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Biomedical subjects

A E Aubert

Publications and source records attributed to A E Aubert.

At least 19 recordsLinked to original sources
PubMed1992

Influence of short atrioventricular delay on late diastolic transmitral flow and stroke volume.

Atrial transport function and the corresponding transmitral flow and stroke volume depend on the timing of atrial contraction. To study the influence of short atrioventricular delay (AVD) on these hemodynamic parameters, transmitral flow velocity (by pulsed wave Doppler) and aortic flow (by electromagnetic technique) were studied and compared (paired t test) during normal and short AVD at fixed rate DDD pacing (80 bpm) in AV-blocked, open-chest canine preparations (n:16). The short AVD resulted in a shorter acceleration (difference 4.1 +/- 4.9 msec, mean +/- SD, p less than 0.05), a lower peak velocity (difference: 7.1 +/- 3.2 cm/sec, p less than 0.001), a shorter (difference: 26.9 +/- 16.2 msec, p less than 0.001) and more rapid deceleration (difference: 220.7 +/- 291.7 cm/sec2, p less than 0.005) of the late diastolic transmitral flow elicited by atrial systole. Stroke volume decreased (7.8 +/- 5.2%, p less than 0.001) during short AVD as a consequence of a reduced left ventricular filling due to the interruption of the active atrial transport by the onset of the ventricular contraction.

Animals↗
PubMed1991

The spectrum of left ventricular filling in severe aortic stenosis.

To assess left ventricular diastolic filling in valvular aortic stenosis, pulsed Doppler echocardiography was used prospectively in 35 patients with severe aortic stenosis (valve area less than 1 cm2) and in 38 age-matched normal subjects. Twenty-seven patients had a normal left ventricular systolic function at rest (ejection fraction greater than 0.50) and a normal or only slightly increased mean pulmonary capillary wedge pressure (mean 11 +/- 4 mm Hg). Eight patients had a poor left ventricular systolic function (ejection fraction: 0.28 +/- 0.10) and an elevated mean pulmonary capillary wedge pressure (mean: 36 +/- 9 mm Hg). The Doppler derived filling parameters were correlated with hemodynamic data, left ventricular wall thickness derived from M-mode echocardiograms, heart rate and atrio-ventricular (A-V) conduction delay using stepwise multiple correlation. The data of this study suggest that left ventricular filling is significantly impaired in patients with severe aortic stenosis and left ventricular hypertrophy with an increase in late diastolic (A-wave) velocity, an increase in the A/E ratio, a decrease in the first one-half filling fraction and a prolongation of early diastolic deceleration time. These changes in filling hemodynamics are associated with alterations in mean pulmonary capillary wedge pressure, left ventricular wall thickness, heart rate and A-V conduction delay. When heart failure develops as a result of impaired left ventricular systolic function, an increase in left atrial filling pressure is associated with a shift of left ventricular filling towards early diastole with a 'normalisation' of the transmitral flow velocity curve. In extreme cases, a progression towards a 'restrictive' filling pattern is found with a marked shortening of the left ventricular early diastolic deceleration time. In the presence of high filling pressures, increased left atrial driving pressure (derived from the mean pulmonary capillary wedge pressure) is associated with changes in the left ventricular filling pattern irrespective of the presence and the degree of myocardial hypertrophy.

Adolescent↗
PubMed1991

Non-invasive estimation of the diastolic elastic and viscoelastic properties of the left ventricle.

The present study applies a non-invasive method to the quantitative evaluation of left ventricular stiffness in normal subjects and in patients with ischaemic heart disease (IHD). We have studied 20 patients with IHD and 25 healthy subjects. The third heart sound (S3) was detectable in all patients. We have correlated the energy spectrum of S3, divided into 15 Hz bands, with a series of echocardiographic parameters. The existence of a significant correlation between the spectrum energy and the diameter and thickness of the left ventricle at the moment of S3 allowed us to explore the possibility of interpreting the origin of S3 based on a mathematical model. Our hypothesis has been that, once the left ventricle starts vibrating, it behaves as a simple physical model composed of a mass and an elastic element. To this purely elastic model one can add a factor accounting for viscosity, with a damping effect, to obtain a more complex viscoelastic model. The stiffness coefficient 'k' was computed in both models from the peak frequency of S3 and the left ventricular mass at the moment of S3. Furthermore, in the viscoelastic model, the damping element 'c' was also computed. Both parameters--k and c--were significantly increased in the group with IHD compared with the control group. Although a simplification of the vibrating system, these models make it possible to obtain non-invasively information on the characteristics of the left ventricle through the combined use of echocardiography and spectral analysis of S3.

