Aortic Regurgitation



Aortic Regurgitation


Praveen Mehrotra

Ira S. Cohen



ASSESSMENT OF AORTIC REGURGITATION (AR) has evolved considerably with advances in echocardiographic technology since Ward et al. (1) first described the use of pulsed-wave (PW) Doppler in conjunction with motion mode (M-mode) echocardiography and auscultation to detect AR. With current ultrasound technology, the exquisite sensitivity of transesophageal echocardiography (TEE) allows the physician to now detect the minute regurgitant jets engineered into the design of the St. Jude prosthetic valve to flush platelet aggregates off the valve surface and small paravalvular leaks after transcatheter aortic valve replacement (TAVR). Few studies have been performed investigating the assessment of AR primarily using TEE because of its relatively invasive nature. However, most assessments of the severity of AR are based on the assumption that transthoracic echocardiographic (TTE) approaches should be equally applicable to TEE.


ETIOLOGY AND MECHANISMS OF AORTIC REGURGITATION

The physiologic functioning of the aortic valve in diastole is dependent on the interplay of several components forming a complex that includes the aortic valve, aortic annulus, sinuses of Valsalva, and the sinotubular junction. The aortic annulus is formed by the basal insertions of the leaflets into the muscle of the left ventricular outflow tract (LVOT) and the fibrosa of the anterior mitral leaflet. The aortic valve leaflets then extend as semilunar structures along the sinuses of Valsalva to end at the sinotubular junction where the commissures are formed and whose diameter is normally 10% to 15% smaller than the diameter of the true aortic annulus (2). A delineation of the mechanisms of AR is of increasing clinical importance as the mechanism impacts on the surgical approach including determination of suitability for valve repair. A proposed classification system (Table 11.1) has been advanced that involves three functional mechanisms (Fig. 11.1) (3,4,5,6):

Type 1: AR is due to the enlargement of any of the components of the aortic root or ascending aorta with normal aortic cusp motion, as seen in idiopathic annuloaortic ectasia, ascending aortic aneurysm, Marfan syndrome, aortitis, or Ehlers-Danlos syndrome image (Videos 11.1 and 11.2). Aortic enlargement results in
outward displacement of the commissures and leaflet tethering which leads to incomplete leaflet closure in diastole generally resulting in a central regurgitant orifice and jet. Type 1 AR has been subdivided into sub-types depending on the location of enlargement: type 1A (ascending aorta and sinotubular junction), type 1B (sinuses of Valsalva and sinotubular junction), and type 1C (aortic annulus). Type 1 AR also includes regurgitation due to aortic cusp perforation (type 1D).








TABLE 11.1 Etiology and Mechanisms of Aortic Regurgitation






















Type 1: Normal cusp motion




  • dilatation of ascending aorta and sinotubular junction (STJ) (1A)



  • dilatation of aortic root at sinus of Valsalva (SOV) and STJ (1B)



  • dilatation of aortic annulus (1C)



  • leaflet perforation (1D)


Congenital aortic root abnormalities



Connective tissue disease (Marfan syndrome, Ehlers-Danlos syndrome, Loeys-Dietz syndrome)


Bicuspid valve-associated aortopathy


Acquired aortic root abnormalities



Autoimmune disease (systemic lupus erythematosus, ankylosing spondylitis)


Aortitis (syphilitic, Takayasu’s)


Aortic dissection


Aortic trauma


Hypertension


Idiopathic


Endocarditis (leaflet perforation)


Type 2: Excessive cusp motion (cusp prolapse or flail)


Bicuspid aortic valve disease


Acute aortic dissection


Ventricular septal defect


Type 3: Restricted cusp motion


Calcific degeneration


Bicuspid aortic valve disease


Radiation valvulopathy


Infective endocarditis


Rheumatic disease


Toxin-induced valvulopathy







FIGURE 11.1 Examples of the various mechanisms of aortic regurgitation. Type 1: Severe dilatation of the aortic root at the sinuses of Valsalva resulting in incomplete leaflet closure and severe, central aortic regurgitation (top). Type 2: Complete prolapse of the right coronary cusp of a trileaflet aortic valve resulting in highly eccentric, severe aortic regurgitation (middle). Type 3: Severe restriction of heavily calcified aortic valve leaflets in a patient with both severe aortic stenosis and severe aortic regurgitation (bottom).

