Bioprostheses Research Articles

What Prosthesis Should Be Used at Valve Re-Replacement After Structural Valve Deterioration of a Bioprosthesis?

The fate of bioprostheses (BP) and mechanical prostheses (MP) after valve re-replacement for bioprostheses is not well-documented. This research compares the late fate of these two valve types after valve re-replacement for structural valve deterioration (SVD) of a bioprosthesis. Between 1975 and 2000, 298 patients had successful aortic valve re-replacements (AVRR) (BP n = 149, average age = 67.1 +/- 12.3 years; MP 149, 58.9 +/- 10.9) and 442 patients had successful mitral valve re-replacements (MVRR) (BP 155, 65.8 +/- 14.1; MP 287, 60.8 +/- 11.7) after SVD of a previous BP. Follow-up was five years in all groups. (1) Aortic position (AVRR): Survival favored MP over BP overall, at 10 years (70.3 +/- 5.4% vs 56.7 +/- 5.7%, p = 0.0220). This survival advantage was seen to be significant only in patients less than 60 years of age (at 10 years, 85.3 +/- 4.9% vs 59.2 +/- 9.8%, p = 0.038). No significant difference in survival between the two valve types was observed in patient age groups greater than 60 years of age. Freedoms from valve-specific complications, including reoperation for SVD-thrombosis, major thromboembolism and hemorrhage, and valve-related mortality were not significantly different between the two groups overall. (2) Mitral position (MVRR): Survival favored MP over BP overall (58.6 +/- 4.2% vs 42.1 +/- 5.2%, p = 0.0011), and in patients greater than 70 years of age (32.8 +/- 8.9% vs 16.7 +/- 7.1%, p = 0.008). Freedoms from valve-specific complications and valve-related mortality favored MP over BP. There was no clinical performance difference between mechanical and bioprosthetic valves in patients greater than 60 years of age upon AVRR. Mechanical valves generally outperformed bioprosthetic valves in all age groups in MVRR.

A Repositionable Valved Stent for Endovascular Treatment of Deteriorated Bioprostheses

We report our animal experience of endovascular valve replacement (VR) of failed bioprosthesis (BP) using an original delivery catheter allowing repositioning of the valved stent (VS). Among the different devices designed for percutaneous VR, none has the potential for repositioning of a fully deployed VS. Five sheep underwent, on beating heart, tricuspid VR with a stented BP. Prolapse of 1 leaflet was induced by tearing. For the endovascular tricuspid VR, we used a VS constructed with a nitinol self-expandable stent and a porcine stentless aortic valve. We also used an original delivery catheter, allowing repositioning of the VS through a compression or relaxation mechanism of the stent. Epicardial echocardiography and right ventriculography showed severe tricuspid regurgitation, with a regurgitant jet extending to the inferior vena cava. After surgical exposure to the infrarenal inferior vena cava, the VS was successfully implanted inside the failed BP in all cases. Repositioning of the fully deployed VS was always possible. Echocardiographic and macroscopic studies revealed adequate VS positioning, excellent leaflet opening, and absence of any intraprosthetic or periprosthetic leak. Endovascular VR was easily performed in sheep with failed BP in the tricuspid position. The novel delivery catheter allowed adequate repositioning of our fully deployed VS before its definitive release. One may anticipate that the safety improvement conferred by this new technology will certainly favor the development of percutaneous VR in clinical practice.

Critical flow regions in tissue artificial heart valve assessed by laser doppler anemometer in continuous flow

Flow diagnosis using non-invasive techniques such laser Doppler anemometer (LDA) is an important tool to improve the design of artificial heart valves. In the present study, an experimental protocol to obtain flow velocity field and colour coded maps of turbulent eddies dimensions using LDA measurements in a 25 mm bovine pericardium bio prosthesis valve is reported. A transparent Plexiglas chamber was specially designed to allow optical access to the flow passing through the valve. Experiments were conducted for non-pulsate flow (to study the valve performance in the peak flow) for the aorta Reynolds number ranging from 3300 to 6800. LDA interrogation volume visited five thousand and one hundred points along the flow (2500 points upstream and 2600 points downstream) for each Reynolds number. Post-processing methodology was employed to obtain haemolytic potential colour-coded maps, which were related to turbulent quantities. It was observed that haemolytic regions tend to move downstream the valve when the flow rate is increased.

