Implantable Transvenous Pacing Leads:

With the dawn of a new millennium, physicians' demands for very thin transvenous leads able to be positioned in nontraditional sites like the Bachmann's bundle, the high and mid-right ventricular septum, and the His bundle have created new and exciting challenges for lead engineers. Bipolar leads can now be as thin and reliable as unipolar leads. Cathode electrodes are very small, porous, and demonstrate high impedance. To optimize stimulation thresholds, steroid-eluting passive- and active-fixation electrodes have become popular for use in the atrium and ventricle. To create thin lead body diameters, new insulation and conductor materials and lead body designs are necessary. Hybrid medical materials having the best features of silicone rubber and polyurethane will allow for reliable insulation. Conductor cables instead of helical coils permit strong thin diameter leads to be designed. Transvenous lead implantation using the traditional stylet may not be possible with thin diameter leads, necessitating the use of sophisticated workstations using steerable catheters to guide these new active-fixation leads to selective sites in the right heart. The pacing lead of the future may be very different from the one used today. Ironically, it will have features and implantation techniques similar to the transvenous leads designed prior to the use of the stylet. We are now approaching full circle in lead development, retracing the footprints of the early implanters of three and a half decades ago. (PACE 2004; 27[Pt. II]:887–893)     

Electrocardiographic and Clinical Predictors of Torsades de Pointes Induced by Almokalant Infusion in Patients with Chronic Atrial Fibrillation or Flutter: A Prospective Study

The aim of this study was to identify predictors of torsades de pointes (TdP) in patients with atrial fibrillation (AF) or flutter exposed to the Class III antiarrhythmic drug almokalant. TdP can be caused by drugs that prolong myocardial repolarization. One hundred patients received almokalant infusion during AF (infusion 1) and 62 of the patients during sinus rhythm (SR) on the following day (infusion 2). Thirty-two patients converted to SR. Six patients developed TdP. During AF, T wave alternans was more common prior to infusion (baseline) in patients developing TdP (50% vs 4%, P < 0.01). After 30 minutes of infusion 1, the TdP patients exhibited a longer QT interval (493 ± 114 vs 443 ± 54 ms [mean ± SD], P < 0.01), a larger precordial QT dispersion (50 ± 74 vs 27 ± 26 ms, P < 0.05), and a lower T wave amplitude (0.12 ± 0.22 vs 0.24 ± 0.16 mV. P < 0.01). After 30 minutes of infusion 2, they exhibited a longer QT interval (672 ± 26 vs 489 ± 74 ms, P < 0.001), a larger QT dispersion in precordial (82 ± 7 vs 54 ± 52 ms, P < 0.01) and extremity leads (163 ± 0 vs 40 ± 34 ms, P < 0.001), and T wave alternans was more common (100% vs 0%, P < 0.001). Risk factors for development of TdP were at baseline: female gender, ventricular extrasystoles, and treatment with diuretics; and, after 30 minutes of infusion: sequential bilateral bundle branch block, ventricular extrasystoles in bigeminy, and a biphasic T wave. Patients developing TdP exhibited early during almokalant infusion a pronounced QT prolongation, increased QT dispersion, and marked morphological T wave changes.     

‘How Do You Remember You Ate…?’: A Delphi Technique Study to Identify Retrieval Categories From Fourth-Grade Children

Objective To develop and validate a consensus set of retrieval categories for how children remember what they have eaten, and to relate retrieval categories to accuracy of reporting items eaten during school lunch.Design A Delphi technique study was conducted using 10 psychologists. The subject matter consisted of responses transcribed from interviews conducted with 89 randomly selected fourth graders within 90 minutes of eating. Retrieval categories were evaluated for accuracy by comparing students’ self-reported lunch intake with observation.Statistical analyses For round 1, a centroid hierarchical cluster analysis was used to identify common sets of rating pairs to propose categories for reaching consensus. For rounds 2 and 3, percent of agreement was calculated. Accuracy was tabulated across meal items and student use by retrieval category.Results After round 3, we found that 23 “near-consensus”categories were used by at least eight raters. Six categories were used 60% of the time, 4 were used 20% of the time, and 5 were used 15% of the time. Less frequently used categories were combined with similar, more frequently used categories for a total of 16 categories. Students used a large variety of retrieval categories when accurately reporting consumption. Of the 16 categories, 12 were used similarly by both accurate and inaccurate students. Where there were differences in accuracy by retrieval category, the more accurate students used “taste/smell/texture”and “visual”in deference to “order items consumed”and “oral cue still present.”Applications These categories provide insight into the broad range of retrieval categories that children use and provide direction for researchers to design and study specific cues to enhance the accuracy of children's self-reports of diet. J Am Diet Assoc. 1997;97:31–36.     

