Ann Thorac Surg 1997;64:421-425
© 1997 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Long-Term Follow-up of Small (Size 20 and 21) Medtronic-Hall Aortic Valve Prostheses
Jean-Francois Obadia, MD, PhD,
Yvan A. Martelloni, MD,
Olivier H. Bastien, MD,
Guy M. Durand de Gevigney, MD,
Jean-Francois Chassignolle, MD
Hôpital Cardiologique Louis Pradel, Lyon, France
Accepted for publication February 7, 1997.
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Abstract
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Background. Our goal was to study the long-term follow-up of patients having aortic valve replacement and to focus particularly on the patients receiving small prostheses.
Methods. Four hundred twenty-eight Medtronic-Hall valves were implanted (156 size 20 or 21 mm, 149 size 22 or 23 mm, and 123 size 25 or 27 mm). Group 20–21 had a higher number of female patients, more associated coronary lesions, and more patients with aortic stenosis.
Results. The actuarial survival rate at 8 years was 80% for group 20–21, 80% for group 22–23, and 76% for group 25–27 (p = not significant). In group 20–21, the actuarial event-free rates at 8 years were as follows: thromboembolic complications, 94%; prosthetic valve endocarditis, 99%; reoperation, 98%; and hemorrhagic complications, 78%. The only factors of prognostic value in this group were age and associated coronary lesions.
Conclusions. The durable nature of the results obtained with the Medtronic-Hall 20- and 21-mm prostheses compared with large-diameter prostheses allows the use of a simple and reliable surgical technique and should mean that indications for ring enlargement become rare.
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Introduction
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During implantation of an aortic prosthesis in a small ring, the surgeon may occasionally have to decide between insertion of a small prosthesis adapted to the size of the ring and insertion of a larger prosthesis at the price of ring enlargement. Residual obstructions to left ventricular outflow have been reported 3 to 5 years after aortic valve replacement [1]. This study was designed to investigate the long-term survival (up to 8 years) of patients receiving a Medtronic-Hall aortic valve prosthesis with particular focus on the patients given small-sized prostheses.
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Material and Methods
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Between January 1984 and June 1993, 428 patients underwent aortic valve replacement with a Medtronic-Hall valve. Of them, 156 consecutive patients received a Medtronic-Hall 20- or 21-mm prosthesis in the aortic position. These two sizes are the smallest Medtronic-Hall prostheses available. The other 272 patients were given a larger Medtronic-Hall prosthesis. The 428 patients were divided into three groups. Group 20–21 comprised 156 patients with a Medtronic-Hall prosthesis of size 20 mm (n = 80) or 21 mm (n = 76). The housing structure is the same for both the 20-mm and the 21-mm prostheses; only the size of the sewing ring differs, being standard for the 21-mm model and thin for the 20-mm model. Group 22–23 comprised 149 patients receiving a size 22-mm (n = 6) or size 23-mm (n = 143) prosthesis. Again, the housing structure is the same for both, and only the size of the sewing ring differs (standard for size 23 and thin for size 22). Group 25–27 comprised 123 patients receiving a size 25-mm (n = 109) or size 27-mm (n = 14) prosthesis; only a standard-size suture cushion is available for these diameters, and sizes 22 and 23 are, in fact, prostheses of different diameters.
The clinical data are given in Table 1
. There was a higher proportion of female patients in group 20–21, and there was a significant difference in body surface areas (BSAs) between the three groups. There were no differences between the three groups in body weight and age. Dyspnea was less marked and angina pectoris less frequent in group 23–25. Group 20–21 included more patients with aortic stenosis (Table 2) and fewer patients with aortic insufficiency than the other two groups. Coronary lesions were also more frequent in the small-size group than in the other two groups. There were no differences between the three groups in terms of hemodynamic function (see Table 2), number of patients having operation for infective endocarditis (3.50%) or on an emergency basis (1.78%), or number of reoperations (0.89%).
Operative Technique
All operations were performed using standard bypass with moderate hypothermia (28° to 30°C). Myocardial protection was afforded by antegrade crystalloid cardioplegia (cannulation of the coronary ostia) given every 20 minutes and supplemented by pericardial cooling. The Medtronic-Hall prosthesis was implanted using individual sutures on the Teflon ring. The prosthesis was positioned with the small aperture facing the noncoronary sinus. Enlargement of the annulus was necessary in 4 patients, and was accomplished using a simplified Manouguian technique [2]. Because coronary lesions were more frequent in group 20–21, more coronary bypass procedures were performed together with valve replacement. A Bentall or Cabrol procedure was rare (only one in this group) (Table 3).
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Table 3. . Distribution of Size of Prosthesis as Function of Surgical Procedure on Aorta and Concomitant Coronary Revascularizationa
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Anticoagulant Management
Continuous intravenous anticoagulation with heparin sodium was initiated immediately after operation. On day 5, this was replaced by an oral anticoagulant. The desired international normalized ratio was between 3 and 4.5. No patient received platelet-aggregation inhibitors.
