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Biomedical subjects

M Dubuc

Publications and source records attributed to M Dubuc.

At least 37 records · Page 2Linked to original sources
PubMed1998

One-to-two atrioventricular conduction causing nonreentrant tachycardia: successful treatment with radiofrequency ablation.

The anatomical substrate for AV nodal reentrant tachycardia (AVNRT) is well known and is due to anterograde conduction through a slow conducting pathway and retrograde conduction using a fast conducting pathway. In this report, we describe a patient with AVNRT who also presented with frequent episodes of paroxysmal nonreentrant tachycardia due to the occurrence of two conducted ventricular beats for each sinus depolarization. Palpitations and arrhythmias were abolished after radiofrequency ablation of the slow pathway.

Adult↗
PubMed1998

Is there a future for antiarrhythmic drug therapy?

Drug therapy has traditionally been the mainstay of treatment for both ventricular and supraventricular arrhythmias. However, increasing knowledge about the potentially significant adverse effects of these medications, together with the emergence of new, nonpharmacological approaches to the treatment of arrhythmias, has led some to question the future of antiarrhythmic drug therapy. Antiarrhythmic drugs are quite effective in terminating a variety of arrhythmias, including atrioventricular (AV) node re-entrant and AV tachycardias (particularly calcium antagonists and adenosine), atrial flutter (class III agents) and atrial fibrillation (class IA and IC drugs. The chronic use of antiarrhythmic drugs has been increasingly limited by a fear of adverse effects (especially proarrhythmia) and the availability of highly effective nonpharmacological alternatives (particularly ablation for re-entrant tachycardias involving the AV node and bypass tracts and cardiovertor/defibrillators for malignant ventricular arrhythmias. Atrial fibrillation (AF) continues to be a therapeutic challenge for which there is no safe and curative nonpharmacological therapy. Antiarrhythmic drugs of classes IA, IC and III show efficacy in preventing recurrence of AF but there are concerns about possible pro-arrhythmic complications. In the future, antiarrhythmic agents will continue to be used acutely to terminate a broad range of sustained arrhythmias. Chronic use is likely to depend on the development of safer and/or more effective compounds, as well as on improved ways of predicting which patients are likely to develop pro-arrhythmic reactions. The development of molecular electrophysiology will allow for the identification of agents with selected ion channel blocking profiles which may prove efficacious with a lower risk of complications. Finally, an improved understanding of arrhythmia substrates may permit the identification of therapy that prevents arrhythmias by acting on the underlying substrate, rather than simply trying to modify the electrical end product.

Anti-Arrhythmia Agents↗
PubMed1998

AIDS talks for adolescents.

The authors discuss how to conduct information sessions on AIDS prevention for adolescents on the basis of experience gained in Marseilles secondary schools. Precautionary messages have to be conveyed without encouraging irrational fear and intolerance.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Pilot study and protocol of the Canadian Trial of Atrial Fibrillation (CTAF).

Antiarrhythmic drug prophylaxis in patients with atrial fibrillation (AF) is associated with a high incidence of arrhythmic recurrence. Uncontrolled studies have suggested that low-dose amiodarone may be superior in terms of efficacy to other antiarrhythmic drugs while having an acceptable side effect profile. The Canadian Trial of Atrial Fibrillation (CTAF) is a 25-center study sponsored by the Medical Research Council of Canada to determine the best treatment strategy to maintain sinus rhythm in patients with persistent or paroxysmal AF. Recruitment began in November 1996 and will continue for 1.5 years. Patients are randomized to receive either low-dose amiodarone or conventional antiarrhythmic drug therapy. Patients assigned to the amiodarone group will receive an oral loading regimen of 10 mg/kg/day during a minimum 14-day period. Patients assigned to conventional antiarrhythmic therapy will receive 1 of 2 agents commonly used in AF prophylaxis: sotalol or propafenone. Drug selection and loading, and electrical cardioversion, if necessary, will be performed within 21 days of randomization. The long-term maintenance dose of amiodarone is 200 mg/day. We have planned a minimum follow-up period of 1 year. The primary end point is the time to the first relapse of AF. Data will be analyzed on an intention-to-treat basis. Secondary outcomes are medication toxicity, mortality, major clinical events, costs of each approach, and quality of life. For the purpose of sample size calculations, it is anticipated that recurrence of AF at 1 year will occur in 50% of patients on conventional treatment compared with 35% in those receiving amiodarone. In order to have an 80% power and a 2-tailed type I error of 0.05, assuming a 15% loss to follow-up rate, a total sample size of 400 patients will be required. A pilot study done at the Montreal Heart Institute has shown that the research protocol is feasible.

