Clin. Cardiol. 15,752-758 (1992)
Single Moving Dipole Obtained from Magnetic Field of the Heart in Patients with Left Ventricular Hypertrophy MASAHIRO NOMURA, M.D., m I K O NAKAYASU,* YUTAKA NAKAYA, M.D., KENSAITO,M.D., SHIGENOBU BANDO,M.D., SUSUMUITO,M.D.
YUKIKO
MIYOSHI, M.D., TETSUZO WAKATSUKI, M.D.,
The Second Department of Internal Medicine, School of Medicine;* Faculty of Integrated Arts and Science, The University of Tokushima, Tokushima, Japan
Summary: Magnetocardiograms (MCGs) were recorded by means of a second-derivative SQUID (superconducting quantum interference device) magnetometer in 20 normal subjects and 28 patients with left ventricular overload to analyze the activation sequence of the heart and amplitude of estimated current source. In the normal subjects, the dipole was directed to the left and gradually superiorly 40 ms after the beginning of the QRS wave mainly due to the activation of the left ventricle. In the patients with hypertension, the direction and location of the dipoles were similar to those of the normal subjects, but their dipole moments were increased. In the patients with mitral regurgitation, the dipoles of late QRS were directed more inferiorly than in the normal subjects and their amplitude was increased. In the patients with aortic valve disease, the amplitude of the dipoles was increased markedly and their location was deviated more to the left than the dipoles of the normal subjects. We established the criterion for diagnosis of LVO from the dipole moment of 50 ms of 3.13X 10-3A or more. The sensitivity of this criterion is significantly higher in the diagnosis of left ventricular overload than the electrocardiogram (ECG). The present study shows that the moving dipole method is useful to determine the increased electromotiveforce in patients with left ventricular overload and that sensitivity in diagnosis of left ventricular overload is increased.
Address for reprints: Masahiro Nomura, M.D. The Second Department of Internal Medicine School of Medicine The University of Tokushima 2-50, Kuramoto-cho Tokushima, Japan 770 Received February 13,1992 Accepted with revision: June 26,1992
Key words: magnetocardiogram,left ventricular overload, single moving dipole
Introduction Detection of the increased electromotiveforce is essential in the diagnosis of left ventricular hypertrophy. However, the amplitude of electrical potential recorded from body surface is influenced by many factors, such as distance from the current source to the electrode and electrical conductivities of the intervening tissue, which makes it difficult to estimate increased electromotive force in each individual by conventionalelectrocardiogram(ECG).' The various voltage criteria are used to diagnose left ventricular overload2but their sensitivities and specificities are not satisfactory. In the present study, we developed for the first time single moving dipole methods from a magnetic field map to estimate the amplitude of the electromotive force and applied them to the diagnosis of left ventricular hypertrophy. One purpose of the electrocardiographic study is to localize the current dipole by the cardiac activities at a certain instant during the heart cycle. Development of the computer made it possible for us to determine the equivalent current dipole from body surface isopotential mapping? However, there have been few studies on the magnetocardiogram (MCG) because of recording difficulties. Recently, MCG has been considered to be a useful method to localize the cardiac source, and this method has been used for the study of the activation wave front, determination of the site of Kent and the origin of ventricular arrh~thmia.~-~ In the present study, we used the MCG to deduce the single equivalent current dipole of the heart at various cardiac cycles to analyze the activation sequence of the heart and the amplitude of estimated current source in patients with left ventricular hypertrophy. The results indicated that the increased electromotive forces can be detected more specifically by the moving dipole method than by ECG.
M. Nomura et al.: Single moving dipole of MCG
753
TABLE I Subjects Number of subjects and sex (M, F)
Normal
19 (13,6)
EH
15 (4,ll)
ASR
8 (33 4 (22)
MR a
Age
LVDd
LVWTh
55.3 f 9.2 59.1 f 7.6 51.0 f 7.6 48.3 f 11.7
46.8 f 4.3 47.5 f 2.9 54.0 f 10.5 55.3 f 8.7
9.3 rt: 1.0 9.8 f 206 12.0 f 2.3" 11.1 f 1.3
pc0.05. p35 mm) MCG (Max value > 2 SD) Dipole moment (Max > 2 SD)
(n= 19)
UCG (+) (n= 17)
1( 5.0) O( 0.0) 2( 10.5)
9(33.3) 5W.4 12(70.6)
UCG(+):LVDd>SO mm or LVWTh > 11 mm a pc0.005. Abbreviations: ECG = electrocardiogram; MCG = magnetocardiogram.
