Isopotential Surface Research Articles

On-line computer-assisted exercise mapping.

The ability of exercise ECG body surface mapping to detect the presence and distribution of coronary artery disease was investigated in 76 patients presenting with chest pain. The ECG data were recorded from 16 leads regularly placed over the left praecordium. All 16 leads were input simultaneously to a PDP8 computer and 8-second samples were stored at rest, at the termination of symptom-limited exercise, and in the recovery period. ST isopotential surface maps were subsequently constructed. The presence and praecordial projection of ST abnormality were related to the arteriographic distribution of coronary disease. The ECG data were abnormal in 56 of 58 patients with coronary disease and permitted the identification of left anterior descending artery disease in 49 of 53, right coronary artery disease in 39 of 43, and circumflex artery disease in 24 of 30. Mapping separated those with single vessel from those with multiple vessel disease in 91% of patients with coronary disease. These preliminary results suggest that exercise ECG body surface mapping may provide an attractive non-invasive approach to the investigation of patients with coronary disease.

Passive properties of the membrane of single freshly isolated smooth muscle cells.

Single, smooth muscle cells were isolated from the stomach muscularis of the toad Bufo marinus and studied on the same day as isolation using standard electrophysiological techniques and direct microscopic observation at high magnification. Following penetration a period of hyperpolarization occurred that appeared to be caused by an increase in K+ conductance activated by Ca2+ entering the cell upon penetration. Ion substitution studies showed that the stable steady-state resting potential was dependent on both [Na+]0 and [K+]0. At [Ca2+]0 = 1.8 mM, active responses could be elicited which, at the higher [Ca2+]0 (< 8mM) generally employed, became action potentials with overshoots. Calculations employing the equations for a short cable and the observed change of membrane potential as a single exponential in response to a small hyperpolarizing current step both indicated that the length constant (lambda) was sufficiently greater than the cell length so that the cell behaved as an isopotential surface during subthreshold perturbations. From photomicrographic measurements of each cell studied and the input resistance, values of specific membrane resistance (Rm) were obtained that ranged as high as 152 k omega x cm2 depending on the ionic environment, most notably on [Ca2+]0. The membrane capacity (Cm) referred to the surface area measured with light microscopy was 1.3 +/- 0.3 microF/cm2 (mean +/- SD). When the best estimate of caveolar membrane area was included, Cm referred to total membrane area (caveolar plus noncaveolar) was approximately 0.8 microF/cm2.

Body surface distributions of repolarization forces during acute myocardial infarction. I. Isopotential and isoarea mapping.

Although ST-segment abnormalities during acute myocardial infarction are clinically important, the total thoracic distribution of these repolarization potentials has not been reported. To provide this information, 24 patients with acute myocardial infarction were studied. Isopotential body surface maps were constructed from potentials sensed by 150 anterior and posterior electrodes. Patterns from 12 patients with anterior lesions demonstrated the appearance of repolarization potentials 21.3 +/- 4.6 msec before the end of the QRS complex. During the ST segment, potential distributions were characterized by a single anterior maximum that remained fixed in location but increased in intensity as repolarization progressed. Distributions in the remaining subjects with inferior lesions were analogously characterized by (1) the onset of repolarization 34.6 +/- 12.4 msec before termination of the QRS complex and (2) a single anterior minimum located on the left anterior superior thorax, with positive potentials distributed around the lower thoracic margins. These data suggest that electrocardiographic changes after acute myocardial infarction include (1) marked overlap between activation and recovery patterns and (2) isopotential surface patterns with relatively simple topographic configurations, such as expected of a single-dipole equivalent cardiac generator.

Isopotential surfaces and the corrugated wall model for gas-solid interactions

The relationship between the gas-solid interaction energy u s ( r), where r is the position of a gas atom relative to the solid lattice, and corrugated wall models is discussed. It is argued that the corrugation in these models, which are often used to calculate intensities of diffracted atom beams, can be identified with the position of an isopotential surface extracted from the repulsive branches of the u s ( z) curves for various positions over the unit surface cell. Results of numerical evaluations for several specific potentials are given, including a model for the interactions in a helium-graphite system. The effects of including more than one type of sinusoidal term in the corrugation equation is discussed. It is argued that one can make a useful connection between corrugated wall models and isopotential surfaces.

