WO2012173583A1

WO2012173583A1 - Method and device for evaluation of myocardial ischemia based on current density maps

Info

Publication number: WO2012173583A1
Application number: PCT/UA2011/000121
Authority: WO
Inventors: lllya Anatoliiovych CHAYKOVSKYY; Mykola Mykolaiovych BUDNYK
Original assignee: Chaykovskyy Lllya Anatoliiovych; Budnyk Mykola Mykolaiovych
Priority date: 2011-06-16
Filing date: 2011-12-02
Publication date: 2012-12-20
Also published as: UA100929C2; RU2014100142A

Abstract

Invention includes performing MCG examination, reconstructing cur¬ rent density vector maps, calculating vectors lengths for each map during cardiocycle intervals ST-T and QRS. Vector directions are divided onto 3 angular sectors within ST-T and 4 sub-intervals of QRS complex including depolarization of inter-ventricular septum (1 ), anterior wall and apex of LV (2), LV side wall (3), basal myocardial regions (4). Next, they were calculated total vector lengths, directed into the normal (LNORM), abnormal (LPATH), medium (LIM) sector, instantaneous abnormality index AI=100xLNORM/(LNORM+LPATH+1/2xLIM) and its mean-average value Alave for each of said intervals. Finally, for said regions 1-4 decision are made about absence/presence of insignificant/significant ischemia if Alave are within range 70≤Alave≤100 (40≤Alave<70, 0≤Alave<40). Device performs at least one method stage, comprises at least one electronic unit which may include embedded microprocessor, or at least one said step is performed by software.

Description

METHOD AND DEVICE FOR EVALUATION OF MYOCARDIAL ISCHEMIA BASED ON CURRENT DENSITY MAPS

FIELD OF INVENTION

The present invention relates to the field of medicine, namely - to cardiology, and could be used for diagnosis of electrophysiology damages and other myocardial injuries. Currently, reliable diagnosis for most of the heart diseases remains the clinical issue of today.

PRIOR STATE-OF-ART

For example, for diagnosis of the myocardial ischemia by means of the most widely used method of the heart's electrical activity analysis - ECG, there are several diagnostic criteria known to be used, characterizing magnitude and direction of the heart's EMF vector in different moments of the cardio-cycle. For example, in the vector-ECG method [Non-invasive diagnosis of coronary artery disease using cardiogoniometry performed at rest, W. Schupbach, B. Emese, P. Loretan et al, Swiss Medical Weekly, 2008; 138(15-16):230-238, www.smw.ch] there are 13 magnitude and angle indexes are used for diagnosis of the ischemic heart disease (IHD), which characterize re- and depolarization processes.

But this method possesses several significant limitations:

1 ) there is only sum vector analyzed, which reflects only integral condition of myocardium; as a result, many of the regional electric processes damages remain undetected.

2) information is used only concerning the potential difference between the body surface points, but not the current density distribution (CDD) inside the myocardium, hence this information could be distorted by the electric properties non-uniformity and anisotropy of the body tissues around the heart.

Hereby, diagnostic accuracy of the ECG method is not enough for clinical diagnosis of IHD. Therefore, further development is reasonable of non-invasive, completely safe methods, non-interfering onto the patients, free of contraindications, and hence - which could be repeated may times in different clinical situations. Namely magnetocardiography (MCG) is completely non-invasive and safe method, providing additional information.

Application perceptiveness of MCG method for the heart pathology diagnosis lies in the fact that any other method doesn't allow to determine direction and magnitude of the local currents in myocardium. Only MCG, which detects magnetic field produced by the heart currents, allows direct measurement of the cardiac currents density.

There are several patents and dissertations known, based on the MCG's ability to provide new useful information, which could be used as availability indicator of the electrophysiology processes damages in heart.

1. WO 0217769, Ischemia identification, quantification and partial localization in MCG, A. Bakharev, Cardiomag Imaging Inc, USA, 2002.

