Correlation of the vector magnetocardiogram with the vector electrocardiogram in normal subjects and in anterior and inferior myocardial infarction

Abstract

The relationship between the unipositional vector magnetocardiogram (VMCG) and the Frank vector electrocar diogram (VECG) was studied with a stepwise multiple regression analysis in 200 normal subjects and in 144 patients with myocar dial infarction (MI). The calculated squared multiple correlation coefficient showed that at most 45% of the variation in the normal VMCG could be explained by the VECG. In MI group the predicting value of the VECG was smaller. IN1RODUCTIONThe relationship of the magnetocardiogram (MCG) and the electrocardiogram (ECG) has been an object of many theoret ical and experimental studies. Our clinical studies have dem onstrated that vector MCG and vector ECG contain com plementary information about the pathological condition of the heart [1]. In contrast, some similarities in the lead fields of the unipositional VMCG leads with the VECG leads ob served in model studies [2] give rise to expect some redun dance in the VMCG and the VECG which was actually observed in the morphological study of the normal and abnor mal material [3].In this paper, the relationship between the VMCG and VECG is approached by means of a multiple regression analysis, applied for the normal subjects and patient with myocardial infarction (MI). It gives quantitative information of how much the independent (BCG) variables can explain the variability in the dependent (MCG) variables. The physiologi cal basis of the regression analysis of these methods is their common electrical cardiac source that they record with differ ent spatial sensitivities. II. MATERIALThe normal material of this study consisted of 200 healthy subjects (116 male and 84 female subjects), aged from 16 to 78 years (mean, 46 ± 15 years). The MI material comprised of 92 patients with old inferior MI aged from 39 to 74 years (mean, 58 ± 9 years) and 72 patients with old anterior MI aged from 33 to 84 years (mean, 59 ± 10 years). The study material has been described in detail in our previous works [1,3]. This work was supported in part by the Academy of Finland. 0-7803-0785-2/92$03.00 ©IEEE 579 III. METHODS The VMCGs were recorded using the unipositional lead system [2,3,4]. Shortly, the three orthogonal components of the magnetic field were recorded inside a magnetically shield ed room with a frrst-order vector gradiometer at a single point above the heart, corresponding the electrode location V 2 of the standard 12-lead ECG lead system. The VECGs were recorded using the Frank lead system. The lead II of the standard 12-lead ECG system was recorded as a common time reference from each subject simultaneously with the VMCG and VECG recordings. The amplified and bandpass filtered (0.01-100 Hz) signals were acquired at a sampling rate of 500 Hz with a 12 bit NO converter [3]. The digitized signals were averaged to find the representative QRS-complex. The instantaneous QRS-ampli tudes were determined in the x-(postero-anterior), y-(right to-left), and z-(infero-superior) components of the cardio grams using a technique of time-normalizing the QRS-wave.The...