Mitral Valvuloplasty

Historically, surgical commissurotomy was the standard treatment for relief of mitral stenosis. The first single-balloon valvuloplasty of the mitral valve was described by Inoue et al in 1984.[1] Percutaneous mitral balloon valvuloplasty (PMBV) has since become the treatment of choice for mitral stenosis. The Inoue balloon catheter remains the most commonly used technique for percutaneous mitral balloon valvuloplasty.

The mitral valve apparatus consists of a fibrous mitral annulus and two mobile valve leaflets (anterior leaflet and posterior leaflet) tethered to the papillary muscles in the left ventricle by chordae tendineae. Blood flows across the valve from the left atrium into the ventricle during diastole. The normal mitral valve orifice size is 4-6 cm2. Commissural fusion of the mitral valve leaflets results in a decrease in mitral valve orifice size and an increase in left atrial pressures.

The anterior leaflet is located posterior to the aortic root and is also anchored to the aortic root, unlike the posterior leaflet. Accordingly, it is also known as the aortic, septal, greater, or anteromedial leaflet. The posterior leaflet is also known as the ventricular, mural, smaller, or posterolateral leaflet. The posterior leaflet is the section of the mitral valve that is located posterior to the two commissural areas. For more information about the relevant anatomy, see Mitral Valve Anatomy.

A transthoracic echocardiographic scoring system (see Imaging Studies section below) is used to evaluate the suitability of valve morphology for percutaneous mitral balloon valvuloplasty (PMBV). Other anatomic considerations in evaluating patients prior to PMBV include exclusion of left atrial thrombus and severe mitral regurgitation, both of which are contraindications to the procedure (see Contraindications section below).

Rheumatic mitral valve stenosis occurs as a result of rheumatic fever, usually decades after the acute illness. Commissural fusion of the mitral valve leaflets leads to obstruction of blood flow from the left atrium to the left ventricle. This obstruction, in turn, leads to chronically elevated pulmonary arterial pressures and symptoms of heart failure, especially with exercise or other conditions associated with tachycardia.

Commisural fusion of the mitral valve leaflets results in loss of the mitral orifice size. This limits blood flow across the valve from the left atrium to the left ventricle. Additionally, there is a loss of valvular reserve, the ability of the valve to open wider for larger blood flows, to facilitate an increase in cardiac output. Left atrial pressure is determined by the transvalvular gradient, which is a function of both orifice area and diastolic filling time. With exercise, heart rate and cardiac output increase, leading to an increase in left atrial and pulmonary arterial pressures.

Mitral orifice size correlates with severity of mitral stenosis and usually correlates with symptoms. The normal mitral valve area (MVA) measures 4-6 cm2. Mild reduction, with MVA measuring 2.0-2.5 cm2, results in elevated left atrial pressures when blood flow or heart rate is increased. Moderate reduction, with MVA 1.5-2.0 cm2, results in mildly elevated left atrial pressures at rest and significantly increased pressures with exercise. Severe mitral stenosis, at valve areas less than 1.5 cm2, results in reduced cardiac output and dyspnea at rest.

Rheumatic mitral valve disease, manifested by commissural leaflet fusion, is the most common cause of mitral stenosis. Nonrheumatic mitral stenosis is unusual, although calcific stenosis is now seen with increasing frequency in hemodialysis patients. Other rare causes of mitral stenosis include carcinoid syndrome, eosinophilic endomyocardial fibroelastosis, and congenital mitral stenosis. These are distinctly different processes from rheumatic mitral stenosis without commissural fusion. Though limited, experience with balloon valvuloplasty for congenital mitral stenosis suggests little benefit from a potentially dangerous procedure. Surgery is usually preferable in these patients who often have associated complex anatomy. These patients should, therefore, be evaluated by a multidisciplinary team at an experienced center.

Rheumatic heart disease remains uncommon in the United States. It is much more prevalent in developing nations, where patients tend to present at a younger age. The prevalence of rheumatic heart disease has, however, seen small but significant increases in recent decades as increasing numbers of immigrants enter the United States from endemic areas. Small recent outbreaks of rheumatic fever have also been reported in the United States by new virulent strains of streptococci.

