Valvular heart disease
ecgwaves.com · Clinical Echocardiography
Chapter 1: Tricuspid stenosis
Tricuspid valve stenosis
Tricuspid stenosis is a rare condition that may be caused by rheumatic valvular disease, congenital heart disease, Whipple’s disease, or tumors. Rheumatic disease is the most common cause, in which scenario tricuspid stenosis is virtually always accompanied by aortic or mitral disease (most commonly mitral stenosis). Simultaneous tricuspid regurgitation is also common.
Echocardiography
Echocardiography has replaced catheterization for the assessment of tricuspid stenosis. Yet, there is no consensus regarding grading of tricuspid stenosis severity.
Tricuspid stenosis is visually characterized by thickened leaflets, with reduced motion and potentially fused commisures. Continuous Doppler is used to assess the stenosis. Doppler recordings are made during inspiration (velocities across the valve are greater during inspiration). The following findings are indicative of tricuspid stenosis:
Maximum flow velocity exceeds 1 m/s.
Pressure half time (PHT) exceeds 190 ms in pronounced stenosis.
Mean pressure gradient >5.0 mmHg suggests a clinically significant stenosis.
Tricuspid stenosis results in increased right atrial pressure, which subsequently causes right atrial dilation. Vena cava inferior may also dilate secondarily.
Principles of management
Medical therapies do not alter disease progression. Diuretics may be used for symptom relief.
Surgical repair or valve replacement is considered when medical therapy is insufficient, or when concomitant valvular disease (e.g mitral stenosis) requires intervention.
Valve replacement can be performed with biological or mechanical prostheses. The former is preferred due to the lower risk of thrombosis and evidence demonstrating long-term durability (Filsoufi et al).
Percutaneous interventions lack long-term safety and efficacy data.
References
ESC EACVI Guidelines for Valvular Heart Disease (2018).
Filsoufi F, Anyanwu AC, Salzberg SP, Frankel T, Cohn LH, Adams DH. Long-term outcomes of tricuspid valve replacement in the current era. Ann Thorac Surg 2005;80:845–850.
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Chapter 2: Tricuspid regurgitation (TR/TI)
Tricuspid regurgitation
The tricuspid valve separates the right ventricle and the right atrium. It normally consists of three leaflets (anterior, posterior and septal leaflet). The leaflets are attached to the subvalvular apparatus, consisting of the chordae tendineae and the papillary muscles. As compared to the mitral valve, the tricuspid valve is located slightly more apically (<0.8 mm / m2 BSA [body surface area]).
Approximately 85%-90% of healthy individuals in the general population exhibit a small tricuspid regurgitation, which is considered a normal finding. Pathological tricuspid regurgitation is more pronounced. Echocardiography is the preferred method for diagnosing tricuspid regurgitation.
Causes of tricuspid regurgitation
The most common causes of tricuspid regurgitation are as follows:
Right ventricular dysfunction due to pressure/volume overload.
Right ventricular infarction.
Ebstein’s anomaly (Figure 1).
Carcinoid heart disease.
Endocarditis (common in intravenous drug addicts).
Myxomatous degeneration.
Rheumatic heart disease.
Dilatation of the right ventricle.
Dilatation of the right atrium.
Pulmonary hypertension.
Left-to-right shunt.
Right ventricular dysfunction due to pressure/volume overload is the most common cause.
Ebstein’s anomaly
The prevalence of Ebstein’s anomaly is approximately 1 case per 200.000 live births (Atthenhofer et al).
Figure 1. Ebstein’s anomaly.
Ebstein’s anomaly is characterized by the following malformations:
The septal and posterior leaflets of the tricuspid valve adhere to the ventricular myocardium (failure of embryological delamination).
The tricuspid valve annulus is displaced apically >0.8 mm/m2 BSA.
Basal segments of the right ventricle (i.e parts on the atrial side of the tricuspid annulus) function as atrium and becomes dilated.
The anterior leaflet is usually larger. It may be fenestrated and swing into the RVOT, obstructing the outflow.
Reumatic heart disease
Thickened chordae tendineae.
Thickened leaflet tips.
Reduced leaflet mobility.
Left-sided rheumatic valvular disease is virtually always present.
Carcinoid heart disease
Short, thick and rigid leaflets.
Echocardiography
Two-dimensional echocardiography is used to evaluate valve anatomy and the subvalvular apparatus. Thickness, mobility and coaptation of the leaflets are assessed visually in multiple views. It should be noted that imaging of the right ventricle requires an experienced echocardiographer. Three-dimensional (3D) echocardiography should be considered in laboratories with expertise; 3D imaging is superior to 2D for estimating right ventricular volumes. Cardiac MRI is, however, the gold standard for assessing right ventricular anatomy and function.
Right ventricular dimensions and function must always be assessed. Left ventricular function, which may be the origin of right ventricular dysfunction, must also be evaluated. The pulmonary, aortic and mitral valve must also be evaluated, particularly in the setting of rheumatic valvular disease.
The regurgitation is considered severe if the tricuspid annulus diameter is >4 cm. Severe tricuspid regurgitation results in right ventricular and atrial dilation.
Tricuspid regurgitation leads to pressure and volume overload in the right ventricle. This results in the septum bulging into the left ventricle, which gives the left ventricle a D-shaped appearance in short-axis views. The increased pressure may also propagate back to the right atrium and venous system, resulting in dilation of vena cava inferior (>2.1 cm). Severe tricuspid regurgitation may lead to systolic reversal in the hepatic veins. This is visualized using pulsed Doppler in the hepatic veins during systole.
The regurgitant jet area (in the right atrium) should be measured and compared to the area of the right atrium. If the jet area is ≥40% of the atrial area, then the regurgitation is severe.
Vena contracta should also be measured; ≥ 0.7 cm is indicative of severe regurgitation.
Continuous Doppler, placed in the tricuspid valve orifice, is used to investigate the appearance of the spectral curve. A dense spectral curve with an early peak indicates a rapid pressure equalization between the atrium and the ventricle.
PASP: Pulmonary Artery Systolic Pressure
PASP (pulmonary artery systolic pressure) is estimated by adding the pressure gradient between the atrium and the ventricle (estimated using continuous Doppler through the tricuspid valve) and the right atrial pressure (RAP), according to the following formula:
PASP = 4v2 + RAPmeanwhere 4v2 equals the pressure gradient between atrium and ventricle
Mean RAP is difficult to estimate if the regurgitation is pronounced.
References
Attenhofer et al. Ebstein’s anomaly. Circulation (2007).
Chapter 3: Pulmonary regurgitation
Pulmonary (pulmonic) regurgitation
Pulmonary regurgitation is also called pulmonic regurgitation.
The majority of all adults exhibit a small pulmonary regurgitation, which is considered a normal finding. The regurgitation results in blood flowing back from the pulmonary artery into the right ventricle during diastole. The most common cause of abnormal pulmonary regurgitation is pulmonary hypertension. Table 1 presents the causes of pulmonary regurgitation.
