Aortic dissection and intramural hematoma ^*: Dissection and intramural hematoma of the root may lead to AI from several mechanisms. Dissection into the root will compromise the support of the adjacent cusp, which then prolapses, resulting in eccentric AI. Another mechanism seen in aortic dissection that may occur is prolapse of the intimal flap into the valve orifice, preventing it from coapting.

The number of possible aortic pathologies and their clinical importance is the basis of use of complementary imaging modalities such as CT and CMR to adequately assess the aorta in some cases of AI.

Valve causes

Thickening

• Age-related

Myxomatous degeneration (approximately 10% of pure severe AI)

Endocarditis ^*

Traumatic ^*

Hypertension: patients with systolic hypertension commonly have mild leaflet thickening and mild AI.¹

Problems with Color Doppler Flow-Mapping “Quantification”

The principal contribution of color Doppler is to detect that AI is present, so that its severity can be determined by other means. Color Doppler flow mapping of the LVOT, LV, or proximal descending aorta is not reliably useful to establish the severity of AI, given the many eccentric and complex jets that are poorly represented by this technique.

LVOT color Doppler flow mapping is dependent on gain, angle, position, jet shape, and orientation, and is not a suitable means to evaluate very eccentric AI (e.g., from flail leaflets). It is not useful as an independent means to establish severity.

Color flow mapping of proximal descending aortic retrograde flow is not useful, because it is non-quantitative and is dependent on gain and image quality. It makes no independent contribution, and, therefore, its use should be discouraged.

AI color jet length into the LV is not useful to determine AI severity, because it cannot reliably distinguish moderate from severe AI.

Spectral and Volumetric Techniques

In general, spectral profiles should be displayed as two-thirds the height of the display, and wide enough so that two or three profiles are available for measurement.

Use of the continuity method for determination of regurgitant volumes is unsuitable if mitral regurgitation of any degree more than mild is present, or if a ventricular septal defect also is present.

It is far more useful to determine that there is retrograde flow in the abdominal aorta than to characterize flow in the proximal descending thoracic aorta. Every effort should be made to record subcostal views/pulsed-wave (PW) Doppler of the abdominal aortic flow profile. If the images obtained using standard echo probes are poor, an abdominal vascular probe is of considerable use to increase the quality of flow recordings.

Retrograde flow velocity time integral (VTI) > 15 cm in the proximal descending thoracic aorta often is used as a sign of severe AI, but the VTI of clearly severe AI often is twice that. The pattern of holodiastolic reversal is consistent with severe AI.

In the context of aortic insufficiency, the anterograde systolic LVOT flow is not the net forward cardiac output—it is the total forward flow (which includes the regurgitant flow).

Total forward stroke volume (if no MR) is described by Simpson’s EDV-ESV or LVOT stroke volume.

Other

Record the systolic and diastolic blood pressure.

If acute severe AI is suspected (as in endocarditis, type A aortic dissection, or trauma), M-mode and PW Doppler examinations of the mitral valve are performed to detect pre-closure signs.

Reporting Issues

Describe the cause of the AI and the severity together: For example, “Severe aortic insufficiency due to a flail leaflet, with a regurgitant fraction of 60%.”

Describe the LV function, both overall and regionally. The presence of overall or regional dysfunction increases the risk of AI.

If the AI is in the severe range, then describe the LV dimensions, as they are indices relevant to surgery.

Recall that color Doppler flow mapping establishes the presence/absence of AI, but does not independently establish severity.

Severe AI

• Severe hemodynamic effect: abdominal (= peripheral) diastolic flow reversal

• R_Volume > 60 mL

• R_Fraction > 60%

Compare all findings to previous studies.

As with the use of deceleration time (DT) or pressure half-time (PHT) to describe MS severity, their use to describe AI severity is easily confounded by anything that renders the LV compliance abnormal.

Describe the aorta in some anatomic detail. Echocardiography should detect signs of most root diseases relevant to AI.