Data Collection and Follow-up
Prospective computerized data collection was performed in our department for all patients. After the postoperative period including a consultation with the surgeon at 2 months, the patients were usually followed by their own cardiologist. However, for this study, all surviving patients were either seen again at our institution or recontacted by letter, and a questionnaire on outcome data was completed. The data entered in our computerized database were completed or confirmed by means of a survey involving the attending physician. This survey ended on November 1, 1996. Cumulative follow-up was 883.55 patient-years for group 20–21, 847.42 patient-years for group 22–23, and 742.76 patient-years for group 25–27. Twelve of the 428 patients were lost to follow-up, ie, a rate of loss to follow-up of 2.8% and a mean follow-up of 5.8 years.
Statistical Analysis
The definitions used are those recommended by The Society of Thoracic Surgeons and The American Association for Thoracic Surgery [3]. Frequency was compared by means of Student's t test or 
2 test with Yates' correction. All events were included in calculation of linearized rates (% per patient-year) and event-free actuarial survival (%). Survival rates were calculated using the Kaplan-Meier method [4]. Testing for significance in the observed differences was performed using the log-rank test.
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Results
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Operative Mortality
Operative mortality was 1.28% for the 156 patients in group 20–21, 0.67% for the 149 patients in group 22–23, and 4.88% for the 123 patients in group 25–27. The difference between the first two groups was not significant, but mortality was higher in group 25–27 compared with the other two groups (p < 0.05).
Course of Dyspnea
Before operation, 49% of the patients receiving a Medtronic-Hall 20- or 21-mm prosthesis were in New York Heart Association class III or IV. At the end of this study, none of the surviving patients were in class IV, 9% were in class III, and 91% were in class I or II. The results were not significantly different for the other two groups (Table 4).
Long-Term Follow-up
Eight-year survival was 80% for the 156 patients in group 20–21, 80% for the 149 patients in group 22–23, and 76% for the 123 patients in group 25–27 (Fig 1). Outcome comparisons for the three survival curves did not show any significant differences.
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Fig 1. . Actuarial survival of 428 patients receiving Medtronic-Hall aortic valve prosthesis as a function of prosthesis size.
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Valve-Related Complications
Neither valve-related deaths nor valve-related complications have occurred.
Prognostic Factors for Patients Receiving Medtronic-Hall 20- or 21-mm Prosthesis
INFLUENCE OF AGE.
The 156 patients in group 20–21 were distributed by age as follows: 50 patients less than 60 years old, 63 patients 60 to 69 years old, and 43 patients 70 years old and older (Fig 2). There was no difference between patients less than 60 years old (88% survival at 8 years) and patients 60 to 69 years old (84% survival at 8 years). However, survival was worse (p < 0.01) for patients 70 years old and older (62% at 8 years).
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Fig 2. . Actuarial survival of 156 patients receiving Medtronic-Hall 20- or 21-mm aortic valve prosthesis as a function of age.
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INFLUENCE OF SEX.
There was no significant difference in 8-year survival between the 62 female patients (82%) and the 94 male patients (78%).
INFLUENCE OF CONCOMITANT CORONARY LESIONS.
The actuarial survival of group 20–21 as a function of coronary lesions exhibits less encouraging results (p < 0.05) in the presence of coronary lesions (Fig 3). Actuarial survival for the 36 patients seen with coronary lesions was 68% at 8 years versus 83% for the 120 patients with no coronary lesions. However, statistical comparison of the 22 patients undergoing revascularization and the 13 patients not undergoing revascularization is not possible because of the small size of the respective populations.
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Fig 3. . Actuarial survival of 156 patients receiving Medtronic-Hall 20- or 21-mm aortic valve prosthesis as a function of presence of coronary artery disease (CAD).
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INFLUENCE OF BODY SURFACE AREA.
There was a difference in BSA between group 20–21 and the other two groups (see Table 1
) but no difference in actuarial survival rate between the three groups (see Fig 1). Further, BSA did not influence the results within group 20–21; the actuarial 8-year survival was 76% for the 50 patients with a BSA smaller than 1.25 m2, 82% for the 62 patients with a BSA between 1.25 and 1.75 m2, and 79% for the 44 patients with a BSA greater than 1.75 m2.
Event-Free Linearized Rate
In group 20–21, event-free actuarial survival rates at 8 years and linearized rates expressed as percent per patient-year were as follows: hemorrhagic complications, 78% and 3.04%, respectively; prosthetic valve endocarditis, 99% and 0.27%; reoperation, 98% and 0.27%; and thromboembolic complications, 94% and 0.54%. There were no instances of prosthetic valve thrombosis, paraprosthetic leakage, or hemolysis.
