Biomedical subjects

X Copie

Publications and source records attributed to X Copie.

35 records · Page 2Linked to original sources

PubMed1996

Effects of bisoprolol on heart rate variability in heart failure.

Analysis of heart rate variability (HRV) provides a non-invasive index of autonomic nervous system activity. HRV has been shown to be reduced in heart failure. Preliminary data indicate that beta blockers improve clinical status in patients with heart failure, but HRV improvement remains to be demonstrated. Fifty-four patients from the randomized double-blind, placebo-controlled Cardiac Insufficiency Bisoprolol Study were included in the HRV study. The bisoprolol daily dose was 5 mg once daily. We assessed HRV during 24-hour Holter recordings before randomization and after 2 months of treatment. HRV as measured in the time domain by root-mean-square successive differences (rMSSD), the percentage of adjacent RR differences >50 ms (pNN50), and the SD of RR intervals (SDNN), and in the frequency domain by high-frequency (0.16 to 0.40 Hz) and low-frequency (0.04 to 0.15 Hz) power. Most patients were in New York Heart Association functional class III. The mean left ventricular ejection fraction was 27 +/- 7%, and heart failure was idiopathic or ischemic. After 2 months, the patients receiving bisoprolol had a reduced mean heart rate compared with that in placebo patients (p=0.0004). Bisoprolol increased 24-hour rMSSD (p=0.04) and 24-hour pNN50 (p=0.04), daytime SDNN (p=0.05), and daytime high-frequency power (p=0.03) power. Bisoprolol induced a significant increase in HRV parameters related to parasympathetic activity in heart failure. Increased vagal tone may contribute to the protective effect of beta blockers and may have prognostic implications.

Adrenergic beta-Antagonists↗

PubMed1996

Predictive power of increased heart rate versus depressed left ventricular ejection fraction and heart rate variability for risk stratification after myocardial infarction. Results of a two-year follow-up study.

OBJECTIVES: The aim of this study was to compare the predictive value of mean RR interval assessed from predischarge Holter recordings with that of heart rate variability and left ventricular ejection fraction for risk stratification after myocardial infarction. BACKGROUND: Heart rate variability is a powerful tool for risk stratification after myocardial infarction. Although heart rate variability is related to heart rate, little is known of the prognostic value of 24-h mean heart rate. METHODS: A total of 579 patients surviving the acute phase of myocardial infarction were followed up for at least 2 years. Predischarge heart rate variability, 24-h mean RR interval and left ventricular ejection fraction were analyzed. RESULTS: During the first 2 years of follow-up, there were 54 deaths, 42 of which were cardiac (26 sudden). Shorter mean RR interval was a better predictor of all-cause mortality as well as cardiac and sudden death than depressed left ventricular ejection fraction. Depressed heart rate variability predicted the risk of death better than mean RR interval for sensitivities < 40%. For sensitivities > or = 40%, mean RR interval was as powerful as heart rate variability. All three variables performed equally well in predicting nonsudden cardiac death. For cardiac death prediction, a left ventricular ejection fraction < 35% had a 40% sensitivity, 78% specificity and 14% positive predictive accuracy; a mean RR interval < 700 ms had a 45% sensitivity, 85% specificity and 20% positive predictive accuracy; and a heart rate variability < 17 U had a 40% sensitivity, 86% specificity and 20% positive predictive accuracy. CONCLUSIONS: Predischarge 24-h mean heart rate is a strong predictor of mortality after myocardial infarction that can compete with left ventricular ejection fraction and heart rate variability.

Cohort Studies↗

PubMed1996

Effects of beta-blockade with bisoprolol on heart rate variability in advanced heart failure: analysis of scatterplots of R-R intervals at selected heart rates.

