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Mitral Valve Disease
As our population ages, there is an increase in the number of people with left ventricular dysfunction and dilation that leads to mitral regurgitation (MR), even in the absence of structural mitral valve abnormality. It is estimated that in the United States, some 800,000 patients have some degree of congestive heart failure and mitral regurgitation yet do not have an intervention. Annular dilation in the presence of a structurally normal mitral valve is the most common reason for MR.
The annular dilation leads to incomplete coadaptation of the arterial posterior leaflet, even though the structural leaflets are intact. The placement of an annuloplasty ring and rearranging the geometry of the mitral annulus has generally been the treatment. However, in patients with comorbidities, particularly older patients, surgery is associated with too much morbidity and mortality. Percutaneous treatment for MR is pursued for these patients.
The coronary sinus, because of its anatomical proximity to the posterior annulus of the mitral leaflet, has been one avenue pursued for percutaneous treatment. The concept is that by pushing against the posterior leaflet anteriorly, via the coronary sinus, it will yield a result similar to that with a surgically-placed annuloplasty ring. Several different prostheses and techniques are used.
The Biacore system is a coronary sinus approach being used at Cleveland Clinic. It is similar in using the concept of pushing the posterior annulus anteriorly to make the coadaptation perfect. Uniquely, in the sheath the rods to push the posterior annulus have different weights and lengths.
Notably, the rods can be exchanged as needed if MR worsens in the future. This Biacore system has also been used on a temporary basis in patients undergoing mitral valve repair and then permanent implants at a later date.
Limitations to the coronary sinus approach include the precise location of the coronary sinus, specifically it is not immediately behind the mitral annulus, but is often a few millimeters or a centimeter apart. Of greater concern is the fact that the circumflex or its branches frequently cross underneath the coronary sinus, and hence it is possible that prosthesis intended to compress only the posterior annulus may also compress the circumflex.
Further, biventricular pacing may be needed in these patients with heart failure and dilated left ventricles. Thus, approaches other than through the coronary sinus are being investigated in animal models. A ventricular approach uses a mitral line system that goes into the ventricle and underneath the mitral valve, and the sutures are placed from the ventricular side through the annulus. Annular reshaping is created by this suture mechanism.
Structural mitral valve abnormalities, often with prolapse of the posterior leaflet, may be the cause of MR. Two percutaneous edge-to-edge approaches have been developed to address this problem. One is a suture-based technique, in which the segments of the anterior and posterior leaflet are sutured into a double, “figure 8” orifice. The other is a clip-based technique, that uses a delivery catheter via a transseptal puncture is sued to open a V-shaped clip in the left atrium and then advanced into the left ventricle and withdrawn and closed to capture the anterior and posterior mitral leaflets and thereby creating a double orifice. A transthoracic echocardiogram is critical. A feasibility trial of the clip-based technique with promising short-term results has led to a clinical randomized multicenter trial.
Aortic Valve Disease
Calcific aortic stenosis is a frequent valve disorder and its prevalence is rising with the aging population. Although aortic valve replacement has been the primary treatment for adults with severe disease, this may not be a feasible option for patients with significant comorbidities.
Percutaneous aortic balloon valvuloplasty was introduced two decades ago to treat these high risk patients. However, the vast majority of patients developed restenosis within two years.
About one-third of patients in the experience of Cleveland Clinic who underwent balloon valvuloplasty did improve sufficiently to undergo surgical aortic valve replacement and then had a good survival.
The Carpentier-Edwards valve is a very simple yet innovative way of addressing this problem. It consists of three bovine pericardial leaflets sutured to a stainless steel balloon expandable stent.
Very precise angiographic pictures of the aortic root, origination of the coronary arteries, the annulus, and the location for the valve placement are required. Angiography and transesophogeal echocardiography are used throughout the procedure, and the patients are paced at 200 to 220 beats per minute. In this retrograde approach, however, the large sheath size and positioning difficulties were a concern. The safety and efficacy is still being evaluated.
The REVIVAL feasibility trial of the aortic valve replacement using the aortofemoral approach included high-risk patients older than 70 years of age with an EuroScore ≥20 or an STS score ≥10 or with totally calcified aorta (porcelain aorta), patients requiring mediastinal radiation, with chest wall deformities that may preclude surgery or were severely symptomatic (NYHA Class III or IV). The cardiologist and cardiac surgeon had to agree that the patient was high risk for surgery, with a ≥ 15% mortality risk. The baseline characteristics of the REVIVAL patients are 82 years old, 54% women, mean aortic regurgitation 2.5, ejection fraction 53%, mean EuroScore 33% and mean STS score 13%.
Of the 55 patients in REVIVAL, 48 had successful deployment with immediate and uniform improvement in hemodynamics. Of the 7 who had unsuccessful deployment, failed access occurred in 3, inability to cross in 3, and malplacement in 1 patient. No in-hospital deaths or 30-day deaths occurred, but there was one death after hospital discharge. At 30 days, no MIs occurred, but there were 5 neurologic events (1 major stroke, 3 minor strokes, 1 TIA).
The transapical direct approach, a much less invasive approach, is now being used in a feasibility study in the United States. An incision about 1 to 2 inches in length is made in the apex of the beating heart and then an antegrade approach is used to deploy the device through the apex.
The CoreValve is a very promising valve being studied in humans. The concept is totally different, with a self-expanding stent valve. The distal portion serves to increase fixation into the aorta, the middle portion carries the valve and is shaped to avoid the coronary ostium, and the proximal segment has the highest radial force to thereby anchor and expand the calcified valve appropriately. The third generation of this device uses an 18 French sheath and is now done without support, not even pacing, which is close to a catheter-like procedure.
In the 59 patients who received this device at Cleveland Clinic, the mean gradient immediately post procedure was 9.1 and the valve area was 1.6 cm2. Only one patient has severe aortic regurgitation.
The two human studies in percutaneous aortic valve replacement have provided proof-of-concept for this approach. However, there is unmet clinical need, with many untreated patients worldwide. Many patients are not even referred to a cardiologist because their primary care physician thinks they are too sick. In Europe it is estimated at least one-third of candidates are not even evaluated. The Edwards and CoreValve have provided immediate superb hemodynamics results and encouraging clinical outcomes showing efficacy and safety. Refinement of devices is needed, including the device profile and the ability to cross the native valve. Predictability of the system is needed and one that is retrievable and repositionable. Durability of the device must also be addressed, along with the problem of aortic regurgitation.
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