Asian Cardiovasc Thorac Ann 2004;12:213-217
© 2004 Asia Publishing EXchange Ltd
Aortic Valve Replacement with the Medtronic Freestyle Stentless Bioprosthesis
Alexander John, MD,
Christoph Glauner, MD,
Mohammad Ali Manoutcheri, MD,
Virgilijus Ziaukas, MD,
Gummiah Muniputtana Mahesh, MD,
Henning Warnecke, MD
Department of Heart Surgery, Schuechtermann Klinik, Bad Rothenfelde, Germany
For reprint information contact: Alexander John, MD Tel: 49 54 2464 1651 Fax: 49 54 2464 1653 Email: htg{at}schuechtermann-klinik.de Schuechtermann Klinik, Ulmenallee 11, 49214 Bad Rothenfelde, Germany.
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ABSTRACT
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During a five-year period from 1996 to 2000, the Medtronic Freestyle stentless bioprosthesis was implanted in 310 patients of advanced age. Age at operation ranged from 60 to 90 years (mean, 76 ± 4 years). 191 patients were female and 119 male. All implants were done by the modified subcoronary method using our own modification which enabled an improved adaptation of the porcine aortic root to the human anatomy. Two sinuses were scalloped and the third left intact. Additional coronary bypass grafts were necessary in 129 (39%) patients and mitral valve procedures in 23 (7%). Mean perfusion time was 109 ± 12 minutes and crossclamp time 87 ± 8 minutes. 16 (5%) patients died perioperatively. Another 17 (5.7%) patients died during a 1 to 5.6 year follow-up (mean, 2.9 years). There was only one valve related death due to infection of the valve. In spite of the advanced age, 95% of the survivors were free from cardiac symptoms and continued to live an active and fruitful life. The biological nature of the valve and the low gradients are perhaps reasons for the good results. The long-term results are expected to be good.
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INTRODUCTION
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Biological valves are preferable in very old patients because they do not require anticoagulant medication and provide improved hemodynamic function.1 The concept of stentless valves came out of the success of homograft valves and the long-term degenerative failure of the stented porcine valves.2 Several major heart valve manufacturers have brought into the market their version of a stentless aortic valve. The Freestyle bioprosthesis (Medtronic, Minneapolis, MN, USA) is one such available model. This valve is a porcine aortic root fixed with 40 mm pressure on the sinuses and zero pressure across the cusps. It is additionally treated with alpha-amino-oleic acid in an attempt to reduce the potential for leaflet calcification. The valve is supplied in a buffered 0.2% gluteraldehyde solution. It has to be washed in isotonic saline for about ten minutes before implanting. It differs from the human valve in some important aspects.3 Although the inflow of the bioprosthesis is circular in a single horizontal plane, the noncoronary sinus is smaller in circumference than the right and left sinuses (Figure 1
). In the human valve the left coronary sinus is usually the smallest. In the Freestyle valve both the coronary sinuses project outwards and each has at its apex the ligated coronary ostium. The porcine ostia are closer together, at about 130° on the circumference of the root, whereas in the human aortic root they lie at about 150° from each other. When the human ostia lie diametrically opposite, at 180° as in a truly bicuspid valve, this is a relative contraindication to the subcoronary implant technique. The porcine right ostium lies vertically at a higher plane than the left. The Dacron cloth covering the muscle bar reaches a height of 10 to 12 mm and lies mainly below the right ostium (Figure 2). Each of these features plays a role in the optimal way of implanting this prosthesis. This versatile prosthesis can be implanted in various ways. The most common technique is the modified subcoronary procedure described by Westaby and colleagues.4 We have further modified this technique and evolved a standard procedure which suits every patient except those with congenital bicuspid valves and coronary ostial abnormalities. The rationale behind our modification was to achieve an optimal adaptation of the porcine aortic root to the human anatomy, enabling a near-perfect "cylinder within a cylinder" seating of the implanted bioprosthesis. In this report we present the operative and intermediate term follow-up results of a group of patients who received the Freestyle valve.
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Figure 1. The Freestyle valve seen from the inflow aspect. Note the smaller size of the noncoronary leaflet and the outward projecting coronary sinuses.
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Figure 2. The lateral view of the valve as the surgeon gets it in hand. Note the Dacron cloth covering the muscle bar on the outside. This is completely excluded from the circulation.
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PATIENTS AND METHODS
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Between June 1996 and December 2000, 310 patients underwent aortic valve replacement with a Freestyle bioprosthesis. All patients above the age of 70 years were recommended a biological valve. A few younger patients who had contraindication to anticoagulant therapy also received this valve. Some of the patients required other cardiac procedures as well. Written informed consent was obtained from each patient prior to operation. The preoperative data of the patients are shown in Table 1.
