Continuing Education Activity

Mitral stenosis is one of the common valvular diseases encountered in cardiology clinics, and rheumatic heart disease is the most common cause of mitral stenosis, especially in low-middle-income countries. Mitral stenosis, if left untreated results in significant morbidity and mortality and there is no definite medical therapy for severe mitral stenosis. Percutaneous balloon mitral commissurotomy (PMBC) is recommended as the first choice of treatment for mitral stenosis if the valve is pliable and there is no evidence of left atrial appendage thrombus. While the surgical valve repair / replacement is limited to patients not deemed candidates for percutaneous intervention. This activity reviews the role of percutaneous intervention in the management of MS. It will also discuss the indications, contraindications, and the role of the interprofessional team in the management of patients with mitral valve disease.

Objectives:

• Review the indications and contraindications of the catheter management of mitral stenosis.
• Explain the importance of perioperative echocardiography for successful catheter management of mitral stenosis.
• Describe the different steps of the catheter management of mitral stenosis.
• .Summarise the most common complications associated with the catheter management of mitral stenosis.

Introduction

Mitral stenosis (MS) is a progressive valvular disorder that results in left atrial enlargement, atrial fibrillation, and heart failure.[1] Despite advances in modern medicine, rheumatic heart disease (RHD) remains the most common cause of mitral stenosis, especially in low-middle-income countries.[2] Rheumatic mitral stenosis 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 those with limited access to healthcare facilities.[3] 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.[4] Patients with symptomatic mitral stenosis usually present with symptoms of heart failure, atrial fibrillation, or thromboembolism. Risk factors for rheumatic mitral stenosis include a history of rheumatic fever and a previously untreated streptococcus infection.[5] Some data suggest that patients with chronic kidney diseases and dialysis are at increased risk for calcific, degenerative mitral stenosis.[6] 

The key physical examination findings in hemodynamically significant mitral stenosis may include irregularly irregular pulse (due to atrial fibrillation), prominent a wave in the jugular venous examination, tapping apex beat, signs of pulmonary hypertension/right-heart failure, an opening snap, and the classic low-pitched, mid-diastolic rumbling murmur with presystolic accentuation.[7] A chest radiograph may show the prominence of the pulmonary arteries, the straightening of the left heart border, the left atrium, and signs of pulmonary edema.[8] The electrocardiogram may show atrial fibrillation or evidence of left atrial enlargement and right ventricle hypertrophy.[9] The two-dimensional (2D) and Doppler echocardiogram is the best imaging modality for the diagnosis of mitral stenosis as well as the assessment of its severity and hemodynamic consequences.[10] 

Medical therapy is used as an initial symptomatic treatment for severe mitral stenosis; however, it does not improve the long-term outcomes of the disease.[11] Percutaneous mitral balloon commissurotomy (PMBC) is recommended as the first choice of treatment for rheumatic mitral stenosis if the patients have suitable mitral valve anatomy on echocardiogram. While the surgical mitral valve repair/replacement is limited to patients whose valve is not suitable.[12][13]  Valves designed for transcatheter aortic valve replacement have been used to treat degenerative mitral stenosis in a technique called percutaneous transcatheter mitral valve replacement (PMVR).[14]  Percutaneous mitral balloon commissurotomy (PMBC) treats mitral stenosis by splitting the fusion of mitral valve commissures, and it works best in rheumatic mitral stenosis and some forms of congenital mitral stenosis.[15] This chapter will describe in detail the mitral valve, the pathology of mitral stenosis, and possible options for catheter management of mitral stenosis, along with indications, contraindications, complications, and the clinical significance of catheter management of mitral stenosis.

Anatomy and Physiology

The mitral valve is located between the left atrium and the left ventricle. The mitral valve apparatus is a complex anatomical structure consisting of a mitral annulus, mitral valve leaflets, chordae tendineae, and papillary muscles.[16] The mitral valve is a bicuspid atrioventricular valve comprised of a large anterior and a small posterior leaflet, also called cusps. Both the leaflets are divided into three scallops for descriptive purposes.[17] Both the leaflets of the mitral valve meet each other at the commissures. 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.

Rheumatic mitral stenosis occurs as a result of a chronic inflammatory process. It is characterized by the thickening of the edges of the mitral valve leaflets leading to commissural fusion and reduction in the mitral valve opening in diastole.[18] Percutaneous mitral balloon commissurotomy works by splitting the fused commissures. Normal mitral valve orifice area is 4 to 6 cm^2; hemodynamic consequences start when the mitral orifice area reduces to 2 cm2. Severe mitral stenosis is characterized by a planimetered mitral valve area of less than 1.5 cm^2 and a diastolic pressure half-time of >150 ms. Very severe mitral stenosis is characterized by a mitral valve area smaller than 1.0 cm2 and diastolic pressure half-time of > 220ms.[19] Patients with severe or very severe mitral stenosis are candidates for PMBC.

