Further Evidence for the “Muscle Bundle” Hypothesis of Cavotricuspid Isthmus Conduction: Physiological Proof,with Clinical Implications for Ablation

Two Line Flutter Ablation . Introduction: It has been suggested that the cavotricuspid isthmus (CTI) is composed of discrete muscle bundles with preferred paths of conduction. An ablation technique targeting high‐voltage local electrograms (maximum voltage guided or MVG technique) has been described with the aim of preferentially targeting the muscle bundles. We hypothesized that the MVG technique could provide isthmus block even if the high voltage targets were clearly separated on different ablation lines. In contrast, conduction over a continuous sheet of muscle would require a single continuous ablation line. Methods: Twenty‐two consecutive patients (mean age 65 ± 11.7, 5 females) underwent ablation using the MVG technique on 2 noncontiguous lines in the CTI. Ablation lesions were first applied at the septal aspect of the CTI, targeting only the ventricular (anterior) aspect of the annulus. A line distinctly lateral and noncontiguous to the first was then chosen to target high voltage potentials on the atrial (posterior) aspect of the CTI. Results: Complete CTI block was achieved in all study patients without complication. A mean of 7.8 ± 3.7 ablation lesions were required. Mean ablation time was 401.0 ± 414.5 seconds. Conclusion: Two nonoverlapping incomplete lines of ablation in the CTI consistently lead to bidirectional conduction block. This further supports the hypothesis that conduction over the CTI occurs over discrete muscle bundles. These bundles can be targeted individually for ablation without the need to ablate a continuous line over the CTI. (J Cardiovasc Electrophysiol, Vol. 24, pp. 47‐52, January 2013)     

Study of Machining of Gears with Regular and Modified Outline Using CNC Machine Tools

Classic methods of machining cylindrical gears, such as hobbing or circumferential chiseling, require the use of expensive special machine tools and dedicated tools, which makes production unprofitable, especially in small and medium series. Today, special attention is paid to the technology of making gears using universal CNC (computer numerical control) machine tools with standard cheap tools. On the basis of the presented mathematical model, a software was developed to generate a code that controls a machine tool for machining cylindrical gears with straight and modified tooth line using the multipass method. Made of steel 16MnCr5, gear wheels with a straight tooth line and with a longitudinally modified convex-convex tooth line were machined on a five-axis CNC milling machine DMG MORI CMX50U, using solid carbide milling cutters (cylindrical and ball end) for processing. The manufactured gears were inspected on a ZEISS coordinate measuring machine, using the software Gear Pro Involute. The conformity of the outline, the tooth line, and the gear pitch were assessed. The side surfaces of the teeth after machining according to the planned strategy were also assessed; the tests were carried out using the optical microscope Alicona Infinite Focus G5 and the contact profilographometer Taylor Hobson, Talysurf 120. The presented method is able to provide a very good quality of machined gears in relation to competing methods. The great advantage of this method is the use of a tool that is not geometrically related to the shape of the machined gear profile, which allows the production of cylindrical gears with a tooth and profile line other than the standard.     

Parallel detection of violations of color constancy

The perceived colors of reflecting surfaces generally remain stable despite changes in the spectrum of the illuminating light. This color constancy can be measured operationally by asking observers to distinguish illuminant changes on a scene from changes in the reflecting properties of the surfaces comprising it. It is shown here that during fast illuminant changes, simultaneous changes in spectral reflectance of one or more surfaces in an array of other surfaces can be readily detected almost independent of the numbers of surfaces, suggesting a preattentive, spatially parallel process. This process, which is perfect over a spatial window delimited by the anatomical fovea, may form an early input to a multistage analysis of surface color, providing the visual system with information about a rapidly changing world in advance of the generation of a more elaborate and stable perceptual representation.     

Structure of a factor VIII C2 domain-immunoglobulin G4kappa Fab complex: identification of an inhibitory antibody epitope on the surface of factor VIII.