Cells of primarily extravalvular origin in degenerative aortic valves and bioprostheses

We assessed aortic valves from patients with non-rheumatic aortic valve stenosis (AS) and with degenerative aortic valve bioprostheses (BP) for the presence of progenitor cell and leukocyte subtype-specific markers. Diseased valve probes from a total of 87 patients (60 AS and 27 BP) were studied. We assessed presence and localization of endothelial progenitor cells (EPCs: CD34, CD133), dendritic cells (DCs: S100), T-lymphocytes (CD3), and macrophages (CD68) by immunohistochemical and morphometric analyses. In the majority of valves, we detected cell-bound signals of CD34 (48% of AS, 74% of BP, respectively), CD133 (58%/81%), S100 (58%/93%), CD3 (62%/81%), and CD68 (78%/93%). Labelled cells were predominantly localized within the valvular fibrosa. As key results, frequency of EPCs, DCs, macrophages, and lymphocytes was found significantly higher in BP when compared with AS (CD34: 19.2+/-23.2 vs. 5.7+/-13.0%; CD133: 13.7+/-12.4 vs. 5.5+/-8.3%; S100: 15.2+/-12.2 vs. 5.7+/-8.9%; CD3: 3.3+/-2.7 vs. 1.1+/-1.4%; CD68: 35.3+/-26.6 vs. 3.4+/-4.1%; each P<or=0.001). EPCs and DCs were detected in a large collective of degenerative aortic valves, more frequently in bioprostheses than in native cusps. Aortoluminal presence of these primarily extra-valvular cells co-localized with inflammatory cells is a novel key feature involved in aortic valve degeneration.

Bioprostheses with Atrial Fibrillation and Mechanical Prostheses in Aortic Valve Replacement

Clinical performance of bioprostheses (BP) with presence of atrial fibrillation and/or paced rhythm and mechanical prostheses (MP) in aortic valve replacement was considered a study of importance. Aortic valve replacement (AVR) was performed in 163 replacements with porcine bioprostheses (Carpentier-Edwards supra-annular) with atrial fibrillation/paced rhythm identified at latest follow-up. Mechanical population was 886 procedures (St. Jude Medical = 436; CarboMedics = 450). Concomitant coronary artery bypass (CAB) was conducted in 40.5 % (66) of BP; 27.0 % (239) of MP. MP patients were all (100 %) on Coumadin and BP patients 35.6 % on acetylsalicylic acid (ASA), 37.4 % Coumadin, 7.4 % Coumadin + ASA, and 19.6 % on no therapy. Major thromboembolism (TE) and hemorrhage (ATH) occurred in 2.4 %/pt-yr (32) for BP and 5.3 %/pt-yr (157) for MP ( p < 0.0001); (TE major 1.6 %/pt-yr [21] for BP and 2.1 %/pt-yr [62] for MP [ p = 0.24]; ATH = 0.8 %/pt-yr [11] for BP and 3.2 %/pt-yr [95] for MP) ( p < 0.0001). There were no predictors of overall TE, TE major, ATH, overall TE + ATH, and TE major + ATH. Age and CAB were predictors of survival. Overall BP survival at 8 years was 97.5 +/- 1.5 %; and for MP 66.4 +/- 4.8 % ( p < 0.01). Actuarial freedom from overall thromboembolism and hemorrhage was 54.5 +/- 10.8 % for MP; 85.9 +/- 3.1 % for BP ( p = 0.0000). For major thromboembolism and hemorrhage, actuarial freedom was 63.4 +/- 11.8 % for MP; 91.4 +/- 2.5 % for BP ( p = 0.0003). Patients with atrial fibrillation/paced rhythm having AVR with bioprostheses with 45 % on Coumadin have greater freedom from thromboembolism and hemorrhage than after AVR with mechanical prostheses on Coumadin.

Peut-on abaisser l’âge d’implantation des bioprothèses ?

The choice between mechanical prosthesis (MP) and bioprosthesis (BP) depends on the respective advantages and disadvantages of the two types of valves. MP theoretically have an indefinite live span but carry the risk of thromboembolic events that requires anticoagulant therapy, which itself is responsible for hemorrages. BP bear a theoretically lower thromboembolic risk but have a limited life span that requires reintervention at a subsequent date, latter when the patient is older at implantation and operated on for aortic replacement. Actually MP is preferred before 60 years and BP after 70 years. Between 60 and 70 years there is not consensus. The limit recomended is around 65 years for aortic replacement and 70 years for mitral replacement. This limit can change either for upper or lower limit depending on patient’s life expectancy, technological improvements of MP as well as BP, improvements of medical follow up of anticoagulant therapy (either self testing or use of anti thrombin). In the future the age limit of implantation of BP can be lowered but MP didn’t have their last word.

