Graft arteriosclerosis-induced myocardial pathology in heart transplant recipients: predictive value of endomyocardial biopsy

BACKGROUND

Ischemic myocardial pathology resulting from graft arteriosclerosis (GA) includes subendocardial myocyte vacuolization (SEMV), indicative of sublethal ischemic injury, and coagulative myocyte necrosis, acute and healing (CMN), indicative of infarction.

METHODS

To assess the sensitivity and specificity of myocardial pathology resulting from GA in endomyocardial biopsy specimens, we correlated SEMV and CMN in the final three biopsy specimens (mean interval from last biopsy to death 23 +/- 20 days) with autopsy findings from 30 heart transplant recipients who survived more than 3 months and died of GA (n = 16) or of other causes (n = 14). The two groups were similar in other parameters.

RESULTS

Myocardial ischemic injury was present at autopsy in all 16 patients with GA with the following distribution: SEMV (n = 13) nine right ventricle (RV) and left ventricle (LV), four LV only; focal CMN (n = 8) six RV and LV, two LV only; subendocardial infarct (n = 3) three LV only; and transmural infarct (n = 3) one RV, two LV. Ischemic injury was present in the RV of 11 of 16 patients with GA. Of patients without GA, one had SEMV at autopsy; none had infarcts. Ischemic myocardial pathology was present in 10 of 48 biopsy specimens from patients with GA compared with one of 41 biopsy specimens from patients without GA (p < 0.05). The specificity of SEMV on biopsy was 98%, but sensitivity was only 17%. The positive predictive value for ischemic injury was 92%, and negative predictive value was 51%.

CONCLUSIONS

Myocardial pathology resulting from ischemia was present at autopsy in all patients dying of GA. Although more prevalent in the LV, 69% of patients had ischemic myocardial pathology in the RV, where it may be accessible to biopsy. Ischemic myocardial pathology in biopsy specimens is highly specific but far less sensitive, for diagnosing GA.

Innovative techniques in skeletal muscle cardiac assistance: first experimental study on minimally invasive aortomyoplasty and cardiomyoplasty

Skeletal muscle cardiac assistance as a treatment modality for heart failure is considered a high-risk procedure subject to strict patient selection. The aim here is to develop minimally invasive techniques to improve surgical outcomes and increase clinical indications. Ten goats (45-55 kg) were studied. In six, the latissimus dorsi muscle (LDM) was harvested via an open technique on one side vs a minimally invasive technique on the other using video assistance through two 3 cm incisions. Surgical maneuvers and length of procedures were noted. Animals were recovered, observed daily for local complications, and killed after 1 week for comparative anatomic and histopathologic studies. In four other goats, minimally invasive aortomyoplasty or cardiomyoplasty was performed using video assistance (2 aortomyoplasty, 2 cardiomyoplasty). In this experimental series, there were no surgical complications. The minimally invasive LDM harvest required a mean of 81 min (range 55-116 mn) with no gross evidence of muscle damage. The technique of LDM harvesting was standardized and is reproducible. Aortic and cardiac wraping were also achieved through three ports and a left minithoracotomy of 4 cm, using the right or left LDM. A scarf technique for the descending aortomyoplasty using the left LDM, and an anterior wrapping for cardiomyoplasty using the left or right LDM was technically feasible with video assistance. This study suggests future clinical applicability.

Vascular MADs: two novel MAD-related genes selectively inducible by flow in human vascular endothelium

Vascular endothelium is an important transducer and integrator of both humoral and biomechanical stimuli within the cardiovascular system. Utilizing a differential display approach, we have identified two genes, Smad6 and Smad7, encoding members of the MAD-related family of molecules, selectively induced in cultured human vascular endothelial cells by steady laminar shear stress, a physiologic fluid mechanical stimulus. MAD-related proteins are a recently identified family of intracellular proteins that are thought to be essential components in the signaling pathways of the serine/threonine kinase receptors of the transforming growth factor beta superfamily. Smad6 and Smad7 possess unique structural features (compared with previously described MADs), and they can physically interact with each other, and, in the case of Smad6, with other known human MAD species, in endothelial cells. Transient expression of Smad6 or Smad7 in vascular endothelial cells inhibits the activation of a transfected reporter gene in response to both TGF-beta and fluid mechanical stimulation. Both Smad6 and Smad7 exhibit a selective pattern of expression in human vascular endothelium in vivo as detected by immunohistochemistry and in situ hybridization. Thus, Smad6 and Smad7 constitute a novel class of MAD-related proteins, termed vascular MADs, that are induced by fluid mechanical forces and can modulate gene expression in response to both humoral and biomechanical stimulation in vascular endothelium.