Indications

The contemporary clinical practice guidelines recommend Percutaneous Mitral Balloon Commissurotomy (PMBC) in the following patients with rheumatic mitral stenosis.[19][20]

• Symptomatic patients with severe rheumatic mitral stenosis having valve morphology suitable for PMBC and do not have left atrial thrombus or moderate to severe mitral regurgitation (MR) qualify for PMBC as class I (Level of Evidence A)
• Severely symptomatic patients with severe mitral stenosis, having valve morphology not suitable for PMBC but are not candidates for mitral valve surgery, qualify for PMBC as class IIb (Level of Evidence B)
• Asymptomatic patients with severe rheumatic mitral stenosis having valve morphology suitable for PMBC and do not have left atrial thrombus or moderate to severe MR qualify for PMBC as class IIa (Level of Evidence B) if pulmonary artery systolic pressure is >50 mmHg.
• Asymptomatic patients with severe rheumatic mitral stenosis having valve morphology suitable for PMBC and do not have left atrial thrombus or moderate to severe MR qualify for PMBC as class IIb (Level of Evidence C) if they developed new-onset atrial fibrillation.
• Severely symptomatic patients with moderate rheumatic mitral stenosis, having valve morphology suitable for PMBC, and do not have left atrial thrombus or moderate to severe MR, qualify for PMBC as class IIb (Level of Evidence C) if found to have hemodynamically significant MS based on pulmonary artery wedge pressure of >25 mm Hg or mean mitral valve gradient of >15 mm Hg on exercise.
• Asymptomatic women with severe rheumatic mitral stenosis, who are considering pregnancy, have valve morphology suitable for PMBC, and do not have left atrial thrombus or moderate to severe MR,  qualify for PMBC before pregnancy as class IIa (Level of Evidence C)

Contraindications

Percutaneous mitral balloon commissurotomy should not be performed in patients with a left atrial thrombus, the heavily calcified mitral valve having morphology unfavorable for PMBC, and moderate to severe mitral regurgitation (3+ or 4+). Other contraindications may include active infective endocarditis, acute thromboembolic stroke, mitral annular calcification, subvalvular fibrosis, and other valvular abnormalities requiring surgical correction. Mitral valve surgery is recommended in patients with symptomatic severe mitral stenosis with a contraindication to PBMV.[15][21]

Equipment

Percutaneous mitral balloon commissurotomy (PMBC) is an invasive procedure performed in the cardiac catheterization laboratory under general anesthesia. The following equipment is required for this procedure.[22][23]

• Fluoroscopy machine
• Echocardiographic machine with transesophageal probe
• Invasive hemodynamic monitoring system
• Vascular access sheaths
• Supporting sheath for transseptal puncture
• Transseptal puncture needle (BRK)
• Inoue balloon

Personnel

Percutaneous mitral balloon commissurotomy requires a multidisciplinary team.[24] The key to a successful procedure is having a trained interventional or structural heart disease cardiologist with special expertise in percutaneous transcatheter procedures. A transesophageal echocardiogram is an essential imaging modality for perioperative assessment of the mitral valve and the procedural success of PMBC; that is why a cardiologist with expertise in echocardiography is an essential member of the team performing PMBC.[25] Other personnel includes a cardiac surgeon, cardiac anesthesia specialist, cardiac nurse, and a cardiac catheterization laboratory technician.[26]

Preparation

Preprocedural Assessment

Preprocedural assessment of the mitral valve is the most crucial step of PMBC, and it determines the procedural success and long-term outcomes of the procedures.[24] Every patient undergoing PMBC shall have a comprehensive echocardiographic examination, and the morphology of the mitral valve shall be assessed. In addition to the valve morphology, the long-term outcomes of the procedure depend on clinical hemodynamics and the immediate results of the procedure.[27]

Multiple echocardiographic scoring systems have been developed to assess the suitability of mitral valve for PMBC and predict the outcomes of the procedure. Wilkin`s score was one of the first scoring systems proposed to predict the results of PMBC, and it is the most commonly used scoring system in the contemporary era.[28] The four echocardiographic variables, including leaflet mobility, leaflet thickening, leaflet calcification, and thickening of the subvalvular apparatus, are used to calculate Wilkin`s score. The sum of the grades of the variables mentioned above gives a maximum score of 16.[29]

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 balloon mitral commissurotomy. Although commissural calcification or fusion is not included in Wilkin`s scoring system, it is another important predictor for poor outcomes after balloon mitral commissurotomy.[30] The combination of Wilkin`s score with another scoring system can be used in selective patients to predict the outcomes of the procedure and choose the best treatment strategy for the patients.[31]

In addition to evaluating valve morphology, a transesophageal echocardiogram is done in every patient before PMBC to assess the degree of mitral regurgitation and left atrial (appendage) thrombus. Left atrial thrombus is most commonly found in the left atrial appendage, and a transesophageal echocardiogram has a higher sensitivity than a transthoracic echocardiogram for evaluating left atrial appendage thrombus.[32]

