Aortic Valve Replacement with Stentless Porcine Bioprostheses

The implantation of stentless porcine valves (SPVs) is technically more demanding than implantation of stented bioprosthetic valves. Implantation of the Toronto SPV bioprosthesis requires an,understanding of the relationships between the leaflets and the aortic annulus and sinotubular junction. In addition to proper alignment of the three commissures within the aortic root, the diameter of sinotubular junction should not exceed the external diameter of the porcine aortic valve after completion of the operation. The Medtronic Freestyle porcine aortic root bioprosthesis can be used for subcoronary implantation as well as for aortic root replacement. Degenerative calcification of a tricuspid aortic valve is the most common cause of aortic valve disease in older patients. Implantation of stentless valves in the subcoronary position is usually feasible because the geometry of the aortic root is well maintained in these patients. The bicuspid aortic valve is the second most common cause of aortic valve disease in older patients and the most common in younger patients. These patients frequently have dilated aortic root, and the Medtronic Freestyle bioprosthesis is ideal for implantation using the root inclusion technique. Stentless porcine bioprostheses are minimally obstructive and associated with low mean systolic gradients. In addition, they have better hemodynamic performance during exercise than stented bioprostheses. For these reasons, patient-prosthesis mismatch has not been described with stentless valves. Left ventricular function after aortic valve replacement appears to be better with stentless than with stented bioprostheses. Comparative, nonrandomized studies of aortic valve replacement with stented and stentless valves suggest that the risk of cardiac death is reduced with stentless valves and the rates of valve-related complications also appear to be lower. What remains unknown is whether stentless valves are more durable than stented ones.     

Stentless porcine and pericardial valve in aortic position.

Fifty-seven patients underwent aortic valve replacement with a stentless glutaraldehyde-fixed bioprosthesis; 27 received a porcine aortic valve and 30 had a bovine pericardial valve. Two groups of 30 patients each who had aortic valve replacement with a tilting-disc mechanical valve or a stented porcine bioprosthesis served as controls. There were no differences in sex, body surface area, valve lesion, and valve size among the four groups. Results were assessed on a Doppler-based determination of maximum velocity across the valve, aortic valve area, and degree of valve regurgitation. Velocity across the valve was significantly less with stentless pericardial valves than with stentless porcine valves, stented bioprostheses, and mechanical valves. Stentless valves had a significantly larger aortic valve area when compared with stented valves. Mild central aortic insufficiency was detected more often with stentless pericardial than with stentless porcine bioprostheses (p = 0.04). Stentless valves showed a higher incidence of complete atrioventricular block when compared with stented valves (p = 0.04). Long-term studies are now warranted to assess the durability of both types of stentless valves.     

Hemodynamic performance of an unstented xenograft mitral valve substitute

OBJECTIVE: Stentless mitral xenografts offer potential clinical benefits because they mimic the normal bileaflet mitral valve. How best to implant them and their hemodynamic performance and durability, however, remain unknown. METHODS: A stentless porcine mitral xenograft valve (Medtronic physiologic mitral valve) was implanted in 7 sheep with papillary muscle sewing tubes attached with transmural left ventricular sutures. Radiopaque markers were inserted on the leaflets, annular cuff, papillary tips, and left ventricle. After 10 +/- 5 days, the animals were studied with biplane videofluoroscopy to determine 3-dimensional marker coordinates at baseline and during dobutamine infusion. Transesophageal echocardiography assessed mitral regurgitation and valvular gradients. Mitral annular area was calculated from the annular markers. Physiologic mitral valve leaflet and annular dynamics were compared with 8 native sheep valves. RESULTS: Average mitral regurgitation grade at baseline was 1.2 +/- 1.0 (range, 0-4), and the mean transvalvular pressure gradients were 3.6 +/- 1.3 and 6.2 +/- 2.2 mm Hg during baseline and dobutamine infusion, respectively. Xenograft mitral annular area contraction throughout the cardiac cycle was reduced (6% +/- 6% vs 13% +/- 4% for physiologic mitral valve and control valve, respectively; P =.03). Physiologic mitral valve leaflet geometry during closure differed from the native valve, with the anterior leaflet being convex to the atrium and with little motion of the posterior leaflet. Three animals survived more than 3 months; good healing of the annular cuff and papillary muscle tubes was demonstrated. CONCLUSION: This stentless xenograft mitral valve substitute had low gradients at baseline and during stress conditions early postoperatively, with mild mitral regurgitation. Preliminary analysis of healing characteristics appeared favorable at 3 months. Additional studies are needed to determine long-term xenograft mitral valve performance and resistance to calcification.     

