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F Leclercq

Publications and source records attributed to F Leclercq.

At least 19 recordsLinked to original sources
PubMed2005

Low-frequency Raman spectra of sub- and supercritical CO2: qualitative analysis of the diffusion coefficient behavior.

We report the results of the low-frequency Raman experiments on CO(2) which were carried out in a wide density range, along the liquid-gas coexistence curve in a temperature range of 293-303 K, and on the critical isochore of 94.4 cm(3) mol(-1) in a temperature range of 304-315 K. In our approach, the qualitative behavior of the diffusion coefficient D is predicted, assuming the following: first, that the low-frequency Raman spectra can be interpreted in terms of the translation rotation motions; second, that the random force could be replaced by the total force to calculate the friction coefficient; and finally, that the Einstein frequency is associated with the position of the maximum of the low-frequency Raman spectrum. The results show that the diffusion coefficient increases along the coexistence curve, and its values are almost constant on the critical isochore. The predicted values reproduce qualitatively those obtained by other techniques. The values of D were also calculated by molecular-dynamics simulation and they qualitatively reproduce the behavior of D.

Journal Article↗
PubMed2005

[Ventricular tachycardia due to branch to branch re-entry].

Ventricular tachycardia due to branch to branch re-entry constitutes a rare clinical entity. This circuit is remarkable by the fact that it is made up of the branches or hemi-branches of the bundle of His bifurcation. They occur under specific conditions, with a combination of left ventricular dilatation and atrioventricular or intraventricular conduction defects. They are also very often found in Steinert's disease. A positive diagnosis can sometimes be difficult and relies on a variety of factors. Recording of the His potential shows His activity preceding each ventriculogram, and variations in spontaneous cycles between 2 ventriculograms preceded by variations between the 2 His potentials. Atrial capture without modification of the QRS is possible, but fusion excludes the diagnosis. Drug therapy is only slightly effective, and the best treatment is ablation of the right branch of the bundle of His, which stops the tachycardia definitively.

Bundle of His↗
PubMed2004

[Right atrial thrombus--a complication of central venous catheters].

We describe the development, in three days, of a pediculate mass hanging on the right atrial lateral wall in a 39-year-old woman with a subclavian venous catheterization. She was a current smoker and alcoholic but without drug addict. The hypothesis of a non valvular right atrial infective endocarditis was considered at first, but subsequent events directed the diagnosis towards a thrombus, which was resorbed by heparin. We discuss the incidence, the complications, the treatment and the differential diagnosis of thrombus caused by a central venous catheter. The prevention of right atrial thrombus caused by a central venous catheter depends on the position of the central venous catheter tip, either in the superior vena cava or at the superior vena cava-right atrium junction. A more distal position is a frequent source of thrombotic and embolic complications.

Adult↗
PubMed2004

[The electrocardiogram of atrioventricular blocks].

Atrioventricular block (AVB) is defined as delay or absence of transmission of one or more atrial excitations to the ventricle. Physiological functional block protects the ventricle against very rapid atrial rhythms. Organic blocks may be transient, due to an acute regressive condition, or chronic, in which case they fall into two groups--permanent blocks or paroxysmal and generally rate-dependant blocks. The blocks are classified in three categories according to whether the atrial activation is delayed, conducted intermittently or not at all. The site of AVB may be determined by His bundle recordings but it may also be deduced from the surface ECG recording. Fundamental studies have questioned the reality of Rosenbaum's phase 3 and 4 blocks and suggest abnormalities of excitability in pathological zones.

Electrocardiography↗
PubMed2003

[Diagnosis of narrow QRS complex tachycardias].

Tachycardias with normal QRS complexes (less than 0.12 seconds) may have multiple origins which may be classified in 4 groups: sinusal, atrioventricular nodal, atrioventricular junctional and finally, some ventricular tachycardias arising from near the conduction pathways. The electrocardiographic diagnosis requires analysis of the QRS complexes to detect an eventual irregularity which would suggest atrial fibrillation. When the tachycardia is regular, analysis of the P waves is fundamental (position in the ventricular cycle and morphology). The relationship of the P waves and the QRS complexes enables identification of those forms independent of the AV node and some rare types of tachycardia. Finally, the response to vagal stimulation is essential whether the tachycardia stops, slows down or persists unchanged.

Atrial Fibrillation↗
PubMed2003

[Concealed phenomena in electrocardiography].

