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Biomedical subjects

S Mashima

Publications and source records attributed to S Mashima.

At least 91 records · Page 5Linked to original sources
PubMed1982

Effects of acute changes in left ventricular size on surface potential in man.

Effects of cardiac size on surface potential magnitude were investigated by induction of acute changes in ventricular dimensions by rapid atrial pacing in 17 cases with ischemic heart disease (IHD) and in 15 cases without IHD. Left ventricular end-diastolic dimensions (LVDd), estimated by echocardiography, decreased along with certain changes in surface potential magnitude during atrial pacing in each case. A positive correlation between LVDd and the amplitudes of RV5, RX, and the maximum spatial QRS magnitude was observed in most of the cases and might be explained by changes in distance between the heart and the chest electrode and/or the Brody effect. However, an inverse correlation was observed in 4 of 17 cases with IHD, and could not be explained by these factors. Other factors, such as changes in the ventricular activation sequence, should be considered as the mechanism.

Adult↗
PubMed1981

Postural changes of vectorcardiogram in defect of the left pericardium.

Effects of postural changes upon the vectorcardiograms (VCGs) of four cases with a defect of the left pericardium (three complete and one partial) were compared to those of 115 control cases. Changes in the direction of a given instantaneous vector brought about by postural changes were significantly larger in cases with a pericardial defect than in controls. By turning to the left lateral position, the magnitude of the maximum leftward force decreased in all cases with complete defect, and increased in the case with partial defect and in 96% of controls. These findings were considered to reflect the increased mobility of the heart in cases with pericardial defect due to the lack of the restraining function of the pericardium.

Adolescent↗
PubMed1981

Pseudo right atrial overloading pattern in complete defect of the left pericardium.

Two cases with complete defect of the left pericardium showing tall and peaked P waves in the right precordial leads are described. A review of the literature has yielded nine cases with uncomplicated complete defect of the left pericardium showing similar P wave changes. Right heart catheterization, performed in nine cases, including the present two cases, revealed no evidence of an intracardiac shunt in any case and normal intracardiac pressure in eight cases. Therefore, this P wave changes seems to be related to intrathoracic shift in cardiac position permitted by the absence of the restraining pericardium.

Adult↗
PubMed1981

Applications of multipole expansion.

With use of a homogeneous torso model, dipole and quadrupole sensitivity was determined for unipolar leads from many sites on the thoracic surface. Representatives of non-dipolar maps were obtained from the sensitivity of each of unipolar leads to the 5 rectangular components of the quadrupole. Over-all sensitivity to the quadrupole or the magnitude of the lead tensor was calculated from the measurements and mapped over the torso surface. This map indicates relative proximity of the thoracic surface and gives a theoretical basis for the selection of electrode locations in the surface mapping technique.

Electrocardiography↗
PubMed1981

The potential distribution on the epicardial surface and in the surrounding volume conductor.

An experimental study was performed on the potential distribution surrounding the heart. The dog heart was isolated, perfused with Tyrode solution and was placed in a spherical container filled with the same solution. The potential measurement was made at 156 sites on the epicardial surface as well as at the same number of locations on the corresponding surface in the solution 0.5 to 2.0 cm apart from the epicardium. The results indicated that considerable simplification of isopotential lines occurred already at a distance of 2 cm from the heart. With the electrode array on the spherical surface enclosing the heart, similar maps were constructed and an index to express the complexity of the map was calculated. With artificial extrasystoles arising from an epicardial site, the potential on the epicardium showed a main negative area with very closely located positive areas. The basis and methods for the determination of epicardial potential from the surface measurements were critically discussed.

Animals↗
PubMed1981

An experimental model of giant negative T wave associated with QT prolongation produced by combined effect of calcium and isoproterenol.

Changes of the surface ECG and monophasic action potential induced by isoproterenol injection were investigated under normo- and hypercalcemic conditions in dogs. (1) Biphasic time course of T wave changes, initially inverted and subsequently uprightly tall, was observed after intravenous injection of isoproterenol in doses of more than 2 microgram. (2) Initial prolongation and subsequent shortening of the phase 2 of action potential were observed on the ventricular surface in accordance with the biphasic time course of the T wave changes on the surface ECG after isoproterenol injection. (3) Giant T wave inversion associated with QT prolongation was obtained by isoproterenol injection under hypercalcemia. (4) Marked prolongation of total duration as well as phase 2 of action potential was observed in accordance with the giant negative T wave on the surface ECG. Although the mechanism of this experimental model of giant negative T wave is not clear, this model could have important suggestions on the unknown mechanism of giant negative T wave observed in various clinical status.

Action Potentials↗
PubMed1980

Clinical evaluation of antiarrhythmic effects of disopyramide by multiclinical controlled double-blind methods.

