Increasing concentrations of MgADP- or MgCDP- in the millimolar range cause an increase in the maximum Ca2+ -activated tension that a skinned rabbit soleus muscle fiber can develop in the presence of 2 mM MgATP2- or MgCTP2- respectively. In contrast, the maximal Ca2+ -activated ATPase activity of the fiber decreases in the presence of MgADP-. As the nucleoside diphosphate (MgADP- or MgCDP-) concentration is increased, the Ca2+ concentration required for half-maximal activation of tension is reduced. MgADP- has a similar effect on the Ca2+ concentration required to half-maximally activate the fiber ATPase. The effects on tension are due to magnesium nucleoside diphosphate and not some other form of nucleoside diphosphate since the effects occur at both low (pMg 4) and control (pMg 3) Mg2+ concentrations. Cooperativity, as judged by the Hill "n" value relating isometric tension and Ca2+, is less in the presence of 5 mM MgADP- as compared to a control (no added MgADP-) "n" value. Increasing concentrations of inorganic phosphate (Pi) in the millimolar range decrease maximum Ca2+ -activated tension, and increase the concentration of Ca2+ required to half-maximally activate tension, effects opposite to those of MgADP. These data are consistent with the hypothesis that cooperative interactions between actin and myosin can affect the affinity of troponin for Ca2+.
PURPOSE. Use of nomograms based on the "heparin correlation value" (HCV)-a value that corresponds to measured activated partial thromboplastin time (aPTT) and that removes the need to revise nomograms in response to a change in the aPTT reagent or coagulometer used-was evaluated as an alternative to traditional aPTT-based anticoagulation nomograms. SUMMARY. Data were collected on patients receiving heparin therapy for selected indications (thrombotic disorders, cardiac conditions, and acute coronary syndromes) during four-month periods before (n = 59) and after (n = 60) implementation of the HCV-based nomograms. The primary endpoints were the rate at which coagulation laboratory measurements were obtained at the appropriate time and the rate of appropriate dosage adjustment in response to reported laboratory values; secondary endpoints included the time to attainment of the first target anticoagulation value. After implementation of HCV-based nomograms, coagulation laboratory measurements were obtained at the appropriate time in (mean ± S.D.) 92.9% ± 12.8% of patients, compared with 80.1% ± 15.5% of patients who received aPTT-based monitoring (p < 0.0001). After implementation of HCV-based monitoring, the rate of correct heparin dosage adjustments was improved (mean ± S.D. 94.7% ± 7.8% versus 89.3% ± 14.0%, p = 0.01), and the time to attainment of the first target anticoagulation value was shorter (mean ± S.D. 16.4 ± 10.6 hours versus 21.5 ± 14.8 hours, p = 0.03). CONCLUSION. The HCV, which relates measured aPTT values to corresponding antifactor Xa concentrations, was substituted for aPTT in heparin nomograms and appeared to be a viable alternative to the aPTT.
A comparison of 24-hour courses of magnesium replacement therapy showed that magnesium sulfate 2 g i.v. was associated with larger changes in SMC than magnesium oxide 800, 1200, or 1600 mg orally when the baseline SMC was 1.4-1.8 mg/dL. At baseline SMCs of 1.4-1.8 mg/dL, oral magnesium oxide provided a consistent median increase in SMC of 0.1 mg/dL. The change in the number of bowel movements did not differ significantly between courses of i.v. magnesium sulfate and oral magnesium oxide.
Purpose To determine if hospital consultant recommendations were clinically applicable to the cardiac catheterization laboratory and to compare medication usage in percutaneous coronary intervention (PCI) to those goals. Methods The medical records of 96 adults on whom PCI had been performed over a 6-month period were reviewed retrospectively. Only PCIs that included intracoronary stent placement were considered. The primary end point was to determine if abciximab usage was 15% or less in all PCI cases. Secondary end points evaluated the use of abciximab, eptifibatide, and bivalirudin based on the acuity of the clinical syndrome. Results Abciximab, eptifibatide, and bivalirudin monotherapy were used in 16.7%, 40.6%, and 42.7% of all cases, respectively. The total consumption of abciximab exceeded the primary end point by 1.7%. Eptifibatide usage was 71% of all glycoprotein (GP) IIb/IIIa inhibitors, less than the 85% target proposed by the hospital consultants. Bivalirudin monotherapy surpassed eptifibatide as the antithrombotic of choice across all PCI cases. The use of provisional GP IIb/IIIa inhibitors in conjunction with bivalirudin was 8.3%, more than the 5% target specified by the consultants. Emergent PCIs comprised 41% of all cases sampled. Conclusion This 6-month retrospective survey demonstrated that the use of abciximab exceeded the percentage recommended by consultants. However, given the large percentage of emergent PCIs during the time period and the literature supporting the use of abciximab in emergent PCIs, a change in GP IIb/IIIa inhibitor usage patterns was not considered necessary.
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