J Thorac Cardiovasc Surg 1998;116:599-608
© 1998 Mosby, Inc.
SURGERY FOR ADULT CARDIOVASCULAR DISEASE |
LONG-TERM DOPPLER ECHOCARDIOGRAPHIC RESULTS OF AORTIC OR MITRAL VALVE REPLACEMENT WITH BIOCOR PORCINE BIOPROSTHESIS
Pia S. U. Mykén, MD, PhDa,
Håkan E. Berggren, MD, PhDa ,
Sture Larsson, MD, PhDa,
Barbro Roberts, RNa ,
Ingemar Wallentin, MD, PhDb,
Kenneth Caidahl, MD, PhDb
Göteborg, Sweden
The Biocor pericardial valve, formerly the trademark of Biocor Industria e Pesquisas Ltd, Belo Horizonte, Brazil, was acquired in 1996 by St Jude Medical, Inc, St Paul, Minn.
Received for publication July 18, 1997. Revisions requested Oct 1, 1997; revisions received May 20, 1998. Accepted for publication June 22, 1998.
Address for reprints: Kenneth Caidahl, MD, PhD, Department of Clinical Physiology, Sahlgrenska University Hospital, S-413 45 Göteborg, Sweden.
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Abstract
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Objectives: Our objectives were to evaluate the long-term bioprosthetic and cardiac functional outcome after insertion (over a 10-year period) of a new-generation porcine zero pressure–fixed Biocor bioprosthesis, as well as to determine the echocardiographic accuracy for selection of patients requiring reoperation. The long-term systematic Doppler echocardiographic assessment after valve replacement with this bioprosthesis is lacking.
Methods: Between January 1983 and January 1993, we inserted 756 Biocor prostheses in the aortic (619) or mitral (137) positions. All 51 patients who had a reoperation during the follow-up time were evaluated echocardiographically before reoperation. Additionally, 263 of 446 patients (59%) with aortic bioprostheses and 42 of 74 patients (57%) with mitral bioprostheses who were alive in January 1993 had long-term echocardiographic follow-up.
Results: Group A: Normally functioning bioprostheses were found in the aortic position in 242 of 263 patients and in the mitral position in 33 of 42 patients. Group B: Thirty patients had abnormal bioprosthetic function. Eleven patients had regurgitation, 3 had a combined lesion, and signs of calcification appeared in 16 patients with aortic valves, all with a peak gradient of above 60 mm Hg. Group C: Patients who had a reoperation (41 aortic and 10 mitral) within the follow-up period were followed up echocardiographically from the detection of a possible valve dysfunction until reoperation, and the findings accorded well with those at operation in 49 of 51 patients.
Conclusions: These findings suggest that, during a long-term follow-up, most bioprostheses function normally, facilitating improved heart function. Abnormalities in a bioprosthesis usually develop gradually, enabling their detection by Doppler echocardiographic evaluations performed regularly or in case of any symptomatic deterioration.
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Introduction
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Porcine bioprostheses have been used frequently in recent decades and numerous clinical reports have been published. Calcifications and cusp tears often develop within 10 to 15 years, necessitating a reoperation. Several long-term follow-up studies have reported the frequency of reoperation and other complications such as thromboembolism and prosthetic valve endocarditis.
1-8 Although Doppler echocardiography is generally accepted as the method of choice for monitoring valve function in individual patients with suspected prosthetic dysfunction, few systematic long-term follow-up studies have been conducted with echocardiography after valve replacement with a bioprosthesis. 9,10 It is of the utmost concern, and probably at present the most important issue, to determine the functional outcome for patients with bioprostheses, both to optimize the time of reoperation and to make a fair estimation of the advantages and disadvantages of bioprostheses.
We have already demonstrated the 10-year actuarial freedom from valve-related mortality to be high, 98% for patients with aortic and 95% for those with mitral Biocor prostheses. 6,7 The aims of this study were to delineate bioprosthetic and cardiac function among patients with this porcine bioprosthesis inserted over a 10-year period and to determine echocardiographic accuracy for selection of patients requiring reoperation.
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Patients and methods
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Study patients.
