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Biomedical subjects

D Lacroix

Publications and source records attributed to D Lacroix.

At least 19 recordsLinked to original sources
PubMed2006

Post-operative use of heparin increases morbidity of pacemaker implantation.

AIMS: The objective of this study is to characterize the incidence of peri-operative severe adverse events (AEs) related to the post-operative use of heparin in patients undergoing pacemaker surgery. METHODS AND RESULTS: We retrospectively compared the outcome of 38 patients with mechanical valves (MVs) and 76 patients with atrial fibrillation (AF) with control cases matched for gender, age, and surgical details. Heparin was systematically used post-operatively in MV patients, but left to clinical judgment in AF patients. The relative risk for severe haemorrhagic AEs was 11 (CI 1.5-81.1, P < 0.01) in the MV group when compared with matched controls and 8 (CI 1.0-62.5, P < 0.05) in the AF group. Overall, the relative risk of heparin use in the post-operative period was 14 (CI 1.88-104, P = 0.0006) and the post-operative stay was prolonged from 7 days in this group when compared with control cases (P < 0.0001).The variables associated with haemorrhage were the delay to restart heparin after surgery and the presence of an MV. CONCLUSION: Post-operative use of heparin increases morbidity of pacemaker implantation. A different approach to management of these patients is possible.

Aged↗
PubMed2006

A recovery model of minimally invasive cardiopulmonary bypass in the rat.

This study was undertaken to develop a rodent (rat) model of cardiopulmonary bypass (CPB) that has been designed to mimic functionally the minimally invasive clinical setting. The circuit is similar to the clinical model in terms of its construction, configuration, material surface area to blood volume ratio, and priming volume to blood ratio. The overall priming volume was 10 mL. Thirty-six male Sprague-Dawley rats (422 +/- 32 g) were anaesthetized while maintaining spontaneous ventilation. Anticoagulation was achieved with heparin (500 IU/kg). Blood arterial pressure was monitored continuously. Normal central temperature was maintained throughout. Intermittent arterial blood gas levels also were monitored. All animals were cannulated in preparation for CPB; however, CPB, utilizing a double roller pump and a flow rate of 100 mL/kg/minute for 60 min, was initiated in only 18 animals, the remaining 18 animals acting as non-CPB controls (Sham). The animals were haemodynamically stable. After the operative procedure, the animals were allowed to recover from the anaesthesia and, after transfer to a recovery facility, were monitored for a period of 1 week. There were no differences between the groups in terms of blood gas analysis and blood pressure data; all animals survived the procedure and had an uneventful follow-up. Differences were found between the CPB animals and the Sham group in terms of TNFalpha used as a marker of inflammatory processes. This trend tends to support this model as an analogue for the clinical scenario for future studies of CPB-related inflammation. Overall, the CPB procedure was easy to perform and was associated with excellent survival. This recovery model is an effective tool to perform pathophysiological studies associated with minimally invasive CPB.

Animals↗
PubMed2005

Cardiac resynchronisation therapy reduces functional mitral regurgitation during dynamic exercise in patients with chronic heart failure: an acute echocardiographic study.

OBJECTIVES: To assess non-invasively the acute effects of cardiac resynchronisation therapy (CRT) on functional mitral regurgitation (MR) at rest and during dynamic exercise. METHODS: 21 patients with left ventricular (LV) systolic dysfunction and functional MR at rest, treated with CRT, were studied. Each patient performed a symptom-limited maximal exercise with continuous two dimensional Doppler echocardiography twice. The first exercise was performed with CRT; the second exercise was performed without CRT. Mitral regurgitant flow volume (RV), effective regurgitant orifice area (ERO) and LV dP/dt were measured at rest and at peak exercise. RESULTS: CRT mildly reduced resting mitral ERO (mean 8 (SEM 2) v 11 (2) mm(2) without CRT, p = 0.02) and RV (13 (3) v 18 (3) ml without CRT, p = 0.03). CRT attenuated the spontaneous increase in mitral ERO and RV during exercise (1 (1) v 9 (2) mm(2), p = 0.004 and 1 (1) v 8 (2) ml, p = 0.004, respectively). CRT also significantly increased exercise-induced changes in LV dP/dt (140 (46) v 479 (112) mm Hg/s, p < 0.001). CONCLUSION: Attenuation of functional MR, induced by an increase in LV contractility during dynamic exercise, may contribute to the beneficial clinical outcome of CRT in patients with chronic heart failure and LV asynchrony.