AI peak velocity is quite variable and depends on blood pressure, the LV diastolic pressure, and the gradient between the two.

In the context of AI, do not report the total forward cardiac output (CO) as the net forward CO.

False-positives of abdominal aortic flow reversal are rare.

Avoid the term “trivial” for AI in general, because it is essentially a normal finding (if the valve is normal); and use of that term may generate confusion about whether or not the valve is pathologic. If the valve is morphologically abnormal, use of the term “mild” is consistent with the inference that the valve is functionally abnormal.

Notes on Echocardiographic Methods to Describe Severity of Aortic Insufficiency

Retrograde Holodiastolic Flow in the Abdominal Aorta

Retrograde holodiastolic flow in the abdominal aorta is sensitive (100%) and specific (96%) for level 3+ or 4+ AI. Consequently, it is one of the best signs to determine whether AI is severe. The potential false-positives include aortopulmonary shunts and patent ductus arteriosus ² and also, possibly, aortic root to left atrial, right ventricular, or right atrial fistulae, all of which should be evident from color Doppler scanning. Abdominal diastolic flow reversal is analogous to the time-honored peripheral pulse signs used in physical diagnosis.

Retrograde Flow Profiles in the Proximal Thoracic Descending Aorta

Although it is more feasible to sample retrograde flow in the proximal descending aorta, it is of less worth to determine the severity of AI.

The amount of regurgitant flow in the descending thoracic aorta (sampled by PW just beneath the aortic isthmus) can be expressed by several echocardiographic means: the peak velocity of the diastolic regurgitant volume; the time velocity interval (TVI) of the regurgitant flow; the TVI of the regurgitant flow indexed to the systolic flow, or the TVI indexed to the diastolic filling period. As would be anticipated, given the multitude of parameters, it is, overall, less trustworthy as a sign.

The peak velocity of the regurgitant (diastolic) flow correlates with the regurgitant fraction (r = 0.82) and the regurgitant grade by angiography (r = 0.81). AI of 3+ by angiography correlates with a TVI of 22 ± 6 cm/sec SD, and 4+ by angiography with 34 ± 9 cm/sec).³ End-diastolic flow velocity of 40 cm/sec or greater predicts a regurgitant fraction of 40% or more with a sensitivity of 89% and a specificity of 96%.⁴

The integral of the spectral display of diastolic flow recorded from the proximal descending aorta (divided by the integral of the systolic flow) mapped in the proximal descending aorta correlates well with angiographic regurgitant fraction: r = 0.91 ⁵ and r = 0.90; standard error of estimate (SEE) 9%.⁶ However, the sign is inaccurate in the presence of aortic stenosis,⁷ because the high-velocity systolic aortic stenosis jet continues around the arch in some cases. Neither the “cut-off” for the diastolic flow nor that for the diastolic flow integral/systolic flow integral that it constitutes has been conclusively established for severe AI. Some centers use 15 cm as the threshold above which AI is defined as severe. Obvious pan-diastolic flow above the baseline correlates well with the presence of severe AI,⁶ as long as no aorticopulmonary shunt is present.

Color Flow Mapping of the Descending Aorta

Color flow mapping of the descending aorta adds little (if anything) to a standard assessment, and is only useful to set up spectral sampling.

Color Doppler Flow Mapping of the Left Ventricular Outflow Tract

Color Doppler flow mapping of the LVOT is useful to detect AI. Indexing improves correlation ⁸ with angiography (r = 0.88) and can classify the majority of central AI jets with thoracic (83%) and abdominal (86%)⁹ aortic flow profiles. It is a poor technique to assess eccentric AI jets, however, and overall tends to be inaccurate. Indexing is performed to the height or area of the LVOT, to the aortic valve area, or to body surface area, and correlates with severity (r = 0.87).¹⁰ Oblique jets are problematic, because they result in overestimation of severity. Jet length into the LV has been proved to be an inaccurate means of describing AI severity, because jets of severe AI can be shorter than jets of moderate AI. Perry⁸ proposed the categorizations shown in Table 3-1.

