Artificial mitral valve chorde: Experimental and clinical experience

Artificial Mitral Valve Chordae: Experimental and Clinical Experience Claudio Zussa, MD, Robert W. M. Frater, MD, Elvio Polesel, MD, Marco Galloni, BS, and Carlo Valfrk, MD Division of Cardiac Surgery, Regional Hospital, Treviso, Italy, and the Cardiothoracic Surgery Department of Albert Einstein College of Medicine, Bronx, New York

Failure of mitral valve reconstructive procedures often may be ascribed to severe or progressive alterations of subvalvar apparatus. Expanded polytetrafluoroethylene sutures were used to replace anterior leaflet mitral valve chordae in 8 animals (hypertensive dogs and growing sheep). After the positive results obtained during a 13-month follow-up, 5-0 sutures of the same material were introduced in clinical practice to replace mitral valve chordae. Twelve patients had two to six anterior leaflet chordae replaced for degenerative or rheumatic disease. In 3 patients, the intraoperative result was not acceptable and a prosthetic valve was inserted during the

M

itral valve repair has obvious theoretical advantages over replacement with an artificial device. For successful repair, all the disordered components of the mitral apparatus must be fixed in each case. Annular dilatation is successfully handled by suture [14] or ring [5, 61 annuloplasty, but neglect of chordal elongation will result in a poor outcome [4]. Chordal elongation may be successfully treated with different shortening procedures [7, 81, and posterior leaflet chordal rupture is repaired with rectangular resection [7]. Multiple rupture of the anterior leaflet chordae still presents difficulty [6, 9, 101. The posterior cusp transposition advocated by Carpentier [7, 111 presents limitations related to the degree of diffuseness of the disease: the posterior scallop that is to be transposed must be normal; if a normal scallop is transposed but the remaining posterior cusp is abnormal, the result may be unsatisfactory. Both experimentally and clinically, pericardium from various sources and prepared in various ways has been extensively used for cusp and chordal replacement and repair [lo, 12-16]. Pericardium prepared with glutaraldehyde behaves better in chordal applications than when it is used as cusp material. However, although it heals well to both cusp and papillary muscle and neither elongates nor shortens, it does thicken with time and would be of questionable utility for multiple chordal replacement. In the cardiothoracic surgery laboratory of the Albert Einstein College of Medicine, 2-0 and 3-0 expanded polytetrafluoroethylene (ePTFE) stitches (W.L. Gore & Assoc, Accepted for publication March 15, 1990 Address reprint requests to Dr Zussa, Divisione Cardiochirurgia, Ospedale Regionale, 31100 Treviso, Italy.

0 1990 by The Society of Thoracic Surgeons

same operation. One case of late failure has been recorded so far (18 months after the procedure), owing to rupture of a natural chorda shortened at operation. Since that event, we have implanted supportive artificial chordae in case of diffuse alteration of natural chordae. The remaining patients show satisfactory hemodynamic results, and no valve-related events have been recognized up to 30 months after operation. We suggest use of 5-0 polytetrafluoroethylene sutures in replacing anterior leaflet chordae in degenerative, rheumatic, and congenital mitral valve diseases. (Ann Thorac Surg 1990;50:367-73)

Flagstaff, AZ) were introduced for chordal replacement in juvenile sheep with striking results [16]. The ePTFE sutures became covered with host tissue so that both histologically and grossly they resembled natural chordae. This observation was confirmed by Revuelta [17]. The combination of 2-0 ePTFE and tissue covering produced chordae that were less flexible than normal, however. In the hope of achieving new chordae with flexibility equivalent to normal chordae, we tested 5-0 ePTFE sutures for chordal replacement in juvenile sheep. We report these experimental studies and the results of introduction of this procedure to clinical use in the cardiac surgery department of Ospedale Regionale, Treviso, Italy.

