Polyurethane: material for the next generation of heart valve prostheses?

OBJECTIVES: The prospects for a durable, athrombogenic, synthetic, flexible leaflet heart valve are enhanced by the recent availability of novel, biostable polyurethanes. As a forerunner to evaluation of such biostable valves, a prototype trileaflet polyurethane valve (utilising conventional material of known in vitro behaviour) was compared with mechanical and bioprosthetic valves for assessment of in vivo function, durability, thromboembolic potential and calcification. METHODS: Polyurethane (PU), ATS bileaflet mechanical, and Carpentier-Edwards porcine (CE) valves were implanted in the mitral position of growing sheep. Counting of high-intensity transient signals (HITS) in the carotid arteries, echocardiographic assessment of valve function, and examination of blood smears for platelet aggregates were undertaken during the 6-month anticoagulant-free survival period. Valve structure and hydrodynamic performance were assessed following elective sacrifice. RESULTS: Twenty-eight animals survived surgery (ten ATS; ten CE; eight PU). At 6 months the mechanical valve group (n=9) showed highest numbers of HITS (mean 40/h, P=0.01 cf. porcine valves), and platelet aggregates (mean 62.22/standard field), but no thromboembolism, and no structural or functional change. The bioprosthetic group (n=6) showed low HITS (1/h) and fewer aggregates (41.67, P=1.00, not significant), calcification and severe pannus overgrowth with progressive stenosis. The PU valves (n=8) showed a small degree of fibrin attachment to leaflet surfaces, no pannus overgrowth, little change in haemodynamic performance, low levels of HITS (5/h) and platelet aggregates (17.50, P<0.01 cf. mechanical valves, P=0.23 cf. porcine valves), and no evidence of thromboembolism. CONCLUSIONS: In the absence of valve-related death and morbidity, and retention of good haemodynamic function, the PU valve was superior to the bioprosthesis; lower HITS and aggregate counts in the PU valve imply lower thrombogenicity compared with the mechanical valve. A biostable polyurethane valve could offer clinical advantage with the promise of improved durability (cf. bioprostheses) and low thrombogenicity (cf. mechanical valves).     

Relationship Between Mechanical and Hydrodynamic Properties of Bioprosthesis Produced from Canine Aortic Valve

Static tensile, stress relaxation, and hydrodynamic tests were carried out to investigate the relationships between the mechanical deformation or stiffness of heart valve leaflets and the opening behavior of bioprosthetic valves. The specimens used were fresh and glutaraldehyde (GA)-treated canine aortic valves. The tensile strength depended on the fiber orientation in the leaflet. The deformability of fresh and 0.05% GA-treated tissues was significantly larger than that induced by 0.1-5.0% GA concentrations according to the stress-strain curves. The stress relaxation function, which expresses the viscoelastic property, did not show significant differences in the 0.05-5.0% range of GA concentrations. In the hydrodynamic tests, the opening resistance of fresh and 0.05% GA-treated valves was less than that of 0.1-5.0% GA-treated valves. Thus, it was shown that the hydrodynamic valve functions were closely related to the material properties of aortic valve leaflets.     

Selection of prosthetic heart valves for adult patients by age

The use of bioprosthetic heart valves has dramatically increased over the last decade. In 2004, the ratio was 52% for mechanical and 48% for bioprosthetic valves in a survey by the Japanese Association for Thoracic Surgery. This increase in the use of bioprosthetic valves is related to evidence demonstrating the durability of such valves over the last 20 years. The guidelines of the Japanese Circulation Society recommend selection of prosthetic heart valves by considering the patient's age. In patients who received a mechanical valve in previous cardiac surgery, selection of another mechanical valve is inevitable. The age of 65 years is when patients are separated into groups receiving either mechanical (<64 years) or bioprosthetic (> or =65 years) valves. However, the evidence that a bioprosthetic valve is better for patients in their 60s is somewhat questionable, particularly in Japanese with a long life expectancy. Anticoagulation with warfarin in patients with mechanical valves leads to a higher incidence of hemorrhagic complications compared with bioprosthetic valves, although the incidence of thromboembolism is the same. Thus patients with contraindications to warfarin or a low risk of thromboembolism who are more than 65 years old are reasonable candidates for a bioprosthetic valve. It is also recommended that women of childbearing age receive bioprosthetic valves after being informed of the possibility and risks of reoperation. In addition to the information in the guidelines and physicians' preference for valve selection, factors such as the patient's lifestyle, wishes, cardiac function, other complications, and longevity must always be considered when selecting a valve prosthesis.     

