[Prospectives in catheter ablation: treatment of atrial fibrillation and recurrent post-infarct ventricular tachycardia].
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Atrial Fibrillation↗
Biomedical subjects
S Riva
Publications and source records attributed to S Riva.
[Analysis of changes in repolarization for the differential diagnosis of narrow QRS supraventricular tachycardia and the site of the accessory pathway].
In view of the growing role of catheter ablation techniques for the treatment of supraventricular tachycardia, noninvasive determination of tachycardia mechanism and preliminary localization of the accessory pathway (AP) can simplify the cardiac catheterization procedure and reduce fluoroscopic exposure. The purpose of this study was to analyze the diagnostic value of repolarization changes during narrow QRS complex tachycardia (< 0.11 s). In 159 12-lead electrocardiograms during narrow QRS complex tachycardia (13 atrial tachycardias, 57 atrioventricular (AV) node reentrant tachycardias and 89 AV reciprocating tachycardias), the following were evaluated: 1) the tachycardia cycle length; 2) the presence of QRS alternans > or = 1 mm in at least 6 leads; 3) the presence of ST segment depression > or = 2 mm and/or T wave changes (inversion, notching); 4) the duration of retrograde atrial activation during tachycardia (right atrium-coronary sinus interval, in ms); the latter parameter, as well as tachycardia mechanism and accessory pathway location, were determined during an electrophysiologic study. There were no significant differences in mean cycle length among the groups. ST segment depression > or = 2 mm and/or T wave changes were present more often in AV reciprocating tachycardias (51/89) than in the other groups (AV node reentrant tachycardias: 14/57; atrial tachycardias: 1/13; p < 0.001), independently from the cycle length. Distinct patterns of repolarization changes during tachycardia were associated with different location of accessory pathway: ST segment depression from V3 to V6 in left lateral AP; T wave inversion in inferior leads in posterior-posteroseptal AP; T wave changes in V2 in all cases of anteroseptal AP location. The magnitude of ST segment depression, significantly more marked in the AV reciprocating tachycardias (1.3 +/- 1.6 mm) than in AV node reentrant tachycardias (0.7 +/- 0.8 mm, p < 0.005), was directly related to the duration of atrial activation time during tachycardia (80 +/- 20 ms, and 32 +/- 12 ms, p < 0.001, respectively). The finding of ST segment depression and/or T wave changes during narrow QRS tachycardia suggest the presence of an AV reciprocating tachycardia; this phenomenon may be related to a different pattern of retrograde atrial activation. In conclusion, analysis of repolarization changes during narrow QRS tachycardia constitutes an additional electrocardiographic criterion to differentiate the tachycardia mechanism and, furthermore, can guide preliminary location of the AP, even in the absence of ventricular preexcitation.
Adolescent↗
Modulation of atrioventricular conduction by ablation of the "slow" atrioventricular node pathway in patients with drug-refractory atrial fibrillation or flutter.
OBJECTIVES: We hypothesized that modulation of atrioventricular (AV) node conduction, allowing a reduction in ventricular rate during atrial fibrillation or flutter without affecting AV conduction during sinus rhythm, might be achieved through ablation of the "slow" AV node pathway. BACKGROUND: In patients with atrial fibrillation or flutter not amenable to a direct atrial approach, ablation of the His bundle is performed to induce complete AV block. This procedure causes pacemaker dependence. METHODS: Fourteen patients with drug-refractory paroxysmal atrial flutter or fibrillation underwent ablation of the slow AV node pathway. Radiofrequency current was delivered in six patients during sinus rhythm, in six during atrial flutter and in two during atrial fibrillation. RESULTS: The anterograde effective refractory period of the AV node was prolonged from 270 +/- 50 (mean +/- SD) to 390 +/- 87 ms (p = 0.005) and the Wenckebach cycle from 346 +/- 33 to 458 +/- 75 ms (p = 0.004) in six patients during sinus rhythm. Mean AV ratio increased from 1.6 +/- 0.5 to 3.0 +/- 0.6 (p = 0.02) in six patients with atrial flutter. Mean ventricular rate decreased from 157 +/- 38 to 67 +/- 10 beats/min in two patients with atrial fibrillation. Complete AV block was induced in two patients (transient in one, permanent in one). During a follow-up period of 5.8 +/- 3.5 months, 11 patients experienced a recurrence of atrial fibrillation at 60 to 95 beats/min. No patient had progression to any degree of AV block. CONCLUSIONS: Ablation of the slow AV node pathway allows reduction of ventricular rate during atrial fibrillation or flutter while maintaining intact AV conduction during sinus rhythm. Modulation of AV node conduction is effective in most patients as an alternative to His bundle ablation for control of ventricular rate in paroxysmal atrial fibrillation or flutter.