2. WO 002313, Machine learning for classification of magneto- cardiograms, Sternickel K. B, Cardiomag Imaging Inc, USA, 2005.

3. Chaikovsky I. Magnetocardiography in unshielded location in coronary artery disease detection using computerized classification of current density vectors maps, Dr. Med. dissertation, University Duisburg-Essen, Germany, 2006.

4. UA 90701 , Method for estimation of degree of electric processes into the heart ventricules, Chaikovskyi I., Budnyk M., 2010.

Patent WO 0217769 considers corresponding method for the IHD diagnosis, where IHD is classified onto 4 severity degrees with presence of changes in vertical coordinate (depth) of the effective dipole during ST- segment. Herewith first degree of I^'HD occurs if dipole depth changes only during the 1-st quarter of said ST-segment, 2-nd degree - when changes occur during first 2 quarters, etc. In health people without IHD, dipole depth has practically constant value.

Limitations of said method are following: inverse problem (IP) is solved in dipole approximation, and also this is approximation of the magnetic, but not of the current dipole, which doesn't correspond to the real electrophysiological processes in heart. Analysis on the base of dipole model doesn't allow detecting of separate damage sources in myocardium, that is why, it's necessary to apply more complex source representations in form of the CDD maps in the frontal plane. CDD map - is a vector field, where each vector represents current density in the given point, and areas of the map with local maximums surrounded by the lower magnitude vectors, represent separate electrical activity zones of myocardium.

Patent WO 002313 considers diagnostic method, based on the one of automatic image recognition techniques with neural networks (Direct Kernel based Self-Organizing Maps). In terms of this recognition magnetic maps are qualified as normal or pathological. Limitation of this method is the fact, that it doesn't use solution of the inverse problem of electrodynamics, and also it doesn't allow qualifying maps just by 2 classes (normal and pathological) without further detalization.

In the PhD thesis by I. Chaikovsky "Magnetocardiography in unshielded location in CAD detection using computerized classification of current density vectors maps" there is diagnostic method analyzed, with reconstruction of the CDD maps set from the J-point (the end of QRS complex) to the end of the T wave, classification of the CDD maps onto 5 grades - from the normal to the highest pathological grade on the base of directions estimation of the largest current density vectors. Limitations of this method are in that it analyzes only ventricular repolarization and that maps classification is performed only by small amount of degrees. In prototype method UA 90701 technique is considered for estimation of the abnormality rate of electrical processes in heart's ventricles by means of MCG-mapping, analysis of CDD maps from the beginning of QRS complex to the end of T wave, determination of the high current density areas and current vortexes on the maps of topologic parameters, calculation of their difference grades compared to the normal quasi-dipole map and its mean value for the set. Method is distinctive in that it takes into account areas with low current density and determines on this base the regional non-homogeneity degree (RNH) by the ternary scale - low, medium, high. Then there is magnitude ratio is calculated R/T of the largest current density vectors on the peaks of R and T waves, and on this base degree of global non-homogeneity (GNH) is determined by the ternary scale: low - for 4<R/T<6, medium - for 6<R/T<8, high - for R/T>8.

As a result, conclusion is made concerning abnormality degree by five-level scale - "normal" for low RNH degree and GNH, "low abnormality level" - for low RNH degree and medium GNH degree and vise versa, "medium abnormality level" - for low RNH degree and high GNH degree and vise versa, or for medium degree of RNH and GNH, "high abnormality level" - for medium RNH degree or high GNH degree and vise versa, "very high abnormality level" - for high degree of RNH and GNH.

Prototype advantage lies in the fact that:

1 ) this technique analyses CDD maps, but not magnetic field maps (MFM);

2) it takes into account topologic parameters of areas not only with high, but also with low density of the current vectors;

3) it determines not only regional, but also global and total non- homogeneity;

4) global non-homogeneity degree is determined on the base of the magnitudes ratio of largest current density vectors on the peaks of R and T waves; 5) total non-homogeneity degree is determined on the base of the sum of regional and global non-homogeneity degrees;

6) both re- and depolarization are taken into account.

