancing Doppler spectra ( Fig. 29.6 ). It should be noted that while echocardiographically derived mean gradients are identical to those obtained invasively, the echo peak instantaneous gradient is typically higher than the peak-to-peak gradient calculated in the catheterization lab. The latter is the arithmetic difference between peak left ventricular and aortic pressures ( Fig. 29.7 ).
