Asian Cardiovasc Thorac Ann 1998;6:183-187
© 1998 Asia Publishing EXchange Pte Ltd
Medium-Term Outcome With Small Size ATS Medical Valves in Aortic Position
Ufuk Demirkiliç, MD,
Erkan Kuralay, MD,
Ertu
rul Özal, MD,
Hakan Bingöl, MD,
Cemal Sa, MD1,
Ahmet T Yilmaz, MD,
Harun Tatar, MD
Department of Cardiovascular Surgery
1 Department of Cardiology Gülhane Military Medical Academy Ankara, Turkey
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For reprint information contact: Ufuk Demirkiliç, MD 60 Sokak No. 30 Emek Ankara 06510, Turkey Tel: 90 312 215 1664 Fax: 90 312 213 0418 Email: karaca{at}hitit.ato.org.tr
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ABSTRACT
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Records of 33 patients (group 1) who received 19-mm or 21-mm ATS aortic valve prostheses were retrospectively reviewed and compared with those of 26 patients who received 25-mm ATS valves (group 2). Group 1 patients were younger (20 ± 2 years versus 43 ± 15 years) and had a smaller mean body surface area (1.6 m2 versus 1.83 m2). Valve pathology was usually congenital aortic stenosis in group 1 and rheumatic in group 2. There was no operative mortality. The mean postoperative Doppler resting gradient was higher in group 1 (21 mm Hg versus 7 mm Hg). Total follow-up was 294 patient-years. There was no perivalvular leak, valve thrombosis, or endocarditis in either group. In group 2, there was 1 anticoagulant-related hemorrhage and 1 late death due to congestive heart failure. We concluded that in spite of the higher transprosthetic gradient, 19-mm and 21-mm ATS aortic valve prostheses performed satisfactorily in adult patients with a body surface area of less than 1.6 m2. This valve can be used in a small aortic annulus as an alternative to performing an annular enlargement procedure.
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INTRODUCTION
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A patient with a small aortic annulus who requires aortic valve replacement presents a difficult surgical problem. The decision to insert a small prosthesis or to enlarge the annulus remains controversial.1 To avoid residual left ventricular outflow tract obstruction, a variety of techniques, usually involving transection of the aortic annulus with patch enlargement have been recommended. These procedures are of varying technical difficulty and may result in increased morbidity and mortality.2
Insertion of a smaller prosthesis without an annular enlargement procedure may be associated with a lower operative risk but it is expected to result in residual left ventricular outflow obstruction. A residual transvalvular gradient may limit the postoperative improvement in left ventricular function and symptomatic recovery as well as adversely affecting postoperative survival.3 In order to resolve this problem, several new mechanical and bioprosthetic valves with larger effective orifice areas even in small sizes have been designed. This study evaluated the hemodynamic characteristics of the 19-mm and 21-mm ATS (Advanced The Standard) valve prostheses (ATS Medical, Inc., Minneapolis, MN, USA) in patients with a small aortic annulus and compared the findings with those obtained in patients who received 25-mm ATS valves.
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MATERIAL AND METHODS
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Between March 1994 and March 1997, 59 patients who underwent replacement of the aortic valve with an ATS valve size 19, 21, or 25 mm, were selected for the study. Thirty-three patients received 19-mm or 21-mm diameter ATS valves (group 1) and 26 patients had 25-mm diameter ATS valves inserted (group 2). Patients who required mitral valve replacement or concomitant coronary surgery, and patients younger than 17 years old were excluded from the study.
Patient demographics are presented in Table 1
. Group 1 patients were younger than group 2 patients (mean age, 20 ± 2 years versus 43 ± 15 years ) and had a smaller mean body surface area (1.6 m2 versus 1.83 m2). Valve pathology was usually congenital aortic stenosis in group 1 and rheumatic in group 2. In group 1, the dominant lesion was stenosis while in group 2 it was regurgitation. Atrial fibrillation was present in 2 patients in both groups. All patients over 45 years old underwent coronary angiography. Diagnosis and pressure gradients were established by transthoracic or transesophageal echocardiography.
OPERATIVE TECHNIQUE
The operative technique included standard cardiopulmonary bypass with a membrane oxygenator and moderate hypothermia. Myocardial protection was achieved by the combination of cold crystalloid induction cardioplegia (St. Thomas' Hospital solution no. 2), 250 mL blood cardioplegia every 20 minutes, and topical hypothermia with ice slush in the pericardial cavity. If the dominant lesion was regurgitation, half of the cold crystalloid cardioplegia induction solution was delivered by hand-held cannulae directly to the left and right coronary sinuses following the aortotomy. After meticulous debridement of the valve annulus, it was measured with a snugly fitting sizer. No annulus-enlarging procedures were performed. All valves were implanted in the intra-annular position. Interrupted U-sutures with Teflon-pledgetted 2/0 polyester suture were used for prosthetic implantation and the prostheses were oriented perpendicular to the interventricular septum. Patients with hemodynamic stability were extubated as soon as they recovered from the anesthesia. They received warfarin on the 1st postoperative day. The international normalized ratio was targeted at 1.5 to 1.7 times normal.
