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Biomedical subjects

C Sebag

Publications and source records attributed to C Sebag.

At least 19 recordsLinked to original sources
PubMed1997

[Radiofrequency ablation of accessory atrioventricular pathways].

Since its introduction at the beginning of the 1980s, radiofrequency ablation of accessory atrioventricular pathways has become method because of its excellent results and the indications have increased to cases in which only symptomatic improvement is the objective. These advances have been made possible by technical innovations to the generators of the radiofrequency current and, above all, to the ablation catheters which enable mapping nearly all the perimeter of the atrioventricular rings and reach all the accessory pathways irrespective of their site. The approach depends on the localisation of the accessory pathway but the criteria of mapping are the same: detection of a specific accessory pathway potential, precession or concordance (depending on the topography) of the initial peak of the endocavitary ventriculogramme and the onset of the delta wave on the surface ECG, QS morphology of the ventriculogramme on monopolar recording, shortest VA' interval in orthodromic reciprocating tachycardia for latent kent bundles. In specialised centres, the global success rate is 90 to 98% but certain sites, especially the right lateral pathways, are more difficult to attain. The complication rate is about 4% but it tends to decrease with the experience of the operating teams and close monitoring of the patients. However, there persists an uncertainty concerning potentially arrhythmogenic effects of the lesions induced which justifies restricting the indications in young children.

Arrhythmias, Cardiac↗
PubMed1997

[Classification and pitfalls of atrioventricular blocks].

Atrioventricular blocks may be classified according to their degree, their site and their aetiology. Assessing the degree of block is not always easy when the P waves are poorly visible and/or masked by the ventricular complexes. Affirmation that a 2nd degree block is a Mobitz II block requires examination of the ECG to differentiate it from "false" Mobitz II due to variable PP intervals or concealed hisian extrasystoles. Complete atrioventricular block is easy to define on the ECG but not always synonymous with totally blocked conduction and should be interpreted taking into account the frequency of escape beats. Determining the site of block is important as it has therapeutic implications; the type of block evaluated from the surface ECG also provides useful but not always decisive information. The investigation of the aetiology of the block is valuable for differentiating acute, transient blocks from chronic (permanent or paroxysmal) blocks, the former sometimes requiring temporary but rarely permanent cardiac pacing.

Body Surface Potential Mapping↗
PubMed1996

Initial and long-term evaluation of escape rhythm after radiofrequency ablation of the AV junction in 50 patients.

Between 1986 and 1994, 50 patients (mean age 63 +/- 13 years), 25 of whom had organic heart disease and presenting with atrial arrhythmias refractory to 5.6 +/- 1.6 antiarrhythmic drugs, underwent radiofrequency ablation (5 +/- 3 pulses by procedure; duration of pulses 50.5 +/- 32 s) of the proximal AV junction to create complete and permanent AV block. The escape rhythm was studied immediately after the procedure and during long-term follow-up. Immediately after the procedure, an escape rhythm was observed in 80% of the patients (junctional in 92%). Over a mean follow-up of 36 +/- 16 months in 47 patients (2 patients died before assessment of escape rhythm and 1 was lost to follow-up), an escape rhythm was present in 39 patients (83%) and absent in the remaining 8 (17%). The only significant difference between the two groups was the initial presence of an escape rhythm (P = 0.008). However, three patients with an initial escape rhythm had none during long-term follow-up. The initial presence of an escape rhythm as a predictive factor of its presence during follow-up had a sensitivity of 87%, specificity of 63%, positive predictive value of 92%, and negative predictive value of 50%. Thus, the absence of an escape rhythm during long-term follow-up causing pacemaker dependency was noted in 1 of 6 patients. This represents a limitation to this palliative treatment, which should be reserved for patients suffering from supraventricular tachycardias refractory to other treatments.

Adult↗
PubMed1996

[Radiofrequency ablation: physical bases and principles].

