The CryoLife-O'Brien composite stentless porcine aortic xenograft valve in 118 patients.

The CryoLife-O'Brien stentless valve is a composite trileaflet porcine aortic valve. It is assembled from 3 non-coronary leaflets and has no foreign material support. It is therefore truly stentless. From December 1992 to January 1996, 118 patients with aortic valve replacement had a CryoLife-O'Brien stentless valve inserted at the Prince Charles Hospital, Brisbane. The mean age was 73 years (range 59-89) and 54% were men. Most patients had aortic stenosis secondary to a calcific degenerative valve. Follow-up is 100% with hematological and echocardiographic studies before discharge, at 6 months, and at 12-18 months. Five deaths (2 early and 3 late) have occurred and morbidity includes 3 strokes, 1 peripheral embolism, 3 perivalvular leaks, and 1 patient with late endocarditis. Valve performance has been good, with low transvalvular gradients and only a trace or no regurgitation in over 95% of patients after 18 months. No structural deterioration or hemolysis has occurred. Echocardiographic surveillance confirms a very effective central orifice. Short-term results show that the overall performance of the CryoLife-O'Brien stentless valve has been very satisfactory, with low mortality and morbidity in this elderly group of patients. The benefits include the absence of prosthetic material, wide leaflet coaptation, and a quick and easy insertion. Long-term anticoagulation is not necessary. It is particularly suitable for elderly patients with a symmetrical aortic root.

Postoperative hemodynamics of two bileaflet heart valves in the aortic position.

BACKGROUND AND AIMS OF THE STUDY: In vivo hemodynamic assessment of bileaflet aortic valve prostheses using standardized echocardiography is still uncommon; hence, adequate comparison of valve types can rarely be made. We compared the postoperative hemodynamics of St. Jude Standard valves (SJS) with those of Sorin Bicarbon valves (BC) implanted in the aortic position, using pulsed, continuous and color Doppler echocardiography. METHODS: The examination was performed four months after aortic valve prosthesis implantation in 76 patients (39 SJS valves, 37 BC valves). Valve sizes varied from 19 mm to 25 mm. Maximal and mean instantaneous pressure gradients were measured by Doppler echocardiography. Effective valve orifice area (EOA) was calculated and prosthetic valve regurgitation was assessed by color Doppler flow imaging. RESULTS: At valve sizes of 21 mm, 23 mm and 25 mm, SJS valves had a significantly lower EOAs than BC valves (p < 0.05). However, for a given nominal size, BC valves are larger, i.e. they have a larger anatomic (AOA) and geometric orifice area (GOA) than SJS valves. Consequently, BC valves were implanted in patients with a larger left ventricular outflow tract (p < 0.05). When EOA is related to the corresponding AOA, BC valves still show a larger EOA than SJS valves (p < 0.05). Prosthetic valve regurgitation is low in both valve types. CONCLUSIONS: (a) Nominal valve size is not always a good basis for comparison of hemodynamic profiles between valve types. (b) Using the relationship between EOA and AOA, the hemodynamic profile of BC valves in the aortic position is shown to be superior to that of SJS valves.

Discrepancy of sizers for conventional and stentless aortic valve implants.

BACKGROUND AND AIM OF THE STUDY: As the hemodynamic performance of an artificial heart valve is closely related to the size of the valve implanted, exact sizing of the prosthesis is important in aortic valve replacement. In the past, discrepancies have been recognized between the actual and labeled diameters of sizers used for conventional aortic valves; this study aimed to examine the accuracy of sizers for both conventional and stentless valves. METHODS: Currently used sets of sizers were analyzed using a high-precision digital micrometer with a resolution of 0.01 mm. Sizers of aortic bileaflet mechanical valves (ATS, CarboMedics, St. Jude Medical Standard, St. Jude Medical HP), conventional aortic bioprostheses (Carpentier Edwards) and stentless aortic bioprostheses (Freestyle, TorontoSPV) were analyzed. The diameters were recorded when the sizer could not be moved laterally while still able to be rotated. RESULTS: Results are given as mean +/- standard deviation for 20 repeat measurements. All mechanical valve sizers were 0.77 +/- 0.03 to 1.01 +/- 0.02 mm larger than labeled, whereas all bioprosthetic valve sizers proved to be sized as labeled (0 +/- 0.01 mm). CONCLUSIONS: Exact sizing is important in stentless valve replacement. The use of accurate sizers is recommended with other types of replacement valves as well. Results of valve replacement procedures worldwide would be more comparable if sizers of identical size were available in all operating rooms. As long as discrepancies between different sizers still exist, surgeons must be made aware of the problem.

