Development and evaluation of a swine model to assess the preclinical safety of mechanical heart valves.

BACKGROUND AND AIM OF THE STUDY: The current standard of in vitro and in vivo preclinical heart valve testing has recently been questioned because of its failure to reveal the thrombogenic potential of the Medtronic Parallel prosthetic valve. The aim of this study was to develop a swine model for the in vivo preclinical evaluation of mechanical heart valves, and to assess the ability of this model to identify mechanical heart valve design features that result in valve-related thrombosis. METHODS: Twenty-two swine underwent mitral valve replacement (MVR) using three different bileaflet mechanical valve designs (St Jude Medical, CarboMedics, Medtronic Parallel). Each animal was placed in an anticoagulation protocol (group I, INR 3.0-3.5; group II, INR 2.0-2.5; group III, no anticoagulation) and followed for up to 20 weeks. Terminal studies were performed on all animals surviving for more than 30 days. RESULTS: Twenty-one animals survived the immediate postoperative period. Four of six group I animals died from hemorrhagic (large wound hematoma; hemopericardium) complications early in the study. In the two long-term (61 and 89 days) survivors, INRs of 3.0 to 3.5 were never achieved (61-day survivor, mean INR 2.0 +/- 1.03; range: 0.8-5.4; 89-day survivor, mean INR 1.92 +/- 1.34; range: 1.0-7.9). Pathological analysis of explants from group I survivors revealed minimally obstructive fibrous sheathing on the inflow orifice without restriction of bileaflet motion (61 and 89 days), and two large perivalvular defects (61 days). Six of seven group II animals died from early hemorrhagic complications (hemopericardium) (mean INR 2.32 +/- 1.84; range: 0.8-8.2). Vegetations resulting in obstruction of both sides of the valve orifice and restriction of bileaflet motion were observed in a group II survivor (mean INR 2.33 +/- 1.58; range: 0.9-7.0). Group III animals (n = 8) survived for a mean of 106 +/- 60 days (range: 1-177 days). In group III, fibrous sheathing was present on all explanted valves and organized thrombi in six valves; orifice obstruction (seven valves) and restriction of bileaflet motion (three valves) were also observed. CONCLUSION: The use of MVR in swine as a preclinical model to evaluate the safety and performance of mechanical heart valves is limited by: (i) difficulty in maintaining safe levels of anticoagulation with warfarin, resulting in a high incidence of hemorrhagic complications; (ii) marked fibrous sheath formation and associated thrombosis; and (iii) an increased incidence of perivalvular defects, believed to result from normal somatic growth occurring in young swine.

A recombinant soluble chimeric complement inhibitor composed of human CD46 and CD55 reduces acute cardiac tissue injury in models of pig-to-human heart transplantation.

BACKGROUND: Inasmuch as complement plays a critical role in many pathological processes and in xenograft rejection, efficient complement inhibitors are of great interest. Because the membrane-associated complement inhibitors are very effective, recombinant soluble molecules have been generated. METHODS: We tested the efficacy of complement activation blocker-2 (CAB-2), a recombinant soluble chimeric protein derived from human decay accelerating factor (DAF, CD55) and membrane cofactor protein (MCP, CD46), in two models of pig-to-human xenotransplantation in which tissue injury is complement mediated. The in vitro model consisted of porcine aortic endothelial cells and human serum, and the ex vivo model consisted of a porcine heart perfused with human blood. RESULTS: In vitro, addition of CAB-2 to serum inhibited cytotoxicity and the deposition of C4b and iC3b on the endothelial cells. Ex vivo, addition of CAB-2 to human blood prolonged organ survival from 17.3 +/- 6.4 min in controls to 108 +/- 55.6 min with 910 nM (100 microg/ml) CAB-2 and 219.8 +/- 62.7 min with 1820 nM (200 microg/ml) CAB-2. CAB-2 also retarded the onset of increased coronary vascular resistance. The complement activity of the perfusate was reduced by CAB-2, as was the generation of C3a and SC5b-9. The myocardial tissues had similar deposition of IgG, IgM, and Clq; however, CAB-2 reduced the deposition of C3, C4, and C9. Hearts surviving >240 min demonstrated trace to no deposition of C9 and normal histologic architecture. CONCLUSION: These results indicate that CAB-2 can function as an inhibitor of complement activation and markedly reduce tissue injury in models of pig-to-human xenotransplantation and thus may represent a useful therapeutic agent for xenotransplantation and other complement-mediated conditions.