So, prototype makes it possible to identify abnormality degree of myocardium CDD deviation vs. normal conditions in consequence of the damage of electrical processes in the heart's ventricles. But prototype also has some limitations, because it uses only index, calculated on the base of current vectors sum on the peaks of R and T waves, i.e. in the certain separate time moments, but not time-averaged over the cardio-cycle period. Averaged index is less sensitive to short-period interferences and to the interpersonal dispersion of physiological parameters.

Therefore, current technical level in the field of myocardial ischemia diagnosis by means of MCG has several limitations:

1 ) instantaneous, but not averaged indexes are used,

2) QRS complex, which characterize depolarization process, is not splitted onto sub-intervals, which doesn't allow analyzing separate phases of ventricles excitation;

3) it doesn't use extraction of 3 direction sectors of the instantaneous current density vector;

Background of proposed invention is based on the task to improve diagnostic method, in which new indexes are used, a-posteriori determined bounds of these indicators, new actions and performance modes, determination of absence or presence of myocardial ischemia, and in the case of its presence - severity degree (non-significant, significant).

In order to implement this objective proposed method and device are based on the calculation of the vectors length sum with normal, medium and abnormal direction for every stage of ventricles depolarization and repolarization, followed by calculation of their ratio. In other words, it determines contributions of the "normal" and "pathologic" vectors to the map. SUMMARY OF THE INVENTION

Problem stated in proposed invention is solved by:

1 ) carrying out of MCG examination;

2) CCD maps reconstruction in the frontal plane;

3) vector lengths calculation for each map during the cardio-cycle intervals QRS and ST-T;

4) extraction of the three angular segments for the current density vectors directions - normal, medium and abnormal for the ST-T interval and sub-intervals of the QRS complex, which reflect depolarization of the interventricular septum, anterior ventricle wall, anterior wall and apex of the left ventricle (LV), LV side wall, basal myocardial regions;

5) calculation of the overall length of all vectors LNORM (LPATH, LIM), during said cardio-cycle intervals with normal (abnormal, medium) directions;

6) calculation of the instantaneous abnormality indexes as a part of the overall vectors length of the map, which have normal direction for given moment of time, in percents according to the expression

Al = 100 x LNORM / (LNORM + LPATH + ½ x LIM) , (1 )

7) calculation of the averaged abnormality index for said intervals Alave as arithmetic average of the instantaneous indexes Al,

8) diagnosis of the ischemia absence/presence for said myocardium regions according to the rule - ischemia of said regions is absent (insignificant, significant) if abnormality index Alave value is in the range, 70≤Alave<100 (40<Alave<70, 0<Alave<40).

9) performance of at least one of steps, said in items 3-8, using electronic unit,

10) implementation at least one of the steps, said in items 3-8, using computer and computer software,

11 ) implementation of at least one of units, said in item 9, using microprocessor-based embedded computing device. Novelty, as compared to the current level, is in following:

1 ) using abnormality index based on the contributions ratio of "normal" and "pathological" vectors according to the equation (1 );

2) using abnormality index, averaged over the certain time interval of the cardio-cycle, but not just instantaneous value of this index, in order to obtain more reliable estimation of the presence and severity grade of ischemia.

3) conclusion is based on analysis of both repolarization and depolarization process of myocardium.

Technical result consists in:

1 ) improvement of ischemia detection reliability.

2) possibility to provide more accurate estimation of ischemia severity grade.

3) possibility to determine ischemia localization.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a schematic diagram of method and device according to the invention, which implements proposed method.