LVO-total (n = 27)
1.1"
9(52.9) 1l(40.7)a]
14(51.9)
M. Nomura et al.: Single moving dipole of MCG
approximately within the actual cardiac region. In normal subjects, two dipoles could be observed in most of the cases in the latter half of the QRS wave.15 In the present study, we analyzed only the dipole on the left because only one dipole could be observed in most patients with left ventricular overload.The direction of inscription of the normal QRS loop in the frontal plane was clockwise in 65% of patients.16In the present study, however, the inscription of the moving dipoles was counterclockwise not only in the LVO group but also in the control group, because only the dipole from the left ventricle could be detected. Tsunakawa et aL3 used moving dipole from isopotential map in patients with left bundle-branch block with and without myocardial infarction and found that the single dipole approximation is appropriate in patients with uncomplicatedleft bundle-branch block but not in those with myocardial infarction. However, they did not study the amplitude of the moving dipoles. As compared with the ECG, few studies on dipole analysis by MCG have been made. Hosaka et a1.17 reported on methods to display the current dipoles in various heart diseases and found that the arrow pattern was in good agreement with the previous results of experimental and simulation studies. Good correlationhas been found between the sites of accessory pathway and the origin of ventricular tachycardias recorded directly and the location deduced from MCG.49 The spatial accuracy of the MCG technique is in the range of 3 mm-5 cm.18 Fenici er aL6 reported that the location of the accessory pathway in Wolff-ParkinsowWhitesyndrome deduced by MCG was in good agreement with operation and electrophysiologicalfindings. In the present study, we used the single equivalent current dipole which is also an effective way to deduce current dipoles and activation sequence in normal and abnormal conditions. Fujino et a1.19 introduced criteria for the diagnosis of LVO by MCG and found that sensitivity and specificity were not different from those in the ECG. In the present study, the criterion of the amplitude of the MCG is as good as that of the ECG, but the corrected values by single equivalent dipole increased the sensitivitiesfor diagnosis of LVO significantly. This is due to the difference in the location of the dipole and peak time. In the LVO group, the dipole at 50 ms is located more deeply than in the control group, which reduced the amplitude of the body surface potential and magnetic field. The control group reaches the peak time earlier than the LVO group, so the amplitude becomes less in the control group at 50 ms compared with the LVH group which shows its largest values in this case. In the vectorcardiogram (VCG), the leftward forces of the QRS vector increase in aortic valve disease, while the posterior forces increase in hypertensive heart disease. We measured only the tangential current parallel to the frontal plane, so the dipole moment of the ASR group is larger than that of the HT group in the present study. In a future MCG study, we shall have to record the three-dimensional MCG with the new generation of SQUID gradiometers.
757
The single equivalent current dipole algorithm is used to localize current sources in the brain and heart. This study also shows that this method is useful to deduce the amplitude of the current sources. In the ECG, the voltage recorded at the body surface is influenced by the body shape and is reduced variously by the inhomogeneous tissues, such as lung, muscle, and fatty tissues.20The electrical conductivities of each tissue differ and the degrees of reduction vary greatly in each individual. Therefore, correct evaluation of the increased electromotive force by ECG is difficult. The current sources of the cardiac activation are not single, as suggested by the multiple activation front in the human model by Durrer et aL2' However, the single moving dipole could provide us with a rough approximation of the location of the activation front in certain instances, as well as with summation of the current dipoles at various portions of the activation front. The present study shows that the moving dipole method is useful to determine the increased electromotiveforce in patients with left ventricular overload and increases sensitivity in the diagnosis of left ventricular overload.