Immunoglobulins and complement deposits in mitroflow pericardial bioprosthetic heart valves--a contributing factor to structural deterioration.

BACKGROUND AND AIMS OF THE STUDY: Twenty-two bovine pericardial Mitroflow prostheses were explanted after 73-114 months from either the aortic or mitral position because of clinical failure. All the samples exhibited cuspal tears and foldings. Eleven prostheses were calcified. The aim was to study biological factors involved in the structural deterioration. METHODS: Histologic and biochemical assays were carried out on the deteriorated, non-calcified and on the calcified leaflets. Labelled antibodies and avidinbiotinyilated peroxydase complex were used to detect plasma proteins and cells in the cusps. RESULTS: Fibrin covered the cuspal surface and accumulated in the deep disrupted layers (19/22). Scattered fibronectin filaments were seen across the transversal sections (20/22). IgG, complement fractions C1q, C3, C4 (20/22), macrophages (sixteen) and cells containing granulocyte elastase were revealed in the altered matrix. These plasma proteins and cells were detected in the disintegrated matrix of non-calcified and of calcified leaflets. IgA was present in amorphous cuspal thickenings with lipid infiltration (12/22). Western blot analysis of the PBS-2% SDS extracts from the leaflets indicated the breakdown of fibrinogen/fibrin, fibronectin and of complement proteins C3, C4 and C5. CONCLUSIONS: The results suggest the activation of the complement by the non-hemocompatible, chemically processed bovine pericardium. The bioactive peptides generated in this process can stimulate monocyte migration, phagocytosis and exocytosis of proteases able to degrade the glutaraldehyde cross-linked macromolecular matrix. These biological factors can contribute, together with the mechanical stress, to the structural deterioration of the bioprosthesis.

Stentless bioprostheses for the small aortic root.

BACKGROUND AND AIMS OF THE STUDY: Despite a variety of different artificial heart valves no ideal prosthesis for the small aortic root is yet available. Conventional stented valves are hemodynamically disadvantageous because of higher transvalvular pressure gradients. Stentless bioprostheses were implanted in such patients to evaluate their performance as an alternative to homografts and to conventional mechanical prostheses. MATERIALS AND METHODS: We analyzed 57 patients with small aortic roots who underwent stentless aortic valve replacement (Toronto SPV) from March 1993 to November 1995. All but two patients had aortic stenosis. The mean age at operation was 70.9 (+/-8.2) years. The annular diameter was 18-23 mm (mean 21.4 +/- 1.1 mm) in all patients. Of the 57 patients, 17 received a 23 mm and 40 patients a 25 mm prosthesis. RESULTS: Using the oversizing technique, valve size was adjusted according to the sinotubular junction diameter, allowing a gain in prosthesis size of 2-4 mm to be achieved in all patients. On pre-discharge echocardiography maximum flow velocity was 2.3 +/- 0.4 m/s, maximum pressure gradient was 19.1 +/- 6.8 mmHg, and effective valve orifice area was 1.46 +/- 0.27 cm2. All patients were in NYHA class I or II at discharge. One patient was reoperated due to a folded annulus caused by too much oversizing. At six months follow up there was a significant reduction in pressure gradients and an increase in effective valve orifice areas in relation to a decrease in pre-existing left ventricular hypertrophy. CONCLUSIONS: Stentless bioprostheses show excellent hemodynamics due to their comparably large internal diameter and flexibility. Controlled oversizing is a safe technique without additional complications. As larger valve sizes can be implanted, aortic root enlargement is not necessary. The superior hemodynamic profile of stentless aortic valves is especially advantageous in patients with small aortic roots.

