Porcine Bioprosthetic Heart Valves Research Articles

Steady flow velocity field and turbulent stress mappings downstream of a porcine bioprosthetic aortic valve in vitro.

Velocity profiles and Reynolds stresses downstream of heart valve prostheses are vital parameters in the study of hemolysis and thrombus formation associated with these valves. These parameters have previously been evaluated using single-point measurement techniques such as laser Doppler anemometry (LDA). The purpose of this study is to map the velocity vector fields and Reynolds stresses downstream of a porcine bioprosthetic heart valve in the aortic root region with particle image velocimetry (PIV) techniques in vitro under steady flow conditions. PIV is essentially a multipoint measurement technique that allows full-field measurement of instantaneous velocity vectors in a flow field, thus allowing us to map the entire velocity or stress field over the aortic root (where single-point measurements are difficult). Coupled with flow visualization techniques, the hydrodynamic consequences of introducing a porcine bioprosthetic heart valve into the aortic root was examined, and compared with data obtained from an empty aortic root and an aortic root with the valve mounting ring alone. From our velocity and stress mappings, we found that the valve mounting ring effectively diminishes the central orifice area, giving rise to a higher central axial flow with strong recirculating regions and a corresponding large pressure drop. This in turn produces an intermixing zone between the central jet and recirculating region further downstream from the valve, which contributes to the high-stress zone measured. The development of the flow is further restricted by the valve stents, giving rise to stagnation regions and wakes. High-velocity gradients were also measured at the interface of the jet and recirculating region in the sinus cavity. The overall view of the velocity and stress mappings helps to identify regions of flow disturbances that otherwise may be lost with single-point measuring systems. Although the PIV measurements may lack the accuracy of single-point measuring systems, the overall view of the flow in the aortic root region compensates for the shortcoming.

Regional distribution of calcification in aortic valve cusps. An in vivo study.

Calcification of porcine bioprosthetic heart valves in the subcutaneous rat model has been shown to occur predominantly within the center of the cusp (the spongiosa). To investigate whether the calcification process can be affected by structure or location, the fibrosa and ventricularis were separated and their propensity to calcify in relation to cusps that were implanted intact was examined. Porcine aortic valve cusps were fixed in 0.5% glutaraldehyde solution for 24 hours. Ten cusps were microdissected to separate the fibrosa from the ventricularis. These layers and 10 intact cusps were separately implanted into 21 day old, male Sprague-Dawley rats. The tissues were explanted at 1, 2, 3, and 4 weeks post implantation. Histologic sections were cut and prepared with Von Kossa's stain to detect phosphates and carbonates. The separated layers displayed intrinsic calcification in a pattern similar to that of intact specimens. The similarity in the pattern of both the separated layers and the intact cusps suggests that differences in collagen fiber density in the spongiosa, ventricularis, and fibrosa do not affect the calcification process. Furthermore, no calcification was observed to occur on the outer surface of the separate layers, including areas that contained residual spongiosa. This study suggests that the process of calcification remains intrinsic regardless of the structure and density of collagen fibers.

901-118 Cellular Expression of Matrix Proteins Mediates Calcification in Native Human and Bioprosthetic Heart Valves

Dystrophic mineralization remains the leading cause of valve stenosis and failure in native human (NHV) and porcine bioprosthetic (PBV) heart valves. We hypothesized that expression of noncollagenous matrix proteins (MP) that induce skeletal mineralization may orchestrate valvular calcification (Ca 2+ ). 18 porcine PBV and 13 NHV obtained during replacement surgery were analysed for cells, calcium, fibrosis and vessels. Immunostaining for macrophages, T-cells, α-smooth muscle (SM) actin, osteopontin (OP), osteocalcin (OC) and osteonectin (ON) was performed with non-immune sera as controls. In situ hybridization analysis utilized antisense oligonucleotide probes for OR OC, ON and sense controls. Results were compared to known positive/negative tissue controls and normal heart valves. A probe averaged in situ score was calculated for each valve. MP in situ was graded positive if ≥2 different probes exhibited >5 signal positive cells/slide. Valves were divided into 4 groups based on presence of calcium: I: PBV non-Ca 2+ (n = 8); II: PBV-Ca 2+ (n = 10); III: NHV-Ca 2+ (n = 8); IV: NHV non-Ca 2+ (n = 5). 2 × 2 contingency table analysis of in situ signal status revealed: Positive PBV (I vs II) 0.03 * versus NHV (III vS IV) 0.01 * negative PBV-Ca 2+ and NHV-Ca 2+ (II vs III) 1.00 in situ PBV-Ca 2+ vs NHV-NonCa 2+ 0.005 * * Significant p value by Fisher's Exact Test Comparison of mean in situ scores revealed significant differences among groups III vs IV and I vs IV PBV age (p < 0.001) and NHV cellularity (p < 0.003) correlated with calcium. For all valves: OR OC and ON mRNA expression localized with calcification and cellular infiltration; immunostaining identified macrophages, OR OC and ON at the calcification front; SM were associated with valve edges and cuspal Ca 2+ . (1) Cell-mediated calcification is promoted by matrix protein expression common to PBV and NHV; (2) matrix protein mRNA expression is quantitatively related to extent and localization of valvular mineralization; (3) macrophage infiltration is closely associated with matrix protein expression and calcification.