Isopotential surfaces and the corrugated wall model for gas-solid interactions

Isopotential surfaces and the corrugated wall model for gas-solid interactions

Surface-induced lamellar orientation of multilayer membrane arrays. Theoretical analysis and a new method with application to purple membrane fragments

The orientation of membrane fragments into a lamellar array by a flat surface is analyzed. This analysis includes processes such as centrifugation and drying and physical effects due to membrane fragment steric interactions, finite size, elasticity, and thermal fluctuations. Several model calculations of optimal orientational order in multilayer membrane arrays are presented. The predictions of a smectic A model agree quantitatively with the measured spatial dependence of the fluctuations in layer orientation in a multilamellar arrays. A new technique, based in part on this analysis, for the preparation of well-oriented multilamellar arrays of natural and artificial membranes, isopotential spin-dry centrifugation, is described. The method involves the use of specially designed inserts for the buckets of a standard vacuum ultracentrifuge. The membrane fragments to be oriented are sedimented from solution or suspension onto a substrate of a convenient material which forms a gravitational isopotential surface at high g. Sedimentation is accompanied by removal of the suspending medium at high g to produce oriented films with a selected degree of solvation. In addition, a method is described whereby small solute molecules can be maintained in constant concentration with the membrane fragments during this process. Initial application of the method to the orientation of purple membrane fragments is described. The degree of orientation obtained in this system is evaluated using freeze-fracture and scanning electron microscopy, optical birefringence, linear dichroism, and microscopy.

Transfer rate calculations for compositionally dissimilar interactiong particles

The method of images is shown to be applicable to the problem of calculating the transfer rates of interacting spherical particles, which differ in size and chemical composition. The method can be applied to any transfer problem in which the governing transport equations can be reduced to the Laplace equation and the particles have iso-potential surfaces. From a sample calculation it is found that, while particle interactions do not affect particle temperatures, they may severly affect the particle transfer rates. The effect of interactions on these transfer rates may be either positive (enhance transfer) or negative (retard transfer). Negative interaction effects may be sufficiently strong as to cause transfer reversal.

Accessory atrioventricular pathway in an infant: Prediction of location with body surface maps and ablation with cryosurgery

A 10-month-old infant with multiple muscular ventricular septal defects, congestive heart failure, Wolff-Parkinson-White syndrome, and supraventricular tachycardia is presented. The site of ventricular pre-excitation was predicted by analysis of ST-T wave isopotential body surface maps to be in the posterior free wall of the right ventricle. The site was confirmed by epicardial mapping of the ventricles during surgery. The pathyway was cryoblated and the ventricular defects were closed. The patient has been free of pre-excitation and supraventricular tachycardia for over two years since surgery.

Isopotential body surface mapping in subjects of all ages: emphasis on low-level potentials with analysis of the method.

Isopotential body surface mapping in subjects of all ages: emphasis on low-level potentials with analysis of the method.

Precordial electrocardiographic mapping after exercise in the diagnosis of coronary artery disease

A technique is described for recording the precordial electrocardiographic body surface map before and after exercise. The technique provides an extra dimension to the conventional exercise electrocardiogram because a measurement can be made of the area and severity of S-T segment changes that are projected onto the front of the chest. Sixteen lead isopotential surface maps were recorded before and after exercise in 109 patients with angina who subsequently underwent coronary arteriography. In addition, exercise electrocardiograms were obtained in 53 of these patients using three orthogonal leads and in all patients using a single chest unipolar chest lead. Precordial surface mapping after exercise was found to have a greater sensitivity (95 percent) than electrocardiography using either the orthogonal leads (68 percent) or a single chest lead (64 percent) ( P < 0.01). The specificity of the three techniques did not differ significantly ( P > 0.05). The technique of precordial surface mapping after exercise improves the ability to diagnose coronary artery disease and can easily be applied to clinical practice.

Simulation studies of the electrocardiogram. II. Ischemia and infarction.

Experimental studies of the myocardial action potentials following coronary artery occlusion have shown that the resulting regional ischemia is reflected by characteristics changes in the shapes of the action potentials in the ischemic region. The principal changes are decreases in the magnitude of the resting potential and in the action potential duration. Action potentials with prolonged durations have been observed in the infarcted regions of experimental animals after the development of inverted T waves in the surface electrocardiogram (ECG). We use such abnormal action potentials in our digital computer model to study the effects of acute myocardial ischemia and infarction on the surface ECG. The heart is represented in sufficient detail to allow variations in the location and size of the ischemic injury and in the distribution of the severity of injury within the injured region. The evolution of acute infarctions is simulated by progressively modifying the abnormal action potentials assigned to the injured region. Calculated standard 12 lead ECGs and torso isopotential surface maps for simulated acute ischemia and infarction are in good agreement with patient data reported in the literature. Typical simulations include anterior and inferior transmural ischemia and infarction and anterior subendocardial ischemia. The model is used to examine relationships between torso surface potentials during ventricular activation and recovery and the site and size of the ischemic injury.