References 1. Mori H, Nakaya Y Present status of clinical magnetocardiography. CV World Report 1,78-86 (1988) 2. Sokolow M, Lyon T P The ventricular complex in left ventricular hypertrophy as obtained by unipolar precordial and limb leads. Am Heart J 37, 161-186 (1949) 3. Tsunakawa H, Nishiyama G, Kanesaka S, Harumi K Application of dipole analysis for the diagnosis of myocardial infarction in the presence of left bundle branch block. J Am Coll Cardiol 10, 1015-1021 (1987) 4. Nomura M, Nakaya Y, Watanabe K, Katayama M, Takeuchi A, Fujino K, Mori H: Detection of accessory pathway in patients with WPW syndrome by means of the isomagnetic map and MRI. In Advances in Biomagnetism (Eds. Williamson SJ, Hoke M, Stroink G, Kotani M). Plenum, New York (1989) 373-376 5. Katila T, Montonen J, Makijarvi M, Nenonen J, Raivio M, Siltanen P Localization of the accessory cardiac conduction pathway. In Biomagnetism '87 (Eds. Atsumi K, Kotani M, Ueno S, Katila T). Tokyo Denki University Press, Tokyo (1987) 274277 6. Fenici RR, Melillo G, Cappelli A, Luca CD, Masselli M: Magnetocardiographic localization of Kent bundles. In Advances in Biomagnetism (Eds. Williamson SJ, Hoke M, Stroink G, Kotani M). Plenum, New York (1989) 365-368 7. Erne SN, Trahms L, Trontelj Z: Current multipoles as sources of biomagnetic fields. In Biomagnetism '87. (Eds. Atsumi K, Kotani M, Ueno S, Katili T). Tokyo Denki University Press, Tokyo (1987) 302-305 8. Schmitz L, Oeff M, Erne SN: Localization of arrhythmogenic areas in the human heart. In Biomagnetism '87 (Eds. Atsumi K, Kotani M, Ueno S, Katila T). Tokyo Denki University Press, Tokyo (1987) 286-289 9. Fenici RR, Masseli M, Lopez L, Melillo G: Magnetocardiographic localization of the arrhythmogenic tissue. In Biomagnetism '87 (Eds. Atsumi K, Kotani M, Ueno S, Katila T). Tokyo Denki University Press, Tokyo (1987) 282-285 10. Nakaya Y, Sumi M, Saito K, Fujino K, Murakami M, Mori H: Analysis of current source of the heart using isomagnetic and vector arrow maps. Jpn Heart J 25,701-711 (1984)
758
Clin. Cardiol. Vol. 15, October 1992
11. Williamson SJ, Kaufman L Magnetic fields of the cerebral cortex. In Biomagnetism (Eds. Erne S, Hahlbohm HD, Lubbig H). Walter de Grutter, Berlin, New York (1984) 353-402 12. Romani GL, Williamson SJ, Kaufman L: Biomagnetic instrumentation. Rev Sci Instr 53, 1815-1845 (1982) 13. Wilson FN, MacLeod AG, Barker PS: The distribution of action c a n t produced by heart muscle and other excitable tissues immersed in extensive conducting medium. J Gen Physiol 16,423456 (1933) 14. Arthur RM, Geselowitz DB, Briller SA, Trost RF:The path of the electrical center of the human heart determined from surface electrocardiogram.J Electmcardiol4,29-33 (1971) 15. Nakayasu K, Nakaya Y, Ishihara S,Nomura M, Mori H: Isomagnetic maps in normal subjects. Comparison with isopotential maps. CV World Report 3,22-27 (1989) 16. Chou TC, Helm RA, Kaplan S: Left ventricular hypertrophy. In Clinical Vectorcardiography. Grune & Stratton, New York, London (1974) 71-84
17. Hosaka H, Cohen D: Visual determination of generators of the magnetocardiogram. J Electrocardiol9,426432 (1976) 18. Hart G: Biomagnetometry: Imaging the heart’s magnetic field. BrHeartJ65,61 (1991) 19. Fujino K, Sumi M, Saito K, Murakami M, Higuchi T, Nakaya Y, Mori H: Magnetocardiograms of patients with left ventricular overloading recorded with a second-derivative SQUID gradiometer. J Electrocardioll7,219-228 (1984) 20. Nakaya Y, Takeuchi A, Nii H, Ishihara S,Nomura M, Fujino K, Saito K, Mori H: Isomagnetic map in right ventricular overloading. J Electrocardiol21, 168-173 (1988) 21. Durrer D, Van Dam RT, Freud GE,Janse MJ, Meijer FL, Arzbaecher RC: Total excitation of the isolated human heart. Circulation 41,899-912 (1970)
Single Moving Dipole Obtained from Magnetic Field of the Heart in Patients with Left Ventricular Hypertrophy MASAHIRO NOMURA, M.D., m I K O NAKAYASU,* YUTAKA NAKAYA, M.D., KENSAITO,M.D., SHIGENOBU BANDO,M.D., SUSUMUITO,M.D.
