Mitral regurgitation (MR) is the most prevalent valvular heart disease in the United States and the world.
MR occurs due to malcoaptation of the mitral leaflets in systole (period of contraction of the ventricles). As a result, a portion of the left ventricular volume in systole is ejected back into the left atrium instead of the aorta. Patients become symptomatic when this regurgitant volume is severe. Additionally, the increase in volume and pressure in the heart causes remodeling of the left ventricle over time, ultimately ending in heart failure. Patients can also develop cardiac arrhythmias such as atrial fibrillation, which increases their risk for stroke.
There are two main etiologies for mitral regurgitation. The first is disease of the mitral valve apparatus itself. In some patients, leaflets are elongated, valvular cords are diseased, or one of the leaflets is flail. These conditions cause prolapse of the diseased leaflet in atria or leave a gap between the leaflets during systole. The second etiology causes regurgitation, not because the mitral valve is diseased itself but because the mitral valve is affected by the anatomy of the left ventricle. In this condition the left ventricle dilates because of either coronary artery disease (CAD) or other pathology resulting in malcoaptation of the mitral leaflets, which is either due to dilatation of the mitral valve annulus or through tethering of the leaflets in systole.
The first type of mitral valve regurgitation is called degenerative (DMR), the second is called functional (FMR). The natural history of the disease progression and patient prognosis is very different in each type and the effectiveness of the treatment options vary as well.
Surgical valve repair is the gold standard of treatment in DMR. During repair, an experienced mitral valve surgeon uses different techniques to ensure appropriate coaptation of the mitral leaflets in systole, effectively reducing the regurgitant volume to negligible. These patients do very well post repair and their long-term prognosis is excellent, barring any secondary disease of the heart such as left ventricular dysfunction. It is also well documented that these patients do much better with valve repair versus valve replacement.
Surgical valve repair does not have as good a result in patients with FMR. It has been shown that patients with FMR experience a recurrence of their regurgitation over the years, and in these patients mitral valve replacement – during which the mitral valve is excised and a prosthesis is placed – might be the better option. Regardless, patients with FMR do not fair as well since their prognosis depends on the disease state of the left ventricle.
There has been tremendous interest generated over the past decade among cardiologists and cardiac surgeons regarding the ability to treat MR via catheter-based techniques. MitraClip® is a catheter-based device that clips the two leaflets of the mitral valve together at the site of the pathology. This device has shown to be effective in symptomatic relief among DMR patients at high risk for surgery and has been commercially available in the US for this indication since 2013. However, this represents a very small portion of patients with severe MR, therefore the utilization of MitraClip has been limited.
The results of the recent landmark trial COAPT, though, were recently published in the New England Journal of Medicine (NEJM). In this study investigators randomized patients with FMR to MitraClip versus medical therapy. These are patients who typically do not undergo surgery since their left ventricular function is poor, their risk higher and surgical results less robust than DMR patients.
The results of the COAPT trial were astounding.
Not only did patients do better with MitraClip in terms of hospitalization and symptomatic relief, but their mortality was also significantly improved. Physicians are optimistic that MitraClip will soon be approved for this indication in the US based on the trial.
The field of transcatheter mitral valve therapies is evolving fast. There are ongoing trials with flexible and semi-rigid devices to mimic surgical annuloplasty via transcatheter techniques. Millipede (Boston Scientific), Cardioband (Edwards), and Carillon (Cardiac Dimensions) are just a few. There is also much activity involving transcatheter mitral valve replacement. Early feasibility trials are ongoing with Intrepid (Medtronic) and Tendyne (Abbott), both of which are delivered by puncturing the tip of the heart. Also, CardiaQ (Edwards) and M3 (Edwards) are two which are delivered via the leg vessels.
The challenge with transcatheter mitral replacement remains how to deliver the valve safely via the leg vessels and through the heart with good anchoring while avoiding obstruction to other areas of the heart such as left ventricular outflow tract.
One thing is certain – we are in the early stages of a big revolution in the treatment of severe mitral regurgitation. There is nothing more satisfying for an interventional cardiologist than to be part of this journey.
Shawn Yazdani, MD, FACC, FSCAI, is an interventional cardiologist specializing in structural heart care – leading the way in innovative new approaches and advanced cardiovascular treatments. For more information, 888.602.3339 / www.shawnyazdanimd.com.