Mechanisms of Cardiac Nerve Sprouting After Myocardial Infarction in Dogs

Cardiac nerve sprouting and sympathetic hyperinnervation after myocardial infarction (MI) both contribute to arrhythmogenesis and sudden death. However, the mechanisms responsible for nerve sprouting after MI are unclear. The expression of nerve growth factor (NGF), growth associated protein 43 (GAP43), and other nerve markers were studied at the infarcted site, the noninfarcted left ventricle free wall (LVFW), and the left stellate ganglion (LSG) at several time points (30 minutes to 1 month) after MI. Transcardiac (difference between coronary sinus and aorta) NGF levels were also assayed. Acute MI resulted in the immediate elevation of the transcardiac NGF concentration within 3.5 hours after MI, followed by the upregulation of cardiac NGF and GAP43 expression, which was earlier and more pronounced at the infarcted site than the noninfarcted LVFW. However, cardiac nerve sprouting and sympathetic hyperinnervation were more pronounced in the noninfarcted than the infarcted LVFW site and peaked at 1 week after MI. The NGF and GAP43 protein levels significantly increased in the LSG from 3 days ( P <0.01 for all) after MI, without a concomitant increase in mRNA. There was persistent elevation of NGF levels in aorta and coronary sinus within 1 month after MI. We conclude MI results in immediate local NGF release, followed by upregulation of NGF and GAP43 expression at the infarcted site. NGF and GAP43 are transported retrogradely to LSG, which triggers nerve sprouting at the noninfarcted LVFW. A rapid and persistent upregulation of NGF and GAP43 expression at the infarcted site underlies the mechanisms of cardiac nerve sprouting after MI.

Scar formation after ischemic myocardial injury in MRL mice

INTRODUCTION

MRL is a strain of mice with the unusual ability to recover from injuries without forming scar tissue. It was recently reported that the MRL mice can recover with little or no scar formation following a cryogenically induced myocardial infarction of the right ventricle. These findings suggest that scarless recovery from myocardial injury is possible in mammalian ventricles. If applicable to humans, these results could have significant clinical implications in the management of patients with myocardial infarction. However, myocardial infarction in human patients usually results from ischemic injury instead of cryoinjury. Myocardial infarction usually occurs in the left ventricle.

METHODS

We performed a prospective study creating left ventricular myocardial infarction in 32 MRL mice using coronary ligation.

RESULTS

Among them, 21 mice survived surgery and had myocardial infarction documented by delayed contrast-enhanced magnetic resonance imaging (MRI) 35+/-10 days after surgery. All 21 mice had evidence of myocardial infarction in follow-up MRI performed 116+/-21 days after surgery. The infarct size was 27+/-12% of the area of visualized myocardium during the first MRI study and was 29+/-11% during the second MRI study (P=NS). Large myocardial infarction with aneurysm formation was documented by histological examinations in all 21 mice. The ventricular aneurysm showed transmural infarction with replacement fibrosis and mummified necrotic myocardium surrounded by collagenous scar tissue. Occasional surviving myocytes are present within the aneurysm.

CONCLUSION

Ischemic myocardial injury in MRL mice is not followed by scarless recovery.

Electrical current-induced atrial and pulmonary vein action potential duration shortening and repetitive activity

The influence of threshold electrical currents (EC) during regular drive on pulmonary vein (PV) and atrial myocardial cell action potential (AP) duration (APD) is unknown. We determined the effects of EC on cellular APD of PV, atria, and ventricles in isolated perfused and superfused male rat hearts (Fisher-344 strain, 3–4 mo old) at 37°C ( n = 14). We determined APD changes caused by subthreshold and threshold EC synchronized with a distant pacing electrode and delivered nearby cells from which transmembrane APs were recorded with a glass microelectrode. Progressive APD shortening ( P < 0.001) and membrane hyperpolarization ( P < 0.05) developed over a 20-s interval in the PV and atrial cells when the EC was delivered at <2 mm but not at >4 mm from the microelectrode. No such effects were seen in ventricular muscle cells. APD fully recovered 25 s after the cessation of EC application. Premature stimuli applied during EC-induced shortening of the APD caused rapid repetitive PV and atrial activity lasting two to five beats. Atropine (2 μM, n = 10) prevented, whereas propranolol (2 μM, n = 5) had no effect, on EC-induced APD shortening or repetitive activity. We conclude that EC shortens the APD and hyperpolarizes the membrane by local release of acetylcholine and causes the steep repolarization gradient in the vicinity of the current source leading to repetitive activity in atrial and PV cells during premature stimulation.