Radiofrequency currents are the reference physical agent for endocavitary ablation, especially of supraventricular tachycardias. They are delivered in a continuous mode or sinusoidal waves. Because of the high frequency between 200 and 3,000 kHz there is no stimulation of the neuromuscular cells. The mechanism of the resulting lesion is essentially related to heating of the biological surroundings of the active electrode. The temperature increase remains localised around the active electrode and its kinetics are progressive, which implies close and stable contact between the active electrode and the tissues. The lesional effect is obtained 60 to 90 degrees C in order to avoid the deleterious effects induced by temperatures of over 100 degrees C: boiling, coagulation, vaporization and carbonization of the tissues leading to an increase in impedence. The volume of lesions depends on many factors which are sometimes difficult to control in vivo. It is more closely correlated to the temperature of the active electrode than to the parameters of delivery (power, duration ...). The histological lesions correspond to scar tissue which respects the surrounding architecture. The major technological innovations of this method have resulted in an increase in the volume of the lesions produced, a reduction in the frequency of undesirable effects such as the formation of coagulum and in an immediate evaluation of the anatomic lesional effect. They have consisted in the introduction of specific electrodes and of systems of monitoring the electrical and thermal effects with the use of imaging techniques such as endovascular and transoesophageal echocardiography and angioscopy. New indications will require development of specific catheter-generator equipment to create lesions of size and shape adapted to the arrhythmogenic substrate.

Animals↗
PubMed1995

[Electrocardiographic aspects of atrial fibrillations].

The electrocardiographic analysis of atrial fibrillation is usually easy. However, some cases may be difficult to interpret: the organisation and voltage of the fibrillation waves can be very variable leading to appearances of atypical flutter in cases with large "f" waves or, conversely, in cases with low voltage fibrillation, to those of sinus mode dysfunction. The ventricular response may be slow: the conduction is usually delayed in the atrioventricular node where concealed conduction plays an important role in determining the ventricular response. Regular ventriculogrammes correspond to a junctional or ventricular escape rhythms. Aberrant conduction in the His-Purkinje system may sometimes be observed after long diastoles (phase 4 block) but often terminates short, preceded by long cycles (phase 3 block). It is usually easy to differentiate them from ventricular ectopics or preexcitation by careful examination and application of classical diagnostic criteria.

Atrial Fibrillation↗
PubMed1995

[Double responses].

Double response is a rare electrocardiographic phenomenon requiring two atrioventricular conduction pathways with very different electrophysiological properties. Double ventricular responses are the usual manifestation: an atrial depolarisation (spontaneous or provoked, anticipated or not) is followed by a first ventricular response dependent on an accessory pathway or a rapid nodal pathway and then a second response resulting from sufficiently delayed transmission through a nodal pathway for the ventricles to have recovered their excitability when the second wave of activation reaches them. A simple curiosity when isolated and occurring under unusual conditions, particularly during electrophysiological investigation of the Wolff-Parkinson-White syndrome, the double response may initiate symptomatic non-reentrant junctional tachycardia when associated with nodal duality and repeating from atria in sinus rhythm. The functional incapacity and resistance to antiarrhythmic therapy may require referral for ablation of the slow pathway.

Atrioventricular Node↗
PubMed1994

[Radiofrequency catheter ablation: theoretical and technical aspects].

Radiofrequency currents produce circumscribed tissue necrosis by progressive and localised heating. Endocardial application via the percutaneous approach with a specific electrophysiological catheter enables destruction of the anatomical substrate of many cardiac arrhythmias. The technique is well tolerated due to the absence of barometric phenomena and general anaesthesia, and the possibility of modulating the energy delivered, which explains why it has supplanted fulguration in most indications. The technological evolution aims to increase the lesional power and decrease the number of complications. This implies the development of catheters capable of delivering greater currents without the risk of thrombus formation and of generators dependent on electrical or thermal parameters. The low incidence of complications reported by centres using the technique is based on an excellent understanding of the technique, the use of appropriate material, the surveillance of parameters which allow detection of unwanted effects and the respect of a strict operation protocol. In the absence of these precautions, the wide diffusion of this technique, favored by its low cost and relative simplicity, may be associated with an increase in the number of side effects which could be lethal. This cannot be accepted in a technique with such wide indications, including arrhythmias with a usually benign long-term prognosis.