An improved pericardial bioprosthetic heart valve : Design and laboratory evaluation

The design and development of a new three-leaflet pericardial valve are described and its function and durability evaluated in the laboratory. The unique design allows the leaflets to be located on small radially projecting pins on a pericardial covered frame. Leaflets are easily interchanged on the frame to allow each set of leaflets to be matched during a function test prior to final assembly. The valve has similar hydrodynamic function to other pericardial valves and accelerated fatigue tests have shown improved durability with the elimination of leaflet tears caused by abrasion at the edge of the frame.     

Cardiac valve replacement in patients on dialysis: influence of prosthesis on survival

BACKGROUND: Mechanical valves have been recommended for patients on dialysis because of purported accelerated bioprosthesis degeneration. This study was undertaken to determine time-related outcomes in dialysis patients requiring cardiac valve replacement. METHODS: From 1986 to 1998, 42 patients on chronic preoperative dialysis underwent valve replacement; 17 received mechanical valves and 25 received bioprostheses. Age was similar in both groups: 54+/-18.5 years (mechanical) and 59+/-15.5 years (bioprosthetic, p = 0.4). Sites of valve replacement were aortic (27), mitral (11), and aortic and mitral (4). Follow-up was 100% complete. RESULTS: Survival at 3 and 5 years was 50% and 33% after mechanical valve replacement, and 36% and 27% after bioprosthetic valve replacement (p = 0.3). Four patients with bioprostheses required reoperation: 3 for allograft endocarditis and 1 at 10 months for mitral bioprosthesis degeneration. One patient who received a mechanical valve required reoperation. CONCLUSIONS: Prosthetic valve-related complications in patients on dialysis were similar for both mechanical and bioprosthetic valves. Because of the limited life expectancy of patients on dialysis, bioprosthesis degeneration will be uncommon. Therefore, surgeons should not hesitate to implant bioprosthetic valves in these patients.     

The role of pannus in the longevity of an Ionescu-Shiley pericardial bioprosthesis

As the population ages, bioprosthetic heart valves are increasingly being used to replace diseased native valves. Bioprosthetic valve durability depends on patient age and other factors, but rarely exceeds 15 years. Explanted bioprosthetic valves commonly show tissue degeneration, tears, and calcification. Host tissue overgrowth (pannus), to the extent of interfering with their function, is another finding in bioprostheses that have been in place for long periods. We present a case in which a bovine pericardial valve was explanted after more than 20 years of implantation. The longevity of this pericardial valve may have been related to excessive pannus growth, which most likely protected the valve from earlier failure.     

Surgical management of valve replacement in children

From 1965 to 1990, 49 valve replacements were performed on 43 patients under the age of 15. Mitral valve replacements were performed on 21 patients, and re-replacements were done on 4 of them afterwards. In the first 9 mitral valve replacements before 1974, Starr-Edwards (S-E) ball valves were used. Five of these patients died in the hospital (early mortality rate was 56%). Since 1975, bioprosthetic valves were used in three cases, but all of these valves ceased to function due to primary tissue failure (PTF) within 3 years. Consequently, SJM valves are now used as a first choice. Ten aortic valve replacements were performed on 9 patients with the results of one early death, two late deaths, and one late re-operation. Tricuspid valve replacements were performed on 11 patients, 5 of whom utilized S-E ball valves. Three of the five patients died in the hospital. One patient was re-operated on, swapping the S-E ball valve for the SJM valve. SJM valves were used primarily in 2 patients, and bioprosthetic valves in 4. Two patients died, one with a SJM valve, and the other with a bioprosthetic valve. Two pulmonary valve replacements were performed, one employing a SJM valve, the other a bioprosthetic valve. Two adult patients with SJM valve in the right side of the heart had thrombotic complications, though the patients with bioprosthetic valves had none. Atrioventricular valve replacements were performed on 5 patients under the age of 3, but all of them died.(ABSTRACT TRUNCATED AT 250 WORDS)     