Small aortic root in the elderly: use of stentless bioprosthesis.

BACKGROUND AND AIMS OF THE STUDY: Aortic root enlargement in the elderly patient prolongs aortic valve replacement procedures and may be problematic if the root is calcified. Mechanical valves have superior hemodynamics compared to tissue valves in the smaller sizes but are often contraindicated in the older patient. MATERIALS AND METHODS: Between January 1993 and November 1995, we implanted 80 Freestyle (Medtronic, Irvine, CA) stentless porcine valves using the freehand subcoronary technique. Twenty-seven of the patients had small aortic roots with an average age of 76.3 years (69-84). Seven patients received size 19 valves and 20 patients had size 21 valves. RESULTS: The average echocardiographic gradient at hospital discharge was 17.9 mmHg (12.1-23.0) for size 19 valves and 15.3 mmHg (5.7-27.9) for size 21. At one year postoperative follow up the average gradient had decreased to 12.9 mmHg (9.3-17.5) for size 19 and 8.0 mmHg (2.2-19.3) for size 21 valves. Effective orifice areas increased from 1.09 cm2 at the time of discharge to 1.29 cm2 at one year follow up for size 19 valves, and from 1.30 cm2 to 1.56 cm2 for size 21. No patient had more than mild aortic insufficiency at most recent follow up. CONCLUSION: This stentless porcine prosthesis has excellent hemodynamics in the smaller valve sizes which improve at least during the first year following surgery. We feel that it is the valve of choice in older patients with small aortic roots.

Stentless aortic valve replacement with the biocor prosthesis: indications and outcome.

BACKGROUND AND AIMS OF THE STUDY: Due to improved hemodynamic properties stentless bioprostheses represent a new therapeutic option in the surgical treatment of aortic valve disease. MATERIALS AND METHODS: Between February 1993 and June 1995 22 patients with a small aortic root regarded as suboptimal for a stented bioprosthesis (diameter < or = 23 mm, mean 21.6 +/- 1.9 mm) underwent aortic valve replacement with a Biocor stentless prosthesis. Mean age was 63.9 +/- 15.4 years (17-85 years). Valve size ranged from 21 to 27 mm (mean 25 mm) and exceeded the root diameter by 4 mm. As compared to a control group of patients with root enlargement (n = 10) total bypass time and cross-clamp time in the stentless group were significantly shorter (83.3 +/- 12.7 and 60.9 +/- 9.2 min versus 95.8 +/- 27.1 and 69.5 +/- 16.5 min, p = 0.054 and p < 0.05), respectively. RESULTS: Three patients died postoperatively unrelated to the choice of valve. There were no late deaths. No thromboembolic or bleeding events were observed. Follow up data are available over a period of 1-25 months (mean 12.5 months, median 16 months). Echocardiographic evaluation revealed no aortic regurgitation; mean valve gradients were 9.9 +/- 4.1 mmHg (peak 19.2 +/- 6.0 mmHg). For specific root diameters these gradients were compared to established data for Hancock bioprostheses demonstrating significant differences in transvalvular gradients between the two valve designs for given root diameters. Unloading the left ventricle resulted in regression of left ventricular hypertrophy (decrease in wall thickness from 13.6 +/- 1.7 mm to 11.2 +/- 2.0 mm). Exercise capacity improved from NYHA III-IV preoperative to I-II postoperative. CONCLUSIONS: In patients with a small aortic root stentless valves represent a new option. Compared to root enlargement with standard bioprosthesis myocardial ischemia is shorter and implantation of larger valve sizes results in superior hemodynamics.

The influence of the design on the medium to long-term hemodynamic behavior of 19 mm pericardial aortic valve prostheses.