YUKIKO
MIYOSHI, M.D., TETSUZO WAKATSUKI, M.D.,
The Second Department of Internal Medicine, School of Medicine;* Faculty of Integrated Arts and Science, The University of Tokushima, Tokushima, Japan
Summary: Magnetocardiograms (MCGs) were recorded by means of a second-derivative SQUID (superconducting quantum interference device) magnetometer in 20 normal subjects and 28 patients with left ventricular overload to analyze the activation sequence of the heart and amplitude of estimated current source. In the normal subjects, the dipole was directed to the left and gradually superiorly 40 ms after the beginning of the QRS wave mainly due to the activation of the left ventricle. In the patients with hypertension, the direction and location of the dipoles were similar to those of the normal subjects, but their dipole moments were increased. In the patients with mitral regurgitation, the dipoles of late QRS were directed more inferiorly than in the normal subjects and their amplitude was increased. In the patients with aortic valve disease, the amplitude of the dipoles was increased markedly and their location was deviated more to the left than the dipoles of the normal subjects. We established the criterion for diagnosis of LVO from the dipole moment of 50 ms of 3.13X 10-3A or more. The sensitivity of this criterion is significantly higher in the diagnosis of left ventricular overload than the electrocardiogram (ECG). The present study shows that the moving dipole method is useful to determine the increased electromotiveforce in patients with left ventricular overload and that sensitivity in diagnosis of left ventricular overload is increased.
Address for reprints: Masahiro Nomura, M.D. The Second Department of Internal Medicine School of Medicine The University of Tokushima 2-50, Kuramoto-cho Tokushima, Japan 770 Received February 13,1992 Accepted with revision: June 26,1992
Key words: magnetocardiogram,left ventricular overload, single moving dipole
Introduction Detection of the increased electromotiveforce is essential in the diagnosis of left ventricular hypertrophy. However, the amplitude of electrical potential recorded from body surface is influenced by many factors, such as distance from the current source to the electrode and electrical conductivities of the intervening tissue, which makes it difficult to estimate increased electromotive force in each individual by conventionalelectrocardiogram(ECG).' The various voltage criteria are used to diagnose left ventricular overload2but their sensitivities and specificities are not satisfactory. In the present study, we developed for the first time single moving dipole methods from a magnetic field map to estimate the amplitude of the electromotive force and applied them to the diagnosis of left ventricular hypertrophy. One purpose of the electrocardiographic study is to localize the current dipole by the cardiac activities at a certain instant during the heart cycle. Development of the computer made it possible for us to determine the equivalent current dipole from body surface isopotential mapping? However, there have been few studies on the magnetocardiogram (MCG) because of recording difficulties. Recently, MCG has been considered to be a useful method to localize the cardiac source, and this method has been used for the study of the activation wave front, determination of the site of Kent and the origin of ventricular arrh~thmia.~-~ In the present study, we used the MCG to deduce the single equivalent current dipole of the heart at various cardiac cycles to analyze the activation sequence of the heart and the amplitude of estimated current source in patients with left ventricular hypertrophy. The results indicated that the increased electromotive forces can be detected more specifically by the moving dipole method than by ECG.
M. Nomura et al.: Single moving dipole of MCG
753
TABLE I Subjects Number of subjects and sex (M, F)
Normal
19 (13,6)
EH
15 (4,ll)
ASR
8 (33 4 (22)
MR a
Age
LVDd
LVWTh
55.3 f 9.2 59.1 f 7.6 51.0 f 7.6 48.3 f 11.7
46.8 f 4.3 47.5 f 2.9 54.0 f 10.5 55.3 f 8.7
9.3 rt: 1.0 9.8 f 206 12.0 f 2.3" 11.1 f 1.3
pc0.05. p35 mm) MCG (Max value > 2 SD) Dipole moment (Max > 2 SD)
(n= 19)
UCG (+) (n= 17)
1( 5.0) O( 0.0) 2( 10.5)
9(33.3) 5W.4 12(70.6)
UCG(+):LVDd>SO mm or LVWTh > 11 mm a pc0.005. Abbreviations: ECG = electrocardiogram; MCG = magnetocardiogram.