Effect of 2-amino oleic acid exposure conditions on the inhibition of calcification of glutaraldehyde cross-linked porcine aortic valves.

Postimplant calcific degeneration is a frequent cause of clinical failures of glutaraldehyde cross-linked porcine bioprosthetic heart valves (BPHV). It was demonstrated previously that 2-amino oleic acid (AOA) used as a bioprosthesis treatment was highly effective in mitigating aortic valve cusp but not aortic wall calcification. Our main objective was to study the efficacy of various AOA exposure conditions for inhibiting calcification of both cusps and aortic wall tissues using rat subdermal implants. BPHV tissues were treated with a saturated AOA solution for different time intervals before experimental. Aortic wall AOA levels were consistently lower than that of the cusps after the same exposure times. The diffusion of calcium ion across both cusp and aortic wall tissues was evaluated, and the results demonstrated that there was an AOA exposure time-dependent retardation of calcium ion penetration for cusp but not aortic wall. An 8-month extraction study was performed to determine the stability of AOA binding. When Tween 80 was used as an extraction medium, cusp and aortic wall retained 12.9 and 48.7%, respectively, of their initial AOA levels. AOA inhibition of calcification in rat subdermal implants (60 days) was found to be exposure time-dependent with maximum treatment time (120 h), resulting in the lowest calcium levels (20.1 +/- 10.3 and 71.4 +/- 5.4 micrograms/mg of cusp and aortic wall, respectively) as compared with controls (219.1 +/- 6.8 and 104.9 +/- 8.5 micrograms/mg of cusp and aortic wall, respectively). The significance of AOA binding on BPHV tissue was determined by either blocking or reducing BPHV's (cusp and aortic wall) free aldehyde residues with lysine or NaBH4, respectively, before AOA treatment. For aortic cusps, the AOA contents after 72 h were 98.3 +/- 2.7, 34.2 +/- 3.6, and 54.1 +/- 3.0 nM/mg of tissue for AOA (control), lysine-pretreated (plus AOA) and NaBH4-pretreated (plus AOA) tissues, respectively. However, their calcium levels after 60 days of rat subdermal implant were all comparable (i.e., 48.1 +/- 6.2, 38.2 +/- 9.1, and 47.0 +/- 15.0 micrograms calcium per mg of tissue). Similar results were observed on BPHV aortic wall. It can thus be concluded that AOA inhibition of BPHV calcification is exposure time-dependent, but the efficacy of AOA for aortic wall is less than that noted for aortic cusps, perhaps because of lower AOA binding and differences in calcium diffusion kinetics.

Mechanism of efficacy of 2-amino oleic acid for inhibition of calcification of glutaraldehyde-pretreated porcine bioprosthetic heart valves.