Rapid and untypical calcification of the Sorin pericarbon stentless pericardial xenograft in a child

Stentless valves are designed to reduce mechanical stress and it is hypothesized that degeneration is reduced. We report early calcification of a Sorin pericarbon stentless pericardial xenograft in aortic position leading to valve failure 2 years after valve replacement in an 11-year-old boy. Morphological evaluation of the explant revealed severe calcification of the leaflets in a uniformly distributed pattern. Positive staining for non-collagen bone matrix proteins was found in the organic matrix of calcific deposits and in infiltrated macrophages. The stentless design of the Sorin valve does not mitigate calcification and therefore cannot be recommended for children.     

Aortic root remodeling with the "cuff" technique for stentless valve implantation

Aortic root and sinotubular junction dilatation and aneurysm of ascending aorta are considered relative contra-indications to implantation of a stentless valve prosthesis, because the modified aortic geometry leads to aortic incompetence and early failure of the prosthesis. Aortic root reconstruction can be performed according to various techniques. We present a surgical technique in which a tubular graft, replacing an ascending aortic aneurysm, allows sinotubular remodeling and satisfactory implantation of a stentless prosthesis. The native aorta is inserted into the vascular prosthesis at the level of the sinotubular junction which is wrapped in order to prevent commissure spreading. Sizing of the vascular and valve prosthesis is made according to annular diameter. Since October 1999, 6 patients have been operated using this technique with good results.     

无支架二尖瓣制备、保存和体外三尖瓣置换技术探讨

目的观察深低温保存猪二尖瓣超微结构,探索无支架二尖瓣制作方法和置换三尖瓣技术。方法采用猪二尖瓣制成无支架瓣膜,抗生素灭菌深低温保存,透射电子显微镜观察深低温保存１个月的猪二尖瓣组织结构。将离体猪心三尖瓣切除,将无支架猪二尖瓣前瓣环缝合于隔瓣环,二尖瓣后瓣环缝合于三尖瓣前后瓣环,两乳头肌缝合于右心室前壁,完成无支架二尖瓣置换三尖瓣,注水试验观察瓣膜启闭功能。结果透射电子显微镜观察到,深低温保存猪二尖瓣内皮细胞结构完整,胶原纤维结构致密,排列整齐,成纤维细胞胞膜完整,细胞核无固缩现象,线粒体无明显肿胀。无支架二尖瓣置换的离体猪心三尖瓣启闭功能良好。结论深低温保存的无支架猪二尖瓣结构完整,活性得到很好保持。瓣膜设计合理,用此瓣膜置换三尖瓣技术可行     

Exercise hemodynamics of aortic prostheses: comparison between stentless bioprostheses and mechanical valves

BACKGROUND: Nonstented bioprostheses have been associated with lower resting gradients than stented bioprostheses or mechanical valves. We compared the hemodynamic performance of nonstented bioprostheses and mechanical valves with normal native aortic valves at rest and exercise. METHODS: Dobutamine echocardiography was used to assess gradients and effective orifice area index at rest and exercise in patients with the Toronto stentless porcine valve (TSPV; n = 13; mean implant size 25.7 mm), Medtronic Freestyle (FR; n = 11; mean implant size 23.9 mm), Sorin Bicarbon (SOR; n = 11; mean implant size 24.5 mm), St. Jude Medical (SJM; n = 10; mean implant size 21.3 mm), and normal native aortic valves (NOR; n = 10). RESULTS: All groups demonstrated a major rise in cardiac output at maximal dobutamine infusion. At rest and exercise, respectively, mean gradients were 5.48 +/- 1.1 mm Hg and 5.83 +/- 0.9 mm Hg for TSPV, 5.68 +/- 1.2 mm Hg and 7.50 +/- 1.7 mm Hg for FR, 10.29 +/- 1.4 mm Hg and 20.78 +/- 2.7 mm Hg for SJM, 5.26 +/- 0.8 mm Hg and 11.1 +/- 1.8 mm Hg for SOR, and 1.54 +/- 0.4 mm Hg and 2.18 +/- 0.7 mm Hg for NOR. In comparison with normal valves, both stentless groups showed no change in mean gradient at exercise, whereas both mechanical groups showed an increase in gradient at exercise (p < 0.04). CONCLUSIONS: Stentless valves behave similarly to normal aortic valves in that there is almost no increase in gradient at exercise. Both mechanical valve groups showed increased gradients at exercise, suggesting that these valves obstruct blood flow. Our data add further evidence that stentless valves are hemodynamically superior to mechanical valves in the aortic position.     

