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Biomedical subjects

R A Nadeau

Publications and source records attributed to R A Nadeau.

At least 19 recordsLinked to original sources
PubMed1991

Epicardial distribution of ST segment and T wave changes produced by stimulation of intrathoracic ganglia or cardiopulmonary nerves in dogs.

Sixty-three ventricular epicardial electrograms were recorded simultaneously in 8 atropinized dogs during stimulation of acutely decentralized intrathoracic autonomic ganglia or cardiopulmonary nerves. Three variables were measured: (1) isochronal maps representing the epicardial activation sequence, (2) maps depicting changes in areas under the QRS complex and T wave (regional inhomogeneity of repolarization), and (3) local and total QT intervals. Neural stimulations did not alter the activation sequence but induced changes in the magnitude and polarity of the ST segments and T waves as well as in QRST areas. Stimulation of the same neural structure in different dogs induced electrical changes with different amplitudes and in different regions of the ventricles, except for the ventral lateral cardiopulmonary nerve which usually affected the dorsal wall of the left ventricle. Greatest changes occurred when the right recurrent, left intermediate medial, left caudal pole, left ventral lateral cardiopulmonary nerves and stellate ganglia were stimulated. Local QT durations either decreased or did not change, whereas total QT duration as measured using a root-mean-square signal did not change, indicating the regional nature of repolarization changes. Taken together, these data indicate that intrathoracic efferent sympathetic neurons can induce regional inhomogeneity of repolarization without prolonging the total QT interval.

Animals↗
PubMed1989

The sympatho-adrenal tone and reactivity in human hypertension.

In the last two decades, remarkable advances have permitted a better understanding of the modulation of sympathetic tone and reactivity at the sympathetic nerve and at the effector cell levels. In man, several indirect approaches have permitted to suggest the possibility of increased sympathetic nerve activity and reactivity in an important subgroup of essential hypertensive patients. The demonstration of significant correlations between circulating levels of sympathetic transmitters and various parameters of cardiovascular functions supports the hypothesis of a participation of the sympathetic system in the maintenance of an elevated blood pressure in those patients. Moreover, several experimental evidences have indicated that the sensitivity of cardiovascular effector cells may be altered in hypertensive patients. The blunted beta receptor responsiveness and the normal or enhanced alpha receptor responsiveness which were observed suggest the possibility of an imbalance between adrenergic receptor functions in hypertension, which may explain the preferential alpha 1 modulation of blood pressure through changes in peripheral resistance in hypertensive patients. Such an abnormality could contribute to the development of cardiac and vascular wall hypertrophy during the evolution of hypertension. These studies therefore suggest that a variety of sympathetic dysfunctions could play a role in the development, maintenance and evolution of human essential hypertension.

Adrenal Glands↗
PubMed1988

Atrioventricular nodal conduction and refractoriness following abrupt changes in cycle length.

The properties of the atrioventricular (AV) nodal conduction and effective refractory period in man are generally evaluated at a constant basic cycle length (CL) and, in most cases, they demonstrate an inverse relationship to the drive cycle. The response of AV node to abrupt change in CL is less defined. We therefore studied the effects of abrupt changes in CL on AV nodal conduction time and refractoriness in 18 patients. AV nodal conduction time, and effective and functional refractory periods were measured during: (1) a constant long CL, (2) a constant short CL, and (3) after an abrupt increase in CL just prior to the introduction of extrastimuli. In 10 of the 18 patients a constant long CL of 600 ms, a constant short CL of 400 ms and a sudden short-to-long change in CL (400 to 600 ms) were tested. AV nodal conduction times (A2H2) were measured at the shortest and longest comparable A1A2 intervals. The mean value of the shortest A2H2 intervals for constant CL of 600 ms was 144 +/- 18 ms; for a constant CL of 400 ms it was 162 +/- 17 ms; after a sudden short-to-long change in CL (400 to 600 ms) it was 142 +/- 14 ms. The mean value of the longest A2H2 intervals at a constant CL of 600 ms was 185 +/- 18 ms; at a constant CL of 400 ms it was 236 +/- 26 ms (p less than 0.01) and after a short-to-long change in CL (400 to 600 ms) 199 +/- 21 ms. AV nodal effective refractory periods measured at the same three CLs had mean values of 279 +/- 13 ms; 300 +/- 15 ms and 294 +/- 13 ms, respectively. Similar results were obtained when other CLs such as 700 to 900, 500 to 900, and 400 to 700 ms were tested. The data suggest that after abrupt short-to-long changes in CL, AV nodal function curves shift from long constant CL toward short constant CL as the coupling intervals decrease, indicating a cumulative pattern. Although the return to baseline conduction time after the fast basic rate is known to be slow, the limitation of this effect to the very early premature beat in the human has not been reported previously.

