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Ann Thorac Surg 1999;67:1299-1303
© 1999 The Society of Thoracic Surgeons

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Original Articles

The CarboMedics "Top-Hat" supraannular prosthesis

^a Department of Cardiovascular Surgery, Hospital Universitario Valdecilla, Universidad de Cantabria, Santander, Spain
^b Department of Echocardiography, Hospital Universitario Valdecilla, Universidad de Cantabria, Santander, Spain

Accepted for publication November 3, 1998.

Address reprint requests to Dr Bernal, Cirugía Cardiovascular, Hospital Universitario Valdecilla, 39008 Santander, Spain

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. The CarboMedics "Top-Hat" supraannular prosthesis was designed to permit the implantation of a larger prosthesis.

Methods. Between June 1993 and November 1996, 127 patients (average age, 61.8 ± 10.2 years) received a CarboMedics "Top-Hat" supraannular aortic prosthesis. The average follow-up was 15.7 months, and all surviving patients underwent echocardiographic study. This group is compared with 656 patients in whom a standard CarboMedics prosthesis was implanted and also with 2,927 patients who received other aortic prostheses.

Results. Using the standard and the supraannular sizers, there was an average increase of one size in favor of the supraannular prosthesis: 18.9 ± 2.8 mm standard versus 20.8 ± 2.6 mm supraannular (p < 0.005). For each prosthesis size (19 to 23 mm), the body surface area of the patients in whom a CarboMedics supraannular prosthesis was implanted was significantly smaller than that in those who received a CarboMedics standard prosthesis or any other model. Hospital mortality was 3.9%, and late mortality was 5.5%. The actuarial survival was 86.5% ± 3.9% at 42 months.

Conclusions. Using the CarboMedics supraannular prosthesis allows implantation of a larger prosthesis compared with the standard CarboMedics prosthesis or other models. This advantage is especially important in patients with a small aortic root.

	Introduction

Top Abstract Introduction Material and methods Results Comment References

 
The diameter of the aortic valve is in direct proportion to the body surface area (BSA) of the patient. In general, BSA values lower than 1.7 m² are highly predictive of a small aortic root and thus indicate the need of a 19-mm prosthesis [1, 2]. In a Doppler echocardiographic study, González-Juanatey and colleagues [3] showed that various 19-mm prostheses of the latest generation result in substantial obstruction of the left ventricular outflow tract and less marked reduction in hypertrophy of the left ventricle compared with larger prostheses. Thus, the solutions to the problem of a small aortic root are to design a small prosthesis with better hemodynamics, to implant a larger prosthesis by aortic root enlargement, or to modify the sewing cuffs to take advantage of supraannular implantation.

The CarboMedics "Top-Hat" supraannular prosthesis (introduced in 1993) is a standard valve in which the cuff has been transferred to the inflow level of the valve. As a result, the prosthesis sits above the annulus rather than within it. The valve housing protrudes into the aortic root like a top hat. Here we describe our clinical and echocardiographic experience with this aortic prosthesis.

	Material and methods

Top Abstract Introduction Material and methods Results Comment References

 
In 1993, a prospective study was started to evaluate the "Top-Hat" prosthesis. Between June 1993 and November 1996, 127 patients underwent aortic valve replacement with the supraannular prosthesis. Of these 127 patients, 68 (53.5%) were women and 59 (46.5%) men. The average age was 61.8 ± 10.2 years (range, 28 to 81 years). In the preoperative period, 26 patients (20.5%) were in New York Heart Association class II, 79 (62.2%) were in class III, and 22 (17.3%) were in class IV. Primary valve replacement was performed on 92 patients (72.4%) and repeat valve replacement, on 35 patients (27.6%), 28 of whom had a previous aortic prosthesis in place. Seventy-six patients (59.8%) were in sinus rhythm, 50 (39.4%) were in atrial fibrillation, and 1 had a pacemaker (0.8%).

Hemodynamic and coronary angiographic examinations were done on 88 patients (69.3%). The remaining 39 patients (30.7%) were diagnosed by echocardiography exclusively. The left ventricular ejection fraction calculated by ventriculography ranged between 0.15 and 0.78 (average ejection fraction, 0.516 ± 0.122). On the basis of echocardiography, left ventricular function was considered normal in 29 patients and depressed in 10. Isolated aortic valvulopathy was diagnosed in 83 patients (65.4%), mitral and aortic valvulopathy in 40 patients (31.5%), and mitral, aortic, and tricuspid valvulopathy in 4 patients (3.1%). The aortic lesion was pure stenosis or a double lesion with preponderance of stenosis in 106 patients (83.5%) and insufficiency in 21 patients (16.5%). The cause of the valvular disease was degenerative or calcific in 63 patients (49.6%), rheumatic in 33 patients (26%), and active infectious endocarditis in 3 patients (2.4%); of the 28 patients (22%) with a previously placed prosthesis, 25 had structural deterioration of the bioprosthesis, and 1 each had valvular thrombosis, valvular dehiscence, and elective bioprosthesis explantation. Thirteen patients (10.2%) had concomitant coronary artery disease.