Preparation for the Procedure

On the day of the surgery, patients receive instructions to fast at least 6 to 8 hours before the procedure. Anticoagulation therapy is held prior to the procedure. At least two peripheral venous lines are required to administer drugs, and electrocardiographic leads are placed to monitor rhythm. Patients are selectively intubated, and the procedure is performed under general anesthesia. Before performing the percutaneous transcatheter balloon mitral valvuloplasty, a right heart catheterization is done to assess the pressures inside the invasive cardiac hemodynamics.[33]

Technique or Treatment

Percutaneous Mitral Balloon Commissurotomy

The guidelines recommend performing percutaneous mitral balloon commissurotomy (PMBC) in a comprehensive heart valve center with cardiac surgery backup.[34] The procedure is performed under general anesthesia and transesophageal echocardiographic guidance. As in any percutaneous transcatheter procedure, to begin the procedure, vascular access is obtained.[35] Most operators use a femoral approach for this procedure. Upon obtaining vascular access, a transseptal puncture is performed to facilitate left atrial access.[36] Wight-based heparin is infused after obtaining access to the left atrium to keep activated clotting time above 300 seconds (300 to 350 seconds).[37] Care is made to avoid introducing any air bubbles into the heart. Arterial access can be obtained to monitor the invasive hemodynamics and perform left heart catheterization. After a transseptal puncture,  the hemodynamics of the left atrium are assessed, and transmitral pressure gradients are calculated.

If the measurements meet the 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 the delivery of the Inoue 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. This procedure is usually monitored under transesophageal echocardiogram (TEE) and fluoroscopy.[38] After confirming the position of the balloon, rapid inflation and deflation of the balloon are done to perform a commissurotomy.[15]  Balloon commissurotomy works similarly to surgical commissurotomy and results in the opening of the mitral valve by the separation of fused commissures.[35]

Following commissurotomy, direct measurement of transmitral gradients is done along with an echocardiographic assessment of the transmitral gradients, and the mitral valve area is calculated using planimetry. Mitral valve regurgitation is also assessed with a transesophageal echocardiogram. If there is still significant stenosis with mild-to-moderate mitral regurgitation, the procedure is then repeated 1 mm below the maximal diameter. Once optimal results are obtained, the left atrial hemodynamics are repeated to calculate a new post-procedure residual transmitral gradient, and the post-operative planimetered mitral valve area is measured.[39]

A right heart catheterization is then obtained to assess the 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 PMBC as the pressure half-time calculation for the 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, surgical mitral valve replacement would be recommended.[40]

Complications

The complications of PMBC depend on the operator`s expertise and patient selection. Vascular access site complications are the most common complications in PMBC, which are compatible with a right heart catheterization. The common vascular access-related complications include hematoma, retroperitoneal bleeding, arteriovenous fistulae, and pseudoaneurysm.[41]] The complications specific to PMBC are rare and may include; thromboembolic events (0 to 4%), cardiac tamponade (0 to 2%), mitral regurgitation (1 to 9%), and procedure-related mortality is less than 0.5%.[24] The interatrial septal defect after transseptal puncture usually results in a trace intracardiac shunt, and the hemodynamically significant shunt is very rare.[42][43]

Clinical Significance

The main advantages of PMBC 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). Therapy with PMBC significantly improves CFR and subsequently leads to improved cardiac output from the right and left chambers.[44][45] 

Proper patient selection and appropriate balloon sizing during the procedure can help improve outcomes and prevent PMBC complications.[46] Percutaneous balloon mitral commissurotomy provides immediate relief of mitral valve obstruction and improves hemodynamics. It has good long-term outcomes in an appropriately selected patient. However, due to the progressive reduction of the mitral valve area over 5 to 10 years, reintervention is required in more than 1/3rd of the patients.[47]

Enhancing Healthcare Team Outcomes

Percutaneous transcatheter mitral valve procedures are complex procedures requiring multiple specialties evaluation to determine the best procedural approach for the best outcome.[48] [level 1] This applies to all interventional and structural heart procedures. The recommendation is that all patients undergo evaluation by at least an interventional and/or structuralist in addition to a cardiothoracic surgeon. Other health professionals who should be involved in patient care may include the patient's primary care physician, a cardiac nurse, a heart failure specialist, a pharmacist, and a cardiac surgeon. 

• The specialty-trained cardiology nurse should assist with patient and family education and patient monitoring throughout the procedure providing feedback to the clinician if untoward changes in vital signs or rhythms occur. They should also assist in providing follow-up care to the patient.
• The specialty-trained pharmacist should evaluate the patient's medication use, making sure that drug-drug interactions that could complicate the procedure are avoided and communicating concerns with the clinical team.
• The clinical team should complete the procedure with surgical specialists readily available to assist with complications.

An interprofessional team approach will lead to the best outcomes. [Level 5]