Biomedical subjects
Publications and source records attributed to G Faivre.
We demonstrate by both experiments and phase-field simulations that lamellar eutectic growth can be stable for a wide range of spacings below the point of minimum undercooling at low velocity, contrary to what is predicted by existing stability analyses. This overstabilization can be explained by relaxing Cahn's assumption that lamellae grow locally normal to the eutectic interface.
We present an experimental study of the directional-solidification patterns of a nematic-smectic-B front. The chosen system is C4H9-(C6H10)2CN (in short, CCH4) in 12 microm-thick samples, and in the planar configuration (director parallel to the plane of the sample). The nematic-smectic-B interface presents a facet in one direction-the direction parallel to the smectic layers--and is otherwise rough and devoid of forbidden directions. We measure the Mullins-Sekerka instability threshold and establish the morphology diagram of the system as a function of the solidification rate V and the angle straight theta(0) between the facet and the isotherms. We focus on the phenomena occurring immediately above the instability threshold when straight theta(0) is neither very small nor close to 90 degrees. Under these conditions, we observe drifting shallow cells and a type of solitary wave, called "faceton," which consists essentially of an isolated macroscopic facet traveling laterally at such a velocity that its growth rate with respect to the liquid is small. Facetons may propagate either in a stationary or an oscillatory way. The detailed study of their dynamics casts light on the microscopic growth mechanisms of the facets in this system.
We present an experimental investigation of the morphological transition of lamellar eutectic growth fronts called "formation of eutectic colonies" by the method of thin-sample directional solidification of a transparent model alloy, CBr4-C2Cl6. This morphological transition is due to the presence in the melt of traces of chemical components other than those of the base binary alloy (impurities). In this study, we use naphthalene as an impurity. The formation of eutectic colonies has generally been viewed as an impurity-driven Mullins-Sekerka instability of the envelope of the lamellar front. This traditional view neglects the strong interaction existing between the Mullins-Sekerka process and the dynamics of the lamellar pattern. This investigation brings to light several original features of the formation of eutectic colonies, in particular, the emission of long-wavelength traveling waves, and the appearance of dendritelike structures called two-phase fingers, which are connected with this interaction. We study the part played by these phenomena in the transition to eutectic colonies as a function of the impurity concentration. Recent theoretical results on the linear stability of ternary lamellar eutectic fronts [Plapp and Karma, Phys. Rev. E 60, 6865 (1999)] shed light on some aspects of the observed phenomena.
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Two types of radioisotope tomography have been developed: single photon emission computed tomography and positron emission tomography. Tomography of the heart meets with several problems due to the mobility and obliquity of that organ and to the heterogeneity of surrounding tissues. Compared with planar tomography, myocardial tomography with thallium 201 improves the detection of ischaemic and sub-ischaemic areas in myocardial infarction and chronic coronary disease. In spite of some technical limitations, tomography with labelled red cells is very helpful to determine pre-operative size and location of aneurysms.
The clinical and echocardiographic features of right atrial thrombi were examined in 9 patients, 5 men and 4 women aged 16 to 86 years. The 2D echocardiographic diagnosis was confirmed at autopsy (4 cases) or by the association of severe recurrent pulmonary embolism (5 cases). Three patients had associated ischaemic heart disease and on patient had dilated cardiomyopathy. The clinical presentation was: acute cor pulmonale (5 cases including 2 patients which biventricular myocardial infarction), chronic post-embolic cor pulmonale (1 case), tricuspid valve obstruction (1 case), general ill health with pyrexia (1 case) and heparin-induced thrombocytopenia (1 case). Predisposing factors included: absence of anticoagulent therapy (7 cases), previous supraventricular arrhythmias (2 cases) and right ventricular failure (6 cases, including 2 of right ventricular infarction). In 2 patients the thrombi were relatively immobile and had a wide base of implantation on the interatrial septum; in 1 patient, multiple thrombi were observed lining the right heart cavities from the inferior vena cava to the pulmonary infundibulum. In the other 6 patients, the thrombi were very mobile with a visible pedicule of implantation (2 cases) or totally free (4 cases). The variable polylobulated appearances, completely irregular whirling motion and intermittent prolapse into the tricuspid valve were characteristic features of the latter 4 cases. They disappeared spontaneously (2 cases) or after fibrinolytic therapy (2 cases) in under 36 hours. Three patients were operated with one postoperative death. The global hospital mortality was 22%. The present occasional detection of right atrial thrombosis will certainly become more common if patients with pulmonary embolism, right ventricular infarction or deep venous thrombosis are systematically examined by 2D echocardiography in the acute phase of their illness.
