Hematopoietic chimerism following allotransplantation of the spleen, splenocytes or kidney in pigs.

BACKGROUND: Mixed chimerism is associated with donor-specific tolerance. Spleen or splenocyte allotransplantation (Tx) is recognized as potentially tolerogenic. There is no definitive report comparing chimerism levels following spleen and splenocyte Tx in a large animal model. We have compared chimerism after spleen, splenocyte, or kidney Tx in pigs. METHODS: Outbred (n = 5) and MHC-defined miniature (n = 1) pigs underwent orthotopic spleen Tx. Outbred pigs received splenocytes through a systemic vein (n = 1) or the portal vein (n = 3). Kidney Tx (n = 2) or concomitant Tx of spleen+kidney (n = 2) was carried out. All except one recipient pigs were irradiated (700 cGy thymic and 100-125 cGy whole body) on day-2. Cyclosporine or tacrolimus was administered for 42 days. All donors were males and all recipients were females; chimerism in the blood was determined by Quantification-PCR for the donor Y chromosome. Mixed lymphocyte reaction (MLR) was performed before and after Tx. RESULTS: One week after spleen Tx in outbred and MHC-defined pigs, chimerism ranged between 0.8 and 22.5%, and 5.4-20.1%, respectively, and remained between 17.7 and 67.4%, and 2.2-7.4%, respectively, until day 28. One week after splenocyte Tx, chimerism ranged between 0.1 and 8.5%, and decreased to 0.1-0.8% at 3-4 weeks. There was no detectable chimerism 14 days after kidney Tx. The response on MLR of all recipient pigs to donor cells was decreased after Tx, except in one case of splenocyte Tx, indicating that this pig might have become sensitized. After discontinuation of immunosuppression, most isolated spleen or kidney grafts were not rejected, but the kidney was rejected after concomitant spleen+kidney Tx. CONCLUSIONS: There was a significantly higher level of blood chimerism following spleen Tx compared to splenocyte or kidney Tx. However, concomitant Tx of spleen+kidney may be associated with accelerated kidney graft rejection.

Whole-slide imaging digital pathology as a platform for teleconsultation: a pilot study using paired subspecialist correlations.

CONTEXT: -Whole-slide imaging technology offers promise for rapid, Internet-based telepathology consultations between institutions. Before implementation, technical issues, pathologist adaptability, and morphologic pitfalls must be well characterized. OBJECTIVE: -To determine whether interpretation of whole-slide images differed from glass-slide interpretation in difficult surgical pathology cases. DESIGN: -Diagnostically challenging pathology slides from a variety of anatomic sites from an outside laboratory were scanned into whole digital format. Digital and glass slides were independently diagnosed by 2 subspecialty pathologists. Reference, digital, and glass-slide interpretations were compared. Operator comments on technical issues were gathered. RESULTS: -Fifty-three case pairs were analyzed. There was agreement among digital, glass, and reference diagnoses in 45 cases (85%) and between digital and glass diagnoses in 48 (91%) cases. There were 5 digital cases (9%) discordant with both reference and glass diagnoses. Further review of each of these cases indicated an incorrect digital whole-slide interpretation. Neoplastic cases showed better correlation (93%) than did cases of nonneoplastic disease (88%). Comments on discordant cases related to digital whole technology focused on issues such as fine resolution and navigating ability at high magnification. CONCLUSIONS: -Overall concordance between digital whole-slide and standard glass-slide interpretations was good at 91%. Adjustments in technology, case selection, and technology familiarization should improve performance, making digital whole-slide review feasible for broader telepathology subspecialty consultation applications.

Repetitive gastric aspiration leads to augmented indirect allorecognition after lung transplantation in miniature swine.