Commissural dehiscence and pannus formation of porcine heart valve bioprostheses.

From May 1976 to June 2001, 95 porcine heart valve bioprostheses (BPs) were explanted. Among them, 85 prostheses were available for an analysis of structural valve deterioration (SVD). There were 32 Hancock (H) BPs and 53 Carpentier-Edwards (CE) BPs, with a mean implantation duration of 12 +/- 3.5 and 11.0 +/- 4 years, respectively. There were two extraordinary complications. One was commissural dehiscence (CD) of the CEBPs in 10/53 cases (18.9%), with a mean duration of 12.7 +/- 2.7 years. This was not observed in the HBPs. The other was pannus formation in both BPs. In the mitral position, it was 25/32 (78.1%) in HBPs and 37/53 (69.8%) in CEBPs. In the aortic position, it was 4/32 (1.3%) in the HBPs and 11/53 (20.8%) in the CEBPs. We conclude that CD could not be diagnosed preoperatively and anticoagulation is therefore indicated to prevent pannus formation of such prostheses, particularly in those located in the mitral position.

Long-term follow-up of patients with mechanical prosthetic valves in the tricuspid position

It remains controversial whether biological or mechanical prostheses in the tricuspid position give better long-term results. The clinical advantage of mechanical prostheses is evaluated in this article. Our subjects were 25 consecutive patients who underwent tricuspid valve replacement (TVR) from January 1985. Five patients underwent TVR with mechanical prostheses (MP), and 20 patients had bioprostheses (BP). The mean age of the patients was 50.8 ± 15.9 years for those with MP and 50.2 ± 11.5 years old for those with BP. The preoperative New York Heart Association (NYHA) functional classification was 3.5 for those with MP and 3.1 for BP. The mean follow-up period was 5.05 ± 2.05 years for MP, ranging from 3 to 7 years, and 7.2 ± 5.6 years for BP, ranging from 1 to 12 years. No operative mortality occurred, but there was a single hospital death in a patient with BP due to sepsis after acute postoperative cholecystitis. One patient with BP suffered from neurological deficiencies. Long-term temporary cardiac pacing was required in one patient with MP and three with BP. A permanent cardiac pacemaker was implanted in one patient with BP. There was one late death in the MP group and three late deaths in the BP group. The actuarial survival rates at 5 and 7 years after surgery were 80% and 80%, respectively, for MP and 88% and 88% for BP. There was one embolic episode, a minor stroke, in the BP group. Four patients with BP had valvular dysfunction at 3, 8, 9, and 10 years after surgery, and two of these required re-TVR. Among BP patients, 93% were free from prostheses dysfunction at 5 years after surgery, and 78% were free from dysfunction after 10 years; all patients (100%) with MP were free from dysfunction at 7 years. This study suggests that TVR with MP shows no late complications and with careful anticoagulant therapy provides highly satisfactory follow-up results.

