Asian Cardiovasc Thorac Ann 2000;8:333-338
© 2000 Asia Publishing EXchange Pte Ltd
Prosthesis Size in Aortic Valve Replacement: Surgeon-Related Variable
Shiv Kumar Choudhary, MCh,
Alok Mathur, MS,
Panangipalli Venugopal, MCh,
Balram Airan, MCh,
Rajesh Sharma, MCh,
Anil Bhan, MCh,
Anita Saxena, DM,
Arkalgud Sampath Kumar, MCh
Department of Cardiothoracic and Vascular Surgery
Cardiothoracic Sciences Centre
All India Institute of Medical Sciences
New Delhi, India
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For reprint information contact: Arkalgud Sampath Kumar, MCh Tel: 91 11 686 4851 Ext. 4843 Fax: 91 11 686 2663 email: askumar{at}medinst.ernet.in Department of Cardiothoracic and Vascular Surgery, Cardiothoracic Sciences Centre, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India.
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Abstract
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A retrospective analysis was performed to determine the surgeon's impact on the selection of the size of prosthesis in aortic valve replacement. From January 1993 through December 1997, 748 patients underwent either isolated aortic valve replacement (530) or double valve replacement (218) with bileaflet valves. Depending on the operating surgeon, patients were divided into group A (367) or group B (381). Preoperative, intraoperative, and postoperative variables in both groups were compared. Groups A and B were identical in demographic and clinical profiles. Cardiopulmonary bypass time, ischemic time, and early and late results in both groups were similar. Significantly more patients undergoing isolated aortic valve replacement in group A (169; 67.9%) received a large (
25 mm) prosthesis compared with group B (69; 24.5%). Compared with group B, a large prosthesis was used in a significantly greater proportion of all patients in group A, irrespective of etiology, predominant aortic valve lesion, and age of the patient. Overall, the operating surgeon was identified as the most important predictor (odds ratio 3.5; p < 0.0001) of use of a large valve.
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Introduction
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A number of reports have demonstrated significant resting and exercise-induced gradients across aortic valves when small prostheses (19 to 23 mm) have been implanted.1–4 Moreover, the prognosis is less favorable for patients with a small prosthetic valve than for those with a larger one.5–8 Considering the natural valve area as the optimum, the area of a prosthesis should be as close as possible to the natural valve area to provide the best hemodynamic performance and prognosis.9 The mean aortic valve area in Western adults is reported to be 4.6 ± 1.1 cm2 and this corresponds to a St. Jude Medical aortic prosthesis of 27 to 31 mm.10 However, in most reported series, valves of these sizes were used infrequently, especially in patients with aortic stenosis.11–16 This study was designed to analyze various factors that might influence selection of the size of prosthesis to be implanted.
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Patients and Methods
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A retrospective analysis was carried out on 748 patients who underwent aortic valve replacement (AVR) at our center from January 1993 through December 1997. In addition, 300 cadaveric hearts were studied to assess the dimensions of the aortic root in the Indian population. The patients were divided in 2 groups: group A comprised 367 patients who were operated upon by a single surgeon; group B was 381 patients who were operated upon by other surgeons in the same department. The demographic and clinical profile of the patients is shown in Table 1
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A mid-sternotomy approach and standard cardiopulmonary bypass with aortic and two-stage cavoatrial or bivenous cannulation were used in both groups. Antegrade cold blood hyperkalemic cardioplegia with topical cooling was employed in all cases. A St. Jude Medical aortic prosthesis (St. Jude Medical, Inc., St. Paul, MN, USA) was chosen to replace the diseased valve. The technique of aortic valve replacement was essentially the same in both groups and the prosthesis was inserted into the annulus using simple interrupted or pledgeted mattress polyester sutures. Root enlargement procedures were not performed in any patient. In group A, 249 patients underwent isolated AVR and 118 had both the aortic and mitral valves replaced. In group B, 281 patients required isolated AVR and 100 had double valve replacement (DVR).