Animals↗
PubMed1994

[Electrophysiological mechanisms of ventricular arrhythmia in myocardial infarction].

In experimental models of coronary occlusion, the physiopathology of ventricular arrhythmias varies with its timing, there being three main phases: early, late and chronic. The early phase covers the first 30 minutes and is dominated by tachycardias and fibrillations resulting from multiple micro-reentry circuits which are the consequence of major changes in conduction and excitability created by acute ischaemia. These arrhythmias may be triggered by extrasystoles which have a different mechanism related to the injury current generated in the border zone between ischaemic and healthy cells. The late phase lasts about 72 hours: it is characterised by polymorphic ventricular extrasystoles and bursts of relatively slow ventricular tachycardia. Much more rapid tachycardia can be induced by stimulation. The origin of these arrhythmias is usually in the surviving Purkinje fibres of the subendocardium. The mechanisms are variable: abnormal automaticity, reentry or activity triggered by delayed after depolarisations. During the chronic phase, reentrant tachycardia is possible but only when induced by stimulation. Delayed conduction is the consequence of non-uniform antisotropism related to the disorientation of the myocardial fibres caused by fibrosis. In the clinical situation, most research has been centered on sustained monomorphic ventricular tachycardias of the chronic phase. Their mechanism is almost exclusively reentry (the circuits usually being located in the subendocardium) as suggested by the triggering and interruption of clinical tachycardias by stimulation, the recording of fragmented activation or prepotentials at the site of emergence of the tachycardia and the phenomena of pacing.

Arrhythmias, Cardiac↗
PubMed1993

Percutaneous double balloon valvuloplasty for stenosis of porcine bioprostheses in the tricuspid valve position: a report of 2 cases.

The feasibility and results of percutaneous double balloon valvuloplasty were evaluated in 2 patients with stenosis of porcine bioprostheses in the tricuspid valve position. The procedures were performed with a Trefoil 3 x 10 and a 15 mm balloon. Long inflations (4 and 3 minutes) were well tolerated. A significant immediate increase in the valve area, without significant valvular regurgitation, was achieved in both cases, from 0.65 to 1.15 cm2 in case 1 and from 0.9 to 1.65 cm2 in case 2. Both patients required valve replacement during the follow-up, at 14 and 21 months. There was no restenosis, but echocardiography showed right atrial thrombosis in case 1. Progressive restenosis with peripheral edema and increase of the mean doppler gradient occurred in case 2. The procedure is feasible, safe, and well tolerated. It provides significant immediate hemodynamic improvement, but it should be considered as a palliative technique since a normal valve area can not usually be obtained and a restenosis is likely to occur at midterm follow-up.

Adult↗
PubMed1993

Cardiopulmonary response during exercise of a beta 1-selective beta-blocker (atenolol) and a calcium-channel blocker (diltiazem) in untrained subjects with hypertension.

The effects of beta-blockers and calcium-channel blockers on cardiopulmonary response during exercise are not well characterized. Sixteen sedentary patients with essential hypertension underwent a randomized, double-blind, cross-over study comparing atenolol and diltiazem sustained-release 300 mg, each administered during 6 weeks, after a 15-day run-in placebo period. Neither atenolol nor diltiazem significantly affected maximal exercise duration, maximal oxygen uptake, ventilatory threshold, or any of the ventilatory parameters during exercise. With atenolol, the maximal oxygen pulse was significantly increased and compensated for the decrease in heart rate during exercise. Atenolol and diltiazem do not limit maximal exercise tolerance in untrained hypertensive subjects, but the circulatory profile is more preserved with diltiazem.

Adult↗
PubMed1992

[Drug treatment of chronic ventricular arrhythmia].