Amiodarone↗
PubMed1997

Spatial resolution and role of pacemapping during ablation of accessory pathways.

The objectives of this study were: (1) to evaluate quantitatively the spatial resolution of pacemapping; and (2) to assess the predictive value and role of pacemapping for the catheter ablation of overt APs. Sixty-three unipolar leads were used instead of the standard 12-lead ECG to acquire more information and assess the intrinsic accuracy of pacemapping. Spatial resolution was evaluated in 19 patients for whom data were recorded during bipolar ventricular pacing near the AV ring using the three electrode pairs of a quadripolar ablation catheter with a 5-mm interelectrode spacing. The predictive value was assessed in 27 patients with overt APs who underwent RF ablation; their data were recorded during pacing at the site of successful ablation and at one or two sites where RF energy delivery was ineffective. Data from different beats were compared visually by using body surface potential maps and quantitatively by computing average correlation coefficients (r). Reproducibility was high for paced beats (r = 0.98 +/- 0.02). Displacements of 5 mm of the pacing site could be detected with a sensitivity of 90% and a specificity of 87%. Correlation between pacing at successful ablation sites and preexcited sinus rhythm was low (r = 0.79 +/- 0.11) and the ablation outcome could be predicted with a negative prediction accuracy of 87% and a positive prediction accuracy of 49%. Despite an excellent spatial resolution, pacemapping is of limited value for the identification of successful AP ablation sites, probably because APs can be interrupted at some distance from their ventricular insertion point.

Adult↗
PubMed1997

[Modalities of reading of detection mammographies of the programme in the Bouches-du-Rhône. Results and costs 1990-1995].

In the Bouches du Rhône breast cancer screening programme, mammograms are read by two separate radiologists of different levels of training. All women with at least one positive reading are recalled for further assessment. During the first round, 3,477 of the 95,967 screenees were recalled by the first reader and 2,321 by the expert reader. The expert increased cancer detection by 15% and 45% of cancers detected by the expert were smaller than 11 mm. The marginal cost of double reading was 21,838 Francs per additional cancer detected. Double reading thus allowed for the detection of cancers of good prognosis which would have gone undetected by a single reader. Its cost seems justified by its impact on the effectiveness of the screening programme.

Aged↗
PubMed1997

Radiofrequency ablation of bundle branch reentrant tachycardia in a patient with atrial septal defect.

A 22-year-old woman with an atrial septal defect surgically corrected during childhood presented with a wide QRS complex tachycardia with left bundle branch block morphology. Electrophysiological study was performed and bundle branch reentrant tachycardia was induced with morphology identical to clinical tachycardia. Radiofrequency catheter ablation of the right bundle branch was successful, resulting in complete right bundle branch block and cure of her ventricular arrhythmia.

Adult↗
PubMed1997

Mass screening programs for breast cancer in France--average values of assessment criteria.

Breast cancer is the most common cancer in women worldwide. Many studies have been performed worldwide to assess the effectiveness of screening in terms of reduced mortality due to breast cancer. Since the end of 1989, 10 breast cancer mass screening programs using mammography have been carried out in France under the sponsorship of the National Fund for Health Prevention, Education, and Information (FNPEIS) from the National Health Insurance of Salaried Workers (CNAMTS). These 10 campaigns, which are on a district scale, are organized according to variable methods and are assessed using a common procedure. Four groups of criteria are measured in this procedure, which investigates the impact, quality, effectiveness, and costs of screening programs. The average and extreme values of each criterion as calculated from the campaigns are presented in this paper. In order to enlighten the judgment on the French results, a comparison with the international standards in force and with the results of foreign screening programs is proposed.

