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Biomedical subjects

P Merlet

Publications and source records attributed to P Merlet.

At least 73 records · Page 4Linked to original sources
PubMed1990

[The role of isotope methods in evaluating the left ventricular function].

Cardiac angioscintigraphy is a non-invasive, reproducible and reliable technique used to obtain a number of cardiac function parameters, the most important of which is left ventricular ejection fraction. Methodologically, the examination is simple. Fourier's analysis (a mathematical decomposition of ventricular mechanics) provides additional information on some abnormalities and is particularly useful in segmental kinetics studies and in the topographical diagnosis of cardiac rhythm disorders. The technique is indicated mainly for prognostic evaluation and follow-up of patients with left ventricular dysfunction. Metaiodobenzylguanidine (MIBG) cardiac scintigraphy makes it possible to evaluate the reuptake of noradrenaline by neurons, which represents the inactivation pathway of adrenergic neurotransmission and is the principal factor of noradrenaline extraction. MIBG scintigraphy is an indirect way of evaluating left ventricular function in congestive heart failure, as suggested by the results of studies showing correlations between MIBG uptake, left ventricular function indices and disease severity as judged on the basis of evolutive parameters.

3-Iodobenzylguanidine↗
PubMed1990

[Cardiac transplantation: indications and results].

Although many problems remain, cardiac transplantation is now associated with a 5 year survival rate of about 70 per cent which is a very acceptable therapeutic result in patients with cardiac failure and no other medical or surgical alternative. Parallel improvement in the medical management of chronic cardiac failure has prolonged survival of many patients. Transplantation should only be considered if the benefits not only in terms of survival but also in terms of quality of life, are greater than of survival but also in terms of quality of life, are greater than those of medical treatment of the cardiac disease. The indications and timing of cardiac transplantation are therefore based on a complex prognostic evaluation adapted to each individual case which may eventually need reconsideration. Satisfactory results depend on strict patient selection with respect for the surgical indications and contra-indications.

Adult↗
PubMed1990

[Hypertrophic and/or obstructive primary cardiomyopathies: genetic, etiologic, physiopathologic aspects].

The morphological features, mode of presentation and physiopathology of hypertrophic cardiomyopathy (HCM) are variable. Autosomal dominant seems to be the usual mode of transmission but with variable presentation. From the anatomical point of view, the hypertrophy is asymmetrical with septal predominance. The main histological features are myocytic architectural disorganisation, fibrosis and abnormal coronary arteries of small diameter. Ventricular hyperkinesis is usually present and sometimes associated with outflow obstruction, the physiological role and mechanisms of which are still not fully understood. On the other hand, abnormal diastolic function is frequently observed, and, quite independently of disease of the epicardial coronary arteries, ischaemic phenomena may occur. Although the biological substrate of HCM is unknown, abnormalities of the adrenergic system and transmembrane calcium flux probably play a part in the expression of the disease.

Cardiomyopathy, Hypertrophic↗
PubMed1990

[The treatment of chronic left ventricular insufficiency].

Left ventricular failure is caused by a variety of myocardial diseases and its symptoms results from adjustments attempted by the left ventricle and the circulatory system to cope with the initial myocardial pathology. Treatment of heart failure has various objectives, depending on whether one tries to correct the initial myocardial disease, or its consequences on the myocardium, or its repercussions on blood circulation, or, more simply, to alleviate the symptoms experienced by the patient. The ideal treatment of heart failure would include a drug acting on its cause, another drug to restore a degree of contraction and relaxation adjusted to the amount of load, a third drug bringing back to normal a perturbed peripheral circulation and a fourth drug to relieve the symptoms due to sodium retention. Such a treatment does not exist, and the management of chronic left ventricular failure can only be composite. Should it be prescribed from the start? This, increasingly, is the current trend.

Cardiovascular Agents↗
PubMed1990

Filters and Fourier analysis of gated blood pool studies: a search for the optimal combination.

