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Human Histopathology of Electroanatomic Mapping After Cooled-Tip Radiofrequency Ablation to Treat Ventricular Tachycardia in Remote Myocardial Infarction (2005)

DENEKE, THOMAS ; MÜLLER, KLAUS-MICHAEL ; LEMKE, BERND ; [et al.]

350 Main Street , Malden , MA 02148-5018 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc

Journal of cardiovascular electrophysiology 16 (2005), S. 0

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ISSN: 1540-8167

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Medicine

Notes: Introduction: Catheter ablation of ventricular tachycardia (VT) in remote myocardial infarction (MI) often requires excessive mapping procedures. Documentation of the electrical substrate via electrogram amplitude may help to identify regions of altered myocardium resembling exit areas of reentrant VTs. Methods and Results: A patient with multiple symptomatic monomorphic VTs (biventricular ICD, remote MI) underwent electroanatomic substrate mapping (CARTO™) for VT ablation. Regions of scar (bipolar electrogram amplitudes ≤0.5 mV), normal myocardium (≥1.5 mV), and “altered” myocardium (0.5–1.5 mV) were identified. Ablation was directed to regions with “altered” myocardium based on pace map correlation. After ablation the clinical VT did not reoccur. The patient died due to worsening of heart failure 7 days afterward. During postmortal evaluation specified sites of electroanatomic mapping were correlated to histopathological findings. Annotated scar areas were documented to consist of areas with massive fibrosis (≥80% of mural composition). Ablations were found to span through regions with intermediate fibrosis (21–79%) mapped as “altered” myocardium. Ablation produced transmural coagulation necrosis of mesh-like fibrotic tissue with interspersed remnants of myocardial cells up to a maximum depth of 7.0 mm. Subendocardial intramural bleedings were universal findings 7 days after ablation. Conclusions: Electroanatomic substrate mapping for VT ablation sufficiently identified regions of scar and normal myocardium. Regions with bipolar electrogram amplitudes between 0.5 and 1.5 mV were found to correlate to areas of “intermediate” fibrosis (21–79%) with only remnant strands of myocardial cells and were identified as target region for ablation. Cooled-tip endocardial radiofrequency ablation lead to transmural coagulation necrosis up to a depth of 7.0 mm.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1540-8167.2005.40826.x

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Modifications of the Extrusion Process of Magnesium Alloys for Improved Mechanical Properties (2008)

Mueller, Soeren ; Mueller, Klaus ; Reimers, Walter

s.l. ; Stafa-Zurich, Switzerland

Key engineering materials Vol. 367 (Feb. 2008), p. 9-16

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ISSN: 1013-9826

Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: In the course of the increasing discussions about a reduction of the CO2 emissionsmagnesium has gained importance since it is the lightest metal for structural applications. Currentlymagnesium alloys are almost exclusively used as cast parts in the automotive industry because dueto their microstructure extruded magnesium profiles exhibit a strong asymmetry in the mechanicalproperties under tensile and compressive loading (strength differential effect).In order to improve the mechanical properties a detailed knowledge about the influence of thedifferent extrusion parameters on the microstructure of the extrudates is necessary. Therefore, theparameters extrusion method, billet temperature, product speed, extrusion ratio and coolingcondition were varied for the extrusion of the magnesium alloys AZ31, AZ61 and AZ80.Subsequently the microstructure was analyzed and the mechanical properties determined. With anadditional analysis of the deformation modes of the extruded and cold deformed products it couldbe discovered that an improvement of the mechanical properties can be achieved by a modificationof the extrusion process.Since the strength differential effect in caused by twinning which due to the texture of theextrudates is only active under a compressive loading along the extrusion direction the modificationof the extrusion process aims at a suppression of this twinning. Because on the one hand comparedto that for dislocation glide the Hall-Petch-Constant for twinning is bigger a grain refinement of theextruded products could be achieved by a predeformation using ECAE similar processes. On theother hand a process has been developed where the profiles are extruded into a hydrostatic counterpressure in order to alter the texture during the extrusion. Thereby the twinning is already activatedduring the extrusion. Both modifications of the extrusion process result in an increase of the criticalresolved shear stress for twinning during the subsequent cold deformation and thus in improvedmechanical properties