Figures 2 represents circular charts of direction of maximum current density vector for ventricular repolarization (Figure 2a), depolarization of interventricular septum (Figure 2b), depolarization of anterior wall and apex of the left ventricle (LV) (Figure 2c), depolarization of LV side wall (d), depolarization of basal myocardial regions (Figure 2e).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In its main realization method contains action sequence, executing individual steps of the algorithm that in consumption implement proposed method. Schematic diagram of the method is represented on Fig. 1 , where dashed steps don't describe proposed method and represented just to illustrate its principle. Step 1. Execution of MCG examination, preliminary signal processing and calculation of the magnetic field maps sets. Particular implementation of the method proposed in this invention provides preliminary carrying out of MCG examination with simultaneous ECG registration in 2-nd standard lead and processing of received data. This processing includes several stages: preliminary processing (filtering, rejection of complexes with pulse interferences, cardio-cycles selection of the same type and averaging), calculation of the MFM maps sets and reconstruction of CDD maps within the square area 20X20 cm. These actions are covered by previous patents UA 77722, UA 77723, UA 20101 , UA 21299 and not the subject matter of this invention.

Step 2. CDD maps reconstruction in the frontal plane. CDD map - is a vector field, where vectors are placed onto the regular (usually square) grid. Each vector reflects the local values, i.e. current density in given point.

Implementation of this method uses procedure of inverse problem solution according to WO/2002/00108 [Computer-based method for automatically processing data, especially magnetocardiographic data, of biomagnetic fields. S. Romanovich, F.Steinberg, SQUID AG, Germany, 2001]. This approach was used in former patents UA 83050, UA 83061 , and also in patent-prototype UA 90701. As a result one obtains CDD maps in the frontal plane, where vectors are placed onto the square grid 10X10 with 2 cm pitch.

Step 3. Vectors magnitude calculation during the QRS and ST-T intervals. In basic implementation of the method there orthogonal projection are calculated of the current density vectors in each of 100 points and their export to ASCII file. Vector magnitudes are calculated using known formula for vector length expression by its projections. Vectors magnitude calculations are performed sequentially for all CDD maps within the QRS and ST-T intervals with time sampling rate 1 ms. Step 4. Extraction of 3 angular sectors for directions of the current density vectors (normal, medium and abnormal) for said cardio-cycle intervals. For instantaneous current density vectors normal direction is known, i.e. sector within the ECG circular chart from 0° to 180° and from - 180° to 0°, where vector direction inside this sector is considered as normal or "appropriate".

As an example, lets review "appropriate" direction for the ST-T interval (Fig. 2, a). During ventricles repolarization stage sum EMF vector in the frontal plane should be directed within the sector from 10° to 80°, painted in green. Adjacent sectors from the left and right sides are painted in yellow. Vector direction into these sectors is medium between the norm and pathology.

Remaining sector of the circular chart is painted in red, because this vector direction within the ST-T interval is abnormal. Similarly, the same charts are represented for all depolarization stages: for the interventricular septum - Fig. 2,b, anterior wall and apex of the left ventricle - Fig. 2,c, left ventricle side wall - Fig. 2,d, basal myocardial regions - Fig. 2,e.

Step 5. Calculation of the sum length of all vectors LNORM, LPATH, LIM for each time point during said cardio-cycle intervals, which belong respectively to the sectors of normal, medium or abnormal directions. These sums contain the lengths of vectors, selected on the Step 4, which directions belong to the normal (abnormal, medium) sector. As a result one obtains total vectors lengths for each time point, which magnitudes are denoted as LNORM (LPATH, LIM).

Step 6. Calculation of the abnormality indexes Al for each time point. For each time point "abnormality index" Al is calculated as ratio of the vectors length sum with normal direction to the vectors length sum with normal, abnormal and medium directions, according to the equation (1). Abnormality index is normalized to 100%, consequently it has a value in the range from 0 to 100. Step 7. Calculation of the averaged abnormality indexes Alave for said intervals. Next step of the algorithm - is abnormality index averaging for the maps over all investigated intervals. This value is obtained as arithmetic mean of instant indexes Al, calculated on the Step 6.

Step 8. Formulation of the diagnostic rule. Finally, diagnostic decision is formulated about ischemia presence and its severity degree for the interventricular septum, LV side wall and apex and basal myocardial regions on the base of the average abnormality index value according to the rule - ischemization of given region is absent (insignificant, significant) if abnormality index Alave is within the normal (medium, pathological) range of values 70≤Alave<100 (40≤Alave<70, 0<Alave<40).

