Ann Thorac Surg 2002;74:1120-1124
© 2002 The Society of Thoracic Surgeons
Original article: cardiovascular
A comparison of the in vivo performance of the 19-mm St. Jude medical hemodynamic plus and 21-mm standard valve
Hiroshi Niinami, MD, PhDa*,
Shigeyuki Aomi, MDa,
Hideyuki Tomioka, MDa,
Kiyoharu Nakano, MDa,
Hitoshi Koyanagi, MDa
a Cardiovascular Surgery, The Heart Institute of Japan, Tokyo Women’s Medical University, Tokyo, Japan
Accepted for publication June 12, 2002.
* Address reprint requests to Dr Niinami, Department of Cardiovascular Surgery, Daini Hospital, Tokyo Women’s Medical University, 2-1-10 Nishiogu, Arakawa-ku, Tokyo 116-8567, Japan.
e-mail: niinamca{at}dnh.twmu.ac.jp
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Abstract
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BACKGROUND: In the present study we analyzed the in vivo performance of the 19-mm St. Jude Medical Hemodynamic Plus aortic prosthesis (19HP), evaluated the midterm performance of 19HP in the aortic position, and compared the implantability and hemodynamic characteristics of this valve with those of the 21-mm standard St. Jude Medical valve (21SD) in adult patients with aortic stenosis and a narrowed aortic annulus.
METHODS: From February 1994 to December 1999, 60 patients who underwent isolated aortic valve replacement with either the 19HP (n = 31) or the 21SD (n = 29) were studied. Comparison between the two models included analysis of early and late mortality and morbidity. Pre- and postoperative echocardiography was performed in all patients to evaluate and compare the hemodynamic performance of both prosthetic valves. The postoperative serum lactic dehydrogenase activity was measured in both groups of patients as an indicator of hemolysis.
RESULTS: The mean body surface area was 1.46 ± 0.16 m2 in the 19HP group and 1.49 ± 0.13 m2 in the 21SD group (p = 0.1577). Other than female dominance in the 19HP group, there was no statistically significant difference between the two groups in terms of preoperative variables (age, preoperative pressure gradients, and New York Heart Association functional class). The average postoperative peak pressure gradient was 23.3 ± 10.5 mm Hg in the 19HP group and 27.9 ± 9.9 mm Hg in the 21SD group (p = 0.0666). There was no hospital death in either group. Six-year follow-up was completed in both groups of patients. Late death occurred in 1 patient in the 19HP group (1.09% per patient-year). Actuarial survival at 6 years was 92.3% ± 7.4% in the 19HP group, and 100% in the 21SD group (p = 0.33). The linearized complication rate was 1.09% per patient-year and 1.02% per patient-year for thromboembolism, and 1.09% per patient-year and 1.02% per patient-year for anticoagulant-related hemorrhage in the 19HP group and the 21SD group, respectively. Freedom from all complications at 6 years did not show any significant difference between the two groups (p = 0.54). Although left ventricular mass indices decreased significantly after aortic valve replacement in both groups (19HP group, p = 0.0002; 21SD group, p = 0.0006), there were no significant differences in the two indices between the groups after aortic valve replacement (p = 0.999). There was no significant difference in the lactic dehydrogenase level between the two groups (p = 0.4915).
CONCLUSIONS: In vivo hemodynamic performance of the 19HP valve as well as the early and intermediate clinical outcome up to 6 years was satisfactory and corresponded closely to that of the 21SD valve in adult patients. The 19-mm Hemodynamic Plus model can be recommended in patients with a measured 19-mm annulus and this valve will minimize the need for the aortic annular enlargement procedure.
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Introduction
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Surgical management for patients with a small aortic annulus remains controversial. To avoid residual left ventricular outflow obstruction, a variety of techniques have been recommended to permit the insertion of a larger prosthesis. Insertion of a smaller aortic prosthesis without an annular enlargement procedure may be associated with a lower operative risk but may result in residual left ventricular outflow obstruction.
