Different Types Of Variants Research Articles

Variants of preexcitation--specialized atriofascicular pathways, nodofascicular pathways, and fasciculoventricular pathways: electrophysiologic findings and target sites for radiofrequency catheter ablation.

In the present report, the electrophysiologic findings in patients with different types of variants of preexcitation, i.e., atriofascicular, nodofascicular, and fasciculoventricular fibers, and the results of radiofrequency catheter ablation using different target sites are described. Twelve patients (mean age 36 +/- 17 years) with variants of the preexcitation syndromes underwent electrophysiologic study and radiofrequency catheter ablation. The atrial origin of atriofascicular pathways remote from the normal AV node was assessed by application of late atrial extrastimuli that advanced ("reset") the timing of the next QRS complex without anterograde penetration into the AV node. In patients with atriofascicular pathways, ablation of the accessory pathway or the retrograde fast AV node pathway was attempted. Ablation of the atriofascicular pathways was guided by a stimulus-delta wave interval mapping in the first five patients and by recording of atriofascicular pathway activation potentials in the next five patients. A nodofascicular pathway was suggested if VA dissociation occurred during tachycardia and if atrial extrastimuli failed to reset the tachycardia without anterograde penetration into the AV node. A fasciculoventricular connection was suggested if the proximal insertion of the accessory pathway was found to arise from the His bundle or bundle branches. The PR interval was expected within normal limits during sinus rhythm and the QRS complex to be slightly prolonged with a discrete slurring of the R wave, suggesting a small delta wave. Ten of the 12 patients had evidence for atriofascicular pathways and one patient each for a nodofascicular and fasciculoventricular pathway. In six patients, the atriofascicular pathways were successfully ablated, and in two patients, the retrograde fast AV node pathway. In one patient, a concealed right posteroseptal accessory AV pathway served as the retrograde limb and was successfully ablated. The nodofascicular pathway was shown to be a bystander during AV node reentrant tachycardia. After successful fast AV node pathway ablation resulting in marked PR prolongation, no preexcitation was present during sinus rhythm because of the proximal insertion of the nodofascicular pathway distal to the delay producing parts of the AV node. The proximal insertion of the fasciculoventricular pathway was suggested to arise distal to the AV node at the site of the penetrating AV bundle. The earliest ventricular activation at the His-bundle recording site indicated the ventricular insertion of this accessory connection into the ventricular summit. The fasciculoventricular connection gave rise to a fixed ventricular preexcitation and served as a bystander during orthodromic AV reentrant tachycardia incorporating a left-sided accessory AV pathway. The majority of patients with variants of the preexcitation syndrome present with specialized atriofascicular pathways that seem to originate from remnants of the specialized AV ring tissue. Nodofascicular and fasciculoventricular pathways exist and may give rise to preexcitation, although their functional role in participation of clinical arrhythmias still needs to be elucidated. In the present study, both a fasciculoventricular pathway and a nodofascicular pathway acted as a bystander.

The effect of variant chromosomes on reproductive fitness in man.

Reproductive fitness of carriers of heterochromatic variants of the human karyotype was found to be normal. The method was based on a comparison between known carriers and known non-carriers from the same pedigree in respect of live births, generation time and survival of offspring to reproductive age. A subset of the data had been included in an earlier study in which reproductive fitness of carriers was found to be significantly reduced. Our analysis suggests that the result may have been fortuitous, since it was not supported by the additional data. There was no evidence of heterogeneity between carriers of different types of variant or of different sex. There were indications of increased fetal losses to carriers, but the number of spontaneous abortions was insufficient to produce a detectable effect on gross reproductive fitness.

Intracellular immunoglobulin chain synthesis in non-secreting variants of a mouse myeloma: Detection of inactive light-chain messenger RNA

The intracellular immunoglobulin chain content of a number of non-secreting variants of MOPC 21 mouse myeloma cells has been examined. Pulse-labelling with [ 14C]lysine, followed by cell lysis, reaction with antibody and analysis of the precipitates on sodium dodecyl sulphate-polyacrylamide gels, reveals three different types of variant. Only one type (NS I) contains light-chains. An abnormal heavy-chain was present in all non-secreting lines and was prominent in one cell line (NS II/1). Pulse-chase experiments indicated a rate of decay of intracellular immunoprecipitable material comparable to its rate of synthesis suggesting intracellular destruction of non-secreted chains. The presence of polyribosomes engaged in immunoglobulin chain synthesis was tested by their addition to a reticulocyte cell-free system. It was confirmed that in the parental cell line immunoglobulin chain synthesis is almost exclusively confined to membrane-derived polyribosomes. Failure of some of the variants (NS II/1 and NS III/1) to synthesize light-chain was not due to misallocation of light-chain mRNA to the free polyribosomes. Isolated 13 S mRNA from the same variants also failed to direct the synthesis of detectable light-chain in the reticulocyte cell-free system. However, fingerprint analysis of the corresponding 32P-labelled 13 S mRNA showed the presence of several oligonucleotides characteristic of the normal light-chain mRNA, indicating the presence of an inactive form of this molecule.

Additional Data and Summary for Albumin-Gc Linkage in Man

Lod scores for linkage of the albumin and Gc loci have been calculated for 21 pedigrees in which six different types of albumin variants are segregating. There is no evidence for heterogeneity in the linkage distance among the different types of variants. The most likely value for the recombination fraction in the combined data is at Ô = 0.023.

Penicillin-resistant and penicillin-dependent staphylococcal variants.

SUMMARY: Four strains of Staphylococcus aureus (coagulase-positive) were each subjected to three or more series of transfers on penicillin ditch plates. The plates were examined for colonial variants and four quite distinct types of penicillin-resistant variant, one of which was penicillin-dependent, were isolated. These types often occurred in association, and sometimes as many as three were isolated from a single culture plate. The main characteristics of the different types are described. Studies on the incidence of penicillin-resistant bacterial variants began soon after the isolation of the antibiotic and have continued in increasing numbers (see Abraham et al. 1941; Todd, Turner & Drew, 1945; Demerec, 1945, 1948; Bellamy & Klimek, 1948; Gale & Rodwell, 1948; Hughes, 1952). In most studies of this description bacteria have been subcultured in fluid medium containing increasing concentrations of penicillin. In the present investigation solid medium was used to determine whether different types of variant could be isolated from the same culture.