Surgical technique and valve measurement
The operation was performed with standard cardiopulmonary bypass and moderate hypothermia (28° to 30°C). Myocardial protection was achieved with intermittent blood cardioplegia, antegrade initially and retrograde as of January 1994. After aortic valve resection and decalcification of the valve root when necessary, both the standard sizer and the supraannular sizer were used in each patient. The aortic prosthesis was implanted in the supraannular position. Pledgets were placed in the ventricular surface of the native aortic ring and knots, in the aortic aspect of the prosthetic sewing cuff. In patients with low-lying coronary ostia or a narrow sinotubular junction, stitches were arranged in an imaginary plane at the level of the most distal point of the annulus of each aortic leaflet.

Forty 19-mm prostheses (31.5%) were implanted, 58 21-mm prostheses (45.7%), and 29 23-mm prostheses (22.8%). Forty-four patients had assoociated mitral valve procedures: mitral valve replacement with the CarboMedics standard prosthesis in 40 and mitral valve repair in 4. Four patients underwent associated tricuspid valve procedures: replacement with a Hancock II bioprosthesis in 1 and repair in 3. Associated myocardial revascularization with an average of 1.5 grafts per patient was performed in 13 patients.

The surviving patients were maintained on a regimen of Coumadin (crystalline warfarin sodium), with a recommended international normalized ratio ranging between 2.5 and 3.5. The ratio was modified according to the individual requirements of each patient during follow-up.

Doppler echocardiographic study was performed after discharge between postoperative months 1 and 42. In 91.3% of the survivors, this study was carried out 3 months or more after operation. All examinations were done with the patient in the left lateral decubitus position with simultaneous electrocardiographic recording. A commercially available echocardiograph with continuous wave (cw), pulsed wave (pw), and color Doppler capabilities (Vingmed 750) was used. All measurements were done on-line and recorded on VHS videotape for off-line analysis if necessary. Peak and mean gradients were calculated using the modified Bernoulli equation [4]: (V²₂, distal velocity; V¹₁, proximal velocity). Because of the usually narrow left ventricular outflow tract in these patients, special care was taken not to neglect V₁. Effective orifice area was obtained with the continuity equation: (A₂, orifice effective area of the prosthesis, A₁, left ventricle outflow tract area) [5–7]. Three consecutive beats in sinus rhythm and eight in atrial fibrillation were analyzed.

At the conclusion of follow-up, 90 (78.3%) of the 115 patients alive were studied at our center by the same observer, and 25 patients (21.7%) were followed in other hospitals by the referring cardiologists. Follow-up of the survivors was completed between October and December 1996. Follow-up ranged from 30 days to 42 months with an average time of 15.7 months and an accumulated follow-up of 175 patient-years. Follow-up was 100% complete.

Statistical analysis
The Patient Analysis and Tracking System database, Version 06.02.03 (Dendrite Clinical Systems, Inc, Portland, OR) was used. Values are shown as the mean ± the standard deviation. The Student t test was used for the comparison of quantitative variables. Actuarial curves were produced by the Cox actuarial method. The implanted prosthesis size study was done by comparing measurements obtained with the CarboMedics standard and "Top-Hat" sizers.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
Mortality and morbidity
Five patients (3.9%) died in the hospital, and 7 patients (5.5%) died late. The causes of the five hospital deaths were low cardiac output (n = 3), sepsis (n = 1), and pulmonary thromboembolism (n = 1). Of the late deaths, five were due to cardiac-related causes: unknown (n = 2), thromboembolism (n = 1), cardiac insufficiency resulting from dehiscence of a mitral valve prosthesis (n = 1), and prosthetic valve endocarditis treated medically, (n = 1). Two of the late deaths had noncardiac causes: cancer of the colon (n = 1) and cancer of the pancreas (n = 1). The overall actuarial survival was 86.5% ± 3.9% at 42 months (Fig 1). Excluding deaths from noncardiac causes, the actuarial survival was 88.9% ± 3.9% at 42 months of follow-up.

View larger version (19K): [in this window] [in a new window]   Fig 1. Actuarial survival curve at 42 months after operation.

Comparison of valve measurements
Figure 2 shows the comparison between the measurements obtained using the CarboMedics standard and "Top-Hat" supraannular prosthesis sizers. The average of values obtained with the standard sizers was 18.9 ± 2.8 mm and that obtained with the supraannular sizers, 20.8 ± 2.6 mm (p < 0.005). Of all 3,710 aortic valve replacements performed in our institution, 406 were reoperations involving a previous 19- to 23-mm aortic prosthesis of any type; the size of the prosthesis implanted and that of the prosthesis explanted were measured. The average size of the "Top-Hat" prosthesis implanted in the 28 patients with a previous aortic valve replacement was 20.7 ± 1.4 mm, and the average size of the prosthesis explanted was 20.9 ± 1.8 mm (p = not significant). Among the 656 patients in whom a CarboMedics standard prosthesis was implanted, 102 had had a previous aortic valve replacement. The average size of the implanted prosthesis was 21.7 ± 1.5 mm, and the average size of the explanted prosthesis was 23.5 ± 2.2 mm (p < 0.001). Of the 2,927 patients in whom an aortic prosthesis other than the CarboMedics standard or the "Top-Hat" was implanted, 276 had undergone aortic valve replacement previously. The average implanted prosthesis size was 21.1 ± 1.8 mm, and the average size of the explanted prosthesis was 22.9 ± 1.4 mm (p < 0.001).