Fourier analysis of gated blood pool studies is performed after filtering the raw data by a spatial median 3 x 3, 9 x 9 or temporo-spatial 9 x 9 x 9 filter. 20 patients and a dynamic cardiac phantom were studied to determine the quantitative effects of these filters and of multiharmonic Fourier filtering (MHFF). The filtered MHFF data, with or without preprocessing, were compared with a 3 D or 2 D filter to the raw data using a chi 2 distribution. The MHFF (two or three harmonics) procedure applied to the raw data of patients without any preprocessing produced the smallest chi 2 value, thus demonstrating the very close relationship between filtered images and raw data. Preprocessing the raw data by the median filter also preserved the signal when two or three harmonics were applied, whereas the 3 D and 2 D (9 x 9) filters did not. The phantom study also demonstrated that MHFF preserved the signal better than any other preprocessing. The median filter introduced a smaller distortion than the 2 D (9 x 9) and 3 D filters. It is concluded that MHFF applied with two or three harmonics on the raw data or after preprocessing by a median (3 x 3) filter is the most successful way of preserving the real signal. It is believed that the other filters should be avoided. The clinical advantage of MHFF processing is to provide both very accurate filtering and parametric images.

Fourier Analysis↗
PubMed1990

[Pre-hospital thrombolysis].

Too few myocardial infarctions are thrombolysed, and the thrombolytic agent is usually administered too late. This situation can conceivably be improved by educating both physicians and patients, by promoting thrombolysis in all hospitals and by performing thrombolysis before admission. We report here our experience of pre-hospital thrombolysis with Eminase in the Val-de-Marne department. This preliminary study is just a small stone added to the big heap of small series of thrombolysis at home published throughout the world. But while the feasibility of pre-admission thrombolysis has been well demonstrated, its effectiveness remains to be accurately determined. Two studies involving large groups of patients are currently in progress: one in Seattle with the left ventricular function as principal criterion of judgment, the other in Europe (The European Myocardial Infarction Project) with mortality as main criterion of judgment. We must wait for the results of these studies to know whether pre-hospital thrombolysis will become the standard treatment of myocardial infarction and if so, to implement the relevant changes required in health structures.

Aged↗
PubMed1990

[Methods for evaluating thrombolytic drugs].

There are two conceptually quite separate objectives to be attained in evaluating a new class of therapeutic agents: the establishment of benefit-risk relationships which allow assessment of their clinical utility; the evaluation of the underlying physiopathological concepts. These two distinct objectives overlap; the criteria of assessment of the benefit-risk studies are based on the physiopathological concepts. Similarly, the relationships observed after analysing the results of the benefit-risk studies increase our understanding of the physiopathology of a disease process. With respect to the use of thrombolytic drugs in the acute phase of myocardial infarction: --the usual criteria of evaluation of the benefits of treatment are coronary artery patency, left ventricular ejection fraction and patient mortality; the severity of blood clotting abnormalities and the frequency of haemorrhage are used to assess the risks; --the physiopathological reasoning behind this choice of criteria of assessment is the direct relationship between coronary artery patency, ejection fraction and mortality. Also, the severity of blood clotting abnormalities seems to be related to the frequency of haemorrhagic complications; We have reviewed these criteria of assessment of the benefit-risk ratio of thrombolysis in the acute stage of myocardial infarction. Our analysis indicates that mortality is the only indiscutable criterion of assessment and that the classical physiopathological concepts are not validated by the results of therapeutic trials.

Clinical Trials as Topic↗
PubMed1990

[Cardiac transplantation. Indications, delays, surveillance].

The number cardiac transplantation has been dramatically increasing for the last year and the results are satisfactory regarding survival or functional capacity. The observed increase of cardiac transplantation may tend to vulgarize it. However, this intervention should be only considered in a selected group of patients who have no other option. Many reports concerned various technical approach for a clearcut determination of high and low risk population of patients with congestive heart failure. But, considering individual patients, the value of each prognostic parameter remains unresolved. Nevertheless the more discriminant parameters for the prognosis assessment are: the left ventricular ejection fraction, the NYHA class, right heart catheterization data, the functional capacity, the cardiothoracic ratio on chest X ray, the ischemic etiology of the disease. The role of neuro-hormonal determinant such as norepinephrine circulating concentration or cardiac uptake on MIBG imaging should be further investigated, especially for patients treated by ACE inhibitors or beta blockers. Contraindications for cardiac transplantation are less restrictive, nowadays. Concerning patients selected, and waiting for heart transplantation or patients non primary selected survival can be improved by adjusting medical therapy on objective efficacy criteria.