Transgenic swine lungs expressing human CD59 are protected from injury in a pig-to-human model of xenotransplantation.

BACKGROUND: Pulmonary xenotransplantation is currently limited by hyperacute rejection mediated in part by xenoreactive natural antibody and complement. Transgenic swine organs that express the human complement regulatory protein CD59 have demonstrated improved survival in models of pig-to-primate xenotransplantation. OBJECTIVE: The purpose of this study was to evaluate transgenic swine lungs that express the human complement regulatory protein CD59 in a model of pig-to-human xenotransplantation. METHODS: Transgenic swine lungs (n = 5, experimental group) and outbred swine lungs (n = 6, control group) were perfused with fresh, whole human blood through a centrifugal pump on an ex vivo circuit. Functional data were collected throughout perfusion. Immunoglobulin and complement studies were performed on perfusate samples, and both histologic and immunofluorescent analyses were performed on tissue sections. RESULTS: Mean lung survival for the experimental group was increased when compared with controls, 240 +/- 0 minutes versus 35.3 +/- 14.5 minutes, respectively, with a P value of less than.01. A decreased rise in pulmonary vascular resistance at 15 minutes was observed in the experimental group (343 +/- 87 mm Hg. L(-1). min(-1), in contrast to the control group (1579 +/- 722 mm Hg. L(-1). min(-1); P <.01). Pulmonary compliance at 15 minutes was improved for the experimental group versus control group (9.31 +/- 1.41 mL. cm(-2) H(2)O and 4.11 +/- 2.84 mL. cm(-2) H(2)O, respectively; P <.01). SC5b-9 generation in the plasma perfusate was delayed for the experimental group versus the control group. Immunofluorescent examination of tissue sections demonstrated equivalent deposition of immunoglobulin G, immunoglobulin M, C1q, and C3 in both groups, with reduced deposition of C9 in the experimental group. CONCLUSIONS: Transgenic swine pulmonary xenografts that express the human complement regulatory protein CD59 demonstrated improved function and survival in an ex vivo model of pig-to-human xenotransplantation.

Pulmonary thromboembolectomy of donor lungs prior to lung transplantation.

Successful bilateral single-lung transplantation was performed after pulmonary thromboembolectomy of the donor lungs. The donor lungs were not thought to contain large amounts of pulmonary thromboemboli because they satisfied all the donor selection criteria. This case reinforces the need of not only meticulous inspection of the donor lungs prior to implantation but also the productive use of available donor organs.

Adjuvant treatment of refractory lung transplant rejection with extracorporeal photopheresis.

BACKGROUND: Extracorporeal photopheresis is an immunomodulatory technique in which a patient's leukocytes are exposed to ultraviolet-A light after pretreatment with 8-methoxypsoralen (methoxsalen). There have been few reports describing the use of extracorporeal photopheresis in lung transplant recipients. METHODS: We reviewed our experience using extracorporeal photopheresis in 8 lung transplant recipients since 1992. All 8 patients had progressively decreasing graft function and 7 were in bronchiolitis obliterans syndrome grade 3 before the initiation of photopheresis. One patient had undergone a second transplant operation for obliterative bronchiolitis. Two patients had a pretransplantation diagnosis of chronic obstructive pulmonary disease, 1 alpha1-antitrypsin deficiency, 1 cystic fibrosis, 1 bronchiectasis, 1 idiopathic pulmonary fibrosis, and 2 primary pulmonary hypertension. Before refractory rejection developed, all patients had been treated with 3-drug immunosuppression and anti-T-cell therapy. The median time from transplantation to the start of extracorporeal photopheresis was 16.5 months and the median number of treatments was 6. RESULTS: The condition of 5 of 8 patients subjectively improved after extracorporeal photopheresis therapy. In these 5 patients photopheresis was associated with stabilization of the forced expiratory volume in 1 second. In 2 patients there was histologic reversal of rejection after photopheresis. With a median follow-up of 36 months, 7 patients are alive and well. Three patients required retransplantation at a median of 21 months after completion of the treatments. Four patients have remained in stable condition after photopheresis. There were no complications related to extracorporeal photopheresis. CONCLUSION: We believe that this treatment is a safe option for patients with refractory lung allograft rejection when increased immunosuppression is contraindicated or ineffective.

