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Biomedical subjects

K Landmark

Publications and source records attributed to K Landmark.

At least 73 records · Page 4Linked to original sources
PubMed1981

N-acetylprocainamide induced changes in refractoriness and monophasic action potentials of the dog heart in situ.

The major metabolite of procainamide (PA) is N-acetylprocainamide (NAPA). The effect of this drug on the electrophysiology of the right ventricle was studied in the dog heart in situ by means of programmed electrical stimulation and monophasic action potential (MAP) recordings. A decrease in the beat interval caused a progressive decrease in refractoriness and MAP duration. Intravenous injection of NAPA 50 mg.kg-1 body weight increased refractoriness to a greater extent than MAP duration at shorter, while the opposite was observed at longer beat intervals. These observations are compatible with delayed recovery of excitability. On the basis of these findings, it is concluded that NAPA belongs to antiarrhythmic drugs of type I according to Vaughan Williams' classification, and NAPA may be an alternative drug for treatment of cardiac arrhythmias.

Acecainide↗
PubMed1981

Classification of cardioactive drugs in vivo by using programmed electrical stimulation in combination with monophasic action potential recordings at different pacing rates.

The effect of antiarrhythmic drugs on myocardial refractoriness may be due to changes either in Vmax of phase 0 or the phase of repolarization of the AP or both. By using programmed electrical stimulation in combination with MAP recordings at different pacing rates in the intact dog heart, it was possible to classify and to a certain extent to elucidate the mode of action of various cardioactive drugs in vivo.

Acebutolol↗
PubMed1979

Disopyramide plasma levels in cardiac patients on maintenance therapy.

The antiarrhythmic agent disopyramide, in a dosage of 200 mg/8 h, was given to 7 cardiac patients. The drug was fairly rapidly absorbed, and the mean peak plasma concentration (3.5 microgram/ml) was measured 1 h after administration of the first dose. The mean biological half-life (7.8 h) was slightly prolonged compared to that reported in normal volunteer subjects. Mean steady state plasma concentrations within the therapeutic range were attained 24--32 h after the start of medication. The fluctuations in the plasma levels were in the order or 30 percent; however, a wide spread of the values was observed. The drug was well tolerated.

Adult↗
PubMed1979

Calcium, nifedipine and arrhythmias in isolated rat atria.

Arrhythmias were induced in isolated rat atrial muscle preparations by increasing the calcium concentration of the Ringer solution, while the potassium concentration was kept low. A rise in the resting tension occurred simultaneously. The release of aspartate aminotransferase (ASAT) from the fibrillating atria was not higher than the release from non-fibrillating atria pretreated with a calcium-antagonistic drug, nifedipine 100 microgram/l. It is suggested that calcium-induced rat atrial arrhythmias in the present experiments are caused by a direct effect on calcium influx through the excitable membrane and not as a result of myocardial lesion caused by calcium overload.

Animals↗
PubMed1979

The effect of nifedipine on the monophasic action potential and refractoriness of the right ventricle of the dog heart in situ after beta-adrenergic receptor blockade.

The effect of nifedipine, a calcium-antagonistic drug, was studied on the electrophysiology of the right ventricle in the dog heart in situ. Monophasic action potential recordings were obtained by the suction electrode technique and refractoriness was measured by means of programmed electrical stimulation. Pentobarbital anaesthesia was used. As the basic cardiac effects of nifedipine can be altered by the release of catecholamines from sympathetic nerves of the heart and vessels, the dogs were pretreated with the beta-adrenergic receptor blocking agent acebutolol which increased the action potential duration and the refractoriness. Intravenous injection of nifedipine 30 microgram/kg body weight decreased the times for 50 and 90 per cent repolarization of the monophasic action potential and to a smaller extent the effective and functional refractory period. It is suggested that nifedipine decreases the action potential duration and the refractoriness of the right ventricle of the dog heart in situ due to a direct effect of the drug on the myocardium.

Acebutolol↗
PubMed1979

Ectopic atrial tachycardia on swallowing. Report on favourable effect of verapamil.

A female patient who suffered from atrial tachycardia associated with the ingestion of food or drink was examined in our department. No signs of organic heart disease were discovered, oesophageal motility was normal, but X-ray revealed a small hiatal hernia. The arrhythmia started with an atrial extrasystole arising well outside the functional refractory period of the AV node, and it could be reproduced by inflation of a balloon. It is suggested that the arrhythmia is induced by a mechanical effect of the passage of food on the left atrial wall. Several drugs were tried in order to stop or relieve the complaints. None of them prevented or stopped the atrial tachycardia but verapamil and edrophonium chloride caused 2:1 AV block, and follow-up study has shown that sufficient doses of verapamil are able to relieve the patient's complaints.

Atrioventricular Node↗
PubMed1978

Acebutolol-induced changes in refractoriness and monophastic action potential of the right ventricle of the dog heart in situ.