Electrode Configurations for a Respiratory Impedance Measurement Suitable for Rate Responsive Pacing

A rate responsive cardiac pacemaker will benefit the patient only if the input parameter is a reliable indicator of exercise, Part of the reliability is dependent upon selection of the best physiological parameter and part is dependent upon the measurement technique. Twenty-six patients have been studied in order to ascertain the best measurement configuration for an intravascular impedance respiratory monitor. Four electrode configurations have been examined at rest and during exercise. The results have been compared using measures of sensitivity and specificity. The ideal configuration requires that a current field be established between the right ventricular blood and the pacemaker case. And, that voltage sensing be done between an electrode in the SVC and the pacemaker case.     

Antibody Mediated Complete Congenital Heart Block in the Fetus

Complete congenital heart block (CCHB) affects 1:20,000–25,000 live births and is usually an atrioventricular block; 30–50% of fetuses with CCHB will have a structural anomaly, though recently attention has focused on the etiological influence of autoimmune disease, such as systemic lupus erythematosus. The diagnosis is established by detailed two-dimensional ultrasound scanning of the heart to exclude anomaly coupled with M-mode echocardiography and Doppler blood velocity patterns in the major vessels to detect the uncoupling of atrial and ventricular rhythms. Risk factors for an affected child are discussed. A previously affected child, high titers of anti-Ro antibodies, the presence of anti-Ro (SS-A) and anti-La (SS-B), and maternal HLA DR3 confer high risk. Antibody mediated CCHB is irreversible. Plasmapheresis and immunosuppression have been attempted in affected mothers, with limited success, to reduce the likelihood of the fetus being affected, and steroids have been used to reduce the inflammatory reaction in the heart. In many cases the underlying pathology of the immune system adversely affects utero-placental function requiring careful monitoring of fetal well-being. CCHB renders fetal heart rate monitoring virtually useless, in the antenatal and intrapartum periods. Alternatives are explored.     

The Broiler Chicken as a Model for Immunotoxicity Assessment: 1. Standardization of in Vitro Immunological Assays

The Broiler Chicken as a Model for Immunotoxicity Assessment.1. Standardization of in Vitro Immunological Assays. BAECHER-STEPPAN,L., NAKAUE, H. S., MATSUMOTO, M., GAINER, J. H., AND KERKVLIET,N. I. (1989). Fundam. Appl. Toxicol. 12, 773–786. Thebroiler chicken was developed as an alternative animal modelto laboratory rodents for immunotoxico-logic assessment. Invivo treatment with 100–200 mg/kg cyclophosphamide (CY)was used as a known immunosuppressive treatment to standardizethe assay systems. Protocols for assessing specific immunologicalfunctions were developed in specific pathogen-free (SPF) broilersto measure lymphocyte blastogenesis to T-cell (concanavalinA and phytohemagglutinin) and B cell (Staphylococcus aureuscells) mitogens, delayed-type hypersensitivity (Dm) to tuberculin,natural killer (NK) cell cytotoxicity, plaque-forming cell (PFC)response to sheep red blood cells (SRBC), and serum antibodytiters to SRBC. CY was an effective immunosuppressant in thebroiler system for assessment of lymphocyte responsiveness tomitogenic stimulation, DTH reactivity, and the antibody responceto SRBC as assessed by PFC and serum antibody titers. NK cytotoxicitywas not altered on a cellular level following treatment withCY at a dose that preduced greater than 75% depletion of spleencellularity. However, under these conditions, it must bc assumedthat the capacity of CY-treated birds to mediate NK effectorfunctions would be reduced. These results demonstrate the applicabilityof the broiler chicken as an animal model for immunotoxicitytesting.     

Linkage relationships between the three phosphoglucomutase loci PGM1, PGM2 and PGM3

1. Phosphoglucomutase phenotypes have been studied in several generations of the family of an individual heterozygous at each of the three loci, PGM₁, PGM₂, and PGM₃. 2. PGM₁ and PGM₂ phenotypes were determined using red cells. Fibroblasts grown in tissue culture were used for PGM₃ phenotyping. 3. The family results support the genetical hypothesis based on the analysis of dizygotic twin pairs that the PGM₃ isozyme patterns found in the placenta are determined by two alleles, PGM¹₃ and PGM²₃. 4. Locus PGM₃ is not closely linked to locus PGM₂ 5. The data also support the previous findings that locus PGM₁ is not closely linked to PGM₂ or PGM₃.