BACKGROUND AND AIMS OF THE STUDY: The hemodynamics of five designs of 19 mm pericardial aortic valve bioprosthesis were examined by Doppler echocardiography in 48 resting patients at medium or long term follow up. METHODS: The salient differences among the five designs are that valve leaflets are mounted inside the support frame in one (the Carpentier-Edwards valve, evaluated in five patients) and outside the frame in the other four (the Ionescu-Shiley (14 patients), Mitroflow (six patients), Bioflo (eight patients) and Labcor-Santiago (15 patients)); and that two models have either total (Bioflo) or partial (Labcor-Santiago) protective pericardial sheaths on the stent, while the other three do not. The hemodynamic parameters determined included transvalvular pressure drop, valve area, left ventricular outflow tract diameter, subvalvular/valvular velocity ratio and subvalvular/valvular velocity-time integral ratio. RESULTS: There were no significant differences among the various valves as regards left ventricular outflow tract diameter, subvalvular/valvular velocity ratio or subvalvular/valvular velocity-time integral ratio. Negative correlation between left ventricular outflow tract diameter and subvalvular velocity (r = -0.63, p < 0.001) confirmed the need to correct for prevalvular velocities when using the Bernoulli equation to calculate the pressure drop across small pericardial aortic valve bioprostheses. The Bioflo design caused significantly greater pressure drops (peak 49.6 +/- 11.3 mmHg, mean 28.1 +/- 6.1 mmHg) and provided smaller areas (0.80 +/- 0.16 cm2) than the Ionescu-Shiley (26.7 +/- 6.6 and 15.2 +/- 4.1 mmHg, 1.17 +/- 0.17 cm2) and Labcor-Santiago (24.8 +/- 5.9 and 15.1 +/- 3.7 mmHg, 1.24 +/- 0.12 cm2) valves. CONCLUSIONS: Of the currently available 19 mm bovine pericardium heart valve bioprostheses, the Mitroflow and Labcor-Santiago valves, in both of which the leaflets are mounted outside the stent, have better hemodynamics in the aortic position than the Carpentier-Edwards valve, which has internal leaflet mounting. Sheathing the stent totally in pericardium, as in the withdrawn Bioflo valve, gives rise to relatively poor hemodynamics.

Aortic valve replacement in elderly women with small aortic roots: comparing sorin pericardial and St. Jude Medical mechanical valves.

After implanting 19mm and 21mm Sorin pericardial aortic valves (AVR) in 35 women over the age of 60 years, it was our clinical impression that these patients had an unduly high incidence of residual valve stenosis. A retrospective comparison of our experience with this valve and the 19mm St. Jude mechanical AVR in a similar group of 26 patients, operated during the same period (October 1987 to July 1994), was carried out. In comparison to the 19mm St. Jude valve, the 19 mm Sorin Pericardial valve was associated with significant residual stenosis in elderly women despite similar body surface areas. This prosthesis/patient mismatch was not eliminated by the use of a 21 mm Sorin pericardial valve. Although the Sorin pericardial valves was associated with a reduced incidence of thromboembolism and anticoagulation related hemorrhage, it had a significantly increased risk of permanent valve related morbidity and mortality. As a result if this experience we have discontinued our use of the Sorin pericardial valve.

The small aortic root and the Medtronic Hall valve: ultrafast computed tomography assessment of left ventricular mass following aortic valve replacement.

