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Percutaneous Mechanical Mitral
Commissurotomy with the Metallic Valvulotome:
Detailled technical aspects and overview of the
results of the multicenter registry on 1164 patients
Alain Cribier, MD; Hélène Eltchaninoff, MD
Department of Cardiology, Hôpital Charles Nicolle, University of Rouen, Rouen, France
Over the last fifteen years, balloon mitral valvuloplasty (BMV) has become an accepted alternative to surgical commissurotomy, especially in young patients with pliable valves, leading to comparable immediate and long term results (1-6). However, the cost of the balloon catheters still limits its application in developing countries which are precisely those countries with the highest incidence of mitral stenosis. Consequently, the balloon catheters, despite being provided as disposable catheters are reused several times, thus carrying potential hazards due to imperfect sterilization and decreasing performance.
Three years ago, we developed a percutaneous metallic valvulotome (7) whose principle is basically similar to the Tubb's dilator used by the surgeons for closed-chest mitral commissurotomy. The main goal was to provide a device that could be reused several times without any loss of performance after proper sterilisation, thus decreasing the procedural cost. Other hopes were to improve the efficacy and tolerance of the technique resulting from the device's mechanical properties which are aimed at acting principally on the mitral commissures.
More than 10 000 patients have been treated with this technique world-wide. The technical aspects of the procedure and the results of an international multicenter registry including 1164 patients will be presented here.
DESCRIPTION OF THE DEVICE
The device (Medicorp-Bolton Inc, Nancy, France) has been described in details elsewhere (8). Briefly, the entire system is made of four components:
- The metallic dilator () in stainless steel, presents like a cylinder 5 cm long and 5 mm wide with a slightly tapered tip. Its distal half consists of two hemicylindrical bars 20 mm in length which can be opened out in parallel up to a maximum extent of 40 mm. Inside the dilator, an internal lumen allows the passage of a traction wire and the recording of the distal pressures. The dilator is screwed on the distal end of the catheter and is detachable.
|Fig 1: The metallic valvulotome in the closed position
and in the opened (40mm) position.
The metallic head is screwed at the distal tip of the 13-Fr catheter
- The catheter, has a diameter of 13-Fr and a length of 170 cm. Its proximal end has a connector for the recording of distal pressures and it enables the connection of the activating pliers ().
Fig 2: Proximal end of the catheter and
- The metallic guidewire (), has a length of 270 cm and a diameter of 0.035 inch. A metallic bead of 2 mm in diameter is soldered at the junction of the stiff core and the 10 cm long floppy distal end ( ). This wire is used first as a guidewire to drive the dilator across the mitral valve, and then as a traction system which enables the opening of the dilator. For that, the metallic bead must be positioned in contact with the distal end of the dilator. The guidewire is then locked into the commissurotome using a threaded fastener located on the activating pliers. Squeezing the arms of pliers causes a backward traction of the guidewire and the metallic bead which is transmitted to the distal end of the dilator thus forcing the distal bars to spread apart.
|Fig 3: The 0.035 inch extra-stiff guidewire. Note the metallic bead soldered at thejonction of the stiffproximal and flexible distal segments of the wire.|
- The activating pliers () are attached to the proximal end of the catheter shaft. A manual pressure exerted on the handle of the pliers enables the opening of the dilator and the release of pressure closes the dilator. The activating pliers also comprise a calmer which allows the degree of bars opening to be altered from outside, offering four degrees of opening (30, 35, 37 and 40 mm), a threaded fastener, and a safety lock which prevents the complete closure of the dilator after release of the pressure exerted on the pliers (it holds the dilator open at 20 mm). To obtain a complete closure of the dilator, this lock must be activated manually.
After dilatation, the metallic dilator can be unscrewed from the catheter and can be sterilised by autoclave for reuse. The activating pliers and the guidewire can also be re-sterilized. Only the catheter is meant for single use.
TECHNIQUE OF PERCUTANEOUS MECHANICAL
MITRAL COMMISSUROTOMY (PMMC)
- Transseptal catheterisation: Transseptal catheterisation constitutes an essential step because the transseptal puncture site greatly influences both the safety of the procedure and the effectiveness of the dilatation itself. The puncture site is ideally situated 1 to 2 centimeters below the spot usually recommended for the Inoue technique. The following approach is recommended:
In the antero-posterior view: the Mullin's sheath with the Brockenbrough needle is pulled back from the superior vena cave, until its distal tip is positioned midway between the tip of the pigtail (lying just above the aortic valve in the ascending aorta) and the top of the right hemidiaphragrn. While maintaining the position of the assembly, the image intensifier is moved to the 90o lateral position. The needle is then rotated in such a way that the distal tip of the dilator points upward (in as straight a vertical line as possible) and makes contact with the septum. Ideally, the contact will be made at a point two thirds of the way down from the pigtail to the posterior border of the heart. The transseptal puncture is then performed. In no case should the septum be punctured high and anterior or low and posterior.