Type 2: AR is due to excessive cusp motion from complete or partial prolapse or flail aortic cusp resulting in below the annular non-coaptation plane image (Videos 11.3 and 11.4). Prolapse or flail cusps can occur in the setting of excessive cusp tissue (e.g., bicuspid aortic valve or congenitally elongated cusp), disruption of aortic commissures (e.g., acute aortic dissection), or in the setting of a ventricular septal defect. Type 2 AR results in an eccentric regurgitant jet.

Type 3: AR is due to restricted leaflet motion and primary cusp damage resulting in poor leaflet coaptation (e.g., calcific degenerative, rheumatic, radiation, or bicuspid valve disease) image (Videos 11.5 and 11.6). Regurgitant jets in type 3 AR may be eccentric or central. The mechanism of AR may also be multifactorial with a single etiology causing AR from more than one mechanism (6). TEE evaluation has been shown to correlate very highly with surgical findings, and the evaluation of the potential mechanisms of AR should be part of the preoperative echocardiographic evaluation along with AR severity assessment (4). Lastly, the assessment of the sizes of the components of the aortic root complex should be performed prior to aortic valve surgery (Fig. 11.2).







FIGURE 11.2 Mid-esophageal aortic valve long-axis view (top) demonstrating appropriate locations for measuring the aortic annulus (a), sinus of Valsalva (b), sinotubular junction (c), and proximal ascending aorta (d). Three-dimensional multiplanar reconstruction (bottom) demonstrating appropriate way to perform “sinus-to-commissure” aortic root measurements in the aortic root long- and short-axis views. Ao, aorta; LVOT, left ventricular outflow tract; RVOT, right ventricular outflow tract.


HEMODYNAMICS OF AORTIC REGURGITATION

AR represents both an increase in preload and afterload to the left ventricle. The increase in preload is a result of the increased end-diastolic volume resulting from the added regurgitant volume. The increase in afterload is a function of the increased radius of the ventricle. Increase in the end-diastolic radius of a ventricle at any wall thickness increases the wall stress and the force needed to eject blood (law of Laplace). The general response of the ventricle to chronic AR is to dilate and become more compliant to accommodate the extra volume and to hypertrophy to reduce wall stress. The hypertrophy occurs both longitudinally as the heart enlarges (so-called eccentric hypertrophy) and concentrically, as evidenced by its maintaining a “normal” wall thickness as it enlarges. Accordingly, the size of the ventricle is an index of the severity and duration of the regurgitation and should be factored into the assessment of the severity of the lesion.

Acute AR, most commonly due to a tear in the valve secondary to endocarditis, deceleration injury in a motor vehicle accident, or an acute aortic dissection offers a contrasting clinical presentation. Acute AR is one of the least well-tolerated valvular lesions because of the limited ability of the heart to compensate for an acute increase in volume load by the mechanisms mentioned in the preceding text. Consequently, the LV diastolic pressure rises rapidly and is transmitted to the lungs resulting in severe pulmonary congestion. Therefore, in acute AR the chamber is often normal in size but with catastrophic hemodynamic consequences. Diagnosis of significant AR in the setting of heart failure is essential as intra-aortic balloon counterpulsation is contraindicated because diastolic pressure augmentation worsens the regurgitation.