The effect of acebutolol, a beta-adrenergic receptor blocking agent, on the electrophysiology of the right ventricle was studied in the dog heart in situ. Pentobarbital anaesthesia which is known to increase the sympathetic tone was used. Monophasic action potential recordings were obtained by the suction electode technique and refractoriness was measured by means of programmed electrical stimulation. A stepwise increase in the frequency of stimulation from 170 to 200, 230, and 260 per min caused a progressive decrease in the refractoriness as well as the duration of the monophasic action potential. Intravenous injection of acebutolol 2.0 mg.kg-1 increased the times for 50 and 90% repolarisation of the monophasic action potential. This increase is probably due to beta-adrenergic receptor blockade in the presence of alpha-adrenergic receptor stimulation. The effective and functional refractory periods, however, were increased to an even greater extent than the monophasic action potential duration. It is suggested that this is the result of a blockade of a catecholamine-induced increase in the velocity of the depolarisation.

Acebutolol↗
PubMed1978

Verapamil and pulmonary hypertension.

We report on the effect of verapamil in 12 patients suffering from pulmonary hypertension. The drug caused a slight, but statistically significant decrease in mean pulmonary artery pressure and in the work performance by the right ventricle. The mean pressure of the right atrium, the end-diastolic pressure of the right ventricle, the pulmonary arteriolar resistance, the cardiac index and the stroke volume were not significantly changed, however, and there was a wide spread of the values observed. In some patients the drug exerted a marked negative inotropic effect, with a concomitant increase in the pulmonary arteriolar resistance.

Adult↗
PubMed1978

Serum levels and electrophysiological effects of N-acetlyprocainamide as compared with procainamide in the dog heart in situ.

The electrophysiological effects of procainamide and its major metabolite N-acetylprocainamide were tested and compared on the heart of the anaesthetized dog by means of His bundle electrography and programmed electrical stimulation. Both drugs exerted a negative chromotropic effect. They also increased intra-atrial and intraventricular conduction times; procainamide was, however, the more potent of the two drugs. In contrast to procainamide, N-caetylprocainamide did not increase His-Purkinje and atrioventricular nodal conduction times, and at the lowest dose employed, atrioventricular nodal conduction times were decreased during atrial pacing. Both drugs increased the functional and effective refractory period of the right atrium and ventricle. N-acetylprocainamide increased the functional refractory period of the atrioventricular node, but to a lesser extent than procainamide.

Animals↗
PubMed1978

The effect of nifedipine on the sinus and atrioventricular node of the dog heart after beta-adrenergic receptor blockade.

The effect of nifedipine (BAY 1040), a calcium-antagonistic inhibitor of the electromechanical coupling process was tested on atrioventricular conduction and refractoriness of the dog heart in situ by means of His-bundle electrography and programmed electrical stimulation. The animals were anaesthetized with sodium pentobarbital. As the basic effects of the compound can be altered by release of catecholamines from sympathetic nerves of heart and vessels, the dogs were pretreated with acebutolol, a beta-adrenergic receptor blocking agent, which decreased heart rate and prolonged atrioventricular conduction and refractoriness. Nifedipine 1,6 and particularly 30 microgram/kg body weight increased the heart rate and decreased atrioventricular conduction time during atrial pacing, whereas atrioventricular conduction time during sinus rhythm and atrioventricular refractoriness were only affected by nifedipine 30 microgram/kg. In this respect, nifedipine differs distinctly from another calcium antagonistic compound, verapamil.

Acebutolol↗
PubMed1977

Determination of effective orifice area in mitral stenosis from non-invasive ultrasound Doppler data and mitral flow rate.

Ten patients with mitral stenosis, but without mitral insufficiency, have been studied during cardiac catheterization. The mitral orifice blood velocities, the mitral pressure gradient, and the mitral flow rate were determined with ultrasound, manometry, and the direct Fick method, respectively. The effective orifice area was calculated from the ultrasound data and the mitral flow rate. The geometric orifice area was calculated from the pressure gradient and the mitral flow rate, using a revised Gorlin formula. A comparison of the two methods showed a correlation coefficient of 0.975. The investigation demonstrated that the ultrasound method represents an alternative to the conventional catheterization methods used for the quantification of mitral flow obstruction.

Blood Flow Velocity↗
PubMed1977

A comparison of the effects of ouabain, noradrenaline and nifedipine on the contractile force of the isolated rat atrium at different calcium levels.

The effects of ouabain 5 x 10-5 M, noradrenaline 10-7 M and nifedipine 100 mug/1 on the contractile force of the isolated rat left atrium were tested and compared at varying concentrations of calcium in the Ringer solution. The effect of ouabain was small, developed slowly and almost independently of the calcium concentration. Noradrenaline, which increases Ca++ influx during excitation, caused an increase in the contractile force which was complete within 2 min. The percentage as well as the absolute increase in contractile force was pronounced at lower, but small at higher calcium concentrations. Nifedipine, which reduces Ca++ influx during excitation, caused a decrease in contractile force which was complete within 2-4 min. The nifedipine-induced depression in contractile force decreased with a rise in the calcium concentration. It is assumed that the ouabain-induced increase in contractile force in the rat, is not mediated by an increase in the magnitude of the inward calcium current, and other modes of action for the inotropic effect of glycosides are discussed.

Animals↗