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Ann Thorac Surg 2005;80:1319-1326
© 2005 The Society of Thoracic Surgeons
Department of Cardiothoracic Surgery, German Heart Center Munich, Technical University of Munich, Munich, Germany
Accepted for publication February 1, 2005.
* Address reprint requests to Dr Wildhirt, German Heart Center Munich, Technical University of Munich, Lazarettstrasse 36, Munich, 80636 Germany (Email: wildhirt{at}gmx.net).
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Abstract |
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METHODS: Between May 2002 and June 2003, 63 consecutive patients underwent aortic valve replacement with a Medtronic Advantage prosthesis (84.1% male; mean age, 56.0 ± 9.7 years; ejection fraction, 56.5 ± 15.8%). Valve lesions were stenosis (n = 20), mixed (n = 34), and insufficiency (n = 9). Concomitant procedures were performed in 34.9%. Follow-up was 100% complete. Echocardiographic data were obtained early postoperatively and at 1 year, combined with stress echocardiography by treadmill. Mean pressure gradients, stroke volume, and left ventricular mass were determined by echocardiography. Data are presented as mean ± standard deviation.
RESULTS: Operative mortality was 0%. Valve-related complications were observed in 2 patients (endocarditis, n = 1; thromboembolic event, n = 1). There was no case of antithromboembolic hemorrhage, prosthesis-related explant, or reoperation. One patient showed moderate paravalvular regurgitation. Mean pressure gradients 1 year postoperatively ranged from 6.3 to 11.0 mm Hg across all valve sizes. Left ventricular mass regression at 1 year was 18.4% across all valve sizes (p < 0.001). No severe patient-prosthesis mismatch (effective orifice area index 
0.65 cm2/m2) could be observed.
CONCLUSIONS: After 1 year, the Medtronic Advantage valve shows comparable transvalvular mean pressure gradients across the valve sizes used during rest and exercise. This is accompanied by a significant left ventricular mass regression, an important indicator for long-term survival.
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Introduction |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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The first bileaflet mechanical heart valve was introduced in 1977. In experimental studies, the bileaflet design has shown to provide a flow pattern closer to that of native aortic valves than that provided by any other type of mechanical heart valve [2]. Today, several bileaflet mechanical heart valves that are comparable in design are available. All of them are considered to offer good hemodynamic function and almost unlimited durability. Thus they serve as the current standard for mechanical valve replacement [3–7].
The Medtronic Advantage (Medtronic, Inc, Minneapolis, MN) valve was first implanted in November 1999 and is a newly designed low-profile bileaflet valve to optimize implantability. Due to the increased distance between the leaflets, the Advantage valve's wider central opening area is supposed to maximize central flow and reduce turbulence. The Advantage valve's patented Sure Flow pivot system is intended to improve washing through the pivot region [8, 9]. The prosthesis is designed for intraannular implantation.
The importance of the hemodynamic performance after aortic valve replacement during rest and exercise has been previously investigated in different heart valves [10–12].
The present study examined rest and exercise performance (including measuring the left ventricular mass regression) in patients receiving the Medtronic Advantage mechanical prosthesis in the aortic position.
In this regard, Pibarot and collegues [10, 11] showed that effective orifice area indices (EOAIs) increased during exercise in patients with aortic bioprostheses. In contrast with this, the EOAIs did not change in patients with mechanical aortic valve prostheses during exercise when compared with measurements performed at rest [12].
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Patients and Methods |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Mean pressure gradients, stroke volume, and left ventricular mass (LVM) (the Devereux formula) were determined by echocardiography. Preoperative data are summarized in Table 1.
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The prosthetic valve size was determined by use of the original sizer provided by the manufacturer. Valves were placed intraannulary with noneverting mattress sutures.
Myectomy
A myectomy was performed in 21 patients. Indication for myectomy was a visible hypertrophy of the interventricular septum in the left ventricular outflow tract (LVOT), which was seen by the surgeon during the operation. Inspection and palpation of the interventricular septum were used to assess the site for septal resection. A horizontal Prolene 4-0 stay suture (Ethicon, Somerville, NJ) was then placed in the most prominent portion of the septum. Two parallel wedge-shaped incisions were then made in the septum, beginning 3 to 5 mm below the aortic anulus and directed toward the left ventricular apex. The length of these incisions was 1 to 2 cm, and the maximum depth was approximately 0.5 cm to increase the cross-sectional area of the LVOT. The removed tissue weighed approximately 3 to 5 grams.