Targeted overexpression of protein kinase C beta2 isoform in myocardium causes cardiomyopathy

Increased cardiovascular mortality occurs in diabetic patients with or without coronary artery disease and is attributed to the presence of diabetic cardiomyopathy. One potential mechanism is hyperglycemia that has been reported to activate protein kinase C (PKC), preferentially the beta isoform, which has been associated with the development of micro- and macrovascular pathologies in diabetes mellitus. To establish that the activation of the PKCbeta isoform can cause cardiac dysfunctions, we have established lines of transgenic mice with the specific overexpression of PKCbeta2 isoform in the myocardium. These mice overexpressed the PKCbeta2 isoform transgene by 2- to 10-fold as measured by mRNA, and proteins exhibited left ventricular hypertrophy, cardiac myocyte necrosis, multifocal fibrosis, and decreased left ventricular performance without vascular lesions. The severity of the phenotypes exhibited gene dose-dependence. Up-regulation of mRNAs for fetal type myosin heavy chain, atrial natriuretic factor, c-fos, transforming growth factor, and collagens was also observed. Moreover, treatment with a PKCbeta-specific inhibitor resulted in functional and histological improvement. These findings have firmly established that the activation of the PKCbeta2 isoform can cause specific cardiac cellular and functional changes leading to cardiomyopathy of diabetic or nondiabetic etiology.

Refinement of the alpha aminooleic acid bioprosthetic valve anticalcification technique

BACKGROUND

Aminooleic acid treatment has been demonstrated to prevent porcine valve calcification and to protect valvular hemodynamic function. Initial enthusiasm was tempered by histologic studies of these AOA valves, which showed cuspal hematomas, structural loosening, and surface roughening. This prompted a systematic review of the AOA treatment process. Unsolubilized particles of alpha aminooleic acid present in the treatment solution were identified as the cause of mechanical abrasion of valve cusps during processing. These particles were eliminated with a revamped protocol, which included filtration of the AOA solution before valve preparation.

METHODS

Porcine aortic valve cusps treated with this modified AOA protocol (AOA II) were studied in a rat subdermal implant model of mineralization. A juvenile sheep trial was then used to confirm the antimineralization effects of AOA II on glutaraldehyde-fixed porcine aortic roots in a circulatory model of accelerated calcification.

RESULTS

Retrieved AOA II-treated cusps from the subdermal model were markedly less calcified than control cusps (AOA II, 1 +/- 0, 17 +/- 4, 23 +/- 6, and 17 +/- 10 versus control, 189 +/- 14, 251 +/- 16, 250 +/- 14, and 265 +/- 10 mg calcium/mg sample at 4, 8, 12, and 16 weeks, respectively; p < 0.0001). Morphologic examination of the AOA II cusps of the valves retrieved from the sheep demonstrated freedom from the structural loosening, surface roughening, and hematoma formation that had limited the utility of the original AOA preparation technique. Cusps from AOA II-treated porcine roots had significantly less calcium than control cusps (AOA II, 5.5 +/- 3.0 mg/g; control, 91.2 +/- 19.5 mg/g; p = 0.0004). The aortic walls had similar levels of calcification (AOA II, 156 +/- 73 mg/g; control, 159 +/- 10 mg/g; p = not significant).

CONCLUSIONS

These data suggest that the modified AOA technique warrants further evaluation as an antimineralization treatment for glutaraldehyde-fixed porcine bioprostheses.