View larger version (30K): [in this window] [in a new window]   Fig 2. Comparison between measurements obtained using CarboMedics standard and supraannular ("Top-Hat") aortic valve sizers.

	Comment

Top Abstract Introduction Material and methods Results Comment References

Another newer option is to modify the sewing cuff so as to create a supraannular prosthesis. This allows the use of a larger size than would be possible for a prosthesis implanted in the intraannular position. Initial experience with these sewing cuff modifications has been published [12–15]. One study analyzes the clinical and echocardiographic results in the largest published series to date with the "Top-Hat" prosthesis.

Analysis of the possible advantages of using prostheses designed specifically for supraannular implantation is complex. In our opinion, the use of sizers to determine prosthesis to implant is subjective. Forcing the use of a prosthesis a size larger than the correct size can cause serious complications, such as obstruction of the coronary ostia or dehiscence around the prosthesis, which are more frequent in cases of severely calcified aortic roots. The surgical technique of implantation of the CarboMedics supraannular valve is crucial to prevent complications such as ostial obstruction of coronary arteries or paraprosthetic leak.

In our experience since 1974, the problem of the small aortic root has been very evident in our patient population. Of the 3,710 aortic valve replacements performed, 27.3% of the patients had a BSA smaller than 1.60 m², which correlates directly with the 28.1% implantation rate of 19- and 21-mm prostheses. Of this 28.1%, 7.4% were 19 mm and 20.7%, 21 mm.

The comparison between the measurements taken with the CarboMedics standard and "Top-Hat" prosthesis sizers showed a significant difference of one size in favor of the "Top-Hat." Although this outcome agrees with that of Roedler and coauthors [15], some subjectivity may be involved. On the other hand, when an aortic prosthesis (mechanical or biological) is explanted, the native aortic root is severely fibrosed and rigid, and it frequently becomes necessary to implant a smaller-sized prosthesis. This was clear in our experience when the average size of the prosthesis implanted and that of the one explanted were measured. For the CarboMedics standard prosthesis or other prostheses, an average of one size is lost: 21.7 ± 1.5 mm and 21.1 ± 1.8 mm, respectively, for prostheses implanted and 23.5 ± 2.2 mm and 22.9 ± 1.4 mm, respectively, for those explanted (p < 0.001). In contrast, in this series, aortic valve prostheses averaging 20.9 ± 1.8 mm in size were explanted from 28 patients, and a "Top-Hat" prostheses of the same size, 20.7 ± 1.4 mm, were implanted (p = not significant). The similarity in sizes demonstrates the advantage of the supraannular implant.

The comparison of the average BSAs shows that patients with a "Top-Hat" prosthesis had a significantly smaller BSA for each of the three sizes (19, 21, and 23 mm) than that of patients for whom a CarboMedics standard prosthesis or other type of valve substitute was used. In practice, this means that BSAs being equal, a larger "Top-Hat" prosthesis can be used. These analyses must be looked at carefully because of the characteristics of the groups studied, although they do suggest that the use of a prosthesis designed specifically for supraannular implantation constitutes an especially interesting advantage in patients with small aortic roots.

The Doppler echocardiographic study was performed in most survivors (91.3%) 3 months or more after operation (range, 3 to 42 months). The data obtained do not differ significantly from those published by other groups [16, 17] for the CarboMedics standard prosthesis. As the mechanical part of the "Top-Hat" prosthesis has not been modified from the CarboMedics standard prosthesis, this finding is reasonable. The difference between the two prostheses does not affect the valve areas for each size, but it does allow the opportunity to implant a larger size in each patient.

Because of the number of patients and the length of follow-up, analysis of the clinical results in terms of mortality and morbidity contributes limited information. As the modification of the "Top-Hat" prosthesis alters only the sewing cuff, the clinical results should not vary in regard to those published for the CarboMedics standard prosthesis [18, 19]. In our experience, modification of the sewing cuff has not produced any incidence of paravalvular leak.

We conclude that in our experience, the CarboMedics supraannular "Top-Hat" prosthesis allows the implantation of a larger-sized prosthesis than would otherwise be possible. This option is especially valuable for patients with a small aortic root.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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6. Oh J.K., Taliercio C.P., Holmes D.R., et al. Prediction of the severity of aortic stenosis by Doppler aortic valve area determination: prospective Doppler-catheterization correlation in 100 patients. J Am Coll Cardiol 1988;11:1227-1234.[Abstract]
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