Cardiology

Mitral Stenosis: Percutaneous Transvenous Mitral Commissurotomy

General description of procedure, equipment, technique

Percutaneous transvenous mitral commissurotomy (PTMC), also known as percutaneous mitral balloon valvotomy, has become the procedure of choice for patients with symptomatic severe mitral stenosis (MS) who have suitable mitral valve (MV) morphology on echocardiography. The principle of PTMC is that when a fluid filled balloon is expanded, equal pressure is applied to the MV, resulting in separation along the plane of least resistance, which are the commissures. PTMC can also be considered in patients with asymptomatic MS, with significant hemodynamic changes and has a suitable MV morphology on echo.

PTMC was developed in the early 1980s and has evolved from a double-balloon technique to the more ubiquitous hourglass-shaped single balloon, Inoue-Balloon Catheter (Toray Industries, Tokyo, Japan) with results comparable to surgical mitral commissurotomy. It is performed via a femoral vein and transseptal access with fluoroscopic guidance. With a declining number of cases in the Western world, the procedure is now often performed with transesophageal echocardiography (TEE) and general anaesthetic support to assist in the transseptal access and assessment of the MV during the procedure.

The Inoue-Balloon Catheter (IBC) is a uniquely designed balloon tip catheter, which allows for five stages of balloon inflation: a completely deflated balloon with the balloon-stretching catheter to allow advancement over a wire across the intraatrial septum (Stage 1); a partially inflated distal portion of the balloon to allow flotation across the MV (Stage 2); a completely inflated distal portion of the balloon to seat it on the ventricular side of the MV orifice in anticipation of commissurotomy (Stage 3); a partially inflated proximal portion to form an hourglass shape, which allows self-centering of the waist on the MV orifice (Stage 4); and a fully inflated balloon (at a predetermined and adjustable diameter), which is inflated forcefully to perform valvuloplasty (Stage 5).

Indications and patient selection

The joint 2014 American College of Cardiology (ACC) and American Heart Association (AHA) guidelines for the indication of PTMC in MS are as follows:

Symptomatic patients

  • Class I (LOE A) - Severe MS (mitral valve area ≤1.5 cm2) with favourable valve morphology and without left atrial thrombus or moderate to severe mitral regurgitation (MR).

  • Class IIb (LOE C) - MS with MV area >1.5 cm2 with significant hemodynamic changes on exercise consisting of a pulmonary artery wedge pressure ≥25 mm Hg or mean MV gradient >15 mm Hg.

  • Class IIb (C) - High surgical risk patients with severe MS (mitral valve area ≤1.5 cm2) and suboptimal valve anatomy.

Asymptomatic patients

  • Class IIa (LOE C) - Very severe MS (mitral valve area ≤1.0 cm2), favourable valve morphology, and without left atrial thrombus or moderate to severe mitral regurgitation (MR).

  • Class IIb (LOE C) - Severe MS (mitral valve area ≤1.5 cm2) with favourable valve morphology and without left atrial thrombus or moderate to severe mitral regurgitation (MR).

Unless as stated above, PTMC is not indicated for patients with mild MS nor in patients with moderate to severe mitral regurgitation (MR) or has left atrial (LA) thrombus.

Severe MS is characterised by a mitral valve area ≤1.5 cm2, diastolic pressure half time ≥150ms, severe left atrial enlargement and elevated pulmonary arterial systolic pressure >30mmHg. Very severe MS is characterised by a mitral valve area ≤1.0 cm2 and diastolic pressure half time ≥220ms.

The Wilkins score is often used (but is not essential) as a measure of MV pliability and success following PTMC (See Table I). It has four categories—leaflet mobility, thickening and calcification, and subvalvular thickening—and is graded from 0 to 4 on echo assessment.

Table I.

Wilkins score
Wilkins score
Grade Mobility SubvalvularThickening Thickening Calcification
1 Highly mobile valve with only leaflet tips restricted Minimal thickening just below the mitral leaflets Leaflets near normal in thickness (4 to 5 mm) A single area of increased echo brightness
2 Leaflet mid and base portions have normal mobility Thickening of chordal structures extending up to one third of the chordal length Midleaflets normal, considerable thickening of margins (5 to 8 mm) Scattered areas of brightness confined to leaflet margins
3 Valve continues to move forward in diastole, mainly from the base Thickening extending to the distal third of the chords Thickening extending through the entire leaflet (5 to 8 mm) Brightness extending into the midportion of the leaflets
4 No or minimal forward movement of the leaflets in diastole Extensive thickening and shortening of all chordal structures extending down to the papillary muscles Considerable thickening of all leaflet tissue (greater than 8 to 10 mm) Extensive brightness throughout much of the leaflet tissue

Completely normal MV is grade 0, whereas the escalating severity of calcification or restriction of motion increase with grades up to grade 4, where the MV has either no or minimal leaflet movement in diastole, >8 mm leaflet thickness, severe calcification all through the leaflets, and severe thickening and shortening of the subvalvular apparatus right down to the papillary muscle.