Simulation studies of the electrocardiogram. I. The normal heart.

A digital computer model is presented for the simulation of the body surface electrocardiogram (ECG) during ventricular activation and recovery. The ventricles of the heart are represented in detail by a three-dimensional array of approximately 4000 points which is subdivided into 23 regions. Excitation sequence and cellular action potential data taken from the literature are used to determine the spatial distribution of intracellular potentials at each instant of time during a simulated cardiac cycle. The moment of the single dipole representing each region is determined by summing the spatial gradient of the intracellular potential distribution throughout the region. The resulting set of 23 dipoles is then used to calculate the potentials on the surface of a bounded homogeneous volume conductor with the shape of an adult torso. Simulated isopotential surface maps during both activation and recovery are in good agreement with data for humans reported in the literature.

On the spherical symmetry of static stars in general relativity

view Abstract Citations (3) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the spherical symmetry of static stars in general relativity. Marks, D. W. Abstract From Einstein's field equation and the second law of thermodynamics it follows that in nonmagnetic thermally conducting static fluids, isobaric surfaces and isothermal surfaces coincide with isopotential surfaces. By symmetry these surfaces must be surfaces of constant curvature. To keep the energy content of the star finite, these surfaces must be closed; that is, positively curved, hence spherical. Since the energy flux divided by the speed of light is small compared with the rest-energy density, spherical symmetry is imposed only on the evolutionary time scale, so that observed stars may depart from perfect spherical symmetry by factors of the order of the ratio of the fluid velocity compared to the speed of light. Publication: The Astrophysical Journal Pub Date: January 1977 DOI: 10.1086/154927 Bibcode: 1977ApJ...211..266M Keywords: Einstein Equations; Relativity; Stellar Structure; Thermodynamics; Cosmology; Spheres; Stellar Evolution; Stress Tensors; Symmetry; Thermal Conductivity; Astrophysics full text sources ADS |

Body-surface maps of heart potentials: tentative localization of pre-excited areas in forty-two Wolff-Parkinson-White patients.

Heart potentials were recorded from the entire chest surface in 42 patients suffering from Wolff-Parkinson-White syndrome. We were able to identify six types of surface maps, according to the location of the potential maximum and minimum during the delta wave. For each of these types we suggested the most likely location of the pre-excited region around the A-V rings (types 1 to 5) or in the interventricular septum (type 6). In 13 patients belonging to Types 1, 2, 3, 5 and 6 our hypotheses were in agreement with intracardiac recordings, epicardial maps or surgical results obtained by others. Isopotential surface maps provide more information on the location of the pre-excited area than conventional ECGs, particularly when these exhibit intermediate features between Types A and B.

The use of isopotential surface maps in understanding clinical ECGs.

A comparison of isopotential surface maps in children with normal and abnormal hearts shows that, in certain conditions, the QRS configuration of the anterior precordial leads may be similar while the isopotential surface maps show marked variations. This difference can be explained when one knows the position of the lead and the total body surface potential changes during QRS. Body surface maps allow one to gain an idea of the location and type of information on the body surface (eg, the presence of multiple maxima and minima give important clues as to the presence of single or multiple intracardiac excitation waves). Quantitative analysis of QRS maps from 45 children show that considerably more information is available by increasing the number of leads to 24, a number not much above that used in current electrocardiography; on the other hand, the data suggest that an increase to above 25 leads will yield primarily redundant information.

Isopotential body surface maps and their relationship to atrial potentials in the dog.

The origin of body surface P waves was evaluated in the intact dog by recording body surface isopotential maps and atrial epicardial potential maps. P waves were recorded from 150 points on the body surface, and 80 atrial unipolar electrograms were recorded by means of permanently implanted atrial electrodes during normal sinus rhythm and during atrial pacing. When the atrial pacing sites were changed, the associated shape changes in body surface P waves were highly dependent on the position of the recording sites. Throughout most of the P wave, multiple maxima were present on the body surface, and these were caused by widely separated right and left atrial excitation waves; however, the presence of several simultaneous atrial excitation waves could not be appreciated from the body surface maps when the atrial excitation waves were close to one another. In the last third of atrial excitation there were two maxima on the body surface, one due to atrial excitation waves and the other due to early atrial repolarization. In contrast to the more complicated patterns during excitation, during the P-R segment a single maximum and a single minimum were present on the body surface. The sequence of potential changes on both body surface and atrial epicardium during repolarization was similar to the sequence of excitation except that there was reversed polarity.