Adult↗
Nucleo-cytoplasmic distribution of human hnRNP proteins: a search for the targeting domains in hnRNP A1.
hnRNP A1 (34 kDa) is an RNA binding protein consisting of two tandemly arranged RNA binding domains C-terminally linked to a glycine-rich auxiliary domain (2 x RBD-Gly). A1 belongs to the set of polypeptides that bind nascent hnRNA in the nucleus to form the so called hnRNP complexes. These complexes seem to be involved both in pre-mRNA processing and in the nuclear export of mRNA. In fact A1, along with other hnRNP proteins, is exported from the nucleus probably bound to mRNA and is immediately re-imported. A1 nuclear re-import, which requires active transcription, is not mediated by a canonical nuclear localisation signal (NLS). To identify the determinants of A1 subcellular localisation we developed an expression vector for studying the localisation, in transiently transfected cells, of the different structural motifs of A1 fused to a small reporter protein (chloramphenicol acetyltransferase, CAT; 26 kDa). We demonstrate that a 30 amino acid sequence in the glycine-rich domain (YNDFGNYNNQSSNFGPMKGGNFGGRSSGPY), which bears no resemblance to canonical NLS, is necessary and sufficient to target the protein to the nucleus. Our data suggest that this targeting sequence might act by mediating the interaction of A1 with a NLS-containing nuclear import complex. On the other hand, the nuclear export of A1 requires at least one RNA binding domain in accord with the hypothesis that A1 exits from the nucleus bound to mRNA. We propose a mechanism for the nucleo-cytoplasmic shuttling of A1 that envisages a specific role for the different structural domains and can explain the dependence of nuclear import from active transcription.
3T3 Cells↗
[Modulation of atrioventricular conduction in patients with atrial fibrillation or flutter. Immediate and long-term results].
The modulation of atrioventricular (AV) conduction by radiofrequency catheter ablation of the "slow" AV node pathway reduces the ventricular rate during atrial flutter (AFL) or fibrillation (AF), without affecting AV conduction during sinus rhythm. In this study the acute and long-term effects of AV node modulation in 41 patients with AFL-AF are presented. The arrhythmia was paroxysmal in 34 and chronic in 7 patients, and was responsible in all patients for severe symptoms of heart failure. The procedure was performed during sinus rhythm in 23, AFL in 8, AF in 10 patients, and caused respectively an increase in Wenckebach cycle from 330 +/- 64 to 452 +/- 91 ms (p < 0.001), and a reduction in ventricular rate from 182 +/- 53 to 95 +/- 40 b/min (p < 0.001) and from 170 +/- 40 to 90 +/- 27 b/min (p < 0.001). The arbitrary endpoint of the procedure (Wenckebach cycle > 500 ms during sinus rhythm, maximum heart rate < 100 b/min during AFL-AF) was achieved in 19/41 patients; permanent complete AV block was induced in 6 "non-responder" patients (15%). At a mean follow-up of 15 +/- 7 months (range 1-31) all patients reported a substantial subjective improvement and a better exercise tolerance--as documented by a quantitative questionnaire concerning quality of life--without any recurrence of acute pulmonary edema, syncope or severe hypotension. In 5 patients during paroxysmal AFL-AF, and in 1 patient with chronic AF, a heart rate higher than 120 b/min was documented, and in 3 cases it was associated with severe palpitations. No late AV block occurred. The mean number of hospital-emergency room admissions per patient per year decreased from 3.9 before to 0.2 after the modulation. Considering complete AV block (6 patients, 15%) and clinical failures (6 patients, 15%), the success of the procedure was 70%, and was independent of the rhythm at the time of the procedure; the percentage of AV block was nevertheless higher during AFL-AF (22 vs 9%). Both endpoints of the procedure (Wenckebach cycle > 500 ms; heart rate < 100 b/min) were confirmed to be good predictors of long-term efficacy; on the other hand, a Wenckebach cycle < 430 ms was demonstrated to represent a specific marker of late failure. In conclusion, the study confirms that modulation of AV conduction is feasible in 70% of patients with AFL-AF: in these patients the procedure allows the long-term control of ventricular rate and a substantial improvement in quality of life, avoiding the need for His ablation and pacemaker implantation. "Non-responder" patients can be acutely identified and should be therefore considered condidates for His ablation during the same session.