Differential calcification of cusps and aortic wall of failed stented porcine bioprosthetic valves

In this study, we examined separately calcification of cusps (C) and associated aortic wall (AW) of 38 (13 aortic and 25 mitral) porcine bioprosthetic heart valves explanted from 37 patients (ages 25-80 years, mean 59) for structural dysfunction, following 54-210 months (mean 125 months aortic, 119 months mitral). Valves were sectioned into C and corresponding AW components; calcification was assessed by atomic absorption spectroscopy for calcium and histologic examination. Overall, AW calcification was half that of C (33.3 +/- 5.4 vs. 65.9 +/- 6.3 microg/mg, mean +/- standard error of the mean respectively, p = 0.002). Correlation of calcification in individual C/AW pairs was weak (r2 = 0.34). Calcification in C was nodular, largely in the valve fibrosa, but AW calcification predominated in the cells between elastic lamellae; large nodules were sparse. We conclude that since AW calcification in these failed porcine valves was neither prominent nor clinically significant, this process should rarely if ever be a limiting factor in the function of stented porcine valves, and that development of anticalcification therapies directed toward the AW of stented valves should be of low priority. However, in stent-free valves, the AW is not covered by prosthetic material, and the level of calcification could be greater and more likely to cause clinical problems through stiffening, embolism, and/or protrusion into the lumen of calcific masses.

Clinical features of hypertrophic cardiomyopathy caused by mutation of a "hot spot" in the alpha-tropomyosin gene

OBJECTIVES

We studied the clinical and genetic features of familial hypertrophic cardiomyopathy (FHC) caused by an Asp175Asn mutation in the alpha-tropomyosin gene in affected subjects from three unrelated families.

BACKGROUND

Correlation of genotype and phenotype has provided important information in FHC caused by beta-cardiac myosin and cardiac troponin T mutations. Comparable analyses of hypertrophic cardiomyopathy caused by alpha-tropomyosin mutations have been hampered by the rarity of these genetic defects.

METHODS

The haplotypes of three kindreds with FHC due to an alpha-tropomyosin gene mutation, Asp175Asn, were analyzed. The cardiac histopathologic findings of this mutation are reported. Distribution of left ventricular hypertrophy in affected members was assessed by two-dimensional echocardiography, and patient survival rates were compared.

RESULTS

Genetic studies defined unique haplotypes in the three families, demonstrating that independent mutations caused the disease in each. The Asp175Asn mutation caused cardiac histopathologic findings of myocyte hypertrophy, disarray and replacement fibrosis. The severity and distribution of left ventricular hypertrophy varied considerably in affected members from the three families (mean maximal wall thickness +/- SD: 24 +/- 4.5 mm in anterior septum of Family DT; 15 +/- 2.7 mm in anterior septum and free wall of Family DB; 18 +/- 2.1 mm in posterior septum of Family MI), but survival was comparable and favorable.

CONCLUSIONS

Nucleotide residue 579 in the alpha-tropomyosin gene may have increased susceptibility to mutation. On cardiac histopathologic study, defects in this sarcomere thin filament component are indistinguishable from other genetic etiologies of hypertrophic cardiomyopathy. The Asp175Asn mutation can elicit different morphologic responses, suggesting that the hypertrophic phenotype is modulated not by genetic etiologic factors alone. In contrast, prognosis reflected genotype; near normal life expectancy is found in hypertrophic cardiomyopathy caused by the alpha-tropomyosin mutation Asp175Asn.

Prevention of bioprosthetic heart valve calcification by ethanol preincubation. Efficacy and mechanisms

BACKGROUND

Calcification of the cusps of bioprosthetic heart valves fabricated from either glutaraldehyde cross-linked porcine aortic valves or bovine pericardium frequently causes the clinical failure of these devices. Our investigations studied ethanol pretreatment of glutaraldehyde cross-linked porcine aortic valves as a new approach to prevent cuspal calcification. The hypothesis governing this approach holds that ethanol pretreatment inhibits calcification resulting from protein structural alterations and lipid extraction.

METHODS AND RESULTS

Results demonstrated complete inhibition of calcification of glutaraldehyde-pretreated porcine bioprosthetic aortic valve cusps by 80.0% ethanol in rat subdermal implants (60-day ethanol-pretreated calcium level, 1.87 +/- 0.29 micrograms/mg tissue compared with control calcium level, 236.00 +/- 6.10 micrograms/mg tissue) and in sheep mitral valve replacements (ethanol-pretreated calcium level, 5.22 +/- 2.94 micrograms/mg tissue; control calcium level, 32.50 +/- 11.50 micrograms/mg tissue). The mechanism of ethanol inhibition may be explained by several observations: ethanol pretreatment resulted in an irreversible alteration in the amide I band noted in the infrared spectra for both purified type I collagen and glutaraldehyde cross-linked porcine aortic leaflets. Ethanol pretreatment also resulted in nearly complete extraction of leaflet cholesterol and phospholipid.