Interpretation of isopotential surface maps in patients with Ostium Primum and Secundum atrial defects.

The purpose of this study was to determine if there were consistent differentiating patterns in body surface potential maps in children with normal hearts and in those with ostium primum versus ostium secundum atrial septal defects. A second purpose was to interpret the isopotential surface maps in terms of the position of intracardiac electrical wave fronts. Body surface activity throughout QRS demonstrated three major intervals: developing, transitional, and declining potentials. Patients with both types of atrial septal defects demonstrated complex distributions (multiple maxima) during the transitional interval which were not encountered in normal subjects. In the primum group, the distribution of positive and negative potentials sequentially changed in an inverted pattern as compared to the pattern in those patients with secundum defects. Furthermore, during the transitional interval the potential distribution was considerably more complex in the primum group. In two additional patients, body surface maps were helpful in clarifying misleading and atypical conventional electrocardiograms. The presence of simultaneous multiple maxima could only be accounted for by the existence of multiple wave fronts simultaneously present within the heart. In particular the emergence of two widely separated anterior chest maxima in patients with secundum atrial defect indicated the simultaneous presence of prominent left and right ventricular wave fronts. Also, the marked differences in the relative positions of the major body surface maximum and minimum could be accounted for only by considerable differences in the position and extent of intracardiac wave fronts. For example, the target distribution, consisting of an isolated minimum surrounded by multiple maxima and positive potentials over the upper body, in the ostium primum patients, indicated epicardial breakthrough in a wave front positioned in the anterosuperior portion of the heart. In contrast, normal subjects and patients with secundum defect had distributions indicating antero-inferior wave front position at the time of right ventricular epicardial breakthrough.

ISOPOTENTIAL SURFACE MAPS

Excerpt To the Editor:Several questions may be raised regarding the data and conclusions of Spach, Barr, Blumenschein, and Boineau in "Clinical Implications of Isopotential Surface Maps" (Ann. Inte...

Successful surgical interruption of the bundle of Kent in a patient with Wolff-Parkinson-White syndrome.

Recurrent supraventricular tachycardia is a frequent complication in patients with the Wolff-Parkinson-White (WPW) syndrome. Our patient was unusual in that the arrhythmia was the predominant rhythm, and it was felt that the sustained tachycardia was responsible for signs and symptoms of congestive heart failure. The arrhythmia could not be controlled adequately with digitalis, quinidine, diphenylhydantoin, or propranolol. Atrial or ventricular pacing also failed to prevent recurrent episodes of tachycardia. Physiological and pharmacological studies suggested that an anomalous pathway was responsible for the WPW abnormality and participated in a re-entrant circuit which sustained the episodes of tachycardia. Isopotential body surface mapping suggested anomalous ventricular excitation at the lateral aspect of the right atrioventricular groove. Epicardial mapping at the time of surgery was used to localize the earliest area of anomalous ventricular activation, and surgical transection of the atrioventricular junction at that point abolished the electrocardiographic features of WPW and the recurrent tachycardia. Five months after surgery neither the ECG features of WPW nor the tachycardia has recurred. The signs and symptoms of congestive heart failure have subsided, and the patient has returned to work.

Genesis of body surface potentials in varying types of right ventricular hypertrophy.

Isopotential body surface maps and the sequence of epicardial excitation were studied in children with three types of pure right ventricular hypertrophy; that is, secundum atrial defects, valvular pulmonic stenosis, and tetralogy of Fallot. Patients with similar types of hypertrophy demonstrated internal consistency as to the anatomy, sequence of epicardial excitation of the right ventricular free wall, and body surface potential distribution; however, these phenomena varied between the three groups for each type of hypertrophy. These studies indicate that diagnostic information is available on the body surface to distinguish: (1) right ventricular hypertrophy due primarily to dilatation (secundum atrial septal defects), (2) right ventricular hypertrophy with symmetrical increase in thickness throughout the right ventricle (valvular pulmonic stenosis with moderate to severe right ventricular hypertrophy), and (3) right ventricular hypertrophy proximal to infundibular narrowing (tetralogy of Fallot) from one another. The body surface events could be accounted for in part by the events measured at the epicardial surface.