We studied the normal spread of excitation on the anterior and posterior ventricular surface of open-chest dogs by recording unipolar electrograms from an array of 1124 electrodes spaced 2 mm apart. ...The array had the shape of the ventricular surface of the heart. The electrograms were processed by a computer and displayed as epicardial equipotential maps at 1-msec intervals. Isochrone maps also were drawn. Several new features of epicardial potential fields were identified(1) a high number of breakthrough points; (2) the topography, apparent widths, velocities of the wavefronts and the related potential drop; (3) the topography of positive potential peaks in relation to the wavefronts. Fifteen to 24 breakthrough points were located on the anterior, and 10 to 13 on the posterior ventricular surface. Some were in previously described locations and many others in new locations. Specifically, 3 to 5 breakthrough points appeared close to the atrioventricular groove on the anterior right ventricle and 2 to 4 on the posterior heart aspect; these basal breakthrough points appeared when a large portion of ventricular surface was still unexcited. Due to the presence of numerous breakthrough points on the anterior and posterior aspect of the heart which had not previously been described, the spread of excitation on the ventricular surface was “mosaic-like,” with activation wavefronts spreading in all directions, rather than radially from the two breakthrough points, as traditionally described. The positive potential peaks which lay ahead of the expanding wavefronts moved along preferential directions which were probably related to the myocardial fiber direction.
The purpose of this study is to report new methods for manufacturing precision electrode arrays for recording high-resolution potential distributions from epicardial surfaces of small-animal hearts. ...Electrode arrays of 64 leads (8 × 8) and 121 leads (11 × 11) were constructed with a tulle substrate to which insulated, fine silver wires (60-μm diameter) were attached by knots at mesh node intervals of 540 × 720 μm. Insulation was removed at the tips of the knots. Potential distributions and waveforms were recorded from saline solutions and rat heart epicardium during ventricular paced beats and during passive current injection in the diastolic interval. Electrical responses obtained from rat epicardium compared favorably with those observed in studies of larger-animal hearts, which used arrays having greater electrode spacing, and revealed the effects of myocardial anisotropy. Epicardial potentials measured early after stimulation in the region surrounding the pacing site were interpreted in terms of potentials generated by an equivalent quadrupolar source. We conclude that electrode arrays for epicardial mapping of small hearts can be constructed with sufficient ease and precision to allow detailed study of fiber structure and electrophysiology in these hearts in normal and pathological conditions.
The potential distribution in a homogeneous, cylindrical volume conductor surrounding an isolated paced dog heart was first measured and then calculated by using a mathematical model that simulates ...an anisotropic excitation wavefront spreading through the heart muscle. The study was performed with a view to establish to what extent the anisotropy of cardiac generators affects the potential field in the extra-cardiac conducting media at a great distance from the heart. The model considers an oblique dipole layer on the wavefront which, assuming axial symmetry of the electrical properties of the fibers, can be viewed as the superposition of an axial and a transverse dipole layer. These layers are, respectively, parallel and perpendicular to the local fiber direction. A notable feature of the model is that, in the case of axial symmetry, the potential field due to such an oblique distribution is also equivalent to the sum of the potentials generated, respectively, by a normal and an axial dipole layer. In this form, the model generalizes the classical, uniform double layer model, upon which the solid angle theory is based, by adding to it an axial component. The features of the measured potential fields, which could not be interpreted on the basis of the solid angle theory, were satisfactorily reproduced by the model, at least on a qualitative basis. The results clearly showed the dominant role played by the axial component of the potential field even at a considerable distance from the heart.
Susceptibility to Ventricular Arrhythmias in Aged Hearts Rossi, S.; Baruffi, S.; Bertuzzi, A. ...
2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society,
01/2007, Letnik:
2007
Conference Proceeding, Journal Article
Cardiac arrhythmias are frequent in the elderly population, perhaps secondary to an increased prevalence of hypertension and coronary artery disease as well as aging related changes resulting in loss ...of pacemaker cells and degenerative alteration of the conduction system. Independent from underlying structural heart disease, advanced age alone appears to be a risk factor for increased susceptibility to ventricular arrhythmia. However, the electrophysiological basis of this phenomenon is still unclear. Thus, it is important to assess and to define the underlying arrhythmogenic substrate. The aim of the present study was to identify a likely structural-functional ventricular arrhythmogenic substrate in aged hearts. For this purpose ventricular activation patterns were measured in control (n = 4) and aged (n = 10) in vivo rat hearts by recording unipolar electrograms with an epicardial, 1 mm resolution, 8 times 8 electrode array, during pacing and spontaneous or induced ventricular ectopic beats. Our results in aged hearts suggest that peripheral conduction system might be involved in perpetuating sequences of ventricular ectopic beats, regardless of their origin.