In-vitro study on the relationship between progressive sinotubular junction dilatation and aortic regurgitation for several stentless aortic valve substitutes.

OBJECTIVE: Stentless aortic valves are widely used due to their excellent hemodynamic properties. However, if the subcoronary implantation technique is used later dilatation of the sinotubular junction (STJ) can cause regurgitation. The aim of the study was to determine the dilatation tolerance of two commercially available stentless xenografts and fresh aortic and pulmonary roots against such dilatation. METHODS: Four groups each comprising five specimens of fresh porcine aortic roots, pulmonary roots, Medtronic freestyle or Toronto SPV Xenografts were tested in a mock circulation using a special device for gradually increasing the diameter of the sinotubular junction. The smallest diameter D(r) where regurgitation occurs was measured and correlated with the starting diameter D(a) and expressed as per cent values. Opening and closing patterns were obtained by a high speed camera and flow characteristics were determined. RESULTS: The highest dilatation tolerance of STJ was found in the fresh porcine aortic roots (165%+/-10) followed by fresh pulmonary roots (146%+/-12), the Freestyle (143%+/-4) and the SPV (132%+/-5) bioprostheses. All differences were significant with P< or =0.05 except that between the fresh pulmonary roots and the two commercial available bioprostheses. CONCLUSIONS: Our results indicate that aortic homografts provide higher resistance against regurgitation induced by dilatation of the STJ than an autograft or the stentless xenografts, Freestyle xenograft followed by the Toronto SPV. The use of the full-root technique should be considered if aortic dilatation seems to be likely.     

Stentless bioprostheses in aortic root disease

INTRODUCTION: The availability of aortic homografts is steadily decreasing. In the meantime, stentless xenografts convey similar flow characteristics, and tissue preservation methods are improving durability. Initially, these valves were contraindicated in aortic roots with discrepancy between annulus and sinotubular junction or with extensive calcification or sepsis. With increasing experience stentless xenografts are now applied in a wide spectrum of aortic root disease. METHODS: I reviewed our own experience with stentless aortic bioprosthesis for aortic valve replacement (AVR) and more taxing root problems. I used these valves in aortic aneurysm repair, acute Type A dissection, and for endocarditis with abcess formation. I studied valve hemodynamics, regression of left ventricular hypertrophy, and comparative survival with stented bioprostheses. RESULTS: Stentless bioprostheses convey hemodynamic and possibly survival benefit through a low incidence of valve-related complications. They provide a useful alternative to aortic homografts in endocarditis, Type A dissection, and aortic aneurysm surgery. CONCLUSIONS: Stentless bioprostheses are no longer confined to AVR alone. Experience supports the use of stentless bioprostheses where aortic homografts were previously applied. With availability in a wide range of sizes.     

Stentless bioprosthetic aortic valve replacement after a homograft root replacement: Toronto SPV implantation after a homograft root

Stentless bioprosthetic valves for the aortic position offer excellent hemodynamic characteristics, making them an attractive choice ahead of other valve prostheses. We present a unique case in which a patient underwent aortic valve replacement with a stentless porcine valve and mitral valve repair for severe aortic and mitral regurgitation 1 year after a homograft root replacement for acute aortic endocarditis. The rationale for our approach is outlined in the context of current surgical trends.     

First pulmonary valve replacement with Freedom Solo stentless valve in an adolescent. A case report

Tetralogy of Fallot (TOF) is a common form of cyanotic heart disease. Complete surgical correction in younger age group offers good long-term results with reasonable morbidity and improved prognosis in patients with TOF. However, following corrective surgery pulmonary valve replacement (PVR) might be required for residual pulmonary regurgitation in order to avoid irreversible right ventricular remodeling. Otherwise, residual uncorrected pulmonary regurgitation may lead to right ventricular dilatation, impaired biventricular function, ventricular arrhythmias and limited exercise capacity. We report the first case of Freedom Solo stentless valve (Sorin Group, Saluggia, Italy) implantation in the pulmonary position in an adolescent with severe pulmonary insufficiency 12 years after the repair of TOF. Pericardial stentless valves may be an alternative choice for pulmonary valve replacement to improve right ventricular contractile recovery and remodeling after PVR and may have impact on long-term survival.     