CONCLUSIONS

Ethanol pretreatment of glutaraldehyde cross-linked porcine aortic valve bioprostheses represents a highly efficacious and mechanistically based approach and may prevent calcific bioprosthetic heart valve failure.

Semaphorin III is needed for normal patterning and growth of nerves, bones and heart

The expression patterns of the recently discovered family of semaphorin genes suggests that they have widespread roles in embryonic development. Some seem to guide neuronal growth cones, but otherwise their functions are unknown. Semaphorin III is a membrane-associated secreted protein with a developmentally dynamic pattern of expression, including particular domains of the nervous system, the borders of developing bones, and the heart. In vitro, semaphorin III causes growth-cone collapse, and repels cutaneous sensory axons from the ventral spinal cord. Mutants in the Drosophila gene semaII, which encodes a related semaphorin, die after eclosion, but no responsible abnormality is evident. We have generated mice mutant in the semaIII gene by homologous recombination. Here we show that in the mutants, some sensory axons project into inappropriate regions of the spinal cord where semaIII is normally expressed. The cerebral cortex of homozygous mutant mice shows a paucity of neuropil and abnormally oriented neuronal processes, especially of the large pyramidal neurons. Certain embryonic bones and cartilaginous structures develop abnormally, with vertebral fusions and partial rib duplications. The few mice that survive more than a few days postnatally manifest pronounced and selective hypertrophy of the right ventricle of the heart and dilation of the right atrium. Thus, semaphorin III might serve as a signal that restrains growth in several developing organs.

Circumferential stress and matrix metalloproteinase 1 in human coronary atherosclerosis. Implications for plaque rupture

Atherosclerotic plaque rupture may occur when regions of weakened extracellular matrix are subjected to increased mechanical stresses. Since collagen is a major determinant of extracellular matrix strength, enzymes that degrade collagen may play an important role in destabilizing the atherosclerotic lesion. To test the hypothesis that matrix metalloproteinase 1 (interstitial collagenase, or MMP-1), which initiates degradation of fibrillar collagens, colocalizes with increased stress in the fibrous cap of the atherosclerotic lesion, 12 unruptured human coronary lesions were studied. Finite-element analysis was used to determine the distribution of stress in the lesion, with estimates of material properties from previous measurements of human tissues. A computerized image analysis system was used to determine the distribution of immunoreactive MMP-1 within the fibrous tissue of the lesion. There was a significant correlation between immunoreactive MMP-1 and circumferential tensile stress in the fibrous cap within a given lesion (median Spearman rank correlation coefficient, .36; interquartile range, -.02 to .81; P < .02). Within a given lesion, the highest-stress region had twofold greater MMP-1 expression than the lowest-stress regions. In unruptured human atherosclerotic coronary lesions, overexpression of MMP-1 is associated with increased circumferential stress in the fibrous plaque. Degradation and weakening of the collagenous extracellular matrix at these critical high-stress regions may play a role in the pathogenesis of plaque rupture and acute ischemic syndromes.

Moderate hypothermia reduces cardiopulmonary bypass-induced impairment of cerebrovascular responses to platelet products

BACKGROUND

The purpose of this study was to determine whether cerebral cortical microvascular responses to platelet-derived vasoactive substances are altered after normothermic cardiopulmonary bypass (CPB), and whether these alterations are modified by moderate hypothermia.

METHODS

Pigs were placed on normothermic CPB (37 degrees C) for 2 hours and then perfused off CPB with normothermic blood for either 15 minutes (n = 8) or 60 minutes (n = 6). Another group was placed on moderately hypothermic CPB (25 degrees C) for 2 hours and then perfused off CPB at 37 degrees C for 15 minutes (n = 6). Alphastat pH management was used. In vitro responses of isolated cortical cerebral arterioles (90 to 170 microns internal diameter) to platelet-derived vasoactive substances were examined in a pressurized no-flow state with videomicroscopy. Microvessels from noninstrumented pigs (n = 14) were used as controls for in vitro studies.