Trans-catheter valve-in-valve implantation: in vitro hydrodynamic performance of the SAPIEN + cloth trans-catheter heart valve in the Carpentier-Edwards Perimount valves

Objective: Since 1990, over 1.2 million bioprosthetic valves were implanted for aortic stenosis. Given the risk of structural valve deterioration, the need to redo AVR will likely rise. Recently, SAPIEN valve-in-valve (ViV) has been advocated. We evaluated the in vitro hydrodynamic performance of the Edwards SAPIEN + cloth trans-catheter heart valve (THV) implanted within the Carpentier-Edwards Perimount (CEP) valve. Methods: Both 23- and 26-mm Edwards SAPIEN + cloth THVs (Model 9000MIS) were deployed within 23- or 25-mm (1) CEP aortic bioprosthesis (Models 2700 and 2800), (2) CEP Magna (Model 3000), and (3) CEP plus pericardial mitral (Model 6900P), respectively. Tests included: (1) mean pressure gradient; (2) pulsatile effective orifice area (EOA); (3) regurgitant volume; (d) migration during accelerated wear testing (AWT; 20 million cycles @ 200 mmHg); and (5) valve dislodgement pressure. Values tested per ISO 5840:2005 valve standards; mean ± SD. Results: Post-deployment pressure gradient across the combined valves ranges from 2.8 ± 0.3 to 8.7 ± 0.5 mmHg. The post-deployment EOA of the valves ranged from 1.7 ± 0.1 to 2.0 ± 0.0 cm². Pulsatile flow regurgitant volume ranged from 2.1 ± 0.7 to 7.6 ± 1.2 ml. Migration during the AWT ranged from 0.01 ± 0.27 to 1.61 ± 0.92 mm. Pressure increase during the tests to quantify migration ranged from >400 to >800 mmHg. Conclusions: Compared with the rigorous ISO 5840:2500 valve standards, the Edwards SAPIEN + cloth THV implanted ViV within the CEP valve demonstrated excellent hydrodynamic performance.     

Evaluation of Tilting Disc Valves after Fatigue Life Testing: Preliminary Results within a Comparison Program

Abstract: A fatigue life test, by accelerating the beat rate, simulates several years of virtual life of a prosthetic heart valve in a short period of time. The correlation between the in vivo life of a valve and in vitro testing expectations is as yet not well established, but reproducible test conditions yield precious information about wear and failure. The paper reports a qualitative analysis of mechanical valve wear as part of a comparison program designed to investigate the significance of fatigue testing with the ultimate aim of defining standard guidelines for these type of tests. Two tilting disc valves (29 mm) were subjected to 16 years of fatigue life simulated by means of a Rowan Ash fatigue tester (accelerated rate of 1, 200 bpm). Fatigue–induced effects on valve disc and ring surfaces were observed under a monitor microscope to identify wear sites and patterns. A high speed cinematographic system was used to investigate the mechanisms responsible for the wear (wear modes). Valve closure was inspected at a 6, 000 frame/s rate. Because of disc rotation during the tilting movement, the points of contact between disc and ring are distributed all around the disc edge but focally on the ring. On both sides of the disc, the surfaces present ring–like concentric grooves. After 16 years of fatigue life the valves showed neither severe wear nor alteration of their fluidodynamic behavior in the pulsatile flow test.     