The effect of beta-blockade on heart-rate variability was assessed at different heart rates in 52 patients with heart failure included in the randomized, placebo-controlled, Cardiac Insufficiency Bisoprolol Study (CIBIS). Scatterplots of R-R intervals display beat-to-beat variability by plotting each R-R interval against the preceding interval. Scatterplot dispersion at different R-R intervals provides a measure of beat-to-beat heart-rate variability at different heart rates. A 24-hour Holter tape was performed at baseline and after 2 months of treatment with bisoprolol or matched placebo. Geometric measurements of scatterplots were used to determine beat-to-beat dispersion for different R-R intervals. Bisoprolol and placebo groups were well matched at base-line. After 2 months of treatment, bisoprolol significantly increased beat-to-beat variability at the longest R-R intervals (p < 0.05); however, there was no change in scatterplot dispersion at the shortest R-R intervals. This suggests that beta-blockade increases parasympathetic or decreases sympathetic tone or both in heart failure patients only at the slowest heart rates.

Adrenergic beta-Antagonists↗

PubMed1996

Correlation between time-domain measures of heart rate variability and scatterplots in postinfarction patients.

Heart rate variability (HRV) is usually measured in time or frequency domains. Beat-to-beat variability, which cannot be assessed by frequency-domain analysis, and can only be assessed globally by time-domain analysis, provides information concerning the nonlinear behavior of heart rate. This beat-to-beat variability can be displayed on scatterplots, where each RR interval is plotted against the preceding RR interval. However, the relationship between scatterplots and other measures of HRV is unknown. We studied the correlations between time-domain measures and scatterplot length, width, and area in 50 postinfarction patients. Scatterplot length and width were measured after printing. Scatterplot area was calculated from length and width, assimilating the plot to an ellipse. Long-term variability indexes (SDNN and SDANN) were strongly correlated with scatterplot length (r > 0.9, P < 0.0001), and short-term variability parameters (pNN50 and variability index) with scatterplot width (r > 0.9; P < 0.0001). Scatterplots are, therefore, a simple way of providing information concerning long- and short-term HRV. Furthermore, measurement of scatterplot width at different given RR intervals could be an approach to the evaluation of short-term HRV for different heart rates. This could provide a simple way of assessing cardiac parasympathetic modulation at different heart rates.

Adult↗

PubMed1996

Decreased heart rate variability in patients with congestive heart failure and chronotropic incompetence.

UNLABELLED: Heart rate variability was studied in 41 patients (aged 48 +/- 12 years) with congestive heart failure secondary to idiopathic dilated cardiomyopathy. All patients underwent a treadmill exercise test and 24-hour Holter ECG monitoring. Chronotropic incompetence was defined as the failure to achieve > or = 80% of the predicted maximal heart rate response given by 220--age (years) at peak exercise. Spectral heart rate variability was analyzed from 24-hour Holter ECGs and was expressed as total (0.01-1.00 Hz), low (0.04-0.15 Hz), and high (0.15-0.40 Hz) frequency components. The standard deviation of all normal RR intervals (SDNN) was also computed. Chronotropic incompetence was observed in ten patients. Peak oxygen consumption was significantly lower in patients with chronotropic incompetence compared with those without chronotropic incompetence. The total (5.11 +/- 1.26 ln [ms2] vs 6.41 +/- 0.92 ln [ms2]; P = 0.009) and low (3.38 +/- 1.65 ln [ms2] vs 5.45 +/- 1.34 ln [ms2]; P = 0.003), but not the high (3.42 +/- 1.04 ln [ms2] vs 4.00 +/- 1.12 ln [ms2]; P = 0.249) frequency components of heart rate variability were significantly lower in patients with chronotropic incompetence, although there was no significant difference in mean heart rate (88 +/- 20 beats/min vs 86 +/- 15 beats/min; P = 0.831) or left ventricular ejection fraction (22% +/- 10% vs 24% +/- 10%; P = 0.619). SDNN was also significantly lower in patients with chronotropic incompetence compared with those without chronotropic incompetence (64 +/- 34 ms vs 102 +/- 37 ms; P = 0.030). CONCLUSIONS: The observation that heart rate variability is significantly decreased in patients with congestive heart failure who have chronotropic incompetence suggests that chronotropic incompetence may relate to an abnormal autonomic influence on the heart in these patients.