Aged↗
PubMed1997

Use of mammography as a breast cancer screening tool in six districts in France.

Mass screening programs to detect breast cancer are currently under way in many countries. In France, several districts have been running mammographic screening programs since 1989. A survey was conducted in five of these districts and in a sixth district where no screening program was implemented. Using a self-addressed questionnaire mailed to a sample of 1500 women aged over 20 years, the survey was aimed at assessing women's use of mammography as well as their knowledge and perception of mammographic breast cancer screening. According to district, the compliance of the women replying to the questionnaire ranged from 72 to 82%. The proportion of women who had at least one mammography during their life ranged from 41 to 54%, according to district. The percentage of women aged 50 to 69 who had one mammography within 3 years before the survey ranged from 57 to 78% in the experimental districts and was only 48% in the control district. In all districts, women did not know exactly at what age it is recommended to start screening and with what periodicity, but, when invited to do so, they were satisfied with the program and intended to participate again.

Adult↗
PubMed1997

[Mass screening programs for breast cancer in France. Comparative evaluation].

OBJECTIVE: The purpose of this work was to comparatively assess the results of mass screening programs for breast cancer implemented in six French departments in 1986, within the scope of the National Fund for Health Prevention, Education and Information of the National Health Insurance Office of Salaried Workers. MATERIAL AND METHODS: The data collected by the screening centres were analyzed by ten assessment teams that were independent from the program promotion staff, all using the same evaluation form. A complementary population study performed in eight French districts then, allowed assessing the frequency of self-referred screening (mammography performed out of program). RESULTS: The rate of participation in screening programs, in relation to the invited population, ranged from 21 to 48%, according to the district (36% in average). This low participation was probably related to the extent of self-referred screening. In fact, 19 to 40% of women, according to the district, had previously had a screening mammographic coverage: rate was around 68% in women aged 50 to 69 years. Positive findings with mammography ranged from 4.5 to 15.8% (10.1% in average), while intervention rates ranged from 0.7 to 1.6% and detection rates from 3.8 to 6.2%. The ratio between benign tumors and cancers ranged from 0.7 to 2.1 according to the district. In order to enlighten the judgement on French results, we propose a comparison with the international standards in force. CONCLUSION: The various experiences with breast cancer screening in France show that this screening is technically feasible on the basis of existing medical structures. However, some criteria are still below the expected values, especially if compared with international standards. This result is probably accounted for by the high rate self-referred screening before age 40 in France. In these conditions, the question is whether extending breast cancer screening programs in France is an appropriate course of action.

Breast Neoplasms↗
PubMed1995

Body surface potential distributions during idiopathic ventricular tachycardia.

BACKGROUND: The purpose of this report is to describe the body surface potential maps (BSPMs) during idiopathic ventricular tachycardia (VT) and to determine what differences exist between different idiopathic VT morphologies. METHODS AND RESULTS: We performed BSPMs during VT on 12 consecutive patients (3 women and 9 men; mean age, 42 +/- 13 years) presenting symptomatic idiopathic VT referred to our institution for electrophysiological study. Basal ECG, chest radiograph, and echocardiogram were normal in all patients. Clinical tachycardia showed left bundle branch block pattern (LBBB) in 9 patients, with sustained VT in 5 and nonsustained VT in 4, and right bundle branch block pattern (RBBB) in 3 with sustained VT. We found a unique pattern of BSPMs in each of the 9 patients during idiopathic LBBB VT configuration, whether sustained or nonsustained VT. This pattern appeared at the onset of the QRS and remained stable during the whole QRS complex. The area of minimal potential located in the upper anterior part of the torso was compatible with an origin of VT in the right ventricular outflow tract, as confirmed in 5 patients by successful radiofrequency ablation. We found an evolving pattern with two phases in each of the three RBBB VTs. The electrical axis during the initial part of the QRS could correspond to an endocardial-epicardial vector. The second phase, with a high voltage and area of minimal potential located in the inferior and anterior part of the torso, was compatible with a left ventricular apical origin that was confirmed by epicardial and endocardial mapping during cryosurgery in 1 patient. For all the VTs, the QRS isoarea maps showed the same pattern as the second phase of the QRS. CONCLUSIONS: Two different BSPM patterns were found. All LBBB VTs had the same stable pattern corresponding to an infundibular origin. All RBBB VTs had an evolving pattern that stabilized in the second part of the QRS complex corresponding to an apical origin.