INTRODUCTION: Lung transplant recipients with documented gastroesophageal reflux disease (GERD) are at increased risk for graft dysfunction. Here, we present the first large-animal model of gastric aspiration after allogeneic lung transplantation and some preliminary data demonstrating the effect of chronic aspiration on the direct and indirect pathways of allorecognition. METHODS: Left orthotopic lung transplants (n=3) were performed in miniature swine across a major histocompatibility complex class I disparity, followed by 12 days of high-dose cyclosporine A. At the time of transplantation, a transtracheal catheter was placed at the carina, above the bronchial anastomosis. A gastrostomy tube was placed for daily aspiration of gastric contents. Subsequently, graft lungs were instilled with gastric aspirate daily (3 mL/hrX8 hr/day) for 50 days. Recipients were followed up with daily complete blood count, scheduled chest radiographs, and biopsies. In vitro studies, including cell-mediated lympholysis, mixed lymphocyte reactions, and peptide proliferation assays, were performed. Results from these three recipients were compared with those of historical controls (n=6) who were treated identically, except for the tracheal cannulation and simulated gastric aspiration. RESULTS: Two of the experimental animals were euthanized with nonviable lungs soon after the postoperative day 50 biopsy. In both cases the native lung was normal. The third animal survived over 180 days without the evidence of chronic rejection. After immunosuppressive treatment, all animals demonstrated donor-specific hyporesponsiveness by assays of direct alloresponse (cell-mediated lympholysis, mixed lymphocyte reaction). A significant response to synthetic donor-derived class I peptide, however, was seen in all animals. A more pronounced and diffuse response was seen in the animals rejecting their grafts. The historical controls showed medium-term graft survival with evidence of chronic rejection in the majority of animals, as previously reported. CONCLUSION: In a model of GERD after lung transplantation, a spectrum of clinical outcomes was observed. The in vitro data suggest that acid reflux enhances the indirect alloresponse to processed donor class I antigen, giving mechanistic insight into the manner in which GERD may be deleterious to the transplanted lung.

Calcified plaque: measurement of area at thin-section flat-panel CT and 64-section multidetector CT and comparison with histopathologic findings.

The purpose of this study was to assess the blooming artifacts in ex vivo coronary arteries at multidetector computed tomography (CT) and flat-panel-volume CT by comparing measured areas of calcified plaque with respect to the reference standard of histopathologic findings. Three ex vivo hearts were scanned with multidetector CT and flat-panel-volume CT after institutional review board approval. The area of calcified plaque was measured at histopathologic examination, multidetector CT, and flat-panel-volume CT. The plaque area was overestimated at multidetector CT by 400% (4.61/1.15) on average, and the predicted difference between the measurements was significant (3.46 mm(2), P = .018). The average overestimation of plaque area at flat-panel-volume CT was twofold (214% [2.18/1.02]), and the predicted difference was smaller (1.16 mm(2), P = .08). The extent of the blooming artifact in visualizing calcified coronary plaque is reduced by using flat-panel-volume CT.

Thrombotic microangiopathy associated with humoral rejection of cardiac xenografts from alpha1,3-galactosyltransferase gene-knockout pigs in baboons.

Heterotopic cardiac xenotransplantation from alpha1,3-galactosyltransferase gene-knockout (GalT-KO) swine to baboons was performed to characterize immunological reaction to the xenograft in the absence of anti-Gal antibody-mediated rejection. Eight baboons received heterotopic cardiac xenografts from GalT-KO porcine donors. All baboons were treated with chronic immunosuppressive therapy. Both histological and immunohistochemical studies were performed on biopsy and graftectomy samples. No hyperacute rejection was observed. Three baboons were euthanized or died 16 to 56 days after transplantation. The other five grafts ceased beating between days 59 and 179 (median, 78 days). All failing grafts exhibited thrombotic microangiopathy (TM) with platelet-rich fibrin thrombi in the microvasculature, myocardial ischemia and necrosis, and focal interstitial hemorrhage. TM developed in parallel with increases in immunoglobulin (IgM and IgG) and complement (C3, C4d, and C5b-9) deposition, as well as with subsequent increases in both TUNEL(+) endothelial cell death and procoagulant activation (increased expression of both tissue factor and von Willebrand factor and decreased expression of CD39). CD3(+) T-cell infiltration occurred in all grafts and weakly correlated with the development of TM. In conclusion, although the use of GalT-KO swine donors prevented hyperacute rejection and prolonged graft survival, slowly progressive humoral rejection--probably associated with non-Gal antibodies to the xenograft--and disordered thromboregulation represent major immunological barriers to long-term xenograft survival.

Operational tolerance to class I disparate lungs can be induced despite pretransplant immunization with class I allopeptides.

