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Biomedical subjects

B G Denys

Publications and source records attributed to B G Denys.

30 records · Page 2Linked to original sources
PubMed1986

Detection of ventricular tachycardia and fibrillation using ECG processing and intramyocardial pressure gradients.

The automatic termination of malignant tachyarrhythmias and of ventricular fibrillation by an implantable device requires a reliable sensing of these episodes of abnormal ECG. Therefore, we induced tachyarrhythmias and fibrillation in eleven dogs and recorded electrograms and intramyocardial pressure. The electrograms were analyzed using the autocorrelation function and the probability density function. Intramyocardial pressure was monitored as a hemodynamic parameter. Results show that in the case of sinus rhythm, all methods are reliable, but in the case of VT and VF, electrogram processing only is insufficient. It is concluded that combined monitoring of ECG processing and a hemodynamic parameter may increase the sensitivity of an automatic tachycardia-fibrillation detection system.

Animals↗
PubMed1986

Orthogonal atrial appendage sensing.

The characteristics of electrograms derived from a solid platinum-iridium pacing catheter tip in contact with the right atrial appendage are compared to those derived from a Target-tip electrode. Both are then compared to electrograms from two noncontacting orthogonal electrodes positioned more proximally within the atrial appendage. Wave form morphology and spectral energy distribution were determined for the three sets of electrograms. It is concluded that orthogonal electrodes placed within the atrial appendage may offer enhanced atrial sensing required by more sophisticated pacemakers.

Electrocardiography↗
PubMed1986

Relationship between left ventricular pressure and the calibrated apexcardiogram during abrupt outflow obstruction.

In order to study the influence of sudden left ventricular pressure rise on the calibrated apexcardiogram, 181 acute aortic occlusions were performed during systole in 7 dog experiments. For each beat preceding (CO) an occlusion and each occlusion (OC), peak systolic amplitude of left ventricular pressure (CO: 118.5 +/- 17.8 mm Hg; OC: 205.8 +/- 38.7 mm Hg) and apexcardiogram (CO: 48.8 +/- 16.7 mm Hg; OC: 63.0 +/- 25.8 mm Hg) were measured. Pressure gradients, ratios and surface areas of all tracings were digitally calculated. The cross-correlation function between pressure and apexcardiogram was also calculated in order to determine time lags. Significant correlations were found: between surface ratios and pressure gradient of pressure (r = 0.80, p less than 0.001) and of apexcardiogram (r = 0.79, p less than 0.001); between surface ratios of pressure and surface of apexcardiogram (r = 0.52, p less than 0.001). The data suggest that during isovolumic systole, the time integral of the left ventricular pressure and its change during the ejection phase define to a large extent the general shape and size of the apexcardiogram.

Animals↗
PubMed1985

Investigation of genesis of gallop sounds in dogs by quantitative phonocardiography and digital frequency analysis.

Several investigators have noted external gallop sounds to be of higher amplitude than their corresponding internal sounds (S3 and S4). In this study we hoped to determine if S3 and S4 are transmitted in the same manner as S1. In 11 closed-chest dogs, external (apical) and left ventricular pressures and sounds were recorded simultaneously with transducers with identical sensitivity and frequency responses. Volume and pressure overload and positive and negative inotropic drugs were used to generate gallop sounds. Recordings were made in the control state and after the various interventions. S3 and S4 were recorded in 17 experiments each. The amplitude of the external S1 was uniformly higher than that of internal S1 and internal gallop sounds were inconspicuous. With use of Fourier transforms, the gain function was determined by comparing internal to external S1. By inverse transform, the amplitude of the internal gallop sounds was predicted from external sounds. The internal sounds of significant amplitude were predicted in many instances, but the actual recordings showed no conspicuous sounds. The absence of internal gallop sounds of expected amplitude as calculated from the external gallop sounds and the gain function derived from the comparison of internal and external S1 make it very unlikely that external gallop sounds are derived from internal sounds.

Animals↗
PubMed1985

Intramyocardial pressure in the canine heart. An experimental study.

During 11 acute open-chest experiments with dogs, intramyocardial pressure was measured in the anterior wall of the left ventricle with a miniature pressure transducer mounted on a 1.6 mm diameter needle. Pressures were measured at the subendocardium (+/- 10 mm), midwall (+/- 7.5 mm), and subepicardium (+/- 5 mm). Simultaneous recordings of left ventricular pressure and two measures of intramyocardial pressure were made during control, acute volume overload, and after administration of verapamil. Maximal amplitude of the subendocardial pressure was higher and the maximal amplitude of the subepicardial pressure was lower than maximal left ventricular pressure for all interventions (p less than 0.001 and p less than 0.01). During volume overload left ventricular pressure increased more than intramyocardial pressure (left ventricular pressure 34%, subendocardial pressure 6%, midwall pressure 14%, and subepicardial pressure 14%). After the administration of verapamil intramyocardial pressure decreased more than left ventricular pressure (left ventricular pressure 16%, subendocardial pressure 26%, midwall pressure 13%, subepicardial pressure 32%). Positive and negative first derivatives of subendocardial pressure were higher than those of left ventricular pressure during control and after verapamil (between p less than 0.01 and p less than 0.001). Positive and negative first derivatives of subepicardial pressure were lower than those of left ventricular pressure during all interventions (p less than 0.001). The timing of the C-point (onset of mechanical contraction) and the positive first derivative of all tracings was synchronous within 8 msec in all interventions. The 0-point (crosspoint of the tangent to the diastolic plateau and the tangent to the relaxation slope; early diastole) of intramyocardial pressure came later than the 0-point of left ventricular pressure, indicating longer relaxation times in the myocardium (subendocardial pressure: control, p less than 0.001, volume, p less than 0.05, verapamil, no significance; midwall pressure: between p less than 0.05 and p less than 0.001; subepicardial pressure: between p less than 0.01 and p less than 0.001).