Mid-Term Follow-Up in Patients with Biocor Porcine Bioprostheses

Background: Prosthetic cardiac valves have increased life expectancy of patients (pts) with valvular heart disease. Bioprosthetic complications required devices replacements within 10 years of implantation; structural valve deterioration (SVD) has emerged as the major cause of reoperation. We reviewed survival and prosthetic complications of Biocor porcine bioprostheses implanted in mitral, aortic and mitro-aortic position. Methods: Between January 1991 and January 2001 446 pts (192 males; 254 females; mean age 73.4±6.7 year, range 40–91) received 258 aortic, 138 mitral and 50 mitro-aortic Biocor porcine valves; of these 83 pts have previous different types of prosthetic devices (15 aortic, 53 mitral and 15 double). Concomitant cardiac procedures, namely myocardial revascularization, were performed in 91/446 pts (20.5%). All explanted bioprostheses (BPS) were available for pathologic investigation. Follow-up included 1319 pt.-years and was 98% complete with a median time of 36 pt.-months. Results: Perioperative mortality was 6.8% (30/446 pts; 12 aortic, 17 mitral and 1 double) and was mostly related to reoperations. At the end of follow-up 18.5% of pts died (77/416), 12 deaths were valve-related with freedom from valve related mortality of 94% at 9 years. Survival was 54% at 9 years. It was 63%, 41% and 62% for aortic, mitral and double valve replacement, respectively. At follow-up 87% of pts. were in NYHA I—II class and 13% were in III—IV class; 55% were in sinus rhythm, 36% in atrial fibrillation and 9% had a pace-maker. Eighty-five percent of pts were anticoagulated. There were 6 thromboembolic and 5 anticoagulant-related haemorrhagic episodes with no significant difference between aortic and mitral position ( p=0.7). The event freeedom was respectively 92% and 98.5% at 9 years. Prosthetic valve endocarditis (PVE) and non-SVD freedom were 96% and 93% at 9 years. SVD due to tissue degeneration, calcification and cusp's tears affected 2 pts with 94% freedom at 9 years. Overall freedom from all valve-related complications was 80% at 9 years and freedom from reoperation was 92% at 9 years. Conclusions: (1) Our intermediate-term follow-up of the Biocor porcine valve (BPS) showed excellent durability in all positions. (2) The aortic patients and especially the oldest group had better results than the mitral patients (41% vs. 63% 9 years survival, p=0.0004). (3) Higher mitral risk was related to higher prevalence of reoperations. (4) The incidence of anticoagulation-related complications is low in both aortic and mitral position without significant difference ( p=0.7). 4) A longer follow-up is required to get more information about SVD timing.

Mid-term follow-up in patients with Biocor porcine bioprostheses

Background: Prosthetic cardiac valves have increased life expectancy of patients (pts) with valvular heart disease. Bioprosthetic complications required devices replacements within 10 years of implantation; structural valve deterioration (SVD) has emerged as the major cause of reoperation. We reviewed survival and prosthetic complications of Biocor porcine bioprostheses implanted in mitral, aortic and mitro–aortic position.Methods: Between January 1991 and January 2001 446 pts (192 males; 254 females; mean age 73.4±6.7 year, range 40–91) received 258 aortic, 138 mitral and 50 mitro–aortic Biocor porcine valves; of these 83 pts have previous different types of prosthetic devices (15 aortic, 53 mitral and 15 double). Concomitant cardiac procedures, namely myocardial revascularization, were performed in 91/446 pts (20.5%). All explanted bioprostheses (BPS) were available for pathologic investigation. Follow-up included 1319 pt.-years and was 98% complete with a median time of 36 pt.-months.Results: Perioperative mortality was 6.8% (30/446 pts; 12 aortic, 17 mitral and 1 double) and was mostly related to reoperations. At the end of follow-up 18.5% of pts died (77/416), 12 deaths were valve-related with freedom from valve related mortality of 94% at 9 years. Survival was 54% at 9 years. It was 63%, 41% and 62% for aortic, mitral and double valve replacement, respectively. At follow-up 87% of pts. were in NYHA I–II class and 13% were in III–IV class; 55% were in sinus rhythm, 36% in atrial fibrillation and 9% had a pace-maker. Eighty-five percent of pts were anticoagulated. There were 6 thromboembolic and 5 anticoagulant-related haemorrhagic episodes with no significant difference between aortic and mitral position (p=0.7). The event freeedom was respectively 92% and 98.5% at 9 years. Prosthetic valve endocarditis (PVE) and non-SVD freedom were 96% and 93% at 9 years. SVD due to tissue degeneration, calcification and cusp’s tears affected 2 pts with 94% freedom at 9 years. Overall freedom from all valve-related complications was 80% at 9 years and freedom from reoperation was 92% at 9 years.Conclusions: (1) Our intermediate-term follow-up of the Biocor porcine valve (BPS) showed excellent durability in all positions. (2) The aortic patients and especially the oldest group had better results than the mitral patients (41% vs. 63% 9 years survival, p=0.0004). (3) Higher mitral risk was related to higher prevalence of reoperations. (4) The incidence of anticoagulation-related complications is low in both aortic and mitral position without significant difference (p=0.7). 4) A longer follow-up is required to get more information about SVD timing.

