Mitral regurgitation is the most common disease of the mitral valve.
The mitral valve is located between the left atrium and ventricle. It opens during systole, when blood enters the left ventricle from the left atrium, and it closes during ventricular contraction, when blood exits the left ventricle to perfuse the rest of the body.
Unlike the aortic valve, a trileaflet structure that passively opens and closes during the cardiac cycle, the mitral valve is a bileaflet structure with a subvalvular apparatus consisting of cords that connect its leaflets to the papillary muscles. Papillary muscles are part of the left ventricle that help keep the mitral valve closed during ventricular contraction (Figure 1).
Mitral regurgitation is the leakage of blood back into the atrium during left ventricular contraction, resulting from inappropriate closure of the valve leaflets in systole. When regurgitation is mild it is well tolerated and no therapy is needed. However, patients can become symptomatic as the severity of the leakage increases.
Symptoms occur because the increased volume in the left atrium ultimately results in increased pressure in this chamber. This increase in pressure can cause congestion of the lungs resulting in shortness of breath, decrease in exercise tolerance and lower extremity swelling among other symptoms. The increase in volume in the left atrium also causes enlargement of this chamber and can result in cardiac arrhythmias such as atrial fibrillation, which manifest as palpitations – putting the patient at risk for stroke.
Diagnosis of mitral regurgitation starts with the physical exam. Patients usually have a harsh murmur present throughout systole, best heard at the apex. Ultimately, the diagnosis is made on echocardiography. The severity of mitral regurgitation is assessed based on color doppler flow with the use of quantitative measurements, as well as presence or absence of flow reversal in pulmonary veins (Figure2).
Generally, pathology of the mitral valve resulting in mitral regurgitation is classified into two separate categories; degenerative and functional.
In degenerative (primary) mitral regurgitation, the pathology involves the mitral valve itself causing malcoaptation of the leaflets. This could be the result of prolapse of one or both leaflets during systole, among other pathologies.
In functional mitral regurgitation, the mitral valve malcoaptation is due to the disease of the left ventricle. For example, patients with advanced congestive heart failure can have dilated left ventricles. This dilation can also stretch the mitral valve annulus and cause malcoaptation of the valve leaflets in systole (Figure3).
Traditionally, surgical repair is shown to be superior to replacement in degenerative mitral regurgitation, while this distinction is not present in functional regurgitation. During repair, the surgeon uses multiple techniques to assure appropriate coaptation of the leaflets during ventricular contraction. Excision of part of the leaflet, suturing part of the leaflets together, and placing a ring along the valve annulus or rearranging the valvular chords are some of these techniques. Mitral valve replacement involves excising the native valve and replacing it with either a bio or mechanical prosthesis.
Over the past decade transcatheter techniques have been developed to mimic surgical ones. In the majority of these techniques, devices are advanced through the femoral vein from the patient’s leg to the mitral valve, avoiding any incisions.
Currently, the most studied and only commercially available transcatheter repair device is MitraClip. By using MitraClip (Figure4), the interventionalist tries to mimic the surgical technique of suturing part of the leaflets together by advancing a clip from the femoral vein and delivering it to the leaflets.
This delivery would require making a small hole in the intra-atrial septum, enabling the operator to deliver the device from the right side of the heart to the left. In the appropriate patient and in experienced hands, severe mitral regurgitation can be reduced to trace or mild, resulting in improvement of the patient’s symptoms as well as prognosis. Multiple trials have shown that MitraClip is superior to medical therapy alone in patients with both functional as well as degenerative mitral regurgitation who are at high surgical risk.
While MitraClip is the only commercially available device currently in the US, many other devices are being investigated in different trials. Most of these devices try to duplicate other surgical techniques such as annuloplasty or chordal repair through transcatheter means.
Enthusiasm for transcatheter methods to treat mitral regurgitation is not limited to repair techniques. There is a lot of research focus on replacing the mitral valve without surgery. One area in which this is commercially available is in patients who have already had a mitral valve replacement with a bioprosthesis. Transcatheter methods can be used for therapy, should the initial bioprosthesis degenerate over time. In most cases a new valve can be delivered inside the degenerated one safely – the bioprosthetic valve functioning as the anchor for the new valve (Figure5).
Unfortunately, the lack of appropriate anchoring is a major obstacle to replace a native mitral valve with severe regurgitation. The other obstacle is the potential obstruction of the blood flow path out of the heart by native leaflets that can be pushed into the left ventricular outflow track by the new valve. Different methods and devices are being developed and investigated to alleviate these obstacles.
In summary, while the MitraClip has matured into a valuable tool to treat mitral regurgitation in appropriate patients suffering from the condition, other modalities are actively being evaluated in trials for their safety and efficacy. Transcatheter techniques to treat mitral regurgitation are sure to expand as some of these techniques prove both safe and efficacious.
The Structural Heart Team at Carient Heart & Vascular has treated many patients with mitral regurgitation and is involved in a number of trials involving the mitral valve.
Dr. Shawn Yazdani has served as the primary investigator in many of the trials observing transcatheter therapy in patients at high or prohibitive risk for surgical valve replacement. To obtain more information or to schedule a consultation, please call 888-602-3339.