Osteopontin modulates angiotensin II-induced fibrosis in the intact murine heart

OBJECTIVES

Osteopontin (OPN) is upregulated in left ventricular hypertrophy and is stimulated by angiotensin II (AngII). Our objective was to determine whether mice deficient in OPN would be protected from AngII-induced cardiac fibrosis.

BACKGROUND

Interstitial fibrosis can lead to myocardial dysfunction and ultimately heart failure. Osteopontin activates integrins that regulate cell adhesion, migration, and growth, thus implicating OPN in the process of cardiac fibrosis.

METHODS

Osteopontin null (OPN(-/-)) mice (n = 18) and wild-type controls (n = 20) were infused with AngII (2.5 or 3.0 microg/kg/min) for four days or three weeks via osmotic mini-pumps. Hearts were assessed morphometrically and histologically, including quantitative assessment of fibrosis via optical microscopic imaging analysis. Cardiac fibroblasts derived from these mice were evaluated for adhesion and proliferation. Cardiac transcript expression for cytokines, extracellular matrix (ECM), integrin, and atrial natriuretic peptide were assessed.

RESULTS

Osteopontin(-/-) mice exhibited less cardiac fibrosis (0.7%) than wild-type mice (8.0%) (p < 0.01) and lowered heart/body weight ratios (0.10% vs. 0.23%) (p < 0.01) after three weeks of AngII infusion. Expression of transforming growth factor-beta, fibronectin, and collagen was not different between OPN(-/-) and wild-type mice, despite the decrease in ECM accumulation in the OPN(-/-) mice. Adhesion to ECM substrates decreased by 30% to 50% in cardiac fibroblasts of OPN(-/-) mice but was restored in OPN(-/-) cells by the addition of recombinant osteopontin.

CONCLUSIONS

Osteopontin mediates cardiac fibrosis, probably through the modulation of cellular adhesion and proliferation. Because OPN is increased in cardiac hypertrophy and its lack attenuates fibrosis, understanding of OPN function is essential to extend our knowledge about molecular determinants of cardiac hypertrophy and failure.

Chemokine Monokine Induced by IFN-γ/CXC Chemokine Ligand 9 Stimulates T Lymphocyte Proliferation and Effector Cytokine Production

Monokine induced by IFN-gamma (MIG; CXC chemokine ligand (CXCL)9) is important in T lymphocyte recruitment in organ transplantation. However, it is not known whether this chemokine, in addition to its chemotactic properties, exerts any effect on T lymphocyte effector functions. For in vivo studies, we used a previously characterized murine model of chronic rejection. The recipient mice were treated with anti-MIG/CXCL9 Ab; graft-infiltrating cells were analyzed for IFN-gamma production. For in vitro studies, exogenous CXCR3 ligands were added to CD4 lymphocytes in MLRs, and the proliferative responses were measured. Separate experiments quantitated the number of IFN-gamma-producing cells in MLRs by ELISPOT. Neutralization of MIG/CXCL9, in the in vivo model, resulted in significant reduction in the percentage of IFN-gamma-producing graft-infiltrating T lymphocytes. In vitro experiments demonstrated that 1) exogenous MIG/CXCL9 stimulated CD4 lymphocyte proliferation in a MHC class II-mismatched MLR, 2) MIG/CXCL9 also increased the number of IFN-gamma-producing CD4 lymphocytes in ELISPOT, 3) neutralization of MIG/CXCL9 in MLR reduced T lymphocyte proliferation, 4) IFN-gamma-inducible protein 10/CXCL10 and IFN-inducible T cell alpha chemoattractant/CXCL11 had similar effects on T lymphocyte proliferation, 5) MIG/CXCL9 stimulated T lymphocyte proliferation in MHC class I- and total MHC-mismatched MLRs, 6) neutralization of CXCR3 reduced MIG/CXCL9-induced T lymphocyte proliferation and the number of IFN-gamma-positive spots on ELISPOT, and 7) the proliferative effects of MIG/CXCL9 were mediated via an IL-2-independent pathway and were controlled by IFN-gamma. This study demonstrates that MIG/CXCL9 stimulates T lymphocyte proliferation and effector cytokine production, in addition to its chemotactic effects. This novel observation expands our current understanding of MIG/CXCL9 biology beyond that of mediating T cell trafficking.