Median sternotomy provides good access to the proximal aorta and the right atrium. Venous cannulation is done using a single two-stage cannula. Retrograde cardioplegia is preferred with occasional supplementary antegrade ostial perfusion and additional local cooling. Aortotomy is done 2 cm above the right coronary ostium (Figure 3). After excising the valve and removing all the calcium from the annulus, sizing is done. A size that provides a snug fit within the aortic root is chosen. Simple interrupted 2-0 braided Dacron sutures are used, taking sufficient bites of the annulus and ensuring that they lie more or less in the same horizontal plane. About 15 to 18 sutures are sufficient (Figure 4). After the valve is washed free of the gluteraldehyde it is prepared before the sutures are taken through it. The valve is rotated clockwise through 120 degrees so that the ligated right ostium faces the noncoronary sinus of the patient. The scalloping of the other two sinuses is done opposite the human coronary ostia. The smallest of the porcine sinuses, namely the noncoronary sinus, now faces the patient’s left coronary sinus which is usually the smallest. The ligated right ostium is also excised with the adjacent sinus wall to leave a hole approximately 6 to 8 mm in diameter. A piece of the excised porcine aortic wall is cut to an appropriate size and sutured with 5-0 Prolene to close this hole (Figure 5). This procedure makes the sinus flatter and prevents the formation of a dead space outside the valve where a hematoma can form. The sutures are taken through the valve which is then seated and tied. The outflow aspect of the xenograft is sutured to the aorta using two double armed 4-0 Prolene continuous sutures, each starting at the depth of the right and left coronary sinuses (Figure 6). If the aortic wall is calcified, calcium is removed from those areas where the continuous outflow suture-line is going to lie, taking care not to get close to the coronary ostia. The aortotomy is closed using a single row of continuous over and over sutures. If the aortic wall is very thin, Teflon strips are laid above and below and the sutures taken through them. After de-airing, the aortic clamp is released and in most cases the heart starts beating spontaneously. Intraoperative echocardiography is not routinely done but will be of help if there is any doubt about the competence of the valve.
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Figure 3. The aortotomy lies 2 cm above the right coronary ostium which can be located from the outside. The cut runs transversely for about two-thirds of the circumference of the aorta.
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Figure 4. The valve prepared for implanting. The noncoronary and left sinuses have been scalloped. The right ostium has been excised and the defect closed using a piece of the excised aortic wall. This enables a snug fit within the aorta.
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Figure 5. Simple interrupted sutures are taken through the annulus more or less in the same horizontal plane. Only 15 to 18 sutures are necessary.
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Figure 6. The valve is seated and the outflow suture line completed. Aortotomy closure starts from the right end.
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The operative data are shown in Table 2. The majority (90%) of the valves implanted were 23, 25 or 27 mm in size. 127 (39%) patients received additional coronary bypass grafts. 23 (7%) patients also had mitral valve procedures. The valves implanted in the mitral position were stented biological prostheses (Hancock, Medtronic, Minneapolis, MN, USA). Five (1.5%) patients came with acute endocarditis of their native valves. Twenty-seven (80%) patients had a previous cardiac operation. Out of these, 17 were coronary bypass operations and 10 valve replacements. Three patients were operated on for acute prosthetic valve endocarditis.
Following the operation all aortic valve patients in sinus rhythm received 100 mg aspirin daily for six weeks only. Coronary bypass patients continued to receive aspirin. Those patients with stented valves in the mitral position received warfarin for three months. In addition, all patients in atrial fibrillation continued to receive anticoagulants in the form of warfarin sodium.
All patients had a Doppler echocardiographic study before discharge from the hospital, 3 to 6 months later and then annually. The patients were contacted either directly or through their house doctors and/or cardiologists. The follow-up was complete.
Descriptive statistics (number of patients, mean, minimum and maximum) were used to describe age at implant and cumulative follow up. The Kaplan-Meier method was used to estimate survival. Peto’s formula was used to calculate the standard errors of the survival estimates.
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RESULTS
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There was a perioperative mortality of 16 (5%) patients. The causes of early deaths were mediastinal sepsis in 3 patients, gastrointestinal bleeding in 6, myocardial infarction in 4 and postoperative low output in 3. Patients requiring isolated aortic valve replacement belonged to a higher age group (mean age 79 ± 4 years) but had a lower mortality of 4.6%.
Follow-up ranged from 1 to 5.6 years with a mean of 2.9 years. An additional 8 patients died during the first year. Six deaths occurred during the second, two deaths during the third, and one death during the fourth postoperative year. The total number of late deaths was 17 (5.7%). The causes of late deaths were: myocardial infarction and cardiac failure in three patients; cerebral bleeding probably due to warfarin in two; renal failure in two and as a result of a hip operation; carcinoma of the stomach; carcinoma of the pancreas and endocarditis of the implanted valve in one patient each. In six patients the cause of death could not be verified. The patient with endocarditis was a 75-year-old lady who presented 8 months after the operation with an infected 21 mm Freestyle valve. Blood cultures grew Staphylococcus Aureus. At operation the leaflets were found to be destroyed by the infection. A mechanical valve was implanted. Four months later she again came back with recurring prosthetic valve endocarditis and died after the third operation. This was the only valve related death in the series.