Beat-to-beat modulation of heart rate is coupled to coronary perfusion pressure in the isolated heart.

A goal of clinicians caring for heart transplant recipients has been to use heart rate variability as a noninvasive means of diagnosing graft rejection. The determinants of beat-to-beat variability in the surgically denervated heart have yet to be elucidated. We used an isolated, blood buffer-perfused porcine heart preparation to quantitatively assess the relationship between coronary perfusion and sinus node automaticity. Hearts (n = 9) were suspended in a Langendorff preparation, and heart rate (HR) fluctuations were quantified while perfusion pressure was modulated between 70/50, 80/60, 90/70, and 100/80 mmHg at 0.067 Hz. In 32 of 32 recordings, the cross spectrum of perfusion pressure vs. HR showed the largest peak centered at 0.067 Hz. In eight of nine experiments during nonpulsatile perfusion, HR accelerated as perfusion pressure was increased from 40 to 110 mmHg (mean increase 24.2 +/- 3.0 beats/min). HR increased 0.34 beats/min per mmHg increase in perfusion pressure (least squares linear regression y = -25.8 mmHg + 0.34x; r = 0.88, P < 0.0001). Administration of low- and high-dose nitroglycerin (Ntg) resulted in a modest increase in flow but produced a significant decrease in HR and blunted the response of HR to changes in perfusion pressure (HR increase 0.26 beats. min-1. mmHg-1, r = 0.87, P < 0.0001 after low-dose Ntg; 0.25 beats. min-1. mmHg-1, r = 0.78, P < 0.0001 after high-dose Ntg). These experiments suggest that sinus node discharge in the isolated perfused heart is mechanically coupled to perfusion pressure on a beat-to-beat basis.

Chronic evaluation of orthotopically implanted bileaflet mechanical aortic valves in adult domestic sheep.

This study was intended to develop a technically feasible and reproducible model for chronic hemodynamic and mechanical evaluation of orthotopically implanted bileaflet mechanical aortic valves in adult domestic sheep. Three adult sheep (mean age 22 weeks, mean weight 76 kg) underwent aortic valve replacement using 19-mm bileaflet aortic valves. Standard cardiopulmonary bypass techniques were followed, including mild hemodilution, systemic hypothermia, and cardioplegic arrest. After performing a left fourth intercostal thoracotomy, the valves were placed using interrupted 3-0 Ticron (Davis + Geck) inverted mattress sutures through a transverse aortotomy. The average cardiopulmonary bypass time was 58+/-1 min. No chronic anticoagulation was used. There were no surgical complications. All three animals (100%) remained clinically well until elective sacrifice after postoperative day 150. The average cardiac output for the animals at sacrifice was 3.8+/-1.0 L/min. The mean aortic ejection velocity was 304.7+/-47.3 cm/s and the mean pressure gradient was 24.6+/-6.7 mm Hg. There was no clinically significant thrombus formation or paravalvular leaks. Thus, we have demonstrated that it is technically feasible to orthotopically implant mechanical aortic valves in sheep. There are several features that contribute to the success of this model, including use of a transverse aortotomy, adequate de-airing, and the use of mild hemodilution during bypass. We believe that this model is reproducible and can be used to study other valve designs. In addition, this model allows for site-specific preclinical assessment of new or modified mechanical heart valves.

Primary esophageal lymphoma: a diagnostic challenge.

A 56-year-old man with primary esophageal lymphoma is presented. Diagnosis of this disease can present a challenge. Clinical characteristics, treatment principles, and a detailed discussion of diagnosis are presented. When primary esophageal lymphoma is diagnosed, combination chemotherapy and radiotherapy afford a significant chance of long-term survival.

Long-term evaluation of orthotopically implanted stentless bioprosthetic aortic valves in juvenile sheep.

