Relationship between connexins and atrial activation during human atrial fibrillation

INTRODUCTION: Gap junctional connexin proteins (connexin40 [Cx40], connexin43 [Cx43]) are a determinant of myocardial conduction and are implicated in the development of atrial fibrillation (AF). We hypothesized that atrial activation pattern during AF is related to connexin expression and that this relationship is altered by AF-induced remodeling in the fibrillating atria of chronic AF. METHODS AND RESULTS: Isochronal activation mapping was performed during cardiac surgery on the right atria of patients in chronic AF (n = 13) using an epicardial electrode array. The atrial activation pattern was categorized using a complexity score based on the number of propagating wavefronts of activation and by grouping atria into those capable of uniform planar activation (simple) and those that were not (complex). The activation pattern was correlated with the levels of Cx43 and Cx40 signal measured by immunoconfocal quantification of biopsies from the mapped region. We studied the impact of electrical remodeling by comparing these findings with the unremodeled atria of patients in sinus rhythm during pacing-induced sustained AF (n = 17). In chronic AF, atria with complex activation had lower Cx40 signal than atria showing simple activation (0.013 +/- 0.006 microm(2)/microm(2) vs 0.027 +/- 0.009 microm(2)/microm(2), P < 0.02), with the relative connexin signal (Cx40/Cx40+Cx43) correlating with complexity score (P = 0.01, r =-0.74). This relationship did not occur in the unremodeled atria, and increased heterogeneity of distribution of Cx40 labeling in chronic AF was the only evidence of connexin remodeling that we detected in the overall group. CONCLUSION: The pattern of atrial activation is related to immunoconfocal connexin signal only in the fully remodeled atria of chronic AF. This suggests that intercellular coupling and pattern of atrial activation are interrelated, but only in conjunction with the remodeling of atrial electrophysiology that occurs in chronic AF.     

Short remission durations in therapy-related leukemia despite cytogenetic complete responses to high-dose cytarabine

Seventeen patients with therapy-related myelodysplastic syndrome (t- MDS) or therapy-related acute nonlymphocytic leukemia (t-ANLL) were treated with single-agent high-dose cytarabine (HDAC; 1 to 3 g/m2 every 12 hours for 12 doses). The initial neoplasm was still present in eight patients when t-MDS/t-ANLL developed. Fifteen of the 16 patients with chromosomal abnormalities in bone marrow cells had loss or rearrangement of chromosomes 5 and/or 7. One patient had a t(15;17), and one had inadequate material for cytogenetic analysis. Twelve patients had normal metaphase cells (3% to 71%). Indications for HDAC therapy were progressive pancytopenia in 13 patients or rising blast count in four. Five patients died of marrow hypoplasia following therapy. Four others had refractory t-ANLL and died within the subsequent 5 months. Only one of ten patients with a poor performance status (PS greater than or equal to 2 using the ECOG scale) achieved a complete remission, but all seven patients with a good performance status (PS less than or equal to 1) had a complete remission. Hematologic remissions were achieved in 8 patients (47%) after one (6 patients) or two (2 patients) induction courses and were confirmed by recovery of a 100% normal marrow karyotype in six of the seven patients who were retested. Patients in remission received one to four consolidation courses with HDAC alternating with cytarabine/doxorubicin, but seven relapsed within 8 months (median remission duration, 5 months). In every case, the original chromosomal abnormality reappeared at relapse. HDAC has a high response rate for good-performance patients with t-MDS/t-ANLL, but complete remissions are short even when confirmed cytogenetically and consolidated intensively.     