The St. Jude Medical Hemodynamic Plus valve (St. Jude Medical, Inc, St. Paul, MN) represents an interesting innovation, allowing a larger valve orifice area with an equivalent tissue annulus diameter. In this new model the sewing cuff of the valve and its attachment to the valve ring have been redesigned to achieve an effectively larger valve orifice with an equivalent tissue annulus diameter (Table 1).
The internal orifice area of the 19-mm St. Jude Medical Hemodynamic Plus valve (19HP) (2.06 mm2) is the same as that of the 21-mm standard St. Jude Medical standard valve (21SD). Theoretically, the 19HP valve produces less pressure loss across the valve than the 21SD valve because the 19HP valve has a more effective orifice-to-annulus ratio than the 21SD valve (0.73 versus 0.58). An in vitro study also revealed the superiority of the 19HP in terms of forward flow pressure drops and energy losses with a small aortic root [1].
The purpose of this study was to evaluate and compare the clinical and hemodynamic performance of the 19-mm St. Jude Medical Hemodynamic Plus and 21-mm St. Jude standard valves implanted in the aortic position for aortic stenosis.
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Patients and methods
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In vivo hemodynamic performance of the 19HP was evaluated and compared with that of the 21SD. Between February 1994 and December 1999, 60 patients who underwent isolated aortic valve replacement (AVR) with either 19HP (n = 31) or with 21SD (n = 29) were studied. The patients’ characteristics are shown in Table 2.
The two groups of patients were almost identical, except that there were more women in the 19HP group than in the 21SD group. In this study, patients who underwent other associated procedures at the same time as AVR or who required annular enlargement for AVR were excluded. Also, patients with pure aortic regurgitation receiving either the 19HP or 21SD were excluded, therefore all patients had predominant aortic stenosis; concomitant aortic regurgitation was observed in 3 patients (9.7%) undergoing AVR with the 19HP and in 4 (13.8%) undergoing AVR with the 21SD (p = 0.6197). Furthermore, patients with renal failure on hemodialysis, hepatic disease, or any kind of hematologic disorder were excluded to avoid interference between valve-related hemolysis and red blood cell damage caused by the other disease.
Operative techniques
Cardiopulmonary bypass was established using moderate hemodilution (hematocrit 20% to 25%) and systemic hypothermia (28° to 32°C). Multidose cold crystalloid or blood potassium cardioplegic solution was used for myocardial protection. After meticulous debridement of the valve annulus, it was measured with a snugly fitting sizer. No patients underwent annular enlargement. All valves in both groups were implanted in the intra-annular position. Pledgeted horizontal mattress sutures were placed from above downward to evert the valve annulus. The hinge area was placed at the commissure between the right and noncoronary cusps, toward the commissure between the left and noncoronary cusps.
Study protocol
Postoperative echocardiography was performed 3 to 4 weeks after operation in each patient. The interval between surgical intervention and follow-up Doppler evaluation ranged from 2 to 56 months (mean, 25.1 months) in the 19HP group and from 5 to 65 months (mean, 27.5 months) in the 21SD group. Echocardiography was performed using a Hewlett-Packard Sonos ultrasound imaging system with a 2.5-MHz phased array transducer (Hewlett-Packard, Inc, Andover, MA). Standard apical, parasternal, and subcostal views were obtained. The following factors were measured pre- and postoperatively and during the follow-up: left ventricular end-diastolic dimension (LVDd) and end-systolic dimension (LVDs); interventricular septal thickness (IVST) and posterior wall thickness (LVPWT); and maximum flow velocity across the valve. Then, ejection fraction (EF) [2], percent fraction shortening (%FS), and left ventricular mass index (LVMI) [3] were calculated as follows:
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where BSA is body surface area. All calculations were the average of three cardiac cycles. The maximum valve gradient was calculated by means of the modified Bernoulli equation.
Serum lactic dehydrogenase (LDH) activity was measured at 4 weeks postoperatively as an indicator of hemolysis.
All patients were treated with oral warfarin sodium starting from the second postoperative day. Prothrombin activity was kept between 20% and 30%, which approximately equals the international normalized ratio between 2.5 to 3.5.