FOLLOW-UP
Regular follow-up examinations at our outpatient department were carried out at 3, 6, and 12 months periods postoperatively and once a year thereafter. None of the patients was lost to follow-up, which ranged from 8 to 36 months. The total follow-up was 294 patient-years. Postoperative evaluation included clinical examination, echocardiographic studies, and a brief interview with regard to lifestyle criteria. A Hewlett Packard Sonos 1000 (Hewlett Packard Inc., Palo Alto, CA, USA) with 3.5 and 2.5 MHz transducers was used for echocardiograms. During follow-up, patients were assessed by transthoracic or transesophageal echocardiography on the 7th day, 3rd month, 6th month, and 12th month by the same cardiology team who were not informed of the size of the prosthesis inserted. The following parameters were measured and calculated: the maximum pressure gradient by dobutamine stress test and the mean pressure gradient according to the simplified Bernoulli equation.4 The continuity equation was applied to calculate the effective orifice area.5 The effective orifice area index is a measure of how well the effective orifice area of the valve matches the body surface area and is calculated as effective orifice area/body surface area. The diastolic interventricular septum thickness and left ventricular posterior wall thickness were measured by M-mode echocardiography.
DOBUTAMINE STRESS PROTOCOL
Following a detailed history and physical examination to exclude the presence of any contraindication to stress testing, complete pretest echocardiography was performed to exclude prosthetic valve malfunction or severe left ventricular dysfunction. Dobutamine was administered intravenously at 10 mg·kg–1 using a peripheral venous cannula. The definitions of valve events were in accordance with published guidelines for reporting valve-related morbidity and mortality.6
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RESULTS
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Results are expressed as mean ± standard deviation. Comparisons of patient characteristics and echocardiographic data were performed by Student's t test and one-way analysis of variance.
The main demographic parameters (age, body surface area, and etiology) showed significant differences between the 2 groups. Preoperative data are listed in Table 1
. There was no perioperative mortality in either group of patients. Early complications were low cardiac output in 6 patients who needed inotropic support. Intra-aortic balloon pumping was not required for any patient. Pericardial tamponade occurred in 1 patient and third-degree atrioventricular block in 2 patients who were restored to sinus rhythm by medical therapy.
Intermediate-term clinical follow-up was marked by a complete absence of valve thrombosis, hemolysis, endocarditis, and paravalvular leakage. There was one anticoagulant-related hemorrhage in group 2 (0.2% per patient-year) due to wrong compliance by the patient. There was no late mortality in group 1 but one patient with a 25-mm prosthesis in group 2 died from congestive heart failure. New York Heart Association functional capacity improved to class I or II in all the other patients (Table 2).
The three different valve sizes were compared to each other by one-way analysis of variance. There were significant differences in Doppler echocardiography-derived pressure gradients among the different valve sizes (Table 3). As expected, patients with 19-mm valves had higher mean and maximal pressure gradients than those with 21-mm and 25-mm valves. The 19-mm valves had the smallest effective orifice areas (mean, 1.1 ± 0.2 cm) and were significantly different from those associated with the 25-mm valves. In patients with aortic stenosis, the diastolic left ventricular posterior wall thickness and interventricular septum thickness were significantly lower in the late postoperative period compared with the thicknesses prior to surgery in each of the three valve sizes (Table 4). There was no statistically significant difference in the changes observed with 19-mm valves.
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DISCUSSION
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The challenge in a valve operation on a small aortic annulus is to obtain the most favorable hemodynamic outcome with the shortest cross-clamp time. Options include root-enlargement techniques and the use of smaller prostheses. The decision is based on patient characteristics (age, lifestyle, and body surface area) and the surgeon's personal experience of root-enlarging procedures and small prostheses. It might be considered that even in experienced hands, aortic enlargement increases the perioperative risk with longer cardiopulmonary bypass and cross-clamp times and an increased probability of bleeding.7 Insertion of a smaller prosthesis without an annular-enlargement procedure may be associated with a lower operative risk but it is expected to result in residual left ventricular outflow obstruction.