BACKGROUND: Using a class I-disparate swine lung transplant model, we examined whether an intensive course of tacrolimus could induce operational tolerance and whether preoperative allopeptide immunization would prevent the development of tolerance. METHODS: Left lung grafts were performed using class I-disparate (class II-matched) donors. Recipients were treated with 12 days of postoperative tacrolimus. Three recipients were immunized prior to transplantation with class I allopeptides. Three other recipients were not immunized. RESULTS: The nonimmunized recipients maintained their grafts long term (>497, >451, and >432 days), without developing chronic rejection. The immunized swine also maintained their grafts long term (>417, >402, >401 days), despite developing a variety of in vitro and in vivo responses to the immunizing peptides, as well as having strong mixed lymphocyte reactions to donor cells prior to transplantation. CONCLUSIONS: Using only a brief course of tacrolimus, we have been able to induce a state of operational tolerance in a class I-disparate preclinical lung transplant model. Moreover, preoperative alloimmunization did not block tolerance induction or induce chronic rejection. These data show that it is possible to create a state of operational tolerance to lung allografts even in the presence of donor-sensitized cells.

Establishment of transplantable porcine tumor cell lines derived from MHC-inbred miniature swine.

The lack of transplantable tumors has limited assessment of graft-versus-tumor effects following hematopoietic cell transplantation in clinically relevant large-animal models. We describe the derivation and characterization of porcine tumor cell lines with initial efforts of tumor transplantation using immunocompromised mice and highly inbred sublines of Massachusetts General Hospital major histocompatibility complex (MHC)-inbred miniature swine. Autopsies were performed routinely on swine that died unexpectedly or had suspicion of malignancy based on clinical symptoms or peripheral blood analysis. Tissue samples were obtained for pathology, phenotyped by flow cytometry, and placed in culture. Based on growth, lines were selected for passage into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice and miniature swine. Porcine tumor recipients were preconditioned with total body irradiation from 0 to 500 cGy or with a 30-day course of oral cyclosporine. We identified 19 cases of hematologic tumors. Nine distinct tumor cell lines were established from 8 of these cases, including 3 derived from highly inbred sublines. In vivo tumor growth and serial transfer were observed in immunocompromised mice for one tumor cell line and in miniature swine for 1 of 2 tumor cell lines expanded for this purpose. These results suggest the possibility of developing a transplantable tumor model in this large-animal system.

Diagnostic accuracy of optical coherence tomography and integrated backscatter intravascular ultrasound images for tissue characterization of human coronary plaques.

OBJECTIVES: The purpose of the present study was to validate the diagnostic accuracy of optical coherence tomography (OCT), integrated backscatter intravascular ultrasound (IB-IVUS), and conventional intravascular ultrasound (C-IVUS) for tissue characterization of coronary plaques and to evaluate the advantages and limitations of each of these modalities. BACKGROUND: The diagnostic accuracy of OCT for characterizing tissue types is well established. However, comparisons among OCT, C-IVUS, and IB-IVUS have not been done. METHODS: We examined 128 coronary arterial sites (42 coronary arteries) from 17 cadavers; IVUS and OCT images were acquired on the same slice as histology. Ultrasound signals were obtained using an IVUS system with a 40-MHz catheter and digitized at 1 GHz with 8-bit resolution. The IB values of the ultrasound signals were calculated with a fast Fourier transform. RESULTS: Using histological images as a gold standard, the sensitivity of OCT for characterizing calcification, fibrosis, and lipid pool was 100%, 98%, and 95%, respectively. The specificity of OCT was 100%, 94%, and 98%, respectively (Cohen's kappa = 0.92). The sensitivity of IB-IVUS was 100%, 94%, and 84%, respectively. The specificity of IB-IVUS was 99%, 84%, and 97%, respectively (Cohen's kappa = 0.80). The sensitivity of C-IVUS was 100%, 93%, and 67%, respectively. The specificity of C-IVUS was 99%, 61%, and 95%, respectively (Cohen's kappa = 0.59). CONCLUSIONS: Within the penetration depth of OCT, OCT has a best potential for tissue characterization of coronary plaques. Integrated backscatter IVUS has a better potential for characterizing fibrous lesions and lipid pools than C-IVUS.

Immunological unresponsiveness in chimeric miniature swine following MHC-mismatched spleen transplantation.