Follow-up and statistical analysis
After hospital discharge, each patient was seen in the outpatient clinic or contacted by telephone on a regular basis. For this report, all patients were contacted again between January and February 2000. The mean follow-up period was 2.92 years (range, 7 to 72 months) and totaled 91.3 patient-years in the 19HP group and 3.33 years (range, 2 to 72 months) and 97.7 patient-years in the 21SD group (p = 0.45). Follow-up was complete (100%) in both groups of patients. Registration of any complications was done according to published guidelines of The Society of Thoracic Surgeons for valve operation [4].
Statistical analysis was performed using the StatView (version 5.0) software package (SAS Institute Inc, Cary, NC). Categorical values of the two groups were compared by using 
2 or Mann-Whitney U tests, whereas continuous variables were compared by using Wilcoxon signed-rank test. Data are expressed as mean ± one standard deviation unless otherwise indicated. Actuarial estimates were calculated using the Kaplan-Meier technique and reported with the standard error of the estimate, and comparisons of these estimates were performed with the Mantel-Cox (log-rank) test. A statistical probability of less than 0.05 was considered as indicating significance.
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Results
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There was no hospital mortality in either group of patients. One patient in the 19HP group died during the follow-up period. This late mortality expressed as a linearized rate was 1.09% per patient-year. The cause of death was sudden death. Six-year actuarial survival did not show any significant difference between the two groups (19HP group, 92.3% ± 7.4%; 21SD group, 100%, p = 0.33).
Thromboembolic events occurred in 1 patient with the 19HP valve (1.09% per patient-year) and in 1 with the 21SD valve (1.02% per patient-year) during the follow-up period. Hemorrhagic complications related to anticoagulant therapy developed in 1 patient (1.09% per patient-year) with the 19HP and 1 (1.02% per patient-year) with the 21SD. No patient underwent reoperation in either group. No structural failure, valve thrombosis, or prosthetic valve endocarditis was observed in either group on follow-up. The probability of freedom from all complications at 6 years did not show any significant difference between the two groups (19HP group, 78.9% ± 11.8%; 21SD group, 90.8% ± 6.4%, p = 0.54) (Fig 1).
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Fig 1. Kaplan-Meier curve for all valve-related complications (thromboembolism, anticoagulation-related hemorrhage, prosthetic valve endocarditis, and reoperation). (19HP= 19-mm St. Jude Medical Hemodynamic Plus aortic prosthesis;21SD= 21-mm standard St. Jude Medical valve prosthesis.)
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In the 19HP group, New York Heart Association functional class improved from 2.39 ± 0.88 preoperatively to 1.30 ± 0.47 postoperatively, and also changed from 2.07 ± 0.92 to 1.31 ± 0.47 in the 21SD group. A significant difference (p < 0.001) was found between the preoperative and postoperative New York Heart Association functional classes in both groups. However, no significant difference was observed in the postoperative New York Heart Association functional class between the 19HP group and the 21SD group (p = 0.9456).
In the 19HP group, early postoperative echocardiography showed EF of 67.1% ± 11.9% and %FS of 32.2% ± 8.6%, which had been 72.6% ± 13.0% and 36.7% ± 10.0%, respectively, before operation. In the 21SD group, the EF changed from 67.3% ± 16.9% preoperatively to 67.9% ± 9.3% postoperatively and %FS changed from 32.9% ± 11.4% preoperatively to 32.7% ± 6.3% postoperatively. However, there were no significant differences in either group, nor were there any differences in either group between the preoperative and postoperative EF and %FS. The EF and %FS did not change significantly over time during the long-term follow-up in either group.
Peak systolic pressure gradients were significantly decreased postoperatively, compared with the preoperative pressure gradients (19HP group, 23.27 ± 10.49 mm Hg, p < 0.0001; 21SD group, 27.86 ± 9.88 mm Hg, p < 0.0001). There was no significant difference between the two groups after the operation (p = 0.0666). Also there was no significant correlation between BSA and postoperative peak pressure gradient in either group (19HP group, r = 0.111, p = 0.5568; 21SD group, r = 0.211, p = 0.2749). This pressure gradient across the prosthetic valve remained over the time during the long-term follow-up in both groups.