Quantitative approach to aortic valve-sparing surgery

Our goal was to understand why it is difficult to achieve reliable valve competence after aortic valve-sparing surgery, and to propose quantitative data aimed at improving the outcome of the procedure. Valve-sparing procedures were performed in patients with dilated aortic roots and aortic regurgitation, and reproduced in physical models to explore what should be the restored dimensions of the aortic root and leaflets for valve sparing to be successful. In parallel, a three-dimensional geometric model of the aortic valve was tested to evaluate its capability to predict the annulus diameter, sinotubular junction diameter, valve height, and leaflet free-edge length and height in competent spared valves. Valve sparing resulted in more or less severe residual regurgitation in all the patients considered. Successful valve-sparing was achieved in vitro by making further changes to the annulus diameter, the leaflet free-edge length and/or graft size. The changes needed were effectively predicted by the geometric model. Tabulated valve dimensions allowing restoration of competence were generated for convenient use by surgeons. A quantitative approach to aortic valve sparing is proposed, putting emphasis on the functional characteristics of the restored valve geometry.     

Thrombocytopenia after aortic valve replacement with the Freedom Solo stentless bioprosthesis

Stentless bioprostheses have been considered to achieve superior hemodynamics over stented bioprostheses for aortic valve replacement with improved long-term performance. We observed severe thrombocytopenia in patients who received the Sorin Freedom Solo aortic stentless pericardial bioprosthesis within the first days after implantation. Absolute and relative platelet counts within 2 weeks after implantation of either a stentless (Sorin Freedom Solo) or a stented (Sorin Mitroflow) bovine pericardial bioprosthesis were compared in a matched-pairs analysis in 40 patients. Except the preoperative values, absolute platelet count was higher at all time points in the Mitroflow group. In the Mitroflow group, the mean platelet count moderately dropped to a minimum of 60% of the initial value on POD 3 and fully recovered by POD 8. In the Freedom Solo group, platelet loss was significantly more severe (minimum relative value 25% on POD 4) with no recovery during follow-up (60% on POD 13). Eight patients of the Freedom Solo group experienced a critical platelet drop towards <20% of their initial values, in five of them absolute numbers decreased below 30,000/microl. No bleeding complications or other morbidity occurred. Attention should focus on the platelet count after implantation of the Freedom Solo bioprosthesis, especially in patients who are supposed to receive platelet inhibitors. However, the described phenomenon remains unexplained.     

Early stenotic prosthesis failure after implantation of a stentless porcine aortic valve prosthesis

Stentless biological aortic prostheses are used routinely in aortic valve replacement surgery, offering beneficial hemodynamics compared to stented biological valves of similar size. We report here a rare case of early stenotic prosthesis failure of a RootElan stentless porcine aortic valve prosthesis due to swelling at the bottom of the right coronary cusp of the prosthesis.     

Surgical treatment for a supra sinotubular junctional saccular aneurysm associated with aortic regurgitation

We reported a patient with a saccular ascending aortic aneusysm located just above the non-coronary sinotubular junction. The aneurysm produced severe aortic regurgitation and two episodes of cardiac tamponade. By intraoperative inspection, the border between the aneurysmal wall and non-dilated portion of the normal aortic wall was distinct, and the aortic valve leaflets and aortic annulus appeared normal. Aortic valve dysfunction appeared to be caused by dilation of the noncoronary sinotubular junction and mild distortion of the noncoronary sinus because of the aneurysmal formation. We performed patch closure of the aneurysmal ostium and repaired the dilated noncoronary sinotubular junction. Postoperative echocardiography and aortograpy demonstrated a good coaptation of the aortic valve leaflets with trivial aortic regurgitation. Although a rupture site, dissection or carcinomatous pericarditis which is attributable to the two episodes of cardiac tamponade could not be found, pathologic examination of the aneurysm wall revealed intramural blood leakage between the mucoid degenerated media and notably thickened adventitia. In addition, there was thinning and interruption of the elastic fibers of the media. These findings are consistent with a leaking aneurysm which cause the slow development of cardiac tamponade.     

Surgical treatment for a supra sinotubular junctional saccular aneurysm associated with aortic regurgitation.