Calcification is a frequent cause of the clinical failures of glutaraldehyde-pretreated bioprosthetic heart valves (BPHV) fabricated from glutaraldehyde-cross-linked porcine aortic valves. 2-Amino oleic acid (AOA) has been shown in previous in vivo studies to be a promising anticalcification agent. Our objective was to investigate the mechanism of calcification inhibition mediated by AOA pretreatment of porcine aortic valve bioprostheses. BPHV tissues were treated with an AOA solution for 72 hours before experimentation. The diffusion of AOA across both cusp and aortic wall was evaluated. The lag time for AOA to diffuse across the aortic wall was prolonged compared with that of the cusp. An extraction study was performed to determine the stability of AOA binding; the results indicated that the binding was relatively stable regardless of solvent extraction conditions. The interaction between ionic calcium and AOA on treated tissue also was investigated by evaluating the patterns of calcium diffusion across both treated and untreated tissues. The results showed that AOA significantly reduced the diffusion of calcium. AOA inhibition of aortic valve calcification (calcium level, 5.5 +/- 3.0 mg/g of tissue compared with control; calcium level, 91.2 +/- 19.5 mg/g of tissue) but not aortic wall (calcium level, 158.7 +/- 10.3 mg/g of tissue compared with control; calcium level, 157.5 +/- 7.9 mg/g of tissue) was demonstrated on representative specimens from valves implanted in left ventricular apicoaortic shunts explanted after 150 days. AOA covalently binds to glutaraldehyde-pretreated bioprosthetic heart valve tissue, presumably as the result of an aldehyde-amino reaction. Covalently bound AOA diminishes Ca2+ diffusion compared with non-AOA-pretreated bioprosthetic tissues. This may explain in part the anticalcification mechanism of AOA. Furthermore, AOA inhibits calcification of porcine BPHV cusps in the circulation.

Physicochemical properties of calcific deposits isolated from porcine bioprosthetic heart valves removed from patients following 2–13 years function

Physicochemical properties of calcific deposits isolated from porcine bioprosthetic heart valves removed from patients following 2–13 years function

Physicochemical properties of calcific deposits isolated from porcine bioprosthetic heart valves removed from patients following 2-13 years function.

The purpose of this study was to characterize the physicochemical properties of calcific deposits that cause the failure of tissue-derived heart valve bioprostheses. This was done in an effort to understand the mechanism of pathologic biomineralization in the cardiovascular system and potentially prevent deterioration of bioprostheses. Calcific deposits taken from 10 failed bioprosthetic valves that had been implanted in patients for 2-13 years were characterized by chemical analysis, x-ray diffraction, FTIR spectroscopy, scanning electron microscopy, polarized light microscopy, and solubility measurements. The combined results identified the biomineral as an apatitic calcium phosphate salt with substantial incorporation of sodium, magnesium and carbonate. The average Ca/PO4 ratio for this "young" pathologic biomineral was approximately 1.3, considerably lower than approximately 1.7 found in mature atherosclerotic plaque biomineral and mature skeletal biomineral, both of which approximate hydroxyapatite in composition. Deproteinated calcific deposits from bioprostheses had thermodynamic solubilities comparable to those of both atherosclerotic plaque, typical pathologic biomineral and hydrolyzed octacalcium phosphate (OCP, Ca4H(PO4)3 x 2.5 H2O), a proposed precursor phase to biomineral apatite. This later finding, together with chemical composition and structural details of the bioprosthetic deposits themselves, supports a mechanism of cardiovascular calcification in which OCP plays a crucial role in the formation of the final apatitic phase. This suggests an approach toward prevention of bioprosthetic tissue calcification through control of the formation of the kinetically favored OCP precursor and/or its transformation into bioapatite.

Anisotropic elasticity and strength of glutaraldehyde fixed bovine pericardium for use in pericardial bioprosthetic valves.

Uniaxial tensile tests were performed on glutaraldehyde fixed bovine pericardial strips prepared from chemically modified pericardial samples. These samples originated from an area which demonstrated anisotropic mechanical properties in the native material and which is suitable for the construction of leaflets for pericardial bioprostheses. After glutaraldehyde fixation the tissue had retained its anisotropicity in stiffness and strength in two orthogonal directions. In the range of the functional stresses for a heart valve leaflet (< 1 MPa) the unconstrained fixation regime had modified the initial anisotropic elastic behavior into a more isotropic one. The implications of these findings are that leaflets manufactured from bovine pericardium can be made to resemble, to a degree, the well known anisotropy found in two orthogonal directions in natural human heart valve leaflets, or porcine bioprosthetic heart valve leaflets.

