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Clinical Outcomes–Valves

Mechanical Valve Replacement in Congenital Heart Defects in the Era of International Normalized Ratio Self-Management

Reiss, N; Blanz, U; Bairaktaris, H; Koertke, A; Körfer, R

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doi: 10.1097/01.mat.0000176119.56534.90
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Abstract

Although conservative surgery is the preferred treatment for valvular lesions in congenital heart defects, valve replacement is sometimes unavoidable. Early calcification and valvular dysfunction of bioprostheses implanted in congenital heart defects have made the use of mechanical prostheses for this particular group more acceptable to cardiac surgeons. Thromboembolism continues to be a major problem after insertion of mechanical valves. The risk of thromboembolism is reduced through treatment with oral anticoagulants, and yet with the newer valves, it is still 1.5% in aortic position and 3% in mitral position.1,2 Hemorrhage rates vary from 4.2% to 15.4% per patient-year depending on the quality of the anticoagulation.1 The incidence of thrombotic events is higher when a mechanical heart valve is implanted in pulmonary or tricuspid position, representing the larger number in congenital heart defects.

The purpose of this study was to evaluate the efficacy and complications of anticoagulant therapy in patients with congenital heart defects receiving mechanical valve prosthesis. Anticoagulation therapy was performed using dicumarol (Marcumar) and subsequent international normalized ratio (INR) self-management.

Patients and Methods

Since February 1994, when INR self-management was introduced in daily clinical routine, 68 patients (33 males, 35 females; mean age, 21 years; range, 5 months to 61 years) were long-term survivors after mechanical valve replacement for congenital heart defects. Of these patients, 16 patients were younger than 6 years, 19 were younger than 18 years, and 33 were older than 18 years at the time of valve replacement. Underlying disease was tetralogy of Fallot in 33 cases, morbus Ebstein in 4 cases, atrioventricular septal defect in 13 cases, transposition of the great arteries in 10 cases, congenitally corrected transposition in 3 cases, and truncus arteriosus communis in 5 cases. Thirty-two patients underwent isolated pulmonary valve replacement, 5 patients isolated aortic valve replacement, 15 patients replacement of the left atrioventricular valve, and 7 patients replacement of the right atrioventricular valve. Nine patients had double valve replacement (four of the aortic and pulmonary valve, two of the left and right atrioventricular valve, one of the pulmonary and right atrioventricular valve, and of the two aortic and left atrioventricular valve). In 46 patients (68%), valve replacement was performed on the right side of the heart.

In 61 of 68 patients (89.7%), valve replacement was a reoperation. St. Jude Medical valve prostheses were implanted in 40 patients; the remaining 28 patients received Carbomedics prostheses. The mean diameter of prostheses implanted in aortic position was 25.3 mm, in left atrioventricular position 26.4 mm, in pulmonary position 23.1 mm, and in right atrioventricular position 30.6 mm.

Anticoagulation Management

Permanent oral anticoagulation after mechanical heart valve replacement was performed using dicumarol (Marcumar). The intended INR value was 1.8–2.8 after aortic valve replacement and 2.5–3.5 after mitral, pulmonary, and tricuspid valve replacement. INR values were determined three or four times per week during the first 6 weeks after operation and after reaching target range one time per week.

All patients and/or their parents were trained in INR self-management 6–11 days after the operation. After successful training, each of them received a coagulation monitor (initially Biotrack from the Ciba Coming company, later to be renamed CoaguCheck; Roche Diagnostics Gmbh, Mannheim, Germany). A booster training was performed 6 months later. In our clinic, there is 24-hour/day hotline support that includes personal care and consultation.