RESULTS

Cerebrovascular resistance and internal carotid artery blood flow were similar 15 minutes after CPB in both normothermic and hypothermic groups. However, relaxations of microvessels to adenosine 5' diphosphate or serotonin were reduced in vessels from both groups. One hour of after CPB cerebral perfusion did not change this pattern of altered vascular reactivity. Hypothermia caused a partial but significant reduction in impairment of responses to adenosine 5' diphosphate and serotonin. Microvascular relaxation to the endothelium-independent agent sodium nitroprusside and contraction to a thromboxane A2 analog were similar in all experimental groups, suggesting normal vascular smooth muscle responsiveness.

CONCLUSIONS

This study demonstrates that normothermic extracorporeal circulation reduces endothelium-dependent relaxation responses to products of platelet activation in the cerebral microcirculation. Moderate hypothermia attenuates the CPB-induced impairment of endothelium-dependent relaxation, but has no effect on baseline cerebral blood flow after rewarming.

Calcification of polyurethanes implanted subdermally in rats is enhanced by calciphylaxis

Calcification complicates the use of the polymer polyurethane in cardiovascular implants. To date only costly experimental circulatory animal models have been useful for investigating this disease process. In this paper we report that polyurethane calcification in rat subdermal implants is enhanced by overdosing with a vitamin-D analog. The calcification-prone state, known as calciphylaxis, was induced in 4-week old rats by oral administration of a vitamin-D analog, dihydrotachysterol. We studied two commercially available polyurethanes (Biomer and Mitrathane) and two proprietary polyurethanes (PEU-2000 and PEU-100). PEU-100 is unique because it is derivatized with ethanehydroxy-bisphosphonate (EHBP) for calcification resistance. Polyurethane calcium and phosphate levels and morphological changes due to calciphylaxis were compared with those of control rat subdermal explants in 60-day studies. Increased polyurethane mineralization was observed due to calciphylaxis with 60-day rat subdermal explants of Biomer, Mitrathane, and PEU-2000 (calcium levels, respectively, 4.13 +/- 0.56, 18.61 +/- 2.73, and 3.37 +/- 0.22 microgram/mg, mean +/- standard error) as compared to control explants (calcium levels, respectively, 1.22 +/- 0.1, 12.57 +/- 0.86, and 0.20 +/- 0.86 microgram/mg). The study also demonstrated that with 60-day implants calciphylaxis had no side effects on somatic growth and serum calcium levels. Explant surface morphology of these polyurethane explants examined by scanning electron microscopy, back scattering electron imaging coupled with energy dispersive X-ray spectroscopy, and light microscopy demonstrated the presence of predominantly surface-oriented calcification. PEU-100, derivatized with 100 n.moles/ mg of EHBP, resisted calcification with explant calcium levels 0.51 +/- 0.01 (calciphylaxis) and 0.38 +/- 0.01 (control) microgram/mg. It is concluded that calciphylaxis enhances superficial polyurethane calcification in rat subdermal implants and that an EHBP-modified polyurethane resists calcification despite calciphylaxis. Rat subdermal implants using calciphylaxis may be generally useful for evaluating the calcification potential of various biomedical polymers.

A mouse model of familial hypertrophic cardiomyopathy

A mouse model of familial hypertrophic cardiomyopathy (FHC) was generated by the introduction of an Arg 403 --> Gln mutation into the alpha cardiac myosin heavy chain (MHC) gene. Homozygous alpha MHC 403/403 mice died 7 days after birth, and sedentary heterozygous alpha MHC 403/+ mice survived for 1 year. Cardiac histopathology and dysfunction in the alpha MHC 403/+ mice resembled human FHC. Cardiac dysfunction preceded histopathologic changes, and myocyte disarray, hypertrophy, and fibrosis increased with age. Young male alpha MHC 403/+ mice showed more evidence of disease than did their female counterparts. Preliminary results suggested that exercise capacity may have been compromised in the alpha MHC 403/+ mice. This mouse model may help to define the natural history of FHC.

Heart transplantation-associated perioperative ischemic myocardial injury. Morphological features and clinical significance

BACKGROUND

The frequency and clinical significance of perioperative ischemic myocardial injury (PIMI) after heart transplantation and the diagnostic features distinguishing PIMI from rejection are not well defined.