Aged↗
PubMed2005

Bimodality as a signal of a liquid-gas phase transition in nuclei?

We use the heavy-ion phase-space exploration model to discuss the origin of the bimodality in charge asymmetry observed in nuclear reactions around the Fermi energy. We show that it may be related to the important angular momentum (spin) transferred into the quasiprojectile before secondary decay. As the spin overcomes the critical value, a sudden opening of decay channels is induced and leads to a bimodal distribution for the charge asymmetry. In the model, it is not assigned to a liquid-gas phase transition but to specific instabilities in nuclei with high spin. Therefore, we propose to use these reactions to study instabilities in rotating nuclear droplets.

Journal Article↗
PubMed2004

Fine structure in the energy region of the isoscalar giant quadrupole resonance: characteristic scales from a wavelet analysis.

Fine structure in the energy region of the isoscalar giant quadrupole resonance in nuclei is observed in high-resolution proton scattering experiments at iThemba LABS over a wide mass range. A novel method based on wavelet transforms is introduced for the extraction of scales characterizing the fine structure. A comparison with microscopic model calculations including two-particle two-hole (2p2h) degrees of freedom identifies the coupling to surface vibrations as the main source of the observed scales. A generic pattern is also found for the stochastic coupling to the background of the more complex states.

Journal Article↗
PubMed2004

Continuous mandibular distraction osteogenesis using superelastic shape memory alloy (SMA).

Distraction osteogenesis is a well-established method of endogenous tissue engineering. It is a biological process of bone neo-formation between segments subjected to tension. The concept of this study was to investigate the distraction osteogenesis with a device capable of creating a permanent and constant force during the whole process as if a very large number of small elongations were applied constantly. The mechanical testing of the device used to produce the constant force and the in vivo analysis of the bone growth after it was implanted in rabbits are presented on this work. The device consists of a NiTi coil spring, superelastic at body temperature, in order to have a stress plateau during the austenitic retransformation during the unloading. The in vivo analysis was made on six female rabbits of 12 months old. A segmental mandibulectomy at the horizontal arm of the mandible and a corticotomy at 5mm distant from the gap were made. Next, following a latency period of five days, the SMA springs were implanted to induce the bone neo-formation. The displacement at the unloading plateau shows that it is necessary to have longer springs or to use several (available commercially) in series in order to fulfil the requirements of a human distraction. The temperature variations induced changes in the spring force. However, when the temperature returns to 37 degrees C the distraction force recovers near the initial level and does so completely when the distraction process continues. For the in vivo study, all six rabbits successfully completed the distraction. The radiographies showed the gap as distraction advanced. A continuity in the newly formed bone with similar transversal and horizontal dimensions than the original bone can be observed on the histologies. In conclusion, the application of a constant force on distraction osteogenesis, using SMA springs, may be a successful alternative to the conventional gradual distraction.

Animals↗
PubMed2004

Local symptoms at the site of pacemaker implantation indicate latent systemic infection.

BACKGROUND: To determine whether local complications at the site of pacemaker implantation indicate infection of the intravascular part of the lead as well as of the pacemaker pocket. METHODS: 105 patients admitted for local inflammatory findings, impending pacemaker or lead exteriorisation, frank pacemaker or lead exteriorisation, or overt infection were studied prospectively. After systematic lead extraction, the initial clinical presentation was related to the results of lead cultures. RESULTS: Regardless of the initial presentation, the intravascular parts of the leads gave positive cultures in 79.3% of patients. Additionally, 91.6% of the cultures of the extravascular lead segments were positive, in contrast to 38.1% positivity for wound swab cultures. No clinical observations or laboratory investigations permitted identification of patients with negative lead cultures. In a subgroup of 50 patients with manifestations strictly limited to the pacemaker implantation site, cultures of intravascular lead segments were positive in 72%. Infection recurred in 4/8 patients without complete lead body extraction (50%) v 1/97 patients (1.0%) whose leads were totally extracted (p < 0.001). CONCLUSIONS: Local complications at the site of pacemaker implantation are usually associated with infection of the intravascular part of the leads, with a risk of progressing to systemic infection. Such local symptoms should prompt the extraction of leads even in the absence of other infectious manifestations.