The development of an immune response to infused factor VIII is a complication affecting many patients with hemophilia A. Inhibitor antibodies bind to antigenic determinants on the factor VIII molecule and block its procoagulant activity. A patient-derived inhibitory immunoglobulin G4kappa antibody (BO2C11) produced by an immortalized memory B-lymphocyte cell line interferes with the binding of factor VIII to phospholipid surfaces and to von Willebrand factor. The structure of a Fab fragment derived from this antibody complexed with the factor VIII C2 domain was determined at 2.0 A resolution. The Fab interacts with solvent-exposed basic and hydrophobic side chains that form a membrane-association surface of factor VIII. This atomic resolution structure suggests a variety of amino acid substitutions in the C2 domain of factor VIII that might prevent the binding of anti-C2 inhibitor antibodies without significantly compromising the procoagulant functions of factor VIII.     

Blockade of human immunodeficiency virus type 1 production in CD4+ T cells by an intracellular CD4 expressed under control of the viral long terminal repeat.

A retroviral vector was constructed in which a gene encoding a mutated soluble CD4 protein that is retained in the endoplasmic reticulum (sCD4-KDEL) is expressed under control of human immunodeficiency virus type 1 (HIV-1) regulatory elements. HIV-1 infection of a human T-cell line transduced with this vector led to induction of sCD4-KDEL synthesis and a block in transport of the HIV envelope protein to the cell surface. There was a complete block to maturation of infectious HIV-1 in the transduced cells, no viral spread, and little or no syncytium formation. Infected cells gradually disappeared from the culture over a period of 2 months. This intracellular trap for HIV has potential application in gene therapy for AIDS.     

Atrial flutter and atrial fibrillation: which relationship? New insights into the electrophysiological mechanisms and catheter ablation treatment.

Atrial fibrillation (AF) and atrial flutter (AFL) are two arrhythmias commonly associated in clinical practice. This association generally reflects a similar arrhythmogenic substrate. It has been observed that the development of isthmus-dependent AFL is often preceded by AF. The conversion from AF to AFL develops thanks to a line of functional block in the right atrial free wall. In this subset a particular condition is represented by typical AFL that occurs during the treatment with class IC or III antiarrhythmic drugs in patients with previous AF. A hybrid approach (antiarrhythmic drugs and catheter ablation) has been proposed as a possible treatment of drug-induced AFL. The conversion from AFL to AF is less frequent and may be due to several mechanisms: a shortening of the length of the line of functional block, atrial ectopic beats or rapid atrial rhythm, focal activation from the pulmonary veins, alternans of atrial action potentials. Also, atypical right and left AFL can determine AF. Finally, atypical AFL may occur after AF ablation, and could be prevented by associated cavotricuspid isthmus ablation.     

Functional evidence for presence of lipid rafts in erythrocyte membranes: Gsalpha in rafts is essential for signal transduction

Membrane microdomains enriched in cholesterol and sphingolipids and containing specific membrane proteins are designated as lipid rafts. Lipid rafts have been implicated in cell signaling pathways in various cell types. Heterotrimeric guanine nucleotide-binding protein (Gsalpha) has been shown to be a raft component of erythrocytes and has been implicated in cell signaling. Rafts are isolated as detergent-resistant microdomains (DRMs) for biochemical analysis. Cholesterol depletion is widely used to disrupt raft structures to study their function in biological membranes. In the present study, we developed an alternate strategy for disrupting raft structures without altering membrane cholesterol content. Lidocaine hydrochloride, an amphipathic local anesthetic, is shown to reversibly disrupt rafts in erythrocyte membranes and alter the Gsalpha dependent signal transduction pathway. These findings provide evidence for the presence of rafts while maintaining normal cholesterol content in erythrocyte membranes and confirm a role for raft-associated Gsalpha in signal transduction in erythrocytes.     