BACKGROUND: In rodents, spleen allotransplantation (SpTx) induces tolerance. We investigated the induction of chimerism and donor-specific unresponsiveness following pig SpTx. METHODS: Thirteen pigs underwent splenectomy (day 0); all received a blood transfusion. In 11/13 pigs, SpTx was performed across a MHC class I (n=1) or full (n=10) barrier; two control pigs received no SpTx. All pigs were monitored for chimerism, and anti-donor immune responses, including suppressor assays. Four pigs (two asplenic controls and two with SpTx) underwent delayed donor-matched kidney transplantation without immunosuppression. RESULTS: Six of the 11 spleen grafts were lost from rejection (n=5) or splenic vein thrombosis (n=1), and five remained viable. All 11 SpTx recipients developed multilineage chimerism, but chimerism was rapidly lost if the graft failed. Two control pigs showed <6% blood chimerism for 4 and 11 days only. Pigs with functioning spleen grafts had multilineage chimerism in blood, thymus and bone marrow for at least 2-6 months, without graft-versus-host disease. These pigs developed in vitro donor-specific hyporesponsiveness and suppression. In 2 pigs tolerant to the spleen graft, donor MHC-matched kidney grafts survived for >4 and >7 months in the absence of exogenous immunosuppression; in two asplenic pigs, kidney grafts were rejected on days 4 and 15. CONCLUSIONS: Successful SpTx can result in hematopoietic cell engraftment and in vitro donor-specific unresponsiveness, enabling prolonged survival of subsequent donor-matched kidney grafts without immunosuppression.

Effects of mycophenolate mofetil on cardiac allograft survival and cardiac allograft vasculopathy in miniature swine.

BACKGROUND: Chronic rejection, as manifested by cardiac allograft vasculopathy, remains the leading cause of late graft failure in heart transplant recipients. Despite recent clinical trials, the efficacy of mycophenolate mofetil in preventing human cardiac allograft vasculopathy remains controversial. We investigated whether mycophenolate mofetil would prevent cardiac allograft vasculopathy and prolong cardiac allograft survival in our well-established miniature swine model of heart transplantation. METHODS: Hearts disparate at the major histocompatibility complex class I locus were heterotopically transplanted into miniature swine recipients treated with a 12-day course of mycophenolate mofetil (n = 3) or cyclosporine A (n = 3). Allograft survival, acute rejection, and chronic rejection were monitored in the two groups. RESULTS: Hearts transplanted with 12 days of cyclosporine were rejected between 46 and 61 days, whereas two of the three hearts transplanted with mycophenolate mofetil remained beating beyond 120 days (p = 0.02). At necropsy, there was a 4.9% mean prevalence of cardiac allograft vasculopathy in the mycophenolate mofetil group as compared with 16.6% in the cyclosporine group (p = 0.03). Cardiac allograft rejection and vasculopathy in the cyclosporine-treated group was associated with prominent myocardial interferon-gamma gene expression, a finding absent in two thirds of the mycophenolate mofetil-treated swine. Moreover, the mycophenolate mofetil-treated swine failed to develop IgM or IgG alloantibodies. CONCLUSIONS: A short course of mycophenolate mofetil resulted in a longer allograft survival than a similar course of cyclosporine. Moreover, mycophenolate mofetil reduced the prevalence of cardiac allograft vasculopathy as compared with cyclosporine-treated controls. The salutary effect of mycophenolate mofetil may be related to its ability to decrease interferon-gamma expression in the myocardium and prevent the generation of alloantibodies.

Heart and en-bloc thymus transplantation in miniature swine.

BACKGROUND: Donor-specific tolerance to organ allografts might be induced by cotransplantation of a sufficient amount of vascularized donor thymus. To facilitate donor thymus-induced cardiac allograft tolerance, we have developed a novel technique for heart and en-bloc thymus transplantation in swine. METHODS: Donor heart and en-bloc thymus grafts were prepared by a technique that preserves the entire arterial supply and venous drainage of the right thymic lobe. En-bloc grafts (n = 4) were transplanted heterotopically into the abdomens of major histocompatibility complex-matched miniature swine. Recipients received 12 days of cyclosporine intravenously. Grafts were monitored by palpation, electrocardiographic monitoring, and periodic open biopsy. Engraftment of the donor thymus was demonstrated by measuring the proportion of recipient-type thymocytes in the donor thymus with flow cytometry. RESULTS: All of the heart and en-bloc thymus grafts had normal cardiac contractility and immediate perfusion of the thymus. All en-bloc grafts were accepted for more than 200 days without significant acute cellular rejection or cardiac allograft vasculopathy. Thymic tissue of en-bloc grafts displayed normal architecture and supported thymopoiesis of recipient-type cells. CONCLUSION: We have validated a new technique of donor thymus transplantation that could have utility in human heart transplantation.