Adolescent↗
PubMed1990

Effect of short atrioventricular delay on cardiac output.

Short atrioventricular (AV) delay modifies late diastolic filling dynamics. The effect of this change on cardiac output (CO) was studied in closed chest, AV blocked canine preparations (N:10), during AV sequential pacing (80 bpm). CO (thermodilution technique) and transmitral flow velocity (TMFV, pulsed-wave Doppler) were measured and compared (paired t-test) on the basis of TMFV pattern, when atrial contraction (A wave) started just after early diastolic transmitral flow deceleration (PR: 219 +/- 25 ms, mean +/- SD) and when A wave occurred at the end of late diastole and shortened due to the next ventricular contraction (PR: 56 +/- 11 ms). The short AV delay resulted in 12.0 +/- 5.9% decrease of CO, reflecting the interrupted late diastolic atrial transport. Properly timed atrial contraction is necessary for optimal AV sequential pacing.

Animals↗
PubMed1990

Clinical value of the pitch of the third heart sound in ischemic heart disease.

The study investigates the genesis of the third heart sound (S3) in ischemic heart disease based on a mass-spring model. In such a system, the natural frequency of vibration, Fn, depends on the elastic constant, k, and the mass, m, according to the following relationship: Fn = 1/2 pi square root of k/m. To identify the cardiac structures representing k and m, the correlations between the energy of the S3 spectrum and the echocardiographic parameters were searched for. The results are consistent with a model in which k is represented by the thickness of the left ventricle and m by its blood content. The k/m ratio emerges as an important determining factor of the acoustic quality of S3, and yields information on the dysfunction of the left ventricle in ischemic heart disease.

Adult↗
PubMed1990

Laser apexcardiogram in healthy young men: a comparative study with the conventional method.

Laser displacement technique is a new method to registrate the low frequency precordial movements. In 16 young healthy men the apexcardiograms were obtained subsequently by conventional way and by laser displacement technique. The basic differences in time intervals and amplitude relations were analyzed with paired t-test. On the laser apexcardiogram the peak of the positive deflection generated by ventricular systole came later (p less than 0.001), the proportion of the positive deflection to the total deflection was smaller (p less than 0.01) and the positive deflection elicited by atrial contraction was proportionally larger (p less than 0.05) than on the conventional apexcardiogram. The timing of the onset of systolic positive deflection and of the nadir of diastolic negative deflection were similar in both apexcardiograms. The observed differences are the consequences of the different physical basis of the two methods. The laser apexcardiogram seems to be more sensitive on the diastolic events and permits a better analysis of diastolic phenomena of the curve, including the atrial contraction.

Adult↗
PubMed1989

Filter characteristics of the atrial sensing circuit of a rate responsive pacemaker. To see or not to see.

The intra-atrial electrograms (P waves) from floating orthogonal atrial electrodes of acutely implanted pacemaker leads (SRT lead) were recorded and the frequency characteristics were determined. The atrial sensing properties of the rate responsive pacemaker (RS4) used in conjunction with these leads, were studied in relation to the frequency spectra of atrial electrograms. Whereas the P waves showed a bandwidth to 65 Hz, the filter had an upper cutoff frequency of 35 Hz. We conclude that unreliable atrial sensing with the RS4-SRT pacing system is primarily due to an inappropriate filter match and therefore no satisfactory rate responsiveness is achieved.

Cardiac Pacing, Artificial↗
PubMed1989

A mass-spring model hypothesis of the genesis of the physiological third heart sound.

A study on the genesis of the third heart sound (S3) based on the mass-spring model is presented. In such a system the natural frequency of vibration depends on the stiffness constant and the mass according to a physical law. The amplitude versus frequency spectra of S3 of 19 patients were obtained using the FFT algorithm together with mono- and two-dimensional echocardiographic parameters. Each echo parameter was correlated with the relative energy contained in each of the 15 Hz bands in which the normalized average spectrum of S3 of each subject was divided. The relative energy of each band was related to echocardiographic parameters. Significant correlation coefficients were found between the diameter of the left ventricle measured at the end of the rapid filling phase. The thickness of the posterior wall and of the interventricular septum at this moment, and the energy contained in certain frequency bands. The statistical correlations we have revealed are consistent with the model postulated in our hypothesis.

Adult↗
PubMed1988

New high-frequency catheter technique for His bundle ablation in dogs.

