Heart valves, such as the mitral and tricuspid valves, are sometimes damaged by diseases or by aging, which can cause problems with the proper function of the valve. The mitral and tricuspid valves consist of leaflets attached to a fibrous ring or annulus. In a healthy heart, the mitral valve leaflets overlap during contraction of the left ventricle, or systole, and prevent blood from flowing back into the left atrium. However, due to various cardiac diseases, the mitral valve annulus may become distended, causing the leaflets to remain partially open during ventricular contraction and thus allowing regurgitation of blood into the left atrium. This results in reduced ejection volume from the left ventricle, causing the left ventricle to compensate with a larger stroke volume. The increased workload eventually results in dilation and hypertrophy of the left ventricle, further enlarging and distorting the shape of the mitral valve. If left untreated, the condition may result in cardiac insufficiency, ventricular failure, and death.
A common repair procedure involves implanting an annuloplasty ring on the superior, or atrial, surface of the mitral valve annulus. The annuloplasty ring is aligned with the valve annulus and then fixedly attached to the valve annulus. The annuloplasty ring generally has a smaller diameter than the distended valve annulus, and when attached to the annulus, the annuloplasty ring draws the annulus into a smaller configuration, bringing the mitral valve leaflets closer together and providing improved valve closure during systole.
Catheter-based repair procedures for implanting an annuloplasty ring on the valve annulus require non-optical visualization of, at least, the heart valve and annuloplasty ring during placement of the ring at the valve annulus. As used herein, the phrase non-optical visualization refers to viewing an indirect image of body tissues and/or devices within a patient. Non-optical visualization of the valve annulus is challenging. Under fluoroscopy, the cardiac tissues do not appear, making it very difficult to accurately align the annuloplasty ring prior to its implantation. In many procedures, radiopaque contrast dye is used with x-ray imaging equipment to increase the visualization of the area of interest. However, when treating the mitral valve, repeated injections of contrast dye are not practical because of rapid wash-out in high-flow area being treated. Additionally, to make the high-volume contrast injections, the annuloplasty catheter system would require more lumens, larger lumens, or an additional catheter, none of which is desirable during catheterization procedures. Furthermore, multiple high-volume contrast injections are not desirable for the patient due to potential complications in the renal system, where the radiopaque contrast medium is filtered from the blood.
Other techniques for viewing images of cardiac structures include ultrasonography such as trans-thoracic echocardiography (TTE), trans-esophageal echocardiography (TEE), and cardiac magnetic resonance (CMR) including magnetic resonance imaging (MRI) or magnetic resonance angiography (MRA). However, none of the above techniques, used alone or in combination provides adequate visualization and guidance during catheter-based valve repair procedures.
Annuloplasty procedures are further challenged by the structure of the valve annulus. In particular, the mitral valve annulus lacks a definable shelf or ledge for conveniently locating an annuloplasty ring. The mitral valve leaflets are little more than flaps or appurtenances attached to the cardiac muscle tissue, creating a pseudo-annulus. During systole, the mitral valve is closed to form a relatively flat floor of the left atrium. However, during diastole, the mitral valve leaflets open towards the ventricular walls such that, in many cases, the valve annulus is not well defined. Since annuloplasty is performed on a beating heart, care must be taken during both systole and diastole when positioning an annuloplasty ring for fixation.
Without the direct optical visualization that is provided during surgery, it is difficult to position an annuloplasty ring in abutment with the superior surface of the valve annulus. With non-optical imaging techniques used during a catheter-based procedure, an annuloplasty ring may be inadvertently affixed in a misaligned position below, above or angled across the valve annulus. Affixing the annuloplasty ring in such a misaligned position could have negative consequences for the patient, such as increasing mitral regurgitation and/or triggering ectopic heart beats.
Therefore, it would be desirable to provide a device, system, and method for aiding implantation of an annuloplasty ring to overcome the aforementioned and other disadvantages.