Adolescent↗
Fine mapping of a replication origin of human DNA.
A highly sensitive procedure was developed for the identification of the origin of bidirectional DNA synthesis in single-copy replicons of mammalian cells. The method, which does not require cell synchronization or permeabilization, entails the absolute quantification, by a competitive PCR procedure in newly synthesized DNA samples, of the abundance of neighboring DNA fragments distributed along a given genomic region. This procedure was utilized for mapping the start site of DNA replication in a 13.7-kb region of human chromosome 19 coding for lamin B2, which is replicated immediately after the onset of S phase in HL-60 cells. Within this region, DNA replication initiates in a 474-bp area corresponding to the 3' noncoding end of the lamin B2 gene and the nontranscribed spacer between this gene and the 5' end of another highly transcribed one. This localization was obtained both in aphidicolin-synchronized and in exponentially growing HL-60 cells.
Animals↗
Two homologous genes, originated by duplication, encode the human hnRNP proteins A2 and A1.
Heterogeneous nuclear ribonucleoprotein (hnRNP) A2 belongs, with A1, B1 and B2, to the basic protein subset of the hnRNP complex in mammalian cells. All these proteins share a modular structure consisting of two conserved RNA binding domains linked to less conserved Gly-rich domains (2xRBD-Gly). In the framework of our studies on the genetic basis of hnRNP proteins structure and diversity we have isolated and sequenced the A2 gene and compared it to the previously described A1 gene. The A2 gene, which exists in a single copy on Ch. 7 band p15, is split in 12 exons including an alternatively spliced 36 nt mini exon specific for the human hnRNP protein B1. In this work we show that the intron/exon organisation of the A2 gene is identical to that of the A1 gene over the entire length, indicating a common origin by gene duplication. Moreover the comparison of corresponding exons evidences significant conservation also in the apparently divergent Gly-rich domains that could define previously unenvisaged structural and/or functional motifs. The A2 gene promoter is also analysed in comparison to that of the A1 gene.
Amino Acid Sequence↗
New insights into the auxiliary domains of eukaryotic RNA binding proteins.
Eukaryotic RNA binding proteins (RBP) are key players in RNA processing and in post-transcriptional regulation of gene expression. By interacting with RNA and other factors and by modulating the RNA structure, they promote the assembly of a great variety of specific ribonucleoprotein complexes. Many RBPs are composed of highly structured and conserved RNA binding domains (RBD) linked to unstructured and divergent auxiliary domains; such modular structure can account for a multiplicity of interactions. In this context, the auxiliary domains emerge as essential partners of the RBDs in both RNA binding and functional specialisation. Moreover, the determinants of biologically important functions, such as strand annealing, protein-protein interactions, nuclear localization and activity in in vitro splicing, seem to reside in the auxiliary domains. The structural and functional properties of these domains suggest their possible derivation from ancestral non-specific RNA binding polypeptides.
Amino Acid Sequence↗
Human hnRNP protein A1: a model polypeptide for a structural and genetic investigation of a broad family of RNA binding proteins.
The hnRNP fiber is the substrate on which pre-mRNA processing occurs. The protein moiety of the fiber (hnRNP proteins) constitutes a broad family of RNA binding proteins that revealed, upon molecular analysis, a number of interesting features. Heterogeneous nuclear ribonucleoprotein A1 is a major component of the human hnRNP complex. In recent years this protein has attracted great attention because of several emerging evidences of its direct involvement in pre-mRNA processing and it has become one of the best characterized RNA binding proteins. Detailed knowledge of the structure of protein A1 has laid the basis for the understanding of its function, and for this reason A1 can be considered as a model polypeptide for the investigation of a large number of RNA binding proteins. In this work we report recent findings regarding the binding properties of protein A1 as well as new data on the gene structure of A1 and of its closely related hnRNP protein A2. Our results show that a single A1 molecule contains the determinants for simultaneous binding of two single-stranded nucleic acid molecules and we demonstrate that the glycine-rich domain of A1, isolated from the rest of the molecule, is capable of sustaining protein-protein interactions. These features probably account for the reannealing activity of the protein and for its capacity to modulate the binding of snRNPs to intron sequences in vitro. Comparison of A1 and A2 gene sequences revealed a remarkable conservation of the overall structural organization, suggesting important functions for the different structural elements.