Comparison of outcomes after mitral valve replacement with a mechanical versus a bioprosthetic valve in patients between forty and sixty years of age

Background  The American College of Cardiology/American Heart Association (ACC/AHA), guidelines for choice of prosthetic valve based on patients’ age are difficult to apply to the developing world because of a lower life expectancy and difficulty in maintaining correct levels of anticoagulation for a variety of reasons. While there is general agreement on the choice of prosthetic valves for patients below 40 years of age (mechanical) and above 60 years of age (biologic), the 40 to 60 age group remains a grey zone. The goal of our study was to compare outcomes after mitral valve replacement with a mechanical versus a bioprosthetic valve in patients between forty and sixty years of age. Methods  From Jan 2003 to July 2008, 250 patients between the ages of 40 and 60, undergoing mitral valve replacement at our institution were randomized to receive either a mechanical or a bioprosthetic valve. Outcomes in the form of incidence of valve thrombosis and thromboembolism, bleeding complications, incidence of prosthetic valve endocarditis and survival were compared in the two groups. Results  Out of 250 patients, 135 patients received mechanical valve and 115 patients were implanted with a bioprosthetic valve. Patients were followed up for a mean period of 3 years (range 6 months to 4.8 years). The incidence of valve thrombosis was higher in mechanical valve as compared to bioprosthetic valve (6% vs. 0.9%, p= 0.04). Similarly there was a higher incidence of thromboembolism in mechanical valves as compared to bioprosthetic valves (4.5% vs. 0%, p=0.03). Bleeding complications occurred more frequently in mechanical than bioprosthetic valve (6% vs. 0.9%, p=0.04). There was no significant difference in the incidence of prosthetic valve endocarditis (2.2% vs. 2.7%, p >0.05) or survival at three years (96.2% vs. 97.2%, p > 0.05) in the two groups. Conclusions  Patients in the age group of 40 to 60 years undergoing mitral valve replacement with a mechanical valve have a higher incidence of thrombotic and bleeding complications as compared to bioprosthetic valve, even though short term survival is similar. This favours implantation of a bioprosthetic valve in this age group.     

Valve replacement in the right side of the heart in children: long-term follow-up

Twenty-five patients (16 male, 9 female) underwent right-sided valve replacement (10 pulmonary valve replacement, 14 tricuspid valve replacement, 3 tricuspid plus pulmonary valve replacement, and 2 replacements of a single atrioventricular valve) at the University of Nebraska Medical Center from June 1977 to December 1986. Twenty-one patients (84%) are long-term survivors with 2,035 months follow-up (range, 41 to 143 months; mean, 96.9 months). Twenty-three Carpentier-Edwards bioprosthetic valves, one Ionescu-Shiley bioprosthetic valve, and nine St. Jude Medical valves were inserted. Follow-up of 17 patients with a Carpentier-Edwards valve ranged from 5 years 9 months to 11 years 9 months (mean, 8 years 11 months). To date there has been one reoperation after 3 years 4 months in this group. One patient who received an Ionescu-Shiley bioprosthesis required re-replacement at 20 months after operation. Three of 4 patients who received St. Jude mechanical valves and are long-term survivors have required replacement after 36 to 56 months. We conclude that the Carpentier-Edwards bioprosthetic valve is a viable option in the right side of the heart in the young age group when annular size is adequate to accommodate an appropriate bioprosthesis.     

Comparative analysis of mechanical and bioprosthetic valves after aortic valve replacement

Comparative long-term performance characteristics of Bj?rk-Shiley mechanical and bioprosthetic valves were analyzed for patients undergoing aortic valve replacement between 1976 and 1981. A total of 419 patients received either a standard Bj?rk-Shiley (n = 266) or bioprosthetic (porcine, n = 126, or pericardial, n = 27) aortic valve. Cumulative patient follow-up was 1,705 patient-years; the average patient follow-up was 4.1 +/- 2.7 years. Survival data were obtained for all but 11 patients (97% complete follow-up) up to 9 years after operation. Survival at 5 years was 81% +/- 4% (+/- standard error) for Bj?rk-Shiley and for bioprosthetic valve recipients. Valve failure in the Bj?rk-Shiley group was predominantly due to valve-related mortality and did not result from structural failure. Patients with bioprosthetic valves experienced valve failure as a result of prosthetic valve endocarditis and intrinsic valve degeneration. Although patients with bioprostheses experienced a lower incidence of valve-related morbidity than Bj?rk-Shiley valve recipients (p less than 0.03), no difference could be demonstrated in the incidence of valve-related mortality or valve failure at 5 years between bioprosthetic and Bj?rk-Shiley valves. Mortality rate from valve failure was higher for Bj?rk-Shiley (86%, 12/14) than bioprosthetic valves (36%, 5/14) (p less than 0.01).     