During a 10-year period from 1983 to 1993, 619 patients underwent aortic valve replacement and 137 patients underwent mitral valve replacement with the Biocor prosthesis, a glutaraldehyde-preserved, zero pressure– fixed, stented porcine bioprosthesis (Fig 1). These 756 patients were studied in terms of mortality and morbidity until January 1993. 6,7 All patients who had a reoperation during the follow-up time (41 with an aortic and 10 with a mitral bioprosthesis) were followed up echocardiographically from initial detection of a suspected lesion to reoperation. In addition, 446 patients with aortic and 74 with mitral bioprostheses were alive at the end of this period and had not been reoperated on or lost to follow-up. Doppler echocardiographic investigations performed until July 1994 (in almost 60% of the patients) are presented; if multiple, the last one was chosen for this report. The mean follow-up time was almost 5 years for the group with aortic bioprostheses (52 months, n = 120 > 5 years) and almost 6 years for the group with mitral bioprostheses (71 months, n = 28 > 5 years). There is no definite rule in our region that specifies when or how often Doppler echocardiographic investigations should be performed. Because almost all the patients lacked symptoms, the selection of patients for Doppler echocardiography has been random. These patients were similar to the entire group in terms of sex, preoperative diagnoses, additional coronary bypass surgery, and postoperative New York Heart Association functional classes, although they were somewhat younger than the group as a whole (Table I).
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Fig. 1. Overview of the total cohort. The patients who are highlighted are presented in this study. AVR, Aortic valve replacement; MVR, mitral valve replacement. *Includes 9 valve-related deaths.  Includes 4 valve-related deaths.
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Doppler echocardiography.
Transthoracic Doppler echocardiography was the method used in all patients. Previous collaboration on recording and interpretational techniques has demonstrated that the evaluations are comparable at the different institutions.
M-mode echocardiography was performed according to the recommendations of the American Society of Echocardiography. 11 Measurements of the atrial diameter (normal 
4.0 cm), septal and posterior walls (normal 1.2 cm), as well as the dimension of the left ventricular cavity (normal dimension at end-diastole 5.8 cm), were made. Left ventricular volumes, stroke volume, and ejection fraction were calculated by the formula described by Teichholtz and associates. 12 Left ventricular mass index was calculated as previously described (normal 140 g/m2). 13 The Doppler assessment of valvular leakage was graded as 0 when absent and as 4 when maximum regurgitation, with the other grades dispersed in between, 14 integrating information from color and continuous-wave Doppler echocardiography, as well as the effects on cardiac dimensions. Valve gradients (P) were calculated from continuous-wave Doppler estimates of maximum velocity (v) as P = 4 · v2. We used the peak gradient, which is always higher than the mean gradient. In cases of mitral stenosis, we calculated the gradient half-time from the early deceleration slope. The left ventricular ejection time was obtained from carotid pulse tracings and adjusted for heart rate (normal adjusted value 90%-110%) and the a/H ratio (ratio of atrial height to total apex cardiographic height) was assessed from apex cardiograms as a measure of left ventricular distensibility (normal 15%).
Statistical analysis.
Values are presented as the mean ± standard error of the mean. Wilcoxon's nonparametric paired signed rank test was used to determine the significance of changes between preoperative and follow-up measurements. Patients were regarded as having normal prosthetic function if the prosthetic leakage was grade 2/4 or less and the peak gradient was 60 mm Hg or less for aortic bioprostheses and 15 mm Hg or less for mitral bioprostheses.
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Results
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We present data for those with normal bioprosthetic function (group A), those with abnormal bioprosthetic function (group B), and those requiring reoperation (group C).
Group A: Normal bioprosthetic function.
A total of 274 patients displayed normal bioprosthetic function echocardiographically. Table II shows the measurements before and after the operation among these patients, stratified in groups according to the preoperative diagnoses among those with aortic (n = 242) or mitral (n = 33) bioprostheses.
In the group with aortic bioprostheses, the mean functional class improved from 2.8 before operation to 1.6 at follow-up. The reduction in maximum gradient was 67 mm Hg in patients with an aortic stenosis and 28 mm Hg with mixed aortic lesions, whereas it was unchanged with aortic regurgitation. There was a relationship between prosthetic size and transvalvular gradient, with a higher gradient for size 21 prostheses (Fig 2).
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Fig. 2. Aortic bioprostheses in the group specified as having normal bioprosthetic findings. Mean values for maximum gradients in relation to valve size.