Material and Methods

Animal Experiments At Albert Einstein College of Medicine in 1985, we performed eight animal experiments: four in dogs (naturally hypertensive greyhounds) and four in weanling sheep. All animals received humane care in compliance with the ”Guide for Care and Use of Laboratory Animals” published by the National Institutes of Health (NIH publication No. 85-23, revised 1985). The anesthetic management and the surgical procedure for establishing cardiopulmonary bypass have been reported previously [MI. In each animal, two to four first-order anterior leaflet chordae (ALC) were replaced by 5-0 ePTFE stitches. The sutures were attached to the papillary muscles in mattress shape and were reinforced with Teflon or PTFE pledgets, one on each side of the muscle, with two chordae obtained for each stitch. The two ends of the suture were fixed separately to the margin of the anterior leaflet, with the 0003-4975/90/$3.50

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AM1

dog died of bleeding 24 hours after operation. The 7 surviving animals were followed for signs of mitral incorripetence; only 1 showed such signs. The animals were killed electively 6 to 13 months after operation; before they were killed, we performed a cardiac catheterization with left ventriculography in 5 animals. After gross examination, the specimens were fixed for light microscopy and scanning electron microscopy.

Clinical Experience

#

,

Fig 1 . Expanded polytetrafluoroethylene suture (c) replacing two main chordae of the rnitral value anterior leaflet (AML).Open arrows indicate PTFE pledgets. Dark arrow shows hemostatic clip. stitch brought through the edge and tied around a hemostatic clip (Edward Weck, Research Triangle Park, NC) or a small PTFE pledget (Fig 1). The exact length of the artificial charda was set according to the rules suggested by Frater and colleagues [lo-121. After the animal was weaned from CPB, left atrial and left ventricular pressures were recorded. Cephalothin, 1 g, was administered subcutaneously for 5 days postoperatively. No anticoagulant regimen was instituted. One

After experimental results were obtained, we began clinical use of 5-0 ePTFE sutures in the treatment of mitral valve pathology in the Treviso (Italy) cardiac surgery department. From November 1986 to November 1988, 12 patients underwent open heart operation with implantation of two to six artificial chordae. Clinical data are shown in Table 1. The procedure was performed using cardiopulmonary bypass with moderate hypothermia (28°C) and crystalloid cardioplegic arrest. The technique of chordal insertion was identical to the experimental procedure except that after the two ends had been fixed at the proper length by the hemostatic clip (Edward Weck) the ends were passed through a small ePTFE pledget and tied. Suture [4] or Carpentier-Edwards ring (American Edwards Laboratories, Santa Ana, CA) anpuloplasties were performed in 7 and 2 patients, respectively; other associated procedures are shown in Table 2. In no patient was chordal replacement the only procedure. The result was evaluated intraoperatively in all patients by left ventricle pressure filling with saline solution under direct vision and, after weaning from cardiopulmonary bypass, by epicardial two-dimensional echocardiography in the last 7 patients. N o anticoagulant therapy was instituted. The follow-up has been obtained from all patients by direct examination, and the result is controlled by twodimensional echocardiography every 6 months.

Table 1. Clinical Data ~~

~~

Patient Age NYHA No. Sex (y) Class 1 2 3 4 5 6 7 8 9 10 11 12

F M F M F F M F M

M F M

65 34 62 41 38 55 49 40 59 61 57 51

IV

I1 I1 I11 111 I1 I1 111 111

IV I11 111

Cause

Mitral Dysfunction

Chordae

Deg. Deg. Rheum. Rheum. Rheum. Deg. Deg. Rheum. Deg. Endoc. Rheum. Rheum.

Incomp. Incorpp. Incomp. Incomp. Sten. Incomp. Incomp. Sten., incomp. Incomp. Incomp. Incomp. Sten., incomp.

Broken, elong. Broken, elong. Broken, fused Elong. Fused Broken, elong. Broken, elong. Elong. Elong. Broken Broken Broken, fused

Commissures Leaflets

... ... ... ... Fused

... ... Fused

... ...

... Fused

Prolapse

Myx. Ant. Myx. Ant. Calcif. ... Calcif. Ant. Calcif. ... Myx. Ant., post. Myx. Ant., post. Calcif. Ant. Myx. Ant., post. ... Ant., post. ... Ant. ... Ant., post.

Associated Valvar Disease

...

...

... AO, sten.

.. ... ... ... ... AO, tric. incomp.

...

...

Ant. = anterior; A 0 = aortic; caldf. = caldfic; deg. = degenerative; elong. = elongated; endoc. = endocarditis; incomp. = incompetence; myx. = myxomatous; NYHA = New York Heart Association; post. = posterior; rheum. = rheumatic; sten. = stenosis; tric. = tricuspid.

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Table 2. Surgical Procedures Intraoperative Patient

PTFE

No.

Chordae

Side

1

4

Ant.