Morphogenesis of Calcification in Porcine Bioprosthesis: Insight from High Resolution Electron Microscopic Investigation at Molecular and Atomic Resolution

High resolution electron microscopy (HREM) coupled with energy dispersive X-ray microanalysis were used to investigate the morphogenesis of calcification in 28 explanted porcine bioprosthetic heart valves. Different morphology and compositions of calcific deposits were consistently observed in various valvular structures of all explanted porcine bioprostheses. The most common forms of calcific deposits were present as spherical particles and needle-shaped structures. HREM investigation of spherical particles of calcium phosphate revealed very fine electron-dense dots about 0.3-1.0 nm in diameter which were packed to form sphere-like clusters of about 2.0-3.5 nm in diameter in the particles. HREM observations of the microneedle-shaped structures even as small as 1.9 nm in thickness could identify the lattice fringes with center-to-center spacings of about 0.8-0.9 nm. Energy dispersive X-ray microanalysis defined the components of needle-shaped calcification as calcium and phosphorus in a ratio typical of hydroxyapatite crystals. The calcific deposits in the collagen tissue have been shown to be at discrete sites on or in the collagen fibrils as the spherical particles or homogeneous electron-dense masses. Based on HREM observations of different types of morphogenesis of calcification it is suggested that chemical processes of calcification accompanying the deposition of calcium in the implanted bioprosthetic heart valves are specific to each substrate system. The formation of amorphous calcium phosphate precursors and direct deposition of microcrystalline hydroxyapatites are considered to be the primary mechanisms of calcification occurring in implanted porcine bioprostheses.

A model of the geometrical changes in aortic valve leaflets in response to leaflet extension and variable boundary conditions.

The function, deformation and performance of heart valve leaflets are dependent on the material properties and the geometry of the leaflet. As the leaflet acts as a constrained membrane the geometry is dependent on the boundary condition applied to the leaflet and any permanent extension of the leaflet. Both of these factors are varied during the preparation of frame-mounted porcine bioprosthetic heart valves and surgical insertion of free-sewn valves. This can result in abnormal geometry and function. A mathematical model has been developed which describes these changes in geometry of a cylindrical leaflet as a function of the diameter of the aortic root (boundary conditions) and the length (or permanent extension) of the leaflet. Both the angle of inclination and the radius of curvature of the cylindrical leaflet were reduced with increased leaflet length or decreased aortic diameter. Agreement was found between the model predictions and experimental observations in porcine bioprosthetic heart valves, where abnormal leaflet geometries are produced by non-physiological boundary conditions and permanent set of the leaflets by fixation with glutaraldehyde. The general solutions developed in this model allow leaflet geometries to be predicted for a range of conditions in free-sewn and frame-mounted valves.

The hydrodynamic function and leaflet dynamics of aortic and pulmonary roots and valves: an in vitro study.

Fresh homograft aortic and pulmonary roots were tested in a pulsatile flow simulator to assess their hydrodynamic function and leaflet opening characteristics. Simultaneous flow and pressure measurements were obtained for a range of cardiac outputs. The effective orifice area and regurgitant volumes were calculated. The mean pressure difference across the pulmonary roots was obtained under both left and right side pressures. A video recording of valve leaflet function was also obtained for each valve. A comparison was made with four porcine bioprosthetic heart valves (21 and 23 mm). The mean pressure difference with respect to flow for the 21 mm Hancock II and Intact porcine bioprostheses was significantly higher than that for all aortic roots tested. The 24 mm aortic root showed significantly lower pressure drop compared to all porcine valves tested. The mean pressure difference across each pulmonary root at pulmonary pressures was significantly greater than at systemic pressures. At systemic pressures the fully open leaflets had a triangular orifice with low leaflet open bending strains at the commissures. At the lower internal pressures, with reduced dilation of the root, higher bending strains were noted. These were not as severe as seen in porcine valves.