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Right ventricular pressure was reduced to a normal or slightly elevated level. The left ventricular dimension was reduced by valve replacement to a normal, average level in all groups, with the most marked decrease, 1.7 cm in diastole and 1.3 cm in systole, among those with preoperative aortic regurgitation. The left atrial dimension did not change significantly. Among patients with preoperative aortic stenosis, there was a marked reduction in wall thickness—4 mm for the interventricular septum and 3 mm for the posterior wall. Despite an unchanged ejection fraction, the left ventricular ejection time was reduced by approximately 15% in all groups, which meant that the resistance to ejection or the amount of blood to be ejected for each beat was reduced, thus enabling ejection to be finished earlier. Left ventricular distensibility tended to improve according to the apex cardiographic a/H ratio. The left ventricular diastolic volume decreased in all groups, although the decrease was most marked in aortic regurgitation. In this group, systolic volume and stroke volume were both reduced to about 50% of the preoperative values. Left ventricular mass and mass index were reduced by valve replacement in both aortic stenosis (by 26%) and regurgitation (by 41%). We found no relationship between functional class and ejection fraction at follow-up (Fig 3).
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Fig. 3. Distribution of ejection fractions in each functional class (New York Heart Association) for patients with normal aortic bioprostheses.
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Among patients with mitral bioprostheses, the functional class improved from a preoperative mean value of 3.0 to 1.8 at the latest follow-up. Patients with mitral lesions had a transprosthetic gradient of 12 to 13 mm Hg at follow-up (Table II
). There was no consistent relationship between the size of the prosthetic valve and gradient (Fig 4). The mean right ventricular pressure was similar in both categories of preoperative mitral lesions and approximately 20 mm Hg higher than in aortic stenosis or regurgitation, as might be expected. Mitral valve replacement caused a reduction in right ventricular pressure of 17 to 20 mm Hg. The left ventricular dimension was enlarged in mitral regurgitation, and this was reduced by valve replacement. Before the operation, the left atrium was 2 cm larger than the normal size, and valve replacement caused a nonsignificant reduction of 4 to 7 mm. Stroke volume, including regurgitant volume, was reduced by almost 50% in the patient group with regurgitation. We found no relationship between functional class and ejection fraction at follow-up (Fig 5).
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Fig. 5. Distribution of ejection fractions in each functional class (New York Heart Association) for patients with a normal mitral bioprosthesis.
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Group B: Abnormal bioprosthetic function.
Individual data for the patients with abnormal Doppler echocardiographic data are presented in Table III for those with aortic bioprostheses and in Table IV for those with mitral bioprostheses. As can be seen in Table III, only 1 patient had a mean aortic gradient of above 45 mm Hg, and this was also the only patient in functional class IV. His condition was considered by the local hospital to be inoperable and he was not reoperated on. Severe regurgitation (grade 3/4) was present in 4 patients. None of the patients with an available ejection fraction had a value lower than 50%.
Table IV presents the data for each of the 9 patients with any suggestion of bioprosthetic problems in the mitral group. One of the patients had definite signs of bioprosthetic stenosis, and 4 other patients had a low ejection fraction. Two patients had a large left ventricle (7.0 and 7.5 cm) without significant mitral or tricuspid regurgitation.
The mean (median) time that elapsed from operation until echocardiography was 51 (54) versus 56 (49) months among those with normal and abnormal aortic bioprostheses and 67 (69) versus 85 (86) months among those with normal and abnormal mitral bioprostheses. In neither case did the time from operation to echocardiography differ significantly between those judged as normal and those judged as abnormal. Consequently, there were weak correlations between time to echocardiography (days) and maximum gradient (r = –0.012, no significant relationship), regurgitation grade (r = 0.15, P = .02), and estimation of leaflet calcifications in 2-dimensional echocardiography (r = 0.19, P = .02). The correlations were somewhat higher between estimated calcification and aortic regurgitation (r = 0.26, P = .001) and maximum gradient (r = 0.39, P < .0001). The possible influence on aortic prosthetic valve gradient was further evaluated in a multivariate analysis. Valve size (P < .0001), body surface area (P < .01), and age (P < .01) contributed to the explanation of maximum gradient, whereas time to echocardiography did not. When groups of valve sizes were being evaluated, a positive correlation was noted between time to echocardiography and prosthetic valve gradient in the groups with a large (
size 29) prosthesis (r2 = 0.29, P < .05), whereas no relation was seen among those with smaller prosthetic valves.
Group C: Reoperations.