The LVMIs before and after operation in both groups are shown in Figure 2.
The LVMI decreased from 247.2 ± 117.2 g/m2 to 158.0 ± 51.6 g/m2 in the 19HP group (36.1%, p = 0.0002) and decreased from 252.7 ± 81.4 g/m2 to 161.0 ± 49.2 g/m2 in the 21SD group (36.3%, p = 0.0006). Although the decreases in LVMI in the two groups were statistically significant, there were no significant differences in the two indices between the groups either before (p = 0.999) or after (p = 0.999) the operation.
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Fig 2. Mean values (± standard error of the mean) of left ventricular mass index in patients with the 19-mm St. Jude Medical Hemodynamic Plus aortic prosthesis (closed circles) or 21-mm standard St. Jude Medical valve prosthesis (open circles) preoperatively and postoperatively. The decreases in left ventricular mass index in the two groups were statistically significant (p < 0.001), although there were no significant differences in the two indices between the groups, either preoperatively or postoperatively.
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The mean LDH value at discharge was high (>300 IU/L) in both groups; however, there were no significant differences between the groups (19HP group, 493.4 ± 150.2 IU/L; 21SD group, 487.2 ± 197.8 IU/L, p = 0.4915).
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Comment
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Aortic valve stenosis is associated with substantial hemodynamic stresses on the left ventricle in the form of pressure. To adapt to the particular stress sustained, the left ventricle hypertrophies in a fashion to maintain systolic wall stresses at or near normal levels [5]. With AVR there is a reduction in the degree of hemodynamic stress faced by the left ventricle as the stenotic valve is replaced with a prosthetic valve, either a mechanical or a biological valve. However, all mechanical valve prostheses are moderately stenotic because the sewing cuff of the valve reduces the effective orifice area to a size smaller than that of the native orifice. This patient–prosthesis mismatch has been reported to be more critical in a larger patient and with exercise [6–8]. To address the problem, St. Jude Medical has introduced a new bileaflet prosthesis model for the small aortic root, the St. Jude Medical Hemodynamic Plus series. In this new model, the sewing cuff of the valve and its attachment to the valve ring have been redesigned to create a larger valve orifice with an equivalent tissue annulus diameter. The actual orifice areas of the HP are reported as being 1.63 cm2 for a 17-mm valve, 2.06 cm2 for a 19-mm valve, and 2.55 cm2 for a 21-mm valve, these being equivalent to those reported for a 19-mm, 21-mm, and 23-mm standard St. Jude Medical valve, respectively. The hemodynamic performance of an HP is thus considered to be theoretically equivalent to that of the standard St. Jude Medical, which is one size larger. An in vitro study demonstrated that the 19HP had lower forward pressure drops and total energy losses than the 19SD, particularly at higher flow rates [1]. Carrel and colleagues [9] demonstrated that the hemodynamic performance of the 21HP in vivo has been better than that of the 21SD and that it corresponded closely to that of the 23SD. Hayashida [10] and Hachida [11] and their colleagues showed that the transvalvular pressure gradient of the 19HP was significantly lower than that of the 19SD, which confirmed in vitro studies. In this study, we revealed that both the hemodynamic performance and clinical results of the 19HP were almost identical to those of the 21SD with the same follow-up period. In a recent in vivo study by Ismeno and associates [12], the 19HP showed better hemodynamic results than that of the 19SD. However, they did not find a significant difference in the clinical results between the two groups. Thus, if we combine their results with ours, the clinical outcome of the 19SD should be the same as that of the 21SD. This raises the question that valve size is really important in terms of the clinical results. Medalion and co-workers [13] recently demonstrated that survival after AVR did not appear to be adversely affected by a moderate patient–prosthesis mismatch.