Mild pulmonary regurgitation is a normal echocardiographic finding that requires no further investigation.
| Table 1. Causes of pulmonary regurgitation |
|---|
| Pulmonary hypertension |
| Endocarditis |
| Myxoma |
| Carcinoid heart disease |
| Tetralogy of Fallot |
| Marfan syndrome |
| Takayasu’s arteritis |
| Iatrogenic (e.g complication of catheterization) |
| Congenital dysplasia/aplasia of the pulmonary valve |
| Idiopathic pulmonary artery dilation |
Pulmonary regurgitation results in right ventricular volume overload, which gradually causes right ventricular failure. The ventricle and RVOT (right ventricular outflow tract) become dilated, which further agravates the regurgitation. The proximal portion of the pulmonary artery may also be dilated in patients with pulmonary hypertension.
Echocardiography in pulmonary regurgitation
Echocardiography is the modality of choice for diagnosing pulmonary regurgitation. Continuous Doppler through the pulmonary valve reveals regurgitant blood flow in the parasternal short-axis view. Pressure gradient and pressure half time (PHT) are also estimated using continuous Doppler. A dense regurgitant jet with rapid deceleration (short PHT) is suggestive of severe regurgitation; the leakage usually ends early in diastole, which is evident by the spectral curve reaching the baseline before the end of diastole.
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Chapter 4: Pulmonary stenosis
Pulmonary (pulmonic) stenosis
Pulmonary stenosis is virtually always a consequence of congenital heart disease. The stenosis can be fixed or dynamic, depending on the underlying etiology. Pulmonary stenosis can be valvular (i.e stenosis localized in the valve), subvalvular (stenosis proximal to the valve) or supravalvular (stenosis distal to the valve). Valvular pulmonic stenosis can be caused by dysplastic, bicuspid or unicuspid valves. Table 1 presents common causes of pulmonic stenosis.
Table 1. Causes of pulmonic stenosis.
| Tetralogy of Fallot |
|---|
| Transposition of the great arteries) |
| Dysplastic, bicuspid or unicuspid pulmonary valve |
| Noonan syndrome: 60% of all individuals with Noonan syndrome have pulmonic stenosis. The stenosis is subvalvular, causing a narrowing of the RVOT (right ventricular outflow tract). |
| Carcinoid heart disease: Carcinoid syndrome is a paraneoplastic syndrome that occurs due to carcinomas secreting kallikrein and serotonin. In the heart, this can lead to thickening of the pulmonary valve and, subsequently, narrowing of the valvular orifice. Carcinoid heart disease may also lead to endocardial fibrosis. |
| Rheumatic heart disease |
| Sinus of Valsalva aneurysm: The aneurysm may compress the pulmonary outflow. |
| Myxoma: Myxomas may compress the pulmonary outflow. |
| Aortic aneurysm: Aortic aneurysms may compresses the RVOT. |
Echocardiography in pulmonic stenosis
In the setting of pulmonary valve stenosis, the pressure in the right ventricle rises, which results in right ventricular hypertrophy. The valve is usually thickened and during systole leaflet doming appears. The proximal part of the pulmonary artery is frequently dilated.
The maximum and mean pressure gradient is calculated using continuous wave (CW) doppler placed along the pulmonary valve in the parasternal short-axis view (PSAX). The gradient is calculated using Bernoulli’s simplified formula:
ΔP = 4v2
Pulmonary artery pressure (PA pressure)
The systolic pulmonary artery pressure (PA pressure, PASP) can be estimated by subtracting the pressure gradient across the valve (ΔP) from right intraventricular pressure. The systolic PA pressure is an indicator of cardiac hemodynamic status and may be estimated with echocardiography. The PASP is an independent predictor of survival and for elevated left ventricular filling pressures (Lam et al). PASP is elevated in pulmonary arterial hypertension (PAH).
Valve area
The continuity equation can be used to calculate the valve area. The equation claims that the volume of blood flowing through the RVOT is equal to the volume flowing through the pulmonary artery.
SVRVOT = SVPASV = stroke volume.
The stroke volumes are calculated using cross-sectional area and VTI (Velocity Time Integral):
SVRVOT = areaRVOT × VTIRVOT
SVPA = areaPA × VTIPA
areaRVOT × VTIRVOT = SVPA = areaPA × VTIPA
The valve area (areaPA) is derived as follows:
areaPA = (areaRVOT × VTIRVOT) / VTIPA
Table 2. Grading of pulmonic stenosis.
Grading of pulmonic stenosis Maximum gradient Maximum velocity Small PS <36 mmHg
<3 m/s Moderate PS 36-64 mmHg
3-4 m/s Pronounced PS
64 mmHg
4 m/s
Table 3. Normal right heart hemodynamics
| RVSP/PASP Echo | < 36 mm Hg* |
|---|---|
| Mean PAP | 8 – 20 mm Hg |
| PAEDP | 4 – 12 mm Hg |
| RAP | 0 – 5 mm Hg |
| PVR | < 2.0 – 3.0 WU |
*up to 40 mm Hg in older and obese patients.
References
Baumgartner et al: Echocardiographic assessment of valve stenosis: EAE/ASE Recommendations for Clinical Practice (2009. JASE).
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Chapter 5: Mitral regurgitation
Mitral regurgitation
Causes of mitral regurgitation
The most common cause of mitral regurgitation in high-income countries is age-related degeneration of the valvular apparatus. Age-related degeneration affects 2% of the population and leads to gradual prolapse of the valve leaflets (Figure 1). Rheumatic heart disease is the leading cause of mitral regurgitation in low- and middle-income countries. Rheumatic heart disease typically results in thickening of the leaflets and may coexist with mitral stenosis.
Idiopathic degeneration (Barlow’s disease), degeneration associated with connective tissue disorders (Marfan syndrome, Ehlers-Danlos syndrome), osteogenesis imperfecta typically causes prolapse of P2 (Figure 1).
Myocardial ischemia affecting the papillary muscles or the connected myocardium may cause mitral prolapse, and thus regurgitation. Ischemia manifests with myocardial akinesia or dyskinesia, which impairs papillary muscle function. Likewise, myocardial infarction affecting the papillary muscle or its connected myocardium may also result in mitral prolapse. Extensive myocardial infarction may lead to papillary muscle rupture. The risk of rupture is greater for the posteromedial papillary muscle, which only receives blood supply from one coronary artery (Coronary arteries).