Echocardiography
Transthoracic Doppler echocardiography was performed in accordance with the data requirements of the Food and Drug Administration Replacement Heart Valve Guidance, version 4.1 [13]. Echocardiograms were performed using a Hewlett-Packard Sonos 5500 ultrasound system (Hewlett-Packard, Andover, MA).
The LVOT diameter was measured from the parasternal long-axis view. Left ventricular outflow tract velocities and gradients were measured with pulsed wave Doppler echocardiography from the apical long-axis or five-chamber view. The heart rate or R-R interval was measured from the corresponding cardiac cycles. Transaortic velocities were measured with continuous Doppler wave echocardiography. To assure detection of the highest velocities, a minimum of two transducer positions was attempted in all patients. From these measurements we calculated the left ventricular stroke volume as the product of the LVOT velocity time integral and the cross-sectional area of the LVOT, and the cardiac output as the product of the stroke volume and heart rate. The maximal transvalvular pressure gradient was calculated using the modified Bernoulli equation; the mean pressure gradient was derived by planimetry of the Doppler echocardiographic envelope and the effective orifice area (EOA) by using the standard continuity equation. The EOA was indexed for body surface area. The same measurements were performed during exercise, except for the LVOT diameter, which was assumed to have remained constant [14].
All Doppler echocardiographic measurements were averaged for three cardiac cycles for patients in sinus rhythm, and for a minimum of five cardiac cycles for patients in non-sinus rhythm.
Prosthetic regurgitation was assessed by color Doppler echocardiographic imaging of the LVOT from the parasternal and apical transducer positions. The severity of regurgitation was categorized as none, trivial, mild, moderate, or severe based on visual estimates of the ratio of the regurgitant jet height or area at its origin to the width or area of the LVOT. Regurgitation was considered transvalvular if the jet appeared to originate from within the sewing ring, and paravalvular if the jet appeared to originate from outside the sewing ring.
Left ventricular end-systolic and end-diastolic dimensions and thickness of the left ventricular posterior wall and interventricular septum were assessed in the short-axis of parasternal view by multiple M-mode measurements with calculation of the shortening fraction [15, 16].
The LVM was calculated using the appropriate formula suggested by the American Society of Echocardiography and was indexed by body surface area [17].
Stress Echocardiography Protocol
Stress echocardiography was performed by treadmill exercise testing, as described by Eriksson and collegues [12] and Pibarot and collegues [18].
During treadmill exercise, patients sat on a seat reclined to a 50° position. The starting workload was 25 watts, which was then increased by 25 watts every 2 minutes. The patients were encouraged to exercise until exhaustion. The test was stopped if there was a rise in blood pressure (diastolic blood pressure < 110 mm Hg), electrocardiographic evidence of ischemia (horizontal or downsloping segement elevation depression, segment elevation lifting), significant arrhythmia (new atrial fibrillation, ventricular arrhythmia), chest pain, vertigo, tachycardia (> 200 bpm), or dyspnea. To facilitate Doppler echocardiographic measurements during exercise, the chest site, at which optimum Doppler echocardiographic waveforms were recorded, was marked before starting exercise. In case of an unsatisfactory Doppler echocardiographic signal, the whole treadmill unit was slightly tilted to the left side until optimal measurements were obtained. Measurements were performed at the end of each 2-minute workload level. Blood pressure was measured noninvasively every 2 minutes using a sphygmomanometer cuff fixed on the right arm. A 12-lead electrocardiogram was continuously recorded [19]. Maximal and mean velocities, maximal and mean pressure gradients, and velocity time integral were calculated by loading the stored values.
In our study population, 15 patients did not enter the exercise protocol. There were 2 late deaths, 2 patients refusing further study participation, 6 patients unable to perform treadmill exercise due to severe peripheral vascular disease (n = 1), coxarthrosis (n = 2), gonarthrosis (n = 1), severe arterial hypertension (n = 1), or atrial fibrillation (n = 1), and 5 patients whose gradients were not assessed because of poor echocardiographic quality.
Statistical Analysis
Data are presented as mean ± standard deviation. Discrete variables were compared by the chi2 test or Fisher's exact test. We used Wilcoxon's test to compare left ventricular mass regression 1 year postoperatively with preoperative values. For differences between the means of dichotomous risk groups, the Mann-Whitney U test was performed. A value of p < 0.05 was considered statistically significant for all comparisons. All statistical analyses were performed with SPSS, version 12.0.2 (SPSS Inc, Chicago, IL).
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Results |
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Hemodynamic Data During Rest and Exercise
Early postoperative mean pressure gradients ranged from 7.3 ± 2.1 to 13.4 ± 3.8 mm Hg across all valve sizes. One year postoperatively, a slight, but not significant regression of mean pressure gradients across all valve sizes was observed (6.3 ± 2.1 to 11.0 ± 1.6 mm Hg).