METHODS AND RESULTS

We evaluated PIMI in the first four weekly endomyocardial biopsies and/or autopsy myocardium from 140 consecutive orthotopic heart transplantation recipients (1984 to 1991) by grading the severity of coagulative myocyte necrosis (CMN) as absent, 0; mild-focal, 1; moderate-multifocal, 2; or severe-confluent, 3, and determining the evolution of morphological features of its healing. CMN (often with contraction bands) was noted in 124 patients (89%); 24 patients (17%) had grade 3 CMN, of which 4 died within 30 days of transplantation. Nevertheless, at 1 year after surgery, survival was similar in patients with and without severe injury. Increased cold ischemic time but neither donor age nor intensity of inotropic support correlated with more severe early ischemic injury. PIMI inflammation was characterized by a predominantly polymorphonuclear/histiocytic infiltrate that contained lymphocytes and plasma cells, expanding the interstitium but not encroaching upon and separable from adjacent viable myocytes. Histological features of PIMI developed and resolved more slowly than those of typical myocardial infarct necrosis in nonimmunosuppressed patients; at 4 weeks, CMN persisted in 20% of patients and residual healing in nearly half. Diagnostic rejection was observed concurrently with PIMI in 54 of 533 biopsies (10%).

CONCLUSIONS

Diagnosed by conventional histological criteria, PIMI is prevalent early after heart transplantation and has a protracted healing phase that can mimic or coexist with rejection. Extensive PIMI has deleterious impact on short-term survival, but the long-term impact of PIMI remains to be established.

Smooth muscle cells of the coronary arterial tunica media express tumor necrosis factor-alpha and proliferate during acute rejection of rabbit cardiac allografts

Graft coronary arteriosclerosis (GCA) frequently limits the long-term success of cardiac transplantation. The pathogenic mechanisms of and stimuli that provoke GCA remain uncertain. Whatever the initiating factors, deranged control of smooth muscle cells (SMC) proliferation likely contributes to the intimal hyperplasia that produces obstructive lesions. To identify mediators that may contribute to ongoing modulation of SMC functions during acute rejection and to explore the mechanisms of the pathogenesis of graft coronary arteriosclerosis, we studied the kinetics of proliferation and the expression of tumor necrosis factor-alpha (TNF-alpha), a proinflammatory and SMC growth-promoting cytokine, in coronary arterial SMCs in rabbit hearts transplanted heterotopically without immunosuppression. Hearts were harvested at 2 (n = 5), 5 (n = 5), and 8.2 +/- 0.4 (mean +/- SD, n = 5) days after transplantation, just before graft failure as judged clinically. SMC proliferation was assessed by continuous bromodeoxyuridine labeling (BrdU 10 mg/kg/d. s.q.). Whole heart cross sections were stained immunohistochemically with monoclonal antibodies that recognize TNF-alpha, BrdU, and SMCs (muscle alpha-actin). Major epicardial coronary arteries (five to nine profiles in each animal) were evaluated. Histological rejection grades by the International Society for Heart and Lung Transplantation scale at 2, 5, and 10 days were 1.6 +/- 0.9, 2.8 +/- 1.1, and 4.0 +/- 0.0, respectively. Medial SMCs in normal hearts and 2 days after transplant expressed little or no TNF-alpha and displayed negligible BrdU incorporation. At 5 days after transplantation, some medial SMCs stained for TNF-alpha and had a low BrdU labeling index (0.5 +/- 0.8%). At 8.2 days after transplant, almost all medial SMCs expressed TNF-alpha intensely and had a high labeling index (29.8 +/- 8.0%). These results demonstrate that acute rejection activates medial SMCs in coronary arteries to express TNF-alpha and that SMC-derived TNF-alpha may contribute to medial SMC proliferation in coronary arteries during acute rejection. This finding of early medial SMC replication suggests a novel and heretofore unsuspected mechanism of intimal expansion consequent to the allogeneic state. These results furnish additional insight into the possible mechanisms that link acute rejection with graft coronary arteriosclerosis. Furthermore, the close association of TNF-alpha expression with SMC replication provides not only a novel marker of SMC activation but also a potential new therapeutic target for the prevention of graft coronary disease.

Acute rejection accelerates graft coronary disease in transplanted rabbit hearts

BACKGROUND

The relation between episodes of acute rejection and the development of graft coronary arteriosclerosis remains controversial. We examined the hypothesis that acute rejection episodes accelerate graft coronary arteriosclerosis lesion formation in rabbit allografts.

