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Biomedical subjects

R Leather

Publications and source records attributed to R Leather.

11 recordsLinked to original sources
PubMed1991

High success rate of atrioventricular node ablation with radiofrequency energy.

Radiofrequency current was introduced as an alternative energy source for transcatheter ablation of cardiac arrhythmias to avoid the complications associated with direct current shocks. Initial use of radiofrequency current for complete ablation of the atrioventricular (AV) node yielded only moderate success rates, presumably because of the small size of electrodes and difficulty in localizing the AV node. The use of a larger 4-mm tip electrode for delivery of radiofrequency current and a method to better localize the AV node were prospectively studied in 32 patients undergoing catheter ablation of the AV node. There were 21 men and 11 women with a mean age of 62 +/- 12 years. Complete AV block was achieved immediately in 31 patients (97%) and it persisted in 28 patients (88%) during a mean follow-up period of 12 +/- 6 months. Three patients who had return of AV condition required no drug therapy for control of ventricular rate during atrial fibrillation. The number of radiofrequency pulses used to achieve complete AV block ranged from 1 to 5 (mean 1.9 +/- 1.1). In greater than 50% of the cases, only one radiofrequency pulse was required. The mean power and duration of radiofrequency pulses were 21.2 +/- 4.5 W and 33 +/- 15 s, respectively. All patients developed a stable junctional escape rhythm within 45 min of successful ablation. The QRS configuration was unchanged in 30 patients. One patient had a new right bundle branch block after ablation. There were no complications related to the ablation procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Clinical and experimental evaluation of aortic polytetrafluoroethylene grafts for aneurysm replacement.

The aortic expanded polytetrafluoroethylene bifurcation graft has a unique taper design. This was studied in an in vitro model using hydrogen bubbles and colored dyes to assess its hemodynamic significance compared with a conventional nontapered graft model. Under conditions of nonpulsatile flow the only significant differences were seen with a high percentage of occlusions of one outflow limb. Clinical experience with this new graft for infrarenal aneurysm replacement was accumulated in 163 elective cases and 53 emergency cases. The results with this new graft were compared with those obtained in the same time frame with alternative Dacron grafts. No detrimental problems with the graft have appeared in its use up to 78 months following aneurysm bypass or replacement.

Aged↗
PubMed1983

Myogenic differentiation of L6 rat myoblasts: evidence for pleiotropic effects on myogenesis by RNA polymerase II mutations to alpha-amanitin resistance.

To assess the functional role of RNA polymerase II in the regulation of transcription during muscle differentiation, we isolated and characterized a large number of independent alpha-amanitin-resistant (AmaR) mutants of L6 rat myoblasts that express both wild-type and altered RNA polymerase II activities. We also examined their myogenic (Myo) phenotype by determining their ability to develop into mature myotubes, to express elevated levels of muscle creatine kinase, and to synthesize muscle-characteristic proteins as detected by two-dimensional polyacrylamide gel electrophoresis. We found a two- to threefold increase in the frequency of clones with a myogenic-defective phenotype in the AmaR (RNA polymerase II) mutants as compared to control ethyl methane sulfonate-induced, 6-thioguanine-resistant (hypoxanthine, guanine phosphoribosyl transferase) mutants or to unselected survivors also exposed to ethyl methane sulfonate. Subsequent analysis showed that about half of these myogenic-defective AmaR mutants had a conditional Myo(ama) phenotype; when cultured in the presence of amanitin, they exhibited a Myo- phenotype; in its absence they exhibited a Myo+ phenotype. This conditional Myo(ama) phenotype is presumably caused by the inactivation by amanitin of the wild-type amanitin-sensitive RNA polymerase II activity and the subsequent rise in the level of mutant amanitin-resistant RNA polymerase II activity. In these Myo(ama) mutants, the wild-type RNA polymerase II is normally dominant with respect to the Myo+ phenotype, whereas the mutant RNA polymerase II is recessive and results in a Myo- phenotype only when the wild-type enzyme is inactivated. These findings suggest that certain mutations in the amaR structural gene for the amanitin-binding subunit of RNA polymerase II can selectively impair the transcription of genes specific for myogenic differentiation but not those specific for myoblast proliferation.

Amanitins↗
PubMed1980

Pathologic interactions between prosthetic aortic grafts and the gastrointestinal tract. Clinical problems and a new experimental approach.

Twenty-one patients presented with pathologic interactions between the gastrointestinal tract and aortic grafts. Seventeen patients were managed by excision of the graft and axillobifemoral bypass. Six patients died. four deaths were due to disruption of the proximal aortic stump after initial therapy that appeared successful. An experimental model of a seromuscular jejunal patch is presented that may be beneficial for closure of the proximal aortic stump.

Animals↗