Fourteen cases of apical hypertrophic cardiomyopathy (i.e. hypertrophy localized to the distal half of the left ventricular wall) are reported. There were 12 men and 2 women aged from 21 to 84 years. Only one of the patients presented, at first consultation, with severe functional symptoms, namely stage IV dyspnoea. ECG tracings were always abnormal, but the classical giant T waves were found in only 7 patients. In the 9 patients who had cardiac catheterization the left ventricular end-diastolic pressure was raised, and angiography showed an "ace of spades" diastolic image of the left ventricle with systolic obliteration of its tip. The distribution of parietal hypertrophy was best studied by two-dimensional echocardiography: the left ventricular apex was affected alone in 7 patients and concomitantly with the adjacent segments of the left or right ventricle in the other 7 patients. A family study showed that 3 patients had a descendant with obstructive cardiomyopathy. At a 4.6 years' follow-up the course of the disease was usually favourable. Apical hypertrophic cardiomyopathy is not a particular entity but one of different possible forms of hypertrophic cardiomyopathy. It seems to be benign in most cases.
Prostacyclin (PGI2) has been shown to reduce the occurrence of experimental ventricular arrhythmias. To assess potential beneficial effects in man, the electrophysiological action of PGI2 was studied in 16 non medicated patients. The protocol used in incremental pacing and programmed stimulation in the right atrium and ventricle. This protocol and measurement of effective refractory periods (ERP) were performed before and during the injection of 2.5, 5 and 10 ng kg-1 min-1 of PGI2. The atrial functional refractory period decreased significantly (P less than 0.05); PGI2 had no influence on the occurrence of inducible non-sustained (NS) atrial tachycardias and was responsible for the occurrence of 2 non-sustained atrial tachycardias in 8 patients with inducible atrial echo beats under basal conditions. Thirteen patients did not have inducible ventricular tachycardia (VT) under basal conditions. Non-sustained VT was induced after PGI2 in 4 of them but in only 1 of them after the administration of propranolol. Three patients had inducible VT under basal conditions (1 non-sustained, 2 sustained VT). PGI2 did not prevent the occurrence of VT (1 non-sustained, 1 sustained VT), except in 1 patient with ischaemic-related VT, who had non-sustained VT after PGI2. In conclusion, PGI2 does not seem to have a cardiac antiarrhythmic effect and may increase the atrial and ventricular repetitive response. This effect could be related to an increase of adrenergic tone.
2 cases of severe pulmonary valvular stenosis in two young adults aged 21 and 29 years respectively are presented. Despite the degree of stenosis (4 mm jet), the right ventricular pressures did not exceed systemic pressures because of severe tricuspid regurgitation. This dominated the clinical and anatomical findings, causing aneurysmal dilatation of the right atrium and displacement of the tricuspid valve to the left. The diagnosis of Ebstein's anomaly was raised in one case but excluded by echocardiography and angiocardiography. In spite of the severity of the symptoms and peripheral clinical signs, surgery of the right ventricular outflow tract, tricuspid valvuloplasty and resection of part of the right atrium led to a complete and rapid cure, confirmed by catheterisation one month after operation.