It is believed that favorable hemodynamics from a large and efficient prosthetic orifice size will improve the late outcome after aortic valve replacement. In part, this logic is based on the exponential increase in the transprosthetic pressure gradient as the indexed effective orifice area decreases. Many studies, in which the performance of different aortic valve prostheses was evaluated, have emphasized that successful AVR should achieve an indexed effective orifice area of more than 0.9 cm2/m2 to minimize prosthetic gradients and obtain postoperative left ventricular mass regression [8, 14]. In our study, average BSA was less than 1.5 m2 in both groups of patients, therefore the effective orifice area should be more than 1.67 cm2, which is almost the same as the internal orifice area of the 19SD. Theoretically, in patients with 1.5 m2 of BSA, the 19SD should be enough. On the other hand, prostheses are not perfectly efficient in vivo. The effective orifice area is generally less than the internal orifice area calculated from the actual (in vitro) valve dimension, because it is a dynamic, not static, measurement that varies with temporal loading conditions and flow. Moreover, small prostheses are known to produce high gradients under conditions of high cardiac output, which are not seen at rest [15]. Furthermore, Sim and colleagues [16] demonstrated that the magnitude of reduction in left ventricular mass was greater in patients with 21-mm valves than in those with 19-mm valves, and was similar in the patients with 21-mm valves or 23-mm valves. In this study, regression of the left ventricular mass index was significant in patients with the 19HP and 21SD, and no significant difference was found in the postoperative left ventricular mass indices between the two groups. The magnitude of reduction in left ventricular mass index was 36% in both groups. Although Ismeno and colleagues [12] demonstrated no significant difference of postoperative left ventricular mass index between the 19HP and the 19SD, they did not show the magnitude of regression in left ventricular mass index. Therefore, it would be better to implant the 19HP in patients with a measured 19-mm annulus, as long as this HP series can be safely implanted.
When the sewing flange is reduced, one may worry about leakage between the sewing ring and aortic annulus, especially with intra-annular insertion using horizontal everting mattress sutures because of a bad fit between the sewing flange and the native aortic annulus. However, an echocardiographic study did not show any significant leakage between the sewing ring and aortic annulus in patients with the 19HP, and clinical hemolysis due to perivalvular leakage indicated by the LDH level did not show a significant difference compared with the 21SD. Ismeno ands colleagues [12] also analyzed postoperative intravascular hemolysis in patients with the 19HP and 19SD, and showed that the LDH serum level was significantly lower in patients with the 19HP than in those with the 19SD, despite the use of intra-annular insertion. Lund and associates [17] reported that the valve orifice diameter was an independent determinant of the serum LDH level, with a direct correlation. It has been reported that perivalvular regurgitation is greater with the St. Jude valve compared with most other mechanical valves, although not of a magnitude to cause volume load of the left ventricle [18]. Despite the relatively high postoperative LDH serum level in our study, none of the patients had frank anemia. It is generally recommended to implant the HP valve in the supra-annular position. Using supra-annular insertion, leakage between the sewing ring and the aortic annulus can be minimized compared with intra-annular insertion. Moreover, by applying this technique, the native aortic annulus can be used more efficiently to ensure a better effective orifice area. On the other hand, using supra-annular insertion, pannus formation from the ventricular side of the prosthetic valve could induce left ventricular outflow obstruction or possible valve malfunction.
The limitation of this study is that the average body size of our patients in both groups was rather small (BSA, <1.5 m2). We also analyzed patients whose BSA were larger than 1.5 m2. There were 11 patients (35.5%) in the 19HP group and 14 patients (48.3%) in the 21 SD group, but there were no significant differences between these two groups in terms of postoperative hemodynamic values and events during follow-up. Furthermore, the residual pressure gradient was independent of the body size, therefore the results of this study might possibly be applied for the adult patient population in general. Since the introduction of the 19HP valve at our institute, we have not performed the annular enlargement procedure in adult patients. However, this does not mean that the annular enlargement procedure is unnecessary in any patient. In patients whose BSA is more than 1.9 m2 and the aortic annulus is less than 19 mm, the annular enlargement procedure would be indicated.
In conclusion, our study demonstrated that in vivo hemodynamic performances of the 19HP valve as well as the early and intermediate clinical outcome up to 6 years was satisfactory and corresponded closely to the results of the 21SD valve in adult patients. It is a reasonable alternative to use the 19HP St. Jude Medical valve for the small annulus in a small-sized patients.
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References
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Abstract
Introduction