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Comment
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Quality of Results in Patients Given Small-Diameter Prosthesis
Our experience with the Medtronic-Hall aortic valve prosthesis with an 8-year follow-up shows that the group receiving a small-diameter prosthesis differs from the other groups. There was a greater number of female patients than in the other two groups, although male patients were preponderant. The main indication was aortic stenosis, and coronary lesions were more frequent in this group. The only significant prognostic factors in group 20–21 were age and presence of coronary lesions.
Although it is not surprising to see lower survival in the elderly patient group, we emphasize that the results were good even for patients older than 70 years. This finding confirms the value of this surgical approach, widely recognized at present, for aortic pathologic conditions in patients of all ages. In this subgroup of patients who are generally less active, a small-diameter prosthesis is a better choice [5] because tissue fragility in elderly patients makes enlargement of the ring more difficult.
Examination of the long-term follow-up findings shows particularly favorable percentages of patients without complications. These are, in fact, superior to those reported in the literature for patients receiving mechanical prostheses [5, 6]. The low rate of thromboembolism is probably explained by the rather heavy regimen of anticoagulation for aortic valve replacement. Hemorrhagic complications were somewhat increased. We also note that the event-free linearized rates took into account the complications reported by the patients at the end of the study or those with permanent sequelae. This probably decreases the overall number of complications, as some minor accidents can be forgotten and not reported by the patients. However, it is difficult to conduct an exhaustive investigation. For instance, it has been reported that even in the absence of clinically apparent stroke, patients have a high incidence of abnormal findings on computed tomography of the brain, indicating prior silent cerebral infarction [7]. Nevertheless, the method of data collection was the same for the three groups.
Our patients did not experience any of the negative effects that might have been expected in patients with small-diameter aortic valve prostheses. The rate of major complications is low and at least comparable to the results obtained with larger prostheses. Further, the dyspnea course and the long-term survival rate suggest that the hemodynamic conditions were acceptable. Long-term survival and quality of life are the main goals of this procedure rather than having a theoretically better transvalvular gradient, which would require a more aggressive and unjustified approach.
Factors Involved in Choice of Prosthesis Size
The choice of aortic valve prosthesis size can be difficult, particularly for small diameters where the surgeon may have to choose between the desire to obtain a minimal transvalvular gradient and the need to perform surgical enlargement of the ring and between the wish to obtain the best functional result and the desire to use a simple, reliable, relatively nonaggressive surgical procedure. The existence of a moderate residual transvalvular gradient, however, is not correlated with the quality of survival, and excellent results have been reported with the Ionescu-Shiley prosthesis [8], Lillehei-Kaster prosthesis [9], and even with small-diameter bioprostheses [10].
Certain recommendations do limit the use of small-sized prostheses. The 19-mm pericardial prostheses should be used only in patients with a BSA of less than 1.3 m2 [11]. The requirements in elderly patients appear less important, as this population is less active, and good results can be obtained even with small prostheses [3]. Nevertheless, not all types of prostheses behave in the same way in the small-diameter versions [12, 13], even if the data in the literature are on occasion contradictory. Further, Kratz and associates [14] have shown that in patients whose BSA is less than 1.9 m2, when a 19- or 21-mm valve is used, the results are the same with either a St. Jude 19-mm device or ring enlargement. He and co-workers [15] found no difference between several types of devices (Starr-Edwards and Carpentier-Edwards) implanted in small-diameter rings.
In addition to monitoring the progress of patients, it is also useful to determine the ability of patients with small-diameter prostheses to adapt to exercise [16]. This has been done in studies involving a dobutamine hydrochloride test. In this way, Ota and colleagues [17] tested patients with a Medtronic 21-mm or 23-mm prosthesis or a Björk-Shiley 23-mm device. The gradients remained quite low, even with high cardiac flow. In contrast, patients with St. Jude 19-mm and Björk-Shiley 21-mm devices exhibited early and steep gradients. In addition, Izzat and coauthors [18] showed that the resting performance of CarboMedics 19- and 21-mm valves was comparable to their performance during dobutamine stress testing.
Overall, the good results reported in the literature for small-sized prosthetic valve implants suggest a cautious approach to indications involving ring enlargement [19], particularly as manufacturers are currently making the rings thinner to facilitate implantation of small prostheses. Further, the fact that Medtronic prostheses are unavailable in sizes smaller than 21 mm means that the surgeon must maintain a minimal aperture of 21 mm, which has given good hemodynamic results, as reported by Ota and associates [13], and which also gave good clinical results, as reported by Akins [20] and in our series. This approach that we recommend leads to few situations requiring ring enlargement.
Conclusions
The good results obtained with the Medtronic-Hall aortic valve prosthesis have been confirmed. The long-term nature of these results for all sizes of prostheses, particularly small-diameter prostheses, allows the use of simple and reliable surgical procedures and should mean that situations requiring enlargement of the ring become rare.
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Footnotes
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Address reprint requests to Dr Obadia, Service de Chirurgie Cardio-Thoracique, Hôpital Cardiologique, 59 Boulevard Pinel, 69003 Lyon, France.
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References
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Abstract
Introduction