2 3

4

4

5

2

2 2

6 7

6

8

4

9

4

10 11

2

12

2

a

4

2

Associated Mitral Procedures

Chordae shortening, suture annuloplasty Ant. Suture annuloplasty CA debridement, suture Ant. annuloplasty Ant. Suture annuloplasty Commissurotomy, CA Ant. debridement, suture annuloplasty Ant., post. Suture annuloplasty Rectangular resection, suture Ant. annuloplasty Ant. Commissurotomy, suture annuloplasty Ant. Rectangular resection, ring annuloplasty Suture annuloplasty Ant. Ring annuloplasty Ant. Ant. Rectangular resection, ring annuloplasty

Associated Valvar Procedures

Two-Dimensional Hydrodynamic Test Echocardiography

...

No incomp.

...

2+ incomp."

...

2+ incomp."

AVR

No incomp. No incomp.

...

...

1+ incomp.

...

No incomp.

2+ incomp." No incomp.

...

No incomp.

No incomp.

...

No incomp.

No incomp.

AVR, tric. annuloplasty

1+ incomp. No incomp. No incomp.

1+ incomp. No incomp. No incomp.

...

...

Mitral valve replaced during the same operation.

AVR = aortic valve replacement;

CA

=

calcium;

ITFE = polytetrafluoroethylene;

Results Animal Experiments Cardiac catheterization performed before the animals were killed showed only 1 case of mild mitral incompetence, which was demonstrated, at gross examination, to result from an incorrect chordal measurement at operation. Gross examination showed all artificial chordae to have retained their original length. In 1 animal, the two ends of the same suture were placed too close, became fused, and formed one chorda with, however, a diameter still similar to that of natural chordae (Figs 2, 3). The healing to the papillary muscle was good in all instances, whereas on the cusp side 2 animals had a mild inflammatory reaction. The pliability was gravity-tested in the fresh specimens, comparing the degree of bending of the explanted host incorporated artificial chordae and the same length of natural chordae in response to gravity; they were identical [19]. At histological examination, the sutures appeared to be progressively covered, from both papillary muscle and leaflet sides, by a uniform sheath of fibrous tissue (Fig 4) connected with the underlying artificial tissue by fibrous bridges. The surface was smooth and almost completely covered by a neointimal cellular sheath (Fig 5). Our observations confirmed previous data [16] from our laboratory suggesting that the fibrous tissue overgrowth is a self-limiting process; no significant differences could be found in the thickness of the sheath among animals investigated from 6 to 13 months after operation. No

other abbreviations as in Table 1.

calcification or thrombi were detected. No differences in gross and histological findings were noted between sheep and hypertensive dogs.

Clinical Experience INDICATIONS. Tables 1and 2 show that clinical application of the technique of chordal replacement as an adjunct to the many other maneuvers of mitral valve repair has rapidly resulted in extension of the indication beyond the simple presence of a ruptured anterior cusp chorda. Calcium debridement was the cause for chordal replacement in 2 patients (see Table 2); in these patients, after we performed a commissurotomy, the leaflet motion was still restricted owing to calcificationof major chordae up to the leaflet junction, while the pliability of the nonappositional part of the leaflet was satisfactory. The calcified chordae were therefore replaced by two ePTFE sutures. Four other patients had four to six artificial chordae inserted as support of diffusely diseased subvalvar apparatus (elongation and weakening of most first-order chordae, besides the rupture of at least one of them).

INTRAOPERATIVE RESULTS. With the hydrodynamic intraoperative test, the result was judged to be satisfactory in 10 patients, whereas 2 patients (1 with rheumatic and the other with degenerative mitral disease) had the valve replaced.

No hospital mortality was registered among the 12 patients, and the 9 who were discharged

FOLLOW-UP RESULTS.

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from the hospital with artificial chordae have been followed by two-dimensional echocardiography (Table 3). So far only 1 patient (the 1 in whom chordae shortening had been performed) showed recurrence of mitral regurgitation 18 months after operation. The sudden manifestation of clinical signs of mitral incompetence indicated urgent operation. At reoperation, one of the shortened natural chordae was torn and the suture annuloplasty dehisced, while the artificial chordae were still in proper position with retained length. Gross and histological examinations showed changes similar to those of the experimental specimens with a slower rate of host tissue overgrowth (Fig 6). Since that experience, in patients with diffuse myxomatous chordal and leaflet degeneration we have inserted new chordae in the presence of attenuated as well as ruptured native chordae and have used a ring for the annuloplasty. No deaths or other valve-related complications have been recorded, and the patients are in functional class 1(7 patients) or I1 (1 patient) after a follow-up ranging from 2 to 25 months (mean, 12.3 months).