The treatment of chronic ventricular arrhythmias depends on the severity and tolerance of the arrhythmia. Extrasystoles, even repetitive, in the healthy heart, are usually respected when asymptomatic or treated with betablockers in first intention when symptomatic. These drugs should also be proposed for patients with ischemic heart disease and non-sustained ventricular tachycardia, a situation in which Class I antiarrhythmics should be avoided. The prevention of sustained ventricular tachycardial may be empirical, with betablockers and/or amiodarone, or guided by the results of pharmacological tests during endocavitary electrophysiological studies.

Adrenergic beta-Antagonists↗
PubMed1992

[How to evaluate the arrhythmogenic risk after myocardial infarction?].

The risk of sudden arrhythmic death after myocardial infarction is high, especially during the first months. The evaluation of this risk should be performed before hospital discharge in the same way as residual ischaemia and left ventricular function, which are independent risk factors for arrhythmia, are assessed. Holter monitoring provides information not only about ventricular hyperexcitability (especially the detection of unsustained ventricular tachycardia) but also about the activity of the autonomic nervous system by analysis of variations of the sinus rhythm, the decrease of which carries a poor prognosis. The search for an arrhythmogenic substrate requires signal averaged electrocardiography, but although the absence of late potentials carries a good prognosis, the positive predictive value of this investigation is very low. The association of non-invasive indices of poor prognosis greatly increases the probability of a major arrhythmic event; this may require consideration of programmed ventricular pacing, another method of substrate and risk assessment, which has the added advantage of sometimes indicating the most appropriate therapy.

Arrhythmias, Cardiac↗
PubMed1992

[Percutaneous ablation of atrioventricular junction by radiofrequency current in resistant atrial arrhythmia. Results of a series of 24 patients].

Catheter ablation of the atrioventricular junction may be proposed for the treatment of certain atrial arrhythmias resistant to antiarrhythmic therapy. One of the methods currently being evaluated uses radio-frequency energy which has certain advantages compared with direct current ablation because of the progressive and limited lesions it produces. This technique was used in 24 patients with atrial arrhythmias resistant to antiarrhythmic therapy. The radio-frequency energy was delivered without general anaesthesia with HAT 100 and 200 (OSYPKA) generators in the unipolar mode (average 17.4 watts) for an average period of 22.3 +/- 8 seconds. The catheter (8F USCI suction catheter in the first 18 patients and a 7F Polaris Mansfield, deflectable catheter with a large distal electrode in the remainder) was positioned at the nodo-hisian junction at a point where the two distal electrodes recorded a large atrial deflection and the smallest possible hisian potential. The conduction defects induced during the acute phase generally remain stable in cases of complete atrioventricular block and tend to regress in cases of incomplete atrioventricular block despite initial control of atrioventricular conduction. During follow-up (21 +/- 16 months), 14 patients (58%) remained in complete atrioventricular block, 4 patients (17%) had controlled atrioventricular conduction with an acceptable ventricular rate with associated previously ineffective antiarrhythmic therapy. Radio-frequency ablation was a failure in 6 patients (25%). There were no haemodynamic, rhythmic or ischaemic complications during the acute phase or during follow-up. These results suggest radio-frequency energy is a seductive alternative to direct current ablation for percutaneous modification of atrioventricular conduction in patients with refractory atrial arrhythmias. However, simple modulation of atrioventricular conduction gives aleatory results due to the tendency to regression during follow-up. On the other hand, complete atrioventricular blocks created by radio-frequency energy are generally definitive and are associated with a junctional escape rhythm which is usually stable.

Adult↗
PubMed1991

Complete atrioventricular block following mediastinal irradiation: a report of six cases.