Postoperative blood loss and the incidence of reexploration were recorded in both groups. All patients were given acenocoumarin after removing the drainage tubes. Anti-coagulation was monitored by prothrombin time and more recently, by the International Normalized Ratio (INR). Patients were followed up clinically and radiologically. Periodic cinefluoroscopy was performed routinely in all patients. Echocardiographic examination was carried out only when valve dysfunction or paravalvular leak was suspected. The definitions of events and the methods of analyzing the results followed the guidelines for reporting morbidity and mortality after cardiac valve operations proposed by the Society of Thoracic Surgeons.17
Cadaveric Study
Aortic homografts were obtained from 300 cadaveric donors. Donors ranged from 2 to 59 years of age and 245 were male. These were apparently healthy people in whom causes of death were various forms of trauma. After dissecting the aortic homograft, the internal diameter of the aortic annulus was measured with a graduated conical sizer.
Statistical Analysis
All interval-related variables were expressed as mean ± standard deviation. The 2 groups were compared using the chi-squared and unpaired Student's t tests or the Mann-Whitney U test; a p value of less than 0.05 was considered significant. The use of a large valve (25 mm) in various subgroups was compared using the chi-squared test; a p value of less than 0.05 was considered significant. Multivariate logistic regression analysis was used to define a subset of variables that were independently predictive of the use of a large prosthesis. Results were expressed as odds ratios on the use of a large prosthesis, with the 95% confidence interval. SPSS statistical software (SPSS, Inc., Chicago, IL, USA) was used for analyses.
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Results
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Both groups were identical in demographic and clinical profiles (Table 1
). In group A, the mean aortic crossclamp and cardiopulmonary bypass times for AVR were 48 ± 10.4 min and 58.4 ± 12.6 min, whereas in group B, these were 50.2 ± 16.8 min and 60.8 ± 18.2 min, respectively. In patients undergoing DVR, mean aortic crossclamp and cardiopulmonary bypass times were 67.2 ± 10.6 min and 84.0 ± 11.6 min in group A, and 70.8 ± 15.7 min and 88.3 ± 16.8 min in group B.
There were no significant differences between the groups in terms of early mortality or morbidity; there were 6 early deaths in group A and 8 in group B. None of the deaths were related to the valve prosthesis. Blood loss was 340 ± 180 mL (range, 90 to 1,340 mL) in group A and 316 ± 210 mL (range, 60 to 1,180 mL) in group B (p > 0.50). Ten patients in groups A and 13 in group B were reexplored for excessive bleeding. Follow-up ranged from 14 to 73 months (mean, 36 ± 14.8 months) and it was 94% complete. Linearized rates of valve-related complications in both groups are shown in Table 2; the complication rates were not statistically different.
In group A, 169 patients (68%) with isolated AVR and 31 (26%) with DVR received a prosthesis sized 25 mm or larger; in group B, 69 patients (25%) with AVR and 27 (27%) with DVR received a large prosthesis (Tables 3 and 4). Thus, a significantly greater proportion of patients in group A undergoing AVR received a large prosthesis compared to group B, but the difference was not significant in patients undergoing DVR. A large prosthesis was used significantly more frequently in group A, irrespective of age, etiology, and predominant physiological aortic valve lesion (Table 5). Even patients with severe aortic stenosis received a large prosthesis significantly more often in group A (Table 5). Similarly, more patients with nonrheumatic etiology received a large prosthesis in group A (Table 5). However, the proportion of patients in group A with severe aortic stenosis receiving a large prosthesis was significantly less than those with severe aortic regurgitation (41% versus 68%).
Various determinants of the use of a large valve, including operating surgeon, etiology, predominant valvular lesion, and the procedure (AVR versus DVR) were analyzed in the whole patient population. The operating surgeon was the most important determinant of the use of a large valve (odds ratio, 3.5; 95% confidence interval, 2.6 to 4.8; p < 0.0001). The presence of aortic stenosis (p < 0.001) and associated mitral valve disease (p < 0.001) were negative predictors of the use of a large valve.