In all, 51 patients were reoperated on during the 10-year period. Most of them were followed up repeatedly with Doppler echocardiography before the reoperation.
Forty-one patients with aortic bioprostheses were reoperated on (Table V). Twenty-seven of these (mean age 55.6 years) had structural valve deterioration, with calcification or stiffness in the cusps or cusp rupture. Six patients with paravalvular leakage were reoperated on, as were 8 patients with prosthetic valve endocarditis. The initial bioprosthesis lasted on average 45.3 months. In only 4 of 27 cases of structural valve deterioration was the reoperation performed within a shorter time than 4 months from the first echocardiographic detection, with just 1 patient undergoing an emergency reoperation. The average time from the detection of an abnormality in the bioprosthesis until the reoperation was performed was 1.5 years. This contrasts with the time frame for those with paravalvular leakage and even more strongly with that for those with prosthetic valve endocarditis. However, the time interval from the initial operation to reoperation for those patients with paravalvular leakage was almost 2 years (23.6 months), and for those reoperated on due to prosthetic valve endocarditis it was 35 months. Actuarial analysis (Cox) did not show any difference in reoperations between those with a small (size 21 or 23) prosthetic valve and those with a larger valve.
Most patients (21/27) who were reoperated on because of structural deterioration in the aortic bioprosthesis had a Doppler-determined regurgitation of greater than grade 2/4, and in only 1 patient was no leakage detected. At operation, paravalvular leakage, with some degree of cusp rupture, was detected in 7 of 27 patients, all but 1 with regurgitation of greater than grade 2/4 before reoperation; the remaining patient had moderate preoperative regurgitation and increasing left ventricular dimension. Another 15 of 27 patients were found to have bioprosthetic cusp rupture at reoperation, 13 with a preoperative regurgitation of greater than grade 2/4 and 2 with moderate regurgitation and an increasing left ventricle. In 3 of 27 patients, calcified or stiff valves were the main operative finding; 2 of these patients had a preoperative gradient of greater than 60 mm Hg, and the third had a leakage of more than grade 2/4. In 2 of 27 patients (1 with a gradient of > 60 mm Hg and the other with regurgitation of > grade 2/4), no major bioprosthetic lesion was detected during reoperation. Because these patients had a gradual deterioration in heart function before reoperation and an obvious recovery after reoperation, we characterized them as valve-dependent. All 6 patients with nonstructural valve dysfunction had paravalvular leakage at reoperation and severe preoperative regurgitation. The patients with prosthetic valve endocarditis had cusp vegetations, destroyed cusps, or an abscess at operation and a preoperative clinical picture, together with Doppler echocardiographic findings, indicative of prosthetic valve endocarditis.
Ten patients with mitral bioprostheses were reoperated on during the follow-up period because of structural valve deterioration with a high gradient (n = 3), nonstructural dysfunction with severe paravalvular leakage (n = 3), or prosthetic valve endocarditis with vegetations (n = 4) (Table VI). The mean age of the patients reoperated on because of structural valve deterioration was 46 years and the mean time from the implantation of a mitral bioprosthesis until reoperation for structural valve deterioration was 79 months. As was the case for the patients with aortic bioprostheses who were reoperated on because of prosthetic valve endocarditis, almost all (3/4) those with mitral endocarditis required an emergency operation. Patients with nonstructural dysfunction all displayed paravalvular leakage at reoperation and a corresponding severe preoperative regurgitation. The findings were also convincing among the patients with prosthetic valve endocarditis.
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Discussion
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The results of this study demonstrate that almost all the patients (92%) without findings leading to reoperation had normal valve function as measured by transthoracic Doppler echocardiography. However, this extrapolation is associated with some uncertainty, because echocardiography was not performed in all patients. Despite the facts that some patients were not evaluated by echocardiography and the noninvasive investigations were not randomized, the only likely selection bias was over-representation of younger ages and atrial fibrillation among those having an investigation. If anything, this factor should have helped to emphasize valve function problems, because we have previously found in the same cohort that lower age is associated with a worse outcome. 6,7 We therefore believe that the functional results presented in this study are representative of the total group undergoing valve replacement with a bioprosthesis.
Doppler echocardiographic functional assessment.