The aim of this study was to develop a technically feasible and reproducible model for chronic evaluation of stentless bioprosthetic aortic valves implanted orthotopically using juvenile domestic sheep. This report summarizes the results of a study conducted to assess orthotopically placed 19-mm stentless aortic bioprosthetic valves. Twenty-seven juvenile sheep underwent aortic valve replacement. Standard cardiopulmonary bypass techniques were followed. The average cardiopulmonary bypass time was 73 min. No chronic anticoagulation was used. There were two deaths (7%) due to surgical complications. In the remaining 25 experiments, 11 animals (41%) died prior to the scheduled sacrifice on postoperative day 150. One early death occurred due to coccidiomycosis infection, one due to technical error, one due to pulmonary embolus, four due to prosthetic annular size disproportion, and four due to thrombi. The remaining 14 animals (52%) underwent left and right heart catheterization, angiography, echocardiography, and sacrifice after postoperative day 150. The average weight of the sheep at elective sacrifice was 60 kg (mean weight gain 12.5 kg). The average cardiac output for the sacrificed animals was 5.1 L/min. The mean velocity of blood across the aortic valve for the sacrificed animals was 317 cm/s and the mean pressure gradient was 26.2 mm Hg. Two features suggest that this model may have broad application. First, we have demonstrated that it is technically feasible to evaluate orthotopically placed stentless bioprosthetic aortic valves in growing sheep. Second, the aortic root size of the juvenile sheep allows for implantation and evaluation of a human size aortic valve (19 mm). We believe that this model is reproducible and can be used to study stentless valve designs.

Management of recurrent ventricular tachycardia with ventricular assist device placement.

Life-threatening, recurrent ventricular tachycardia developed in a 54-year-old heart transplant candidate with ischemic cardiomyopathy. The episodes of ventricular tachycardia were refractory to aggressive medical management and implantable cardiac defibrillator placement. A Heartmate left ventricular assist device was implanted, in combination with isolated right coronary artery bypass grafting, which abolished any further episode of ventricular tachycardia. The patient successfully underwent cardiac transplantation 79 days later.

Detection of occult micrometastases in non-small cell lung carcinoma by reverse transcriptase-polymerase chain reaction.

BACKGROUND: The 5-year survival rate following surgical resection of Stage I or Stage II non-small cell lung carcinoma (NSCLC) is 30% to 50%, probably because of undetected occult micrometastases (OMs) at the time of surgery. Other investigators have detected OMs in bone marrow and histologically negative lymph nodes from patients with NSCLC using immunohistochemical staining to cytokeratins and cell surface glycoproteins. STUDY OBJECTIVE: To develop and evaluate an assay based on the reverse transcriptase-polymerase chain reaction (RT-PCR) for the detection of OMs in NSCLC. PATIENTS: Twenty-eight patients with benign or malignant thoracic pathology. Samples of primary tumors and lymph nodes were collected at the time of surgical resection or mediastinoscopic lymph-node biopsy. RESULTS: Using RT-PCR to detect messenger RNA (mRNA) transcripts for MUC1 (a cell surface glycoprotein present in lung tissue but absent from normal lymph nodes), OMs were identified in 33 of 88 lymph nodes determined to be free of tumor by hematoxylin and eosin staining. Eleven of 11 control mediastinal lymph nodes from patients without malignancy failed to express detectable MUC1 transcripts. Dilutional experiments demonstrate that the assay can detect one MUC1-positive NSCLC cell in 1x10(7) MUC1-negative cells. A comparison of our RT-PCR assay to immunohistochemistry specific for the MUC1 glycoprotein suggests that RT-PCR may be more sensitive than immunohistochemistry for the detection of NSCLC OMs. CONCLUSIONS: This study demonstrates that RT-PCR for MUC1 mRNA can detect the presence of MUC1 mRNA in histologically negative lymph nodes from patients with NSCLC. The prognostic significance of these findings is currently unknown.

Surgical therapy for pulmonary aspergillosis in immunocompromised patients.