Comment

Fig 2. Experimental specimen in which two artificial chordae, although fused in one sheath (arrows), retained a diameter similar to natural chordae.

Fig 3 . Same specimen as in Figure 2 observed by scanning electron microscopy. Natural chordae (A) and artificial chordae (B) show the two fused expanded polytetrafluoroethylene sutures (arrows). ( ~ 3 . before 5 29% reduction.)

After the disappointing results obtained with the triangular resection of the anterior mitral leaflet, two valuable techniques have been suggested for correcting ALC multiple rupture [7, 111: fixing the leaflet free edge to secondary chordae and transposition of posterior leaflet cusp and chordae. In both cases, almost normal strong chordae, adjacent or opposite to the damaged area, are required to obtain a satisfactory result; such chordae are not present in most degenerated valves. Moreover, the potential for progression of the disease of residual abnormal chordae

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Fig 4. Expanded polytetrafluoroethylene chordae (A) partially covered by growing fibrous tissue (arrows). ( ~ 2 before 5 29% reduction.)

has always been a concern. In the past, these factors caused multiple ALC rupture to be a contraindication to mitral valve repair [4, 6, 91. Postrheumatic calcification of ALC often results in restricted motion of the anterior leaflet even after a proper commissurotomy with papillary muscle splitting [4];only replacement of the calcified chordae would restore an adequate valve motion in these cases. The tendency of biological materials used for this purpose to stiffen [lo, 12-15] led us to be cautious about their use in this application. For these considerations we began a program to evaluate the feasibility of replacing ALC with artificial chordae.

The new ePTFE was chosen for the theoretical advantages connected with the microstructure of this material with its property of permitting attachment and infiltration of collagen cells and potential neointimal growth [16]. Vetter and co-workers [16] showed, however, that 2-0 and 3-0 sutures covered by a neofibrosa and neointima became thicker than natural chordae. Our experiments with 5-0 ePTFE sutures completely confirmed the previous findings with thicker sutures but yielded new chordae as flexible as the native chordae. With further independent experimental confirmation from Revuelta [17], we proceeded to clinical trials. At first, indications were limited Fig 5 . The sheet of neoendothelial cells covering the fibrous tissue is incomplete, resulting in a portion of exposed expanded polytetrufluoroethylene sutures (A).

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Table 3. €allow-up Patient No. 1 4 5 7 8 9 10 11 12

NYHA Months Class 18 25 20 15 15 7 6 3 2

111

I I I I I I1 I I

Two-Dimensional Echocardiography (6 mo) No incomp. No incomp. No incomp. No incomp. No incomp. No incomp. Mild incomp.

... ...

Valvar Area (cm2) MVR 2.8 2.2 2.5

3.0 2.6

3.0 2.8

... ...

Yes” No No No No No No No No

Eighteen months after operation owing to recurrent mitral regurgitation. MVR = mitral valve replacement; Incomp. = incompetence;

a

NYHA = New York Heart Association.

to y o u n g patients with degenerative pathology and multiple rupture of ALC. The preliminary reassuring findings i n these cases, a n d t h e report of similar clinical results by David [20], led us to extend the application to rheumatic

disease a s well when the stiffness of s o m e chordae maintained a restricted motion of t h e anterior leaflet after commissurotomy. Finally, the only postoperative failure in o u r series, which resulted from progression of degenerative disease, indicated a further application as support in patients with diffuse myxomatous chordal alterations. The relative ease of this technique does n o t result i n excessive ischemic time and allows t h e possibility of prompt valve replacement without excessive risk. The conventional limits i n mitral valve reconstruction can be pushed without increasing operative risk [21]. In o u r experience the intraoperative assessment of mitral valve function, performed by hydrodynamic tests a n d two-dimensional echocardiography, was shown to be reliable i n predicting postoperative results. So far, we have observed no failure of t h e artificial chordae i n clinical use u p to 30 months of follow-up. The early clinical experience using ePTFE as chordal replacement in rheumatic a n d degenerative mitral valve disease h a s been encouraging. Its use as a n adjunct t o t h e other maneuvers of mitral valve repair has m a d e it possible to retain valves that otherwise would have needed replacement. The laboratory investigation could not have been done without the technical skills of A. Leon, P. Bon, F. Rivera, and F. Wasserman. During the laboratory investigation, Dr C. Zussa was Research Fellow of the W. R. Heart Foundation at Albert Einstein College of Medicine, Bronx, New York.