Histopathology of spleen allograft rejection in miniature swine.

Spleen transplantation (SpTx) has established donor-specific tolerance in rodents, but not in large animals or humans. We report the histopathology of rejection in an established model of SpTx in major histocompatibility complex (MHC)-defined miniature swine. Of the 17 SpTx, rejection was observed in two grafts transplanted into untreated, MHC-matched, minor antigen-disparate recipients (group 1, n=4), but not in the two that received a 12-day course of cyclosporin A (CyA). Rejection also occurred in five grafts transplanted into fully MHC-disparate recipients (group 2, n=12), one of which was untreated and four of which received some form of immunosuppressive therapy. One recipient of an MHC class-I-mismatched spleen treated with 12 days of CyA did not show rejection. Following biopsy and/or necropsy, fixed allograft tissue sections were treated with multiple stains, immunohistochemical markers and TUNEL assay. Common features of rejection occurred in grafts from both groups, but with varying time courses. Necrosis developed as early as day 8 in group 2 and day 27 in group 1, ranging from focal fibrinoid necrosis of arteriolar walls and sinusoids to diffuse liquefactive necrosis, usually associated with haemorrhage. Other features of rejection included white pulp expansion by atypical cells and decreased staining of basement membranes and reticular fibres. A doubling of the baseline TUNEL index preceded histologically identifiable rejection. This study establishes histologic guidelines for diagnosing and, perhaps, in future studies, predicting acute rejection of splenic allografts transplanted across known histocompatibility barriers in a large-animal model.

Focal and multi-focal plaque macrophage distributions in patients with acute and stable presentations of coronary artery disease.

OBJECTIVES: This study was designed to utilize optical coherence tomography (OCT) images of coronary atherosclerotic plaque macrophages to investigate the relationship between macrophage distributions and clinical syndrome. BACKGROUND: The relative significance of focal macrophage infiltration and generalized coronary inflammation for predicting acute coronary events is a currently a source of considerable controversy in cardiology. Lack of a high-resolution cross-sectional imaging modality has limited macrophage evaluation in vivo. METHODS: Intracoronary OCT imaging was performed at culprit and non-culprit plaques in patients presenting with stable angina pectoris, unstable angina pectoris,and ST-segment elevation myocardial infarction. Macrophage densities were quantified from these images and analyzed with respect to the clinical presentations of the patients under investigation. RESULTS: A significantly greater macrophage density was found in unstable patients, both for fibrous and lipid-rich plaques (p = 0.025 and p = 0.002, respectively). Within each patient, the macrophage densities at culprit and non-culprit lesions correlated significantly (r = 0.66, y = 0.88x + 0.43, p = 0.01). Sites of plaque rupture demonstrated a greater macrophage density than non-ruptured sites (6.95 +/- 1.60%, 5.29 +/- 1.17%; p = 0.002). Surface macrophage infiltration was a stronger predictor of unstable clinical presentation than subsurface infiltration for culprit lesions (p = 0.035) but not for remote lesions (p = 0.80). CONCLUSIONS: Our results demonstrate that increases in both multi-focal and focal macrophage densities are highly correlated with symptom severity. By providing a means of detecting increases in plaque macrophage content before an acute event, this technique may aid in determining prognosis and guiding preventive therapy.

Posttransplant lymphoproliferative disease after allogeneic transplantation of the spleen in miniature swine.

Spleen transplantation (SpTx) was performed in miniature swine across full major histocompatibility complex barriers to study the tolerogenic effect of the spleen. This study describes the development of posttransplant lymphoproliferative disease (PTLD) after allogeneic SpTx. Recipient pigs underwent whole body irradiation (100 cGy), thymic irradiation (700 cGy), and native splenectomy (day 0), and received a 45-day course of intravenous cyclosporine (trough level 400-800 ng/ml). After SpTx, two of seven pigs developed PTLD (1 donor-type, 1 host-type). These two pigs had greater T cell depletion and higher trough levels of cyclosporine. Early changes that occurred prior to the development of clinical features of PTLD were increased porcine lymphotropic herpesvirus-1 viral loads in blood and tissues, and increased numbers of leukocytes, B cells, and total serum IgM. PTLD can occur after allogeneic SpTx in swine. This model may be useful in studies of the pathogenesis of PTLD.

