Differences between heart valve allografts and xenografts in the incidence and initiation of dystrophic calcification.

Following surgical removal because of primary tissue failure, 30 antibiotic-sterilized human aortic valve allografts and 27 glutaraldehyde-treated porcine aortic valve xenografts were examined for macroscopic and microscopic evidence of dystrophic calcification. These grafts had been mounted on stents and used for from 34 to 166 months to replace diseased mitral valves. After explantation the grafts were carefully examined then prepared for light microscopy, for transmission electron microscopy and for energy dispersive X-ray microanalysis. Gross calcification occurred significantly (p = 0.002) more frequently in xenografts (89%), and was more extensive than in allografts (53%). Calcification usually appeared as nodular excrescences on the cusps, although occasionally it formed plates within them. This reduced tissue pliability and was usually associated with either valvular stenosis or regurgitation. The calcified deposits contained calcium and phosphate in ratios approaching those of hydroxyapatite. In xenograft valves the smallest discrete deposits of calcification were spherical and usually associated with membranous debris of porcine donor fibroblasts, but allografts did not contain donor cell remnants and early calcification was linearly arranged along collagen fibres.

Chemically determined mineral content of explanted porcine aortic valve bioprostheses: correlation with radiographic assessment of calcification and clinical data.

Bioprosthetic valve calcification is usually assessed pathologically by gross inspection, radiographic studies, and histologic examination. Quantitation of mineral content by chemical assay has not been reported for failed clinical valves removed from adults. In this study, calcium determination by atomic absorption spectroscopy was done on 52 removed porcine valves after routine pathologic examination, including specimen radiography done by a standard technique. Specimens included 31 valves with calcific primary tissue failure, two calcified (but not overtly dysfunctional) valves removed simultaneously with failed valves, 14 nondeteriorated valves obtained at reoperation or autopsy after long-term implantation, and five valves removed within 1 month after insertion. Chemically determined mineral content varied widely among patients and duration of function. Valves with calcific failure had 113 +/- 68 micrograms/mg calcium overall (mean +/- SD) after 36 to 156 months (mean 87) of function. Almost all dysfunctional porcine valves with radiographically demonstrated calcific deposits had greater than 34 and 67 micrograms/mg calcium for mitral and aortic valves, respectively. Nondeteriorated valves (implanted 8 to 145 months, mean 57) had 5 +/- 6 micrograms/mg calcium. Failed aortic valves had more calcium than failed mitral valves and valves with calcific stenosis more than valves with regurgitation caused by calcification with tearing. Correlation of semiquantitative radiographic grading with chemically determined valve mineral was good, indicating that radiographic assessment of calcification may be used reliably for clinical comparisons between valves.

Crystallochemical characteristics of the inorganic phase of human calcific aortic valvar stenosis.

To determine the elemental composition of the mineral deposits found in human calcific aortic valvar stenosis and to verify by x ray diffraction crystal class previously reported by electron diffraction 138 quantitative energy dispersive analyses and x ray diffraction of pooled specimens were performed on samples of aortic valves excised from 12 patients. The principal components of the calcified portions of the valves were 38.15% calcium and 17.68% phosphorus. The weight percentage calcium to phosphorus ratio was 2.16 and an elemental distribution related to the simplest ideal unit cell formulation Ca10(PO4)6(OH)2 was determined as: (Ca0.952Mg0.044Na0.097K0.005)10 (P0.952S0.025C0.023)6O23.96(Cl0.0184O0. 982H)2. The hexagonal unit cell was found to have an a axis of 9.424 A(0.9424 nm); c axis of 6.787 A(0.6787 nm); volume of 522 A3(0.522 nm3); and density of 3.2 g.cm-3. On the bases of the composition, the axial dimensions, and the density the material was classified as the dahllite form of apatite. There was no evidence of crystalline cholesterol. Variations in elemental composition showed no significant correlation with age or sex of the patient; statistically, neither the cusp involved nor the location on the leaflet affected the mineral composition.

Serum bactericidal titer as a predictor of outcome in endocarditis.