Autonomic Nervous System↗

PubMed1996

Spectral turbulence versus time-domain analysis of signal-averaged ECG used for the prediction of different arrhythmic events in survivors of acute myocardial infarction.

INTRODUCTION: Spectral turbulence analysis of the signal-averaged ECG (SAECG) combines spectral analysis with statistical evaluation of spectrograms of individual parts of the QRS complex. It has been suggested that it may be superior to conventional time-domain analysis of the SAECG. METHODS AND RESULTS: This study compared the power of conventional time-domain (40 to 250 Hz) and spectral turbulence analyses of SAECG for the prediction of cardiac death, ventricular tachycardia, sudden arrhythmic death, and arrhythmic events (ventricular tachycardia or fibrillation, and/or sudden arrhythmic death) after acute myocardial infarction in 603 patients. The population excluded patients with bundle branch block and other conduction abnormalities. During the first 2 years of follow-up, there were 40 cardiac deaths, 21 cases of ventricular tachycardia, 1 sudden arrhythmic deaths, and 29 arrhythmic events. The positive predictive accuracy of spectral turbulence analysis was significantly higher than time-domain analysis for cardiac death at most levels of sensitivity (e.g., 26% vs 20% at 40% sensitivity, P < 0.05). The positive predictive accuracies of the two techniques were not statistically different for the prediction of ventricular tachycardia. For the prediction of sudden arrhythmic death and arrhythmic events, the positive predictive accuracy of spectral turbulence was better than that of time-domain analysis only at the higher levels of sensitivity (9% vs 2%, P < 0.001 for sudden arrhythmic death at 60% sensitivity, and 14% vs 11%, P < 0.05 for arrhythmic events at 60% sensitivity). CONCLUSIONS: Spectral turbulence analysis is essentially equivalent to time-domain analysis for the prediction of arrhythmic events after myocardial infarction. However, it performed significantly better than time-domain analysis for the prediction of cardiac death.

Acute Disease↗

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↗

PubMed1996

[Reproducibility of signal-averaged electrocardiography].

The reproducibility of the parameters defining the presence of late potentials on the signal-averaged electrocardiogram is one of the limiting factors of the method. The authors studied the coefficients of correlation and reproducibility of these parameters in patients with coronary artery disease. In addition, they tried to determine which parameter was most often responsible for changing a diagnostic conclusion (i.e., presence or absence of late potentials). Two signal-averaged ECGs were recorded one after the other in 127 patients. The presence of late potentials was defined as the presence of a least two of the following criteria: total amplified and averaged QRS duration (tQRS) > 114 ms: duration of the last signal of under 40 microV (LAS) > 38 ms, and root mean square of the amplitude of the last 40 ms (RMS) < 20 microV. The correlation coefficients were 0.98, 0.96 and 0.94 for the duration of tQRS, LAS and RMS respectively (p < 0.0001). The coefficients of reproducibility were 7.0 ms. 7.0 ms and 16.1 microV respectively. Late potentials were present in 22% of patients. A change in diagnosis between the first and second recording was observed in 10 subjects (8% of the population). A combined change in LAS and RMS was responsible for 6 of these revised diagnoses, a change in LAS alone in 2 cases, of the RMS alone in 1 case and the tQRS alone in 1 case. In patients with coronary artery disease, the immediate reproducibility of the diagnosis of late potentials is affected by changes in LAS and RMS. The tQRS is only rarely responsible for a change in diagnosis. This study suggests that the result of the signal-averaged ECG should be interpreted with caution when the LAS or RMS are near their threshold values.

Action Potentials↗

PubMed1996

[Influence of the duration of recording in the reproducibility of the signal averaged electrocardiogram].

