Mitral stenosis (MS) is a common valvular disorder. Despite advances in modern medicine, rheumatic heart disease (RHD) remains the most common cause of mitral stenosis. It usually presents in patients between 20 and 40 years of age and about 10 to 15 years after the onset of rheumatic fever. In the United States, mitral stenosis secondary to RHD most commonly presents in the immigrant population and the impoverished with limited access to healthcare. Calcific degenerative mitral valve stenosis disease (DMS) is another cause of mitral stenosis but is far less common and more often seen in the elderly. Patients with symptomatic mitral stenosis usually present with symptoms of heart failure, atrial fibrillation, or thromboembolism. Risk factors for mitral stenosis include a history of rheumatic fever and/or a previously untreated streptococcus infection.
Some data exists suggesting that patients on dialysis are at increased risk for mitral stenosis. Physical examination may reveal prominent a wave in the jugular pulse, prominent tapping apical pulse, signs of right-heart failure, accentuation of the P2, an opening snap, and the classic low-pitched, rumbling diastolic murmur with presystolic accentuation. A chest radiograph may show prominence of the pulmonary arteries, left atrium, right ventricle, and right atrium which is a result of the build of pressure behind the valve. The electrocardiogram may show right ventricle hypertrophy along with a notched p-wave with a duration of >0.12 seconds in lead II; this is referred to a P mitrale. The diagnostic test of choice for percutaneous transcatheter mitral valve replacement (PMVR) remains to be the echocardiogram.
While surgery is the procedure of choice for severe, symptomatic mitral stenosis, another option for patients not deemed candidates for open heart surgery is percutaneous transcatheter balloon mitral valvuloplasty (PBMV). However, these patients must also have suitable mitral valve anatomy on echocardiogram. Other transcatheter procedures have been developed. Valves designed for transcatheter aortic valve replacement have been used to treat degenerative mitral stenosis in a procedure called percutaneous transcatheter mitral valve replacement (PMVR). This chapter will describe in detail the mitral valve, pathology of mitral stenosis, possible options for catheter management for mitral stenosis, indications, contraindications, Wilkins scoring system, techniques, complications, and the clinical significance of catheter management of mitral stenosis.
The mitral valve is located between the left atrium and left ventricle. The mitral valve is a bicuspid valve because it is made up of two flaps, also called cusps. A healthy mitral valve permits blood to flow from the left atrium to the left ventricle, but not in the opposite direction. A common pathology of the mitral valve is stenosis or narrowing of the mitral valve orifice. Mild mitral stenosis is defined as a narrowed mitral valve orifice with a valve area of greater than 1.5 cm2, mean gradient (MG) of less than 5 mmHg, and pulmonary artery pressure (PAP) less than 30 mmHg. Moderate mitral stenosis is defined by a valve area of 1 to 1.5 cm2, MG of 5 to 10 mmHg, and PAP of 30 to 50 mmHg. Severe mitral stenosis is characterized by a mitral valve area of less than 1.0 cm, MG greater than 10 mmHg, diastolic pressure half time of 150ms, severe left atrial enlargement and elevated pulmonary arterial systolic pressure higher than 50 mmHg. Very severe mitral stenosis is characterized by a mitral valve area of 0.5 cm2 and diastolic pressure half time of 220ms. Patients with severe or very severe mitral stenosis are candidates for intervention.
Percutaneous Transcatheter Balloon Mitral Valvuloplasty
Percutaneous Transcatheter Mitral Valve Replacement
Off-label use for moderate to severe degenerative mitral stenosis who are not candidates for surgical intervention. This use is supported by the MITRAL Trial which showed high technical and procedural success and low 30-day mortality in patients without surgical alternatives using the transseptal mitral valve-in-valve procedures in failed surgical bioprostheses.
Percutaneous transcatheter balloon mitral valvuloplasty is not performed in patients with a left atrial thrombus, heart anatomy impervious to catheter placement, moderate to severe mitral regurgitation (3+ or 4+), mitral valve area larger than 1.5 cm, active infective endocarditis, severe mitral valve calcification making it difficult to safely inflate the balloon-tipped catheter, aortic regurgitation (greater than 2+), or subvalvular fibrosis who are surgical candidates. Mitral valve surgery is recommended in patients with symptomatic severe mitral stenosis with a contraindication to PBMV.
Percutaneous transcatheter mitral valve replacement is not recommended in patients who are surgical candidates. These patients are candidates for surgical mitral valve replacement (SMVR). Other contraindications include active endocarditis, left atrial thrombus, or heart anatomy that precludes safe delivery of the mitral valve via a percutaneous catheter.
The key to having a successful percutaneous mitral valve procedure is to have a trained interventional or structural cardiologist skilled in the techniques of mitral valve percutaneous transcatheter procedures. Other personnel includes a cardiac nurse, cardiac technician, and cardiothoracic surgeon.
In patients undergoing mitral valvuloplasty for mitral stenosis, an echocardiographic scoring system called the Wilkins score can be used to predict the procedural outcome. Its basis is leaflet mobility, valve thickening, calcification, subvalvular thickening. Each item receives a grade from 1 to 4 which yields a score from 4 to 16. A score of 8 or less predicts a more favorable outcome than those with a higher score. However, a score higher than 8 does not exclude a patient from having a mitral valvuloplasty. Commissural calcification or fusion is another important predictor for poor outcome after mitral valvuloplasty. Not all operators use this scoring system to determine the viability of percutaneous transcatheter balloon mitral valvuloplasty intervention; however, it is useful as a tool in patients for whom procedural success is a question.
