Aortic Regurgitation

Aortic Regurgitation: Etiology

Aortic regurgitation (AR) arises from either primary leaflet disease or secondary aortic root/annular disease, and often a combination of both.

• Primary (valvular): bicuspid aortic valve, infective endocarditis (leaflet destruction or perforation), rheumatic disease, myxomatous degeneration, and iatrogenic causes (post-TAVR, post-balloon valvuloplasty).
• Secondary (root-based): aortic root dilation prevents leaflet coaptation despite structurally normal leaflets — annuloaortic ectasia, Marfan syndrome and other connective-tissue disease, aortic dissection, chronic hypertension, and aortitis.

The distinction matters clinically: root-based AR may be treated with valve-sparing aortic root replacement rather than valve replacement.

Severity Grading

As with AS, AR severity uses an integrated multiparametric approach combining color Doppler jet characteristics, spectral Doppler, descending-aorta flow patterns, and quantitative PISA-derived volumetric parameters:

The most specific signs of severe AR are a wide vena contracta (≥0.6 cm), a short pressure half-time (<200 ms), and holodiastolic flow reversal in the descending thoracic aorta on pulsed-wave Doppler. An end-diastolic flow velocity ≥20 cm/s in the descending aorta is highly specific for at least moderate AR; the same finding recorded in the more distal abdominal aorta raises specificity further and is a hallmark of severe AR.

Pressure half-time reflects how quickly the aortic-to-LV diastolic pressure gradient equalizes: the more severe the regurgitation, the faster LV pressure rises to meet aortic pressure, and the shorter the PHT. Because PHT is also shortened by any process that raises LV diastolic pressure independent of AR severity (reduced LV compliance, concurrent AS, or acute decompensation), it should never be used in isolation.

Jet Geometry Pitfalls

Color Doppler jet width and jet area are the least reliable AR parameters because eccentric jets — common with bicuspid valves or leaflet prolapse — hug the LVOT wall (Coanda effect) and visually underestimate severity relative to their true volumetric regurgitant flow. Vena contracta width, measured just below the coaptation point in the LVOT, is less angle- and flow-dependent and is preferred over jet area for semiquantitative grading. When feasible, the PISA method can also be applied to the AR jet to calculate EROA and regurgitant volume, analogous to its use in mitral regurgitation (Section 7.4).

Additional Echocardiographic Signs

The parasternal short-axis view of the aortic valve can localize the jet's origin at the coaptation defect — a central jet suggests root dilation or a symmetric leaflet process, while a commissural or eccentric jet points to a focal leaflet abnormality such as a bicuspid valve, prolapse, or endocarditis-related perforation, and should prompt closer structural evaluation of that leaflet segment. A classic, though nonspecific, M-mode finding in significant AR is fine diastolic fluttering of the anterior mitral leaflet (and sometimes the interventricular septum), produced by the regurgitant jet striking the leaflet; its presence supports at least moderate AR but its absence does not exclude it, so it is never used as a standalone severity criterion.

Acute vs. Chronic Severe AR

The hemodynamic tolerance of severe AR differs dramatically by time course:

• Chronic severe AR: the LV has time to dilate and hypertrophy (eccentric hypertrophy), maintaining forward stroke volume at a normal end-diastolic pressure for years; patients may remain asymptomatic despite severe AR. LV end-systolic dimension and ejection fraction are the key trending parameters that trigger surgical timing even before symptoms develop.
• Acute severe AR (endocarditis, dissection, trauma): the non-dilated, non-compliant LV cannot accommodate the sudden regurgitant volume, so LV diastolic pressure rises rapidly, closing the mitral valve prematurely (premature MV closure) and producing a very short PHT with low cardiac output — a surgical emergency, even though chronic quantitative volume criteria may not be met.

LV Size and Function as Intervention Triggers

Because chronic severe AR can remain asymptomatic for years while progressively remodeling the LV, serial trending of LV end-systolic dimension (LVESD) and ejection fraction is central to timing intervention before irreversible LV dysfunction develops. Per current ACC/AHA guidance, intervention is indicated for severe chronic AR when LVEF falls to ≤55% or symptoms develop (both are strong indications), and is also reasonable once LVESD exceeds 50 mm (or an indexed LVESD >25 mm/m² in patients of small body size) even in the absence of symptoms or LVEF decline. These thresholds make serial 2D or 3D LV volumetric and M-mode/2D linear-dimension measurements — not a single-visit gradient or vena contracta — the parameters that most directly drive the timing of aortic valve intervention in chronic severe AR.

Key Testing Points

• Severe AR = vena contracta ≥0.6 cm, PHT <200 ms, holodiastolic descending aorta flow reversal — the three most specific signs.
• Quantitative severe AR = EROA ≥0.30 cm², regurgitant volume ≥60 mL/beat, regurgitant fraction ≥50%.
• Jet width/area is the least reliable sign because eccentric jets underestimate severity.
• Premature mitral valve closure with a short PHT in a non-dilated LV suggests acute, poorly tolerated severe AR.