Adult↗
PubMed1988

Catheter recording of left atrial activation from left pulmonary artery in the Wolff-Parkinson-White syndrome: validation of the technique with intraoperative mapping results.

Accurate localization of accessory pathways (AP) in the Wolff-Parkinson-White (WPW) syndrome requires detailed atrial mapping. Coronary sinus catheterization is so far the most accurate method of left atrial mapping, but it can be technically difficult in some patients. We evaluated the feasibility of left atrial mapping from the left pulmonary artery in 24 patients with WPW syndrome. All patients except one underwent surgical cryoablation of their AP and the results of intraoperative mapping are available for comparison. Mapping in sinus rhythm showed recording of atrial activity in the distal left pulmonary artery occurred 56 +/- 20 ms after activation of high right atrium and 24 +/- 4 ms after activation in the His bundle area, but coincident with left atrial activation in the distal coronary sinus (56 +/- 20 and 53 +/- 13, respectively). Mapping during ventricular pacing or orthodromic tachycardia could differentiate patients as having a right sided, left sided or paraseptal first site of activation. Eleven patients had a left lateral AP, four had a left posterior AP, five had left posteroseptal AP and one had a left anterior AP. The remaining three patients had a right sided AP. Intraoperative results correlated with pre-operative findings in 22 out of 23 (95%) patients who underwent surgical ablation of AP. Thus, recordings form the left pulmonary artery reflect left atrial activity and may be of aid in localizing an AP, especially when coronary sinus recordings cannot be obtained. This technique, however, should not replace the more accurate method of coronary sinus mapping.

Adult↗
PubMed1987

The spatial distribution of late ventricular potentials.

Body surface potential mapping (BSPM) was used to study the spatial distribution of late ventricular potentials. In a group of 15 normals and 21 patients with documented ventricular tachycardia (VT), BSPM performed with 63 averaged and high-pass filtered ECG leads (LP-BSPM) showed that late potentials have a mostly dipolar distribution and that they can be reasonably well detected with only three orthogonal leads. In a group of 17 VT patients who also had BSPM performed during induced VT (VT-BSPM), six patients had LP-BSPM similar to one of the VT-BSPM, suggesting that the locations and orientations of both types of sources are similar. In a group of 12 VT patients who had epi-endo VT mapping at surgery, LP-BSPM showed close extrema (reflecting antero-apical delay) for patients with anterior or apical VT sites, suggesting that VT originates in delayed regions. BSPM thus provides useful information about the detection and significance of late potentials.

Adult↗
PubMed1986

Echocardiographic assessment of left ventricular performance before and after marathon running.

Echocardiography was used to indirectly assess the effects of marathon running on myocardial performance. Thirteen marathon runners (mean +/- SEM:30 +/- 1.6 years) were submitted to a resting echocardiographic examination before racing and during early recovery from marathon racing. Indices of left ventricular performance were computed from M-mode recordings of left ventricular dimensions and aortic valve motions. Comparison of basal and post-marathon indices of left ventricular performance showed no significant differences in either pre-ejection period (PEP), left ventricular ejection index (LVEI), fractional shortening (% delta D), ejection fraction (EF), or mean rate of circumferential fiber shortening (mVcf). Cardiac output (Qc) computed from left ventricular end-diastolic (LVEDV) and end-systolic volumes (LVESV) were significantly higher following marathon running (4.9 +/- 0.4 to 6.7 +/- 0.7 L/min) because of a marked increase in resting heart rate (HR) (58 +/- 3 to 76 +/- 3 bpm). A significant decrease in systolic blood pressure (118 +/- 4 to 108 +/- 3 mm Hg), associated with a slight reduction in calculated total peripheral resistance was also observed after the race. These circulatory adjustments probably reflect thermoregulatory activity that allows a greater blood flow to the skin for heat dissipation, as well as persistence of reactive muscle hyperemia. Echocardiographic evidence suggests that marathon running does not lead to marked impairments in left ventricular performance. However, the absence of change in the end-systolic volume, despite a marked reduction in cardiac afterload, may suggest a slight alteration in contractility that could not be detected with the use of echocardiography.