Coronary in-stent restenosis following beta brachytherapy: a histopathological examination.

Two cases of in-stent restenosis of a coronary artery bypass vein graft following beta (beta) brachytheraphy are presented. Previously unreported histopathology of directed atherectomy specimens of such restenotic lesions and a discussion of their proposed significance form the basis of this report.

Histomorphometric comparison of cardiac allograft vasculopathy in miniature swine.

BACKGROUND: Whether the pathologic characteristics of vascular lesions manifested in recipients with cardiac allograft vasculopathy (CAV) differ with the severity of the histocompatibility barrier crossed at transplantation or with the type or amount of immunosuppression used to prolong graft survival is unclear. We used miniature swine to determine whether a wide variance in heart transplantation protocols, both in histoincompatibility and immunosuppression, affects the histomorphometry of CAV. METHODS: We compared explanted hearts from major histocompatibility complex Class I-disparate recipients who were treated for 12 days with cyclosporine (Group 1) with minor-antigen-disparate hearts transplanted into mixed chimeric recipients previously engrafted with donor hematopoietic progenitor cells (Group 2). We analyzed coronary intimal lesions using computerized morphometry, immunohistochemistry, and TUNEL assay. Myocardial cytokine-gene expression was determined using RNAse protection assays and reverse-transcriptase polymerase chain reaction. RESULTS: The prevalence of CAV in Group 2 was significantly less than that observed in Group 1, but the severity of the lesions in both groups was similar. The vascular lesions that developed in both groups demonstrated the presence of alpha-smooth-muscle-actin-positive spindle cells expanding the intima, with few inflammatory cells. We noted an absence of proliferating cell nuclear antigen activity and TUNEL-positive cells in both groups. We observed prominent myocardial interferon-gamma gene expression only in Group 1. CONCLUSION: Despite differences in myocardial interferon-gamma gene expression, the histology and severity of the vascular lesions in CAV did not vary significantly with different histoincompatibilities or treatment protocols. These results suggest that the origin of CAV cannot be determined by histology alone.

Induction of tolerance to heart transplants by simultaneous cotransplantation of donor kidneys may depend on a radiation-sensitive renal-cell population.

BACKGROUND: To determine the mechanism by which cotransplantation of a donor kidney and heart allograft induces tolerance to both organs in miniature swine, we examined the renal elements responsible for tolerance induction. METHODS: Recipients received 12 days of cyclosporine, and transplants were performed across a major histocompatibility complex (MHC) class I mismatch. Group 1 animals received heart transplants (n=5); group 2 animals received heart and kidney allografts with no other manipulation (n=4); group 3 animals received heart transplants and donor-specific renal parenchymal cells (n=4); group 4 animals received heart and kidney allografts from lethally irradiated donors (n=7); group 5 animals received irradiated hearts and nonirradiated kidneys (n=2); group 6 animals received nonirradiated hearts and peripheral blood leukocytes from swine MHC matched to recipients and becoming tolerant to donor antigen (n=2); group 7 animals received nonirradiated hearts and donor-specific peripheral blood monocyte cells (PBMC) (n=2). RESULTS: Animals in group 1 developed vasculopathy and fulminant rejection by day 55. Animals in group 2 never developed vascular lesions. Parenchymal kidney cell infusion (group 3) did not prolong cardiac survival. Animals in group 4 developed arteriopathy by postoperative day (POD) 28. Group 5 recipients accepted allografts without vascular lesions. Adoptive transfer of leukocytes from tolerant swine (group 6) prolonged cardiac graft survival as much as 123 days, whereas donor PBMC infusion (group 7) did not affect cardiac survival or development of arteriopathy. CONCLUSIONS: Radiosensitive elements in kidney allograft may be responsible for tolerance induction and prevention of chronic vascular lesions in recipients of simultaneous heart and kidney allografts.

Quantification of macrophage content in atherosclerotic plaques by optical coherence tomography.