During treadmill exercise at 1 year, mean pressure gradients ranged from 10.8 ± 4.6 to 20.0 ± 6.5 mm Hg across all valve sizes at 100 watts workload. Data are shown in Table 3.
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Effective Orifice Area and Effective Orifice Area Index
The early EOAs ranged from 1.55 ± 0.21 to 2.94 ± 0.96 cm2 across all valve sizes. The early EOAIs, using the patient's body surface area, ranged from 0.97 ± 0.14 to 1.51 ± 0.55 cm2/m2 across all valve sizes.
One year postoperatively, the EOAs ranged from 1.37 ± 0.31 to 2.71 ± 0.54 cm2 and the EOAIs ranged from 0.85 ± 0.15 cm2/m2 to 1.36 ± 0.26 cm2/m2 across all valve sizes (Table 3). No severe patient-prosthesis mismatch (PPM) (EOAI 0.65 cm2/m2) was observed. Moderate PPM (EOAI 0.85 cm2/m2) was observed in 8 patients (12.7%).
Regurgitation
In 40 patients, there was a mild or trivial regurgitation; in all of these cases the regurgitation was considered to be transvalvular due to the bileaflet valve design. In addition, one patient showed moderate paravalvular regurgitation.
Regression of Left Ventricular Mass and Left Ventricular Mass Index
The statistical analysis of the course of all patients demonstrated a marked and highly significant reduction in LVM and left ventricular mass index. The left ventricular mass index regression at 1 year was 18.4% across all valve sizes (p < 0.001) (Fig 1A). Regarding the different valve sizes, left ventricular mass index regression was 39.4% for valve size 21 (p = 0.216), 15.5% for valve size 23 (p = 0.054), 13.3% for valve size 25 (p = 0.085), and 20.6% for valve size 27 (p = 0.070) (Fig 1B).
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Figures 2A and 2B echocardiographically show a representative example of LVM regression in a patient with a 27 Medtronic Advantage valve.
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Comment |
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The operative 30-day mortality was 0%, despite the fact that concomitant procedures such as coronary artery bypass grafting or ascending aorta repair/replacement were necessary in 34.9% of the cases. There were 2 late deaths; one late death was from prosthetic valve endocarditis and the other was from ventricular fibrillation. One patient had a major thromboembolic event with dysarthria and hemiataxia 9 weeks postoperatively (international normalized ratio, 2.3). There were no cases of antithromboembolic hemorrhage, prosthesis-related explant, or reoperation.
Hemodynamic Performance
The present study reveals low mean pressure gradients, large EOAs and EOAIs associated with the Medtronic Advantage aortic valve prosthesis. The hemodynamic parameters are comparable with those reported for other intraannular bileaflet valves in the literature [20–23]. However, in many cases comparisons of pressure gradients may be difficult because of lack of information on the corresponding cardiac output. Use of the continuity equation normalizes the gradient data and improves direct comparisons.
Doppler echocardiographic evaluation of prosthetic heart valve function is usually performed at rest, although this situation does not reflect the patient's daily activities. To simulate this situation and to elicit the presence of abnormal hemodynamics and elevated transvalvular gradients, the function of a valve prosthesis needs to be evaluated under various flow conditions, such as during exercise.
Despite some difficulties in obtaining reliable images in the tachypneic exercising patient, treadmill exercise testing seems to be the most physiologic approach [12, 24].
During treadmill exercise, mean pressure gradients ranged from 10.8 ± 4.6 to 20.0 ± 6.5 mm Hg across all valve sizes at a workload of 100 watts. At the same time, the increase in stroke volume, heart rate, and cardiac index was 27.7%, 58.9%, and 99.8%, respectively. These data are comparable with data reported in a previous report [12].
Patient-Prosthesis Mismatch
Focusing on valve size distribution, there was a striking trend to use large valve sizes with an average labeled valve size of 24.5 ± 1.8 and an aortic annulus measured by hegar dilator of 25.1 ± 1.0 mm. To omit bias regarding valve size distribution, we analyzed the 21 patients who had no exclusion criteria, but refused their study participation and were therefore chosen for an aortic valve of supraannular design. There was no significant difference regarding labeled valve size (23.5 ± 2.5; p = 0.068) and annulus diameter (24.0 ± 2.7; p = 0.289).