Immunoperoxidase Staining for C4d on Paraffin-embedded Tissue in Cardiac Allograft Endomyocardial Biopsies

C4d deposition in microvasculature is a marker for humoral rejection. The authors compared a recently developed C4d immunoperoxidase (IP) method for paraffin-embedded tissue to immunofluorescence (IF) of frozen tissue. Of 315 frozen endomyocardial biopsies with IF staining for C4d, 280 were negative and 35 were positive. Negative controls were 17 negative biopsies and 11 biopsies with myocyte necrosis. The extent of IP and IF staining was graded as 0 to 3+. Staining intensity and the number and type of positive vessels were recorded. Staining patterns in Quilty lesions (QL) and foci of acute cellular rejection (ACR) were also evaluated. In 34 biopsies with sufficient tissue, IP criteria of 2+/3+, or more than 10 to 20 positive vessels per 10 high-power fields detected 25.0% (1/4), 18.2% (2/11), and 84.2% (16/19) of 1+, 2+, and 3+ IF-positive biopsies, respectively, without false positives. Considering C4d IF 3+ as positive resulted in 84.2% (16/19) sensitivity and 93.0% specificity (40/43). Intensely stained capillaries predominated in six of seven biopsies when more than 100 capillaries per 10 high-power fields were positive. Seventy percent (7/10) of IP 2+ and 3+ biopsies showed positive capillaries in QLs, while 36.4% (4/11) of IP 1+ and negative biopsies did. All eight IP 2+/3+ biopsies showed positive capillaries in ACR foci, while 25.0% (1/4) of IP-negative biopsies did. Capillary staining in QLs and areas of ACR reflects overall C4d deposition. In conclusion, IP staining of 2+/3+ is highly sensitive and specific for C4d positivity. The authors recommend considering 2+ and 3+ as positive staining when using the IP technique.

Sudden, unexpected death in cardiac transplant recipients: an autopsy study

BACKGROUND

Clinical studies indicate that sudden death (SD) is common after heart transplantation. Autopsy reports of such patients are sparse.

METHODS

We performed a retrospective study of clinical and pathologic findings on all autopsied patients who underwent heart transplantation at our institution from January 1984 to July 2002.

RESULTS

There were 74 patients who survived >2 months. Of these, 28 (37.8%) died suddenly. The major causes of sudden death (SD) included acute cellular rejection (ACR) (n = 11, 39.3%) and graft coronary artery disease (GCAD) (n = 11, 39.3%). In 9 patients (32.1%), there was no anatomic cause of death. These deaths, assumed to be primary arrhythmic death (PAD), occurred 5 to 36 months post-transplantation. Pre-transplant diagnosis of idiopathic dilated cardiomyopathy (IDCM) was more common in SD (13 of 28, 46.4% vs 9 of 46, 19.6%; p = 0.014). Hypertrophy was not statistically different in SD vs non-SD (79.4% vs 88.4%; p = 0.38). Coronary thrombosis was also not statistically different in sudden GCAD deaths vs non-sudden GCAD deaths (3 of 11, 27.3% vs 8 of 13, 61.5%; p = 0.09). ACR SD patients had fewer episodes of ACR in biopsies than ACR non-SD patients (93 of 190, 48.9% vs 99 of 159, 63.3%; p = 0.01). Biopsies with Quilty lesions (QL) were more frequent in patients with SD (206 of 461, 44.7% vs 243 of 710, 34.2%; p < 0.001). QL were more common in patients with GCAD (44.4%) and ACR (39.6%) than in patients who died of infection (25.7%; P < 0.001 and p < 0.01, respectively).