The authors studied the possibility of improving the reproducibility of the signal averaged ECG by increasing the number of averaged QRS complexes. One hundred patients were included in the study. In each cases, 400 QRS complexes were recorded on twice, consecutively, in strictly identical conditions. During each recording, the total duration of the amplified and averaged QRS complex (tQRS), the duration of the terminal signal below 40 microV (LAS) and the root mean square of the amplitude of the last 40 ms (RMS) were determined for 100, 200, 300 and 400 recorded QRS complexes. The presence of late potentials was defined as the positivity of two of the following criteria: tQRS > 114 ms, LAS > 38 ms, RMS < 20 microV. The number of contradictory diagnostic conclusions between two successive recordings of the same duration decreased progressively with the number of averaged QRS complexes: 10 for 100 QRS, 10 for 200 QRS, 9 for 300 QRS and 6 for 400 QRS complexes, but this improvement was not statistically significant. The absolute differences of tQRS and RMS between two successive recordings of the same duration were statistically different for the four durations of recording (p = 0.05) and there was a tendency towards statistical significance for LAS (p = 0.09). The best quantitative reproducibility of the 3 parameters was obtained with the recording of 300 QRS complexes. In conclusion, the reproducibility of the signal averaged ECG is improved when the number of average QRS complexes is increased. The authors' results suggests that reproducibility this is optimal with the amplification and averaging of 300 QRS complexes.

Action Potentials↗

PubMed1996

[Risk of mortality after myocardial infarction: value of heart rate, its variability and left ventricular ejection fraction].

Heart rate variability is a useful parameter for risk stratification after myocardial infarction. However, the relationship between heart rate itself and its variability has not been adequately studied. The authors compared the average RR interval of 24 hours recorded by Holter monitoring with the variability of heart rate and of left ventricular ejection fraction to assess the risk of death after myocardial infarction. A total of 579 patients was followed up for 2 years after acute myocardial infarction. During this period, there were 54 deaths, 42 of cardiac origin, 26 being classified as sudden death. The positive predictive value of left ventricular ejection fraction was lower than those of mean RR interval and the variability of heart rate for overall mortality, cardiac mortality and sudden death. The three indices were essentially equivalent for the prediction of non-sudden cardiac death. The positive predictive value of heart rate variability was better than the mean RR interval for sensitivities < 40%, for all cause mortality. However, for sensitivities > 40%, the two parameters were equivalent or slightly in favour of the mean heart rate over 24 hours. The authors conclude that the mean RR interval over 24 hours is an important prognostic index after myocardial infarction. This index is more powerful than left ventricular ejection fraction and comparable to heart rate variability.

Aged↗

PubMed1995

Numeric processing of Lorenz plots of R-R intervals from long-term ECGs. Comparison with time-domain measures of heart rate variability for risk stratification after myocardial infarction.

The so-called "Lorenz plots" are scatterplots that show the R-R interval as a function of the preceding R-R intervals. Repeatedly, it has been proposed that these plots might be used for visualizing the variability of the heart rate and that the assessment of heart rate variability (HRV) from these plots might be superior to conventional measures of HRV. However, a precise numeric evaluation of the images of Lorenz plots have never been suggested. To classify the images of Lorenz plots, a computer package that measures their density was developed. For each rectangular area of the plot, the relative number of R1/R2 samples in that area is established and a function is created that assigns the maximum relative number of samples (i.e., the maximum density) to each size of an area of the plot. Plots that are very compact result in a sharply falling density function, while plots that are more diffuse lead to a flat density function. The distinction between such types of density function may be expressed as a logarithmic integral of the density function to express the "compactness" of the plot numerically. As the computational demands of this approach are intensive, an approximate method that restricts the measurement of the density to the area around the peak of the plot was also developed. The results of this approximate method correlate strongly with the full results (r = .98), and approximate measurement of one plot requires less than 1 minute of computer time. The approximate method has been applied to a set of 24-hour Holter records obtained from 637 survivors of acute myocardial infarction. For each record, the SDNN and SDANN values were also calculated as conventional measures of HRV. Both the density of the Lorenz plots and the conventional measures of HRV were used to investigate the differences among 48 patients who suffered an arrhythmic event (sudden death or sustained symptomatic ventricular tachycardia) during a 2-year follow-up period and the remaining 589 patients without arrhythmic postinfarction complications. At a sensitivity of 30%, the Lorenz plot density distinguished the patients with events with a positive predictive accuracy of 58%, while the SDNN and SDANN led to a positive predictive accuracy of only 23 and 18%, respectively. Thus, a detailed analysis of Lorenz plots is feasible and more clinically useful than the conventional measures of HRV.