Determination of INR Value

A finger puncture was made by a dedicated puncture device to release a small sample of capillary whole blood (approximately 25 μl) placed on a test strip (CoaguCheck PT-test, Roche Diagnostics Gmbh), which is inserted in a portable CoaguCheck analysis apparatus. After less than 2 minutes of analysis, the INR value was presented in the apparatus display. The test strip contains iron oxide particles, which are incorporated on the strip together with rabbit brain thromboplastin (International Sensitivity Index value = 1.0). Blood contact with the thromboplastin triggers the coagulation cascade. The instrument measures the time from the first contact of the blood sample with thromboplastin to the completion of coagulation process and converts this measure to the INR value. The claimed INR-measuring range is 0.7–13.0. The physical measures of the apparatus (height × width × depth) are 5.6 cm × 14 cm × 22 cm, and the weight (including batteries) is 600 g.

To aid review of the data, the CoaguCheck apparatus has a facility to store the previous 30 INR values. These can be downloaded to a personal computer via an adapter cable or reviewed in the apparatus display. Time and date are stored along with the INR value.

Each production lot of test strips is calibrated separately by the manufacturer. To assure consistent data, each package of test strips is accompanied by a calibration code chip that is inserted into the apparatus front end. The patient evaluates the equipment’s performance quality by through periodic analysis of a standardized control solution dripped onto a test strip.

Incidence of Thrombotic Events

The mean follow-up period after mechanical heart valve replacement was 72 months (range, 6–132 months; 409 patient-years). In this time interval, valve thrombosis developed in 3 of the included 68 patients (4.4%).

Case 1.

At the age of 6 months, the patient underwent Blalock-Taussig shunt operation in tetralogy of Fallot and pulmonary atresia. At the age of 4 years, a Waterstone anastomosis was performed. One year later, a homograft was implanted. One year after that, a St. Jude Medical prosthesis with a diameter of 21 mm was implanted in pulmonary position. One year later, a first valve thrombosis led to surgical revision and thrombectomy. The next 5 years were uneventful. At the age of 12 years, valve thrombosis occurred again, though the last measured INR values ranged between 2.7 and 4.3. A successful rtPA lysis was performed. During the clinic stay, a heterozygote Factor V mutation was identified.

Case 2.

At the age of 10 months, surgical correction of tetralogy of Fallot was performed. After a period of about 4 years, pulmonary valve replacement (St. Jude Medical 23 mm) was necessary because of progredient dilatation and dysfunction of the right ventricle. At the age of 8 years, a subvalvular stenosis was resected. Valve thrombosis developed only 6 months later. The INR value after admission was 1.4. The thrombosed valve was explanted and a Carbomedics valve (diameter of 23 mm) was implanted. Thereafter the course was uneventful over a 6-year period.

Case 3.

The diagnosis of tetralogy of Fallot was made after birth and surgical correction was performed after 7 months. At the age of 8 years, a St. Jude Medical prosthesis (23 mm) was implanted in progredient right ventricular dilatation and dysfunction. After 6 years without complications, valve thrombosis developed and was successfully treated by thrombolysis. Unfortunately, 6 months later, a new valve thrombosis occurred (INR 3.0 during admission). Therefore, the mechanical heart valve was explanted and a bovine Contegra conduit (22 mm) was implanted. Technical examination showed a defect of the CoaguCheck device.

Discussion

Advances in operative techniques have made successful repair of failing valves in congenital heart defects possible for many patients, but sometimes valve replacement is the only solution. Mechanical prostheses, favored by most cardiac surgeons because of their durability, present a risk of thromboembolism and require permanent anticoagulation. Controversy still exists regarding the form of anticoagulation to use in patients with congenital heart defects after mechanical valve replacement.

Valid studies to find an appropriate anticoagulation intensity, i.e., an intensity that results in the lowest possible morbidity (thromboembolic and hemorrhagic complications), are not available to date in congenital heart defect patients after mechanical valve replacement. Current recommended therapies in this field are therefore largely empirically based. The previously available studies also omit inclusion of INR self-management and its goal of improved therapy compliance as the basis for stable anticoagulation intensity.