References 1. Pakrashi BC, Mary DA, elMufti ME. Clinical and hemodynamic results of mitral annuloplasty. Br Heart J 1974;36:768. 2. Kay JH, Zubiate P, Mendez MA. Mitral valve repair for significant mitral insufficiency. Am Heart J 1978;96:253. 3. Reed GE, Pooley RW, Moggo RA. Durability of measured mitral annuloplasty. Seventeen year study. J Thorac Cardiovasc Surg 1980;79:349. 4. Shore DF, Wong P, Paneth M. Results of mitral valvuloplasty with a suture plication technique. J Thorac Cardiovasc Surg 1980;79:349. 5. Duran CG, Pomar JL, Revuelta JM. Conservative operation for mitral insufficiency. Clinical analysis supported by post-

6. 7. 8.

9. 10.

Fig 6. Clinical specimen from the only reoperated patient (see text for explanation). The artificial chordae (A) are still almost completely uncovered by fibrous tissue (B), demonstrating a slower rate of tissue overgrowth in comparison with experimental specimens.

11.

operative hemodynamic studies of 72 patients. J Thorac Cardiovasc Surg 1980;79:326. Carpentier A, Chauvaud S, Fabiani JN. Reconstructive surgery of mitral valve incompetence. Ten-year appraisal. J Thorac Cardiovasc Surg 1980;79:338. Carpentier A. Cardiac valve surgery-the ”French correction.” J Thorac Cardiovasc Surg 1983;86:32?-37. Duran CMG. Reconstructive procedures of the mitral valve including ring annuloplasty. In: Cohn LH, ed. Modern technics in surgery, 2nd ed. New York: Futura, 1979. Shore DF, Wong P, Paneth M. Surgical management of ruptured chordae. Thorax 1980;35:80. Frater RWM, Gabbay S, Shore D, Factor S, Strom J. Reproducible replacement of elongated or ruptured mitral valve chordae. Ann Thorac Surg 1983;35:14. Lessana A, Romano M, Lutfalla G, et al. Treatment of ruptured or elongated anterior mitral valve chordae by par-

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tial transposition of the posterior leaflet: experience with 29 patients. Ann Thorac Surg 1988;45:404-8. Frater RWM, Berghuis J, Brown AL, Ellis FH. The experimental and clinical use of autogenous pericardium for the replacement and extension of mitral and tricuspid valve cusps and chordae. J Cardiovasc Surg 1965;6:214. Bortolotti U, Gallo JI, Gabbay S. Replacement of mitral valve chordae with autologous pericardium in dogs. Thorac Cardiovasc Surg 1984;32:15. Gabbay S, Bortolotti U, Factor S. Calcification of implanted xenograft pericardium. Influence of site and function. J Thorac Cardiovasc Surg 1984;87782. Bortolotti U,Zussa C, Factor S, Frater RWM. Glutaraldehyde treated auto, homo and xenograft pericardium in atrial, mitral, aortic and pericardial applications. Life Support System 1986;4(Suppl 2):148.

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16. Vetter HO, Burack JH, Factor SM, Frater RWM. Replacement of chordae tendineae of the mitral valve using the new expanded PTFE suture in sheep. In: Bodnar E, Yacoub M, eds. Biologic bioprosthetic valves. New York: Yorke Medical Books, 1986:7724. 17. Revuelta JM. Discussion of [16], page 785. 18. Vetter HO, Factor SM, Frater RWM. The use of glycerdtreated homologous pericardium as a substitute for cusp and chordae tendineae of the mitral valve in sheep. Thorac Cardiovasc Surg 1986;3511. 19. Zussa C, Frater RWM, Galloni M. Expanded polytetrafluoroethylene as mitral valve chordae substitute. In: Proceedings of The Third World Biomaterials Congress, Kyoto, Japan, April 21-25, 1988. 20. David TE. Discussion of [ll]. Ann Thorac Surg 1988;45:408. 21. Frater RWM. Mitral valvuloplasty. Cardiac Chron 1987;2:1.

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