CONCLUSIONS

SD after cardiac transplantation is common (37.8% of all deaths). ACR, in the first year, and GCAD, afterwards, are associated with SD. PAD occurred in 32.1% of SD cases, 5 to 36 months after transplantation. Pre-transplant diagnoses of IDCM and QL are more common in SD. Surprisingly, cardiac hypertrophy is not increased and coronary thrombosis is not more frequent in patients who died suddenly.

Thoracic vein ablation terminates chronic atrial fibrillation in dogs

The thoracic vein hypothesis of chronic atrial fibrillation (AF) posits that rapid, repetitive activations from muscle sleeves within thoracic veins underlie the mechanism of sustained AF. If this is so, thoracic vein ablation should terminate sustained AF and prevent its reinduction. Six female mongrel dogs underwent chronic pulmonary vein (PV) pacing at 20 Hz to induce sustained (>48 h) AF. Bipolar electrodes were used to record from the atria and thoracic veins, including the vein of Marshall, four PVs, and the superior vena cava. Radio frequency (RF) application was applied around the PVs and superior vena cava and along the vein of Marshall until electrical activity was eliminated. Computerized mapping (1,792 electrodes, 1 mm resolution) was also performed. Sustained AF was induced in 30.6 ± 6.5 days, and ablation was done 17.3 ± 8.5 days afterward. Before ablation, the PVs had shorter activation cycle lengths than the atria, and rapid, repetitive activations were observed in the PVs. All dogs converted to sinus rhythm during ( n = 4 dogs) or within 90 min of completion of RF ablation. Rapid atrial pacing afterward induced only nonsustained (<60 s) AF in all dogs. Average AF cycle lengths after reinduction were significantly ( P = 0.01) longer (183 ± 31.5 ms) than baseline (106 ± 16.2 ms). There were no activation cycle length gradients after RF application. We conclude that thoracic vein ablation converts canine sustained AF into sinus rhythm and prevents the reinduction of sustained AF. These findings suggest that thoracic veins are important in the maintenance of AF in dogs.

Effects of procainamide on electrical activity in thoracic veins and atria in canine model of sustained atrial fibrillation

Focal discharges (FDs) are present in thoracic veins during atrial fibrillation (AF). We hypothesize that procainamide exerts its anti-AF action by suppressing FDs in the thoracic veins. We studied six mongrel dogs (22-27 kg) with sustained (>6 h) AF induced by 47 +/- 20 days of chronic rapid LA appendage (LAA) or pulmonary vein (PV) pacing. Procainamide was infused intravenously until AF was terminated or a cumulative dose of 20 mg/kg was reached. High-resolution mapping during AF showed FDs in the vein of Marshall, PVs, and the LAA. Procainamide significantly (P < 0.05) reduced the frequency of these FDs and suppressed the interactions of wave fronts between PVs and LA. The cumulative dose of PA needed to terminate AF correlated negatively (r =-0.9, P < 0.05) with the baseline effective refractory period (ERP) of PV and positively (r = 0.8, P < 0.05) with the baseline maximum dominant frequency (DF) of AF. In four of five dogs, AF converted to atrial tachycardia originating from the PVs before termination. Attempts to reinduce sustained AF were unsuccessful in these five dogs. AF was resistant to procainamide in the sixth dog. In conclusion, procainamide reduced the rate of FDs in the thoracic veins and the LA and suppressed the interaction between PVs and LA. Second, FDs in the PV are more resistant to procainamide's action than FDs in the atria. Third, inherent PV ERP is important in determining the antifibrillatory efficacy of procainamide.

Surgical pathology of cardiac tumors. Two decades at an urban institution

BACKGROUND

As better diagnostic techniques and new operative approaches are developed pathologists will be called upon more often for intraoperative consultation to render a pathologic diagnosis and assess adequacy of resection.

METHODS

We conducted a retrospective survey of all patients presenting to our institution from 1979 to 1999. The surgical pathology and cardiothoracic surgery databases were used to identify these patients.