Perioperatives Mortalitätsund Komplikationsrisiko nach biologischem Aortenklappenersatz bei älteren Patienten: ungestentete vs. gestentete Bioprothesen

Recently published studies suggest that the hemodynamic advantage of stentless bioprostheses in comparison to stented bioprostheses positively influence the long-term survival after aortic valve replacement. However, the more complex and time consuming implantation technique may increase the risk of operative death. Between April 1996 and September 2000, 201 patients with the mean age of 75 ± 5 years underwent aortic valve replacement (AVR) with a stentless Medtronic Freestyle Bioprothesis (FP) and 166 patients with a mean age of 77 ± 5 years received a stented Medtronic Mosaic Biopros thesis (MP). Patients requiring concomitant procedures other than coronary artery bypass grafting (CABG) were excluded. The operative mortality was 3.5% after AVR with the FP and 6% after AVR with the MP. Multiple logistic regression analysis considering the different patient populations revealed no increased risk of operative death after AVR with FB (p = 0.46). Previously heart operations (p = 0.046) and emergency operation (p = 0.022) were risk factors for operative death after AVR with the biological bioprostheses. The risk for postoperatively neurological impairment (p = 0.15) and other complications (p = 0.46) was furthermore not increased after implantation of a Freestyle stentless valve. The risk of delayed mobilization (p < 0.001) was 2.4-fold increased for patients after AVR with the Freestyle valve. A positive influence on survival due to the implantation of a stentless Freestyle valve could not be shown within the observed period. However, in spite of the more complex and time-consuming operation technique, the risk of operative death and postoperative complications is not increased after aortic valve replacement with the stentless FB.

Mechanical or bioprosthetic valves in the elderly: a 20-year comparison

Background. Our objective was to compare long-term results of mechanical and bioprosthetic valve replacement in patients older than 70 years.Methods. Patients older than 70 years who had either a St. Jude Medical (SJM) mechanical prosthesis or any bioprosthesis (BP) implanted between January 1977 and December 1997 were identified. Alive patients were interviewed by telephone during a closing interval of 130 days.Results. Complete follow-up was achieved with a total follow-up of 2,264 patient years. A total of 547 patients had 448 aortic valve replacements (199 SJM and 249 BP) and 99 had mitral valve replacements (76 SJM and 23 BP). A further 30 patients had double valve replacement. One hundred ninety of the 577 patients (33%) had coronary artery bypass grafting in addition to the valve replacement. Survival analysis showed no advantage for either mechanical or bioprosthetic valves. There was also no difference in thromboembolic rates, paravalvular leaks, structural dysfunction, and endocarditis rates. However, patients with mechanical valves had a significantly greater risk of major (p < 0.0001) and minor bleeding (p = 0.002) events.Conclusions. Bioprosthetic valves do not offer a survival advantage over mechanical valves among the elderly. However, anticoagulant-related mortality and morbidity is statistically higher for patients with mechanical valves.

Survival advantage of stentless aortic bioprostheses

Background. Bioprostheses (BPs) are used to avoid anticoagulation after aortic valve replacement (AVR) in patients over 65 years of age. Stentless BPs offer established hemodynamic benefits. We sought to determine whether these advantages translate into improved survival. Methods. Between 1993 and 1997, follow-up data (for Food and Drug Administration submission) were collected prospectively for 160 consecutive, unselected hospital survivors who received the Freestyle valve (FS). Equivalent data were collected for 247 Carpentier-Edwards (CE) porcine xenograft patients. Detailed comparative statistical analysis was used to compare events and survival between the groups. Follow-up was 100% complete for the FS (5.2 years maximum; mean 3.2 ± 1.0 years) group and 98% (7.2 years maximum; mean 3.8 ± 2.0 years) for CE. Results. The groups were well matched in age (FS, 73 ± 6 years; CE, 74 ± 6 years), gender (FS, 58% male; CE, 62% male), ventricular function, and number of patients requiring coronary grafts (FS, 41%; CE, 37%). Actuarial survival at 5 years was 84% for FS versus 69% for CE ( p = 0.023 Kaplan Meier, p = 0.009 Cox). Annual mortality rates were 3.6% for FS versus 7.1% for CE ( p = 0.001). Thromboembolic rate was 0.8% per year for FS and 2.4% for CE ( p = 0.024) without a difference in cardiac rhythm. Incidence of nonstructural dysfunction (paravalvular leak) was 0.2% for FS versus 1.3% for CE ( p = 0.020). Conclusions. By 5 years, the stentless valve patients had improved survival and reduced adverse events. Though differences in durability are yet to be proved, our findings support the use of stentless bioprostheses in this age group.