METHODS AND RESULTS

A control group (n = 5) received cyclosporine 5 mg.kg-1.d-1 for 6 weeks after heterotopic heart transplantation. In a rejection group (n = 5), cyclosporine was omitted for 4 days at 1 and 4 weeks after transplantation. We studied cross sections of grafted hearts at 6 weeks and evaluated myocardial rejection grade, incidence, and severity and cell composition of intimal lesions in multiple coronary artery profiles. Episodic withdrawal of cyclosporine augmented myocardial rejection (International Society for Heart and Lung Transplantation grades 0, 0, 0, 0, and 1A in the control group to grades 1A, 1B, 2, 3A, and 3B in the rejection group). Episodes of acute rejection significantly increased the incidence (7.8 +/- 2.7% to 49.7 +/- 1.9%) and severity (from grade 0.10 +/- 0.04 to 0.79 +/- 0.24) of intimal thickening in graft coronary arteries. Most intimal lesions consisted of smooth muscle cells and contained various degrees of T-lymphocyte infiltration but sparse macrophages.

CONCLUSIONS

In this experimental model, episodes of acute rejection precipitated by cyclosporine withdrawal accelerated the development of graft vascular lesion formation. Activation of vascular cells and leukocyte recruitment during acute rejection may thus contribute to the pathogenesis of graft arteriosclerosis.

Structure-function correlations in cryopreserved allograft cardiac valves

This communication briefly summarizes a morphologic investigation of explanted cryopreserved heart valves and discusses the findings in the context of ongoing debates regarding modes of failure, cellular viability, durability of the extracellular matrix, and the contribution of immune responses. We studied 20 cryopreserved human heart valve allografts functioning up to 9 years as either orthotopic aortic valves/root replacements or right ventricle-to-pulmonary artery conduits explanted for valve failure, infection, or growth-related conduit or valve stenosis. Implanted valves had progressively severe loss of normal layered structure and were devoid of stainable deep connective tissue cells. Inflammation was minimal. Other late findings included minimal inflammation, mild cuspal hematomas, mural thrombus, and calcification, most prominent in the aortic wall. Transmission electron microscopy of late explants revealed nonviable cells and their debris, and a collagenous skeleton that was largely intact. We conclude that cryopreserved allograft heart valves have minimal, if any, viable cells, but largely retain the original collagen network; preservation of the autolysis-resistant collagenous skeleton likely provides the structural basis of function. Our results also suggest that immune responsiveness has little, if any, impact on late allograft function or degradation.

Physicochemical characterization of natural and bioprosthetic heart valve calcific deposits: implications for prevention

This investigation was performed to provide a comprehensive physicochemical characterization of calcific deposits (CDs) that form on human heart valves under various pathological conditions. We examined and characterized CDs associated with aortic stenosis on congenitally bicuspid valves (n = 10), degenerative aortic stenosis on valves with previously normal anatomy (n = 10), and rheumatic aortic (n = 10) and mitral (n = 10) stenosis. Native and deproteinated CDs underwent chemical analysis and structural characterization, whereas deproteinated CDs were measured for thermodynamic solubility. The CDs in valvular heart disease were microcrystalline apatitic products containing substantial amounts of sodium, magnesium, carbonate, fluoride, and organic fraction. The properties of natural heart valve CDs were compared with those of previously measured CDs that form on or in heart valve bioprostheses. Compared with bioprosthetic valve CDs, natural valve CDs have a higher ratio of calcium to phosphorus, higher crystallinity, and lower solubility. These differences indicate that natural heart valve CDs appear to comprise a more mature biomineral. If the formation of mature CDs proceeds through transient stages involving unstable precursors, then the main strategy for prevention of calcific deterioration of bioprosthetic heart valves would be the development of locally applied long-term inhibitors that both (1) suppress nucleation and growth of more soluble precursors and (2) inhibit subsequent augmentation of less soluble CDs.