Chronic myocardial ischemia may also lead to left ventricular dilation, which is referred to as ischemic cardiomyopathy (Dilated Cardiomyopathy). Ventricular dilation leads to dilation of the mitral annulus and papillary muscle displacement (i.e the distance between the papillary muscle and the mitral annulus increases), both of which lead to regurgitation. Table 1 presents the most common causes of mitral regurgitation.
| Table 1. Causes of mitral regurgitation |
|---|
| Degeneration, prolapse |
| DCM (dilated cardiomyopathy) |
| Ischemic heart disease (coronary heart disease) |
| Rheumatic valve disease |
| Endocarditis |
| Congenital mitral regurgitation |
| Amyloidosis |
| SLE |
| Hypertrophic obstructive cardiomyopathy (HOCM) |
| Rupture of papillary muscle |
| Rupture of chordae tendineae |
Figure 1. Anatomy of the mitral valve
Acute mitral regurgitation
Acute mitral regurgitation is relatively rare. The most common causes are as follows:
Endocarditis
Papillary muscle rupture (complication of acute myocardial infarction)
Rupture of chordae tendineae.
Acute regurgitation of blood into the left atrium results in sudden volume and pressure overload in the atrium, leading to increased LAP (left atrial pressure). However, left ventricular end-diastolic pressure (LVEDP) also rises; the left ventricle becomes volume overloaded since less blood is ejected into the aorta. Thus, acute regurgitation results in a sudden increase in preload, which the ventricle counteracts by increasing heart rate and stroke volume (Preload, Afterload, Stroke Volume and Frank Starling’s mechanism). Compensatory mechanisms may alleviate the condition temporarily, but the elevated left atrial pressure will rapidly propagate to the pulmonary circulation and cause pulmonary edema. Also, left ventricular exhaustion results in diminished cardiac output, potential hypotension and cardiogenic shock.
Chronic mitral regurgitation
Chronic mitral regurgitation causes a gradual volume and pressure overload, such that LVEDP and LAP rise slowly. This leads to compensatory dilatation of chambers. The mechanism underlying ventricular and atrial dilation proceeds from Laplace’s law, which states that increased pressure results in increased wall stress, which can be alleviated by ventricular hypertrophy and dilation:
Wall stress = (PressureLV × radiusLV) / (2 × WTLV)LV = left ventricle; WT = wall thickness
Laplace’s law shows that wall stress can be reduced by increasing wall thickness, which is equivalent to developing hypertrophy. The ventricle also dilates, which reduces the volume overload.
According to the Frank-Starling mechanism, stroke volume increases to handle the increase in preload. Stroke volumes may be supranormal in the early stages of mitral regurgitation. However, continuing dilation results in a successive increase in regurgitation, and, thus, deteriorating ventricular function. Contractile dysfunction commences, leading to reduced left ventricular ejection fraction (EF). Ultimately, mitral regurgitation results in pulmonary hypertension, pulmonary edema and systolic heart failure.
Chronic mitral regurgitation ultimately causes pulmonary hypertension, pulmonary edema and systolic heart failure.
Echocardiographic assessment of mitral regurgitation
Key points 2D assessment
Assess the leaflets, chordae tendineae, papillary muscles.
Are all structures visible and intact?
Calcifications?
Ruptures papillary muscles or chordae tendineae?
Vegetations?
Assess the left ventricle:
Structure (dimensions) and function?
Assess the left atrium:
Atrial dimension?
Assess the mitral annulus:
Dilated mitral annulus? Calcifications?
Prolapse: If the valve bulges >1 mm (during systole) into the atrium, there is prolapse.
Prolapse of the posterior leaflet results in an anteriorly directed regurgitant jet.
Prolapse of the anterior leaflet results in a posteriorly directed regurgitant jet.
Left ventricular dilation results in the papillary muscles being pulled further away from the mitral annulus. This impairs leaflet coaptation, which is evident in the ultrasound image as tenting. Tenting is quantified by measuring the height from the valvular plane to the tips, where the leaflets coapt.
Flail leaflets: ruptured or prolonged chordae results in the leaflets swinging back into the left atrium.
Vena contracta
Vena contracta is the narrowest part of the regurgitant jet and reflects the regurgitant orifice area. The measurement is acquired in parasternal long-axis view (PLAX) with the valve zoomed. Degree of regurgitation can be estimated using the diameter of vena contracta, as follows:
Vena contracta <3 mm: mild regurgitation.
Vena contracta >7 mm: severe regurgitation.
Vena contracta may be used to estimate severity of the regurgitation if the orifice (regurgitant area) is circular. Mean value of vena contracta measured in several views may be used.
Figure 2. Mitral regurgitation. Measurement of vena contracta.
PISA (Proximal Isovelocity Surface Area)
Using PISA (proximal isovelocity surface area), the area and volume of the regurgitation may be calculated. The measurement is acquired in apical four-chamber view (A4C) with the valve area zoomed. Color Doppler is used to visualize vena contracta, PISA and the jet. The baseline is adjusted (between 14 cm/s and 40 cm/s) until PISA assumes the shape of a semicircle. The largest PISA radius during systole is measured. Maximum velocity and VTI across the mitral valve is obtained using continuous wave doppler. The regurgitant orifice area is calculated using the following formula:
EROA = 2 × 𝛑 × rPISA2 × valiasing / vmax MR jetEROA = effective regurgitant orifice area; MR = mitral regurgitation.
Calculating the regurgitant volume
The regurgitant volume (Vregurg) can be calculated using the following three methods.
Method 1: Pulsed wave doppler
Pulsed Doppler can estimate the regurgitant volume (milliliters, ml) by calculating the difference between transaortal blood volume (Vaorta) and transmitral blood volume (Vmitral), according to the following formula:
Vregurg = Vmitral – Vaorta
Transaortal and transmitral flow are calculated using each respective valve area and VTI (pulsed Doppler):
Vaorta = areaLVOT x VTILVOT
Vmitral = areamitral x VTImitral
This method is not applicable in the setting of severe aortic regurgitation. In most cases, however, it is sufficient to take the ratio of VTImitral and VTILVOT:
VTImitral / VTILVOT
This is the ratio of the mitral inflow and the flow across the aorta. A ratio of >1.4 strongly suggests severe regurgitation. A ratio of <1.0 indicates a mild regurgitation.
Method 2: difference in stroke volume
The stroke volume can be estimated using Simpson’s modified method:
LVSV = LVEDV-LVESVLVSV = left ventricular stroke volume; LVEDV = left ventricular end-diastolic volume; LVEDV = left ventricular end-systolic volume.
This formula estimates the volume ejected from the left ventricle, but it does not consider the direction of the blood flow (i.e whether it flows through the aortic valve and/or the mitral valve). Therefore, we also obtain the volume flowing through LVOT (SVLVOT), and subtract it from LVSV, which yields the volume leaking back into the left atrium.
Start by calculating the volume flowing across the LVOT:
SVLVOT = areaLVOT × VTILVOT
Calculate the regurgitant volume by subtracting SVLVOT from the total stroke volume:
Vregurg = LVSV – SVLVOT
Method 3: PISA
EROA = 2 × 𝛑 × rPISA2 × valiasing / vmax MR jet
Vregurg = EROA × VTIMRjet
The regurgitant fraction (Fregurg) can be calculated as follows:
Fregurg = Vregurg / SVtotal
SVtotal = areamitral annulus × VTImitral annulus
Other echocardiographic findings in mitral regurgitation
High LAP (left atrial pressure) yields higher E-wave velocity.