Very few studies have been described comparing the value of exercise myocardial scintigraphy and left ventricular angioscintigraphy. The authors designed a study comparing these two investigations with conventional exercise stress testing and coronary angiography. The isotopic investigations were carried out within 48 hours of coronary angiography. A total of 143 patients undergoing coronary angiography (35 normal, 108 coronary patients: 36 single vessel, 36 double vessel and 36 triple vessel disease) were included in this study. The lesions were located of the LAD (77 cases), left circumflex (77 cases) and right coronary arteries (62). The sensitivity and specificity of both radionuclide investigations were evaluated to assess their diagnostic value; the best results were obtained with myocardial scintigraphy (sensitivity 86 p. 100; specificity 100 p. 100); angioscintigraphy had a sensitivity of 71 p. 100 and specificity of 97 p. 100, and conventional exercise stress testing of 42 p. 100 and 70 p. 100 respectively. The sensitivity seemed to increase with the degree of stenosis; although the sensitivity of myocardial scintigraphy increased progressively, that of angioscintigraphy doubled in cases of stenosis 90 p. 100 (stenosis less than 90 p. 100, sensitivity = 37 p. 100; stenosis greater than 90 p. 100, sensitivity = 73 p. 100). The sensitivity of myocardial scintigraphy with respect to the severity of the coronary artery disease was best in cases of right coronary artery stenosis (sensitivity in cases of RCA stenosis = 74 p. 100; sensitivity in LAD stenosis = 58 p. 100; sensitivity in left circumflex stenosis = 43 p. 100). The sensitivity of left ventricular angioscintigraphy was best in LAD stenosis (RCA stenosis = 50 p. 100, LAD stenosis = 64 p. 100, left circumflex stenosis = 36 p. 100). The sensitivity of both investigations was poor in left circumflex artery stenosis even when severely diseased. The sensitivity of both investigations was better in diffuse coronary artery disease: myocardial scintigraphy (single vessel disease: 72 p. 100, double vessel disease: 92 p. 100, triple vessel disease: 94 p. 100), left ventricular angioscintigraphy (61 p. 100, 69 p. 100, and 83 p. 100 respectively). Although the association of these two radioisotopic investigations does not improve diagnostic sensitivity, it does provide more information about the localisation and extension of the coronary artery disease especially in LAD and right coronary artery stenosis. These results suggest that these investigations are complementary in the evaluation of patients with coronary artery disease.(ABSTRACT TRUNCATED AT 400 WORDS)
The authors report a series of 13 patients, 8 men and 5 women, with an average age of 68 years (range 39 to 87 years) presenting with documented inferior infarction with anteroseptal extension in 2 cases. These patients developed LBBB (complete in 9 cases, incomplete in 4 cases). This complications occurred in the acute phase in 8 cases and 4 months to 9 years later (average 4,5 years) in the other 5 cases. The block was intermittent in 4 patients and became permanent in all cases. The diagnosis of inferior infarction with LBBB was made by vectorcardiography (VCG) in 5 out of the 13 patients (38,4 p. 100) on the criteria suggested by Starr. 3 of the 8 false negative results were directly related to the block which masked the ECG and VCG signs of inferior infarction. The VCG signs observed were an upwards displacement of the QRS loop with preservation of the superior orientation of the initial forces (5 cases). Atypical appearances of LBBB were observed in 2 cases with a posterior and right-sided shift of the efferent loop following the anterior and left-sided orientations of the initial forces. The sensitivity of the VCG and ECG is mediocre in inferior infarction with LBBB because the block may mask the electrical signs of inferior infarction. The specificity of the VCG could not be assessed because of the mode of selection of the patients and the small number of cases.
The diagnostic value of programmed pacing in the investigation of tachycardia (greater than 5 premature complexes) was studied in 155 patients admitted for evaluation of dizzy attacks and/or tachycardia by determining a relationship between the induction of tachycardia by endocavitary pacing and the presence of spontaneous attacks on ECG and/or 24 hour Holter monitoring. Right atrial and ventricular programmed pacing comprised: an extrastimulus during sinus rhythm (method I), during paced rhythm (method II), 2 extrastimuli during sinus rhythm (method III) and paced rhythm (method IV). The protocol was applied in 20 cases of spontaneous atrial tachycardia (AT) and 40 patients without tachycardia, and in 20 cases of spontaneous sustained ventricular tachycardia (VTS) (Group A), 15 cases of non-sustained ventricular tachycardia (VTNS) (Group B), 20 cases of ventricular doublets or triplets on Holter monitoring (Group C) and 40 patients without ventricular arrhythmias. The following results were obtained: At atrial level, method I was associated with a 75% sensitivity and a 62.5 p. 100 specificity when the triggering of atrial echos was considered. It was difficult to induce AT with methods I, II and III (sensitivity 15, 20 and 45 p. 100 - but they were very specific (greater than 90 p. 100). The induction of echos with methods II, III and IV was very sensitive but not specific and could not be retained as a pathological criterion. Using method IV, only the triggering of sustained AT could be considered to have a good specificity (90 p. 100), but sensitivity remained low (30 p. 100). At ventricular level, more aggressive methods were needed to induce an arrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)
