10.1 Mitral Regurgitation Mechanism, Quantitation, and Severity Integration

Start with mechanism, not jet size

CCI task C6 requires assessment of mitral regurgitation (MR). First document blood pressure, heart rate, rhythm, symptoms, and whether the presentation appears acute or chronic. Then image the mitral apparatus—annulus, anterior and posterior leaflets, chordae, papillary muscles, LV, and LA—from parasternal long- and short-axis, apical four- and two-chamber, and apical long-axis views. Sweep rather than relying on one frozen plane. Describe visible A1–A3 and P1–P3 segments only when localization is secure; eccentric jet direction can suggest the involved leaflet but does not prove the lesion.

Primary MR results from intrinsic disease such as myxomatous prolapse or flail, chordal rupture, endocarditis with perforation, rheumatic restriction, or cleft. Secondary MR occurs when remodeling prevents coaptation without a primary leaflet lesion. Ventricular secondary MR commonly has LV dilation, papillary displacement, systolic tethering, and annular enlargement. Atrial secondary MR is associated with LA and annular dilation, often atrial fibrillation, with relatively preserved LV geometry and less tethering. Carpentier motion terminology helps connect anatomy to function: type I has normal motion with annular dilation or perforation, type II excessive motion from prolapse or flail, type IIIa restriction in systole and diastole as in rheumatic disease, and type IIIb systolic restriction typical of ventricular secondary MR.

Assemble independent severity evidence

Optimize color gain just below random speckle and use a velocity scale appropriate for detecting the jet without obscuring the convergence region. Save multiple views and cine loops because a wall-hugging eccentric jet may lose momentum through the Coanda effect and look deceptively small. Jet area also varies with gain, scale, driving pressure, LA pressure, and chamber size. A large central mosaic supports important MR only in context; jet area alone does not grade it.

Measure vena-contracta width perpendicular to the jet at the narrowest neck. A width at least 0.7 cm supports severe MR for a single primary jet, but a two-dimensional width can misrepresent an elliptical orifice and cannot simply be added across multiple jets. Three-dimensional vena-contracta area can display complex orifices more directly when spatial and temporal resolution are adequate.

For a suitable hemispheric proximal isovelocity surface area (PISA), shift the color baseline toward the jet to create a measurable convergence shell, then measure the radius from the orifice to the first aliasing boundary. Calculate:

EROA = 2πr² × aliasing velocity / peak MR velocity

Regurgitant volume = EROA × MR VTI

Use measurements from the same physiologic state and appropriate systolic frame. Hemispheric assumptions often fail with wall constraint, eccentricity, multiple jets, an elliptical secondary-MR orifice, or marked systolic variation. A single mid-systolic PISA may overstate a brief late-systolic prolapse jet or misrepresent dynamic secondary MR.

A volumetric method subtracts forward LVOT stroke volume from total LV stroke volume; regurgitant fraction is regurgitant volume divided by total LV stroke volume. Doppler inflow-versus-outflow methods are vulnerable to annular diameter, sample-position, rhythm, and concomitant regurgitation errors. Three-dimensional LV volumes can reduce geometric assumptions if borders are complete. Audit inputs when a calculated volume conflicts with anatomy or other Doppler findings.

Integrate severity and explain discordance

For chronic primary MR, EROA at least 0.40 cm², regurgitant volume at least 60 mL, regurgitant fraction at least 50%, and vena contracta at least 0.7 cm are standard severe-pattern markers. They are not four automatic diagnoses. Dense triangular early-peaking CW flow, systolic pulmonary-vein flow reversal, a flail leaflet, and appropriate LV/LA response strengthen the conclusion. CW peak velocity alone cannot quantify MR: a low velocity may reflect low systemic pressure or high LA pressure, while a high velocity can accompany a small jet.

Secondary MR often has a crescentic or elliptical orifice, lower forward flow, and dynamic loading, so a circular PISA and primary-MR thresholds can underrepresent or misclassify it. Report the measured values and mechanism, then let the interpreting clinician apply disease-specific context. Acute severe MR may show a small color jet, normal chamber size, low velocity, rapid pressure equalization, and pulmonary edema; absence of chronic dilation is not reassurance.

When findings disagree, verify BP and rhythm, color settings, Doppler alignment, jet multiplicity, PISA geometry, vena-contracta plane, pulmonary-vein placement, and chamber measurements. Reacquire rather than selecting the convenient value. Clearly label nonquantifiable data and communicate flail tissue, suspected endocarditis, acute severe MR, or hemodynamic instability promptly. The interpreter may use TEE for lesion anatomy or CMR for regurgitant volume when a technically adequate TTE still remains discordant.

For serial assessment, reproduce blood pressure, rhythm, color scale, view, and quantitation method; compare source images rather than report labels, because altered afterload or a different vena-contracta/PISA plane can mimic interval change.