In severe mitral regurgitation, systolic reversal is seen in the pulmonary veins.
Pulmonary pressure is always increased in severe mitral regurgitation.
Chapter 6: Mitral valve stenosis
The mitral valve
The mitral valve separates the left atrium and the left ventricle. The valve is attached to the mitral annulus, which is continuous with annulus fibrosus (the fibrous ring). The mitral valve has an anterior leaflet and a posterior leaflet. The anterior leaflet has a semi-circular shape and is firmly attached to two fifths of the circumference of the mitral annulus. The aorto-mitral curtain separates the aortic valve and the anterior leaflet of the mitral valve. The anterior leaflet is anatomically divided into three segments referred to as A1 (anterior segment), A2 (middle segment), and A3 (posterior segment) (Figure 1). The posterior leaflet of the mitral valve has a semilunar shape and is attached to three fifths of the annular circumference. The posterior leaflet generally has two distinct indentations which divide it into three scallops, P1 (anterior or medial scallop), P2 (middle scallop), and P3 (posterior or lateral scallop).
Figure 1. Anatomy of the mitral valve
The leaflets are connected to the papillary muscles via chordae tendineae (Figure 1). The anterolateral papillary muscle receives blood supply from the left anterior descending artery (LAD) and the left circumflex artery (LCX), whereas the posteromedial papillary muscle receives blood supply from either LCX or the right coronary artery (RCA). For details, refer to chapter The Coronary Arteries.
Mitral valve disease
A wide range of conditions may cause mitral valve disease, which results in changes in the pressure-volume relationships in the ventricle and the atrium. Pressure and/or volume overload causes dilation of the ventricle and/or atrium, which compensates by dilating. The dilation may also lead to dilatation of the mitral annulus, which further impairs coaptation of the leaflets and thus causes mitral regurgitation. The term coaptation is used to describe how well the leaflets meet and close the valve during systole. Poor coaptation leads to regurgitation.
Mitral stenosis
Mitral stenosis is defined as a narrowing of the mitral valve orifice. There are many causes of mitral stenosis, the most common of which are rheumatic heart disease, congenital malformations, radiation complications, metastases, myxoma, cardiac thrombi, etc (Table 1).
Most causes of mitral stenosis yield a progressive narrowing of the mitral valve. Mitral stenosis is a slowly progressing disease that eventually causes heart failure. Mitral stenosis typically becomes symptomatic at rest when the valve area is reduced to 1.5 cm2. During physical activity, mitral stenosis may become symptomatic already at 2.5 cm2. A normal mitral valve has an area of 4 to 6 cm2. A valve area <1 cm2 indicates severe mitral stenosis.
Table 1. Causes of mitral stenosis Rheumatic heart diseaseCongenital mitral stenosisCalcification of the mitral valveComplications to radiation therapyMucopolysaccharidosisCarcinoid tumorSystemic lupus erythematosus (SLE)Rheumatoid arthritis (RA)Iatrogenic stenosis after mitral valve surgeryMyxoma obstructing outflow from the left atriumAtrial thrombus obstructing atrial outflowEndocarditis
Hemodynamic consequences of mitral stenosis
Mitral stenosis hinders atrial emptying. This results in an increase in left atrial pressure (LAP), which gradually leads to atrial hypertrophy and dilation. Atrial dilation causes a significantly increased risk of atrial fibrillation. The increase in left atrial pressure may also propagate backward to the pulmonary circulation, causing pulmonary hypertension (PH). Additionally, pulmonary hypertension can propagate further backward to the right ventricle and right atrium, leading to right heart hypertrophy, dilation and ultimately right heart failure.
Echocardiography in mitral stenosis
Echocardiographic assessment of mitral stenosis includes visual and 2D imaging, as well as Doppler measurements to assess the degree of stenosis and evaluation of complications.
Visual assessment in 2D
Is the mitral valve normal, thickened, calcified or are there vegetations?
Are both leaflets moving normally?
Does leaflet doming occur during diastole?
Can the chordae tendineae be discerned? Are the strands calcified or fused?
Classification of mitral stenosis severity
The severity of mitral stenosis is classified on the basis of valve area and pressure gradients across the valve. Table 2 presents criteria for classification of disease severity. The required measurements and techniques are discussed below.
Table 2. Criteria for echocardiographic diagnosis of MS severity
Mild Moderate Severe Mean pressure decrease <5 mm Hg 6–10 mm Hg >10 mm Hg Pressure half-time <139 ms 140–219 ms ≥220 ms Valve area 1.6–2.0 cm2 1.5–1.0 cm2 <1.0 cm2
Calculation of valve area
Valve area is a key parameter in the assessment of disease severity. The smaller the valve orifice, the more pronounced the stenosis. There are three methods to calculate valve area.
Method 1: Direct measurement of valve area in PSAX
The valve area can be measured directly in the parasternal short-axis view (PSAX) during diastole. The ultrasound beam should be positioned so as to intersect the leaflet tips, otherwise, the valve area may be overestimated (Figure 2).
Figure 2. Mitral valve area.
Method 2: Pressure Half Time (PHT)
Using continuous wave Doppler, placed in the mitral valve, the PHT of the E wave is measured. PHT is the time it takes for the pressure difference between the atria and ventricles to halve. Table 2 presents grading criteria for PHT. The valve area (MVA, Mitral Valve Area) can then be estimated by the formula:
MVA = 220/PHT
The same Doppler measurement is used to calculate the mean pressure gradient across the mitral valve (ΔP, mmHg). Note that the formula cannot be used in the setting of prosthetic valves, atrial septal defect, severe aortic regurgitation or very high left ventricular filling pressures.
Method 3: The continuity equation
According to the continuity equation, the amount of blood flowing through the mitral valve during diastole must be equal to the volume flowing through LVOT during systole. Hence, MVA (mitral valve area) can be calculated as follows:
MVA = 𝛑 × (DLVOT/2)2 × (VTILVOT/VTImitral)D = diameter in cm.VTILVOT measured with pulsed Doppler i LVOT.VTImitral measured with continuous Doppler in the mitral valve.
The above formula should not be used in the setting of atrial fibrillation, significant mitral regurgitation or aortic regurgitation.
Mean and maximum pressure gradient across the mitral valve
The mean pressure gradient (difference) and maximum pressure gradient are calculated using continuous wave Doppler through the mitral valve (apical view). The maximum pressure gradient is calculated using the maximum velocity and Bernoulli’s simplified formula, as follows:
ΔPmax = 4vmax2
Mean pressure gradient (ΔPmean) reflects the mean pressure difference between the left atrium and ventricle during diastole and it is calculated using the obtained VTI. Note that the mean pressure gradient is affected by heart rate, filling time, cardiac output and mitral regurgitation, if present. The heart rate should always be noted.
Pulmonary arterial pressure (PASP, pulmonary artery systolic pressure)
PASP and Mean Pulmonary Arterial Pressure (MPA) should be measured.