The assessment of the severity of valvular insufficiency is complicated by the potentially dramatic effects of even transient changes in loading conditions and peripheral vascular resistance on Doppler indices of AR severity. Because the operating room environment is one in which a multitude of factors affect both the preload and afterload of the ventricle, the potential impact of these changes must be borne in mind when the severity of a valvular lesion is evaluated. Acute increases in peripheral vascular resistance (e.g., following surgical stimulation or the administration of vasopressors) can increase the apparent degree of valvular
insufficiency by increasing systemic vascular resistance and impeding peripheral runoff. Conversely, vasodilators (e.g., volatile anesthetics, angiotensin-converting enzyme inhibitors and receptor blockers, or calcium channel blockers) reduce peripheral vascular resistance and decrease the apparent degree of insufficiency, both clinically and by Doppler interrogation. The physical properties (e.g., distensibility, elasticity, compliance) of the source (aorta) and recipient (the left ventricle) of regurgitant flow, in addition to the size of the regurgitant orifice and the physical properties of the involved valve, are other dynamic variables that further complicate intraoperative assessment. In fact, some clinicians feel that it is not possible to definitively assess regurgitant lesions in the operating room environment. As a result of the multitude of factors influencing any assessment of the severity of AR, the estimate should be based on an integration of the results of all Doppler approaches providing technically adequate data in any given patient.


ECHOCARDIOGRAPHIC EVALUATION OF THE AORTIC VALVE

The aortic valve can be evaluated by M-mode, two-dimensional (2D), Doppler, and three-dimensional (3D) echocardiographic techniques. Transesophageal 2D echocardiographic imaging of the aortic valve is generally superior to transthoracic imaging because of the improved resolution of the higher frequency TEE probe which makes it possible to delineate the size of regurgitant jets more accurately than with transthoracic techniques. Three-dimensional TEE is playing an emerging role in the assessment of AR and reference is made to current observations utilizing 3D imaging for the assessment of regurgitant severity. Three-dimensional imaging, like 2D imaging, however, shares the limits inherent to all ultrasound techniques determined by the interrelation of sector (volume) size, frame (volume) rate, and depth on image resolution.

When imaging the regurgitant aortic valve and aortic root complex, it is, first, essential to determine the etiology of regurgitation by assessing leaflet structure, motion, and function. Two- and three-dimensional imaging of the aortic root complex should also be performed for precise measurement of dimensions of the aortic annulus, aortic root (at the sinuses of Valsalva), sinotubular junction, and ascending aorta (Fig. 11.2). Following this structural assessment, a comprehensive Doppler echocardiographic assessment of the aortic valve should follow. In general, the assessment of AR severity involves an integrative approach which utilizes both qualitative and quantitative Doppler techniques. The various approaches to assessing the severity of AR with TEE will be presented in the order of their relative clinical applicability. The American Society of Echocardiography has also published detailed recommendations for the echocardiographic assessment of AR which should be utilized as an important reference (5).


RECOMMENDED VIEWS

The most useful views are generally obtained by starting from the standard mid-esophageal (ME) four-chamber view and changing the angle of interrogation to approximately 45° to obtain the aortic valve short-axis view. In this view, the individual aortic cusps and sinuses are visualized in exquisite detail. Occasionally, the probe may need to be withdrawn or anteflexed to improve the image in this view. The angle of interrogation is then further advanced to 120 to 150° to produce the ME long-axis view of the LVOT, aortic valve, and proximal aorta. Further withdrawal from this position and, occasionally, slight anteflexion with or without rotation can be used to visualize the proximal ascending aorta, while the angle of interrogation can be decreased to 100 or 110° to better visualize the distal tubular ascending aorta. Biplane imaging of the aortic valve is also very useful for simultaneous short- and long-axis imaging of the aortic valve and root. In addition, 3D imaging of the aortic valve can be performed either in the short-axis or long-axis view for the creating of unique en face volume renderings of the aortic valve complex and for multiplanar reconstruction of the regurgitant jet’s vena contracta (VC) area.

