This state-of-the-art paper reviews the main questions to be answered by echocardiography for the assessment of mitral regurgitation (MR) and illustrates some common tips, tricks, and pitfalls in the echo/Doppler assessment of MR. The following are key points to remember:

1. The three main questions to be answered in the assessment of MR are its mechanism, its severity, and consequences of MR on the left ventricle (LV), left atrium (LA), and pulmonary circulation.
   1. MR mechanism. If more than mild MR is suspected or if the mitral valve is structurally abnormal, then the mechanism of MR should be determined.
      • Assessment of MR mechanism involves the assessment of the morphology of the mitral apparatus (leaflets, annulus, subvalvular apparatus, LV myocardium) and mitral leaflet motion defined by the Carpentier classification.
      • Primary MR refers to MR caused by structural abnormalities of the mitral apparatus.
      • Secondary MR most commonly is caused by global or regional LV dysfunction and/or LV dyssynchrony. Atrial functional (secondary) MR is caused by pure mitral annular dilation due to LA dilation in chronic atrial fibrillation or restrictive cardiomyopathy.
      • Mixed MR is used to describe MR with both primary and secondary mechanisms.
   2. MR severity. MR severity ideally would be measured using quantitative parameters and a continuous scale.
      • Effective regurgitant orifice area (EROA), regurgitant volume (RVol), and regurgitant fraction (RF) interact in complex ways.
      • All guidelines recommend using EROA, RVol, and RF together; along with other qualitative parameters to define MR severity as mild, moderate, or severe.
      • If transthoracic echocardiography data are internally inconsistent or in conflict with the clinical presentation, then either transesophageal echocardiography (TEE) or cardiac magnetic resonance imaging should be performed.
   3. MR consequences on the LV, LA, and pulmonary circulation.
      • Chronic severe primary MR should result in dilation of the LV and LA, and increased LA and pulmonary venous pressure.
      • In acute MR, the LV and LA might not be dilated, but LA and pulmonary pressures should be elevated.
      • Secondary MR is more difficult to evaluate because LV and LA dilation and elevated LA and pulmonary venous pressures could be due to underlying LV dysfunction. The severity of secondary MR is best assessed after optimal treatment of LV dysfunction.
2. If MR is severe, and once the mechanism of MR is defined, then detailed evaluation using three-dimensional TEE and multidetector computed tomography often is needed to assess whether a given device or procedure is anatomically suitable and feasible in a given patient.
3. Published guidelines are referenced for the treatment of primary and secondary MR:
   • Surgery is indicated for severe primary degenerative MR (mitral valve prolapse [MVP], flail).
   • Transcatheter edge-to-edge repair is indicated in symptomatic patients with severe primary degenerative MR who are at prohibitive risk for surgery, and for patients with severe secondary MR that persists after optimization of medical therapy (potentially including revascularization and cardiac resynchronization therapy) and have LV ejection fraction 20-50% and LV end-systolic diameter <70 mm.
   • There is no evidence that surgery for secondary MR improves mortality.
   • Mitral valve replacement usually is required if leaflets are restricted both in systole and diastole (Carpentier IIIa motion); transcatheter edge-to-edge repair usually is contraindicated in such patients due to concern for resulting mitral stenosis.
   • Atrial functional MR ideally is treated with annuloplasty.
4. Tips, tricks, and pitfalls in assessing MR:
   • To determine the mechanism MR, color Doppler should be turned off and the entire mitral apparatus visualized in multiple views at high frame rate (>50 Hz).
   • Among patients with secondary MR, leaflet override due to asymmetric leaflet restriction is common, and can be misinterpreted as MVP.
   • Non-holosystolic MR is common (late systolic MR among patients with MVP, biphasic MR among patients with secondary MR), and leads to overestimation of MR severity using single-frame measurements (EROA, or vena contracta width or area).
   • Because jet momentum flux (flow x velocity [v], or EROA x v²) is the largest determinant of color-flow Doppler jet size, a high MR peak velocity (potentially seen among patients with aortic stenosis, LV outflow tract obstruction, or severe hypertension) can lead to color-flow Doppler overestimation of MR severity.
   • Useful for 'on-the-fly' estimation of MR severity during a procedure, a simplified proximal isovelocity surface area (PISA) formula for EROA assumes an LV-to-LA systolic peak pressure gradient of 100 mm Hg, uses a Doppler aliasing velocity of 40 cm/s, and the aliasing radius (r):
     EROA = r²/2
   • Small errors in PISA radius measurement lead to potentially large changes in the quantitative assessment of MR severity.
   • Noncircular and multiple orifices complicate the PISA-based quantitation of MR.
   • MR, and especially secondary MR, is dynamic; and should be assessed after appropriate diuresis and optimization of guideline-directed medical therapy.
   • Adjunctive echo/Doppler findings (including the mitral inflow and pulmonary vein flow patterns) should be used in an attempt to avoid overestimation of MR severity.
   • Volumetric calculations are difficult, with implications for the assessment of MR severity using LV stroke volume defined by the difference between diastolic and systolic volumes.
   • The proximal convergence of the MR jet (used for PISA calculations) also can help localize the origin and direction of MR jets.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Prevention, Valvular Heart Disease, Implantable Devices, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure, Interventions and Imaging, Interventions and Structural Heart Disease, Computed Tomography, Echocardiography/Ultrasound, Magnetic Resonance Imaging, Nuclear Imaging, Hypertension, Mitral Regurgitation

Keywords: Aortic Valve Stenosis, Atrial Fibrillation, Cardiac Resynchronization Therapy, Cardiomyopathy, Restrictive, Diagnostic Imaging, Diastole, Dilatation, Echocardiography, Echocardiography, Transesophageal, Heart Failure, Heart Valve Diseases, Hypertension, Magnetic Resonance Imaging, Mitral Valve Insufficiency, Mitral Valve Prolapse, Mitral Valve Stenosis, Multidetector Computed Tomography, Myocardium, Stroke Volume, Systole, Ultrasonography

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