LVO-total (n = 27)
1.1"
9(52.9) 1l(40.7)a]
14(51.9)
M. Nomura et al.: Single moving dipole of MCG
approximately within the actual cardiac region. In normal subjects, two dipoles could be observed in most of the cases in the latter half of the QRS wave.15 In the present study, we analyzed only the dipole on the left because only one dipole could be observed in most patients with left ventricular overload.The direction of inscription of the normal QRS loop in the frontal plane was clockwise in 65% of patients.16In the present study, however, the inscription of the moving dipoles was counterclockwise not only in the LVO group but also in the control group, because only the dipole from the left ventricle could be detected. Tsunakawa et aL3 used moving dipole from isopotential map in patients with left bundle-branch block with and without myocardial infarction and found that the single dipole approximation is appropriate in patients with uncomplicatedleft bundle-branch block but not in those with myocardial infarction. However, they did not study the amplitude of the moving dipoles. As compared with the ECG, few studies on dipole analysis by MCG have been made. Hosaka et a1.17 reported on methods to display the current dipoles in various heart diseases and found that the arrow pattern was in good agreement with the previous results of experimental and simulation studies. Good correlationhas been found between the sites of accessory pathway and the origin of ventricular tachycardias recorded directly and the location deduced from MCG.49 The spatial accuracy of the MCG technique is in the range of 3 mm-5 cm.18 Fenici er aL6 reported that the location of the accessory pathway in Wolff-ParkinsowWhitesyndrome deduced by MCG was in good agreement with operation and electrophysiologicalfindings. In the present study, we used the single equivalent current dipole which is also an effective way to deduce current dipoles and activation sequence in normal and abnormal conditions. Fujino et a1.19 introduced criteria for the diagnosis of LVO by MCG and found that sensitivity and specificity were not different from those in the ECG. In the present study, the criterion of the amplitude of the MCG is as good as that of the ECG, but the corrected values by single equivalent dipole increased the sensitivitiesfor diagnosis of LVO significantly. This is due to the difference in the location of the dipole and peak time. In the LVO group, the dipole at 50 ms is located more deeply than in the control group, which reduced the amplitude of the body surface potential and magnetic field. The control group reaches the peak time earlier than the LVO group, so the amplitude becomes less in the control group at 50 ms compared with the LVH group which shows its largest values in this case. In the vectorcardiogram (VCG), the leftward forces of the QRS vector increase in aortic valve disease, while the posterior forces increase in hypertensive heart disease. We measured only the tangential current parallel to the frontal plane, so the dipole moment of the ASR group is larger than that of the HT group in the present study. In a future MCG study, we shall have to record the three-dimensional MCG with the new generation of SQUID gradiometers.
757
The single equivalent current dipole algorithm is used to localize current sources in the brain and heart. This study also shows that this method is useful to deduce the amplitude of the current sources. In the ECG, the voltage recorded at the body surface is influenced by the body shape and is reduced variously by the inhomogeneous tissues, such as lung, muscle, and fatty tissues.20The electrical conductivities of each tissue differ and the degrees of reduction vary greatly in each individual. Therefore, correct evaluation of the increased electromotive force by ECG is difficult. The current sources of the cardiac activation are not single, as suggested by the multiple activation front in the human model by Durrer et aL2' However, the single moving dipole could provide us with a rough approximation of the location of the activation front in certain instances, as well as with summation of the current dipoles at various portions of the activation front. The present study shows that the moving dipole method is useful to determine the increased electromotiveforce in patients with left ventricular overload and increases sensitivity in the diagnosis of left ventricular overload.