TABLE 3-1 Categorization of AI Severity by Color Doppler Flow Mapping Indexed to the LVOT

AI GRADE	JET HEIGHT/LVOT	JET AREA/LVOT
I	1–24%	<4%
II	25–46%	4–24%
III	47–64%	25–59%
IV	≥65%	≥60%

AI, aortic insufficiency; LVOT, left ventricular outflow tract.

Vena Contracta Width and Area

The vena contracta imaged in the posterior long-axis view correlates well (P < 0.0001) with Doppler effective regurgitant orifice (ERO; r = 0.89) and R_Volume (0.90), and 2D methods (r = 0.90, r = 0.90), as well as with angiographic grading (r = 0.82; P = 0.01).^11,¹² A vena contracta width of ≥6 mm is 95% sensitive and 90% specific for diagnosing severe AI (ERO ≥ 30 mm²),¹¹ and vena contracta area ≥7.5 mm² is 100% sensitive and specific for severe AI (R_Volume > 50 mL).¹² Vena contracta width appears to be afterload independent.¹²

Because small differences in vena contracta dimension measurement (1–2 mm) result in different grading, the technique is very demanding and image quality dependent, and its applicability can be disappointing. The advent of anti-aliasing software may improve the utility of this method.

Effective Regurgitant Oriface Method: Proximal Isovelocity Surface Area and Doppler

The proximal isovelocity surface area (PISA) ERO method correlates well with reference techniques (P < 0.0001) but exhibits a trend to underestimate ERO due to cases where the AI jet is obtuse.⁴ Doppler ERO correlates well with angiographic estimates of ERO (r = 0.97) when the aortic diameter is less than 4.8 cm.¹³ Aortic pressure changes may influence the ERO, depending on whether the defect causing the AI is central (dynamic ERO: 51 ± 33% change with pharmacologic hypertension) versus a perforation in a leaflet proper (minimally dynamic orifice (9 ± 7%).¹⁴ Aortic root area is strongly dependent on the aortic diastolic pressure and can vary widely with pharmacologic hypertension.¹⁴

Regurgitant volume of AI (R_Volume):

where Diam = diameter, PA = pulmonary artery, and SV = stroke volume.

Regurgitant fraction of AI (R_Fraction):

The regurgitant fraction of AI can be calculated by left ventricular outflow as the total forward systolic volume (R_Volume + net forward SV) minus anterograde flow anywhere there is no regurgitant flow (mitral level or PA).^3,^15,¹⁶ R_Fraction by Doppler correlates well with R_Fraction by catheterization: r = 0.96.³ Using this technique, 3+ and 4+ AI by angiography are associated with 53% and 62% R_Fraction by Doppler.³ The technique is less accurate with depressed left ventricular ejection fraction, and, as would be anticipated, in the presence of mitral regurgitation.¹⁵

Suggested grading for AI:

Aortic Insufficieny Deceleration Time, Pressure Half-Time, and Slope

The PHT assessment of AI is feasible when the spectral profile can be obtained, and AI spectral profile DT and PHT correlate with angiographic AI severity (r = −0.79 and r = −0.89, respectively)¹⁷^{¹⁹ and are independent of the alignment of sampling.¹⁷ Echo PHT correlates well with catheter-derived PHT, but factors such as systemic vascular resistance and aortic and LV compliance all affect AI PHT. Thus, unless the PHT is <300 msec where AI is always severe, the PHT method is not reliable for distinguishing different grades of AI.²⁰ Slope also correlates with left ventricular end-diastolic pressure (LVEDP; r = 0.80¹⁸ and r = 0.84),²¹ but in two studies^18,²¹ the SEE has been reported to be 5 mm Hg. Therefore, this technique is unreliable in the presence of an abnormal ventricle,²² or varying aortic load on the AI.}