BACKGROUND: Medical management for invasive pulmonary aspergillosis (IPA) is often unsatisfactory. Antifungal therapy may be unable to eradicate IPA in the immunocompromised or neutropenic patient. METHODS: We retrospectively reviewed the surgical management of IPA in 13 immunocompromised patients at our institution. Twelve patients underwent perioperative bone marrow transplantation (4 autologous, 8 allogenic). All 13 patients received antifungal therapy. Eleven patients were neutropenic at the time of operation. RESULTS: The mean interval from diagnosis of aspergillosis to operation was 42 days (range, 3 to 135 days). Eighteen operations were performed on the 13 patients. Seven patients had resections from multiple pulmonary sites, whereas 6 had a single lesion resected. The average lesion resected was 3.7 cm in greatest diameter (range, 1 to 9 cm). After a mean follow-up of 21 months (range, 0 to 9 years), 3 patients (23%) are alive with no evidence of aspergillosis, 6 patients (46%) died without evidence of aspergillosis, and 4 patients (31%) died secondary to aspergillus infection. All 4 patients who died of aspergillus infection received an allogenic bone marrow transplantation. Two patients with direct extrapulmonic extension of IPA at time of operation died of recurrent aspergillus infections. Three of 4 patients who died of aspergillus infection had an absolute neutrophil count less than 1,300 cells/microL at time of operation. The mean absolute neutrophil count of the patients who cleared the aspergillus infection was 5,538 cells/microL. The mean survival of allogenic bone marrow transplant recipients was 5.2 months, and for recipients of autografts was 51.4 months. CONCLUSIONS: In this series, surgical resection of IPA cleared the aspergillus infection in 69% of the patients. Neutropenia, extrapulmonic extension of IPA, and allogenic bone marrow transplantation may predict a worse prognosis. Surgical resection of IPA in immunocompromised patients is an effective form of therapy in a properly selected patient population.

Current state of in vivo preclinical heart valve evaluation.

The use of animals to predict prosthetic valve performance in humans has now been in operation for over 25 years. Studies have focused on improvements in structural integrity, anti-thrombogenicity and anticalcification, and provide extensive in vivo analysis and validation of a valve before its clinical evaluation. Many animal models have been developed for such investigations, including calves, goats, pigs, baboons, dogs and adult sheep. Recent models used to assess prosthetic mitral valves have involved site-specific testing in several species; the present study represents the largest series of orthotopically implanted stentless bioprosthetic aortic valves and the first to utilize a juvenile sheep model for the aortic position.

Donor-derived antibodies and hemolysis after ABO-compatible but nonidentical heart-lung and lung transplantation.

BACKGROUND: Organ donors and transplant recipients are routinely tested for ABO compatibility. ABO-identical organs are preferred, but occasionally the use of an ABO-compatible but nonidentical donor is clinically warranted. In heart-lung transplantation, the incidence of hemolysis from donor-derived anti-ABO antibodies is as high as 70%. The incidence of hemolysis for lung-only transplantation is not known. Our current posttransplantation transfusion policy for ABO-compatible but nonidentical lung-only transplant recipients is, when indicated, to use donor ABO group red blood cells. METHODS: To evaluate the efficacy of our transfusion policy, we reviewed our experience from 1986-96. One heart-lung transplant, four single lung transplant, and three bilateral single lung transplant recipients received ABO-compatible but nonidentical organs. RESULTS: The heart-lung transplant recipient developed a positive direct antiglobulin test (DAT), with anti-A eluted, and severe hemolysis on postoperative day 8 requiring plasma and whole blood exchange. Four of six lung-only transplant patients tested developed a positive DAT with anti-A eluted. Two early lung-only patients, who did not receive donor ABO group red blood cells, demonstrated clinical and laboratory evidence of hemolysis. Three bilateral lung transplant recipients were followed prospectively. The first patient had a negative DAT. The next two patients developed positive DATs on postoperative day 8 and 10, respectively. No evidence of hemolysis was detected in any of these cases. CONCLUSIONS: These results confirm that donor-derived anti-ABO antibodies develop with lung-only transplants. Our current transfusion policy is justified for both heart-lung and lung recipients of ABO-compatible but nonidentical organs. A high index of suspicion for donor-derived antibody causing hemolysis and communication with blood bank personnel are mandatory in this setting.

Coronary artery bypass after single lung transplant: a case report.

Chronic obstructive pulmonary disease (COPD) is the most common indication for adult single lung transplantation. These patients commonly have one or more risk factors for coronary artery disease. Traditionally previous lung transplantation has been considered a contraindication to coronary artery bypass grafting (CABG). This report describes a case of CABG 3 yr after single lung transplantation and briefly discusses the risks of cardiac surgery in lung transplant patients.