Aged↗
PubMed2004

[Role of ablation in the treatment of ventricular tachycardia].

Radiofrequency ablation of ventricular tachycardia in cardiopathy essentially concerns the post-infarct period, but also dilated cardiopathy and arrhythmogenic right ventricular dysplasia. This technique relies greatly on the new computer assisted mapping techniques and intracardiac navigation. The mechanism is usually a macro-reentry which is formed on contact with a scarred, fibrous or dysplastic area. The activation site has a figure of eight appearance with a slow conduction zone activated in diastole and surrounded by areas of anatomical or functional block. This protected isthmus can be confirmed with exercising manoeuvres. Failing that, it can be identified by indirect criteria, notably when the tachycardia is not triggered or not tolerated haemodynamically. The success rates are higher in trained centres, and the morbidity/mortality of such procedures are low. Ablation is aimed at continuous or frequent tachycardias in order to limit interventions in patients fitted with an implanted defibrillator. Radiofrequency ablation in the case of idiopathic ventricular tachycardia is different because it is relatively easy when there is a right infundibular origin or a fascicular ventricular tachycardia, which is usually derived from the left posterior hemibranch conduction tissue. The situation is more delicate in the case of atypical localisation. Faced with this type of symptomatic tachyacardia, ablation is a fall-back method after failure of medical treatment.

Cardiomyopathy, Dilated↗
PubMed2003

[Complications of permanent cardiac pacing].

The implantation of a pacemaker is an everyday medical procedure. New indications are under evaluation. However, it should be recalled that this is a surgical intervention with implantation of a prosthesis with possible complications. This should, therefore, be a considered decision. There are early complications which occur in the first 6 weeks after implantation. Their incidence is underestimated (up to 7%) as is their seriousness. There are late complications. Some are responsible for pacemaker dysfunction, the risk of which is proportional to the dependence of the patient on permanent cardiac pacing. The migration of a pacing catheter or the fracture of an Accufix catheter expose the patient to much greater risk. Venous complications are overlooked as they are usually asymptomatic. The superior vena cava syndrome is, however, a serious complication of cardiac pacing. Two recent studies (MOST and DAVID) underline the deleterious haemodynamic effects of unnecessary right ventricular pacing. This right ventricular pacing may have a pro-arrhythmic effect on the ventricles and be responsible for sudden death. It may also cause atrial arrhythmia even if atrio-ventricular synchronisation is preserved. Infectious complications are also under-reported, partially because of the difficulty of diagnosis. They may be life-threatening and require extraction of the implanted material. In conclusion, it is wrong to think that even if a patient does not benefit from his implanted device this cannot have deleterious consequences. Pacemakers should be adjusted especially to avoid inappropriate right ventricular stimulation.

Cardiovascular Diseases↗
PubMed2002

Biomechanical model to simulate tissue differentiation and bone regeneration: application to fracture healing.

Bone regeneration is a common biological process occurring, for example, during fracture healing or osseo-integration of prostheses. Computer simulation of bone regeneration is difficult to carry out because it is a complex sequence of cell-mediated processes regulated by mechanobiological stimuli. An algorithm to predict the time-course of intramembranous and endochondral ossification has been developed. The algorithm assumes that there are precursor cells in the undifferentiated tissue and that these cells differentiate into either fibroblasts (to form fibrous connective tissue), chondrocytes (to form cartilaginous tissue) or osteoblasts (to form bone), based on a combination of biophysical stimuli derived from strain in the collagenous matrix and flow of the interstitial fluid. Both these stimuli are known to deform the precursor cells, and the authors hypothesise that this causes activation of cell differentiation pathways. The observation that precursor cells take time to spread throughout the fracture callus has been included in the algorithm. The algorithm was tested in an investigation of the fracture healing of a long bone using an axi-symmetric finite element model. The spatio-temporal sequence of tissue phenotypes that appear in the course of fracture healing was successfully simulated. Furthermore, the origin of the precursor cells (either surrounding muscle, bone marrow or periosteum) was predicted to have a fundamental effect on the healing pattern and on the rate of reduction of the interfragmentary strain (IFS). The initial IFS = 0.15 drops to 0.01 within seven iterations if cells originated from the surrounding soft tissue, but took more than 50% longer if cells originated in the inner cambium layer of the periosteum, and four times longer if precursor cells originated from the bone marrow only.