Note the following:

• The first complaints with mitral stenosis are usually of dyspnea on exertion.

• Early symptoms may be very subtle, and a history of rheumatic fever is often difficult to elicit.

• Patients are sometimes initially diagnosed with upper respiratory illness before re-evaluation prompts consideration for cardiovascular disease.

• In selected patients, formal exercise testing can help to elicit exercise-induced symptoms.

• Women with mitral stenosis frequently present during pregnancy when cardiac output and circulating intravascular volume increase.

• Physical examination may demonstrate a diastolic rumble or an opening snap.

• Chest radiography rarely shows pulmonary edema unless precipitated by an exacerbating illness; however, in advanced mitral stenosis, Kerley B lines from chronically elevated pulmonary venous pressures are sometimes visualized.

• Left atrial enlargement is typically present on the lateral chest radiograph.

• Left atrial enlargement is usually evident on the electrocardiogram.

• Atrial fibrillation often occurs in mitral stenosis as a result of left atrial dilatation and chronically elevated left atrial wall stress.

• Transthoracic echocardiography (TTE), the diagnostic test of choice, is usually necessary and sufficient to confirm the diagnosis of mitral stenosis.

Table 1. Mitral valve area and severity of mitral stenosis (Open Table in a new window)

American Heart Association (AHA)/American College of Cardiology (ACC) guideline recommendations are as follows[2] :

• Perform percutaneous mitral balloon valvuloplasty (PMBV) for patients with severe mitral stenosis (mitral valve area [MVA] < 1.5 cm2), favorable valve morphology and absence of contraindications such as left atrial thrombus or significant mitral regurgitation (class I).

• Asymptomatic patients with MVA < 1.5 cm2, pulmonary hypertension (systolic pulmonary pressure >50 mmHg at rest or >60 mm Hg with exercise), and favorable valve morphology should also be considered for PMBV (class I).

• Patients with calcific mitral stenosis who are at high risk for surgical commissurotomy should be considered for PMBV when advanced heart failure (New York Heart Association [NYHA] class III-IV) and severe mitral stenosis (MVA < 1.5 cm2) are present (class IIa).

• Similar patients who are at lower risk for surgical commissurotomy may also be considered for PMBV (class IIb).

• Symptomatic patients (NYHA class II-IV) with milder stenosis (MVA >1.5 cm2) and pulmonary hypertension may be considered for PMBV (class IIb).

• Asymptomatic patients with MVA less than 1.5 cm2 with new atrial fibrillation may also be considered for PMBV (class IIb).

Similar recommendations have been made by the European Society of Cardiology.[3] Palliative treatment may be considered in patients who are not suitable candidates for surgery even when valve morphology is not ideal.

Table 2. Indications for percutaneous mitral balloon valvuloplasty - AHA/ACC guidelines (Open Table in a new window)

The presence of left atrial thrombus is an absolute contraindication to percutaneous mitral balloon valvuloplasty (PMBV) because of the high risk for systemic embolism. Prior to proceeding with PMBV, all patients should be evaluated by transesophageal echocardiogram (TEE) with specific focus on the left atrial appendage to exclude thrombus. If left atrial thrombus is found, the patient should be treated with systemic anticoagulation for 3-6 months and undergo repeat TEE to confirm resolution of thrombus prior to PMBV. Patients with left atrial thrombus requiring more urgent therapy should be considered for surgical mitral valve replacement with ligation of the left atrial appendage.

Moderate to severe mitral regurgitation is also a contraindication to PMBV because of the risk of worsening regurgitation as a result of the procedure. Severe organic tricuspid stenosis and severe functional tricuspid regurgitation with an enlarged annulus are also relative contraindications to PMBV. Patients with severe concomitant aortic valve disease should be evaluated by an experienced multidisciplinary structural and/or valvular heart team to consider surgical versus transcatheter (ie. transcatheter aortic valve replacment [TAVR]) therapies.

Severe concomitant coronary artery disease requiring bypass surgery is a relative contraindication to PMBV. These patients should be considered for a combined coronary artery bypass and surgical mitral valve procedure. Patients considered high risk for cardiac surgery may still be considered for PMBV, especially if the coronary artery disease (CAD) can be treated percutaneously.