BACKGROUND AND AIMS OF THE STUDY: The selection of an appropriate size aortic valve substitute with respect to patient size and life-style, in the presence of a small aortic root, is problematic, and a decision to enlarge the aortic annulus is often arbitrary. An aortic valve substitute-patient mismatch may place an excessive load on the left ventricle resulting in residual left ventricular mass with attendant patient morbidity and mortality. The aim of this study was to assess the adequacy of the Medtronic Hall valve in the small aortic root using ultrafast computed tomography analysis of left ventricular mass. MATERIALS AND METHODS: In 13 patients the smallest Medtronic Hall valves (size 20 and 21; measured internal orifice area of 2.01 cm2 for both) were used to replace the native aortic valve. All patients had aortic stenosis, and left ventricular hypertrophy was established by echocardiography. The mean body surface area was 1.8 +/- 0.2 m2 (range 1.50-2.06 m2) and the mean weight was 75 +/- 15 Kg (range 50-97 Kg). The mean preoperative New York Heart Association functional class was 3.54 +/- 0.5. RESULTS: There was no operative or late mortality. At a mean follow up of 22 months after aortic valve replacement, the mean left ventricular mass index was 89 +/- 11.4 g/m2 (normal left ventricular mass index by ultrafast computed tomography = 97 +/- 14 g/m2) and mean New York Heart Association functional class was 1.6 +/- 0.8 (p (Binomial) = 0.0001 compared to preoperative). Doppler echocardiogram demonstrated a mean gradient across the prosthetic valve of 17 +/- 7 mmHg. There was no trend towards greater left ventricular mass index in patients with greater body surface area or weight. In no patient was the aortic annulus enlarged. CONCLUSIONS: Trends from this preliminary data suggest that implanting the smallest Medtronic-Hall aortic valves (sizes 20 and 21) results in normal left ventricular mass following aortic valve replacement in patients up to a body surface area of 2.06 m2 and provides support for the notion that an aortic annulus enlarging procedure was not necessary in this group of patients.

Doppler-echocardiographic assessment of the carbomedics supra-annular 'Top-Hat' prosthetic heart valve in the aortic position.

Twenty-one CarboMedics 'Top-Hat' bileaflet prostheses were implanted in the aortic position between May 1993 and May 1994 at our institution. Valve performance was assessed by repeat echocardiography. We found it very easy to implant this prosthesis even in the small aortic annulus and it allowed us to implant a valve that is at least one size larger than implantation in the intra-annular position allows. The only contraindication to the implantation of this prosthesis is when the coronary ostia are displaced downwards, which would apply to any supra-annular prosthesis. The Doppler echocardiographic assessment showed acceptable transvalvular gradients and velocity indexes. The Top-Hat prosthesis is now our valve of choice in the small aortic annulus.

Hemodynamic performances of small diameter carbomedics and St. Jude valves.

BACKGROUND AND AIMS OF THE STUDY: Optimal hemodynamic performances are of paramount importance when implanting a mechanical valve in patients with a small aortic annulus. A Doppler echocardiographic study was performed to compare the hemodynamic performances of small CarboMedics and St. Jude valves. MATERIALS AND METHODS: Twenty-nine patients receiving either a 19 mm (n = 10) or a 21 mm (n = 10) CarboMedics valve or a 19 mm (n = 9) St. Jude Med HP valve were evaluated. A Doppler echocardiographic study was performed at rest and two minutes after treadmill exercise with the Bruce protocol. Peak and mean gradients across the valve were estimated; effective orifice area, performance index and discharge coefficient were calculated. Heart rate, blood pressure and cardiac output were all significantly increased with exercise. RESULTS: Peak and mean gradients at rest were significantly higher (p < 0.05) in the 19 mm CarboMedics valve (40.2 +/- 15 mmHg and 22.6 +/- 9 mmHg, respectively) when compared either with 21 mm CarboMedics valve (27.6 +/- 6.8 mmHg and 14.2 +/- 3.4 mmHg, respectively) or with the 19 mm St. Jude HP valve (23.6 +/- 10.4 mmHg and 13.6 +/- 5 mmHg, respectively). Peak and mean gradients were not modified with exercise for the 19 mm CarboMedics valve and significantly increased for the 21 mm CarboMedics and the 19 mm St. Jude HP valves. Although these values were still higher in the 19 mm CarboMedics valve, they did not reach the level of statistical significance when compared with the other two valve groups. CONCLUSIONS: The 19 mm St. Jude HP valve shows hemodynamic performances at rest that are similar to those of the 21 mm CarboMedics valve and superior to those of the 19 mm CarboMedics valve. With exercise both sizes of the CarboMedics valve show an in vivo discharge coefficient close to one, testifying to a full utilization of the internal orifice area.

Double valve replacement with the Carpentier-Edwards pericardial valve: 10-year results.