Tricuspid valve replacement: an analysis of 25 years of experience at a single center

BACKGROUND: Tricuspid valve replacement is seldom used in clinical practice, but the choice between mechanical and biologic prostheses remains controversial. METHODS: Between 1977 and 2002, 97 patients underwent tricuspid valve replacement and were followed at the Montreal Heart Institute Valve Clinic. Patients underwent replacement with bioprostheses (n = 82) and mechanical valves (n = 15). RESULTS: Patients with bioprosthetic tricuspid replacements averaged 53 +/- 13 years of age compared with 48 +/- 11 years in those with tricuspid mechanical valve replacements (p = 0.2). Isolated tricuspid valve replacement was performed in 11 patients (73%) in the mechanical valve group compared with 31 patients (38%. p = 0.01) in the bioprosthetic replacement group. In patients undergoing bioprosthetic tricuspid replacement, 51 (62%) underwent multiple associated valve replacements. The 5-year survival after tricuspid replacement averaged 60% +/- 13% in the mechanical valve group and 56% +/- 6% in the biologic replacement group (p = 0.8). The 5-year freedom rate from tricuspid valve reoperation averaged 91% +/- 9% in patients with mechanical valves and 97% +/- 3% in those with biologic valves (p = 0.2). CONCLUSIONS; Patient survival after tricuspid valve replacement is suboptimal but related to the clinical condition at operation. The use of biologic prostheses for tricuspid valve replacement remains a good option in young patients because of limited life expectancy unrelated to the type of tricuspid prostheses at long-term follow-up.     

Hydrodynamic function of the second-generation mitroflow pericardial bioprosthesis

BACKGROUND: The hydrodynamic function of the smaller size Mitroflow Synergy stented pericardial bioprostheses has been studied in an in vitro fresh tissue aortic root model and compared with previous studies of free-sewn bioprostheses. METHODS: Three valves of each of the sizes 19, 21, and 23 mm were sutured into fresh tissue aortic roots and tested in a pulsatile flow simulator using two different ventricular input impedance conditions. A high-speed camera was used to study the leaflet opening and closing configurations. Mean pressure difference as a function of root mean square forward flow, effective orifice area, regurgitant volumes, and total energy loss across the valves was measured. RESULTS: Mean pressure difference with respect to root mean square forward flow decreased as the valve size increased. Thus effective orifice area increased as the valve size increased. The open leaflet configuration images showed that all three sizes of Mitroflow valves had a large circular orifice with minimal open leaflet deformation. All valves closed competently with no visible leakage and no closed regurgitant volume. The Mitroflow valves showed better effective orifice areas compared with previously tested frame-mounted porcine bioprostheses but lower effective orifice areas compared with porcine stentless bioprostheses; however, the open leaflet bending deformation was better than for any of the previously tested bioprosthetic valves. CONCLUSIONS: The hydrodynamic function of the Mitroflow Synergy stented pericardial bioprosthesis shows potential for good in vivo hemodynamic performance. The good hemodynamic performance combined with relative ease of implantation technique makes the pericardial valve a good valve in the aortic position, particularly in older patients with small annuli.     