If the patient has atrial fibrillation, measurements should be made on 5 consecutive cardiac cycles and the mean values of each parameter used to make the calculations.
In addition to the above parameters, the size of the left atrium should also be measured to clarify whether the atrium is dilated.
References
Baumgartner et al. Echocardiographic Assessment of Valve Stenosis: EAE/ASE Recommendations for Clinical Practice.
Chapter 7: Aortic regurgitation
Aortic regurgitation
Aortic regurgitation implies that the aortic valve leaks during diastole, such that blood regurgitates back from the aorta into the left ventricle. This results in volume overload in the left ventricle during diastole. The hemodynamic consequences of aortic regurgitation depend on whether the condition develops acutely or gradually.
Acute aortic regurgitation
Acute aortic regurgitation results in rapid volume overload on the left ventricle. The rapid onset results in a sudden increase in LVEDP (left ventricular end-diastolic pressure) and LAP (left atrial pressure). The left ventricle compensates by increasing cardiac output (CO); this is achieved by increasing heart rate and producing larger stroke volumes. Failure to increase cardiac output sufficiently will result in the following compilations:
Pulmonary edema develops due to rising LAP and LVEDP.
Cardiogenic shock develops if the cardiac output is insufficient.
Aortic regurgitation may cause myocardial ischemia because cardiac output diminishes in parallel with increasing myocardial load (and hence oxygen demand).
The most common causes of acute aortic regurgitation are aortic dissection, endocarditis and trauma.
Chronic aortic regurgitation
If aortic regurgitation develops gradually, then the ventricle will adapt to the volume overload. Unfortunately, adaptation implies that the left ventricle dilates, which induces irreversible cellular and extracellular processes that ultimately lead to heart failure. This initially results in greater diastolic volume and increased compliance. Increasing diastolic volumes requires that the myocardium becomes hypertrophic. Dilation and hypertrophy allow the ventricle to maintain cardiac output and prevent, or alleviate, the pressure increase in the left ventricle and left atrium.
Chronic aortic regurgitation leads to dilatation and hypertrophy of the left ventricle.
Cardiac remodeling
Ventricular dilatation and hypertrophy lead to myocardial remodeling and neurohormonal changes that further worsen the hemodynamic situation. Thus, chronic aortic regurgitation gradually leads to impaired contractile function and the development of myocardial fibrosis. Contractile dysfunction further aggravates the regurgitation (the regurgitation volume increases). Mechanically, wall stress (the load on individual muscle fibers) increases while the contractile function worsens.
Chronic aortic regurgitation also leads to increasing LVEDP and LAP, which in turn results in pulmonary hypertension and pulmonary edema.
| Table 1. Causes of aortic regurgitation |
|---|
| Bicuspid aortic valve |
| Rheumatic heart disease |
| Calcified aortic valves |
| Idiopathic aortic dilatation (aneurysm) |
| Hypertension |
| Aortic dissection, proximal |
| Marfan syndrome (may also cause aortic dissection) |
| Trauma |
| Vasculitis, rheumatic diseases |
| Ehlers-Danlos syndrome (may also cause aortic dissection) |
| Subaortic membrane |
| Endocarditis |
Echocardiography in aortic regurgitation
2D Echocardiography
The images are acquired in PLAX (parasternal long-axis view) and PSAX (parasternal short-axis view), with the valve zoomed. The following parameters are evaluated:
Can all three cusps be visualized, or is the valve bicuspid?
Is there cusp prolapse?
Are there vegetations on the valve?
Is the valve calcified?
Is the aortic root dilated?
Is the left ventricle dilated?
Is the left ventricle hypertrophic?
Is left ventricular ejection fraction (LVEF) normal?
A normal-sized ventricle with hyperdynamic contractility suggests acute aortic regurgitation.
The severity of aortic regurgitation can be evaluated using the following parameters.
Diameter of the regurgitant jet
The diameter of the regurgitant jet is measured in PLAX, and then compared with the diameter of the LVOT. A jet diameter smaller than 25% of the LVOT diameter suggests moderate aortic regurgitation. A jet diameter >65% of the LVOT diameter suggests severe aortic regurgitation (Figure 1).
Figure 1. Diameter of the regurgitant jet (aortic regurgitation).
| Table 1. Severity of aortic regurgitation | Jet size ratio |
|---|---|
| Mild | <24 |
| Moderate | 25-45 |
| Moderate-severe | 46-64 |
| Severe | > 65 |
Vena contracta
Vena contracta is also measured in PLAX with the aortic valve zoomed (Figure 2). Vena contracta is the narrowest diameter of the jet and reflects the regurgitant orifice area. A vena contracta <0.3 cm wide suggests mild aortic regurgitation, whereas vena contracta >0.6 cm indicates severe aortic regurgitation.
Figure 2. Measurement of the width of vena contracta in aortic regurgitation.
PHT (Pressure Half Time)
Pressure half time (PHT) is defined as the time it takes for the initial maximal pressure gradient across the aortic valve to fall by 50% during diastole. The drop in the pressure gradient is gradual in patients with mild aortic regurgitation. The drop is rapid in patients with severe aortic regurgitation (Figure 3, Table 2). Pressure half time is measured with continuous Doppler in apical views (3C or 5C).
Figure 3. Assessing severity of aortic regurgitation using pressure half time (PHT).
| Table 2. Severity of aortic regurgitation | Pressure Half Time (ms) |
|---|---|
| Mild | >500 ms |
| Moderate | 500-349 ms |
| Moderate-severe | 349-200 ms |
| Severe | < 200 ms |
It is important to note that the estimated severity of aortic regurgitation depends on the hemodynamic circumstances; severity is overestimated in patients with a significantly increased LVEDP.
Diastolic flow reversal
Diastolic flow reversal can be detected with Doppler recordings in the suprasternal window. Pulsed wave Doppler is placed along the ascending or descending aorta (Figure 4). The Doppler signal reveals whether there is flow reversal in the aorta during diastole; this backflow is referred to as diastolic flow reversal.
Note that the elasticity of the aorta depends on age; young patients have high compliance in the aorta, which during diastole produces a recoil that forces blood in the retrograde and antegrade direction. Hence, mild (physiological) flow reversal is normal in young individuals.
Normal and pathological flow reversal can be distinguished by means of the spectral curve. Pathological diastolic flow reversal exists throughout diastole and, generally, has velocity >20 cm/s at the end of diastole. The term holodiastolic flow reversal is used to denote flow reversal proceeding throughout diastole.
Figure 4. Diastolic flow reversal in aortic regurgitation.
Estimation of regurgitation volume and effective regurgitant orifice area (EROA)
Regurgitation volume (Vregurg) can be calculated using the following three methods.