Doppler echocardiographic study of porcine bioprosthetic heart valves in the aortic valve position in patients without evidence of cardiac dysfunction

To study the natural history of the hemodynamic performance of bioprostnetic heart valves, Doppler echocardiograms were recorded in a group of clinically stable patients at 2 and 5 years after replacement of native aortic valves with bioprostnetic valves. Eighteen patients completed a 2-year and 26 patients a 5-year follow-up examination. The effective orifice areas of identical models of bioprosthetic valves (Hancock II) were determined in vitro in a left-sided heart pulse duplicator system. In vivo Doppler-derived effective orifice areas were compared with the in vitro measurements for the same valve size. At both the 2- and 5-year followup examinations, the Doppler-derived effective orifice area was significantly less than the in vitro area (p < 0.0001 at each interval). Ten of 16 valves evaluated serially decreased >0.20 cm 2 in the Doppler-derived effective orifice area between studies. The mean decrease in effective orifice area in valves evaluated serially was 0.25 ± 0.29 cm 2 (p < 0.005). The peak transaortic gradient increased from 21 ± 6 to 27 ± 8 mm Hg (p < 0.01). The mean transaortic gradient increased from 12 ± 4 to 15 ±7 mm Hg (p < 0.05). It is concluded that serial Doppler echocardiographic studies demonstrate a deterioration in the hemodynamic performance of bioprostnetic valves over time in patients with no symptoms or signs of valvular dysfunction and that Doppler echocardiography may be useful for identifying subclinical bioprostnetic valvular dysfunction.

Pericardial and porcine bioprosthetic heart valves: Function, durability and clincial failure modes

Pericardial and porcine bioprosthetic heart valves: Function, durability and clincial failure modes

Comparison of pattern recognition methods for computer-assisted classification of spectra of heart sounds in patients with a porcine bioprosthetic valve implanted in the mitral position

The diagnostic performance of two pattern recognition methods (or classifiers) to detect valvular degeneration was evaluated in 48 patients with a porcine bioprosthetic heart valve inserted in the mitral position. Twenty patients had a normal porcine bioprosthetic valve and 28 patients had a degenerated bioprosthetic valve. One method was based on the Gaussian-Bayes model and the second on the "nearest neighbor" algorithm using three distance measurements. Eighteen diagnostic features were extracted from the sound spectrum of each patient and, for each method, a two-class supervised learning approach was used to determine the most discriminant diagnostic patterns composed of 6 features or less. The probability of error of the classifiers was estimated with the leave-one-out approach. The performance of each method to discriminate between normal and degenerated bioprosthetic valves was verified by clinical evaluation of the valves. The best performance in evaluation of the sound spectrum (98% correct classifications) was obtained with the Bayes classifier and two patterns of six features each. The percentage of false positive classifications of valve degeneration was 0% and the percentage of false negative classifications was 4%. Sensitivity for the detection of valve degeneration was 96%, specificity was 100%, positive predictive value was 100%, and negative predictive value was 95%. The best performance of the nearest neighbor method (94% correct classifications) was obtained by using the Mahalanobis distance and five patterns composed of three, four, five, or six diagnostic features. Using a pattern composed of only three features, the percentage of false positive classifications for degeneration was 10% and the percentage of false negative classifications was 4%.(ABSTRACT TRUNCATED AT 250 WORDS)

12 Hancock弁置換術後8〜14年における遠隔成績の検討

12 Hancock弁置換術後8〜14年における遠隔成績の検討

Incidence of Primary Tissue Valve Failure in Porcine Bioprosthetic Heart Valves

This report provides retrospective follow-up data on 324 consecutive patients who received a Hancock-I porcine valve in the aortic or the mitral position, or in both positions, between June, 1974, and December, 1976. This analysis included 319 valves (193 mitral, 126 aortic) available for study of the incidence of primary tissue valve failure after 10 to 12.5 years of follow-up. Of the 319 prostheses at risk, 114 instances of primary tissue valve failure occurred. Seventy-three of the failed valves were in the mitral position, and 41 were in the aortic position. The calculated actuarial probability of freedom from primary tissue valve failure was 52 ± 5% for the mitral and 58 ± 6% for the aortic prostheses at 12.5 years of follow-up. For patients older than 40 years at the time of operation, the rate of freedom from primary failure was 68 ± 8% and 55 ± 6% for aortic and mitral prostheses, respectively, at 12.5 years. Comparison of both actuarial curves disclosed no meaningful difference. However, a tendency toward greater failure rate was observed in the mitral prosthesis group.