Risk of left ventricular assist device as a bridge to heart transplant following postinfarction ventricular septal rupture.

Heart transplantation is an effective treatment for end-stage heart failure. However, due to the persistent shortage of donor hearts, many patients die awaiting a transplant. Implantable left ventricular assist devices are now available as a reliable bridge to cardiac transplantation. This report presents a patient with terminal heart failure as a result of a post-myocardial infarction ventricular septal rupture (VSR), who underwent a successful placement of the HeartMate left ventricular assist device (LVAD) and velour patch closure of an apical VSR. Despite this therapy, the patient expired after developing a second VSR, which created a high-flow right-to-left shunt and caused hypoxic irreversible brain injury. We suggest that use of a left ventricular assist device as a bridge to transplantation be approached with extreme caution in a patient with a postinfarction ventricular septal rupture.

Human lung carcinomas express Fas ligand.

To reach a clinically detectable size, neoplasms must be able to suppress or evade a host immune response. Activated T cells may enter apoptosis in the presence of Fas ligand (FasL) (1), and tissue expression of FasL has been shown to contribute to immune privilege in the eye and testis (2, 3). We have demonstrated that all human lung carcinoma cell lines tested (16 of 16) express a Mr 38,000 protein consistent with FasL by immunoblotting, whereas the majority of resected tumors (23 of 28) show positive staining for FasL by immunohistochemistry. DNA sequencing of reverse transcription-PCR products from lung cancer cells and resected lung tumors confirms the presence of human FasL mRNA in these neoplastic tissues. Furthermore, lung carcinoma cells are capable of killing a Fas-sensitive human T cell line (Jurkat) in coculture experiments; this killing was inhibited by a recombinant form of the soluble portion of the Fas receptor (FasFc). FasL expression by neoplastic cells represents a potential mechanism for peripheral deletion of tumor-reactive T-cell clones.

The role of electrolyte in lesion size using an irrigated radiofrequency electrode.

Multiple attempts have been made to eliminate atrial fibrillation by performing the surgical maze procedure with radiofrequency energy. Currently, this is limited because of the risk of atrial perforation and the lack of transmural penetration. Saline irrigation has been investigated as a method of radiofrequency cautery tip cooling to prevent rapid temperature and impedance rises, which have been shown to lead to perforation or decreased radiofrequency penetration after eschar formation. There are few data on the influence that different types of electrolyte irrigation solutions have on lesion depth. Using a novel hollow cautery pen, we infused either an electrolyte solution (0.9%, 3%, 14.6%, or 23.4% sodium chloride), a nonelectrolyte solution (1.5% glycine), or no irrigation to produce 819 lesions on 14 left ventricles in swine using radiofrequency energy (450+/-10 kHz) applied at two output settings (20 and 75 watts). The nonelectrolyte solution increased lesion depth compared with no infusion at 20 watts but produced shallower lesion depths compared with electrolyte solutions at 75 watts. Compared with the other electrolyte solutions, the 0.9% sodium chloride solution produced the deepest lesions (3.34+/-0.06 mm) at 75 watts (p < 0.001). As the concentration of electrolyte increased, lesion depth decreased unless generator output increased. Formation of eschar and tissue destruction was seen in the noninfusion and nonelectrolyte groups but not in the electrolyte group. A conductive media coupled with radiofrequency energy allowed for greater lesion depth than irrigated cooling with a nonelectrolyte solution or no irrigation. There was an inverse relationship between electrolyte concentration and lesion depth. We conclude that the concentration of electrolyte irrigant is an important consideration when choosing a solution to improve transmural penetration and decrease the risk of tissue destruction from radiofrequency energy.

Coronary sinus injury during retrograde cardioplegia: a report of three cases.

Coronary sinus injuries related to the use of retrograde cardioplegia are uncommon. In most cases injuries are encountered with overinflation of the coronary sinus catheter balloon or traumatic catheter insertion. This article describes three cases of coronary sinus injury during retrograde cardioplegia administration in patients with ventricular hypertrophy, while the heart was manually retracted to expose the posterior myocardium. We propose that the risk of coronary sinus injury during retrograde cardioplegia, in patients with left ventricular hypertrophy, can be minimized by avoiding excessive retraction of the heart, deflation of the retrograde catheter during retraction, and the use of a left ventricular vent.