Adult↗
PubMed1994

Radiofrequency catheter ablation of an accessory pathway in a young man with dextroversion.

We report an observation of a radiofrequency catheter ablation of an accessory pathway (AP) in a patient with Wolff-Parkinson-White syndrome (WPW) and dextroversion. Atrioventricular rings were mapped by the ablation catheter to locate the shortest local atrioventricular conduction time in sinus rhythm and ventriculoatrial conduction time during orthodromic tachycardia or ventricular pacing. Successful ablation confirmed a right posteroseptal AP localization. Thus, the electrocardiographic modifications due to an AP in this location in the presence of dextroversion were defined.

Adult↗
PubMed1993

Bipolar transseptal radiofrequency ablation of AV node: an alternative to high energy shocks?

Atrioventricular (AV) node ablation to control ventricular response was attempted in two patients with recurrent drug refractory atrial flutter. Standard radiofrequency (RF) procedure, which delivers energy through the 4-mm tip electrode of an ablation catheter positioned at the right AV junction and a large back plate (unipolar mode), failed in both patients. As an accepted second step, high energy direct current (DC) ablation under general anesthesia was then performed in patient one. After two shocks of 200 J, complete AV block occurred, but complete recovery was noted 3 hours later. In a third session for patient 1 and in the first session for patient 2 (after 15 unsuccessful unipolar right-sided RF applications), a second ablation catheter was introduced via the femoral artery on the left side of the His bundle area under the aortic valves. Energy was then delivered in a bipolar fashion between the tip electrodes of the right-sided and the left-sided catheter. Complete and permanent AV block (follow-up: 3 and 1 months) was created within 4 and 1.5 seconds, respectively, in each patient. No complication was encountered and echocardiograms and blood levels of cardiac enzymes were all normal after the procedures. This new approach, after further evaluation, may represent a useful additional step in the strategy of AV node ablation and could be applied before high energy DC shock when the standard RF procedure is unsuccessful.

Adult↗
PubMed1993

Pace mapping using body surface potential maps to guide catheter ablation of accessory pathways in patients with Wolff-Parkinson-White syndrome.

BACKGROUND. A pace mapping technique using body surface potential maps (BSPMs) was developed to guide the positioning of an ablation catheter at the ventricular insertion point of accessory pathways (AP) in patients with the Wolff-Parkinson-White syndrome (WPW). METHODS AND RESULTS. The study was performed on 30 WPW patients. BSPMs were recorded with 63 leads distributed over the entire torso surface. The catheter used for radiofrequency ablation was first placed in the vicinity of the ventricular preexcitation site predicted by BSPMs recorded during the delta wave. BSPMs were then recorded during pacing with this catheter, the comparison between the preexcited and paced BSPMs indicated whether the pacing site was too anterior or posterior with respect to the preexcitation site, and the catheter was moved accordingly. This process was repeated until the preexcited and paced BSPMs were highly correlated (r > or = 0.8), and ablation then was attempted. It was possible to successfully ablate the AP in 28 patients after an investigation that lasted 54 +/- 44 minutes between the recording of the first paced BSPM and that of the BSPM paced at the successful ablation site. Patients with left free wall pathways needed less investigation time compared with patients with pathways of other locations (46 +/- 9 versus 100 +/- 25 minutes, p = 0.031). The sensitivity of BSPM pace mapping was assessed using pacing with a multipolar catheter, and significant changes were observed on the BSPMs for beats with pacing sites that were only 5 mm apart. CONCLUSIONS, BSPM pace mapping allowed us to achieve a 93% success rate with short investigation durations, provides significant information that cannot be obtained with the standard 12-lead ECG, is a self-correcting procedure that reduces the importance of BSPM alterations due to individual differences in the shape of the torso or heart, and is applicable only to patients with AP showing antegrade conduction.

Adolescent↗