Algorithms↗
PubMed2002

A mechano-regulation model for tissue differentiation during fracture healing: analysis of gap size and loading.

Bone has a capability to repair itself when it is fractured. Repair involves the generation of intermediate tissues, such as fibrous connective tissue, cartilage and woven bone, before final bone healing can occur. The intermediate tissues serve to stabilise the mechanical environment and provide a scaffold for differentiation of new tissues. The repair process is fundamentally affected by mechanical loading and by the geometric configuration of the fracture fragments. Biomechanical analyses of fracture healing have previously computed the stress distribution within the callus and identified the components of the stress tensor favouring or inhibiting differentiation of particular tissue phenotypes. In this paper, a biphasic poroelastic finite element model of a fracture callus is used to simulate the time-course of tissue differentiation during fracture healing. The simulation begins with granulation tissue (post-inflammation phase) and finishes with bone resorption. The biomechanical regulatory model assumes that tissue differentiation is controlled by a combination of shear strain and fluid flow acting within the tissue. High shear strain and fluid flows are assumed to deform the precursor cells stimulating formation of fibrous connective tissue, lower levels stimulate formation of cartilage, and lower again allows ossification. This mechano-regulatory scheme was tested by simulating healing in fractures with different gap sizes and loading magnitudes. The appearance and disappearance of the various tissues found in a callus was similar to histological observation. The effect of gap size and loading magnitude on the rate of reduction of the interfragmentary strain was sufficiently close to confirm the hypothesis that tissue differentiation phenomena could be governed by the proposed mechano-regulation model.

Bone Remodeling↗
PubMed2002

Three-dimensional simulation of fracture repair in the human tibia.

Finite element models of bones can be generated based on images obtained non-invasively in the clinic. One area where such models may prove useful is in the assessment of fracture healing of long bones. To establish the feasibility of such a proposal, a three dimensional finite element model of a fractured tibia was generated, and a model of tissue differentiation and bone regeneration was used to simulate the progress of healing under two different loading magnitudes. Healing is successful under the lower load and unsuccessful under the higher load--this proves that the model has the potential to identify loads that would cause healing to fail. Following a proposal by Richardson et al. [J. Bone Jt Surg. Vol. 76B (1994) pp. 389-394] that the bending stiffness can be used to assess the extent of healing, the bending stiffness was computed during healing--it was shown that the stiffness changed in a similar manner that observed clinically. In conclusion, the paper establishes that 3D computer simulation could be a tool for assessment of the fracture healing under different orthopedic treatments.

Algorithms↗
PubMed2002

[Contribution of the implantable ECG monitor in the etiologic diagnosis of syncope and unexplained recurrent syncopal attacks. Initial experience with 32 patients].

UNLABELLED: Following an exhaustive aetiological investigation, 10 to 26% of syncopal attacks remain unexplained. In these cases the correlation between symptoms and rhythm is a deciding step for the aetiological diagnosis. We report our initial experience using an implantable electrocardiographic monitor, a new diagnostic tool in patients suffering from syncope and recurrent unexplained syncopal attacks. RESULTS: The study included 32 patients (average age 55 +/- 22 years; 23 males) suffering from syncope and/or recurrent syncopal attacks remaining unexplained following an exhaustive aetiological investigation. The average follow up was 10.2 +/- 2.5 months. No case of sudden death was registered, and the device was removed in only one patient due to poor tolerance. During follow up, 21 recordings were memorized and analysed in 15 patients (45%), giving an average of 1.4 recordings per patient. The average interval for recurrence of symptoms after implantation was from 84 +/- 104 days, 75% of the episodes coming in the first 2 months following implantation. An arrhythmia was detected on 10 occasions: a malignant ventricular arrhythmia in 2 patients, a non-sustained ventricular tachycardia in 1 patient, a junctional tachycardia in 1 patient, entry into paroxysmal atrial fibrillation in 4 patients, a sinus bradycardia in 1 patient, and a sinus pause for 19 seconds in 1 patient. In one patient ST segment depression was documented following anterior chest pain. The tracing was normal with sinus rhythm recorded on 10 occasions, representing the only documented information in 4 patients. In total, an aetiology was found in 11 of the 32 patients evaluated (34%). Once the aetiological diagnosis was established and a specific treatment initiated, all the patients became asymptomatic. CONCLUSIONS: Our preliminary results underline the significance of the implantable ECG monitor in the diagnostic approach to recurrent unexplained syncopal attacks. The exact place of this tool in the decisional algorithm for syncope remains to be defined with further studies.