Complete atrioventricular block (AVB) following radiotherapy has been reported rarely, usually after high dose mediastinal irradiation for Hodgkin's disease or lung or breast carcinoma. We report six new cases of episodic complete infranodal AVB, requiring permanent pacemaker implantation. The mean age was 48-years old (ranging from 25-60) at the first Adams Stokes attack, mean delay was 12 years after irradiation (10-18), and mean radiation dose was 5,200 rads (4,000-6,500). All patients had abnormal interval electrocardiograms (right bundle branch block in two, left bundle branch block in three, alternating left and right bundle branch block in one). Electrocardiograms during the episode of AVB or Holter recordings were consistent with infranodal block in all patients; electrophysiological study performed in five patients confirmed infranodal AVB in four, and one was normal. Pericardial disease was constant, which included pericardial constriction in four patients. Two patients died after failure of pericardiectomy to improve congestive heart failure, due to epicardial, myocardial, and endocardial involvement. Noncardiac mediastinal lesions were present in four cases. Since this delayed complication may occur in patients of such age that the relation between the AVB and the chest irradiation is questionable, we propose the following etiologic criteria; high radiation dose (over 4,000 rads); delay of 10 years or more; abnormal interval tracings; pericardial involvement; and associated cardiac or mediastinal radiation-induced lesions.

Adult↗
PubMed1990

Predictive value of electrophysiologic studies during treatment of ventricular tachycardia with the beta-blocking agent nadolol. The Working Group on Arrhythmias of the French Society of Cardiology.

Sixty patients with recurrent inducible sustained ventricular tachycardia were prospectively treated with nadolol (40 or 80 mg/day). Old myocardial infarction was present in 43 patients and dilated cardiomyopathy in 12. In group I (n = 36), nadolol was given alone, whereas in group II (n = 24), previously ineffective treatment with amiodarone was continued in combination with nadolol. Left ventricular ejection fraction was higher in patients in group I (0.40 +/- 0.12) than in group II (0.30 +/- 0.10, p less than 0.01) patients. Electrophysiologic study was repeated after short-term treatment with nadolol, which was continued regardless of the results of this test, according to the scheme of the parallel approach. Recurrence of spontaneous tachycardia or sudden death occurred in 21 patients after 10 +/- 9.2 months; sustained tachycardia was inducible in 19 on nadolol therapy. The remaining 39 patients (of whom 21 had inducible tachycardia while taking the drug) have had no recurrence of tachycardia after 27.8 +/- 9.3 months of follow-up study. Sensitivity, specificity and predictive value of a positive and negative test were 90.5%, 46%, 47.5% and 90%, respectively. The results differ between group I and group II patients, the latter having a high percent of false positive responses. This difference is even more obvious with respect to left ventricular ejection fraction: the predictive value of a positive test was 86% when ejection fraction was greater than 0.40 and 39% when it was less than 0.40.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

[Clinical electrophysiologic properties of magnesium and correlations with its anti-arrhythmia efficacy in acquired torsade de pointes].

Recently, intravenous administration of low doses of magnesium has proved remarkably effective in the treatment of acquired torsade de pointe, but its electrophysiologic effects remain poorly understood. Three clinical cases are reported in three distinct situations (quinidine treatment, hypokalemia, bradycardia with complete atrioventricular block). These cases confirm the efficacy of magnesium, which acts without notable modification of ventricular cycles or the duration of repolarization. In ten patients undergoing intracavitary exploration, the electrophysiologic parameters were analyzed before and after injection of magnesium sulfate (35 mg/kg). Only three parameters were significantly altered; the corrected sinusal recovery time (increase from 245 +/- 92 ms to 296 +/- 96 ms), the effective nodal refractory period (increase from 333 +/- 98 ms to 346 +/- 93 ms), and the Wenckebache period (decrease from 157 +/- 28/min to 144 +/- 21/min). No changes were noted in other parameters, notably ventricular (QT interval, QRS duration, HV interval, and effective ventricular refractory period). The arrhythmic action on the ventricle is therefore remarkable and is not accompanied by patent electrophysiologic effects. The efficacy of magnesium in torsade de pointe may suggest action on calcium currents.

Aged↗