The Challenge of Producing Fiber-Based Organic Electronic Devices

The implementation of organic electronic devices on fibers is a challenging task, not yet investigated in detail. As was shown earlier, a direct transition from a flat device structure to a fiber substrate is in principle possible. However, a more detailed investigation of the process reveals additional complexities than just the transition in geometry. It will be shown, that the layer formation of evaporated materials behaves differently due to the multi-angled incidence on the fibers surface. In order to achieve homogenous layers the evaporation process has to be adapted. Additionally, the fiber geometry itself facilitates damaging of its surface due to mechanical impact and leads to a high surface roughness, thereby often hindering commercial fibers to be used as substrates. In this article, a treatment of commercial polymer-coated glass fibers will be demonstrated that allows for the fabrication of rather flexible organic light-emitting diodes (OLEDs) with cylindrical emission characteristics. Since OLEDs rely the most on a smooth substrate, fibers undergoing the proposed treatment are applicable for other organic electronic devices such as transistors and solar cells. Finally, the technique also supports the future fabrication of organic electronics not only in smart textiles and woven electronics but also in bent surfaces, which opens a wide range of applications.     

Distribution of Ia-like molecules on the surface of normal and leukemic human cells.

Antiserum to a glycoprotein antigen complex of 23,000 and 30,000 dalton subunits (p23,30), isolated and purified from a human lymphoblastoid B cell line, was shown to be highly specific for human bursal-equivalent-processed (B) cells, reactive with 15-20% of human Null cells, but completely unreactive with human thymus-processed (T) cells. The p23,30 antigen is widely distributed on chronic lymphatic leukemic cells, 85% of acute lymphatic leukemic cells, all acute myelogenous leukemic cells, but not on chronic myelogenous leukemic cells. A rabbit antiserum specific for normal human thymocytes has also been prepared; it is reactive only with precisely that subset of acute lymphatic leukemic cells (15%) whose members do not have p23,30 on their surfaces.     

Evidence of three-dimensional scroll waves with ribbon-shaped filament as a mechanism of ventricular tachycardia in the isolated rabbit heart

INTRODUCTION: Rotating vortices have been observed in excitable media of different nature. Vortices may sustain life or kill in different species, by underlining morphogenesis in Dictiostelium discoideum during starvation, or arrhythmias during sudden cardiac death in mammals. Investigation of vortices in the heart has been limited by two-dimensional experimental techniques. In contrast, three-dimensional (3D) Belousov-Zhabotinsky excitable medium and mathematical models have been shown to sustain scroll-shaped waves. The heart is a 3D structure; therefore, scroll waves may underlie cardiac arrhythmias. METHODS AND RESULTS: We used potentiometric dye and optical mapping techniques to study vortices during ventricular arrhythmias. The core of all observed vortices were linearly shaped and > or = 9 mm (48 episodes, six hearts). As shown by Allessie et al. in the rabbit atrium, ventricular signals recorded within 1 to 2 mm from the line of block were dual humped, suggesting there is electrotonic interaction across the line of block. We hypothesized that the line of block represents epicardial intersection of ribbon-shaped filaments, which in some cases may be oriented under an angle or parallel to the epicardium. In 14 episodes we observed dual-humped optical recordings at one side of the line of block at a distance up to 12 mm. The two humps may represent the signatures of two activation wavefronts propagating above and below the filament, which in this area is close to the epicardial surface. The activation sequence of the two waves is consistent with the idea of a scroll wave with ribbon-like filament. CONCLUSION: Our data provide new insights into the shape and dynamics of the filament of the 3D scroll wave, which underlies the mechanism of ventricular tachycardia in the rabbit heart. The filament of the scroll wave may be ribbon shaped, with a significant width > or = 9 mm and a thickness of 1 to 2 mm. No evidence of fully excitable cells in the core of vortex was observed.     

Complement receptor type three (CD11b/CD18) of human polymorphonuclear leukocytes recognizes fibrinogen.