Cadaveric Study
Age and sex-related diameters of aortic homografts are shown in Table 6. The mean diameter in adult males (aged 16 to 60 years) was 23.2 ± 1.9 mm; in adult females (aged 16 to 45 years) it was 21.2 ± 2.5 mm. These correspond to valve areas of 4.2 cm2 (range, 3.6 to 4.9 cm2) and 3.5 cm2 (range, 2.8 to 4.4 cm2), respectively.
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Discussion
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The ideal prosthesis should have an area equal to or more than the area of the natural value.9 Clinically important gradients across smaller valves and a poorer prognosis have been well documented.1–8 Although there may be marked symptomatic and hemodynamic improvement after valve replacement with a small prosthesis, a patient-prosthesis mismatch exists.9 Therefore, a larger prosthesis is more physiological and gives a better prognosis.5–9 Based on our observations of aortic root dimensions in cadavers, and considering the reported dimensions of the aortic root, valve prostheses of 25 mm to 31 mm can be considered to match native valves in terms of area.10
In this study, early and late valve-related complications were not statistically different between the groups. However, the functional capacities of the patients were not assessed so valve performance was not determined. Other investigators have convincingly demonstrated better hemodynamics, thus better prognoses, with larger valves.5–9 Similarly, the impact of the size of the prosthetic valve on long-term survival could not be assessed with the available data, which may be an important consideration.
There are several factors that contribute to the selection of the size of prosthesis. This experience has shown that the operating surgeon is an important factor, as reported by others.11–16,18,19 In this series, only associated mitral disease, especially mitral stenosis, precluded the use of a large prosthesis. The study on cadaveric hearts showed that the dimensions of aortic valves in the Indian population are similar to those of the Western population.10 However, when the findings in group A are compared with published results, a higher proportion of these patients received a large prosthesis.4–16 The mean aortic diameter (23.2 ± 1.9 mm) of Indian adult males corresponds to a St. Jude Medical aortic valve of 25 to 31 mm. Thus, the larger prostheses are closer to the size of the natural valve.
Although the surgical techniques of valve insertion were essentially the same in both groups, there were a few minor technical differences that might have helped the surgeon in group A to insert a larger prosthesis. A com-paratively low aortotomy incision was used in group A patients; the aortotomy incision was started approximately 5 mm above the right coronary ostium. On the right side, the incision was extended into the noncoronary sinus to 5 mm from the aortic annulus. This incision gave an excellent and unobstructed exposure of the aortic valve. Before excising the diseased aortic valve, a 2/0 polyester stay-suture was passed through each commissure and strong traction was applied. This delivered the valve at the level of the aortotomy and permitted complete excision and decalcification of the valve. Calcification was removed manually in a piecemeal fashion and it was possible to debride the annulus completely in all cases. A thickened fibrous layer covering the endocardium of the left ventricular outflow tract, especially the ventricular surface of the anterior mitral leaflet, could be peeled off in most cases, avoiding the possibility of a subvalvular gradient. An optimal number of simple interrupted sutures were used; 18 to 21 sutures for a 25-mm prosthesis. After placing all sutures, the prosthesis was lowered into the left ventricular outflow tract and the sutures were tied, starting with the 3 commissural sutures, followed by those at the right coronary-noncoronary commissure, and proceeding in an anti-clockwise fashion. When in doubt about the most appropriate size of prosthesis, a graduated conical sizer provided correct sizing of the valve annulus.
As to why surgeons might choose a small prosthesis, some investigators have reported mechanical problems with larger valves and discouraged their use.19,20 However, these problems occurred with tilting-disc valves and there have been no reports of similar problems with bileaflet valves. Excessive hemorrhage and left-ventricular-aortic disruption have also been considered a possibility with a large prosthesis, but our experience has shown that bleeding and valve-related complications in both groups were similar, thus both small and large prostheses are equally safe. It was concluded that the surgeon is an important factor in determining the size of the prosthesis and with a conscientious approach, a larger and hemo-dynamically superior prosthesis could be inserted in a greater proportion of patients.
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Acknowledgments
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We gratefully thank Mr. Rajvir Singh, MSc (stat) for the statistical analysis.
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References
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Abstract
Introduction