- Positionning of the guidewire into the left ventricle: In the 30o RAO position, the Mullins catheter is advanced into the left atrium and both dilator and needle withdrawn. Inside the left atrium, the Mullins sheath should now appear with its distal curvature directed toward the mitral orifice, lying in a plane close to horizontal, and entirely below the pigtail catheter. If the two catheters appear on the screen to cross over each other then the septal puncture was too high, and will render difficult or even impossible crossing the mitral valve with the commissurotome. In this setting, it is recommended that the transseptal puncture be repeated at a slightly lower point of the septum.
At this point, 2000 IU of heparin are given intravenously.
Using the Mullins sheath and the pigtail catheter advanced into the left ventricle, the transmitral pressure gradient is recorded. The pigtail catheter is then withdrawn into the ascending aorta, to a point just in contact with the aortic valve; this position is important because it serves as a marker for the subsequent positioning of the commissurotome
Through the Mullins sheath, a 7F Critikon type balloon catheter is advanced and used for crossing the valve. The balloon is advanced ideally all the way to the apex. The Mullins sheath is then advanced over the balloon catheter until it contacts the tip of the balloon. The balloon is then deflated and the catheter withdrawn.
The commissurotomy guidewire is advanced through the Mullins sheath into the left ventricle. The flexible distal tip of this guidewire is left in place in the apex of the left ventricle and the Mullins sheath is removed. Ideally, the bead on the guidewire is maintained in the center of the ventricular cavity. During the dilatation maneuvers, the bead should under no circumstances move all the way to the apex to avoid the risk of laceration of the ventricular wall by the rigid portion of the guidewire.
- Dilatation of the interatrial septum: A 14F polyethylene dilator is pushed over the guidewire, advanced 2 to 3 cm across the interatrial septum, and left in place for approximately 30 seconds (). The same procedure is performed using a 1 8F dilator. This dilator should be left in place across the septum for approximately 60 seconds.
|Fig 4: Dilatation of the septal puncture site with the 14-Fr polyethylene dilator. The guide wire is positioned in the left ventricle|
Before removal, the 18F dilator, is passed back and forth through the femoral venous puncture site several times to facilitate the introduction of the metal commissurotome into the femoral vein. At this point, additional intravenous heparin (50 IU/kg) should be administered.
- Mitral commissurotomy: Before use, the commissurotome must be assembled and flushed and the degree of opening selected. The tightening screw is relaxed in order to permit the advance of the catheter over the guidewire. A pressure line is connected to the proximal port of the catheter. As much as possible, active flushing of heparinized saline should be maintained throughout the procedure. It is necessary to confirm that the safety latch is raised into the locked position. The extent of bars opening is determined according to the patient height and the degree of severity of the disease. Above a height of 1.5 m, the device can be opened to 40 mm at first. In other patients, 37 mm (or 35 mm in children) is scheduled and a stepwise increase in opening is performed according to the results. In cases with high echo-score (>10), severe calcifications or severe involvement of the subvalvular apparatus, the first opening is decreased by one size.
|Fig 5: position of the metallic commissurotome across the mitral valve in the closed and the opened position (40 mm)|
THE MULTICENTER REGISTRY
From November 1995 to May 2001, PMMC was performed at 70 centers in 17 countries, a majority of patients being recruited in India, Egypt and France. The series included 1164 patients with mitral stenosis considered suitable for percutaneous valvotomy. Mean age was 35 ± 14 (12 to 86) and 67% were female; 57% of the patients were in functional class III or IV and 168 (14%) had a previous surgical or balloon commissurotomy. Contraindications to the procedure were: no commissural fusion, mitral regurgitation (MR) Sellers' grade > 2, recent embolic event, left atrial thrombus on transesophageal echocardiography which was performed within two weeks before the procedure in the vast majority of cases.
Data collection and analysis
In each case, M-mode and 2D echocardiography and Doppler were performed to assess the severity of mitral stenosis. The valve area was determined by planimetry oon the short axis view and by Doppler half-time method. The Wilkins score in 16 grades (9) was used to assess the severity of the disease. The planimetry at day 1 after PMMC was the reference method for assessment of the results. Immediately before and after PMMC, left and right heart pressures and the mean transmitral gradient were measured, and a left ventricular angiogram was performed to assess the left ventricular function and the severity of any MR. Transatrial shunting was assessed after PMMC on transthoracic color flow Doppler and transesophageal color flow Doppler in a subset of 85 patients. Procedural success was defined as a mitral valve area > 1.5 cm2 in absence of MR > grade 2.