Unfavorable valve morphology is a relative contraindication to PMBV, although in selected patients, especially in those who are high surgical risk or in cases of palliation, PMBV can be considered.

No specific laboratory studies are necessary for patients with mitral stenosis in the absence of an abnormal bleeding history, although most proceduralists order routine screening laboratory tests, including platelet count and prothrombin time, prior to any catheter-based intervention.

A transthoracic echocardiogram (TTE) scoring system is widely used to assess the suitability of valve morphology for percutaneous mitral balloon valvuloplasty (PMBV). The system evaluates four components of the valve, each receiving 1-4 points: leaflet mobility, leaflet thickening, valvular calcification, and subvalvular apparatus deformity.[4] A score less than 8 predicts excellent long-term results. Scores from 9-12 deliver intermediate results whereas scores greater than 12 predict poorer long-term outcomes.

A three-dimensional TTE scoring system has demonstrated feasibility and reproducibility for assessing mitral valve morphology for suitability for PMBV.[5]

Symmetric fusion of the mitral leaflets is associated with better outcomes than asymmetric fusion. A commissural calcium score has also been used to complement the standard scoring system for patient selection; those with a higher degree of calcium are less likely to have successful outcomes.[6, 7]

Intracardiac echocardiography (ICE), a more invasive mode of cardiac imaging involving an ultrasound catheter in the right atrium, has also been used to evaluate mitral valve stenosis. ICE detects more extensive subvalvular disease than TTE or transesophageal echocardiography (TEE) and may improve patient selection for PMBV. Preprocedural ICE evaluation can be performed in the catheterization laboratory immediately prior to PMBV if it will be used to guide valvuloplasty during the procedure.

Interatrial septum thickness measurement on TEE does not appear to change in the presence of moderate to severe rheumatic mitral stenosis relative to those reported as normal values in cadaveric heart specimens.[8]

Coronary arteriography should be performed in selected patients prior to percutaneous mitral balloon valvuloplasty (PMBV). American College of Cardiology/American Heart Association (ACC/AHA) guidelines recommend coronary arteriography in men older than 35 years as well as women older than 35 years with coronary risk factors or who are postmenopausal. Patients with chest pain, evidence of ischemia, decreased left ventricular (LV) function, or a history of coronary artery disease should also undergo preprocedural coronary arteriography.

Transesophageal echocardiography (TEE) should be performed in all patients prior to PMBV to exclude left atrial thrombus.

Transthoracic echocardiography (TTE), which allows two-dimensional evaluation of valve morphology and Doppler evaluation of transmitral gradients, is the principle method of diagnosis. Exercise echocardiography can be helpful in patients with ambiguous symptoms. Cardiac catheterization with measurement of left and right heart pressures and either pulmonary capillary wedge pressure or direct left atrial pressure (by transseptal puncture) was at one time the criterion standard for diagnosis prior to modern Doppler echocardiography. Although not necessary for diagnosis, cardiac catheterization is still sometimes helpful when echocardiographic data do not correlate well with symptoms.

Symptoms in mild to moderate mitral stenosis can be improved with medical therapy. Beta blockers and calcium channel blockers help to control heart rate and increase diastolic filling time. Diuretics can help with heart failure symptoms. Severe symptomatic mitral stenosis should be treated with percutaneous mitral balloon valvuloplasty (PMBV) or surgically.

Surgical commissurotomy has been compared with percutaneous valvuloplasty in several randomized trials.[9, 10, 11, 12] Outcomes are consistently better with percutaneous valvuloplasty in patients who are good candidates. Surgical commissurotomy should, however, be considered in patients with severe subvalvular or calcific mitral valve disease.

A study compared surgical mitral valve replacement (MVR) with percutaneous valvuloplasty in patients with combined mitral stenosis and severe tricuspid regurgitation.[13] In this clinical setting, MVR with tricuspid repair was associated with improved clinical outcomes compared with PMBV. Surgical mitral valve replacement should also be considered in patients with valve morphology not amenable to percutaneous mitral balloon valvuloplasty (PMBV). In patients with persistent left atrial thrombus despite anticoagulation, surgical mitral valve replacement with left atrial appendage ligation should be considered.