Human polymorphonuclear leukocytes (PMN) have previously been shown to bind to aggregates of fibrin and to fibrinogen-coated surfaces. During their interactions with fibrinogen-coated surfaces, PMN make such close contact with the surface that a portion of the secreted elastase activity is protected from macromolecular protease inhibitors in the surrounding medium. Here we show that the receptor on PMN that mediates this interaction is complement receptor type 3 (CR3; CD11b/CD18), a molecule previously identified as a receptor for the complement protein fragment C3bi. Monoclonal antibodies against CR3 that block the binding of C3bi also block the binding of PMN to fibrinogen-coated surfaces and the formation of a protected compartment. The region of fibrinogen recognized by CR3 lies at the carboxyl terminus of the gamma chain, since peptides based on this sequence effectively inhibit the binding of PMN to fibrinogen-coated surfaces. These peptides also block the binding of C3bi-coated erythrocytes to CR3, thus indicating that a single binding site is used for binding both C3bi and fibrinogen. Sequence analysis shows strong structural similarity between this region of fibrinogen and other known ligands of CR3. These studies thus indicate that CR3 functions as a receptor not only for C3bi but also for fibrinogen.     

Global right atrial mapping delineates double posterior lines of block in patients with typical atrial flutter: a study using a three dimensional noncontact mapping system

Double Posterior Lines of Block in Typical Atrial Flutter. INTRODUCTION: The crista terminalis (CT) has been shown to be a barrier to transverse conduction during typical atrial flutter (AFL). However, some studies have demonstrated the presence of functional block in the sinus venosa region but not at the CT. The aim of this study was to define these regions of block in the right atrium using a three-dimensional noncontact mapping system. METHODS AND RESULTS: In 39 AFL patients (33 men and six women, mean age 56 +/- 13 years), a noncontact multielectrode array was used to reconstruct electrograms in the right atrium. Isochronal and isopotential propagation mapping was performed during AFL and during pacing from the coronary sinus ostium and the low lateral wall (cycle length from 600 to 240 msec) in sinus rhythm after creation of isthmus block. A single line of block along the CT area was found in 18 patients (46%). Two lines of block were found in 21 patients (54%), with the first line located along the CT area. The second was located in the sinus venosa region in 20 patients (51%) and in the lateral wall in 1 patient (3%). In all patients, the block in the lower part of the CT was observed during AFL (60%) and during pacing at all cycle lengths (48%-62%). The length and proportion of block were inversely proportional to pacing cycle length. CONCLUSION: Double lines of block were frequently observed in patients with AFL, and both lines may form the posterior boundaries of the AFL circuit. Block was fixed in the lower part of the CT and was functional in the upper part of the CT.     

Atrial flutter update

Typical atrial flutter has long been considered a reentrant arrhythmia, but it is only recently that the full structure of the right atrial circuit was understood, leading to de devise of ablation techniques. Recognition of the role of functional block, based on anisotropic conduction was crucial to understanding of the flutter circuit. Anisotropy at the terminal crest creates a line of block that, with the orifices of superior and inferior vena cava, constitutes the posterior boundary of the flutter circuit. The anterior boundary is the tricuspid ring, and the circuit is a ring of myocardium made by the septal and anterior right atrial walls, linked on top by the right atrial roof and inferiorly by the inferior vena cava-tricuspid ring isthmus. This isthmus, a relatively narrow part of the circuit, has become the established target for typical flutter ablation. Complete, bidirectional isthmus block is the final goal of flutter ablation. This has to be assessed, after flutter interruption, by pacing both sides of the ablation line while recording electrogram sequences from the opposite right atrial wall and the isthmus itself. Success is great in terms of prevention of flutter recurrence, however a 30% incidence of atrial fibrillation during follow-up casts a large shadow on long-term prognosis.Understanding of the myocardial abnormalities underlying atrial flutter and fibrillation will be necessary to improve this long-term outlook.     

Use of multisite electroanatomic mapping to facilitate ablation of intra-atrial reentry following the Mustard procedure

Ablation of intra-atrial reentrant tachycardia following Mustard or Senning procedures has low success rates. The Biosense Carto system was used to map intra-atrial reentry in a 22-year-old woman who had undergone a Mustard procedure. A line of block was created connecting a Mustard baffle suture line to the tricuspid valve annulus, which terminated the arrhythmia and prevented its reinitiation. Multisite electroanatomic mapping was invaluable in defining atrial anatomy and the intra-atrial reentrant pathway, and in creating a contiguous line of block. This mapping may improve ablation success rates in patients following the Mustard or Senning repair.     

