Aortic Insufficiency

3 Aortic Insufficiency image





Determination of the Cause of Aortic Insufficiency


The cause of AI usually is apparent from transthoracic echocardiography (TTE), although transesophageal echocardiography (TEE) often is needed to assess the mechanism and probable underlying disease. Fenestrations and some perforations are difficult to image even by TEE. Because some underlying diseases require independent treatment, it is important to recognize the etiology of AI to the fullest extent possible.





Spectral and Volumetric Techniques






Reporting Issues




image 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%.”


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


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


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


image Severe AI





image Compare all findings to previous studies.


image 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.


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


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


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


image False-positives of abdominal aortic flow reversal are rare.


image 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 arteriosus2 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 = 0.915 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 Doppler Flow Mapping of the Left Ventricular Outflow Tract


Color Doppler flow mapping of the LVOT is useful to detect AI. Indexing improves correlation8 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.




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



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





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)1719 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 studies18,21 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.




Aortic Insufficiency Deceleration Time


Measurement of AI DT is possible when the spectral profile is clear. Although DT correlates with angiographic grade (r = 0.85), Labovitz et al.23 found that DT >2 m/sec establishes that AI is worse than mild, but DT is not nearly as helpful in distinguishing severe from moderate AI. The same authors found that PHT did not distinguish moderate from severe AI.



Mitral Valve Preclosure


Preclosure is an uncommon sign seen with some cases of acute, severe (“torrential”) AI, usually due to infective endocarditis, proximal aortic dissections, and trauma. Preclosure also may result from a long PR interval24 or from complete heart block, both of which may occur with aortic valve endocarditis if there is a root abcess.25 Pulsed-wave Doppler offers timing and the chance to record the valve leaflet “click.”26 Although the sign is spectacular, it is disappointingly absent in many cases where it seems it should be present.





Jun 12, 2016 | Posted by in CARDIOLOGY | Comments Off on Aortic Insufficiency

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