The ventricular gradient and altered ventricular activation patterns.

The ventricular gradient vector was determined in normal persons and in cases with left and right bundle branch block (BBB) by means of the best fit method from body surface potential mapping data. Similar measurements were also made in cases with artificial ventricular pacing and the G vector during sinus rhythm was compared with that of the paced beats. Results indicated that the magnitude of the G vector in cases with BBB was smaller than in normal persons. The directional change in the G vector was found to be along the direction of the QRS change in the majority of cases with left BBB. In right BBB, the direction of the G change was variable but the angle between the QRS change was less than 90 degrees on average. Following right ventricular pacing a small increase of the G magnitude was observed acutely, which was opposite in direction to the QRS change. Possible mechanisms are discussed. The G changes in left and right BBB are considered to be based on certain chronic processes, different from those involved in the acute immediate effect of altered activation.

The absolute voltage and the lead vector of Wilson's central terminal.

The absolute potential value of Wilson's central terminal was calculated at 2 msec intervals during a cardiac cycle in 60 clinical cases. Starting from the body surface potential data at 128 thoracic locations, the effect of immersion of the body into an infinite conductor on the surface potential was calculated to obtain values with reference to zero potential at infinity. The conductivity of the outside medium was then made to approach zero. Comparison of the result with the original map showed nearly a constant shift of the potential, corresponding to the voltage of Wilson's terminal. In addition, the cardiac vector was calculated as the first approximation of the cardiac electromotive force and the lead vector of Wilson's terminal was obtained in order that the scalar product of the cardiac vector and the lead vector approximated the observed voltage of Wilson's terminal. The results indicate that the voltage of the Wilson electrode depended on the surface voltage with a peak value near the maximal QRS force in most of the cases. The peak voltage of Wilson's terminal was either positive or negative, and was 0.15 mV in absolute value on average. Voltage variations of Wilson's terminal during a cardiac cycle were 0.20 mV as an average of all cases. The voltage of Wilson's terminal also depended on the direction of the equivalent cardiac vector. The lead vector of Wilson's terminal was found to be directed superiorly in most of the cases. The average magnitude of the lead vector of Wilson's terminal was 0.097 omega/cm, which corresponded to about 1/4 of that of lead I.

On the potential of the Wilson central terminal with respect to an ideal reference for unipolar electrocardiography.

Body surface potential mapping was performed in 60 clinical cases and an ideal 0 potential was calculated in each case at 2msec intervals, which corresponds to the potential at infinity. Maximal deviation of the Wilson terminal voltage the ideal potential was 0.14mv on the average. Time course of potential variations of the central terminal was in proportion to the measured surface potentials. The lead vector of Wilson terminal was determined for each case, with a method to make a minimal difference between calculate and observed Wilson terminal voltage. The lead vector was directed superiorly and posteriorly with the magnitude of 24% of that of lead I on the average.

[Body surface potential mapping system].

Body surface potential mapping systems have been developed by several laboratories in our country as well as many other countries all over the world. In most laboratories the basic procedure is the same. Body surface potentials are measured simultaneously using a multiplexer with or without sampling bold, with Wilson's central terminal and stored on a floppy disk in a digital form. Editing for waveform and drift of the baseline was performed in each leads and invalid leads were interpolated from surrounding leads values. Then, different types of maps such as isopotential map, isointegral map, isochronal map and departure map suitable for each clinical evaluation are constructed automatically. However, although body surface mapping provides detailed information about cardiac electrical activity, its clinical use has been limited by the following reasons summarized by B. Taccardi in 1985. 1) Lack of standardization: Different electrode replacement prevents comparing the results. 2) The equipment is comparably expensive. 3) Application of electrode is time-consuming. 4) Analysis of data is not standardized. Further clinical studies may improve some of above described difficulties. And the availability of high performance microcomputers and clinically acceptable electrodes are essential.

[Dipole analysis of data base for body surface potential maps of normal population].

The dipolarity of the body surface potential distribution and locus of the main dipole were estimated by means of the least square method in data base for body surface potential maps of normal population. The main dipole moved smoothly within the actual cardiac region and was inscribed in a clockwise direction during the QRS. The nondipolar content (residue) showed time-dependent fluctuation the QRS. The main dipole during the T wave moved near the center of the heart. The nondipolar content during the ST-T period was less fluctuation than that during the QRS. These results indicated that a large percentage of the body surface potential maps of normal population could be represented by a single moving dipole.

Determination of the site of the accessory pathway in WPW syndrome by an electrocardiographic inverse solution.