Amino Acid Sequence↗
Human hnRNP protein A1 gene expression. Structural and functional characterization of the promoter.
hnRNP protein A1 (34 kDa, pl 9.5) is a prominent member of the family of proteins (hnRNP proteins) that associate with the nascent transcripts of RNA polymerase II and that accompany the hnRNA through the maturation process and the export to the cytoplasm. New evidence suggests an active and specific role for some of these proteins, including protein A1, in splicing and transport. Contrary to the other hnRNP proteins, the intracellular level of protein A1 was reported to change as a function of proliferation state and cell type. In this work we analyse the A1 gene expression in different cells under different growth and differentiation conditions. Proliferation dependent expression was observed in lymphocytes and fibroblasts while purified neurons express high A1 mRNA levels both in the proliferative (before birth) and in the quiescent (after birth) state. Transformed cell lines exhibit very high (proliferation independent) A1 mRNA levels compared to differentiated tissues. A structural and functional characterization of the A1 gene promoter was carried out by means of DNase I footprinting and CAT assays. The observed promoter features can account for both elevated and regulated mRNA transcription. At least 12 control elements are contained in the 734 nucleotides upstream of the transcription start site. Assays with the deleted and/or mutated promoter indicate a co-operation of multiple transcriptional elements, distributed over the entire promoter, in determining the overall activity and the response to proliferative stimuli (serum).
Animals↗
Phosphorylation of human hnRNP protein A1 abrogates in vitro strand annealing activity.
In HeLa cells metabolically labeled in vivo with [32P] orthophosphate in the presence of okadaic acid the concentration of phosphorylated A1 protein was increased significantly as compared to controls. Purified recombinant hnRNP protein A1 served as an excellent substrate in vitro for the catalytic subunit of cAMP-dependent protein kinase (PKA) and for casein kinase II (CKII). Thin layer electrophoresis of A1 acid hydrolysates showed the protein to be phosphorylated exclusively on serine residue by both kinases. V8 phosphopeptide maps revealed that the target site(s) of in vitro phosphorylation are located in the C-terminal region of A1. Phosphoamino acid sequence analysis and site directed mutagenesis identified Ser 199 as the sole phosphoamino acid in the protein phosphorylated by PKA. Phosphorylation introduced by PKA resulted in the suppression of the ability of protein A1 to promote strand annealing in vitro, without any detectable effect on its nucleic acid binding capacity. This finding indicates that phosphorylation of a single serine residue in the C-terminal domain may significantly alter the properties of protein A1.
Amino Acid Sequence↗
Inhibition of heterologous DNA replication by the MVMp nonstructural NS-1 protein: identification of a target sequence.
The nonstructural protein NS-1 of minute virus of mice (MVMp), an autonomous parvovirus, trans-inhibits the replication of a chimeric plasmid containing the SV40 origin of replication (ori) embedded in the MVMp genome. It appears that a 157-bp 5' proximal sequence of MVMp DNA is sufficient, in the presence of NS-1, to cause the inhibition of DNA replication driven by the SV40 ori placed on the same molecule. This effect is not dependent on the orientation of the MVMp target sequence and results from both a reduced level of utilization of SV40 ori and the blockage of progressing replication forks at the level of the target. Furthermore, replication driven by Epstein-Barr virus origin (oriP) is trans-inhibited by MVMp but this inhibition does not require the presence of parvoviral sequences in cis. On the basis of sequence homologies between EBV oriP and MVMp 5' terminal sequence, it is proposed that the direct or indirect interaction of NS-1 with parvovirus-like sequences present in heterologous viral and possibly also cellular genomes may result in an inhibition of DNA replication.
Animals↗
A simple procedure for enhancing PCR specificity.
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Base Sequence↗
Modification of exercise performance by sharp reduction of blood pressure. A study in patients with uncomplicated hypertension.