RESULTS

Of the 29 patients with primary cardiac neoplasms, 15 were male and 14 female. The mean age at surgery was 51.9 years (range, 7 months to 84 years). Twenty-six of 29 patients had a benign pathological diagnosis. The majority (20/26) of the benign tumors were myxomas. Other benign pathologic diagnoses included rhabdomyoma, fibroma, papillary fibroelastoma, localized fibrous tumor and lipoma. Three out of 29 were malignant: 1 fibrosarcoma, 1 malignant mesenchymoma, and 1 rhabdomyosarcoma. Six of the patients presented with thrombo-embolism, 8 with congestive heart failure symptoms, and three with chest discomfort. Five were asymptomatic or the neoplasm was an incidental finding. 2-D echocardiography established the diagnosis in all of the patients except one. Twenty-two of the 29 tumors were located in the atria (LA=15, RA=6, biatrial=1) and 5 in the ventricles (LV=1, RV=2, biventricular=2). Two patients in this series were referred for reresection. A median sternotomy approach was used for tumor extirpation in all patients. Three of the 29 patients have died at a mean follow-up period of 757 days (median, 118 days). There were two late deaths and one hospital (early) death in a reoperation for recurrent malignancy employing cardiac autotransplantation. One additional patient required cardiac reoperation.

CONCLUSIONS

Primary cardiac neoplasms are rare and occur less commonly than metastatic disease of the heart. Congestive heart failure symptoms and thrombo-embolism account for close to half of the presenting signs and symptoms. 2-D echocardiography remains the mainstay of detection. Distinguishing between benign and malignant, thrombus and vegetation, and extracardiac structure is usually established by the size, shape, mobility and attachment of the mass. Clinical presentation and transesophageal echocardiographic views are extremely helpful in sharpening the accuracy of the diagnosis. Since surgery is the only reliable therapy pathologists will be called upon for intraoperative consultation. The majority of the neoplasms are benign. Malignant neoplasms are difficult to excise completely and portend a grave prognosis.

Alveolar septal deposition of immunoglobulin and complement parallels pulmonary hemorrhage in a guinea pig model of severe pulmonary leptospirosis

Human patients suffering from leptospirosis present with a diverse array of clinical manifestations, including the more severe and often fatal pulmonary form of the disease. The etiology of pulmonary hemorrhage is unclear. Isolates of Leptospira acquired from patients suffering from pulmonary hemorrhage were used to develop a guinea pig model of pulmonary hemorrhage. Gross findings post-infection confirmed extensive hemorrhage in the lungs and on peritoneal surfaces as the likely cause of death. Immunohistochemistry confirmed the presence of large numbers of leptospires in kidney, liver, intestinal tissues, and spleen, but few inflammatory cells were seen. In marked contrast, few leptospires were detected in infected hemorrhagic lung tissue. Blood chemistries and hematology did not reveal the etiology of the hemorrhage observed. There was no chemical or microscopic evidence for disseminated intravascular coagulation. To ascertain an immunopathologic role during disease, immunofluorescence was performed on infected lung tissues and confirmed the presence of IgM, IgG, IgA, and C3 along the alveolar basement membrane. This suggests that an autoimmune process may be the etiology of fatal pulmonary hemorrhage in leptospirosis.

Biopsy-negative cardiac transplant rejection: etiology, diagnosis, and therapy

PURPOSE OF REVIEW

As the frequency of cellular rejection after heart transplantation is decreasing, biopsy-negative episodes of rejection are being recognized more often. This article reviews the features of humoral rejection, which we believe is responsible for most episodes of biopsy-negative rejection. Hemodynamic compromise, in the absence of acute cellular rejection, called biopsy-negative rejection occurs in 10 to 20% of cardiac allograft recipients. These episodes of rejection are often more severe, and more difficult to treat, than classical acute cellular rejection. Histologic, immunofluorescence, and immunoperoxidase studies of endomyocardial biopsies from such patients often reveal intravascular macrophages, and immunoglobulin and complement deposition in capillaries, in the absence of lymphoid infiltrates, suggesting an antibody-mediated or humoral form of rejection.

RECENT FINDINGS

Humoral rejection is associated with increased graft loss, accelerated transplant coronary artery disease, and increased mortality. Severely ill patients require intense therapy, which includes high-dose corticosteroids, cytolytic agents, intravenous heparin, intravenous gamma globulin, plasmapheresis, and/or antiproliferative agents.