Alternatively, but less frequently, good views can be obtained from a deep transgastric (TG) position at an angle close to 0° or greater, subject to individual variation, or from a standard midpapillary TG view at an angle of approximately 120° (TG long-axis view). These approaches have the advantage of aligning the ultrasound beam nearly parallel to the direction of blood flow, which is essential for accurate quantitative Doppler analysis of both the pressure half-time of the regurgitant jet as well as stroke volume. However, far-field beam widening and the greater distances traveled reduces spatial resolution in these views making them a poor choice for visualizing the cross-sectional area of an AR jet immediately below the valve plane. However, they may be the only means of assessing the outflow tract in the presence of a prosthetic mitral valve (MV), which frequently causes acoustic shadowing of the aortic annulus in more standard views, and occasionally, of an aortic prosthesis when its ring obscures the outflow tract image by acoustic shadowing.

The pressure gradient between the regurgitant and recipient chambers in regurgitant valvular lesions is always high and in AR corresponds to the diastolic gradient between the aortic root and the left ventricle. By
the simplified Bernoulli equation, the gradient equals four times the square of the peak jet velocity. In aortic regurgitant lesions, it is the rate of change in pressure gradients that provides clinically useful information unlike the peak velocity measurement used to assess stenotic lesions. While these data are best obtained in the TG views where the Doppler beam is most parallel to flow, fortunately, color Doppler techniques for the assessment of AR can also provide clinically useful information that is, to a significant degree, independent of the beam angle in relation to the regurgitant flow.


APPROACHES TO THE QUANTITATIVE ASSESSMENT OF AORTIC REGURGITATION


Color Flow Doppler

In the initial echocardiographic efforts of quantifying AR severity, color flow Doppler assessment of AR jets in the LVOT were validated against contrast aortography in human subjects (7,8,9,10,11), electromagnetic flow probes in animal models (12,13), intraoperative flow probes in human subjects (14), and in vitro models (15). From these studies, three main 2D techniques for color flow Doppler evaluation of AR jets were devised and are now recommended by current guidelines (5).


Ratio of Jet Height to Left Ventricular Outflow Tract Diameter

In the ME long-axis view of the aortic valve, the height of the AR jet is measured immediately below (within 1 cm of) the aortic valve plane and is then compared with the diameter of the LVOT at that same point (Fig. 11.3 and image Video 11.7). The long-axis view that shows the maximal height of the color jet during diastole is selected for analysis and is identified during slow motion freeze-frame review. When performing this measurement, all three components of the jet—the proximal convergence, the VC, and distal jet—should be visualized so that an optimal measurement can be performed. A ratio of less than 25% indicates mild AR, 25% to 64% indicates moderate AR, and greater than or equal to 65% indicates severe AR (Table 11.2). Alternatively, an M-mode cursor can be placed perpendicular to the outflow tract. If color flow Doppler is then activated, the regurgitant jet will appear in color in the M-mode view of the outflow tract, and the relative dimensions can be measured from this display by using the caliper function of the ultrasound machine (Fig. 11.4).






FIGURE 11.3 Mid-esophageal short-axis (left) and long-axis (right) views of the aortic valve with central regurgitant jet. The biplane cursor is placed through the center of the proximal flow convergence and regurgitant orifice in the shortaxis view to create the corresponding long-axis view on the right. The maximal vena contracta width (dotted red line) and maximal jet height (red line) can then be measured with the latter being compared to the LVOT diameter (green line). The vena contracta width is 8 mm. The jet height (1.4 cm) to LVOT diameter (2.1 cm) ratio is 66%. These findings are consistent with severe aortic regurgitation.