Contraindications↗
PubMed1990

[Treatment of chronic left ventricular insufficiency].

Left ventricular failure results from many myocardial diseases: the symptoms of left ventricular failure are the consequence of adaptations which the left ventricle and circulatory system activate to counteract the initial myocardial disease. The aims of treatment of cardiac failure are diverse depending on whether treatment is directed to correct the initial myocardial disease, its myocardial consequences, its circulatory consequences or, more simply, the patient's symptoms. The ideal treatment of cardiac failure would include a drug acting on the cause, a drug restoring left ventricular contraction and relaxation adapted to the conditions of cardiac load, a drug correcting regional blood flow disturbances and a drug relieving symptoms related to salt retention. An ideal drug for chronic left ventricular failure does not exist, and so treatment is a composite effort. Should it be in first intention? This is the current trend.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1990

[Medical strategy in patients awaiting emergency heart transplantation].

Cardiac transplantation is theoretically the optimal final treatment of terminal cardiac failure but the indications, especially in the emergency situation, should be carefully considered. Sympathomimetic agents are of limited use in patients with severe cardiac failure partly because of the down regulation of the myocardial beta-receptors. The phosphodiesterase inhibitors, represented by enoximone, are valuable because of their action on the cardiac muscle (inotropic and lusitropic) and their direct systemic vasodilator effect. Enoximone can be administered by intravenous bolus resulting in a rapid onset of action (peak at 30 minutes) with a prolonged effect due to its hepatic metabolites. The authors' experience in this indication dates over 5 years and over 50 patients were included. A preliminary study in 34 patients with cardiac failure resistant to betamimetic drugs, referred to the intensive care unit for urgent cardiac transplantation, or, in the absence of a donor, circulatory assistance is reported. A Swan Ganz catheter and radial artery canula were inserted for haemodynamic monitoring and enoximone was administered in an intravenous bolus over 15 minutes every 8 hours in addition to sympathomimetic agents. A haemodynamic improvement was observed after the 30th minute in 30 patients. The cardiac index increased from 1.82 to 2.67 l/mn/m2 and the pulmonary capillary pressures decreased from 30.8 to 18.9 mmHg. Systemic arterial resistances fell from 2,170 to 1,520 dynes.s.cm-5. No haemodynamic improvement was observed in 4 patients who were treated by mechanical ventricular assistance. After investigations to detect contra-indications to cardiac transplantation, 12 of the 30 patients remained candidates for cardiac transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

MIBG scintigraphic assessment of cardiac adrenergic activity in response to altitude hypoxia.

High altitude hypoxia induces a decrease in the cardiac chronotropic function at maximal exercise or in response to isoproterenol infusion, suggesting an alteration in the cardiac sympathetic activation. Iodine-123 metaiodobenzylguanidine [( 123I]MIBG) was used to map scintigraphically the cardiac sympathetic neuronal function in six male subjects (aged 32 +/- 7 yr) after an exposure to high altitude that created hypoxic conditions. Results obtained just after return to sea level (RSL) were compared with the normal values obtained after 2 or 3 mo of normoxia (N). A static image was created as the sum of the 16-EKG gated images recorded for 10 min in the anterior view of the chest at 20, 60, 120, and 240 min after injection. Regions of interest were located over the heart (H), lungs (L), and mediastinum (M) regions. There was a significant decrease in the H/M and the L/M ratios in RSL compared to N condition. Plasma norepinephrine concentration was elevated during the stay at altitude but not significantly different in RSL compared to N. In conclusion, cardiac [123I]MIBG uptake is reduced after an exposure to altitude hypoxia, supporting the hypothesis of an hypoxia-induced reduction of adrenergic neurotransmitter reserve in the myocardium. Furthermore, the observed significant decrease in pulmonary MIBG uptake suggests an alteration of endothelial cell function after exposure to chronic hypoxia.

3-Iodobenzylguanidine↗
PubMed1990

Improved detection of anterior left ventricular aneurysm with multiharmonic fourier analysis.

