The following are key points to remember from this review on secondary mitral regurgitation (MR):

1. Primary mitral regurgitation (MR) is a disease of the mitral leaflets or chords, whereas secondary MR is caused by disease of the left ventricle (LV) or left atrium (LA).
2. MR most commonly is assessed with transthoracic echocardiography, which should include evaluation of mitral leaflet anatomy and motion, mitral annular calcification, LA and LV volumes, regional and global LV systolic function, pulmonary vein flow, pulmonary artery systolic pressure, right ventricular function, and the presence of tricuspid regurgitation.
3. Restricted (Carpentier IIIb) leaflet motion is usually seen in patients with secondary MR due to ischemic or nonischemic (dilated) cardiomyopathy. Normal (Carpentier I) leaflet motion is seen in patients with atrial functional MR.
4. The assessment of the severity of secondary MR on echocardiography should include multiple parameters, including objective quantitation. However, quantitation can be difficult. The American Heart Association/American College of Cardiology guidelines and the European Society of Cardiology/European Association for Cardio-Thoracic Surgery guidelines have different quantitative thresholds for severe secondary MR.
5. Guideline-directed medical therapy is the first-line treatment for patients with heart failure (HF), reduced LV ejection fraction (LVEF), and secondary MR. Among patients with HF with reduced LVEF (HFrEF), a survival benefit has been demonstrated for therapy with beta-blockers, renin-angiotensin-aldosterone system inhibitors, and sodium-glucose cotransporter 2 inhibitors; a reduction in the severity of secondary MR has been demonstrated both with carvedilol and with sacubitril-valsartan.
6. Cardiac resynchronization therapy can result in decreased LV size, improved LV systolic function, and reduced secondary MR severity among selected patients with HFrEF and left bundle branch block.
7. Surgery for secondary MR predominantly involves either repair with a downsized (reduction) annuloplasty ring, or chordal sparing valve replacement. Based on data from one randomized, controlled trial that showed a lower incidence of postoperative significant MR, fewer serious HF-related adverse events, and fewer cardiovascular hospital admissions after mitral valve replacement compared to mitral valve repair, chordal-sparing mitral valve replacement may be the preferred treatment for ischemic MR. Notably, surgery (repair or replacement) has not been shown to improve long-term survival among patients with secondary MR.
8. Transcatheter edge-to-edge mitral valve repair has been studied in two prospective, randomized, controlled trials among patients with HFrEF and secondary MR, but with different findings. In the COAPT (Cardiovascular Outcomes Assessment of the MitraClip Percutaneous Therapy for Heart Failure Patients With Functional Mitral Regurgitation) trial, the addition of transcatheter edge-to-edge mitral valve repair to medical therapy resulted in fewer hospitalizations for HF and improved survival at 2 years. In contrast, the MITRA-FR (Percutaneous Repair With the MitraClip Device for Severe Functional/Secondary Mitral Regurgitation) trial showed no significant difference in a composite outcome of all-cause death or unplanned hospitalizations between patients who received medical therapy alone compared to those who also underwent transcatheter edge-to-edge mitral valve repair.
9. The disparate results of the COAPT and MITRA-FR trials at least in part might be explained by the concept of whether secondary MR was proportionate or disproportionate to the degree of LV enlargement. Prospective validation is still needed for the concept of proportionate versus disproportionate MR.

Clinical Topics: Arrhythmias and Clinical EP, Cardiac Surgery, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Valvular Heart Disease, Implantable Devices, EP Basic Science, Cardiac Surgery and Arrhythmias, Cardiac Surgery and Heart Failure, Cardiac Surgery and VHD, Acute Heart Failure, Interventions and Imaging, Interventions and Structural Heart Disease, Mitral Regurgitation

Keywords: Adrenergic beta-Antagonists, Blood Pressure, Bundle-Branch Block, Cardiac Resynchronization Therapy, Cardiac Surgical Procedures, Diagnostic Imaging, Cardiomyopathies, Heart Failure, Heart Valve Diseases, Heart Valve Prosthesis, Hypertrophy, Left Ventricular, Mitral Valve Insufficiency, Myocardial Ischemia, Renin-Angiotensin System, Stroke Volume, Tricuspid Valve Insufficiency, Ventricular Function, Right

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