Concealed phenomena in electrocardiography are events which, having no direct effect on the electrocardiogramme, nevertheless change the following sequences giving rise to very unusual appearances. They are diagnosed by deduction. First of all, there is concealed anterograde or retrograde conduction in the AV node, the consequences of which are either a block or the suppression of an escape rhythm or even facilitation of the transmission of activation. Concealed conduction is also possible in the Bundle of His and its branches, explaining the frequency of dependent blocks and aberrant conduction. There is also concealed conduction in accessory pathways. The second form is concealed rhythms: hisian extrasystoles giving rise to pseudo A-V block, and concealed extrasystoles and parasystoles. With temporary pacing of tachycardia, it has finally been possible to describe "visible" concealed phenomena, not on the surface but on the endocavitary electrogramme.

Arrhythmias, Cardiac↗
PubMed2003

[Atypical forms of atrioventricular nodal reentrant tachycardia].

The concept of functional dissociation of atrioventricular nodal conduction on an underlying structure with different nodal inputs is well established. In the common form of AVNRT, the circuit comprises the slow pathway for antegrade conduction and the fast pathway for retrograde conduction. However, the tachycardia circuit may be slightly or totally different as it is not based on discrete anatomical pathways but on functional pathways due to non-uniform anisotropy of the perinodal atrial tissue involved in the circuit. First, there are variations of the common form. The fast retrograde pathway may be posterior or left instead of being anteriorly-located. The so-called uncommon forms of AVNRT consist in slow-slow and fast-slow forms. The slow-slow form uses two different slow pathways as antegrade and retrograde limb of the circuit. These pathways may be posterior or left. The fast-slow form appears to be complex and heterogeneous. The retrograde slow pathway may be located posteriorly, anteriorly, in-between or sometimes left-sided. Whatever the circuit, targeting the antegrade or retrograde slow pathway remains the aim of ablation and the only therapeutic issue. However, a 1%-AV block rate has to be kept in mind.

Atrioventricular Node↗
PubMed2002

[Parasystole].

Parasystole is usually an extrasystolic rhythm which can occur at every level, but particularly in the ventricle. It is admitted that the parasystolic focus is protected from the environing myocardium by an entry block but can manifest itself. Actually, a pure unidirectional block does not exist and the environing myocardium affects the parasystolic rhythm by an electrotonic current which modulates the output. A non-parasystolic complex which occurs prematurely in the parasystolic cycle delays it. Conversely it accelerates the cycle when it occurs late. By this fact, a parasystole pacing is possible and can lead to a fixed coupling. This arrhythmia is frequently unknown and can be experimentally, reproduced by a sucrose gap preparation.

Animals↗
PubMed2001

Synthesis of new cationic lipids from an unsaturated glycoside scaffold.

[see structure]. We report the synthesis of new cationic lipids. These amphiphiles present a hydrophobic domain connected to a guanidinium entity by an unsaturated glycoside scaffold. The synthetic strategy using amide or acetal linkage led to various mono- and bicatenar derivatives. Investigation of their physicochemical properties indicated that these new compounds compact DNA.

Cations↗
PubMed2001

Comparison of direct coronary stenting with and without balloon predilatation in patients with stable angina pectoris. BET (Benefit Evaluation of Direct Coronary Stenting) Study Group.

The purpose of this study was to compare the effects of stent placement with and without balloon predilatation on duration of the procedure, reduction of procedure-related costs, and clinical outcomes. Although preliminary trials of direct coronary stenting have demonstrated promising results, the lack of randomized studies with long-term follow-up has limited the critical evaluation of the role of direct stenting in the treatment of obstructive coronary artery disease. Between January and September 1999, 338 patients were randomly assigned to either direct stent implantation (DS+; 173 patients) or standard stent implantation with balloon predilatation (DS-; 165 patients). Baseline clinical and angiographic characteristics were similar in the 2 groups. Procedural success was achieved in 98.3% of patients assigned to DS+ and 97.5% of patients assigned to DS- (p = NS), with a crossover rate of 13.9%. Compared with DS-, DS+ conferred a dramatic reduction in procedure-related cost ($956.4 +/- $352.2 vs $1,164.6 +/- $383.9, p <0.0001) and duration of the procedure (424.2 +/- 412.1 vs 634.5 +/- 390.1 seconds, p < 0.0001). At 6-month follow-up, the incidence of major adverse cardiac events including death, angina pectoris, myocardial infarction, congestive heart failure, repeat angioplasty, or coronary artery bypass graft surgery was 5.3% in DS+ and 11.4% in DS- (p = NS). Multivariate analysis demonstrated that major adverse cardiac events rates were related to stent length of 10 mm (relative risk [RR] 3.25, 95% confidence intervals [CI] 1.36 to 7.78; p = 0.008), stent diameter of 3 mm (RR 2.69, 95% CI 1.03 to 7.06; p = 0.043), and complex lesion type C (RR 2.83, 95% CI 1.02 to 7.85; p = 0.045). Thus, in selected patients, this prospective randomized study shows the feasibility of DS+ with reduction in procedural cost and length, and without an increase in in-hospital clinical events and major adverse cardiac events at 6-month follow-up.