Adult↗
PubMed1986

Characterization of the spatial distribution of late ventricular potentials by body surface mapping in patients with ventricular tachycardia.

Low-level activity at the end of the QRS complex was analyzed from 63 thoracic leads in 15 normal subjects and in 21 patients with ventricular tachycardia (VT). The latter had old myocardial infarction and no conduction disturbances and had not been receiving antiarrhythmic drugs. In both normal subjects and patients with VT, isopotential maps of the time-averaged and filtered (25 Hz high-pass) electrocardiograms during the terminal portion of the QRS were dipolar, i.e., they showed single positive and negative regions. For patients with VT, the extrema were either distant, with one over the precordial area and the other over the back, or close together in the precordial region. In 10 patients, maps recorded after administration of antiarrhythmic drugs remained the same while QRS duration was prolonged. In six patients, maps recorded before antiarrhythmic surgery showed distant extrema for septal or posterobasal VT sites of origin and close extrema for anterior or posteroapical sites. Generally, QRS duration was reduced and maps were modified after surgery. Late potentials can be well detected with only three orthogonal leads because their distributions are dipolar, but maps provide additional information about their distribution, which may be related to conduction delay sites and possibly to VT sites of origin. Sources near the torso surface would produce close extrema, whereas deeper sources would produce distant extrema.

Adult↗
PubMed1985

Localization of cardiac ectopic activity in man by a single moving dipole. Comparison of different computation techniques.

The accuracy of different computation techniques for the non-invasive localization of cardiac ectopic activity was evaluated. Body surface potentials were recorded from 63 leads in 14 patients with implanted pacemakers. The location, orientation and magnitude of a single moving dipole (SMD) were computed from the first eight terms of a truncated multipole expansion estimated from the body surface potentials. The SMD trajectories obtained during the QRS complex were plotted along with the heart outlines and pacing leads obtained independently from chest x-rays. The origin of the SMD trajectories was compared to the position of the pacing lead to evaluate the accuracy of the SMD. The optimum computation technique used a least-squares (LS) estimation of the multipole expansion truncated at 15 multipoles, in conjunction with a torso model that included regions of lower conductivity representing the lungs. With this method, the SMD trajectories originated near the pacing lead (25 +/- 12 mm) and adequately represented the progression of the ectopic wavefront across the entire heart silhouette. With the LS techniques using 8 or 24 multipoles, the spans of the trajectories were respectively too short, or too long to cover the heart, and the average distance between the SMD at QRS onset and the pacing lead was larger. With a surface integration technique, the SMD-pacing lead distances were similar, both for a finite homogeneous torso model with a fixed geometry, as well as for torso models adapted to the torso geometry of each patient. The SMD was found adequate to represent the progression of an ectopic wavefront, and to localize its origin in man.

Aged↗
PubMed1984

Application of the single moving dipole inverse solution to the study of the Wolff-Parkinson-White syndrome in man.

The single moving dipole (SMD) inverse solution was performed in 28 patients with the Wolff-Parkinson-White preexcitation syndrome to see if the calculated position of the SMD during the initial delta wave could indicate the site of the underlying accessory pathway. This site was first estimated to be at one of eight locations around the atrioventricular ring, from the patient's QRS and ST segment body surface potential maps, as has been described by others. Next, SMD parameters were calculated during the delta wave so as to approximate, on a numerical torso model, the patient's body surface potential map. Visualization of the calculated position of the SMD around the atrioventricular ring was done by projecting it on a plane parallel to this ring. This plane corresponded to the most basal transverse section of a heart model present in the torso model. One limitation was the use of non-varying heart and torso models for all patients. As a result, the SMD technique lacked the precision to separate accessory pathway sites into eight atrioventricular locations. However it was capable of distinguishing between patients belonging to the larger classes of right-sided, posterior, and left-sided preexcitation, formed by combining adjacent atrioventricular accessory pathway locations. With more accurate heart and torso models, it may be possible to increase SMD resolution so as to locate accessory pathway sites deep within the heart. This would represent an advantage over the surface potential map approach which only identifies the site of earliest epicardial breakthrough associated with the accessory pathway.

