Genyo Nishiyama

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.

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.

Determination of the site of 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.

What Does an Electrocardiologist Expect of a Magnetocardiogram

Electric phenomena in the heart are of low frequency or even quasistatic, so that accompanying magnetic events are at quite low level in intensity. Nevertheless, recent development of magnetocardiographyl 1,2 enables us to expect a contribution to the solution of several problems in the field of electrocardiography. The latter has a longer history with accumulation of empirical knowledge and recently additional techniques such as the body surface potential mapping and signal averaging method. Limitations of the method are still apparent in certain clinical applications, because of the essential complexity of the phenomenon or of the technical problems. Several examples are selected here, which have been challenged by electrocardiographers with unsatisfactory results. They will hopefully be improved by the combination with magnetocardiography.