Pregnancy and prosthetic heart valves: a French cooperative retrospective study of 155 cases

A French cooperative retrospective study analysed 155 pregnancies in 103 women with prosthetic heart valves: 95 mechanical prosthesis (MP) and 60 bioprostheses (BP). Among them 13 MP and 10 BP were bivalvular and four were mixed implants. In all, 182 (108 MP and 74 BP) prostheses were exposed to the risk of pregnancy. Among the 108 MP-bearing patients, 16 thromboembolic accidents (TEA) were recorded: 10 thromboses in 13 mitral, two aortic and one pulmonary MP. TEA were four times more frequent under oral anticoagulant therapy. Among the 74 BP, seven suffered premature valve failure. Ninety-nine infants were born to 50 MP-bearing women (53%) and 48 BP-bearing patients (80%) (P < 0.001). Twenty miscarriages were reported; they occurred more often under anticoagulant treatment (17%) than without it (4%) P < 0.02). Coumarin-induced embryopathies were rare (only one definitively identified). Because pregnancy with an MP under anticoagulant therapy is dangerous for the mother and may effect the fetus, the therapeutic indications for women of child-bearing age must be taken into consideration. In a women already with an MP at the time of conception, the duration of heparin therapy should be limited to the following two periods: from the 6th to the 12th week (coumarin-induced embryopathies) and during the last 2 weeks of gestation (haemorrhages during delivery and the neonatal period).

Porcine aortic valve bioprostheses: A morphologic comparison of the effects of fixation pressure

It has been suggested that the mechanical durability of glutaraldehyde-treated porcine aortic valve (PAV) bioprostheses (BPs) may be increased if collagen crimp approximating that observed in native valvular tissue is maintained during preimplantation processing. Among the factors affecting PAV fixation, the magnitude of the pressure applied to the aortic valve during fixation influences the extent of collagen crimp. Polarized light microscopy is useful for both the qualitative assessment of collagen morphology and the quantitative measurement of collagen crimp in BPs. The purpose of this study was to determine the feasibility of using this optical method to detect quantitative differences in PAV collagen crimp following zero-, low-, and high-pressure fixation. The results of this study demonstrate the following: 1) coupling polarized light microscopy and morphometric measurements provides a quantitative method for the evaluation of the relationship between fixation pressure and collagen crimp in PAVs; 2) a significant association between increasing fixation pressure and absence of collagen crimp was observed in cords and the mid-cusp region; 3) collagen crimp length in the cords is affected by fixation pressure; 4) the alteration of collagen crimp by low- and high-pressure fixation does not uniformly affect all regions of the cusp; and, 5) collagen crimp was consistently present in all cusp regions in zero-pressure fixed PAVs.

A study of the biological behavior of the meniscus as a transplant in the medial compartment of a dog's knee.

A surgical procedure was developed such that a meniscus could be reimplanted in the medial compartment of canine knees. The medial meniscus was removed and reimplanted in one group of seven animals, removed and reimplanted with a glutaraldehyde-preserved bioprosthesis in a second group of five animals, and removed and replaced by an allograft meniscus preserved 2 to 3 weeks in tissue culture in a final group of ten animals. All animals were autopsied at 2 months and the knees were examined by gross dissection and histologic study of the joint capsule meniscal interface. Results showed that implantation by the surgical technique was effective and no loose bodies or partial detachments were found in the reimplantation or tissue culture-stored allogenic menisci. Allogenic menisci preserved in glutaraldehyde and termed a bioprosthesis attached to the joint capsule less satisfactorily. There was minimal inflammation of the synovium in any group at 2 months; however, the glutaraldehyde group showed repeated effusions at 1 and 2 weeks.

Glutaraldehyde-Preserved Porcine Bioprosthesis: Factors Affecting Performance as Determined by Pathologic Studies

The causes of porcine valve failure were evaluated pathologically in 129 bioprostheses (BP) removed at surgery or necropsy. Fifty-one BP had been in place for less than two months (early explants); most of the complications of this group were observed in the mitral position: left ventricular outflow obstruction (43 percent), thrombosis (23.5 percent), myocardial dysruption (20 percent), cardiac rupture (10 percent), and perivalvular leak (3.5 percent). Among the 78 explants in place for more than two months (late explants), 66 had evidence of dysfunction. Calcification was the leading cause of failure (46 percent), followed by thrombosis (17 percent), endocarditis (12 percent), fibrous tissue overgrowth (10 percent), perivalvular leak (9 percent), and primary cusp tears (6 percent). Calcific degeneration is a hallmark of the phenomenon of biodegradation, and experimental animal models are encouraged since they may represent the clue to preventing calcification and therefore enhancing performance and durability of the porcine BP.