A study was conducted in 89 rabbits with experimental aortic valve endocarditis caused by three different strains of Staphylococcus aureus to determine whether there was a correlation between the peak serum bactericidal titer of the four drugs tested and the vegetation titer. After four days of therapy both the rabbits with and those without sterile vegetations had median peak bactericidal titers of 1 : 8. The mean vegetation titers did not correlate with the mean bactericidal titers. The serum bactericidal test does not measure the relative rate of killing of the bacteria by the drugs. Although the test remains clinically useful for documentation of bactericidal activity, the minimum level of activity necessary for the test to serve as a predictor of outcome remains to be defined.

In vitro fluid dynamic characteristics of aortic bioprostheses: old versus new.

The in vitro fluid dynamic characteristics of a variety of old- and new-generation porcine and pericardial aortic bioprostheses were investigated under pulsatile flow conditions. The pressure drop results indicate that the old valve designs have performance indices in the range of 0.30 to 0.42, while the new, low-pressure fixed designs have performance indices of 0.50 to 0.70. Leaflet photography indicated that the new designs also have superior opening and closing characteristics. Flow visualization, and velocity and turbulent shear stress measurements, conducted with a two-dimensional laser Doppler anemometer system, indicated that all the tissue valve designs create jet-type flow fields. The intensity of the jets and turbulence levels were less severe with the new designs. The old designs created turbulent shear stresses of as little as 1500 dynes/cm2, while the new designs created turbulent shear stresses of as little as 750 dynes/cm2.

An instrument for the measurement of in vitro velocity and turbulent shear stress in the immediate vicinity of prosthetic heart valves.

The measurements of velocity and turbulent shear stress in the immediate vicinity of prosthetic heart valves play a vital role in their design and evaluation. In the past, hot-wire/film and one-component laser Doppler anemometer (LDA) systems have been used extensively. Hot-wire/film anemometers, however, have some serious disadvantages, such as not being able to measure the directionality of the flow, disturbing the flow field with the probe, and requiring frequent calibration. One-component LDA systems do not have these problems, but they cannot measure turbulent shear stresses directly. Since these measurements are essential, and are not available in the open literature, a two-component LDA system was assembled to measure velocity and turbulent shear stress fields under pulsatile flow conditions. The experimental methodology used to create an in vitro data base of velocity and turbulent shear stress fields in the immediate vicinity of various designs of prosthetic heart valve in current clinical use is also discussed in this paper.

Aortic valvular tophus: identification by X-ray diffraction of urate and calcium phosphates.

A typical gouty tophus with birefringent, dichroic, needle shaped crystals was found in a resected calcified aortic valve on routine histological examination. The patient, an elderly man, had a long history of gout. X-ray diffraction confirmed the presence of sodium acid urate monohydrate and identified hydroxyapatite and whitlockite in the accompanying dystrophic calcification of the aortic valves. Previous reports indicate that gouty tophi of the cardiac valves are rare: of the nine cases reported, eight occurred in the mitral valve.

Amyloid deposits in aortic and mitral valves. A clinicopathological investigation of material from 100 consecutive heart valve operations.

The material from 100 consecutive aortic and mitral valve operations has been studied histologically with particular reference to the presence of amyloid deposits. Sixty seven per cent were positive (aortic 88%, mitral 45%). The simultaneous occurrence of calcification of the valves and amyloid degeneration as well as of calcification and hyalinization was significant. Similarly there was significantly more amyloid in the older age groups, as well as a significant correlation between the degree of hyalinization of the valve and amyloid. Thirty-two patients had previously suffered from rheumatic fever. The heart valves of these patients did not differ histologically from the others, whereas significantly more amyloid was observed in the stenotic mitral valves than in the mitral valves which were insufficient.

Calcifications of cardiac valve bioprostheses. Biochemical, histologic, and ultrastructural observations in a subcutaneous implantation model system.