Classically, the frequency of latent left-sided Kent bundles and ventricular tachycardia (VT) is increased in mitral valve prolapse (MVP). To verify this hypothesis, 23 patients with clinical and echocardiographic (M mode and 2D) signs of MVP underwent electrophysiological studies for dizziness or syncope (12 cases) or palpitations (11 cases). In addition to the standard electrophysiological studies, analysis of sinoatrial and atrioventricular conduction, they underwent programmed ventricular pacing (St V2): coupled and then paired St V2 in sinus rhythm and during ventricular pacing (100-150/min) under basal conditions (15 patients), after injection of 2 mg Atropine (6 patients), and 10 micrograms of Isoproterenol (4 patients). These manoeuvres showed that symptoms of dizziness were due to increased vagal tone in 6 cases (associated with paroxysmal nodal tachycardia--PNT--in 3 cases), to sinoatrial block in 2 cases (associated with atrial tachycardia in 1 case), to suprahisian conduction defects in 3 cases (associated with atrial tachycardia in 1 case) and to VT in 1 case. Palpitations were due to VT in 1 case, atrial tachycardia in 1 case and PNT in 9 cases. Our analysis showed a high incidence of PNT (10 cases) with normal inter critical ECG. These arrhythmias were due to intranodal reentry in 7 cases (70%), to a latent left-sided Kent bundle in 2 cases and to a paraseptal Kent bundle in 1 case. These PNT were characterised by induction during exercise (6 cases) and by their association with flutter-type reentry (5 cases).(ABSTRACT TRUNCATED AT 250 WORDS)
The electrophysiological effects of prostacyclin (PGI2) at increasing doses (2.5, 5 and 10 ng/kg/min) were assessed in 16 patients during classical investigations of sinus node function and atrioventricular conduction and during programmed atrial and right ventricular under basal conditions and during prostacyclin perfusion. Ten patients had normal sinus node function and atrioventricular conduction under basal conditions. Stastistically significant changes were observed during PGI2 perfusion: shortening of the sinus cycle length (p 0.01), decreased intraatrial conduction time (p less than 0.05), reduced atrial functional refractory period (p less than 0.01) and reduced effective and functional refractory periods of the AV node (p less than 0.05), increased anterograde (p less than 0.01) and retrograde (p less than 0.05) Wenckebach point. The changes were dose dependent. No significant changes were observed in sinus node recovery periods of the His Purkinje system. Similar changes were recorded on 4 other patients with various conduction defects. Paired atrial stimulation induced manifestations of hyperexcitability in 5 patients. In 2 patients with normal responses under basal conditions it was possible to induce non-sustained atrial tachycardia during PGI2 administration. In 3 patients with inducible atrial tachycardia under basal conditions, it was still possible to induce the tachycardia after PGI2 but this disappeared in all but one patient with the sick sinus syndrome after the addition of propranolol. The changes in ventricular excitability were studied by a specific protocol in 16 patients. Of the 13 patients without inducible ventricular tachycardia under basal conditions, 4 developed inducible non-sustained ventricular tachycardia after PGI2. Three patients had inducible VT under basal conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
Two cases of sudden death are reported in patients with mitral valve prolapse with mitral insufficiency. Both had significant impairment of left ventricular function. Irreversible ventricular fibrillation occurred in one patient one-half hour preceding a catheterization, whereas the other patient died during sleep. Review of the literature revealed 42 cases of sudden death in patients with prolapse. Occasionally left ventricular dysfunction or medication overdosage can explain or favor development of the terminal arrhythmia, but usually no precipitating factor other than prolapse can be identified. It appears impossible to identify actual subgroups at risk, although sudden death does occur more frequently in patients with a large amount of prolapse of both valves, previous syncopal episodes, and ECG abnormalities at rest. Complex ventricular arrhythmias are also reported, but their predictive importance is difficult to evaluate. Sudden death is a rare complication of mitral prolapse, fact which should conservatively influence indications for further supplementary testing and treatment in these patients.