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Ann Thorac Surg 1999;67:966-971
© 1999 The Society of Thoracic Surgeons

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Original Articles

Left ventricular mass reduction after aortic valve replacement: homografts, stentless and stented valves

^a Department of Cardiac Surgery, Ospedale Maggiore della Carità, Novara, Italy
^b Istituto di Statistica Medica dell’Università di Genova, Genova, Italy

Accepted for publication August 28, 1998.

Address reprint requests to Dr Maselli, Divisione di Cardiochirugia, I.R.C.C.S. Policlinico S. Matteo, Pavia 27100, Italy;
e-mail: dmasel{at}tin.it

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. We studied the effect of four different types of prosthetic aortic valves on time course and extent of regression of left ventricular hypertrophy after aortic valve replacement for aortic stenosis.

Methods. Four groups of 10 patients each were randomly assigned to receive: (1) aortic homograft preserved in antibiotic solution at 4°C, (2) Toronto stentless porcine valve, (3) Medtronic Freestyle stentless valve, or (4) Medtronic Intact aortic valve. The left ventricular mass index, effective orifice area index, and peak and mean transaortic gradients were measured by Doppler echocardiography before the operation and 8 months postoperatively.

Results. The hemodynamic performance indices were much better for the homograft and stentless valves than for the stented one. The absolute left ventricular mass index reduction was greater in the homograft group compared with the Intact (p = 0.0004) and Toronto (p = 0.007) groups. The extent of percent left ventricular mass index reduction was greater only in the homograft group versus Intact group (p = 0.005). The multilinear regression analysis showed that the only predictors of a larger percentage of left ventricular mass index reduction were the homograft type, a higher valve size index, and a higher preoperative left ventricular mass index.

Conclusions. When a stentless or homograft aortic valve was used instead of a stented valve to replace a stenotic aortic valve there was more complete or at least faster regression of left ventricular hypertrophy. The hemodynamic performance of stentless porcine valves was similar to that of aortic homografts, nevertheless the aortic homografts preserved in antibiotic solution offered a faster regression of left ventricular hypertrophy during the same period of time.

	Introduction

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The replacement of the aortic valve with a prosthesis of any kind implies the acceptance of a residual gradient across the prosthesis. The residual gradient has been proposed to be the driving stimulus for persistence or incomplete regression of left ventricular hypertrophy (LVH) after aortic valve replacement, which has been related to higher long-term mortality rate [1]. The aortic porcine stentless valves, introduced in surgical practice for aortic valve replacement, demonstrated better hemodynamic performance than the stented bioprostheses, which resulted in better short-term left ventricular performance [2] and in a greater reduction of LVH [3]. Assuming that the residual gradient and a higher pressure in the left ventricle are primarily responsible for an incomplete reduction of LVH after aortic valve replacement, the objective of this study was to assess whether the lower gradient achieved by implanting an aortic stentless porcine valve or an aortic homograft instead of an aortic stented bioprosthesis could influence the extent of LVH regression. We chose a strictly selected group of patients, all of whom had pure or predominant aortic stenosis without hypertension or associated coronary artery disease or other valvular heart disease. We randomly assigned them to one of the following four different aortic valve prostheses: group 1, Medtronic Intact stented bioprosthesis (Medtronic, Inc., Minneapolis, MN); group 2, aortic homograft preserved in antibiotic solution; group 3, Saint Jude Medical Toronto stentless porcine valve (St. Jude Medical, Inc, St. Paul, MN); and group 4, Medtronic Freestyle stentless porcine valve (Medtronic, Inc., Minneapolis, MN). The results were compared with a control group of healthy subjects.