Adult↗

PubMed1995

Identification of atrial fibrillation episodes in ambulatory electrocardiographic recordings: validation of a method for obtaining labeled R-R interval files.

Current systems for analyzing ambulatory electrocardiograms (ECGs) are unable to distinguish precisely between sinus rhythm and atrial fibrillation (AF) episodes, and are unable to produce RR interval listings that distinguish AF from sinus rhythm on a beat-to-beat basis. We describe a method for obtaining such a computerized listing ("Composite Rhythm" file) from ambulatory recordings containing episodes of AF. The file lists the rhythm of each beat, its real time, and the QRS complex morphology. A visual inspection is made of a full printout of the recording to identify the precise time of onset and termination of each episode of AF. These times are entered into a computer and identified with the corresponding beats on a conventional RR interval file generated by Holter analysis. The method was validated using 1-hour segments from 20 ambulatory ECGs containing 145 episodes of AF. These were visually identified by four independent observers with a mean sensitivity of 99.1%. The first beat of AF was identified concordantly in 96% of episodes, with a discrepancy of < or = 3 beats in the other episodes. The times of 200 selected QRS complexes were then entered into the computer by each observer; 91.1% of these complexes were identified exactly and 100% were identified to within one beat. The Composite Rhythm files have several potential applications for testing AF detection algorithms and studying the mode of onset of AF.

Algorithms↗

PubMed1995

[Changes in heart rate variability after myocardial infarction. Value of Poincareé's diagram].

The variability of the heart rate is reduced after myocardial infarction. It then progressively increases, to return to near normal values after several months. However, these changes in heart rate variability occur at the same time as slowing of the heart rate which makes interpretation difficult. Poincaré's diagram is constructed from a Holter recording plotting each RR interval against the preceding RR interval. The authors have developed a geometric approach to this diagram to evaluate parasympathetic tone for a given heart rate. By measuring the dispersion in height of the Poincaré's diagram, the authors evaluate the shor-term variability for a given RR interval. Two 24 hr Holter recordings were performed in 52 patients at one and two weeks after a myocardial infarction. The dispersion in the height of the Poincaré's diagrams was measured at the 10th, 25th, 50th, 75th and 90th percentiles of the total dispersion. The authors have shown an increase in the short-term variability of the shortest RR intervals (1th, 25th and 50th percentiles) which is not observed in the longer RR intervals (75th and 90th percentiles). In conclusion, theres is an increase in the heart rate variability at the shortest RR intervals. This suggests that the recovery of parasympathic tone after myocardial infarction occurs mainly at the fastest heart rates.

Aged↗

PubMed1994

Noninvasive detection of an increased vascular mass in untreated hypertensive patients.

Structural changes of the arterial vasculature are of major pathophysiologic and prognostic significance in human hypertension. A high-resolution ultrasonic echotracking device was used to measure internal diameter and intima-media thickness of the radial artery, a medium-sized muscular conduit artery, in 60 hypertensive patients and in 40 age-matched control subjects. Of the 60 hypertensives, 33 were never treated and 27 were well-controlled by antihypertensive therapy. Radial artery mass and thickness/radius ratio were used to describe the radial artery structure. Radial artery mass was validated in vitro by comparing the weight of arterial segments to the ultrasonographic determination of their mass, calculated as: rho L(pi Re2-pi Ri2), where rho is the arterial wall density, L the length of the arterial segment, and Re and Ri the ultrasonic values of internal and external radii, respectively. Diastolic internal diameter did not differ among the three groups, but wall thickness, radial artery mass, and thickness/radius ratio were significantly higher in the untreated hypertensive group than in the control group. In treated well-controlled hypertensive subjects, radial artery mass and thickness/radius ratio were not different from that of control subjects. Among the population of untreated patients, significant univariate relations existed between radial artery mass and blood pressure and radial artery mass and age. In multivariate analysis, radial artery mass was independently predicted by mean blood pressure, age, and sex. Circumferential wall stress, calculated from diastolic internal diameter, wall thickness, and diastolic blood pressure, was not different in the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1994