Aortic valve selection in the elderly patient

To determine the influence of valve selection on valve-related morbidity and mortality and patient survival, comparative long-term performance characteristics of mechanical (N = 68) and bioprosthetic (N = 73) heart valves were analyzed for 141 patients more than 70 years old who underwent isolated aortic valve replacement between 1970 and 1985. Cumulative patient follow-up was 491 patient-years (average, 4.3 years per patient). Hospital mortality was 18% and 19% for patients with mechanical valves and bioprosthetic valves, respectively. Survival at 5 years was 61 +/- 7% (+/- the standard error) and 67 +/- 10% for recipients of mechanical valves and bioprosthetic valves, respectively. Male sex (p = 0.014) and urgency of operation (p = 0.006) were independent risk factors for hospital mortality. Atrial fibrillation increased valve-related mortality (p = 0.01). No patient required reoperation or experienced structural valve failure. While anticoagulant-related hemorrhage was increased in recipients of mechanical valves (9.2 +/- 2.1%/patient-year) compared with recipients of bioprosthetic valves (2.3 +/- 1.1%/patient-year), it did not result in a death or lead to permanent disability. There was no difference in freedom from any valve-related complication at 5 years. However, when all morbid events are considered, recipients of bioprosthetic valves experienced fewer valve-related complications than patients receiving mechanical valves (10.7 +/- 2.3%/patient-year versus 17.6 +/- 2.5%/patient-year, respectively; p less than 0.05). The reduced incidence of anticoagulant-related hemorrhage and the infrequent need for warfarin sodium anticoagulation favor selection of a bioprosthetic heart valve in patients older than 70 years.     

The porcine bioprosthetic valve. Twelve years later

The porcine bioprosthetic heart valve has been commercially available since 1970 and has been the prosthetic heart valve of choice in our institution since 1971. Since that time 817 patients with 951 porcine valves have been discharged from the hospital and were available for long-term follow-up. Patient survival rates, with operative mortality excluded, were 80% +/- 1.7% (standard error) at 5 years and 68% +/- 2.7% at 10 years. Survival rates for patients with aortic valve prostheses were 78% +/- 2.8% at 5 years and 57% +/- 5.4% at 10 years; for patients with mitral valve prostheses, survival rates were 80% +/- 2.2% at 5 years and 69% +/- 3.2% at 10 years. Freedom from thromboembolism for aortic valves was 93% +/- 1.4% at 5 years and 88% +/- 2.6% at 10 years; for mitral valves the freedom from degeneration or primary tissue failure for aortic valves was 97% +/- 1.3% at 5 years and 71% +/- 7.6% at 10 years; for mitral valves these figures were 96% +/- 1.2% at 5 years and 71% +/- 4.1% at 10 years. Valves in patients 35 years of age and below had a significantly greater rate of degeneration (p less than 0.001). After 12 years' experience the porcine bioprosthetic valve has performed well with regard to patient survival and low rate of thromboembolism. For patients older than 35 years the freedom from primary tissue failure is 80% at 10 years.     

Porcine bioprosthetic valve calcification in bovine left ventricle-aorta shunts: studies of the deposition of vitamin K-dependent proteins

Calcification of glutaraldehyde-preserved bioprosthetic cardiac valves represents a serious clinical problem. Previous work from this laboratory has established the presence in clinical bioprosthetic valve calcifications of vitamin K-dependent calcium-binding proteins, which contain the calcium-binding amino acid gamma-carboxyglutamic acid; no proteins containing gamma-carboxyglutamic acid are present in nonmineralized valves. The purpose of the present study was to examine a series of bovine circulatory bioprosthetic valve explants for calcification and proteins containing gamma-carboxyglutamic acid. Biochemical analyses of explanted bioprosthetic valves from calves demonstrated proteins with gamma-carboxyglutamic acid accumulating in calcified valves during both the onset and progression of valve calcification; calcium levels in the explanted calf bioprostheses were in the same range as those noted in clinical material. Accumulation of calcium and protein with gamma-carboxyglutamic acid occurred simultaneously and progressively, beginning 2 months after implantation. Small amounts of osteocalcin, the bone-derived protein containing gamma-carboxyglutamic acid, were present in both human and bovine bioprosthetic valve calcifications at comparable levels. No osteocalcin was detectable in non-mineralized valve tissue. Warfarin anticoagulant therapy did not prevent calcification or accumulation of protein with gamma-carboxyglutamic acid. It is concluded that proteins containing gamma-carboxyglutamic acid are involved in both the onset and progression of bioprosthetic valve calcification, and that conventional means of vitamin K antagonism do not alter this association or the course of bioprosthetic valve mineralization.     