We reported a patient with a saccular ascending aortic aneurysm located just above the non-coronary sinotubular junction. The aneurysm produced severe aortic regurgitation and two episodes of cardiac tamponade. By intraoperative inspection, the border between the aneurysmal wall and non-dilated portion of the normal aortic wall was distinct, and the aortic valve leaflets and aortic annulus appeared normal. Aortic valve dysfunction appeared to be caused by dilation of the noncoronary sinotubular junction and mild distortion of the noncoronary sinus because of the aneurysmal formation. We performed patch closure of the aneurysmal ostium and repaired the dilated noncoronary sinotubular junction. Postoperative echocardiography and aortography demonstrated a good coaptation of the aortic valve leaflets with trivial aortic regurgitation. Although a rupture site, dissection or carcinomatous pericarditis which is attributable to the two episodes of cardiac tamponade could not be found, pathologic examination of the aneurysm wall revealed intramural blood leakage between the mucoid degenerated media and notably thickened adventitia. In addition, there was thinning and interruption of the elastic fibers of the media. These findings are consistent with a leaking aneurysm which cause the slow development of cardiac tamponade.     

Aortenklappenersatz mit gerüstlosen Bioprothesen

Stentless valves were designed to improve postoperative hemodynamics in comparison to stented bioprosthesis. The implantation technique of stentless valves is very different from conventional bioprostheses: a stented bioprosthesis maintains its form, due to the rigid stent, whereas the form of a stentless valve depends on the surgical suture lines. The general goal is to snugly fit a stentless valve into the aortic root and, thereby, to ensure optimal hemodynamic results. Insufficient coaptation of the cusps and bulging of the prosthesis into the outflow tract are the results of suboptimal implantation techniques. Residual gradients after stentless valve implantation impede postoperative quality of life and long-term survival. The present paper aims to describe the principles of implantation of stentless valves and to standardize the procedure using the Freestyle prosthesis as an example. The standardization of surgical technique and the identification of common pitfalls are mandatory to avoid unfavorable learning curves and to improve quality of life and long-term survival.     

The extended Biocor stentless aortic bioprosthesis. Early clinical experience.

In the "Extended" Biocor stentless aortic bioprosthesis, supra- and subvalvular extensions to a bovine pericardium ring carry three porcine leaflets. The extensions cover the "non-coronary" sinus of the prosthesis and allow optional enlargement of the aortic root down towards the mitral valve as well as upwards into the aortotomy. Seventy-one patients with this stentless valve (62 with predominantly aortic stenosis, 28 with concomitant CABG) are being prospectively studied. This paper reports follow-up one year after insertion. The upper and lower pericardial extensions were used in 61 and 11 patients, respectively. The average prosthetic valve size was 23.2 +/- 1.6 mm. Early mortality was 7% (5/71); late mortality (4/66, 5%/patient year) was not valve-related. Symptoms of thromboembolism (new neurological defects) occurred in four patients. There was no valve failure or late endocarditis. One year postoperatively the transvalvular mean pressure difference for all valves was 7.9 (3.1-18.4) mmHg. None of the patients had haemodynamically significant aortic regurgitation at follow-up; nine had trivial regurgitation. The "Extended" Biocor stentless bioprosthesis thus has a favourable haemodynamic profile and can be advantageous in elderly patients with narrow aortic roots, and often with thin and/or calcified aortic walls.     

Modified tricuspid ring annuloplasty to reduce residual regurgitation in functional tricuspid regurgitation

We describe a modified technique of tricuspid ring annuloplasty to reduce postoperative residual regurgitation in patients with functional tricuspid regurgitation; first, an adjustable segmental tricuspid annuloplasty is performed to obtain coaptation of the valve leaflets with two 5-0 monofilament annular sutures, and then a prosthetic ring of the same size as the competent valve area is implanted with continuous 3-0 polypropylene sutures.     

A novel stentless mitral valve

Stentless mitral valves have found little clinical utility to date due to difficulty in insertion. A new design for a stentless mitral valve, a modification of an existing aortic stentless prosthesis, is described. The new design mimics the native mitral physiology, and its insertion is easier than with existing stentless mitral valves. Commercially available stentless aortic valves were inserted into 2 pigs. The valves were modified so that the commissural posts were restrained. The valves were partially recessed into the left ventricular cavity, secured to the annulus, and anchored to the native papillary muscles. Both pigs were weaned from bypass successfully, and both valves functioned normally with trace regurgitation noted on echocardiography. This design affords the benefit of the reapproximation of native physiology. Preservation of papillary-annular continuity should allow maximal left ventricular function. Lack of a stent should allow avoidance of long-term anticoagulation.