Single and multiharmonic Fourier analysis of LAO 30-45 degrees gated blood-pool studies were performed in a selected group of 30 patients with a left ventricular anterior aneurysm proven by contrast angiography. The sensitivity of the first harmonic phase image for the diagnosis of ventricular aneurysm was 80%. The clear phase shift (greater than 110 degrees) between the normal and the aneurysmal areas was missing in six patients. Peak acceleration images (negative maximum of the second derivative of the Fourier series) were calculated for each pixel with the analytical Fourier formula using two or three harmonics. A clear phase shift (greater than 126 degrees) than appeared in all the patients. This improvement was related to the increased weight of the second and third harmonics in the aneurysmal area when compared to control patients or to patients with dilative cardiomyopathy. Multiharmonic Fourier analysis clearly improved the sensitivity of the diagnosis of anterior left ventricular aneurysm on LAO 30 degrees-45 degrees gated blood-pool images.

Cardiomyopathy, Dilated↗
PubMed1989

Reversal of hypoxia-induced decrease in human cardiac response to isoproterenol infusion.

A decrease in heart rate response to isoproterenol (IP) infusion has been previously described in humans exposed to acute (2-3 days) or chronic (21 days) exposure to altitude hypoxia (J. Appl. Physiol. 65: 1957-1961, 1988). To evaluate this cardiac response in subacute (8 days) hypoxia and to explore its reversal with restoration of normoxia, six subjects received an IP infusion under normoxia (condition N), after 8 days in altitude (4,350 m, condition H8), on the same day in altitude after inhalation of O2 restoring normoxic arterial O2 saturation (SaO2, condition HO), and 6-11 h (condition RN) and 4-5 mo (condition ND) after the return to sea level. Cardiac chronotropic response to IP, evaluated by the mean increase in heart rate from base value (delta HR, min-1), was lower in condition H8 [mean 30 +/- 13 (SD)] than in condition N (50 +/- 14, P less than 0.03); it was slightly higher in condition HO (38 +/- 14) or condition RN (42 +/- 15) than condition H8 but still significantly different from condition N (P less than 0.03), despite normal values of SaO2. delta HR in condition ND (55 +/- 10) returned to base N value. These findings confirm the hypothesis of a hypoxia-induced decrease in cardiac chronotropic function. Two possible mechanisms are suggested: an O2-dependent one, rapidly reversible with recent restoration of normoxia, and a more slowly reversible mechanism, probably a downregulation of the cardiac beta-receptors.

Adult↗
PubMed1989

[Physiopathologic basis of the use of thrombolytic agents during the acute phase of myocardial infarction].

Experimental animal studies have shown that coronary occlusion is followed by myocardial infarction and that coronary reperfusion can limit infarction size. Myocardial necrosis and the recovery of function are progressive phenomena in these animal models. Similarly, human myocardial infarction is caused by coronary occlusion and the size and severity of the infarct can be reduced by spontaneous or therapeutic coronary reperfusion. However, there are important differences between the animal models and clinical myocardial infarction. The results of randomised therapeutic trials of thrombolytic drugs show that the theoretical equation between reperfusion, myocardial protection and reduction of mortality has not yet been fully validated. This may be explained either by the fact that the intermediary criteria of assessment (patency at 90 minutes and ejection fraction at the 3rd week) have been badly chosen or by the fact that some of the therapeutic benefit of thrombolytics on mortality is not due to reperfusion or myocardial protection. The physiopathological rationale behind the use of thrombolytics in the acute phase of myocardial infarction is coronary reperfusion, but is reperfusion beneficial in all myocardial infarcts? What is or are the intermediary factors between reperfusion and the decrease in mortality? Is reperfusion the only benefit of thrombolysis? Clear answers to these questions are not yet available.

Animals↗
PubMed1988

Automatic drawing of the left epicardial region of interest on thallium 201 scintigraphic images.

An algorithm has been written which automatically selects a left epicardial region of interest on 201Tl myocardial images. It accomplishes a radial search from the geometric center of the myocardium. On each of the 30 profiles, the local maximum of the 1st derivative is selected as the epicardial edge. The algorithm has been tested in 40 patients at stress and redistribution. In ten patients, conventional planar images were obtained in three views. In 30 patients conventional short axis tomographic images were obtained after reconstruction of 32 projections acquired over 180 degrees. The rate of success is 97% for both imaging modalities. This procedure is another step towards fully automated assessment of myocardial defects and redistribution.

Algorithms↗