Although the aim of aortic valve replacement in patients with aortic stenosis is to remove the stenosis and provide the lowest transvalvular gradients, a residual stenosis represented by low EOAI is frequently observed, especially with small valve sizes. We rated the extent of PPM as not present for EOAIs < 0.85cm2/m2, moderate for EOAIs between 0.65 and 0.85cm2/m2, and severe for EOAIs 0.65cm2/m2, as described by Pibarot and colleagues [25]. This graduation corresponds to the general concept that moderate aortic stenosis of a native valve is present with EOAIs < 0.90 cm2/m2 [26].
Recently, PPM was identified as an important and independent risk factor for short-term mortality in patients undergoing aortic valve replacement [27]. Controversial debate exists with regard to PPM, focusing on the long-term results after aortic valve replacement. Two studies failed to demonstrate a negative impact of PPM on medium-term and long-term mortality in a small series of patients [28, 29]. However, Rao and colleagues [30] identified PPM in 2,516 patients undergoing aortic valve replacement as an independent predictor for valve-related mortality in the late postoperative period. These findings, with regard to moderate to severe PPM, are important because of their 19% to 70% prevalence as reported in the literature [31].
In our study, severe PPM was not observed in any patient. Moderate PPM was observed in only 12.7% of our patients. In contrast, Jazayeri and colleagues [32] reported an incidence of 35% for patients with an indexed EOA < 0.85cm2/m2 for the ATS AP prosthetic heart valve in the aortic position. The low prevalence of PPM may be a specific finding in our study population because of the small number of 19 and 21 sized valves. Furthermore Pibarot and colleagues [10, 11] reported an increase in EOAs during exercise in bioprostheses. In accordance with other studies, we did not observe this phenomenon in reference to the Medtronic Advantage prosthesis [12].
Regurgitation
The Medtronic Advantage valve allows backflow on either side of both pivotal points to reduce the likelihood of thrombus formation on the prosthesis. Therefore, we observed a mild or trivial regurgitation in 40 patients; in all of these patients the regurgitation was considered to be transvalvular due to the bileaflet valve design. In addition, 1 patient showed moderate paravalvular regurgitation. However, due to the excellent clinical condition of this patient, there was no need for further intervention.
Left Ventricular Mass Regression
In patients with aortic valve lesions, persisting LV hypertrophy is likely to be an independent risk factor for long-term survival after aortic valve replacement [33]. The aim of aortic valve replacement is to relieve stenosis or insufficiency and to allow LV regression because of a marked reduction in long-term complications, such as sudden death and congestive heart failure associated with left LV hypertrophy [34].
Our study demonstrates a marked and highly significant reduction in LVM and LV mass index across all valve sizes with or without myectomy (p < 0.001).
The extent of LVM regression within 1 year was comparable with that seen in other studies of about 20% [15, 35, 36]. Most of the patients did not achieve normal LV dimensions. One year after aortic valve replacement, 72.4% of the patients still presented with LV hypertrophy compared with 84.5% during early follow-up, when defining LV hypertrophy with LV mass index < 131g/m2 in males and < 100g/m2 in females [37].
However, LVM regression after aortic valve replacement is dependent on a variety of factors. For example, Kühl and colleagues [38] identified sex and LV function as determinants of LVM regression. We examined the influence of age, coronary artery disease, PPM, hypertension, and LV function with regard to LVM regression.
In our population, age greater than 60 years was identified as an independent risk factor for declined LVM regression (p = 0.007). Furthermore, there was no significant difference in LVM regression with regard to the hypertension measurements (p = 0.541), PPM (EOAI < 0.85cm2/m2) (p = 0.966), coronary artery disease (p= 0.123), and impaired ejection fraction (ie, ejection fraction < 40%) (p = 0.554). Multivariate analysis with regard to these factors was negative, but may be specific in this particular series of patients (eg, 12.5% in the case of mismatch), and this may not necessarily reflect what may occur in other series.
Other reasons for incomplete LVM regression may be nonhemodynamic factors, such as genotype [39]. Furthermore, conventional one-dimensional and two-dimensional echocardiographic methods tend to overestimate LVM compared with magnetic resonance imaging [40].
In conclusion, 1 year after implantation, the Medtronic Advantage valve provides low mean pressure gradients and high effective orifice areas in comparison with other mechanical aortic valve substitutes during rest and exercise. Patient-prosthesis mismatch was rare, and a significant LV mass regression, which is an important indicator for long-term survival, was observed in all patients. However, a definitive conclusion with regard to the present data can not be drawn for smaller valve sizes (ie, sizes 19 and 21) because of the fewew number of patients being implanted. Further investigation and data collection will allow the assessment of valve performance beyond 1 year after implantation, particularly for smaller valve sizes.
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References |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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= LVMI early; 
= LVMI at 1 year. (n.s. = not significant.)