Used orally, in double-blind cross-over controlled trials conducted on 73 patients, disopyramide, a newly developed antiarrhythmic agent, was found to be more effective than an inert placebo (lactose), with a statistically significant difference, and to be as effective as quinidine sulfate in suppressing ventricular and supraventricular premature beats. In double-blind studies with 42 patients, it was also found to be as effective as quinidine sulfate in preventing the recurrence of atrial fibrillation after successful cardioversion. In non-blind studies attacks of paroxysmal supraventricular and ventricular tachycardia and transient atrial fibrillation were effectively prevented in the respective arrhythmias in more than 70% of the cases.

Arrhythmias, Cardiac↗
PubMed1980

Nocturnal angina pectoris. Comparison between angina with ST segment elevation and depression documented by continuous orthogonal ECG recording.

In 30 patients with nocturnal angina, the night-time ECGs were continuously recorded, and the time and duration of attack, cyclic character of attacks, the relation of chest pain to ischemic ECG changes and arrhythmias during attack were compared between 18 cases with ST elevation and 12 cases with ST depression during attack. In cases with ST elevation, 1) attacks occurred between 2:00 and 8:00 a.m., being most frequent between 4:00 and 5:00 a.m. 2) the duration of attack measured from the duration of ischemic ECG changes was less than 5 min in 88% of the attacks, 3) the attack often recurred with intervals less than 30 min and ECG changes were often unaccompanied bt chest pain, 4) the attack was complicated with various kinds of arrhythmias. These features were in marked contrast to the cases with ST depression, in which attacks were evenly distributed over the night-time, of longer duration, sporadic in occurrence and far less complicated with arrhythmias. These data suggest that the difference of mechanisms causing attacks between both groups.

Adult↗
PubMed1978

The magnitude of the electromotive force of canine ventricular myocardium.

The isolated and perfused dog heart was placed in a cubic container filled with Tyrode's solution. Ventricular ectopic beats were produced by electrical stimulation of the left ventricular wall, and initial QRS vectors of these beats were determined with orthogonal leads from the surface of the container. At the same instants, the activated area on the epicardial surface was measured by means of a large number of contiguous bipolar leads from the epicardial surface. The QRS vector and the activated epicardial area were found to be nearly porportional. By use of these results and a calibration system with artificial dipoles, the double layer moment of the ventricular activation wave was calculated as 0.13 mA.cm per unit area. This value corresponds to 60% of the maximal possible strength of the tissue electromotive force. Lowering the conductivity of the surrounding solution increased the QRS voltage but not as much as the potential caused by a constant-current dipole within the solution. The relationship between the QRS voltage and the conductivity of the medium was analyzed by a simplified model of the system and was found to correspond approximately to that of a constant-current source within a spherical heart with a resistivity 2 to 3 times that of Tyrode's solution.

Animals↗
PubMed1977

Prolongation of ventricular action potential due to sympathetic stimulation.

The changes of monophasic action potential durations due to stellate stimulation for the period of 3 sec were studied in dogs with suction electrodes from the anterior surface of the right ventricle and the posterior surface of the left ventricle. Prolongation of monophasic action potential duration was observed from the period of 2 to 3 sec during stimulation to that of 10 to 20 sec after the termination of stimulation. Prolongation of monophasic action potential duration due to right stellate stimulation was predominant in the right ventricle and that due to left stellate stimulation was predominant in the left ventricle. The transient T wave change in the surface electrocardiogram occurring immediately after the beginning of stellate stimulation could be explained by this local difference in prolongation of ventricle repolarization. Since the onset of prolongation of monophasic action potential duration preceded increase in blood pressure following stellate stimulation, this prolongation of monophasic action potential duration did not result from the hemodynamic changes and could be a primary effect of the sympathetic nerve stimulation.

Action Potentials↗
PubMed1976

Theoretical considerations on the electrocardiogram of ventricular hypertrophy.

The electrical effect of ventricular hypertrophy is evaluated with an idealized model. Perfectly symmetrical hypertrophy is expected to enlarge the QRS complex with a certain proportion of the amplitude and duration. If the conduction velocity is unaltered, the QRS area will be increased proportionally to the myocardial mass. 2) Based on the preservation of the ventricular gradient, the secondary T change is expressed as a function of the QRS and G vectors. A theoretically interesting parameter, G/QRS ratio, is defined as a measure of the "ventricular gradient density," which is important for the over-all recovery pattern. This ratio is decreased in ventricular hypertrophy and is closely related to the QRS-T angle. 3) From the viewpoint of the theory, clinical cases with left ventricular hypertrophy are examined. The theory describes the cases with uncompicated hypertension fairly well, although variations from case to case are not small. Underlying assumptions and causes of deviations in actual cases are discussed.

Aortic Valve Insufficiency↗