Method 1: Stroke volume
According to the continuity equation, flow across the mitral valve is equal to flow across the aortic valve. Using pulsed wave Doppler, the volume flowing across the aortic valve (i.e stroke volume) and the mitral valve can be calculated. The difference between these two volumes is equivalent to the regurgitation volume (Vregurg). The stroke volume across the aortic valve (SVaorta) is equivalent to the volume of blood flowing through the aortic valve in anterograde direction minus the volume leaking back during diastole. This volume can be calculated by the following formula:
SVaorta = areaLVOT × VTILVOT
The volume of blood flowing across the mitral valve is equivalent to the anterograde stroke volume across the valve (SVmitral):
SVmitral = Areamitral × VTImitral
Thus, the regurgitation volume (Vregurg) can be calculated as follows:
Vregurg = SVaorta – SVmitral
This formula must not be used in the setting of mitral regurgitation.
It is also possible to calculate SVaorta using the following formula:
SVaorta = LVEDV – LVESV(Simpson’s method)LVEDV = Left ventricular end-diastolic volume; LVESV = left ventricular end-systolic volume
Method 2: PISA (Proximal Isovelocity Surface Area)
The regurgitation volume is the product of the effective regurgitation orifice area (EROA) and the regurgitant jet VTI:
Vregurg = EROA × VTIAR jet
EROA is the effective regurgitant orifice area and is calculated using PISA (Proximal Isovelocity Surface Area). PISA is the semicircle visualized with color Doppler. PISA should be measured carefully, which requires zooming the area and minimizing the color sector in order to increase the resolution (higher frame rate). If the regurgitation is obliquely directed, a parasternal view should be used for the measurement. If the regurgitation is centrally directed, an apical view should be used. The Doppler baseline (Nyquist limit) should be adjusted to optimize the image. The following measurements are made:
rPISA (PISA radius)
vmax AR (maximum velocity of the regurgitation, measured using CW doppler)
VTIAR jet
Calculation of EROA:
PISA = 2𝛑 × rPISA2
EROA = PISA × valiasing / vmax AR
If the regurgitation volume (Vregurg) has already been calculated, EROA can be obtained using the following formula:
EROA = Vregurg / VTIAR jet
Grading the regurgitation using EROA
EROA <0.1 cm2 suggests mild aortic regurgitation. If EROA is >0.3 cm2, then the regurgitation is severe.
Grading the regurgitation using Vregurg
Regurgitation volume <30 ml/stroke implies that aortic regurgitation is moderate. Regurgitation volume >60 ml/stroke is classified as severe aortic regurgitation.
Method 3: Regurgitation fraction (Fregurg)
Regurgitation fraction (Fregurg) is the proportion of blood that regurgitates back into the ventricle. The fraction is calculated by the following formula:
Fregurg = Vregurg / SVaorta
SVaorta = areaLVOT x VTILVOT
Regurgitation fraction < 30% indicates moderate aortic regurgitation.
Regurgitation fraction > 50% indicates severe aortic regurgitation.
Chapter 8: Aortic stenosis
Aortic stenosis
The aortic valve area is normally 3.0 to 4.0 cm2. Aortic stenosis is a progressive disease that leads to a gradual reduction in the orifice area. As the area is reduced, transvalvular flow resistance increases. This results in increased left ventricular load, while simultaneously affecting systemic perfusion. Aortic stenosis is a serious condition with poor long-term outcomes. Patients with low-flow low-gradient aortic stenosis (discussed below) have a 3-year survival rate of 50% (Eleid et al).
The cause of aortic stenosis displays marked geographical variations. In high-income countries, the majority of cases are caused by calcification of the aortic valve. Calcification has traditionally been considered a passive degenerative process, but emerging evidence suggests it is propelled by a biologically active process. Risk factors for calcification overlap with risk factors for coronary heart disease (atherosclerosis). The average age at diagnosis of aortic stenosis is 75 years in high-income countries.
In low- and middle-income countries, rheumatic heart disease is the leading cause of aortic stenosis. Rheumatic heart disease is a complication of rheumatic fever, which is caused by streptococcal infections (group A Streptococcus). Rheumatic heart disease can occur at any age and multiple valve lesions are common (typically the aortic and mitral valve). Rheumatic heart disease is rare in high-income countries, presumably because streptococcal infections are treated very liberally.
Figure 1 shows the aortic valve in PSAX (parasternal short-axis view).
Figure 1. The aortic valve visualized in PSAX (parasternal short-axis view).
Individuals with bicuspid aortic valves have substantially elevated risk of developing aortic stenosis. The prevalence of bicuspid aortic valves is 1% to 2% in most Western populations. Individuals with bicuspid aortic valves may develop symptomatic aortic stenosis already at the age of 60 years. Bicuspid aortic valves also increase the risk of aortic aneurysm, aortic dissection, and endocarditis. Figure 2 shows the normal tricuspid aortic valve.
Figure 2. Normal (tricuspid) aortic valve with three cusps (RCC, NCC and LCC). The right coronary artery (RCA) departs from the right coronary cusp (RCC), and the left main coronary artery (LMCA) departs from the left coronary cusp (LCC). NCC = non-coronary cusp.
Natural course and prognosis in aortic stenosis
Aortic stenosis is generally asymptomatic until the valve area is <1 cm². This condition causes hemodynamic changes that alter ventricular volume load, myocardial wall stress and coronary artery perfusion. These changes gradually lead to insufficient coronary perfusion (i.e myocardial ischemia and angina pectoris), ventricular dysfunction (heart failure) and arrhythmias. The annual risk of sudden cardiac arrest is <1% and median survival is 3 years. Long-term prognosis in aortiv stenosis is presented in Figure 3.
Figure 3. Prognosis in aortic stenosis according to type of stenosis. The patients with low flow (stroke volume index <35 ml/m²) and low gradient (<40 mmHg) displayed the worst prognosis. Adapted from Eleid et al. NF = normal flow; LF = low flow; HG = high gradient; LG = low gradient.
Pathophysiology of aortic stenosis
As aortic stenosis progresses, pressure conditions on the left side change dramatically, including in the left ventricle, left atrium, aorta and coronary arteries.
As the valve area becomes smaller, the transvalvular resistance increases, making it more difficult to eject blood into the aorta. In the early stages of aortic stenosis, stroke volume becomes smaller. Reduced stroke volumes and increased resistance in the valve result in compensatory left ventricular hypertrophy. This allows the left ventricle to generate greater pressure, thereby overcoming the resistance in the stenosis and maintaining adequate stroke volumes.
Thus, ventricular hypertrophy is a compensatory mechanism, the purpose of which is to maintain sufficient stroke volumes. As discussed previously, afterload is the resistance that the muscle fibers must overcome to eject blood into the aorta; this is equivalent to the force that the myocardium must generate during systole. Afterload is described in terms of wall tension (wall stress), which is the load on individual muscle fibers. Wall stress per surface area (σ) can be calculated with Laplace’s law:
Wall stress = σ = (pLV × rLV) / (2 × thicknessLV)LV = left ventricle; p = transmural pressure; r = radius,
This formula provides a mathematical explanation as to why aortic stenosis leads to hypertrophy. Aortic stenosis causes increased wall stress (i.e load on individual muscle fibers), which can be alleviated if the numerator becomes smaller or if the denominator becomes larger. In the early stages of aortic stenosis, wall thickness increases (i.e the denominator becomes larger), which results in a reduction in wall stress.