Severe stenosis of bioprosthetic valve due to late valve thrombosis

The typical cause of bioprosthetic valve dysfunction over years is calcification of leaflets, pannus formation, or tears due to structural degeneration. Thrombosis is rare as the valves get endothelialized early on, and, hence, anticoagulation is not recommended beyond 6 months after valve replacement. While bioprosthetic valve thrombosis is unusual (0.03% to 0.34%/year), it can be associated with significant mortality and morbidity. Here, we present a case of a middle-aged man with history of bioprosthetic mitral valve who presented with syncopal episode and was referred to us for mitral valve replacement for tentative bioprosthetic valve degeneration and stenosis. However, preoperative work up revealed prosthetic valve thrombosis which was successfully treated with anticoagulation.     

Ventricular assist device in patients with prosthetic heart valves

Ventricular assist device (VAD) support inpatients with a prosthetic heart valve had previously been considered a relative contraindication due to an increased risk of thromboembolic complications. We report our clinical experience of VAD implantation in patients with prosthetic heart valves, including both mechanical and bioprosthetic valves. The clinical records of 133 consecutive patients who underwent VAD implantation at a single institution from January 2002 through June 2009 were retrospectively reviewed. Six of these patients had a prosthetic valve in place at the time of device implantation. Patient demographics,operative characteristics, and postoperative complications were reviewed.Of the six patients,four were male.The mean age was 57.8 years (range 35–66 years). The various prosthetic cardiac valves included a mechanical aortic valve (n = 2), a bioprosthetic aortic valve (n = 3), and a mechanical mitral valve (n = 1).The indications for VAD support included bridge to transplantation (n = 2), bridge to recovery (n = 1), and postcardiotomy ventricular failure(n = 3). Three patients underwent left ventricular assist device placement and three received a right ventricular assist device. Postoperatively, standard anticoagulation management began with a heparin infusion (if possible)followed by oral anticoagulation.The 30-day mortality was50% (3/6). The mean duration of support among survivors was 194.3 days (range 7–369 days) compared with 16.0 days(range 4–29 days) for nonsurvivors. Of the three survivors,two were successfully bridged to heart transplantation and one recovered native ventricular function.Among the three nonsurvivors,acute renal failure developed in each case, and two developed heparin-induced thrombocytopenia. This study suggests that VAD placement in patients with a prosthethic heart valve, either mechanical or bioprosthetic,appears to be a reasonable option.     

Late failure of porcine valve heterografts in children.

Heterograft porcine valves have gained wide acceptance in replacement of diseased cardiac valves, and their clinical performance in adults has been very satisfactory over follow-up periods of up to 8 years. Valve replacement in children is relatively infrequent and experience with porcine xenografts is necessarily small. Our combined experience at three university hospitals has been with 25 children, 17 months to 16 years of age, who have been followed for 10 to 54 months (mean follow-up 33 months). Porcine valves were used to replace the aortic valve in nine, the mitral valve in seven, both valves in two, the tricuspid valve in two, and the pulmonary valve in five patients. Severe bioprosthetic valve dysfunction has occurred in five (20%) of these patients so far and necessitated replacement because of severe stenosis in mitral (two) or aortic (three) valve prostheses at 18 to 45 months after implantation; one postoperative death occurred among the five reoperations. Pathological examination showed extensive fragmentation of collagen with focal heavy calcification and degeneration. In addition we have encountered deterioration and calcification of two porcine valves in 23 valved conduits followed for 12 to 70 months (mean 43 months), requiring removal and replacement of the valves 65 and 67 months after implantation. This experience indicates a disquietingly high incidence of relatively early failure of porcine xenograft valves in children. This is significantly higher than the failure rate observed in adult patients. The failure rate is not consistently related to the small size of an implanted valve which becomes relatively narrow with the growth of the patient, leading to excessive turbulence and trauma to the prosthesis. Other factors, including increased turnover of calcium and accelerated rejection in growing children, may contribute to these failures and should be examined in order to improve long-term results. A satisfactory performance would make heterografts the ideal valvular prosthesis in children, since anticoagulation is avoided.