Out of an overall score of 16, a score of 8 or less lends PTMC to optimal results with >90% success rate, <3% complication rate, and 80% to 90% sustained improvement over a 3- to 7-year follow-up period.

PTMC should be performed in symptomatic pregnant patients if the MV is pliable and the risk to the patient and fetus is usually minimal (especially in a skilled center). In patients >65 years old, the MV is usually more calcific and fibrotic (higher Wilkins score), lending itself to a success rate less than 50% with higher procedural mortality and morbidity.

Contraindications

PTMC is not performed in patients with a LA thrombus, moderate to severe (3+ or 4+) MR, MV area >1.5 cm2, aortic regurgitation >2+, infective endocarditis, severe MV calcification, or subvalvular fibrosis who are surgical candidates.

Details of how the procedure is performed

Patient’s undergoing PTMC are usually admitted the day of procedure with instructions to fast from midnight; they have their anticoagulation with warfarin withheld for three days, aiming for an international normalized ratio of 1.7 on procedure day. In most centers, TEE is used to assist the proceduralist and the patient will be anesthetized. A right heart catheterization is performed to obtain full preprocedure hemodynamics and a left ventriculogram can be performed to assess for baseline MR.

Once transseptal puncture is performed at the mid fossa, heparin is administered aiming for an activated clotting time (ACT) ≥ 250 seconds, and the LA pressure is measured with a simultaneous left ventricular pressure to calculate the transmitral gradient.

Using the transseptal sheath, the supplied 0.025-inch in diameter, 175-cm long stainless steel spring coil guidewire is introduced into the LA. Over this wire, the supplied 14 Fr, 70-cm tapered dilator is used to dilate the femoral vein and the intraatrial septum, and is removed.

Based on the patient’s height, the required size of the IBC is chosen (required maximal diameter = 10+ (Patient’s height (cm)/100)). The IBC’s inner tube is then flushed with heparinized saline.

Dilute contrast (3 to 1) is used to flush the balloon via the vent tube, which outflows through the main tube. The main and vent stopcocks are then closed.

The supplied syringe is checked to ensure it matches the alphabetical code on the W-connector. The syringe is then filled with dilute contrast to the minimal diameter and slowly injected into the balloon via the main stopcock.

Once the balloon is fully dilated, the supplied caliper is used to measure the waist and it should correspond to the minimal diameter. The balloon is then fully sucked down. This step is then repeated using the maximal diameter on the syringe.

The supplied 19G 80-cm balloon stretching tube is then flushed with heparinized saline. This is then used to stretch the balloon to allow crossing the intraatrial septum.

It is inserted into the catheter inner tube and the two metal hubs are luer locked (“metal to metal”). These hubs are then pushed toward the W-connector where its plastic hub is luer locked to the metal hub (“metal to plastic”).

This assembly is inserted over the wire and partially into the LA. As it nears the LA wall, as seen on TEE (and most of the balloon is across the septum), the tip is made elastic by unlocking the balloon stretching tube and withdrawing 2 to 3 cm (unlocking “metal to metal”). Once the entire balloon has crossed the septum as seen on TEE, the inner tube is unlocked and pulled back from the W-connector (unlocking “metal to plastic”).

The system is then advanced further into the LA, stopping when it is in the shape of the LA arch. The guidewire and balloon stretching tube are removed together.

Fill the supplied syringe to 2 mm below the maximum diameter and attach to main stopcock. Insert the supplied 0.038-inch in diameter, 80-cm long stainless steel stylet and direct the curve balloon into the MV. Partially inflate the distal balloon and withdraw the stylet 3 to 5 cm; the balloon will move forward and across the MV. Counterclockwise motion of the stylet can help direct the balloon across the MV.

The distal balloon is inflated fully and pulled back and forth a few times to ensure it is not lodged into the chordae. It is then pulled against the MV gently, and the proximal balloon is inflated quickly to perform valvuloplasty.

The balloon is then deflated and pulled back into the LA. The result of valvuloplasty is checked on TEE, specifically the degree of residual stenosis and severity of MR.

If there is still significant stenosis with mild to moderate MR, the process is repeated at 1 mm below the maximal diameter and, if necessary, at maximal diameter balloon inflation. At the conclusion, an LA pressure is acquired and simultaneous left ventricular pressure could be acquired to calculate the residual transmitral gradient.

To remove the IBC, the wire is inserted and coiled in the LA, and the balloon stretching tube is inserted and locked into the inner tube (“metal to metal”). The W-connector is then brought backward to the inner tube hub (“plastic to metal”) to avoid damaging the LA. The whole assembly is then removed.

Right heart catheterization is performed to assess final hemodynamics and a left ventriculogram can be performed to assess final mitral regurgitation severity. An echo is required a few days after PTMC as the pressure half-time calculation for MV area maybe inaccurate due to postprocedure compliance changes in the atrium and ventricle.