Angina Pectoris↗
PubMed2001

Isolation of bovine follicular dendritic cells allows the demonstration of a particular cellular prion protein.

As interaction of cellular prion protein (PrPc) and the infectious agent (PrPres) appears to be a crucial pathogenic step promoted by homology, variation in PrPc isoforms on bovine immune cells may explain the absence of infectivity in most bovine lymph organs. In this study, we examined PrPc expression in bovine lymph organs (tonsils and lymph nodes) and on isolated follicular dendritic cells (FDCs). We used a panel of different monoclonal antibodies (MoAbs) raised against different epitopes of prion protein. Two MoAbs recognise amino acids 79-92 (SAF 34 and SAF 32 Mo-Abs); the 6H4 antibody reacts with a specific peptide comprising the 144-152 amino acids, and the 12F10 MoAb recognises the sequence 142-160. After immunolabelling of frozen sections of lymph organs with 6H4 or 12F10 MoAbs, we detected cellular prion protein in germinal centres. However, using the SAF 34 or SAF 32 antibodies, PrPc was revealed outside the lymphoid tissues. No PrPc was observed in the germinal centres. Therefore, we adapted the method of FDC isolation, making it suitable for the study of PrPc expression on their surface. Using electron microscopy, the presence of PrPc on the surface of FDCs was demonstrated only with 6H4 MoAb. These results suggest that bovine follicular dendritic cells express a particular form of prion protein. Either the N-terminal part of PrPc is cleaved or the accessibility of the specific epitope (79-92) of SAF 34 MoAb is abolished by interaction with other molecules. This particular isoform of PrPc on bovine FDCs might be related to the apparent absence of infectivity in lymph organs in cattle affected by bovine spongiform encephalopathy.

Animals↗
PubMed2001

Transcranial Doppler detection of cerebral microemboli during left heart catheterization.

The role of transcranial Doppler ultrasonography (TCD) in individual risk assessment of embolic complications and the development of prevention strategies during coronary angiography remains to be determined. The purpose of this study was to assess the prevalence, time of occurrence and potential significance of microembolic signals (MES) detected with TCD during femoral left heart catheterization. TCD monitoring of the right and left middle cerebral artery was performed in 51 consecutive patients (36 men, 15 women) who were referred for coronary angiography. Percutaneous coronary angioplasty was performed during the same procedure in 16 patients. MES were counted manually during and after (off-line analysis) the procedure. Two patients were excluded from analysis because of the absence of an adequate acoustic temporal window. No neurological event occurred within 24 h in the 49 included patients. MES were detected in all except 2 patients (mean number 17.1 +/- 12.8 per patient), mainly during left ventriculography (38%) and contrast media injection into the coronary arteries (55%), suggesting their gaseous origin. There was no statistically significant association between the number of MES and patient age, cardiovascular history and risk factors, or catheterization results. The presence of coronary artery disease was inversely related to the number of MES (15.8 +/- 0.3 compared to 21.8 +/- 0.2 per patient when a normal angiogram was present; p < 0.05). In conclusion, although asymptomatic microemboli commonly occur during left heart catheterization, the majority of them are probably of gaseous origin, since they occurred predominantly during contrast media injection in this study, and were not related to cardiovascular history or to atheroma risk factors. Because air embolism has been reported to be harmful, attempts to reduce its occurrence during catheter-based procedures could be pertinent.

Aged↗
PubMed2001

[Bouveret's tachycardia].

In 1889, in an age preceding the invention of the electrocardiogram, a physician working in the hospitals of Lyon published a remarkable paper on essential paroxysmal tachycardia, of which Bristowe in England and Huppert in Germany had already spoken. The study described 12 cases (including 3 personal cases) of essential paroxysmal tachycardia and 6 secondary tachycardias. They were not all benign, there being 4 deaths out of the 12 cases. From this period on, the term "Bouveret's tachycardia" has been used in France and, with the advances in rhythmology, some have assimilated it to paroxysmal nodal tachycardia. In fact, many forms of paroxysmal essential tachycardia have been recognised at atrial (nodal tachycardia, accessory pathway tachycardia, idiopathic atrial flutter and fibrillation) and ventricular levels (benign or ventricular Bouveret's tachycardia). This is an occasion to review the variety of clinical medicine in the accuracy of a rhythmological diagnosis without forgetting that the electrocardiogram is essential when the recordings are analysable. The term of Bouveret's tachycardia should be retained but, before electrocardiographic analysis, it englobes all paroxysmal tachycardia occurring in healthy hearts, and not only paroxysmal nodal tachycardia.