On the day of the surgery, patients will receive instructions to fast at least 6 to 8 hours before the procedure. Anticoagulation will also be held prior to the procedure. If the patient is on warfarin, it will need to be held, and an international normalized ratio (INR) of at least 1.7 is necessary prior to the day of the procedure. Before performing the percutaneous transcatheter balloon mitral valvuloplasty, a right heart catheterization is done to assess the pressures inside the heart and in the lungs. Also, a left ventriculogram is performed to evaluate concomitant mitral regurgitation.
Preparation for percutaneous transcatheter mitral valve replacement is very similar to PBMV. An echocardiogram is recommended, but there is no current scoring system available to determine procedure outcome. On the day of the procedure patient should be placed NPO and anticoagulation should be held. If not done recently, a right heart catheterization is also recommended prior to PMVR to determine the hemodynamics of the heart.
Percutaneous Balloon Mitral Valvuloplasty
As in any percutaneous transcatheter procedure, to begin the procedure, vascular access must be obtained. Most operators use a femoral approach for this procedure. Upon obtaining vascular access, a transseptal puncture is performed to facilitate left atrial access. Heparin is then infused through the sheath (usually 5000IU). Care is made to avoid introducing any air bubbles into the heart. Hemodynamics of the left atrium is then taken to calculate the transmitral gradient. If the measurements meet criteria to continue the procedure, then a guide wire is advanced into the left atrium. The femoral vein and interatrial septum are both dilated to ease delivery of the of the balloon-tipped catheter. Once dilated, the balloon-tipped catheter is threaded over the guide wire in the left atrium and positioned at the site of the mitral valve. The tip of the balloon is dilated first, then the rest of the balloon is dilated to open the narrowed orifice of the mitral valve. Monitoring of this procedure is usually under transesophageal echocardiogram (TEE) and fluoroscopy. Following valvuloplasty, the results of the procedure undergo TEE evaluation for any residual mitral stenosis or new mitral regurgitation. If there is still significant stenosis with mild-to-moderate mitral regurgitation, the process is then repeated 1 mm below the maximal diameter and, if required, with maximal diameter balloon inflation. Once optimal results are obtained, the left atrial hemodynamics are repeated to calculate a new post-procedure residual transmitral gradient.
A right heart catheterization is then obtained to assess right-side of the heart hemodynamics along with a left ventriculogram to evaluate mitral regurgitation severity. Guidelines recommend obtaining an echocardiogram a few days after PBMV as the pressure half-time calculation for mitral valve area may be inaccurate due to post-procedure compliance changes in both the atrium and ventricle.
An assessment of mitral regurgitation and atrial septal defect should be performed as well. A yearly clinic review and echocardiographic assessment are required. Anticoagulation should be continued in patients with paroxysmal or chronic atrial fibrillation. If mitral stenosis recurs, PBMV can be repeated. At that time, if there are significant valvular anatomic abnormalities, the surgical mitral valve replacement would be recommended.
Percutaneous Transcatheter Mitral Valve Replacement
Once the transeptal approach is complete, heparin is administered. A balloon-tipped catheter is then passed over the guide-wire and positioned at the site of the mitral valve. The balloon is inflated to open of the narrowed mitral opening. The balloon catheter is then deflated are removed from the guide-wire. The new artificial mitral valve is crimped onto a delivery catheter which makes the valve small enough to be transported through sheath and vasculature to the heart. Under fluoroscopy, the delivery catheter attached to the new valve is threaded over the guide-wire and positioned at the site of the degenerative mitral valve. The balloon on the delivery catheter is then inflated to expand the new valve inside the diseased valve replacing the diseased valve. This process is why the procedure is called "valve-in-valve." The balloon is then deflated, and the delivery catheter along with the guide-wire is removed. An intraoperative echocardiogram is then performed before closure. If the position of the valve is determined to be ideal, then the sheath is removed, and a compression device is placed to prevent hemorrhage or hematoma formation.
The most common complication to the PBMV procedure is the development of mitral regurgitation when the valve opens excessively. Other complications are less common being that of iatrogenic Lutembacher syndrome with an atrial septal defect, vascular complications, left ventricular perforation, left ventricular pseudoaneurysm, cerebral neurologic event, myocardial injury, arrhythmia, pacemaker dependence, cardiogenic shock, and possible death.
The most common complication to the PMVR procedure is moderate-severe residual mitral regurgitation or left ventricular outflow tract (LVOT) obstruction. Other complications include valve malposition, arrhythmia, vascular complications, stroke, and death. Little data is available on long-term complications for this relatively new to the market procedure.
The main advantages of PBMV and PMVR are the lower cost and avoidance of a thoracotomy and cardiopulmonary bypass. One study revealed that the pathophysiology of mitral stenosis results in a decrease in coronary flow reserve (CFR) and therapy with PTMC significantly improves CFR and subsequently leads to improved cardiac output from the right and left chambers. Appropriate balloon sizing can help prevent PBMV complications.
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