The initial portion of the QRS complex in WPW syndrome might be represented by a single dipole, since the delta wave corresponds to the localized ventricular activation propagated over the accessory atrioventricular pathway. In order to examine whether the site of the accessory pathway in WPW syndrome could be localized by an equivalent dipole method, the dipole positions during the delta wave were determined in 30 patients using a three dimensional model of the torso and were then compared with the sites of accessory pathways localized by body surface maps. The single dipole approximation during the delta wave appeared to be appropriate since the index of the nondipolarity of the potentials was as low as 28% on average. The dipole positions determined on the atrioventricular ring during the delta wave were compatible with the sites of accessory pathways localized by body surface maps in 22 of the 30 patients. The dipole positions were adjacent to the sites of accessory pathways in 7 of the remaining 8 patients. Thus the equivalent dipole method might be an additional noninvasive tool to determine the site of the accessory pathway in WPW syndrome.

Identification of susceptibility to ventricular tachycardia after myocardial infarction by nondipolarity of QRST area maps.

The QRST area map has been related to susceptibility to ventricular tachyarrhythmias because it reflects the disparity of ventricular recovery properties. However, the clinical value of the nondipolarity of the QRST area map, a marker of nonuniform ventricular repolarization, has not been fully studied in myocardial infarction. The nondipolarity of the QRST area map (residue), the ratio of minimized deviation by an optimal dipole to the total measured potentials, was quantitatively studied in relation to susceptibility to ventricular tachycardia after myocardial infarction. The residue of the QRST area map was higher in 59 patients with myocardial infarction than in 44 normal subjects (25.0 +/- 9.0 versus 17.8 +/- 3.3%, p less than 0.01). Seventeen patients with ventricular tachycardia in the chronic phase (greater than 10 days) of myocardial infarction showed higher residue in their QRST area map (34.5 +/- 10.3%) than that in 29 patients without ventricular tachycardia throughout the study (22.7 +/- 6.7%) or that in 13 patients with ventricular tachycardia only in the acute phase (21.2 +/- 7.5%). QRST area maps with a residue greater than or equal to 25% (mean + 2 SD of normal subjects) identified patients with ventricular tachycardia in the chronic phase of myocardial infarction with a sensitivity of 82% and a specificity of 71%. These results suggest that quantitative assessment of the nondipolarity of the QRST area map is clinically useful for identifying susceptibility to ventricular tachycardia in the chronic phase of myocardial infarction.

Clinical application of electrocardiographic computer model.

A three-dimensional computer model was developed to stimulate the ventricular depolarization and repolarization in a clinical setting. The ventricle is composed of approximately 50,000 units arranged in a cubic close-packed structure and the specialized conduction system is distributed so as to obtain the excitation sequence resembling normal ventricular depolarization. The normal distribution of action potential waveforms with the longest duration on the endocardium and the shortest on the epicardium is used in the model. The heart model is mounted in a homogeneous torso model, and the body surface potential distribution generated by the electric dipoles is calculated using the boundary element method. The QRST waveforms corresponding to the normal and some abnormal heart conditions, such as bundle branch block, myocardial infarction, apical hypertrophic cardiomyopathy, and Wolff-Parkinson-White syndrome, is obtained by assuming the abnormal area with altered electrical properties. Thus the three-dimensional computer model may provide further insight into the genesis of the clinical electrocardiogram.

Application of dipole analysis for the diagnosis of myocardial infarction in the presence of left bundle branch block.

The residue value on dipole analysis (the ratio of non-dipolar component to the measured body surface potentials) was estimated mathematically in 16 patients with left bundle branch block. Patients were classified into those with (group A, nine patients) and those without (group B, seven patients) a perfusion defect on thallium-201 myocardial scintigraphy. For the entire QRS complex the residue of group B was smaller than that of normal subjects (20.0 +/- 4.1% versus 24.6 +/- 3.5%, p less than 0.05). Group A showed a greater mean residue value than group B (27.4 +/- 4.4% versus 20.3 +/- 2.4%, p less than 0.01) only during the initial one-third of the QRS complex. All but one patient of group A and only one patient in group B showed a high peak on the residue curve during the initial stage of the QRS complex. The maximal residue value of group A during the initial QRS complex was significantly greater than that of group B (40.9 +/- 10.9% versus 23.4 +/- 5.4%, p less than 0.01). An arbitrarily selected criterion of the maximal residue value greater than or equal to 30% during the initial QRS complex showed a sensitivity of 89% with a specificity of 86% for the diagnosis of myocardial infarction in the presence of left bundle branch block. These results might be related to the complex ventricular activation around the infarcted area even in the presence of left bundle branch block in which intramyocardial conduction with a simple activation front predominates. Dipole analysis appeared to be a valuable method of diagnosing myocardial infarction in the presence of left bundle branch block.