	Material and methods

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Patient population
From January 1996 to December 1996, 40 patients aged 65 years or older, who had aortic valve replacement for isolated aortic stenosis and who preferred a biologic valve substitute were included in the present study. All patients were randomly assigned to receive a Toronto stentless porcine valve (St. Jude Medical, Inc, St. Paul, MN) (10 patients), a Medtronic Freestyle stentless porcine valve (Medtronic, Inc, Minneapolis, MN) (10 patients), a Medtronic Intact stented porcine valve (Medtronic, Inc, Minneapolis, MN) (10 patients), or an aortic homograft preserved in antibiotic solution at 4°C. A fifth group of 10 healthy subjects in the same age range and free from hypertension or heart disease was used as a control group. The randomization protocol had been approved by the ethics committee of the "Maggiore di Novara" Hospital. The preoperative demographic and clinical characteristics are shown in Table 1. All patients were in sinus rhythm preoperatively and at 8 months postoperatively. In the Toronto and Freestyle groups there was a slight predominance of women and a lower mean body surface area. Despite this, both groups received the bigger valves and expressed the significantly higher valve size indices of all groups. No significant difference in valve size index was found between homograft and Intact groups (Table 2). This is probably a result of the different criteria adopted for sizing the Toronto and Freestyle valves which led to a more pronounced oversizing. The cardiopulmonary bypass time and the aortic cross-clamp time were significantly lower in the Intact group versus all the other groups (Table 2).

Echocardiography
All the patients were followed up by echocardiography. The examinations were done on the day before the operation, before discharge, and after 8 months. The echocardiograms were done by a single operator using an Acuson XP 10 Ultrasound System (Acuson Corp. Mountain View, CA) and according to the indications of the American Society of Echocardiography. Standard parasternal, apical, subcostal, and suprasternal views were obtained. The mean of five measures on two different cardiac cycles was assumed as the measure of the following variables: end-diastolic septal thickness, left ventricular end-diastolic dimension, end-diastolic left ventricular posterior wall thickness, and end-systolic left ventricular dimension. All the measures were indexed for the body surface area. Left ventricular mass was calculated according to the indications of the American Society of Echocardiography. Parasternal long axis view was also used to study the shape of the native aortic valve or the prosthesis in aortic position and to measure the inner diameter of the left ventricular outflow tract. Continuous-wave, pulsed-wave, and color Doppler studies were done to assess the peak transvalvular gradient, the mean transvalvular gradient, the effective orifice area of the aortic valve, and the grade of aortic regurgitation. The peak and mean gradients were calculated by the modified Bernoulli equation. The effective orifice area was calculated by the simplified continuity equation [4].

Statistical methods
One-way analysis of variance with Scheffé’s internal comparison was used to compare preoperative patients characteristics, intraoperative data, postoperative data, and postoperative hemodynamic performance indices. Student’s paired t test was used to compare preoperative and postoperative data in the same group. Analysis of covariance (preoperative left ventricular mass index [LVMI] as covariant), two-way analysis of variance (preoperative LVMI 180 g/m² or LVMI 180 g/m² and type of surgical treatment) with internal comparison, or both were used to assess interactions between preoperative LVMI and type of surgical treatment. To assess the influence of different dependent variables on absolute and percentage of LVMI reduction, and to enhance the significance of our observation in this small group of patients, we used two multivariate regression analyses with the absolute LVMI reduction and the percent LVMI reduction as dependent variable and valve type, valve size, valve size index, sex, body surface area, New York Heart Association class (I and II versus III and IV), cross-clamp time, and preoperative LVMI as the dependent variables. Data are expressed as mean ± standard deviation; p values less than 0.05 were considered significant.

	Results

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At 8 months follow-up, 33 of 40 (82.5%) patients were in New York Heart Association class I and 7 (17.5%) in class II. The preoperative and postoperative echocardiographic measurements are shown in Table 3. The LVMI before the operation was significantly greater than normal in all groups. Before the operation, no significant differences were found between the four groups for LVMI, interventricular septal thickness index, left ventricular posterior wall thickness index, left ventricular end-diastolic dimension index, and left ventricular end-systolic dimension index. The left ventricular systolic performance indices were slightly but not significantly lower in the homograft group. At 8 months follow-up there was a significant reduction of LVMI in all groups, with the smallest significance level for the Intact group (p = 0.034). The amount of the absolute LVMI reduction in the homograft group was significantly higher than that of the Intact (p = 0.001) and Toronto (p = 0.015) groups (Fig 1A) independent of the preoperative values (analysis of covariance p = 0.0004 for Intact group and p = 0.007 for Toronto group).

View larger version (26K): [in this window] [in a new window]   Fig 1. Left ventricular mass index (LVMI) preoperatively (PREOP) and 8 months after (POSTOP) aortic valve replacement. The homograft and freestyle valves expressed the maximum LVMI reduction. This is evident in all cases (A) and in patients with a preoperative LVMI of 180 g/m2 or less (B). In patients with a preoperative LVMI of 180 g/m2 or more (C) the homograft treatment achieved the best results. (I = intact; H = homografts; T = Toronto; F = freestyle; C = controls).