Animals↗
PubMed1983

Transfer characteristics of an ink-jet writer for cardiovascular studies.

The transfer characteristic of a 16 channel ink-jet writer used in a cardiovascular laboratory is described. The test method for measuring linearity, gain and phase response is described and results given. The transfer function was calculated from the normalized experimental results and allows prediction of the behaviour of the writer for different input signals. It is shown that the ink-jet galvanometers are linear for signal input amplitudes between 0 and 2.5 V, and have a flat frequency response between DC and 640 Hz (+/- 1%).

Biomedical Engineering↗
PubMed1983

Noninvasive determination of stiffness of the left ventricle by combined M-mode echo- and apexcardiography. An experimental method.

In order to compare an invasive with a noninvasive index of left ventricular stiffness during late diastole, M-mode echocardiogram, left ventricular pressure (LVP) and apexcardiogram (QLAC) were recorded simultaneously during acute dog experiments. The slope of the log pressure (P)-log volume (V) relationship is expressed by the ratio VdP/PdV. This index has been proven to be valid for the evaluation of left ventricular stiffness during late diastole. Diameter (D) changes were assumed to be proportional to volume changes. Continuous data from the ascending part of the A wave (due to atrial contraction) and the corresponding diameter change were used to calculate the slope (k1) of the log LVP--log D relation. During the same period the slope (k2) of the log QLAC--log D relation was also calculated. A significant linear correlation was found between values obtained semi-invasively from LVP-D (k1) and noninvasively from QLAC-D (k2) data: n = 21, r = 0.93, p less than 0.001. This shows the usefulness of VdP/PdV derived noninvasively from QLAC and M-mode echo for the assessment of stiffness of the left ventricle during late diastole.

Animals↗
PubMed1982

Relationship between apexcardiogram, left ventricular pressure and wall stress.

Simultaneous measurement of left ventricular dimension and wall thickness by M-mode echocardiography, of left ventricular pressure by a tip-transducer manometer, and of the calibrated apexcardiogram with a pixie beam transducer, were made during acute experiments on anaesthetized dogs. Instantaneous values for chamber dimensions and wall thickness were obtained throughout the heart cycle by digitizing the echo-mechanocardiograms. From these data myocardial stresses, derived from a thick shell theory (meridional and circumferential components) and from Laplace's law, were computed. Laplace stress if shown to be an adequate expression for average wall stress. Its value was correlated with the calibrated apexcardiogram. The present investigation suggests that to a certain extent, the apexcardiogram not only reflects pressure changes but also dimensional changes of the left ventricle.

Animals↗
PubMedDate not supplied

Cardiac events after heart transplantation: incidence and predictive value of coronary arteriography.

Cardiac events from graft arteriopathy, including myocardial infarction, heart failure resulting from previous myocardial infarction, and sudden death, may limit long-term survival after heart transplantation. To determine the incidence of cardiac events and the use of coronary arteriography in predicting these events, the long-term results (mean follow-up, 3.5 years; standard deviation +/- 2.0) of heart transplantation in 427 patients were reviewed. Cardiac events included 19 cases of myocardial infarction, 13 cases of sudden death, and 10 cases of congestive heart failure. All these events occurred after the first year except for three cases of sudden death and one case of myocardial infarction. Cumulative incidence of cardiac events per patient year was 0.9% within the first year, increasing to 1.9% by 5 years. Cardiac events accounted for 3.8% of the deaths by the end of the first year, rising to 18% of total mortality by 7 years after heart transplantation. In patients dying after the first year of transplantation, deaths from sequelae of coronary artery disease occurred in 36% (20/55). The relative risk ("odds ratio") of any cardiac event was 3.44 (p less than 0.05) in patients with angiographic evidence of obstructive disease compared with those without evidence of disease, risk of cardiac death 4.6 (p less than 0.05) and risk of sudden death, 2.4 (not significant). Of the 13 patients who died suddenly, five seen at autopsy were found to have had a recent myocardial infarction. Of all patients who died of heart disease, recent myocardial infarction was detected in nine who were seen at autopsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