Medical case 1. Healthy volunteer A., 48 years old, with normal ECG results at rest and under physical exercise, Echo-CG at rest, without record of heart diseases in anamnesis. According to the MCG examination data, during ST-T interval and QRS complex of the cardio-cycle Alave index was equal respectively to 24 and 30. So, averaged abnormality index values are within the normal range, so, according to proposed method, ischemization of said myocardium region is absent.

Medical case 2. Patient K., 56 years old, ECG and Echo-CG at rest without pathological changes, stress-EchoCG reveals hypokinesia in the apex/anterior region of the LV, according to the coronary ventriculography data - 85% stenosis in the medium third part of the anterior interventricular branch of the left coronary artery. According to the MCG examination data, during ST-T interval and QRS complex of the cardio-cycle Alave index was equal respectively to 79 and 47. So, averaged abnormality index values are within the pathological range. Therefore, according to proposed method, ischemization of the anterior/apex myocardium region is significant, because one of Alave indexes value was higher than 70%.

In the main realization all said actions and calculations are implemented using at least one electronic unit. In the intermediate realization all steps are implemented using separate units. In this case device contains several electronic modules, which implement separate steps of the algorithm, which realize the method. Schematic diagram of this device is also illustrated on Fig. 1. Dashed modules aren't included to the proposed device and represented just to illustrate its principle.

In other implementation at least one of said electronic modules contains embedded computing device on the microprocessor base.

In additional implementation one or several steps of proposed method are performed not by electronic unit, but using computer software program.

Particular embodiments of the invented method is described in details just for the illustrative purposes. It's clear, that in practice people experienced in MCG data analysis, and generally - in cardiology, could introduce some changes and modifications, for example, to use another weight coefficients in equation (1 ), to split cardio-cycle intervals onto another number of sub-intervals, to modify the sector scale, to increase or decrease the number of its grades, to change averaging method and numerical values ranges of the abnormality index, or to introduce another interpretation of the ischemia presence and severity degree. But we consider, that both said changes and modifications, and other ones, introduced without significant differences from the essence and claims of proposed invention, they fall under this patent.

Claims

1. Method for evaluation of myocardial ischemia based on current density maps,

method including execution of magnetocardiographic examination, current density vectors (CDV) maps reconstruction in the frontal plane, calculation of the CDV lengths for each map during ST-T interval and QRS complex of the cardio-cycle, calculation of the averaged diagnostic index,

characterized in that it includes selection of three angular sectors of the CDV directions - normal, medium and abnormal - separately for the ST-T interval and 4 sub-intervals of the QRS complex, which represent depolarization of the interventricular septum (1 ), anterior wall and apex of the left ventricle (2), left ventricle side wall (3), basal myocardial regions (4),

calculation of the sum length of all vectors for each map during said segments of the cardio-cycle LNORM (LPATH, LIM), directed into the normal (abnormal, medium) sector,

calculation of instantaneous abnormality indexes Al as a relative part of the vector with normal direction, according to the equation

Al = 100 x LNORM / (LNORM +LPATH + ¹/₂ x LIM) , calculation of the average abnormality index Alave for each of said intervals as an arithmetic mean of the instantaneous abnormality indexes Al,

making decision about ischemia absence or presence according to the rule - ischemia for each of said myocardium regions 1-4 is absent (insignificant, significant), if averaged abnormality index Alave fall within the range 70<Alave<100 (40<Alave<70, 0<Alave<40), and

2. Apparatus for evaluation of myocardial ischemia based on current density maps, device comprises of at least one electronic unit and performing one or several of actions, according to the claim 1 , characterized in that said electronic units include embedded computation device on the base of microprocessor.

3. Said apparatus according to the claim 1 or claim 2, characterized in that at least one electronic unit is replaced by computer program, i.e. software, and is done with help of computer.