The so-called ESCAT study (Early Self-Controlled Anticoagulation Trial), started in February 1994 in our clinic, has shown the superiority of INR self-management in patients with aortic, mitral, or aortic/mitral valve replacement. Introduction of this anticoagulation regimen led to a highly significant improvement in the quality of the anticoagulation controls. Nearly 80% of the INR values submitted by the self-management group were within the ideal therapeutic range, compared with just 62% of values submitted by the practitioner-controlled group.3

Furthermore, all patients (and/or their parents) undergoing mechanical valve replacement in congenital heart defects in our clinic were also introduced in INR self-management beginning in February 1994. Self-management is an attractive feature for young patients (the mean age in this study was 21 years) receiving lifelong anticoagulation treatment, because the conventional treatment requires frequent blood sampling to allow proper dosage adjustment.

One important factor is whether the mechanical valve is implanted in the left or right side of circulation. Of the total number of prosthetic cardiac valves placed, those required on the right side of the heart comprise a small percentage.4 In contrast, in the population with congenital heart defects, more patients receive mechanical heart valves on the right side. The percentage in the present study was 68%.

Experience with the low-profile St. Jude Medical valve and the Carbomedics valve has shown that the incidence of valve thrombosis is relatively rare in comparison with other types of mechanical valve prosthesis.5 However, use of these prostheses as a pulmonary or tricuspid substitute has a higher risk for prosthetic thrombosis compared with that in the left-sided position.6,7 In our study, the pulmonary valve was replaced in 37 of 68 cases. Valve thrombosis developed in 3 of 37 patients (8.1%) under the INR self-management regimen after a mean follow-up of 3.5 years. The underlying disease in these three patients was tetralogy of Fallot. These results represent a significant improvement compared with previous reports. Miyamura et al.8 reported that the prostheses thrombosed in two of five patients with a St. Jude Medical prosthesis in the pulmonary position after tetralogy of Fallot repair. Fyfe and associates9 reported the same findings in three of six patients with tetralogy. Anticoagulation in these studies was performed using salicylate and/or dipyridamole. From these and other earlier studies, it was concluded that the St. Jude Medical prosthesis is unsuitable for use in pulmonary position. In our opinion, implantation of a St. Jude Medical valve or a Carbomedics valve in pulmonary position is a good therapy option when INR self-management with improved anticoagulation stability is used.

We found no severe thrombotic events during follow-up in patients with implantation of mechanical heart valves in the aortic, left atrioventricular, and right atrioventricular positions, which is remarkable—especially for the right atrioventricular position—and may be an indicator of good-quality anticoagulation control using INR self-management. Whereas anticoagulation using dicumarol or warfarin is commonly accepted for the mitral and tricuspid position, the optimal anticoagulation for patients with aortic valve replacement in congenital heart defects is still controversial. Rao et al.10 found a lower incidence of complications in a group of patients treated with salicylate plus dipyridamole compared with a group treated with warfarin; nevertheless, the linearized rates were not significantly different. Therefore, the investigators recommended only antiplatelet drugs as the therapy of choice after aortic valve replacement in the pediatric and adolescent group.

It is our current policy to use dicumarol with an intended INR value of 1.8–2.8 in patients with mechanical aortic valve replacement in congenital heart disease. The improved anticoagulation stability may permit this strategy with a lower intended INR range.11

Conclusion

Mechanical valve replacement in congenital heart defects is a good therapy option with a low incidence of thrombotic events in the era of INR self-management. Compared with the use of porcine xenografts with early fibrocalcific degeneration and the need for a third or fourth operation, it seems to be the preferable procedure. The operative risk is very low in this group, with a high percentage of redo procedures. Acceptance of INR self-management is good. The incidence of valve thromboses is acceptable with dicumarol anticoagulation therapy, especially when the valve is implanted in the right side of circulation. Our experience indicates that fibrinolytic treatment may be reasonable for a first thrombotic episode. The surgical approach, which is effective and has a low operative risk, is advisable in patients in whom recurrent thrombosis develops.

References

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Copyright © 2005 by the American Society for Artificial Internal Organs