PMMC could be achieved in 1140 out of the 1164 patients (98%). It was not possible to cross the mitral valve in 7 patients, with the Critikon balloon catheter in 4 and with the commissurotome in 3. A crossover to the Inoue technique was performed in 5 cases and was successful in 3, while a direct cross-over to surgery was performed in the other patients. Maximal extent of bars opening was 40 mm in 86% of the cases, 37 mm in 12% and 35 mm in 2%. The mean number of openings was 3.3+1.6 (1 to 10). PMMC was successful in 91% of the patients. The technique resulted in a significantly decreased transmitral gradient and increased valve area as shown in . At day-1, the mitral valve area had increased from 0.94 ± 0.23 cm2 to 2.11 ± 0.36 cm2 (p<0.001). Bilateral splitting of the commissures was noted in 86% of the patients. The results according to the echo-score are shown in . The mean duration of the procedure from the time the septal puncture was completed to the withdrawal of the catheters was 28 ± 14 min.
|Fig 6: Changes in transvalvular gradient (LV-LA gradient), mitral valve area (MVA), pulmonary and left artium pressures before and after PMMC in the entire series.|
|Fig 7: Post-PMMC mitral valve area (cm2) at day 1 after the procedure according to the echo-score (n= No of patients)|
Severe complications occurred in 50/1164 patients (4.3%). There were 17 pericardial tamponades (1.5%), 8 requiring surgery and 2 leading to death. The incidence of MR > grade 2 was 2.6%, including 6 grade 4 (surgical) and 30 grade 3 (surgical in 2 cases) MR. Finally, 3 patients had a transient stroke with no neurologic sequel.
On transthoracic color flow Doppler, transseptal shunting was not detected or was trivial after the procedure. In the subgroup of 106 patients who also had transesophageal color flow Doppler, transseptal shunting was detected in 58 patients, trivial in 47 and small in 11
There were no other complications. The patients were discharged on an average of two days after the procedure.
The role of the learning curve in the occurrence of complications has been clearly demonstrated. When two subgroups are compared according to the investigator's experience of < 20 patients (n= 633) or > 20 patients (n= 531), the incidence of complication is respectively 5.4% vs 3.0% (p= 0.048). This is particularly confirmed as per the incidence of pericardial tamponades (1.9% vs 0.9%) and > grade 2 MR (3.2% vs 1.9%).
Comparison with the balloon techniques
The present series which, of note, includes the early experience of all the investigators, shows that this new technique using a metallic commissurotome offers at least similarly good results that the balloon techniques currently used (10-13). More particularly, the final valve area obtained and the percentage of double commissural splitting compare favourably with those reported with the Inoue technique. However, it is clear that randomised studies would be necessary for an accurate comparison of the results. The low incidence of complications in this series and the role of the learning curve are clearly demonstrated. More particularly, the low rate of severe post-PMMC Mitral must be pointed out with a rate of severe (grade 3 and 4) MR of 2%. Four patients only required in-hospital mitral valve replacement for massive MR. BMV is associated with 1.4 to 7.5% severe MR in the literature (13,14,15-17). At the opposite, the rate of pericardial tamponade (1.4%) was relatively high in this series, resulting from a wrong interatrial puncture site, generally situated too low and/or too posterior. This was easily corrected with more experience, as shown by a decrease of cardiac perforation to 0.6% above a learning curve of 20 patients. With BMV, the rate of tamponade is reported to be 1 to 9% (14,17,18). Finally, no significant interatrial shunting was detected by echocardiographic methods.
Mechanism of action
It has been demonstrated by 2D echocardiography that the device enlarges the stenotic orifice primarily by separating the fused commissures. Actually, the two bars start to open in the way of less resistance, i.e. on the commissures line. No hand rotation of the catheter is necessary. Stretching and separation of the commissures are obtained without injury to the leaflets or the chordae, thus decreasing the risk of MR.
An important potential advantage of the metallic dilator is the expected decrease in procedural cost. The detachable metallic head allows multiple safe reuse after sterilisation using autoclave, as for any other metallic surgical tool. Some investigators have performed above 40 procedures with a single device without any deterioration of the dilator components. Consequently in India, the cost/procedure has been recently evaluated to be about US $ 100. Thus, it is expected that the final cost per patient will be confirmed to be markedly lower than that of the balloon catheters in current use. This should be considered as a major advantage, particularly in countries with low financial resources.
Future of the procedure
This clinical experience with the new technique is promising. The multicenter prospective international registry is kept ongoing and will definitely determine the benefits, limitations and cost-effectiveness of the procedure. Finally, several randomised studies comparing the technique with the balloon techniques have been or are being performed in India, Brazil, Thailand and Egypt, and have been either presented in various meetings or published (19). The improved results (more particularly in patients with high echo-score) and the economic impact of the commissurotome over the balloon have been consistently reported.
Furthermore, a small size (9-Fr) device, similar
otherwise to the present dilator has been designed, and the clinical experience
with it started a few weeks ago in Egypt. This very early experience on 7 cases
showed that the technique was feasible and lead to satisfactory results despite
the reduction in size. This improved device should widen in the next future
the indications of this technique to children below 12 years of age with mitral
stenosis, and to some other indications such as congenital or rheumatic aortic
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