Long-term performance of porcine heart valve bioprostheses

To assess the results after long-term implantation of porcine bioprosthetic heart valves, 320 patients with 381 valves were retrospectively reviewed. This group included all patients receiving one such xenograft in the mitral or aortic position (or both) in our institution between June 1974 and December 1976. The patients had a follow-up of 9-11.5 years. Actuarial patient survival rats (hospital mortality excluded) were 85%-90% at 6 years and 68%-79% at 11.5 years. Thromboembolic episodes did not show any significant clustering over the first weeks or months, in fact, they appeared at a constant rate. Actuarial rates of freedom from thromboembolism were greater than 90% for aortic patients at 11.5 years and greater than 80% for mitral and mitroaortic patients at 11.5 years. The linearized rate of anticoagulant-related haemorrhage for the whole group of patients was 0.4 events/100 patient years with a related mortality of 0.2 events/100 patient years. Prosthetic valve endocarditis and paravalvular leak appeared at linearized rates of 0.6 (0.1 of related mortality) and 0.4 (0.1 of related mortality) events/100 patient years. Primary tissue valve failure constituted the most prevalent complication (82 cases) in the long term but did not significantly worsen patient survival. Actuarial rates of freedom from primary tissue failure were 91% +/- 2% at 6, and 40% +/- 14% at 11.5 years for mitral valves, and 95% +/- 4% at 6 and 64% +/- 6% at 11.5 years for aortic valves.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary failure of Hancock porcine bioprosthetic valves: two dimensional echocardiographic assessment.

To reveal the process of primary failure of the Hancock porcine bioprosthetic heart valve, a real-time two-dimensional echocardiography was undertaken. There were 75 cases (84 valves) with 26 in the aortic valve position, 39 in the mitral valve position, 9 in both the aortic and mitral valve positions, and 1 in the tricuspid valve position. The subjects comprised 35 males and 40 females, whose ages ranged from 18 to 65 years with a mean of 44.7 years. Valvular changes such as thickened valve cusps or abnormal valve movement were observed in 27 (32%) of the 84 valves; more specifically, in 5 (14.3%) of the 35 aortic valves and in 22 (45.8%) of the 48 mitral valves, indicating that valvular changes occurred most frequently in the mitral valve position (p less than 0.01). In the period between valve replacement surgery and the appearance of valvular changes, no significant difference was noted between aortic and mitral valve bioprostheses. The duration ranged from 14.5 to 74.5 months with a mean of 50.2 months. Valvular changes were evident in more than 50% of the valve bioprostheses implanted 6 or more years ago. In the mitral valve position, valve cusp changes appeared more frequently at the anterior cusp than at the inner and outer cusps. The frequency was 17 cases at the anterior cusp, 6 at the inner and 9 at the outer. In 7 of the 11 cases followed up after the appearance of valvular changes, an increase in the changes was recognized 7.5 to 29.5 months (a mean of 16.4 months) later.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Inhibition by diphosphonate compounds of calcification of porcine bioprosthetic heart valve cusps implanted subcutaneously in rats.

Calcification limits the long-term success of heart valve bioprostheses fabricated from glutaraldehyde cross-linked porcine aortic valves. The pathophysiology of calcification of bioprostheses has been studied experimentally with subcutaneous implants of the valve cusps in rats; in this preparation, the accumulation of calcific deposits is biochemically and morphologically identical to that occurring in clinical specimens. The objective of the present study was to determine whether mineralization of bioprosthetic valve cusps (BC) subcutaneously implanted in 3-week-old male rats could be inhibited through the use of diphosphonate compounds. Ethanehydroxydiphosphonate (EHDP), administered by daily subcutaneous injection (25 mg/kg/24 hr) for 21 days inhibited calcification (BC Ca++ = 154.9 +/- 4.1), but caused somatic growth retardation and disruption of epiphyseal development. However, local administration of EHDP by osmotic pump (5 mg/kg/24 hr) implanted in direct contact with the cuspal tissue for 14 days prevented BC calcification (BC CA++ = 4.3 +/- 0.7) without adverse effects. Furthermore, EHDP given by osmotic pump had a prolonged effect on reducing calcification, as demonstrated by implants harvested 21 days (BC CA++ = 12.2 +/- 6.4) after the drug supply was exhausted. Finally, BC preincubated in aminopropanehydroxydiphosphonate for 24 hr before 21 day implantation underwent less calcification (CA++ = 24.2 +/- 7.4) than control valves (BC CA++ 126.6 +/- 7.5) with no adverse effects. We conclude that diphosphonates inhibit BC calcification, and that adverse effects of systemic therapy can be avoided by local administration.