BACKGROUND AND AIMS OF THE STUDY: The first generation of pericardial valves was withdrawn from the market because of an excessive rate of premature failure. With an original design, the Carpentier-Edwards pericardial valve promised improved results. MATERIALS AND METHODS: From July 1984 to December 1993, 71 patients underwent double mitral and aortic valve replacement with the Carpentier-Edwards pericardial valve. Mean age was 63.4 years. 58% were male, mean clinical status was 2.9 with 71% of patients in NYHA class III or IV, 55% were in atrial fibrillation. All patients were followed for an average of 4.17 years after their operation, and total follow up was 296 patients years. RESULTS: Operative mortality was 7% (5/71). At this point of the study, 70% of patients are in clinical NYHA class I or II, 42% of patients are in atrial fibrillation and 66% receive anticoagulation treatment. We observed 19 late deaths with an actuarial survival of 58% +/- 14% at ten years. Valve-related complications include four endocarditis, four reoperations, seven anticoagulant-related hemorrhages, two structural failures, one thromboembolic episode, and one sudden death. Two patients died of valve-related causes. After 10 years, freedom from valve related death is 97% +/- 3%, from endocarditis 90% +/- 8%, from reoperation 87% +/- 10%, from thromboembolic complications 98% +/- 2%, from valve failure 93% +/- 7%, and freedom from all complications is 58% +/- 18%. No failure in patients older than 60 years was noted and no leaflet tear was observed. CONCLUSIONS: The 10-year results of this pericardial bioprosthesis make this valve an outstanding choice when a bioprosthesis is required and in patients over 60 years old.

Toronto stentless aortic valve replacement in elderly patients.

From July 1992 to October 1994, we inserted new Toronto SPV stentless aortic heterografts (SJM Med. Inc., St Paul, Minneapolis, USA) in 40 of a series of 50 consecutive patients older than 70 years. The mean age was 75.7 years (range 70 - 86 years). All, except 4 patients, were pre-operatively in NYHA functional class III or higher. The aortic clamp time was significantly higher in the stentless groups (75 v. 53 minutes, P < 0.001). The average 25.5 mm size of the implanted valves stands in stark contract to the low body surface area (1.69 m2) of this patient groups. The surgeon's (in)experience was the major reason for the drawbacks (5/50) associated with a stentless procedures. The follow-up period ranged from 2 to 27 months and was complete in 100% of cases. We encountered 1 hospital death and no late deaths (97.5% actuarial survival). The mean NYHA class at follow-up was 1.5, and without exception patients were in class I or II. We noted one transient ischaemic attack immediately postoperatively and another later incident in a patient with a previous severe vascular history. With a low-intensity anticoagulation regiment for the first 3 months, there were two incidents of haemorrhaging necessitating premature anticoagulation withdrawal. Echocardiographic transthoracic valvular gradients compared favourably with the reported gradients of other biological valves, especially the smaller ones the significantly better haemodynamics were noted in most cases 6 months after implantation. Comparison of data with stented valves implanted during the same period indicates that the average size of the stentless valves was significantly higher (22.3 v. 25.5 mm, P < 0.001) in an equivalent population.

Echocardiographic assessment of aortic valve replacement with stentless porcine xenografts.