Unfortunately, left ventricular hypertrophy leads to cardiac remodeling, which in turn leads to reduced myocardial compliance. This is due to increased wall thickness and the development of interstitial fibrosis. As compliance decreases, passive filling of the left ventricle is reduced. Atrial contraction (active filling) becomes increasingly important. Impaired passive filling leads to higher end-diastolic pressure in the ventricle. It is believed that this results in reduced myocardial perfusion pressure, consequently, subendocardial ischemia. Elevated end-diastolic pressure can also propagate backward to the left atrium and further to the pulmonary circulation. Therefore, individuals with aortic stenosis may develop pulmonary edema.
As the stenosis becomes more pronounced, the progression of hypertrophy and fibrosis accelerates. Ventricular compliance decreases and filling pressure increases. Subendocardial ischemia develops, which, along with hypertrophy and fibrosis, leads to an increase in the risk of ventricular arrhythmias. Furthermore, stroke volumes are reduced as contractile function diminishes. When the myocardium can no longer compensate by hypertrophy, the ventricle begins to dilate. Ventricular dilatation leads to a decrease in intraventricular pressure and, consequently, a decrease in wall stress. This second compensatory mechanism ultimately leads to heart failure.
Angina pectoris (chest pain) and arrhythmias caused by aortic stenosis
Angina pectoris is common in aortic stenosis. Ischemia is explained by a decrease in coronary perfusion (the stenosis prevents normal blood flow through the aorta) in parallel with increased oxygen demand in the hypertrophic myocardium.
Aortic stenosis (AS) can also cause syncope, especially during physical activity. The mechanisms explaining how physical activity leads to syncope remain incompletely understood. With regards to arrhythmias, acute heart failure and syncope, the following explanations have typically been proposed:
Ventricular arrhythmias in aortic stenosis (AS) are provoked by physical activity.
Acute heart failure in AS occurs due to sudden ventricular overload.
Sudden peripheral vasodilatation during or immediately after physical activity may also cause syncope.
Echocardiographic assessment of aortic stenosis
The majority of all patients with aortic stenosis can be diagnosed and monitored with echocardiography. In selected cases, assessment and follow-up may be supplemented by cardiac catheterization, magnetic resonance imaging (cardiac MRI) or computed tomography (CT). The key parameters for assessing aortic stenosis are presented in Table 1. As evident in Table 1, aortic stenosis is graded from sclerosis to severe aortic stenosis.
Table 1. Aortic stenosis grades of severity
Echo parameter Aortic valve sclerosisMild ASModerate ASSevere ASPeak velocity, m/sec<2.52.5-33-4>4Mean gradient, mmHgNormal<2020-4040Aortic valve area, cm²Normal ≥1.51-1.5<1 cm²Calcium scoring, AU* Male: 2,065Female: 1,275
*Calcium scoring obtained with computed tomography (CT).
Visual (2D) assessment of the aortic valve
Bicuspid aortic valves
In 80% of cases with bicuspid aortic valves, the RCC and LCC are fused, and in remaining cases, the RCC and NCC are fused. A normal (tricuspid) aortic valve has three cusps, which is most often evident in the parasternal short-axis (PSAX) view. During systole, the valve orifice is circular (Figure 4). A bicuspid aortic valve, on the other hand, has two cusps, which are usually asymmetric and differ in size. Occasionally, bicuspid valves may exhibit a clear raphe, which results in a tricuspid appearance of the valve on echocardiogram. A bicuspid aortic valve displays an elliptical orifice during systole (Figure 4).
Figure 4. The difference between normal (tricuspid) and bicuspid aortic valves during systole and diastole.
During systole, the cusps often display doming, as illustrated in Figure 5.
Figure 5. Doming of the aortic valve during systole.
Calcification of the aortic valve
Calcification of the aortic valve appears as deposits with high echogenicity. Calcifications may be seen on the cusps, aortic annulus and proximal aorta. The extent and severity of valvular calcification can be graded semiquantitatively as mild (presence of small hyperechogenic areas with little acoustic shadowing), moderate (multiple large areas with dense echogenicity), or severe (extensive thickening with increased echogenicity and high acoustic shadowing).
Rheumatic heart disease
Aortic stenosis as a result of rheumatic heart disease results in a homogeneous thickening of the cusps, especially at the tips. In pronounced cases, the cusps may be fused at the tips. The cusps often display doming during systole (Figure 4).
Subvalvular obstruction
Subaortic obstruction implies that the stenosis is located in the LVOT (left ventricular outflow tract). Subvalvular stenosis is typically due to the presence of a subaortic membrane or HOCM (hypertrophic obstructive cardiomyopathy).
Subaortic membrane
A subaortic membrane is best visualized in apical views (4C, 5C) and appears as a distinct fibrous ring proximal to the aortic valve. The existence of a subaortic membrane causes turbulence in the LVOT. This can lead to incomplete valve closure during diastole, which in turn may lead to aortic regurgitation.
In HOCM, there are two factors contributing to the narrowing of the LVOT:
Hypertrophy of the septum leads to narrowing of the LVOT.
SAM (Systolic Anterior Motion) implies that the anterior mitral leaflet is pulled into the LVOT during systole, thereby obstructing the LVOT.
Supravalvular obstruction
Obstruction in the proximal aorta is a rare congenital malformation. It is typically visualized in PLAX (parasternal long-axis view).
Two-dimensional (2D) echocardiography
LVOT and proximal aorta
The following measurements, illustrated in Figure 6, should be performed:
LVOT (left ventricular outflow tract)
Aortic annulus
Sinus of Valsalva
Sinotubular junction (STJ)
Ascending aorta
Figure 6. Measurements in LVOT, aortiv valve and proximal aorta.
Measurements are made when the valve is open (i.e during systole). Dilatation of the aortic annulus, sinus of Valsalva, STJ (sinotubular junction) and ascending aorta should lead to suspicion of Marfan syndrome or bicuspid aortic valves, especially among younger individuals. Dilatation is also seen in systemic hypertension and in older individuals.
Evaluation of the left ventricle
The left ventricle should be investigated in terms of hypertrophy and dilatation. Refer to Left Ventricular Size and Dimensions.
Doppler studies
Doppler examination provides the most objective quantification of the severity of aortic stenosis. It is of prime importance to record the peak flow velocity, using continuous Doppler, across the aortic valve. The peak velocity is used to calculate the pressure gradient (i.e pressure difference) across the aortic valve. The more severe the stenosis, the greater the pressure gradient and, accordingly, the velocity across the valve. Measurements are always performed in multiple apical views, and mostly also from right-sided parasternal view and suprasternal view.