BACKGROUND: Macrophage degradation of fibrous cap matrix is an important contributor to atherosclerotic plaque instability. An imaging technology capable of identifying macrophages in patients could provide valuable information for assessing plaque vulnerability. Optical coherence tomography (OCT) is a new intravascular imaging modality that allows cross-sectional imaging of tissue with a resolution of approximately 10 micro m. The aim of this study was to investigate the use of OCT for identifying macrophages in fibrous caps. METHODS AND RESULTS: OCT images of 26 lipid-rich atherosclerotic arterial segments obtained at autopsy were correlated with histology. Cap macrophage density was quantified morphometrically by immunoperoxidase staining with CD68 and smooth muscle actin and compared with the standard deviation of the OCT signal intensity at corresponding locations. There was a high degree of positive correlation between OCT and histological measurements of fibrous cap macrophage density (r=0.84, P<0.0001) and a negative correlation between OCT and histological measurements of smooth muscle actin density (r=-0.56, P<0.005). A range of OCT signal standard deviation thresholds (6.15% to 6.35%) yielded 100% sensitivity and specificity for identifying caps containing >10% CD68 staining. CONCLUSIONS: The high contrast and resolution of OCT enables the quantification of macrophages within fibrous caps. The unique capabilities of OCT for fibrous cap characterization suggest that this technology may be well suited for identifying vulnerable plaques in patients.

Characterization of human atherosclerosis by optical coherence tomography.

BACKGROUND: High-resolution visualization of atherosclerotic plaque morphology may be essential for identifying coronary plaques that cause acute coronary events. Optical coherence tomography (OCT) is an intravascular imaging modality capable of providing cross-sectional images of tissue with a resolution of 10 micro m. To date, OCT imaging has not been investigated in sufficient detail to assess its accuracy for characterizing atherosclerotic plaques. The aim of this study was to establish objective OCT image criteria for atherosclerotic plaque characterization in vitro. METHODS AND RESULTS: OCT images of 357 (diseased) atherosclerotic arterial segments obtained at autopsy were correlated with histology. OCT image criteria for 3 types of plaque were formulated by analysis of a subset (n=50) of arterial segments. OCT images of fibrous plaques were characterized by homogeneous, signal-rich regions; fibrocalcific plaques by well-delineated, signal-poor regions with sharp borders; and lipid-rich plaques by signal-poor regions with diffuse borders. Independent validation of these criteria by 2 OCT readers for the remaining segments (n=307) demonstrated a sensitivity and specificity ranging from 71% to 79% and 97% to 98% for fibrous plaques, 95% to 96% and 97% for fibrocalcific plaques, and 90% to 94% and 90% to 92% for lipid-rich plaques, respectively (overall agreement, kappa=0.83 to 0.84). The interobserver and intraobserver reliabilities of OCT assessment were high (kappa values of 0.88 and 0.91, respectively). CONCLUSIONS: Objective OCT criteria are highly sensitive and specific for characterizing different types of atherosclerotic plaques. These results represent an important step in validating this new intravascular imaging modality and will provide a basis for the interpretation of intracoronary OCT images obtained from patients.

Transmyocardial coil implants: a novel approach to transmyocardial revascularization.

BACKGROUND: Transmyocardial laser revascularization (TMLR) has potential benefit for patients with end-stage coronary artery disease and intractable angina not amenable to conventional revascularization techniques. Neovascularization has been proposed to occur around the laser channels. Our aim was to determine the feasibility of a novel nonlaser myocardial revascularization technique and its effect on angiogenesis in a nonischemic porcine model. METHODS: In the first phase, six transmyocardial stainless steel coil implants (TMI) were deployed to the lateral wall of the left ventricle in each of 6 pigs. The animals were sacrificed at 8 and 12 weeks, with a single animal dying prematurely at 4 weeks, and the myocardium was assessed for new vessel growth. In the second phase, 8 implants were deployed in each of 12 pigs with regular fluoroscopic follow-up until sacrifice at 2 weeks to assess implant stability. RESULTS: The deployment procedure was safe and feasible with no complications evident. A significant increase in new vessels at implant sites with 5.43 +/- 3.67, 4.97 +/- 2.44, and 3.57 +/- 2.29 seen per high power field at 12, 8, and 4 weeks, respectively, compared to 1.00 +/- 1.06 (p < 0.0001) in control myocardium. There was no evidence of implant migration in Phase 2. CONCLUSIONS: TMIs can feasibly be deployed in the nonischemic pig model with a high success rate. The presence of angiogenesis at the implant site and the maintenance of this reaction for 3 months implies that TMI may offer an alternative to TMLR while providing a platform for delivery of angiogenic factors.