Stentless porcine xenografts (SPXs) implanted in the aortic position have potential hemodynamic advantages over traditional valve prostheses because of the lack of a rigid stent. Twenty-four patients (mean age 59 years) who underwent aortic valve replacement with SPXs were studied by echocardiography early after and 26 +/- 10 months (range 8 to 40) after operation. Peak and mean gradients, as well as aortic valve area, did not change significantly from baseline (16.3 +/- 8 and 9.8 +/- 5.6 mm Hg, and 1.78 +/- 0.63 cm2, respectively) to follow-up study (12.5 +/- 5 and 7.7 +/- 3 mm Hg, and 1.8 +/- 0.65 cm2, respectively). At baseline, color flow Doppler imaging showed aortic valve regurgitation where the leaflets coapted centrally in 17 of 24 patients (trivial, n = 14; mild, n = 3). Besides the central leak, paravalvular regurgitation was seen in 4 patients (trivial, n = 3; mild, n = 1). At follow-up, 18 of 24 patients had aortic valve regurgitation (trivial, n = 11; mild, n = 6; and moderate, n = 1). New valvular regurgitation (graded as trivial, n = 2; mild, n = 2; and moderate, n = 1) was detected in 5 patients, and new paravalvular regurgitation (graded as mild) developed in 1 patient. Two patients underwent repeat operation for valve-related complications: (1) rupture of a valve cusp with acute pulmonary edema, and (2) fibrotic stenosis of the left coronary ostium with unstable angina. In conclusion, this study demonstrates good hemodynamic performance of the SPX in the aortic position.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of precoating surface treatments on fatigue of Ti-6A1-4V.

Grit blasting is a common procedure of roughening surfaces to promote physical attachment of porous coatings, but it has been shown to reduce fatigue strength. Shot peening is known to increase fatigue strength by inducing compressive surface stresses; however, it is not known how subsequent grit blasting affects these benefits. This study examines the endurance limits, Se, of ELI grade Ti-6A1-4V specimens under rotating cyclic bending, including polished (control); belted and beaded; belted, beaded, and grit blasted; and belted, beaded, shot peened, and grit blasted. Belting and beading resulted in a slight increase in Se, grit blasting caused a 15% reduction in Se from polished. Fifty percent of this reduction was recovered when shot peening preceded grit blasting, suggesting that residual compressive surface stresses, induced by peening, were not eliminated by the blast process. Roughness averages and RMS values did not correlate with Se trends. SEM results showed classical fatigue fractures, consistent with surface crack initiation.

Biological materials fixed with an epoxy compound: comparison of the effects with or without ionically bound heparin.

Biological materials have been used as prosthetic devices such as heart valves, vascular grafts, and pericardial patches. These biological materials have to be fixed with crosslinking reagents and sterilized subsequently before they can be implanted in humans. Recently, a new crosslinking reagent, epoxy compound, has been used to fix bioprostheses. In this fixation technique, heparin may be ionically bound on the tissue surface. It has been shown that the amount of heparin bound to the tissue surface is proportional to the quantity of protamine impregnated in the biological tissues. However, it is not known if the impregnation of protamine will affect the crosslinking density of the biological tissues. This study was designed to compare the crosslinking densities of the epoxy compound fixed biological tissues with or without heparinization. Fresh porcine aortic valves procured from a slaughter house were first impregnated in various concentrations of protamine sulfate (0, 0.5, 1.0, or 1.5%) for about 30 min. The porcine aortic valves were then crosslinked in a 4% epoxy compound solution (Denacol EX-313). The porcine samples were taken out at various elapsed fixation periods: 18, 25, 48, 72, 96, and 120 h. Finally, the crosslinked porcine aortic valves were heparinized in a 0.5% sodium heparin solution for about 1 h. The crosslinking densities of the porcine leaflet and the aortic wall of each sample were determined by measuring their shrinkage temperatures. It was revealed that the impregnation of various concentrations of protamine did not seem to significantly alter the shrinkage temperatures of the porcine leaflet and the aortic wall throughout the entire fixation process (p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of diametral shrinkage of centrifuged and uncentrifuged Simplex P bone cement.

Reducing the porosity of bone cement substantially strengthens the cement in fatigue. However, concern has been raised that reducing the porosity of the cement would increase the shrinkage of the cement and thus compromise the cement-bone interface. We measured diametral shrinkage of cement mantles prepared with and without centrifugation of the cement. Four cement preparations (centrifuged and uncentrifuged mixed with monomer at either room temperature or 0 degrees C) were used to form cement mantles of four different thicknesses (2, 4, 6, and 8 mm) around a stainless steel rod. We conclude that porosity reduction dramatically increases the fatigue strength of bone cement without substantially changing the diametral dimensions of the polymerized cement when studied in the shape and volume of a cement mantle that would be used for total hip replacement.