SUMMARY

Currently, our knowledge of the pathogenesis, diagnostic criteria, and optimal therapy for biopsy-negative rejection is incomplete, and evolving.

Eosinophilic myocarditis in patients awaiting heart transplantation*

OBJECTIVE

To determine the possible causative agents of eosinophilic or hypersensitivity myocarditis in patients awaiting heart transplantation.

DESIGN

Consecutive patient series.

SETTING

Large university-affiliated hospital.

PATIENTS

A total of 190 consecutive patients who had heart transplantation at our center.

INTERVENTIONS

The myocardium of the explanted heart was examined for a mixed inflammatory cell infiltrate containing an identifiable component of eosinophils. The relative quantity of each cell type was evaluated by a semiquantitative grading system (scored 0 to 3). The clinical findings and medications were reviewed, and patients were followed after heart transplantation.

MEASUREMENTS AND MAIN RESULTS

Eosinophilic myocarditis (EM) was found in the explanted heart in 14 patients (7.4%). Myocardial infiltration by eosinophils ranged from mild (n = 6), often focal involvement to marked (n = 8), usually multifocal or widespread involvement. Twelve patients (86%) had peripheral blood eosinophilia before transplant, and in ten (71%), the eosinophil count at least doubled. Loop or thiazide diuretics were used in all 14 patients, and angiotensin-converting enzyme inhibitors were used in 12. Preoperative characteristics were similar in patients with and without EM, except for a higher frequency of inotropic support and assist devices in EM patients. Dobutamine was used in 12 (86%) and dopamine in seven (50%; one with dopamine alone), and one patient (7%) received neither dopamine nor dobutamine. In two patients receiving dobutamine and one receiving dopamine, tapering or discontinuation of the inotropic infusion resulted in a significant diminution of the peripheral eosinophilia and the EM before transplantation. Postoperative survival in patients with and without EM was similar at 8 yrs (50% +/- 13% and 54% +/- 4%, p =.34). No patient in this study has had EM on biopsy after transplant.

CONCLUSIONS

EM is a complication of multiple drug therapy in patients awaiting heart transplantation, and should be suspected when peripheral blood eosinophilia is present or the eosinophil count increases by at least two-fold. EM may be related to intravenous inotropic therapy, and this is the first study to document improvement in myocardial pathology after inotropic drug withdrawal. Hypersensitivity to thiazide and loop diuretics, angiotensin-converting enzyme inhibitors, and antibiotics must also be considered. Survival after heart transplantation is not impaired, and postoperative steroid therapy may prevent EM.

Long-term subthreshold electrical stimulation of the left stellate ganglion and a canine model of sudden cardiac death

OBJECTIVES

We sought to develop a high-yield canine model of sudden cardiac death (SCD).

BACKGROUND

Because electrical stimulation is a powerful means to elicit nerve sprouting, we hypothesize that subthreshold electrical stimulation is more effective than nerve growth factor (NGF) infusion in inducing nerve sprouting and SCD in dogs with myocardial infarction (MI) and complete atrioventricular block (CAVB).

METHODS

We gave subthreshold electrical stimulation to the left stellate ganglion (LSG) in six normal dogs for 41 +/- 9 days (protocol 1) and to six dogs with MI and CAVB for 41 +/- 29 days, while continuously monitoring their cardiac rhythm (protocol 2). We also monitored the rhythm of two dogs with MI, CAVB, and NGF infusion to the LSG and determined the ventricular nerve density in six healthy control dogs.

RESULTS

In protocol 1, the hearts from dogs with LSG electrical stimulation had a higher density of nerve fibers immunopositive to tyrosine hydroxylase, synaptophysin, and growth-associated protein-43 than those of normal control dogs (p < 0.01). In protocol 2, there was a high magnitude of cardiac nerve sprouting in all dogs studied. Ventricular tachycardia > or =8 beats and > or =20 beats was more frequent in dogs with electrical stimulation than in dogs with NGF infusion to the LSG (36 +/- 60 and 11 +/- 17 vs. 4.7 +/- 6.1 and 0.1 +/- 0.33 episodes per day, p < 0.05 and p < 0.03, respectively). Four of six dogs in protocol 2 had SCD.