Cooperative effect of tumor necrosis factor and gamma-interferon on chemotactic peptide receptor expression and stimulus-induced actin polymerization in HL-60 cells

We studied the effect of tumor necrosis factor (TNF) and gamma interferon (IFN-gamma), alone and in combination, on the expression of chemotactic peptide receptors, stimulus-induced actin polymerization, hydrogen peroxide production (H2O2), and expression of nonspecific esterase (NSE) positivity in human promyelocytic leukemic cell line HL- 60. These parameters were analyzed following a five-day culture with the cytokines. Chemotactic peptide receptor expression was studied using the fluoresceinated hexapeptide, formyl-norleucyl-leucyl- phenylalanyl-norleucyl-tyrosyl-lysine and flow cytometry. Actin polymerization, an important event required for chemotaxis and phagocytosis, was studied using NBD-phallacidin labeling, following stimulation with the chemotactic peptide formyl-methionyl-leucyl- phenylalanine (FMLP) or phorbol myristate acetate (PMA). TNF increased the expression of chemotactic peptide receptors in a dose-dependent fashion, and there was good correlation between the receptor expression, stimulus-induced actin polymerization, H2O2 production, and NSE positivity. IFN-gamma was less potent in inducing all the parameters studied but exerted a positive cooperative effect when combined with TNF. IFN-gamma at high concentrations induced chemotactic peptide receptors comparable in magnitude to that seen with TNF but failed to prime these cells to undergo actin polymerization in response to FMLP or PMA. Undifferentiated HL-60 cells showed a decrease in F- actin content on stimulation with PMA. This suggests that protein kinase C might have a negative regulatory role in stimulus-induced actin polymerization. The observations reported here indicate that appropriate combinations of different inducing agents with different modes of action might be necessary to duplicate the functional abilities of mature phagocytic cells.     

Duration of the effect of aspirin on the synthesis of thromboxane by density subpopulations of rabbit platelets stimulated with thrombin

The controversy concerning the relationship between platelet buoyant density and platelet age is unresolved. Our earlier results with rabbit platelets indicate that the most-dense subpopulations are enriched in young platelets and that some platelets become less dense as they age. Other investigators have concluded that platelets either do not change in density upon aging or become more dense. In the present experiments, rabbit platelets were separated on discontinuous gradients of Stractan. Most-dense platelets synthesized significantly more thromboxane B2 (TXB2) (1.27 ng per 10(6) platelets) in response to thrombin (0.75 U/mL) than did least-dense platelets (0.70 ng per 10(6) platelets), indicating that the arachidonate pathway in most-dense platelets is more active than in least-dense platelets. After aspirin administration to rabbits, most-dense platelets recovered their ability to synthesize thromboxane B2 significantly more quickly than did least-dense platelets. Because the platelet cyclooxygenase that is responsible for TXB2 formation is permanently inhibited by aspirin, it is only the new platelets entering the circulation that will be able to form TXB2. These results indicate that, at least in rabbits, the most-dense platelets are enriched in young platelets, and that platelets decrease in density as they age in the circulation.     

Extrinsic obstruction of the main coronary arteries in a child with hypertrophic cardiomyopathy

Phasic narrowing of the coronary arteries on angiography is a well-known entity in both children and adults and has been described in relation to all epicardial arteries. There is a high incidence of myocardial bridges in hypertrophic cardiomyopathy. We report the case of a 6-year-old girl with hypertrophic obstructive cardiomyopathy who had extrinsic obstruction of the left main and right coronary arteries.     

Graft-v-host disease is associated with autoimmune-like thrombocytopenia [see comments]

Persistent thrombocytopenia after allogeneic marrow transplantation is associated with poor patient survival. To identify the mechanisms of the thrombocytopenia, we studied platelet and fibrinogen kinetics and antiplatelet antibodies in 20 patients between 60 and 649 days (median 90) after transplantation. Seventeen patients had isolated thrombocytopenia (less than 100 X 10(9) platelets/L): the marrow cellularity was normal in five patients and slightly reduced in 12, and there was no discrepancy between thrombopoiesis and myeloerythropoiesis. Three patients had pancytopenia following marrow graft rejection (two) and relapse of leukemia (one). Only three patients had evidence of increased platelet production, indicating that in most cases there is a poor marrow response to thrombocytopenia early after marrow grafting. There was no correlation between platelet count and splenic pooling, suggesting that hypersplenism was an unlikely mechanism of the thrombocytopenia. Although there was a direct relationship between platelet count and platelet survival, the reduction in platelet survival was greater than what could be explained by the fixed platelet removal found in thrombocytopenic patients; this suggests increased platelet destruction. Seven patients had intercurrent infections that reduced both platelet and fibrinogen survivals. In addition, platelet antibodies bound to autologous or marrow donor platelets were present in five of the 12 patients studied. Patients with antiplatelet antibodies had lower platelet counts (30 +/- 10 X 10(9)/L v. 49.1 +/- 28.7 X 10(9)/L, P less than 0.05) and platelet survivals (1.32 +/- 0.92 days v. 3.58 +/- 2.02 days, P less than 0.05) than patients without antiplatelet antibodies. Furthermore, platelet- bound autoantibodies were present in five of six patients with grade II- IV acute or chronic graft-versus-host disease (GVHD), but were not present in six patients free of GVHD (P less than 0.01). We conclude that persistent thrombocytopenia after marrow transplantation is most often secondary to increased platelet destruction mediated by multiple mechanisms and that platelet autoantibodies are found in patients with acute or chronic GVHD.     