The absolute postoperative LVMI was significantly greater in all groups than in the control group, and a larger difference was observed for the Intact group (Fig 1A). We further divided each group in two subgroups using an arbitrary threshold value for LVMI of 180 g/m². In all treatment groups, LVMI always remained higher than LVMI of the control group, particularly in patients with preoperative LVMI of at least 180 g/m² (homograft and Toronto p = 0.0002; Freestyle and Intact p = 0.0001) (Fig 1C). In the subgroup with a preoperative LVMI of 180 g/m² or less, the LVMI at 8 months was significantly higher for the Intact group versus control group and Freestyle group (p = 0.0001 and p = 0.0321, respectively) and for the Toronto group versus control group (p = 0.0037). No significant differences were found between the homograft and Freestyle groups and the control group (Fig 1B).

The left ventricular systolic performance indices showed no significant changes, except for a slight improvement in the Toronto group. A trivial aortic regurgitation or absent aortic regurgitation were found in most cases, and only one case of moderate aortic incompetence was observed in 1 homograft patient. The hemodynamic performance indices were significantly better for the homograft, Toronto, and Freestyle groups compared with the Intact group (Table 4). The calculated effective orifice area index in the homograft, Toronto, and Freestyle groups was greater than in the Intact group, with no difference between those 3 groups. The transaortic peak gradient and mean gradient were significantly smaller in the homograft, Toronto, and Freestyle groups than in the Intact group.

	Comment

Top Abstract Introduction Material and methods Results Comment References

In our patients, 8 months after aortic valve replacement, the LVMI decreased independent of the type of aortic valve replacement used (Fig 1A). The hemodynamic performance of the stentless valves was significantly better than that of the stented valves, as demonstrated by lower peak and mean transvalvular gradients and by greater effective orifice area index. Even if no differences were found between the three components of the stentless group in terms of hemodynamic performance, in the whole group, the homograft and Freestyle valves performed better than the other valves in terms of absolute and percentage of LVMI reduction. This is even more evident if we consider the preoperative LVMI value. In fact, in patients with a preoperative LVMI of 180 g/m² or less, 8 months after aortic valve replacement, the LVMI in the homograft and Freestyle groups was the most similar to that of controls (Fig 1B). In patients with a preoperative LVMI of 180 g/m² or more, 8 months after aortic valve replacement, the LVMI did not reach normal limits in all groups, but the homograft group was the most similar to the control group (Fig 1C). This finding is even more interesting if we consider that the homograft group expressed the lower valve size index of all groups.

The multivariate regression analysis revealed that the homograft type of treatment, a higher valve size index, and a higher preoperative LVMI value were the most significant predictors of a greater percentage of LVMI reduction. The percentage of LVMI reduction in the homograft group was the greatest even if the valve size index was the lowest. We conclude that, in terms of LVMI reduction, the performance of the homograft valve was better than all other prosthetic aortic valves even if their hemodynamic performance was very similar to that of stentless porcine valves. A possible explanation for this finding, as suggested by Jin and colleagues [3], is that the Doppler-derived indices of valve performance do not reflect the overall disturbance to ejection. Previous studies demonstrated that the mechanical behavior of glutaraldehyde-treated aortic roots is significantly different from that of fresh human or pig aortic roots, with less extensibility and less capacity to relax [12]. Moreover, the Dacron fabric that covers the porcine stentless valves is probably an obstacle to the diastolic dilation of the aortic root, which can cause a delayed opening of the aortic leaflets. We think that this can translate into different impedance to left ventricular ejection and into different stress on the left ventricular wall. It is more difficult to find an explanation for the difference found between Freestyle valves and other stentless valves. The difference might be due to the greater area of Dacron fabric in the Toronto valve. Moreover the fixed configuration of the Toronto valve makes it less adaptable to the variously configured pathologic aortic roots with respect to the Freestyle valve, which probably resulted in suboptimal implantation of the Toronto valve.

This was a short-term study and the conclusions are limited to the observation period. Moreover the limited number of patients might account for a less accurate statistical validation of the results. It should be considered, however, that the patient selection criteria were very restrictive.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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