Pathological considerations in cryopreserved allograft heart valves

Since structure-function correlations have not been determined for cryopreserved allograft heart valves, we studied 20 explanted valves in place several hours to nine years, as either orthotopic aortic valves/root replacements or right ventricle to pulmonary artery conduits. They were explanted primarily due to growth-related conduit or valve stenosis, valve regurgitation, or infection. Controls included seven unused cryopreserved allograft valves and 16 aortic valves removed from transplanted allograft hearts obtained at either autopsy (n = 15) or retransplantation (n = 1), two days to four years postoperatively, following myocardial rejection (n = 4), graft coronary arteriosclerosis (n = 4), and other (n = 8). Analysis included gross inspection, radiography, light microscopy, electron microscopy, and immunohistochemical studies (to allow identification/localization of endothelial cells, mononuclear inflammatory cells, and T and B lymphocyte subsets). Cryopreserved allograft valves implanted more than one day had progressively severe loss of normal structure and were devoid of surface endothelium and stainable deep connective tissue cells. Inflammatory cellularity varied from none (most valves) to prominent (primarily T lymphocytes in one valve). Transmission electron microscopy of three long term valvular allografts revealed no viable cells, remarkable preservation of the collagenous valve matrix and focal cell-oriented calcification. In contrast, aortic valves from transplanted hearts showed remarkable structural preservation, including layered architecture, endothelium and deep connective tissue cells; inflammatory infiltrates were generally sparse, even in cases with fatal myocardial rejection. We conclude that cryopreserved allograft valves are morphologically non-viable valves, whose structural basis for function seems primarily related to the largely preserved collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural history of focal moderate cardiac allograft rejection. Is treatment warranted?

BACKGROUND

The rate of progression and potential long-term consequences of isolated foci of moderate acute rejection (FMR) on endomyocardial biopsy (EMB) have not been defined; therefore, whether FMR necessitates augmented immunosuppression remains controversial.

METHODS AND RESULTS

At our institution, recipients with EMBs having FMR, defined as one or two isolated foci of cellular infiltrates with associated myocyte damage (International Society for Heart and Lung Transplantation [ISHLT] grade 2 and a subset of grade 3A), do not routinely receive intensified immunosuppression. Accordingly, to determine the outcome of untreated FMR, we reviewed 4398 EMBs (mean, 4.4 samples each) obtained after orthotopic heart transplantation in 208 consecutive recipients maintained on triple immunosuppressive therapy. The incidence of progression versus resolution of FMR, the time interval after transplantation when FMR was detected, and the relation of untreated FMR to recipient survival were analyzed. FMR categorized as one (n = 312) or two (n = 89) foci was present in 401 EMBs (9% of total) obtained 10 days to 7.5 years after transplantation from 149 recipients (72%). EMBs with FMR resolved without treatment in 341 of 401 (85%), and only 60 of 401 (15%) progressed to higher grade rejection. EMBs that progressed occurred 7.5 +/- 7.9 months (mean +/- SD) after transplantation compared with 14.0 +/- 16.5 months after transplantation for those that resolved (P < .005). Of the 60 EMBs that progressed, 55% occurred within the first 6 months, 78% within the first year, and 97% within the first 2 years after transplantation. EMBs with two foci of FMR were no more likely to progress than those with one focus. Thirty-nine recipients experienced one (n = 25), two (n = 9), three (n = 3), or four (n = 2) episodes of FMR that progressed. One or more episodes of FMR that did not progress occurred in 110 recipients. By Kaplan-Meier analysis, survival at 1 and 5 years was similar in recipients with and those without FMR progression.

CONCLUSIONS

First, untreated FMR consisting of either one or two foci has a low rate of progression. Second, progression of FMR decreases with increasing postoperative interval and becomes rare after 2 years. Last, FMR progression did not identify recipients with decreased survival.

Calcification of valved aortic allografts in rats: effects of age, crosslinking, and inhibitors

Experiments were carried out to investigate rat aortic allograft calcification using valved abdominal aortic allografts. Results indicated that this was a potentially useful model for investigating fresh allograft calcification, as well as mineralization of glutaraldehyde-crosslinked valved allografts. Valve cusp results, however, were not comparable to those noted in large animal or human studies, while aortic wall calcification was more comparable. Calcification inhibitor investigations demonstrated that nearly complete inhibition of the calcification of the aortic wall of glutaraldehyde-crosslinked allografts was achieved using a number of individual inhibitors, including controlled release diphosphonates, and pretreatment with either ferric chloride or aluminum chloride. However, aminopropanehydroxydiphosphonate pretreatment was not efficacious, and sodium dodecyl sulfate pretreatment was only partially effective for inhibiting the aortic wall calcification in the glutaraldehyde-crosslinked allografts. It is concluded that valved aortic allografts in rats provide a useful model for investigating aortic wall (but not valve cusp) calcification and its inhibition.