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J Thorac Cardiovasc Surg 1999;118:767-769
© 1999 Mosby, Inc.

LETTERS TO THE EDITOR

Mechanical mitral valves without long-term anticoagulation up to thirteen years

Department of Clinical Physiology^b
Thoracic Clinics
Karolinska Institute^a
Stockholm, Sweden

Servidores do Estado Hospital^c
Rio de Janeiro, Brazil

To the Editor:

If a mechanical valve could be left without anticoagulation, a continuous risk factor for severe bleeding, with an incidence of around 1% every year, could be avoided.

Ordinary Björk-Shiley Monostrut heart valves (Shiley, Inc, Irvine, Calif) were inserted in the mitral position in goats. After 1 year without anticoagulation, we found no instances of thrombosis on the pyrolytic discs or on the metal struts, but the suture rings in all cases were covered by an endothelialized layer of thrombus. From this layer a thrombus did protrude into the valve orifice in 8 of 9 goats.

View larger version (129K): [in this window] [in a new window]   Fig. 1. The microporous surfaced 25 mm mitral Björk-Shiley Monostrut heart valve after 2 years without anticoagulation in a goat. The valve is viewed from the left ventricle with the disc in the open position. The carbon-coated Teflon suture ring is covered with thin, smooth, glistening yellow endothelium extending over the groove and adjacent part of the valve flange.

In 1984 we started to implant the microporous surfaced mitral valve in goats. After 2 months without anticoagulation, the microporous area showed a homogeneous endothelialized surface with nutrition direct from the blood so that it stayed thin for more than 5 years. ³ The continuous covering from the suture ring went over the groove down in the valve, and after 5 years without anticoagulation the valve was still nicely covered and the goats produced offspring without problems. ³

The pilot study.
This microporous surfaced mitral valve prosthesis has the same strength as the Björk-Shiley Monostrut valve, ⁴ which has been implanted in about 140,000 patients during a 17-year period without any mechanical failures. We operated on a small group of 12 patients 11 and 13 years ago. ⁵ All these patients had sinus rhythm. There were 5 children aged 7 to 15 years with mitral insufficiency and cardiomegaly. ⁵ Patient 10 was cachectic and needed enteral nutrition for weeks before the operation. An 8-year-old boy (case 9) had a severe form of sickle cell anemia, with a hemoglobin S value of 95%, and required exchange transfusion before the operation. He died 3.8 years after the operation of a sickle cell crisis with joint hemorrhage. The valve was normal at autopsy. The second death (patient 12) occurred 4.4 years after the operation from the rupture of a mycotic cerebral aneurysm. The valve sounds were normal.

The entire surface was microporous in the 3 first patients (1, 2, and 3). In all others (patients 4-12) the contact area between the disc and the struts was polished. As soon as the chest tubes were removed, heparin was given together with warfarin until an effective level was reached. The heparin was then discontinued and the warfarin continued for 3 months, that is, until the endothelialization of the microporous surface was complete. The patient then remained in the hospital for 7 days during subcutaneous heparin treatment after warfarin was withdrawn. No anticoagulant has been given since for 11 to 13 years.

Cardiologists have performed the follow-up every third month for those living close to the hospital and once a year for the others. A Doppler echocardiogram (including transesophageal echocardiography) was performed in July 1995. The last clinical and echocardiographic follow-up examination was in the fall of 1998.

Results.
Not a single thromboembolic complication has been observed. Transesophageal echocardiographic Doppler investigation performed during the summer of 1995 did not show any thrombi. During the follow-up period, 9 pregnancies occurred. All surviving patients were followed up during the fall of 1998. Only patient 1 did not come to the clinic but was contacted by telephone. No thromboembolic episode had occurred. Patients 6 and 10 were in New York Heart Association class II and the remaining 8 patients were in class I. Patients 6 and 10 had moderate tricuspid regurgitation and patient 10 also moderate aortic regurgitation. No one else had any other significant native valvular dysfunction. All 10 survivors were in sinus rhythm and had normal kidney function. The follow-up results are summarized in Tables I and II.

The area adjacent to the suture ring is the important place to have a microporous surface to bind down the covering from the suture ring. After 11 to 13 years of follow-up of 12 patients with the Björk-Shiley Monostrut mechanical mitral valve with a microporous surface and without anticoagulation, 9 children have been born and no thromboembolic complications have been encountered.

Summary.
This microporous surface will be covered in 3 months by a thin, smooth, glistening endothelium, free from excrescence formation and fibrin precipitation, extending over the groove and adjacent part of the suture ring. Thus the thicker fibrous covering over the suture ring will be connected with the microporous covering. This will prevent a thrombotic protrusion into the valve orifice with risk for emboli. As the Monostrut valve has been accepted by the Food and Drug Administration after 16 years of successful clinical use, the results achieved from this pilot study indicate the necessity of a multicenter study, the outcome of which could solve valve surgery problems, especially for young girls.

References

1. MacGregor DC, Pilliar RM, Wilson GJ, et al. Porous metal surfaces: a radical new concept in prosthetic heart valve design. Trans Am Soc Artif Intern Organs 1976;22:646-53.[Medline]
   
2. Björk VO, Sternlieb JJ, Kaminsky DB. Optimal microporous surface for endothelialization of mitral valves in the blood stream. Scand J Thorac Cardiovasc Surg 1990;24:97-100.[Medline]
   
3. Björk VO, Kaminsky DB. The five-year evaluation of a mechanical heart valve without anticoagulation in goats. J Thorac Cardiovasc Surg 1992;104:22-5.[Abstract]
   
4. Björk VO, Henze A, Lindblom D. The Monostrut strength. Scand J Thorac Cardiovasc Surg 1985;9:13-9.
   
5. Björk VO, Ribeiro A, Canetti M, Bomfim V. Mitral mechanical valve without long-term anticoagulation. Scand J Thorac Cardiovasc Surg 1994;28:19-24.[Medline]
   

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