Adolescent↗
PubMed1982

Electrophysiology of the chemically sympathectomised dog.

The contribution of the sympathetic nervous system in the definition of various electrophysiological variables was studied in chemically sympathectomised dogs. Chemical sympathectomy was obtained following intravenous injection of 50 mg X kg-1 of 6-hydroxydopamine. Sympathectomised dogs presented significant increases in: basic sinus period, sino-atrial conduction time (SACT), AH and HV intervals of the His bundle electrogram, atrial functional (AFRP) and effective (AERP) refractory periods, atrio-ventricular node functional (AVNFRP) and effective (AVNERP) refractory periods, ventricular functional (VFRP) and effective (EVRP) refractory periods and atrial (AMAP) and ventricular (VMAP) monophasic action potential durations. Corrected sinus recovery time (CSRT) was not affected by chemical sympathectomy. Neither was the atrial ERP/MAP duration ratio. This new form of sympathectomy affects all the levels of the cardiac conduction system. Such results are in accordance with those obtained with surgical sympathectomy or the use of beta-blocking agents.

Animals↗
PubMed1981

A comparative evaluation of three different approaches for detecting body surface isopotential map abnormalities in patients with myocardial infarction.

Three approaches for detecting abnormalities in body surface potential maps recorded from patients with myocardial infarction were evaluated. The maps are generated from 26 simultaneously recorded unipolar electrocardiograms. All three approaches detect the deviations in certain parameters from control values determined from 50 normal subjects. The first approach emphasizes qualitative deviations in the trajectories of the surface potential map extrema during QRS and correctly classified all but one infarct in a test group comprising 30 normals and 30 cases of myocardial infarction. The second approach classifies a test subject as abnormal if any one of his 26 lead waveforms deviates appreciably at any instant during QRS from the mean waveform for the particular lead plus or minus two standard deviations, these being determined from the control group. This method, while correctly identifying all infarcts, resulted in a large number of false positives, misclassifying 22 of 30 normals. A final method was to obtain an instant by instant plot of the correlation coefficient between the mean surface potential map during QRS for the 50 normals and that of the subject being tested. Test cases were classified as abnormal if any correlation coefficient value fell below an envelope determined from the correlation coefficient plots obtained by correlating the maps of all 50 normals with their own mean. Twenty-nine normals and 26 infarcts were correctly classified. On the basis of these results, the first approach is superior to the other two for detecting surface potential map abnormalities in patients with myocardial infarction.

Electrocardiography↗
PubMed1981

Liberation of cyclic AMP and catecholamine from the heart during left stellate stimulation in the anesthetized dog.