Alternating-day cyclosporine and prednisone for treatment of high-risk chronic graft-v-host disease

Therapy of chronic graft-v-host disease (GVHD) has been unsatisfactory in patients with platelet counts less than 100,000/microL. Survival at 5 years after marrow transplant is only 26% in such patients treated with trimethoprim-sulfamethoxazole (TMP-SMX) and every other day with prednisone. Since October 1982, 61 patients with high-risk extensive chronic GVHD were treated with a new alternating-day regimen of prednisone (1 mg/kg every other day) and oral cyclosporine (6 mg/kg every 12 hours every other day) with one double-strength TMP-SMX tablet twice daily. Forty patients (group I) received primary treatment of thrombocytopenic chronic GVHD (median platelet count 35 [range 7 to 87] x 10(3)/microL). Twenty-one patients (group II) received salvage treatment after failing initial prednisone +/- azathioprine. Twenty-one patients in group I and 15 in group II survive with a minimum of 2 years and a median of 3.7 years follow-up. At 4 years after transplant, actuarial survival is 51% (group I) and 67% (group II). Causes of death included interstitial pneumonia (six), relapse (five), GVHD without infection (five), infection (four), organ failure (three), and hemorrhage (two). Mortality increased with the progressive type onset of chronic GVHD and treatment failure. Toxicity included hypertension (13), nephrotoxicity (nine), nausea (seven), aseptic necrosis (five), neurologic abnormalities (four), and diabetes (three). Median cyclosporine levels at four and 36 hours were 296 and 64 ng/mL, respectively. Four patients required permanent discontinuation of cyclosporine, but none required renal dialysis. Karnofsky performance scores for 25 survivors are 90% to 100%, scores for six survivors are 70% to 89%, and scores for five survivors are less than 70%. Alternating-day cyclosporine and prednisone has acceptable toxicity and appears to improve survival in patients with high-risk chronic GVHD.     

Decreased incidence of marrow graft rejection in patients with severe aplastic anemia: changing impact of risk factors

Patients with severe aplastic anemia were conditioned with cyclophosphamide (200 mg/kg) and given marrow grafts from HLA-identical family members. Among 233 patients transplanted, 225 survived greater than or equal to 14 days and could be evaluated for engraftment. Forty- four of the 225 rejected their graft; 33 of these died and 11 survive. One hundred eighty-one patients had sustained engraftment; of these, 46 died and 135 survived. Binary logistic regression analyses revealed five risk factors for graft rejection: year of transplant, a large number of platelet transfusions, a positive relative response in mixed leukocyte culture, a low marrow cell dose, and omission of donor buffy coat cell infusion for transfused patients. These data show that patients transplanted recently had a lower likelihood of graft rejection than did patients transplanted in earlier years. Conceivably, this was related to changes in transfusion practices, but other factors as yet unidentified are likely to be involved. The data confirm that the largest possible number of marrow cells should be transplanted. Although the difference in the incidence of graft rejection between untransfused and transfused patients was not significant, it should be noted that transfused patients were given buffy coat cells. Because the addition of buffy coat cells results in a higher incidence of chronic graft-v-host disease (GVHD), it is still desirable to transplant patients with marrow alone early in their course before they have been transfused.