Voltage-guided ablation technique for cavotricuspid isthmus-dependent atrial flutter: refining the continuous line

Ablation of the cavotricuspid isthmus has become first-line therapy for "isthmus-dependent" atrial flutter. The goal of ablation is to produce bidirectional cavotricuspid isthmus block. Traditionally, this has been obtained by creation of a complete ablation line across the isthmus from the ventricular end to the inferior vena cava. This article describes an alternative method used in our laboratory. There is substantial evidence that conduction across the isthmus occurs preferentially over discrete separate bundles of tissue. Consequently, voltage-guided ablation targeting only these bundles with large amplitude atrial electrograms results in a highly efficient alternate method for the interruption of conduction across the cavotricuspid isthmus. Understanding the bundle structure of conduction over the isthmus facilitates more flexible approaches to its ablation and targeting maximum voltages in our hands has resulted in reduction of ablation time and fewer recurrences.     

Isolation of a Chinese hamster fibroblast mutant defective in hexose transport and aerobic glycolysis: its use to dissect the malignant phenotype.

A procedure is described for the selection of glucose uptake mutants based upon radiation suicide of Chinese hamster fibroblasts by 2-deoxy[3H]glucose. In one of these mutants, DS 7, the ability to transport either 2-deoxyglucose or 3-O-methylglucose was decreased to one-fifth to one-fourth. Besides this defect, DS7 produces 1/14th the lactic acid produced by the parent when grown on 5 mM glucose. This block in aerobic glycolysis is due to a mutation that affects the expression of the phosphoglucose isomerase gene because no isomerase activity is detected in cell extracts of DS7. This glycolytic block makes that cell line dependent exclusively on respiration for its energy requirement. Consequently, DS7 survives well after removal of glucose but dies quickly in the presence of oligomycin. The parental line O23 (subclone of CCl39) grows at low serum concentration, is anchorage-independent, and is tumorigenic in nude mice. The derived glycolytic mutant DS7 has retained both the in vitro transformed phenotype (low serum dependence and loss of anchorage dependence) and the tumor-forming capability. The tumor cells derived from the injection of DS7 cells have kept the original glycolytic defect. This finding suggests that the transformed properties (high hexose transport and aerobic glycolysis) that can be uncoupled from abnormal growth control are not necessary for the expression of the malignant phenotype in fibroblasts.     

Utility of virtual unipolar electrogram morphologies to detect transverse conduction block and turnaround points of typical atrial flutter

Background

Noncontact mapping is useful for the diagnosis of various arrhythmias. Virtual unipolar electrogram morphologies (VUEM) of the conduction block and the turnaround points, however, are not well defined. We compared the VUEM characteristics of a transverse conduction block in the posterior right atrium (RA) with those of contact bipolar electrograms obtained during typical atrial flutter (AFL).

Methods

Contact bipolar electrograms were used to map the posterior RA during typical AFL in 16 patients. Twenty points of the VUEM recorded along the block line were analyzed and compared with contact bipolar electrograms.

Results

Seventeen AFLs were analyzed. Fifteen AFLs showed an incomplete transverse conduction block in the posterior RA by contact bipolar mapping. A double potential on the block line corresponded to the two components of the VUEM, in which the second component showed an Rs, RS, or rS pattern. At the turnaround point, a fused double potential of the contact bipolar electrograms corresponded to a change of the second component of the VUEM from an rS to a QS morphology. Two AFLs showed a complete block line in the posterior RA. The contact bipolar electrogram showed double potentials from the inferior vena cava to the superior vena cava, whereas the second component of the VUEM remained in an unchanged Rs, RS, or rS pattern.

Conclusion

VUEM analysis was a reliable method for identifying the posterior block line during AFL. This method may also be applicable for detecting block lines and turnaround points of circuits in other unmappable arrhythmias.     