In open-chest pentothal-chloralose anesthetized dogs, plasma catecholamine and cyclic AMP levels were evaluated in the aortic and coronary sinus blood, during stimulations of the left ansa subclavia (1, 2, and 4 Hz). Basal aortic and coronary sinus catecholamine levels were respectively 0.373 +/- 0.090 and 0.259 +/- 0.048 ng/mL and cyclic AMP levels averaged 21.4 +/- 1.4 and 20.9 +/- 1.6 pmol/mL. Statistically significant increases in cyclic AMP levels were induced by sympathetic stimulations at 1 Hz (2.0 +/- 0.6 pmol/mL, 2 Hz (2.5 +/- 1.2 pmol/mL) and 4 Hz (6.5 +/- 1.5 pmol/mL), concomitantly with elevations of coronary sinus catecholamine levels. Sotalol (5 mg/kg) abolished the increases in coronary sinus cyclic AMP levels induced in coronary sinus cyclic AMP output averaged 282 +/- 30 pmol/min (1 Hz), 662 +/- 160 pmol/min (2 Hz), and 1679 +/- 242 pmol/min (4 Hz). Sympathetically induced cyclic AMP output (4Hz) was blunted by sotalol (-81 +/- 14 pmol/min). Aortic cyclic AMP levels were not significantly influenced by stellate stimulation. Intense correlations were found between increased in coronary sinus plasma catecholamines and cyclic AMP concentration levels (r = 0.81, slope - 1.45, ordinate = -1.42, n = 15) as well as between delta cyclic AMP output versus delta catecholamine output values in the coronary sinus (r = 0.93. slope output levels. Intracoronary infusion of phenylephrine (10 micrograms/min) or nitroprusside (200 micrograms/min) had no influence on cyclic AMP plasma levels whereas aortic and coronary sinus levels were respectively increased 5.5 +/- 1.9 and 7.3 +/- 1.4 pmol/mL during the administration of isoproterenol (5 micrograms/min). These data suggested that plasma cyclic AMP constitutes a sensitive index of cardiac beta-adrenergic activity elicited by the release of endogenous catecholamine during stellate stimulations.

Adrenergic beta-Antagonists↗
PubMed1981

Exercise plasma catecholamines in dogs: role of adrenals and cardiac nerve endings.

The plasma norepinephrine concentration (NE, ng . ml-1) in the pulmonary artery of dogs increased above resting values (0.22 +/- 0.04) for moderate (0.53 +/- 0.06) and severe exercise (1.45 +/- 0.23) and during prolonged exercise of moderate intensity (2.06 +/- 0.14). The plasma epinephrine concentration (E) increased above resting values (0.14 +/- 0.04) for severe exercise only (0.76 +/- 0.10) or when moderate exercise was prolonged (1.81 +/- 0.24). The E response, which appeared greater than that found in humans, is probably related to the species difference in the vasomotor response to exercise between humans and dogs, the latter not being subjected to compensatory vasoconstriction in nonworking areas. The activity of the adrenal medulla is confirmed by the plasma catecholamine (CA) gradient between proximal and distal posterior vena cava at rest (0.20 +/- 0.09) and during short- (0.35 +/- 0.08) and long-duration exercise (1.37 +/- 0.23). On the contrary, the heart is not a source of plasma CA in dogs: coronary sinus CA did not exceed aortic CA at rest and for moderate exercise and was lower than aortic CA for severe exercise (4.80 +/- 0.25 vs. 6.55 +/- 0.76 ng . ml-1).. The sources of plasma NE remain unclear in exercising dogs. Significant amounts of NE may be released by the adrenal medulla.

Adrenal Glands↗
PubMed1979

Plasma catecholamines in acute myocardial infarction.

Plasma catecholamine levels were determined in 26 cases of uncomplicated myocardial infarction within 24 hours of onset of acute chest pain. Blood samples were collected at time of entry and at 4-hour intervals during the 48 hours following admission. Average values of plasma catecholamines within 1 hour of onset of pain were 0.87 ng./ml +/- 0.21 and remained elevated during the first 24 hours period. A gradual fall in catecholamine values was observed during the second 24-hour period. Catecholamines were higher in patients with sinus tachycardia and lower in patients with sinus bradycardia, and were higher in patients with anterior or anterolateral infarction. Catecholamine values were significantly higher when determined while patients presented ventricular ectopic beats or ventricular tachycardia. Sinus tachycardia, ventricular arrhythmias, and elevated plasma catecholamine values may be considered indicators of pain, anxiety, and/or left ventricular dysfunction without necessarily being causally related between themselves.

Adult↗
PubMed1979

Computer processing of intracardiac electrograms for conduction studies.

Computer techniques developed to process intracardiac signals recorded in dogs are presented. The signals under measurement are the auricular and ventricular monophasic action potentials and the His bundle electrogram. Computerized measurement of significant timing parameters on simultaneous recordings of these signals can assess quite precisely changes in the normal conduction scheme of the heart provoked by different experimental protocols. Increased accuracy is mainly due to the objective way of defining wave onsets and the processing power of the system used. Signal recording, signal acquisition, automatic waveform measurements, interactive process and production of end result graphs by computer are all described.

Action Potentials↗