References 1. Mori H, Nakaya Y Present status of clinical magnetocardiography. CV World Report 1,78-86 (1988) 2. Sokolow M, Lyon T P The ventricular complex in left ventricular hypertrophy as obtained by unipolar precordial and limb leads. Am Heart J 37, 161-186 (1949) 3. Tsunakawa H, Nishiyama G, Kanesaka S, Harumi K Application of dipole analysis for the diagnosis of myocardial infarction in the presence of left bundle branch block. J Am Coll Cardiol 10, 1015-1021 (1987) 4. Nomura M, Nakaya Y, Watanabe K, Katayama M, Takeuchi A, Fujino K, Mori H: Detection of accessory pathway in patients with WPW syndrome by means of the isomagnetic map and MRI. In Advances in Biomagnetism (Eds. Williamson SJ, Hoke M, Stroink G, Kotani M). Plenum, New York (1989) 373-376 5. Katila T, Montonen J, Makijarvi M, Nenonen J, Raivio M, Siltanen P Localization of the accessory cardiac conduction pathway. In Biomagnetism '87 (Eds. Atsumi K, Kotani M, Ueno S, Katila T). Tokyo Denki University Press, Tokyo (1987) 274277 6. Fenici RR, Melillo G, Cappelli A, Luca CD, Masselli M: Magnetocardiographic localization of Kent bundles. In Advances in Biomagnetism (Eds. Williamson SJ, Hoke M, Stroink G, Kotani M). Plenum, New York (1989) 365-368 7. Erne SN, Trahms L, Trontelj Z: Current multipoles as sources of biomagnetic fields. In Biomagnetism '87. (Eds. Atsumi K, Kotani M, Ueno S, Katili T). Tokyo Denki University Press, Tokyo (1987) 302-305 8. Schmitz L, Oeff M, Erne SN: Localization of arrhythmogenic areas in the human heart. In Biomagnetism '87 (Eds. Atsumi K, Kotani M, Ueno S, Katila T). Tokyo Denki University Press, Tokyo (1987) 286-289 9. Fenici RR, Masseli M, Lopez L, Melillo G: Magnetocardiographic localization of the arrhythmogenic tissue. In Biomagnetism '87 (Eds. Atsumi K, Kotani M, Ueno S, Katila T). Tokyo Denki University Press, Tokyo (1987) 282-285 10. Nakaya Y, Sumi M, Saito K, Fujino K, Murakami M, Mori H: Analysis of current source of the heart using isomagnetic and vector arrow maps. Jpn Heart J 25,701-711 (1984)
758
Clin. Cardiol. Vol. 15, October 1992
11. Williamson SJ, Kaufman L Magnetic fields of the cerebral cortex. In Biomagnetism (Eds. Erne S, Hahlbohm HD, Lubbig H). Walter de Grutter, Berlin, New York (1984) 353-402 12. Romani GL, Williamson SJ, Kaufman L: Biomagnetic instrumentation. Rev Sci Instr 53, 1815-1845 (1982) 13. Wilson FN, MacLeod AG, Barker PS: The distribution of action c a n t produced by heart muscle and other excitable tissues immersed in extensive conducting medium. J Gen Physiol 16,423456 (1933) 14. Arthur RM, Geselowitz DB, Briller SA, Trost RF:The path of the electrical center of the human heart determined from surface electrocardiogram.J Electmcardiol4,29-33 (1971) 15. Nakayasu K, Nakaya Y, Ishihara S,Nomura M, Mori H: Isomagnetic maps in normal subjects. Comparison with isopotential maps. CV World Report 3,22-27 (1989) 16. Chou TC, Helm RA, Kaplan S: Left ventricular hypertrophy. In Clinical Vectorcardiography. Grune & Stratton, New York, London (1974) 71-84
17. Hosaka H, Cohen D: Visual determination of generators of the magnetocardiogram. J Electrocardiol9,426432 (1976) 18. Hart G: Biomagnetometry: Imaging the heart’s magnetic field. BrHeartJ65,61 (1991) 19. Fujino K, Sumi M, Saito K, Murakami M, Higuchi T, Nakaya Y, Mori H: Magnetocardiograms of patients with left ventricular overloading recorded with a second-derivative SQUID gradiometer. J Electrocardioll7,219-228 (1984) 20. Nakaya Y, Takeuchi A, Nii H, Ishihara S,Nomura M, Fujino K, Saito K, Mori H: Isomagnetic map in right ventricular overloading. J Electrocardiol21, 168-173 (1988) 21. Durrer D, Van Dam RT, Freud GE,Janse MJ, Meijer FL, Arzbaecher RC: Total excitation of the isolated human heart. Circulation 41,899-912 (1970)