CONCLUSIONS

Subthreshold electrical stimulation of the LSG induces cardiac nerve sprouting and sympathetic hyperinnervation and facilitates the development of a high-yield canine model of ventricular arrhythmia and SCD.

Incidence of thrombus formation on the CardioSEAL and the Amplatzer interatrial closure devices

Transcatheter closure for atrial septal defect (ASD) and patent foramen ovale (PFO) is a promising alternative to surgical closure or anticoagulant therapy. A potential complication is thrombus formation on the device after implantation. From February 2001 to June 2003, 66 patients with atrial communication were treated successfully with the Amplatzer device (16 septal and 20 PFO occluders) or the CardioSEAL device (30). Patients were discharged on antiplatelet medication (aspirin and clopidogrel) and/or anticoagulation. Fifty patients (76%) had transesophageal echocardiography (TEE) 1 month after device implantation (28 +/- 10 days). No patient experienced a thromboembolic episode during follow-up. TEE revealed that thrombus formation occurred more frequently on the CardioSEAL device (5 of 23 patients; 22%) than on the Amplatzer device (0 of 27 patients; 0%) (p = 0.02). Although thrombus disappeared or markedly diminished after additional anticoagulation therapy in 3 patients, 1 patient had surgical explantation of the device due to progressive increase in the size of thrombus with hypermobility despite intensive anticoagulation therapy. There was no variable associated with the presence of thrombus formation on the occluder other than the use of the CardioSEAL device. One month after insertion, the CardioSEAL device is more likely to have thrombus present than the Amplatzer device.

Signal-averaged electrocardiogram in Ebstein's anomaly

We sought to establish pathogenetic links between electrophysiology, histopathology, and ventricular tachyarrhythmias in patients with Ebstein's anomaly. The atrialized right ventricle (ARV) is the site of mechanically inducible ventricular tachyarrhythmias, but relations between the arrhythmogenic substrate, the type of tachyarrhythmias, and the trigger(s) have not been established. This study comprised 23 patients (10 men and 13 women; aged 18 to 58 years; mean 32 +/- 3) who did not undergo surgery and 6 pre- and postoperative patients with Ebstein's anomaly, diagnosed by transthoracic and transesophageal echocardiography. Twenty-one patients had classic Ebstein's anomaly and 2 had mild forms. Signal-averaged electrocardiograms (SAECGs) identified slow conduction by using 3 time-domain variables calculated by an automated algorithm and inspected visually. Two variables were required to establish the presence of late potentials. SAECGs were repeated in 6 patients after surgical exclusion of the ARV. Five surgical specimens of the ARV and the true right atrium were examined histologically. Mathematic simulations were used to illustrate anchored and unanchored spiral/scroll waves. SAECGs were positive in 21 patients with classic Ebstein's anomaly and were negative postoperatively in the 6 so studied. The ARV was characterized histologically by clusters of cardiomyocytes isolated within a fibrous matrix. We hypothesize that SAECGs identify slow conduction residing in the ARV, and that excitation of this arrhythmogenic substrate provokes spiral/scroll waves that cannot anchor because clusters of cardiomyocytes are isolated within a fibrous matrix. The waves meander erratically as polymorphic ventricular tachycardia or break up into ventricular fibrillation.

Combined blockade of the chemokine receptors CCR1 and CCR5 attenuates chronic rejection

BACKGROUND

Chemokine-chemokine receptor interaction and the subsequent recruitment of T-lymphocytes to the graft are early events in the development of chronic rejection of transplanted hearts or cardiac allograft vasculopathy (CAV). In this study, we sought to determine whether blockade of chemokine receptors CCR1 and CCR5 with Met-RANTES affects the development of CAV in a murine model.

METHODS AND RESULTS

B6.CH-2(bm12) strain donor hearts were transplanted heterotopically into wild-type C57BL/6 mice (myosin heavy chain II mismatch). Recipients were treated daily with either Met-RANTES or vehicle starting on postoperative day 4 and were euthanized on postoperative days 24 and 56. We found that Met-RANTES significantly reduced intimal thickening in this model of chronic rejection and that Met-RANTES markedly decreased the infiltration of CD4 and CD8 T lymphocytes and MOMA-2+ monocytes/macrophages into transplanted hearts. Met-RANTES also suppressed the ex vivo and in vitro proliferative responses of recipient splenocytes to donor antigens. Finally, Met-RANTES treatment was associated with a marked reduction in RANTES/CCL5 and monocyte chemoattractant protein-1 gene transcript levels in the donor hearts.