Diagnosis, Differential↗
PubMed2000

Synthesis of glycosylated polyethylenimine with reduced toxicity and high transfecting efficiency.

A safe and efficient synthesis of glycosylated polyethylenimine using titanium (IV) isopropoxide and sodium borohydride has been carried out as a substitute for the highly toxic sodium cyanoborohydride method currently used. Poryplexes formed between DNA and the various glycosylated polyethylenimines appeared to be much less cytotoxic than polyethylenimine (PEI)/DNA polyplexes.

Cell Survival↗
PubMed2000

Facilitation of L-type calcium currents by diastolic depolarization in cardiac cells: impairment in heart failure.

OBJECTIVE: Decay kinetics of the voltage-gated L-type Ca(2+) current (I(CaL)) control the magnitude of Ca(2+) influx during the cardiac action potential. We investigated the influence of changes in diastolic membrane potential on I(CaL) decay kinetics in cardiac cells. METHODS: Cells were isolated enzymatically from rat ventricles, human right atrial appendages obtained during corrective heart surgery and left ventricles from end-stage failing hearts of transplant recipients. The whole-cell patch-clamp technique was used to evoke I(CaL) by a 100-ms depolarizing test pulse to -10 mV. Conditioning potentials between -80 and 0 mV were applied for 5 s prior to the test pulse. RESULTS: Depolarizing the cells between -80 and -50 mV prior to the test pulse slowed the early inactivation of I(CaL) both in rat ventricular and human atrial cells. This slowing resulted in a significant increase of Ca(2+) influx. This type of facilitation was not observed when the sarcoplasmic reticulum (SR) Ca(2+) content was depleted using ryanodine which reduced the rate of inactivation of I(CaL), or when Ba(2+) replaced Ca(2+) as the permeating ion. Facilitation was favored by intracellular cAMP-promoting agents that, in addition to increasing current peak amplitude, enhanced the fast Ca(2+)-dependent inactivation of I(CaL). Facilitation was impaired in atrial and ventricular human failing hearts. CONCLUSION: Decay kinetics of I(CaL) are regulated by the diastolic membrane potential in rat and human cardiomyocytes. This regulation, which associates slowing of I(CaL) inactivation with reduced SR Ca(2+) release and underlies facilitation of Ca(2+) channels activity, may have profound physiological relevance for catecholamines enhancement of Ca(2+) influx. It is impaired in failing hearts, possibly due to lowered SR Ca(2+) release.

Adrenergic beta-Agonists↗
PubMed2000

Postoperative exercise tolerance after aortic valve replacement by small-size prosthesis: functional consequence of small-size aortic prosthesis.

OBJECTIVES: The objective of this study was to determine whether a small-size valve prosthesis contributes to exercise intolerance, as assessed by VO2 measurement during an exhaustive cycle ergometer exercise. BACKGROUND: The determinants of exercise capacity after mechanical aortic replacement are not well known. The selection of small valve sizes has, however, been described as an independent predictor of exercise intolerance as assessed by exercise duration. Maximal oxygen uptake (VO2max) is a good index of exercise tolerance. METHODS: Fourteen patients were eligible, with a mean age of 62 +/- 6 years. Before surgery, the mean left ventricular ejection fraction (LVEF) was 73 +/- 8%. Two valve types with small diameter (19 to 21 mm) were used: Medtronic Hall and St Jude Medical. A healthy sedentary control group (n = 14) paired for age, weight and size was constituted. After one year of follow-up, cardiorespiratory tests were performed. In addition, the gradients through the prostheses were determined by continuous pulse Doppler at rest and immediately after the cardiorespiratory test. RESULTS The exercise tolerance was not significantly different between the control group and patient group: VO2 peak (21.7 vs. 20.4 ml/kg/min; p = 0.42), workloads (115 vs. 93 W; p = 0.13) and ventilatory parameters were similar. The mean and peak gradients at rest and during exercise were not correlated with VO2max. CONCLUSIONS: Valve replacement by small aortic prosthesis does not seem to be a factor of exercise intolerance as assessed by VO2max in patients without LVEF dysfunction before surgery.

Aged↗