We evaluated exercise performance in 14 patients with uncomplicated essential hypertension 1 h after the administration of a single dose of placebo, nifedipine (20 mg), captopril (50 mg), and propranolol (80 mg). Drugs were administered at the same time of day following a randomized, double-blind protocol. Mean resting blood pressure (+/- SE) was 135 +/- 3 mm Hg with placebo administration, 118 +/- 4 with captopril, 110 +/- 4 with nifedipine, and 115 +/- 5 with propranolol and increased with exercise to 163 +/- 4, 146 +/- 3, 136 +/- 4, 136 +/- 4, respectively. Oxygen consumption at peak exercise and at ventilatory anaerobic threshold (VAT) was 25.2 +/- 1.1 and 18.1 +/- 1.0 ml/min/kg with placebo. Only propranolol (-2.3 ml/min/kg) decreased peak exercise oxygen consumption. Oxygen consumption at VAT was reduced by nifedipine and propranolol but unaffected by captopril. The effects on exercise capacity of blood pressure reduction in hypertensive patients are dependent on the drug utilized and are not related to the amount of blood pressure reduction. The lowered oxygen consumption at VAT observed with nifedipine and propranolol, and not with captopril, might be due to an excessive downward shift of the muscle perfusion pressure--oxygen consumption relationship which might take place during exercise.
Anaerobic Threshold↗
A novel procedure for quantitative polymerase chain reaction by coamplification of competitive templates.
A method is described for the absolute quantification by polymerase chain reaction (PCR) of nucleic acids present in low abundance. The method entails the addition to the sample of competitor DNA molecules that share the same sequence as the amplified target (including primer recognition sites), except for a 20-bp insertion in the middle, which allows easy resolution by gel electrophoresis (competitive PCR). Among the advantages of competitive PCR is that any predictable or unpredictable variable that affects amplification has the same effect on both target and competitor species and that the final ratio of amplified products reflects exactly the initial rate of targets, rendering the reaction independent of the number of amplification cycles. An easy and reliable method for the construction and quantification of competitive templates obtained as recombinant PCR products was developed. The technique was used for the absolute quantification of human genomic DNA with primers from a single copy, subtelomeric region of chromosome 19.
Base Sequence↗
Interaction of hnRNP A1 with snRNPs and pre-mRNAs: evidence for a possible role of A1 RNA annealing activity in the first steps of spliceosome assembly.
The in vitro interaction of recombinant hnRNP A1 with purified snRNPs and with pre-mRNAs was investigated. We show that protein A1 can stably bind U2 and U4 snRNP but not U1. Oligo-RNAse H cleavage of U2 nucleotides involved in base pairing with the branch site, totally eliminates the A1-U2 interaction. RNase T1 protection and immunoprecipitation experiments demonstrate that recombinant protein A1 specifically binds the 3'-end regions of both beta-globin and Ad-2 introns. However, while on the beta-globin intron only binding to the polypyrimidine tract was observed, on the Ad-2 intron a 32 nt fragment encompassing the branch point and the AG splice-site dinucleotide was bound and protected. Such protection was drastically reduced in the presence of U2 snRNP. Altogether these results indicate that protein A1 can establish a different pattern of association with different pre-mRNAs and support the hypothesis that this protein could play a role in the annealing of U2 to the branch site and hence in the early events of pre-splicing complex assembly.
Adenoviruses, Human↗
H-NMR studies of native and fragmented subtilisin Carlsberg.
NMR studies have been carried out on subtilisin Carlsberg in order to identify the sharp resonances observed in the proton spectra of the enzyme dissolved in aqueous solution. NMR spectra, obtained with the combination of spin-echo and selective excitation sequences, from both the native and inactivated protein, enabled us to assign sharp signals to subtilisin fragments derived from enzymatic autolysis (monitored by high-performance size-exclusion chromatography), rather than to mobile segments of the intact protein.
Chromatography, High Pressure Liquid↗
A human DNA replication origin: localization and transcriptional characterization.
A single-copy 13.7 kb human DNA region (L30E) located on Ch. 19 p13.3 contains an origin of DNA replication in myeloid HL-60 cells. The origin was localized, by means of quantitative PCR within approximately 3000 bp, in a highly transcribed region containing at least two closely spaced genes with the same polarity of transcription, one encoding lamin B2 and the other an unidentified protein. The origin region overlaps an undermethylated "CpG island" at the 5'-end of the second transcription unit. A binding site (CACGTG) for basic helix-loop-helix (bHLH) DNA binding proteins such as USF/MLTF or MYC-MAX was located by DNase I footprinting analysis in the promoter of the second gene. DMSO differentiation of HL-60 cells, that completely shuts off replication, also drastically reduces the transcription of L30E region. On the other hand such treatment does not modify the methylation pattern of the CpG island and does not abolish the DNase I protection of the bHLH binding site.
Base Sequence↗