In patients with isolated rheumatic mitral stenosis, there appears to be an association between balloon mitral valvuloplasty and a significant reduction of left atrial (LA) volume accompanied by significant improvement in LA volumetric functions.[14]

A study that evaluated maternal and fetal outcomes in 117 pregnant women in their second trimester who underwent PMBV for rheumatic mitral stenosis found the procedure was safe and effective as well as offered favorable maternal and short-term neonatal outcomes.[15] PMBV provided symptomatic relief and hemodynamic improvement, and a 100% success rate.

Percutaneous mitral balloon valvuloplasty (PMBV) should be performed in a qualified cardiac catheterization laboratory with experience in this procedure. transesophageal echocardiography (TEE)-guided PMBV usually requires intubation prior to the procedure and comanagement with an anesthesia team.

Dilatation is most often performed via an antegrade approach with transseptal puncture. A balloon catheter inserted from the femoral vein is advanced to the right atrium and across the atrial septum to access the mitral valve. The procedure can also be performed by a retrograde approach from the aorta across the aortic valve to access the mitral valve. This approach, however, requires arterial access with a large catheter.

Catheter placement and balloon inflation are guided by one or more of several available imaging modalities. Fluoroscopy is routinely performed and allows visualization of catheters during transseptal puncture and balloon inflation. Echocardiography is usually performed to assess mitral valve gradients pre- and postprocedurally. Transthoracic echocardiography (TTE), though less invasive, is sometimes limited as an intraprocedural imaging technique. TEE, the most commonly used echocardiographic modality in PMBV, can more reliably provide intraprocedural imaging and can confirm the location of the transseptal needle prior to septal puncture but usually requires patient intubation and anesthesia. Intracardiac echocardiography (ICE) decreases the risks of transseptal puncture by visualizing the fossa ovalis and tenting as the transseptal needle crosses, but ICE requires an additional venous puncture and is costly. ICE is also limited in accuracy for assessing mitral valve gradients and regurgitant flow.

The most commonly used device for percutaneous mitral balloon valvuloplasty (PMBV) is the Inoue balloon catheter. The single balloon inflates in three stages. After crossing the mitral valve, the distal portion of the balloon is first inflated. The catheter is then pulled back until the distal balloon opposes the valve. The proximal portion of the balloon is then inflated, securing the position of the balloon across the mitral valve. The middle portion of the balloon is then inflated with enough pressure to partially split the fused mitral valve leaflets. Repeated inflations are then performed at successively larger balloon diameters until a minimum gradient reduction is achieved or an increase in mitral regurgitation occurs. In cases of symmetric leaflet fusion, 40-60% of procedures result in a split of both commissures, whereas the remainder split only a single commissure. See video below.

Double balloon valvuloplasty can also be performed. This procedure requires 2 wires or a monorail balloon to be placed across the mitral valve into the left ventricle, potentially increasing the risk of left ventricular perforation. As compared with Inoue balloon, double balloon technique may increase subchordal damage. This is because the wires, instead of the balloon, are used to cross the valve and may trap between the chordal structure. A metal commissuratome has also been recently developed, though it is not available in the United States.[16] This reusable device is appealing in developing nations where cost prohibits the use of other balloon techniques. The stiff metal device requires a large catheter, increasing the risk of cardiac and vascular trauma.

The enlarged mitral orifice resultant from percutaneous mitral balloon valvuloplasty (PMBV) results in an immediate decline in left atrial pressure, a decrease in the transmitral pressure gradient, and a rise in cardiac output (see images below). Left atrial stiffness decreases, resulting in improved left atrial contraction and pump function (in sinus rhythm) or increased left atrial reservoir function (in atrial fibrillation). Older patients, who tend to have increased left ventricular diastolic pressures, and patients with diastolic dysfunction may have persistently elevated left atrial pressures. These patients’ symptoms may not be completely relieved with PMBV.