Adolescent↗
PubMed2001

Long-term follow-up of children and adolescents with syncope; predictor of syncope recurrence.

BACKGROUND: Previous studies have shown that investigation by tilt testing is very appropriate in paediatrics, but the characteristics of children and adolescents who are at high risk of recurrent syncope, once the diagnosis is established, remain unclear. This study was set up to analyse the risk factors attributed to syncope recurrence in paediatric patients. METHODS: One hundred and one children and adolescents aged 7 to 18 years, undergoing a tilt test for recurrent syncope, were studied. They were subsequently followed-up in clinic visits with a final interview at the clinic or by telephone at the end of the follow-up period. RESULTS: A head-up tilt test elicited syncope or pre-syncope in 67 children. The positive responses included vasovagal syncope in 58 patients and psychogenic syncope in nine patients. Gender, age, number of pre-tilt test syncopal episodes or duration of symptoms made no difference to children with positive or negative tilt test results. Following the tilt test, 43 of 67 children with a positive tilt test were treated empirically. No treatment was prescribed for the remaining 24 with a positive test, or for those with a negative tilt test. There were no differences between treated and untreated children with respect to the number of pre-tilt test syncopes, duration of symptoms and duration of follow-up. Follow-up data were available in 97 children. During a mean follow-up of 46+/-28 months, syncope recurred in 31 children (32%). The recurrence rate was similar between positive and negative tilt test groups (22/66 vs 9/31, respectively; P=ns), as well as between treated and untreated children (14/43 vs 8/23, respectively; P=ns). When comparing syncope-free children at follow-up in a univariate analysis, children with recurrent syncope reported a greater number of historical syncopal spells (7+/-8 vs 3+/-3, P=0.01). In addition linear correlation (r=0.6, 95% CI 0.47 to 0.72, P<0.0001) was significant between the number of historical syncope episodes and the risk of recurrent syncope. CONCLUSIONS: These findings suggest that the risk of syncope recurrence for children and adolescents with such a history is not correlated to the tilt test result or prophylactic treatment. The number of historical syncopal spells is, however, predictive.

Adolescent↗
PubMed2001

Prospective evaluation of a simplified approach for common atrial flutter radio frequency ablation with only two catheters.

UNLABELLED: Intra-atrial conduction block within the inferior vena cava-tricuspid annulus isthmus (IVCT) has been shown to predict successful common atrial flutter ablation. However, its demonstration requires the use of several electrode catheters and mapping of the line of block. The aim of this study was prospectively to test the feasibility of a simplified ablation procedure using only two catheters. METHODS: Radio frequency (RF) ablation of common atrial flutter was performed in 30 patients with the sole use of a catheter for atrial pacing and a RF catheter. RF ablation lesions were created in the IVCT. Surface ECG criteria were used to monitor the conduction within the IVCT. The end point during low lateral atrial pacing was an increment in the interval between the pacing artefact and the peak of the R wave in surface lead II >50 ms and clockwise rotation of the P wave axis beyond -30 degrees and inferiorly. Then, the line of lesions was mapped during atrial pacing with the RF catheter. Additional RF lesions were applied if mapping disclosed a zone of residual conduction. Otherwise the procedure was stopped if mapping showed parallel double potentials all along the line. Finally, the block was reassessed with a 'Halo' catheter. RESULTS: Surface ECG criteria were met in 26 patients. Mapping the line of lesions showed a complete corridor of parallel double potentials in these 26 cases and in 3 of the 4 patients in whom ECG criteria were not met. Conduction evaluated with the Halo catheter showed bi-directional complete block in these 29 patients. After a follow-up of 16 +/- 4 months there was no recurrence of atrial flutter. CONCLUSION: Surface ECG criteria combined with mapping of the line of block demonstrate evidence of bi-directional IVCT block. This simplified RF ablation of common atrial flutter is feasible with a low recurrence rate.