Body surface maps recorded from 35 ischemic patients with normal resting 12-lead electrocardiograms were compared with those obtained from 36 age- and sex-matched normal subjects. From instantaneous ...maps of each subject 187 variables were derived relating to the configuration (80 variables) and magnitude (104 variables) of the potential distribution and duration of the electrocardiographic intervals (3 variables). By using stepwise discriminant analysis we selected 3 variables whose linear combination enabled us to correctly allocate 91% of the study population (jacknife procedure; specificity 92%, sensitivity 91%). To substantiate the validity of the results the discriminant function was tested on a new independent population consisting of 27 ischemic patients and 54 normal subjects from another laboratory. A proper allocation was obtained in 86% of the cases (specificity 87%, sensitivity 85%). The large number of correctly classified ischemic patients and the repeatability of the results indicate that the adopted criteria are good markers of ischemic heart disease.
Quantitative data on the normal variability of body surface maps (BSM) are scarce in the literature. This is one of the reasons why BSM are not yet widely used in clinical practice despite their ...superior information contents. In this study we determined the average value and variability of a number of parameters derived from BSM in a group of 36 normal adult males, ages 22 to 60. Forty to 60 homogeneous beats were averaged for each subject. This enabled us to extend our study to the low voltage intervals (P,PQ,ST,U) which encompass more than 60% of the entire P-U duration and to contribute new data to controversial issues, such as the presence of two simultaneous maxima during atrial excitation. The following parameters were measured: a) the coordinates of the absolute potential maximum and minimum on the chest surface during the entire cardiac cycle; b) the time course of four voltage-related functions, namely: highest instantaneous potential value on the chest surface, lowest (most negative) potential, highest potential difference, and surface integral of the absolute value of the potential function. In recent studies these parameters were shown to be of considerable value in discriminating normal subjects from different categories of cardiac patients.
We provided a topographic and quantitative description of body surface maps (BSM) during the entire QRST interval in seven uncomplicated LBBBs and 31 LBBBs complicated by: myocardial infarction (MI, ...seven cases), left ventricular hypertrophy (LVH, eight cases), myocardial ischemia (IS, seven cases), MI + LVH (six cases) and LVH + IS (three cases). In all patients we observed abnormal map configurations attributable to the LBBB. We were unable to identify consistent effects of the complicating heart condition(s) on the general pattern of chest potentials. Conversely, the surface voltages were generally decreased by MI and IS and increased by LVH. By considering the 38 patients as a preliminary learning set we applied a stepwise discriminant analysis to 77 voltage-related variables derived from BSM to produce a model for discriminating between LBBBs with and without MI. We properly allocated more than 90% of the patients. We also attempted to classify the patients into four groups: pure LBBB, LBBB + MI, LBBB + LVH and LBBB + IS, with a percentage of correct classification of about 80%. The two classifying procedures were applied to ten new LBBB patients with results similar to those obtained in the 38 of the study group.
We used comprehensive electrophysiological/anatomical digital computer models of atrial excitation and the human torso to study the mechanism of generation of body surface P-waves in normal sinus ...rhythm, and in middle and lower sinus rhythm. Simulated atrial surface isochrone maps for normal sinus rhythm support the validity of the atrial excitation model. The results suggest that the presence of specialized internodal tracts containing fast-conducting fibers is not essential to account for propagation of excitation in apparent preferential directions from the sinoatrial (SA) node to the atrioventricular node. However, in the absence of fast conducting fibers, a slowly conducting segment in the intercaval region is necessary to achieve proper excitation of the interatrial septum. P-wave notches occur in the absence of specialized fast conducting atrial tracts and anisotropies due to fiber orientation. These notches are due to the atrial geometry and the separate contributions of the right atrium, left atrium, and interatrial septum to the P-waves, and become more pronounced as the pacemaker site shifts downward in the SA node. Thus, slight changes in the origin of excitation, which result in subtle changes in the atrial excitation isochrones, produce significant and complex changes in the simulated body surface P-waves. Circ Res 48168-182, 1980
The authors extend their previous technique of localizing an ectopic focus by utilizing the entire potential distribution on the probe to compute the spatial coordinates of the site of origin of ...ectopic ventricular beats as solution of an inverse problem in terms of sources. On the basis of previous investigations, they represent the unknown source, at QRS onset, by two equal-strength opposing dipoles located at the ends of a short segment whose midpoint was at the ectopic site. The two dipoles simulate the anisotropic properties of both cardiac sources and myocardial tissue in an infinite homogeneous conducting medium. Preliminary results indicate that the model gives a better estimate of the location of an ectopic focus than can be obtained by taking only into account the position of the potential minimum on the probe surface.< >
In order to study the effect of electrically anisotropie tissue on extracellular and extracardiac potentials we simulated the potential generated by a single dipole in a block of myocardium ...surrounded by a homogeneous conducting medium. The dipole represents a surface element of the oblique dipole layer model of the excitation wavefront. The block of myocardium is represented by a set of superimposed layers of parallel fibres with fibre direction rotating from epicardium to endocardium. A finite element approximation is proposed as solution of the Neumann problem for the Poisson's equation Lu=f where f represents the dipolar source.
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