CONCLUSIONS

Antagonism of the chemokine receptors CCR1 and CCR5 with Met-RANTES attenuates CAV development in vivo by reducing mononuclear cell recruitment to the transplanted heart, proliferative responses to donor antigens, and intragraft RANTES/CCL5 and monocyte chemoattractant protein-1 gene transcript levels. These findings suggest that chemokine receptors CCR1 and CCR5 play significant roles in the development of chronic rejection and may serve as potential therapeutic targets.

The yield of surveillance endomyocardial biopsies as a screen for cellular rejection in pediatric heart transplant patients

Endomyocardial biopsy is commonly used to screen for cellular rejection in pediatric heart transplant patients. The yield of EMBs when combined with newly developed immunohistochemical techniques and modern immunosuppression in pediatric heart transplant patients is unknown. After OHT, surveillance biopsies were performed on a routine basis on all pediatric patients. EMBs were also performed on symptomatic OHT patients suspected to have rejection. All positive results (greater than ISHLT grade 1B) were confirmed with immunohistochemical staining. A retrospective review of consecutive EMBs performed in this institution from January 1995 to January 2003 was performed. The echocardiographic results, clinical history and treatment changes at the time of every biopsy were also catalogued. Of the 1093 EMB results from 136 pediatric heart transplant grafts (127 patients, 64 male) reviewed, 825 biopsies were performed on patients managed with tacrolimus and 268 were performed on patients managed with cyclosporine. The patients managed with tacrolimus had an incidence of 0.85% (7/825) for significant rejection (greater than ISHLT grade 1B rejection) vs. an incidence of 4.1% (11/268) for the patients on cyclosporine (p < 0.0005). In the asymptomatic tacrolimus patients, only two screening biopsies (0.26%) manifest significant rejection, and both of these were performed within the first month after transplantation. Of the symptomatic tacrolimus patients, 9.1% (n = 5) had findings on biopsy consistent with significant cellular rejection. There were 25 patients with grade 1B rejection. Twenty-two of these patients were not treated, and all cases of grade 1B rejection resolved without clinical sequelae. For pediatric patients more than 30 days after OHT, EMB has failed to reveal significant episodes of cellular rejection in asymptomatic patients managed with tacrolimus.

Angiotensin II-accelerated atherosclerosis and aneurysm formation is attenuated in osteopontin-deficient mice

Osteopontin (OPN) is expressed in atherosclerotic lesions, particularly in diabetic patients. To determine the role of OPN in atherogenesis, ApoE-/-OPN+/+, ApoE-/-OPN+/-, and ApoE-/-OPN-/- mice were infused with Ang II, inducing vascular OPN expression and accelerating atherosclerosis. Compared with ApoE-/-OPN+/+ mice, ApoE-/-OPN+/- and ApoE-/-OPN-/- mice developed less Ang II-accelerated atherosclerosis. ApoE-/- mice transplanted with bone marrow derived from ApoE-/-OPN-/- mice had less Ang II-induced atherosclerosis compared with animals receiving ApoE-/-OPN+/+ cells. Aortae from Ang II-infused ApoE-/-OPN-/- mice expressed less CD68, C-C-chemokine receptor 2, and VCAM-1. In response to intraperitoneal thioglycollate, recruitment of leukocytes in OPN-/- mice was impaired, and OPN-/- leukocytes exhibited decreased basal and MCP-1-directed migration. Furthermore, macrophage viability in atherosclerotic lesions from Ang II-infused ApoE-/-OPN-/- mice was decreased. Finally, Ang II-induced abdominal aortic aneurysm formation in ApoE-/-OPN-/- mice was reduced and associated with decreased MMP-2 and MMP-9 activity. These data suggest an important role for leukocyte-derived OPN in mediating Ang II-accelerated atherosclerosis and aneurysm formation.