Several studies have examined the impact of small aortic prostheses on long-term results. Wortham and colleagues8 in one of the early reports on this issue, suggested that even the 19-mm St. Jude Medical valve prostheses demonstrated a relatively large effective orifice area but the patient should have a body surface area of less than 1.7 m2. In a study by Hayashi and colleagues9, 19-mm or 21-mm prosthetic valves were inserted mainly in elderly patients having a mean body surface area of 1.45 m2 and favorable long-term outcomes similar to those with 23-mm or larger valves were reported. Although several investigators have shown that 19-mm or 21-mm bileaflet valves have acceptable gradients, they used these valves only in patients with a body surface area less than 1.7 m2. Furthermore, Kratz and colleagues10 identified a subset of patients with body surface area greater than 1.7 m2 who received small St. Jude Medical valves and were prone to late sudden death. Dumesnil and colleagues11 demonstrated that a 0.8 to 0.9 cm2·m–2 effective orifice area index was a transition point below which gradients became high. Sommers and David12 also recommended using one of the techniques of annulus enlargement when the predicted valve area index was less than 0.8 cm2·m–2. In our study, the effective orifice area index was significantly different between groups 1 and 2. However, functional capacity improved in spite of this difference because of the decrease in transvalvular gradient.
The transvalvular gradient is still the most frequently used parameter to characterize a prosthetic heart valve. Doppler findings significantly correlate with catheter gradients.13 Doppler echocardiography is currently the standard technique for noninvasive evaluation of the structure and function of a heart valve prosthesis. Carrel and colleagues7 emphasized that Doppler echocardiography is of great value in comparing different sizes of the same valve model. In our study, the preoperative mean peak systolic gradient was reduced from 92 mm Hg to 21 mm Hg but rose to 34 mm Hg (range, 23 to 42 mm Hg) during dobutamine stress testing. A gradient of 42 mm Hg may be considered as mild stenosis. However, Burckhardt and colleagues14,15 suggested that a peak aortic pressure gradient of up to 40 mm Hg did not bear any clinical significance for up to a decade in the majority of patients.
Aortic valve stenosis induces left ventricular hypertrophy due to chronic pressure overload. The treatment of aortic stenosis by valve replacement is usually followed by a reduction of left ventricular hypertrophy. In this study, the significant regression of myocardial hypertrophy documented by echocardiography in the small-sized valve group was similar to that in the large-sized valve group and probably contributed to the favorable clinical outcome. The reason for this clinical improvement while the valves were still stenotic was explained by Rahimtoola16 who suggested that all prostheses have an in vitro effective orifice area that is smaller than that of the normal human valve, thus it is clear that the abnormality in many of the patients has in practice been converted from severe aortic stenosis to mild-to-moderate left ventricular outflow obstruction. He reported that no outflow gradient can be demonstrated across narrowed aortic valves until the effective orifice size is reduced to less than 40% to 60%. In addition, Gorlin and Gorlin17 described the relationship of the gradient to valve area as curvilinear and once the effective orifice size of the aortic valve is critically reduced to less than 35% of normal, the gradient rises precipitously. As a result, small increases in valve area of critically narrowed valves will result in large reductions of the gradient, consequently reducing the afterload on the left ventricle significantly and eventually causing ventricular hypertrophy to regress and ventricular performance to improve.16 Therefore, it should not be expected that the optimum effective prosthetic orifice area is required for symptomatic improvement.
The newer mechanical and stentless valves have larger effective orifice areas. Recent literature suggests that a 19-mm bileaflet prosthesis is adequate for patients with a body area surface up to 1.7 m2. Our findings indicate that prosthetic valve size does not influence intermediate-term results. Aortic valve replacement resulted in excellent symptomatic improvement for all valve sizes. We found that the performance of 21-mm or 19-mm valves was similar to that of 25-mm valves in patients with a body surface area less than 1.6 m2. Although the valve areas were smaller and the valve gradients were higher for the small-sized valves, the variations were unlikely to produce clinical differences.
Our study was limited by the duration of follow-up and the number of patients. Therefore, we will continue to follow-up this group of patients to detect adverse effects of smaller valves. However, within these limitations, we think it is reasonable to suggest that a 19-mm or 21-mm ATS valve can be used as an alternative to an annular enlargement procedure for a patient with a body surface area less than 1.6 or 1.7 m2.
This paper was presented at the VII World Congress of the International Society for Cardiothoracic Surgery, Düsseldorf, Germany, September 2–5, 1997.
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Acknowledgments
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Statistical analyses were made by Yavuz Sinoplu, biostatistic department, Ankara University Faculty of Science.
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ABSTRACT
INTRODUCTION