A pencil probe (PEDOF [Pulse Echo DOppler Flow] probe) may be necessary to capture high velocities (>3.5 m/s) with precision. The pencil probe is a small dual-crystal continuous wave transducer, which allows for optimal transducer positioning, angulation, and measurement of high velocities. The pencil probe may be used in any view, particularly right parasternal and suprasternal views. However, it is generally not necessary if flow velocity is low (<3 m/s) and cusp opening can be visualized clearly. The disadvantage of the pencil probe is the lack of a 2D image to guide the ultrasound.
Peak gradient across the aortic valve
The maximum (peak) gradient represents the greatest pressure difference recorded across the valve during systole. This is obtained by recording the peak velocity (using continuous Doppler) across the valve during systole. The peak velocity is entered into Bernoulli’s simplified formula to calculate the peak gradient (ΔP, mmHg):
ΔP = 4v2
Mean gradient across the aortic valve
The mean gradient represents the mean pressure difference between the left ventricle and the aorta during systole. This is calculated by using continuous Doppler to obtain VTI (Velocity Time Integral) across the valve. If the mean gradient across the aortic valve is ≥40 mmHg, then the aortic stenosis is graded as severe.
Aortic valve area (AVA)
The opening area of the aortic valve is calculated using the continuity equation. The underlying principle is that the volume of blood that flows (per unit time) through the aortic valve must be equal to the volume flowing through LVOT. Recall that VTI and area can be used to calculate volume: volume = area × VTI. According to the continuity equation, the product of area and VTI must be equal in the LVOT and aortic valve:
areaLVOT × VTILVOT = areaaortic valve × VTIaortic valve
To calculate aortic valve area, we measure areaLVOT, VTILVOT and VTIaortic valve. The areaLVOT is obtained by measuring the diameter (D) of LVOT:
areaLVOT = DLVOT × π
VTILVOT is calculated using pulsed wave Doppler with sample volume placed in LVOT. VTIaortic valve is measured with continuous wave Doppler through the aortic valve. Then areaaortiv valve is calculated as follows:
areaaortic valve = (areaLVOT × VTILVOT)/VTIaortic valve
The aortic valve area can be adjusted for body surface area (BSA). If the aortic valve area is <1 cm2 or BSA normalized area is <0.6 cm2/m2, then the aortic stenosis is severe.
If the velocity in LVOT is >1.5 m/s or if the velocity across the aortic valve is <3.0 m/s, the pressure gradient should be calculated using the following formula:
ΔP = 4(v2aortiv valve – v2LVOT)
VTI ratio
VTI ratio can also be used to estimate the degree of stenosis.
VTILVOT / VTIaortic valve
The lower the ratio, the more pronounced the stenosis. VTI ratio <0.25 implies severe aortic stenosis. VTI ratio is especially useful in individuals with small ventricular volumes.
In the setting of atrial fibrillation, all measurements should be made on 5 consecutive cardiac cycles and the mean value of each respective parameter should be used to perform the calculations.
Pressure recovery phenomenon: overestimation of the pressure gradient
According to Bernoulli’s law, pressure drops and velocity increases as a liquid travels towards a narrowing. Once the liquid has passed the narrowing, the opposite occurs; velocity decreases and pressure increases. This also applies to blood flow through stenotic valves. The phenomenon is called pressure recovery phenomenon (Figure 7).
Figure 7. Pressure recovery phenomenon. The pressure falls between p1 and p2, but then increases between p3 and p4. The pressure measured in the aorta with continuous wave Doppler is p3, which is thus lower than p4. So the pressure in the aorta is higher than the measurement with Doppler suggests.
Pressure recovery implies that the pressure increases rapidly immediately after a stenosis, while velocity diminishes. With continuous wave Doppler, the highest velocity is recorded, which is the velocity immediately after stenosis and where the pressure is actually lower than the pressure further up in the aorta. Thus, Doppler will overestimate the pressure drop across the aortic valve; i.e, the difference between the pressure in the aorta and the left ventricle is lower than what the Doppler measurement suggests. The smaller the aortic diameter, the more pronounced the pressure recovery. If the ascending aorta is <3.0 cm, then, generally, there is significant pressure recovery in aortic stenosis. If the ascending aorta is wide, then pressure recovery can be ignored.
Classification of aortic stenosis
Patients with an aortic valve area <1 cm² (and preserved ejection fraction) can be classified into four groups according to mean pressure gradient (MPG) and stroke volume index (SVI). The latter is the stroke volume normalized to body surface area (BSA).
| High flow / High gradient | MPG >40 mmHgSVI ≥35 ml/m² |
|---|---|
| High flow / Low gradient | MPG <40 mmHgSVI ≥35 ml/m² |
| Low flow / High gradient | MPG >40 mmHgSVI <35 ml/m² |
| Low flow / Low gradient | MPG <40 mmHgSVI <35 ml/m² |
Low flow, low gradient, low EF aortic stenosis
The pressure gradient is fundamental in aortic stenosis. In the setting of contractile (systolic) dysfunction, the left ventricle is unable to generate a normal increase in pressure and, accordingly, the pressure gradient across the aortic valve decreases, regardless of the stenosis. Hence, a patient with aortic stenosis who develops contractile dysfunction will display improvement in the pressure gradient, despite the fact that the stenosis remains unchanged, or even more severe.
This scenario is referred to as low flow, low gradient, low ejection fraction aortic stenosis. On echocardiography, this is characterized by the following:
Aortic valve area <1 cm2
LVEF (ejection fraction) <40%
Mean pressure gradient <30–40 mmHg.
Furthermore, contractile dysfunction may lead to the aortic valve appearing less mobile than it actually is. This is explained by the fact that the dysfunctioning ventricle is unable to generate enough force to open the valves properly (particularly if they are calcified). In this scenario, moderate aortic stenosis may appear as severe. This is referred to as pseudosevere aortic stenosis. In such cases, it is especially important to calculate the aortic valve area.
Low flow, low gradient, normal EF aortic stenosis
Individuals with small ventricular volumes may exhibit low flow, low gradient, normal EF aortic stenosis, which implies that aortic stenosis is present with low flow and low gradient despite normal ejection fraction. In these situations, the VTI ratio should be given greater importance in the assessment.
Echocardiographic assessment of the severity of aortic valve stenosis relies on peak velocity, mean pressure gradient and aortic valve area (AVA), which should ideally be concordant. In 25% of patients these parameters are discordant (usually aortic valve area <1 cm² and mean pressure gradient <40 mmHg). In most cases, these patients present with a normal flow (stroke volume index ≥35/ml/m²) but low flow provides important prognostic information. To assess whether these patients truly present with severe aortiv stenosis, calcium score should be measured using computed tomography (thresholds are 2,000 AU in male and 1,250 AU in female) [1].
References
[1] Messika-Zeitoun et al. Aortic valve stenosis: evaluation and management of patients with discordant grading.
[2] Baumgartner et al. Recommendations on the Echocardiographic Assessment of Aortic Valve Stenosis: A Focused Update From the European Association of Cardiovascular Imaging and the American Society of Echocardiography.