Aged↗
PubMed2000

Randomized comparison of two targets in typical atrial flutter ablation.

Typical atrial flutter ablation has become anatomically guided to 2 separate sites within the isthmus at the inferior right atrium: (1) between the inferior vena cava and the tricuspid annulus (anterior side of the isthmus [A]), (2) between the eustachian crest, the coronary sinus ostium and tricuspid annulus (posterior side of the isthmus [P]). We prospectively compared ablation results at these sites in 72 consecutive patients. Patients were randomized in group P or A according to the initial target site. If ablation failed at 1 site after 15 radiofrequency (RF) pulses, the other side of the isthmus was targeted. Before 15 RF pulses, complete bidirectional isthmus block was achieved in 30 of 36 group A patients and in 25 of 36 group P patients, with similar mean RF pulses number, procedure time, and fluoroscopy time. After shifting to the other target, success was finally obtained at P in 2 of 6 group A patients, and at A in 8 of 11 group P patients before a maximum of 30 RF pulses. Among successful patients, number of RF pulses, procedure time, and fluoroscopy time were significantly lower in group A (7.2 +/- 5.4 vs 11.0 +/- 8.1 pulses, p = 0.03; 131 +/- 44 vs 163 +/- 66 minutes, p = 0.03; 31 +/- 19 vs 46 +/- 24 minutes, p = 0.01, respectively). Impairment of atrioventricular (AV) nodal conduction occurred in 5 patients only during ablation at P. AV block was transient in 4 patients and permanent in 1. Although atrial flutter ablation is equally effective at P and A, success seems easier to obtain when A is first targeted. Ablation at P is associated with a significant risk of AV block.

Adult↗
PubMed2000

Long-term evaluation of autonomic tone in patients below 50 years of age with unexplained cerebral infarction: relation to atrial vulnerability.

UNLABELLED: Preliminary studies have described, in young patients with unexplained cerebral infarction, electrophysiological abnormalities similar to those observed in paroxysmal atrial fibrillation. Moreover, in young adults with 'normal' hearts, increased susceptibility to paroxysmal atrial fibrillation with autonomic abnormalities as assessed by heart rate variability analysis have been reported. METHODS: The long-term time and frequency domain measures of heart rate variability were analysed prospectively from 24-h Holter ECG recordings in 25 patients (39 +/- 8 years) with unexplained cerebral infarction, and in 25 age-, sex- and cigarette-smoking-matched healthy control subjects. The day following the Holter ECG recordings, 9 +/- 4 months (mean) after the stroke, stroke patients underwent an electrophysiological study in order to analyse the electrical characteristics of their right atria and also to determine their vulnerability to atrial fibrillation. The correlations between autonomic tone parameters and electrophysiological findings were therefore assessed with linear regression analyses. RESULTS: All the measured components of heart rate variability either in time (SDNN, pNN50, SDANN/5, rMSSD) or frequency domains (total power, low-frequency, high-frequency power, low-frequency/high-frequency power ratio) were similar between stroke patients and controls. During electrophysiological study, atrial fibrillation was induced in 80% of stroke patients. Among these patients, atrial refractory periods were significantly shorter, local electrograms were longer, and latent atrial vulnerability index was markedly decreased when compared with patients having no inducible atrial fibrillation. Concerning heart rate variability analysis, no difference was found between patients with induced atrial fibrillation when compared with a matched subgroup of healthy control subjects. Furthermore, there was no statistically linear correlation between any of the measured autonomic tone parameters and any of the discovered atrial vulnerability markers. CONCLUSIONS: The long-term autonomic tone parameters of young patients presenting with a history of unexplained cerebral infarction are similar to those of healthy control subjects and are not correlated with atrial vulnerability parameters or atrial fibrillation inducibility.

Adult↗