PMBV results in an immediate 10-25% improvement in pulmonary hypertension.[17] Pulmonary pressures continue to decline over the ensuing weeks or months, although severe pulmonary hypertension usually does not resolve. Atrial fibrillation resolves spontaneously in few patients after PMBV. One study found that direct-current cardioversion to sinus rhythm was successful in approximately 50% of patients 1 month after valvuloplasty with amiodarone administration, although atrial fibrillation recurred in half of these patients.[18] A left atrial diameter of less than 60 mm predicts a higher likelihood of maintaining sinus rhythm.

Baseline atrial fibrillation in patients with significant mitral stenosis appears to be significantly associated with worse symptoms and higher event rates following successful percutaneous mitral valvuloplasty relative to patients with baseline sinus rhythm.[19]  Consideration may be given to the clinical benefits of this procedure for patients with mitral valve area less than 1.5 cm2 before the onset of atrial fibrillation.

The severity of mitral stenosis and/or mitral regurgitation should be assessed by echocardiography after percutaneous mitral balloon valvuloplasty (PMBV) and patients should maintain regular follow-up with a cardiologist. Participation in sports and exercise should be based on the degree of residual mitral stenosis, mitral regurgitation, and/or left ventricular dysfunction. The patient’s capacity to exercise should be formally evaluated at least to the level of anticipated activity.

Up to 20% of patients will develop recurrent symptomatic mitral stenosis. Repeat PMBV can be considered in these patients. Predictors for event-free survival after repeat valvuloplasty are the same as those for primary therapy.

Percutaneous mitral balloon valvuloplasty (PMBV) carries a significant risk of worsening mitral regurgitation, which usually arises at the site of commissurotomy and less frequently from leaflet laceration or subchordal damage. Approximately 30% of patients undergoing PMBV have some detectable increase in mitral regurgitation.[20] Approximately 12% of patients will have regurgitation that is greater than mild in severity. Severe regurgitation requiring mitral valve surgery during the initial hospitalization for PMBV occurs in only 2.5% of patients. The degree of resultant mitral regurgitation correlates with event-free survival rate.

The risk of death with PMBV is less than 1%. This risk is higher in elderly or severely ill patients and those in shock at the time of the procedure.

The risk of transient ischemic attack and or cerebrovascular accident is minimized with routine preprocedural transesophageal echocardiography (TEE) to exclude left atrial thrombus. With TEE, this risk is equivalent to other catheter-based procedures.

The risk of cardiac perforation is approximately 1%.

An iatrogenic atrial septal defect is almost always present immediately after PMBV by antegrade approach. This small puncture, however, almost always closes spontaneously within weeks. Less than 2% of patients have a persistent shunt fraction greater than 1.5:1, which is more likely if left atrial pressures are persistently elevated.[21]

 

Mitral valve area increases on average from 1.0 cm2 to 2.0 cm2 after percutaneous mitral balloon valvuloplasty (PMBV). Overall survival rates at 5 years are approximately 70% in the United States.[22] A preprocedural echocardiographic score of less than 8 predicts a 5-year event-free survival rate of 80%.[23] Mitral stenosis does occasionally progress. A mitral valve area (MVA) reduction greater than 0.3 cm2 occurs in 27% of patients. Mitral regurgitation usually does not progress.[24]

The National Heart, Lung, and Blood Institute (NHLBI) Balloon Valvuloplasty Registry followed up with 736 patients after PMBV.[25] Event-free survival (free from death, mitral valve surgery, or repeat valvuloplasty) was 80% at 1 year, 71% at 2 years, 66% at 3 years, and 60% at 4 years.

A study followed patients for up to 20 years following PBMV (mean follow-up: 11.6 ± 4.9 years) in 441 patients.[26] The rate of cardiovascular death, need for mitral valve surgery or repeat PMBV were 9.1%, 27%, and 5.9% respectively. Survival free of major adverse cardiac events at 20 years was 35.9 ± 4.7%.[26]  

 

A novel echocardiographic scoring system based on calcification, especially commissural, and subvalvular involvement predicted outcomes after percutaneous mitral balloon valvuloplasty (PMBV) better than the standard score and may offer a complementary evaluation to the current scoring system.[27]

Controversy remains over the best treatment and role for mitral valvuloplasty in patients with asymptomatic moderate to severe mitral stenosis, symptomatic mild mitral stenosis, and symptomatic severe mitral stenosis with unfavorable anatomic characteristics.