The information on survival is given in the actuarial survival curve (Figure 7). One of the double valve patients was diagnosed as having a significant incompetence at the aortic valve 3 days after operation, and was subsequently reoperated on. The second row of sutures was taken down. The inflow suture line was intact. The continuous suture was redone and the valve was competent. There was probably distortion caused by the outflow suture line.
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Figure 7. The linearized rate of freedom from death following aortic valve replacement using the Freestyle stentless valve.
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During the follow-up there were a number of problems related to the advanced age of the patients. 27 patients required pacemaker implantation. 14 needed carotid artery endarterectomy. Four patients developed hemiplegia with varying degrees of residual disability. Four others had transient neurological problems with full recovery. Six patients had their hip joints replaced, four of them after a fracture. One patient developed a spinal canal narrowing and now needs a wheelchair to move around. Patients who developed tumours of the pancreas, stomach, colon, breast, uterus, urinary bladder and prostate were successfully operated on.
Echocardiographic assessment showed a continuing decrease in valve gradients during the first year (Table 3). There were no cases with significant incompetence. Trivial incompetence was seen in 15 patients which did not increase during the period of follow-up.
The vast majority of patients (85%) were satisfied with the operation and were leading an active life. Another group (10%) was fairly well but had some limiting problems. A small group (5%) was quite unwell and had a variety of major problems not related to the heart.
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DISCUSSION
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The Freestyle stentless valve, because of its special features, can be implanted in a number of ways.5 In very old patients it provides an ideal substitute. The very low gradients across the valve and the minimum of synthetic surfaces exposed to the circulation are definite advantages. Anticoagulants are not necessary, thus reducing the morbidity and mortality caused by hemorrhagic problems in this age group. However, the accurate sizing and the proper technique of implantation using two rows of sutures are important and can be surgically demanding.
The question of how best to implant the valve has not yet been resolved. Different centres use different methods but in very old patients and in those with small aortic roots the method has to be reliable and reproducible. Long-term results are necessary to judge the merits and shortcomings of a particular method. The technique described here can be applied in all patients except those with true bicuspid valves and congenital coronary ostial abnormalities.
Various problems with this valve have been reported. Dehiscence at the annulus occurred when a continuous suture was used at the inflow.6 Distortion with leaflet immobility leading to thrombosis and high gradient was another problem. This can occur if one tries to accommodate the valve in an abnormal aortic root.7 Coronary ostial abnormalities are definite contraindications to this method. Infective endocarditis can occur like in any implanted valve but the flexibility and the virtual absence of prosthetic material in the circulation are perhaps reasons why this valve shows a high resistance to infections. In fact, in patients with native or prosthetic valve endocarditis, this valve provides a good solution.8 In the entire series only one valve got infected. It is important to avoid a dead space between the bioprosthesis and the human aorta.9 Buckling of the cloth under the right coronary ostium, causing obstruction and turbulence, has been reported.10 This is the other reason why we routinely rotate the valve to the right to bring the Dacron cloth covering the muscle bar to lie in the human noncoronary sinus. Central incompetence due to splaying of the valve outlet can occur in cases of dilated sinotubular junction.11 This is unlikely to occur by this method as the valve has the proximal aorta with it and most of the circumference of the aorta gets tailored to the porcine aorta. This is the reason why we do not scallop all three of the sinuses. The incidence of incompetence was negligible both in the short-term and long-term follow-up.
The issue of durability of these valves is still open. Longer follow up is necessary to know when these valves begin to degenerate. Good results with stented porcine valves in elderly patients have been reported.12 David and associates have further compared stented and stentless valves and shown superior results in terms of immediate and late survival and freedom from complications and reoperation using the Toronto SPV stentless bioprosthesis.13 However, Lucianiand colleagues, using five different models of stentless valves and differing methods of implantation, reported increased reoperation rates compared to stented valves although valve-related mortality was better.14 It is expected that the stentless valves perform better, given the improved hemodynamics and the dissipation of stress away from the leaflets to the natural elastic aortic annulus. In our experience the clinical and hemodynamic results using the Freestyle stentless bioprosthesis have proven to be excellent. Proper sizing and standardised technique of implantation are essential for better long-term results.
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ACKNOWLEDGMENTS
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We thank Mr. Dieter Goerbing for preparing the illustrations and Ms. Vicki Hench, the Statistics Manager of the Medtronic company, for the statistical analysis of the data.
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REFERENCES
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- Westaby S. The stentless aortic bioprosthesis. In: Piwnica R, Westaby S, editors. Surgery for acquired aortic valve disease. Oxford, UK: ISIS Medical Media Ltd 1997:83–101.
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ABSTRACT
INTRODUCTION