TABLE 11.2 Echocardiographic Indices of Aortic Regurgitation Severity



































































Parameter


Mild


Moderate


Severe


Caveats


▪ Structural Parameters


Leaflets


Variable


Variable


Flail, wide coaptation defect




  • Not reliable


LV size


Normal


Variable


Usually dilated




  • Enlarged in other conditions



  • Normal in acute AR


▪ Quantitative Doppler Parametersa


Jet/LVOT heightb (%)


Jet/LVOT areab (%)


<25


<5


25-45, 46-64


5-20, 21-59


≥65


≥60




  • Variable in eccentric jets



  • Affected by direction and shape of jets


VC widthb (cm)


<0.3


0.3-0.6


>0.6




  • Problematic with multiple jets



  • May be less accurate in noncircular orifice


RVol (mL)


RF (%)


ERO area (cm2)


<30


<30


<0.1


30-44, 45-59


30-39, 40-49


0.1-0.19,


0.20-0.29


≥60


≥50


≥0.30




  • Requires multiple measurements



  • Technically challenging



  • Time consuming


▪ Qualitative Doppler Parameters


Jet density


Faint


Dense


Dense




  • Overlap between moderate and severe AR


Regurgitant slope (m/s2)


Pressure half-time (ms)


Slow


>500


≥2


200-500


≥3


<200




  • Effected by aortic and LV compliance



  • May be less accurate if beam is not oriented with jet


Diastolic flow reversal


Brief, early diastolic reversal


Intermediate


Prominent holodiastolic reversal




  • Brief reversal is normal



  • May be present in stiff aorta (in absence of severe AR)


a Quantitative parameters allow for subclassification of moderate regurgitation into mild to moderate and moderate to severe AR.

b Performed at a Nyquist limit of 50-70 cm/s.


AR, aortic regurgitation; ERO, effective regurgitant orifice; LV, left ventricular; LVOT, left ventricular outflow tract; RF, regurgitant fraction; RVol, regurgitant volume; VC, vena contracta.



Ratio of Jet Area to the Left Ventricular Outflow Tract Area

In this second color flow Doppler technique, the short-axis area of the regurgitant jet in the LVOT is compared with the area of the LVOT at that same level (Fig. 11.5 and image Video 11.8). The preferred view for this approach is the ME aortic valve short-axis view, but with the probe advanced to immediately below the valve plane. Again, diastole is evaluated by slow motion freeze-frame review, and the maximal jet area is traced and compared with the area of the LVOT. Alternatively, biplane echocardiographic imaging can be utilized with the long-axis view of the LVOT as the reference plane; the biplane cursor is positioned 1 cm below the aortic valve to produce the corresponding short-axis view of the LVOT. A ratio of less than 5% indicates mild AR, 5% to 59% indicates moderate AR, and greater than or equal to 60% indicates severe AR (Table 11.2). This method is slightly more accurate than the jet height to LVOT diameter ratio method but is technically more difficult to perform.


Vena Contracta Width

The third, and probably most important color Doppler technique, is the measurement of the VC width (Fig. 11.3). The VC is the narrowest portion of the jet as flow converges immediately after crossing the valve plane downstream from the regurgitant orifice. The size of the VC is directly related to the size of the regurgitant orifice and is therefore considered a true measure of AR severity. Advantages of the VC measurement is that it is felt to be less dependent on the driving pressure (i.e., diastolic blood pressure) and flow rate through the regurgitant orifice. In fact, changes in afterload obtained with phenylephrine or volume loading have been shown not to change

the size of the VC (14). Measurements of the VC width have also been shown to have excellent correlation (better than jet height and area to LVOT ratios) with quantitative Doppler parameters of AR severity (10).






FIGURE 11.4 Color M-mode assessment of aortic regurgitation. From the mid-esophageal aortic valve long-axis view, the M-mode cursor is positioned perpendicular to the left ventricular outflow tract as close to the origin of the regurgitant jet as possible. The jet and the outflow tract are well delineated in the color M-mode display. Caliper measurement of the jet height is compared to that of the outflow tract (white arrows), and the resulting ratio of 60% corresponds to moderate to severe regurgitation.

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Apr 16, 2020 | Posted by in ANESTHESIA | Comments Off on Aortic Regurgitation
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