To study the process of calcification in bioprosthesis, 108 glutaraldehyde-treated porcine aortic valve leaflets were implanted subcutaneously in rabbits and removed 1 day to 6 months later; morphologic findings were correlated with biochemically determined levels of calcium (Ca++) and gamma-carboxyglutamic acid (Gla), a vitamin K-dependent Ca++-binding amino acid known to be present in a variety of tissues with pathological calcification. Gla and Ca++ levels began to increase about 2 months after implantation and increased progressively with time. Ca/Gla molar ratios were comparable to those in leaflets of bioprostheses explanted from patients, 22 to 64 months after implantation. Morphologically evident calcification began at the same time that Gla and Ca++ increases were detected biochemically and also increased in severity with time. Electron microscopy showed that calcification primarily involved the surface of collagen fibrils and the interfibrillar spaces. The biochemical and morphological findings in this experimental system are similar to those described in calcified porcine bioprosthetic valve leaflets removed from patients, but occurred much more rapidly. As with pathological calcification of other tissues, progressive calcification was accompanied by increased Gla levels, suggesting that Gla plays a role in the calcification of the leaflets. This model allows rapid comparative evaluation of large numbers of valve leaflets maintained under similar host conditions.

Maturation of the extracellular material of the semilunar heart values in the mouse. A histochemical analysis of collagen and mucopolysaccharides.

The developmental changes of collagen and mucopolysaccharides in the semilunar values of the mouse were studied during the embryonic, fetal and postnatal period. The valvular collagen was investigated using Van Gieson and Sirius red-polarization microscopy methods. These procedures showed that the establishment of the fibrosa layer of the cusps does not occur until the second week of the postnatal period. The nature and distribution of the valvular mucopolysaccharides were investigated by staining with Alcian blue at specific pH values and at various critical electrolyte concentrations, with the appropriate enzymatic controls using Streptomyces and testicular hyaluronidase. The results show that hyaluronate and chondroitin 4- and 6-sulphate are the major components during the embryonic and fetal period. In the older fetal stages and during the postnatal period the relative amount of hyaluronate decreases, while chondroitin sulphate increases. It is concluded from this study that the maturation of the valves occurs over a long period of the postnatal life.

Acid mucopolysaccharides of congenitally defective, rheumatic, and normal human aortic valves.

The qualitative nature, total amount, and relative proportion of various acid mucopolysaccharides (AMPSs) found in congenitally defective (bicuspid), young rheumatic, and normal aortic valvular tissue were compared. No differences in the qualitative nature of AMPSs were found in any of the aortic tissues studies; hyaluronic acid, chondroitin sulfate B, and chondroitin sulfate A/C were the primary AMPS components, with a trace amount of heparin. Congenitally defective aortic valves showed increasing amounts of calcification, a lowering of total AMPS content, and an alteration in the relative proportions of various AMPS with advancing age, as compared with age-matched normal aortic valves. The total AMPS content of rheumatic aortic valves from individuals under the age of 21 years was found to be significantly higher than that of age-matched normal controls. In addition, these rheumatic aortic valves showed an alteration in AMPS composition that was similar to that of congenitally defective aortic valves obtained from older individuals. These observations suggest nonspecific changes in the AMPS composition caused by chronic tissue damage, calcification, and fibrosis.

[Histochemical study of mucopolysaccharides of the tissue of fibrous rings of the human heart in the age aspect]. / Gistokhimicheskoe izuchenie mukopolisakharidov tkani fibroznykh kolets serdtsa cheloveka v vozrastnom aspekte

The content of mucopolysaccharides (MPS) and its dynamics with age in the tissue of fibrous rings of the human heart was studied. The studies were conducted on 88 hearts of patients who had died of various causes not connected with disorders of the cardiovascular system. The tissues of the human heart fibrous rings were extremely rich in both acid and neutral (of the type glyco- and mucoproteids) MPS. In newborns in the main substance of fibrous rings, along with hyaluronic acid, there were found chondroitin sulphate A and C, in the fibrous ring of the aortic valve--in small amounts chondroitin sulphate B. In childhood the content of chondroitin sulphate B continues to grow. In adulthood chondroitin sulphate B becomes a predominant component, no hyaluronic acid is detected. After 45 years of age a gradual decrease in the total amount of histochemically identifiable acid MPS takes place.