[Measurement of the vascular mass of the human radial artery by ultrasonics].

OBJECTIVE: To determine the reproducibility of radial artery mass (RAM), in hypertensive patients. DESIGN AND METHODS: In 49 patients, RAM was measured using a high resolution echotracking device (Nius-02) which allows noninvasive measurement of diameter and wall thickness of the radial artery. RAM was validated in vitro by comparing weight of arterial segments to ultrasonographic measurement and determined as RAM = r (pi Re2-pi Ri2) where r is the arterial wall density (1.06 g/cm3), and Re and Ri are values of internal and external radii, respectively. Repeatability coefficient (RC2 = SDi2/n) was 1.3 mg. RESULTS: Blood pressure was (mean +/- SD) 146 +/- 19/85 +/- 15 mmHg, radial arterial diameter was 2,449 +/- 376 microns, radial wall thickness was 302 +/- 68 microns, RAM was 28 +/- 9 mg (range 13-43 mg). CONCLUSION: These results indicate that radial artery mass can be measured using a high resolution echotracking device.

Humans↗

PubMed1994

[Mechanisms of atrial fibrillation: recent advances].

Atrial fibrillation (AF) is due to the presence of multiple reentry pathways. Although this mechanism has been known for some time, new information has recently been acquired about the factors of atrial vulnerability and the conditions of myocardial alteration. There are two main factors of atrial vulnerability: intra-atrial conduction defects and abnormalities of the refractory periods. In addition, the concept of critical mass and the influence of the autonomic nervous system have to be taken into consideration. The abnormalities of the refractory periods liable to increase atrial vulnerability are their shortening, spatial dispersion and poor adaptation to the heart rate. All these changes may be demonstrated at cellular level. The product of the intra-atrial conduction velocity and the duration of the refractory period defines the wave length. The risk of developing reentry pathways increases as the wave length shortens. Moreover, the more the atrium fibrillates, the greater will be the decrease of the refractory periods, atrial fibrillation giving rise to atrial fibrillation. Histological lesions of the atrial tissue may be demonstrated, even in the absence of underlying cardiac disease. They mainly consist of fibrosis, fatty degeneration and myocytic hypertrophy. In the long-term, atrial fibrillation leads to a number of structural abnormalities of the atrial, and sometimes ventricular tissues, progressing to cardiomyopathy in some cases.

Action Potentials↗

PubMedDate not supplied

[Effect of dimethicone on pharmacokinetics and pharmacodynamics of ethyl biscoumacetate].

The influence of dimeticone (Gel de Polysilane Midy) on the pharmacokinetics and pharmacodynamics of oral ethyl biscoumacetate was studied in 6 healthy volunteers in a randomised single dose, two-way cross-over study. Each volunteer received at one week interval a single dose (300 mg) of ethyl biscoumacetate, either alone or with dimeticone. Ethyl biscoumacetate levels were measured in plasma for 24 hours. Pharmacodynamic parameters were measured for 96 hours. Ethyl biscoumacetate peak concentration was significantly higher when administered with dimeticone (40.3 +/- 25.3 mg/l vs 31.0 +/- 25.7 mg/l; p = 0.031), without significant change in the area under curve. Other pharmacokinetic and pharmacodynamic parameters did not differ significantly. The slight increase of the ethyl biscoumacetate bioavailability with dimeticone in repeated dosing might have pharmacodynamic consequence; a clinical trial should address this question.

Adult↗