We were not able to find any correlation between functional class (New York Heart Association) and ejection fraction (Figs 3 and 5). Inasmuch as the patients have estimated their own functional class, the assessment is obviously not merely based on physical capability but is probably also influenced by psychologic factors. However, even the relationship between objectively measured exercise capacity and ejection fraction is low or lacking among patients with congestive heart failure. 15
Our normal mitral Doppler gradients are concordant with the data reported by Alam and colleagues. 16 In patients with aortic bioprostheses, these authors found a somewhat lower transprosthetic gradient than we did; however, our data are identical with those reported by Eriksson and associates 17 and compare well with review data of earlier reports. 18 In accordance with previous findings of an inverse relationship between valve size and gradient in aortic prostheses, 19 the peak gradient with a size 21 aortic bioprosthesis was higher than that of size 23 or larger valves.
Valve replacement caused both a hemodynamic improvement in valve function and improved left ventricular function. The diastolic left ventricular cavity dimension and volume decreased in all groups apart from mitral stenosis. Another beneficial and anticipated finding was a reduction in the thicknesses of the septal and posterior walls in patients with aortic stenosis, with normalization of diastolic function as measured by the apex cardiographic a/H ratio.
We considered prosthetic regurgitation of more than grade 2/4 or a maximum aortic gradient of more than 60 mm Hg or a mitral gradient of more than 15 mm Hg to be putatively abnormal, and the individual data for such patients are therefore presented separately. The limit for causing suspicion of a malfunction can be discussed and lower, but increasing, gradients or leakages may be taken as warning signs. Most patients of this type are likely to require a future reoperation. However, in the early postoperative phase, an intraventricular increase in flow velocity may increase the estimated prosthetic gradient 20 and, in patients with an outflow tract velocity of above 1.5 m/s, the correction of the Doppler calculation of maximum gradient may be justified. 21 Among our patients regarded as having potentially abnormal function of their bioprosthesis according to Doppler echocardiography, there was only a nonsignificant tendency toward longer time from operation to the echocardiographic evaluation. Prosthetic valve age did not explain valve gradient in a multivariate analysis, whereas size of the valve as well as size and age of the patient contributed significantly. Thus other factors than time contribute to valvular deterioration, and the weak correlation between bioprosthetic age and Doppler echocardiographic findings indicates a low risk that a high proportion of valves should fail after a certain time period. Time to reoperation also varied considerably (Table V).
Evaluation of candidates for reoperation.
Reoperations cannot be avoided with any type of bioprosthetic valve. An early Doppler echocardiographic investigation is therefore recommended for future comparisons when prosthetic valve malfunction is suspected. 22 When a high gradient or an abnormal leakage is found, it is important to conduct repeated investigations; the appropriate time interval is dependent on the severity of the findings. Thereby, only 1 of our patients had to be reoperated on on an emergency basis because of valve deterioration. As has previously been claimed by others 23,16, we received valuable information from the single or serial echocardiographic investigations performed before reoperation, with good correspondence to the intraoperative findings. Nowadays we apply not only transthoracic but also transesophageal echocardiography in cases of acute endocarditis or suspected prosthetic valve dysfunction, and these methods were also in some cases used to describe the findings among our patients who underwent reoperation. Transesophageal echocardiography can be used for an evaluation of the aortic valve 24, but its greatest potential and value is in the evaluation of malfunctioning mitral valves, particularly for paravalvular regurgitation 25,26. It is highly recommended that transesophageal echocardiography be performed in cases of suspected prosthetic valve malfunction and negative transthoracic investigation 27,28.
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Conclusions
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Most of the patients (275/305, 90%) had a bioprosthesis that functioned well, as determined by echocardiography in a majority of patients and clinical absence of important symptoms in the remaining patients. A small number of patients (30/305, 10%) had abnormalities in their biologic valves, possibly necessitating reoperation in the future. In the subgroup of patients who had already undergone reoperation, the preoperative Doppler echocardiographic investigations corresponded almost completely to the intraoperative findings. Bioprosthetic abnormalities in terms of calcification or cusp rupture (or both) and their hemodynamic consequences develop gradually and can be monitored safely by Doppler echocardiography to choose the optimum time for reoperation.
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Acknowledgments
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We appreciate the performance of Doppler echocardiographic evaluations by the staff at the Departments of Clinical Physiology and Medicine at the hospitals in western Sweden and in particular the Borås, Mölndal, Norra Älvsborg, Sahlgrenska, Skövde, Uddevalla, Varberg, Örebro, and Östra Hospitals.
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Abstract
Introduction