Caveolae from luminal plasmalemma of rat lung endothelium: microdomains enriched in caveolin, Ca(2+)-ATPase, and inositol trisphosphate receptor.

A distinctive feature of many endothelia is an abundant population of noncoated plasmalemmal vesicles, or caveolae. Caveolae have been implicated in many important cellular processes, including transcytosis, endocytosis, potocytosis, and even signal transduction. Because caveolae have not been purified from endothelial cell surfaces, little is known directly about their structure and function in the endothelium. To delineate the transport role of these caveolae, we purified them from isolated luminal endothelial plasma membranes of rat lung. The rat lung luminal endothelial cell surfaces were isolated after coating them, in situ, with positively charged colloidal silica. The caveolae were then separated from these coated membranes and purified to yield a homogeneous population of morphologically distinct vesicles enriched in the structural protein caveolin. As with caveolae found on the endothelial cell surface in vivo, these highly purified caveolae contained the plasmalemmal Ca(2+)-ATPase and inositol 1,4,5-trisphosphate surface receptors. By contrast, other plasma membrane proteins were excluded from the caveolae, including angiotensin-converting enzyme, beta-actin, and band 4.1. The purified caveolae appeared to represent specific microdomains of the cell surface with their own unique molecular topography.     

Prospective evaluation of a simplified approach for common atrial flutter radio frequency ablation with only two catheters.

Intra-atrial conduction block within the inferior vena cava-tricuspid annulus isthmus (IVCT) has been shown to predict successful common atrial flutter ablation. However, its demonstration requires the use of several electrode catheters and mapping of the line of block. The aim of this study was prospectively to test the feasibility of a simplified ablation procedure using only two catheters. METHODS: Radio frequency (RF) ablation of common atrial flutter was performed in 30 patients with the sole use of a catheter for atrial pacing and a RF catheter. RF ablation lesions were created in the IVCT. Surface ECG criteria were used to monitor the conduction within the IVCT. The end point during low lateral atrial pacing was an increment in the interval between the pacing artefact and the peak of the R wave in surface lead II >50 ms and clockwise rotation of the P wave axis beyond -30 degrees and inferiorly. Then, the line of lesions was mapped during atrial pacing with the RF catheter. Additional RF lesions were applied if mapping disclosed a zone of residual conduction. Otherwise the procedure was stopped if mapping showed parallel double potentials all along the line. Finally, the block was reassessed with a 'Halo' catheter. RESULTS: Surface ECG criteria were met in 26 patients. Mapping the line of lesions showed a complete corridor of parallel double potentials in these 26 cases and in 3 of the 4 patients in whom ECG criteria were not met. Conduction evaluated with the Halo catheter showed bi-directional complete block in these 29 patients. After a follow-up of 16 +/- 4 months there was no recurrence of atrial flutter. CONCLUSION: Surface ECG criteria combined with mapping of the line of block demonstrate evidence of bi-directional IVCT block. This simplified RF ablation of common atrial flutter is feasible with a low recurrence rate.     

Coupling interval, exit block, and periodicity of ventricular parasystolic rhythm.

The electrocardiograms in this study of parasystolic rhythm were tape recorded and then analysed with a special purpose hybrid computer. The rate of appearance of specific inter-ectopic intervals was shown to change significantly with small changes in either the sinus or parasystolic pacemaker period. Natural changes in the period of the ectopic pacemakers were observed over several hours. Changes amounting to 14% within 10 min and 18% overall were observed in one patient, and a gradual lengthening of 10% over 3 h in another. A previously undescribed form of exit block has been discovered in one patient where the block remained active for a given time only after propagation from the parasystolic focus. Different interectopic intervals were shown to contribute to specific and restricted coupling interval locations in diastole. Hence this form of exit block, by preventing some inter-ectopic intervals from propagating, limited the locations in diastole in which parasystolic ectopic complexes could appear. In this case later diastolic complexes were inhibited and hence fusion complexes were completely absent. Parasystolic rhythm, with and without the exit block described, was simulated successfully by a digital computer. The simulations aided our understanding of the clinical data.