An assessment of MR and atrial septal defect should be performed as well. A yearly clinic review and echocardiographic assessment is required. Anticoagulation is continued in patients with paroxysmal or chronic atrial fibrillation.

If MS recurs, PTMC can be reattempted; but if there is significant valve deformity, surgical MV replacement may be required.

Interpretation of results

Successful PTMC is an uncomplicated procedure with a final MV area >1.5 cm2with a LA pressure of <18 mm Hg. This usually occurs in 80% to 90% of cases and leads to an immediate symptomatic relief with a 50% to 60% decrease in transmitral gradient. Over a few months, there is a gradual regression in pulmonary artery pressure.

Post-PTMC in patients with a Wilkins score greater than 8 have a higher recurrent rate of symptoms as a result of restenosis or inadequate valvuloplasty.

Performance characteristics of the procedure

PTMC outperforms closed mitral commissurotomy (CMC) as does open mitral commissurotomy (OMC); as such CMC has been abandoned. In comparison to OMC, PTMC results are similar; some studies have shown similar improvements in mitral valve area and NYHA, and freedom from reintervention and restenosis rates. The main advantages of PTMC are the lower cost and avoidance of a thoracotomy and cardiopulmonary bypass.

Outcomes

Main predictors of immediate PTMC success includes larger pre-PTMC mitral valve area, lower grade of pre-PTMC MR, younger patients, no prior surgical commissurotomy, males and Wilkins score ≤8.

Main predictors of combined outcomes of death, mitral valve surgery, or repeat PTMC includes post-PTMC MR grade ≥3+, Wilkins score >8, older patients, prior surgical commissurotomy, baseline NYHA class IV, pre-PTMC MR grade ≥2+, and post-PTMC pulmonary artery pressure. Additionally atrial fibrillation, low post-PTMC mitral valve area and high post-PTMC mean gradient contributes to poor outcomes.

Alternative and/or additional procedures to consider

In patients not suitable for PTMC, surgical repair could be performed if the valve morphology is suitable for repair. If not, than MV replacement is indicated.

Surgical in-hospital mortality with MV replacement is less than 5% in younger groups but increases up to 10% to 20% in older groups with severe pulmonary hypertension or other medical problems. However, the benefits outweigh the risk in these patients, especially if there are in NYHA functional class IV, with surgical MV replacements.

Complications and their management

The most common complication is a 2% to 10% risk of severe MR. Other complications are less than a 5% risk of significant residual atrial septal defect (1.5:1 left to right shunt or greater), 0.5% to 4.0% risk of left ventricular perforation, 0.5% to 3% embolic events, 0.3% to 0.5% myocardial infarction, and less than 1% mortality. In patients with severe MR or significant atrial septal defect, an early surgical referral is required.

What’s the evidence?

Wilkins, GT, Weyman, AE, Abascal, VM, Block, PC, Palacios, IF. "Percutaneous balloon dilatation of the mitral valve: an analysis of echocardiographic variables related to outcome and the mechanism of dilatation". Br Heart J. vol. 60. 1988. pp. 299-308.

(Optimal outcomes following PTMC had a mean Wilkins score of 7.36.)

Ben Farhat, M, Ayari, M, Maatouk, F. "Percutaneous balloon versus surgical closed and open mitral commissurotomy: seven-year follow-up results of a randomized trial". Circulation. vol. 97. 1998. pp. 245-50.

(Prospective randomized single center study of 90 patients. PTMC and OMC had similar outcomes including follow-up mitral valve area [both 1.8 ± 0.4 cm2], restenosis with MVA <1.5 cm2 [both 6.6%] NYHA I [87% vs. 90%] and freedom from reintervention [90% vs. 93%]. CMC had more unfavorable results.)

Cotrufo, M, Renzulli, A, Ismeno, G. "Percutaneous mitral commissurotomy versus open mitral commissurotomy: a comparative study". Eur J Cardiothorac Surg. vol. 646-51. 1999. pp. 651-2.

(Nonrandomized, single center study of 193 patients. Mid- to long- term follow-up, operative risk and complications were similar; however, OMC resulted in a larger mitral valve area [2.05 ± 0.35 vs. 1.81 ± 0.33 cm2], improved NYHA functional recovery [1.14 ± 0.3 vs. 1.39 ± 0.7] and lower incidence of moderate to severe mitral regurgitation [4% vs. 26%]).

de Souza, JA, Martinez, EE, Ambrose, JA. "Percutaneous balloon mitral valvuloplasty in comparison with open mitral valve commissurotomy for mitral stenosis during pregnancy". J Am Coll Cardiol. vol. 37. 2001. pp. 900-3.

(Nonrandomized, single-center study of 45 pregnant women. PTMC success rate was 90.5% with a lower neonatal and fetal mortality [4.8% vs. 37.9%]).
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