A new method is presented for the production of complete atrioventricular heart block. It consists of a special catheter, which is inserted into the right atrium via a femoral vein and positioned in the region of the His bundle for His bundle potential recording. Production of heart block is achieved by a high frequency current pulse from an electrocautery unit.

Animals↗
PubMed1987

Simultaneous right atrial appendage sensing with a target tip, a solid tip and J orthogonal electrodes.

To compare the sensing characteristics of a solid tip, target tip (Medtronic) and orthogonal electrodes within the right atrial appendage, atrial electrograms were simultaneously recorded from 2 pacing leads in 11 patients. No significant differences were noted between atrial electrograms derived from target tip or a solid tip electrode in contact with atrial myocardium. Mean values for P-wave amplitudes of 3.0 vs 3.1 mV and slew rates 0.4 V/s vs 0.6 V/s, and QRS amplitudes of 1.0 vs 1.2 mV and slew rates 0.4 vs 0.2 V/s were obtained. The frequency content was also similar, with spectral maxima at 8 vs 9 Hz (P wave) and 7 vs 6 Hz (QRS). In contrast, atrial electrocardiograms derived from the orthogonal electrodes were significantly different: P-wave amplitude of 6.1 mV (p less than 0.025) and slew rate of 1 V/s and QRS of 0.13 mV and slew rate of 0.04 V/s. Spectral analysis was also dissimilar with maxima at 34 Hz (P wave) and 3 Hz (QRS). Orthogonal noncontacting sensing electrodes positioned within the atrial appendage offer substantially better electrographic P-wave amplitude detection and QRS rejection than contacting tip electrodes. These leads yield a significant improvement when discriminate atrial sensing is required.

Atrial Function↗
PubMed1987

LILLY--a linear least squares curve fitting program for one independent variable.

A program was written to perform a linear least squares curve fitting on data. It includes facilities to report the usual statistics and digital plotter output. Seven types of curves are available for fitting the data. Other features of LILLY include provision of facilities for the selection of subsets in different symbols and separate curve fitting for these subsets. The program also provides a confidence region about the fitted line and the prediction interval for data points. Examples of the use of the program are described.

Mathematical Computing↗
PubMed1987

Sensing and pacing with floating electrodes in the right atrium and right atrial appendage.

Unipolar and bipolar floating atrial electrograms from 58 pacemaker patients were recorded and compared. Twenty-four floating unipolar electrodes and 29 floating bipolar electrodes were used at mid-right atrial level and five orthogonal atrial J leads within the right atrial appendage. Each signal was analyzed in the time domain: peak to peak deflection of P wave and QRS complex, duration of P wave and QRS complex and slew rate; and in the frequency domain: maximum of the energy spectrum and frequency at which a decrease of 3 dB from the maximal amplitude occurred. Atrial P (1.31 +/- 0.94 mV, mean +/- SD) and QRS (1.0 +/- 0.56 mV) waves from unipolar floating electrodes were comparable, whereas they were significantly different from bipolar floating electrodes (1.15 +/- 0.77 mV and 0.25 +/- 0.39 mV). Amplitudes of P waves from orthogonal J leads were largest (3.1 +/- 2.6 mV) and QRS complexes (0.21 +/- 0.13 mV) smallest. The P waves had the highest frequency content (17.1 +/- 19.4 Hz). It is concluded that atrial electrograms from orthogonal electrodes (bipolar or orthogonal J) offer superior sensing characteristics because of the large amplitude P wave and discriminating power between P and QRS waves (P/QRS voltage 15:1). An orthogonal J lead can thus be used for P synchronous pacing at the atrial level, whereas an orthogonal ventricular lead can be used for rate-response pacing systems.

Atrial Function↗
PubMed1986

Sensing characteristics of unipolar and bipolar orthogonal floating atrial electrodes: morphology and spectral analysis.

We investigated wave morphology and spectral energy distributions of signals picked up by floating atrial unipolar and bipolar orthogonal sensing electrodes. Our data show that atrial P and QRS waves from unipolar floating electrodes are comparable. On the other hand, atrial P and QRS waves from bipolar orthogonal floating electrodes are significantly different. Even at high and mid right atrial locations, QRS waves are either absent or much smaller in amplitude and lower in frequency content than P waves. We conclude that the bipolar orthogonal floating atrial electrode is superior to the unipolar one for sensing due to its P to QRS wave discriminating power, which makes complex input filters or algorithms unnecessary. Our data support the idea that physiologic pacing with a VDD or VAT pacemaker is possible using a single pass lead.

Electrocardiography↗