CORRELATION OF RESULTS OF SPECT EXAMINATION
AND LINEAR TRANSFORMATION METHOD

R. Krzyminiewski , G. Panek , R. Stępień¹, R. Junik², U. Schmidt
Institute of Physics, A.Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland
¹Ministry of Internal Affairs Hospital, Poznań, Poland.
²Endocrinology Clinic, Karol Marcinkowski University of Medical Sciences, Poznań, Poland

Abstract: The paper presents the main principles for obtaining enhanced resolution in  standard ECG records by linear transformation method, determining of activities of particular segments of the cardiac muscle and high-resolution vectorcardiogram constructing. Standardized electric activities of the ventricles and septum in healthy people are given. Electric activities of particular fragments of the cardiac muscle were measured by the linear transformation method for a group of healthy subjects and for people with clinically recognised infarct of the inferior wall, and for patients subjected to single photon emission computed tomography (SPECT) examination.

INTRODUCTION

Perfusion scintiscanning by single photon emission computed tomography (SPECT) brings the information on the blood supply of the cardiac muscle, while radioisotopic angiocardiography allows an assessment of the muscle functioning. The perfusion scintiscanning has become the method of key importance when choosing the way of treatment of angina pectoris sufferers: pharmacological or invasive. It has also proven valuable for determination of the strength of the cardiac muscle and monitoring of patients after revascularisation of the cardiac muscle. The fragments supplied by a narrowed artery and showing ischaemia on exercise are characterised by a decreased capture of the marker. The study on the sensitivity and specificity of SPECT applied to detection of angina pectoris relative to the golden standard of coronary angiography proved very high and equal 96% and 83%, respectively. Detection of large disturbances in perfusion of the cardiac muscle testifies to a high risk of heart infarct (sudden death) and the significance of this information is higher than that inferred from coronarography and exercise ECG.

In view of the above, much effort has been given to devise new diagnostic methods which would ensure a non-invasive and cheap way of inferring about the status of the cardiac muscle. One of such methods is linear transformation method.

METHODS

Literature provides descriptions of many computer methods for enhancement of resolution of various signals which thus give more information on the object of the study. Such methods are most often based on Fourier transformation, convolution and deconvolution techniques, filtration, etc. [1]. One of such  programs, based on the method of linear transformation was written by us [2, 3, 4]. This program was applied for analysis of electrocardiographic signals. The results were curves similar to standard ECG records, however, of much increased resolution of the QRS complex [5, 6], Fig. 1. In order to facilitate interpretation of these high-resolution ECG signals we applied the well known method of vectorcardiography [7]. The high-resolution vectorcardiogram combines the records from particular electrodes, each of computer enhanced resolution [4, 8], Fig. 1. The vectorcardiogram is constructed on the basis of the recordings of 12 standard ECG electrodes, figure 1 presents an exemplary recording of only one electrode I. The horizontal vector loops are shown in three mutually perpendicular planes: the transverse, sagittal and frontal planes. The curve corresponds to the motion of the end of the transient vector of depolarization of the intraventricular septum as well as the left and right ventricle during a single evolution of the cardiac muscle. The excited region enlarges from the middle part of the septum to the right and down reaches the apex of the cardiac muscle and then is directed along free walls towards the base of the cardiac muscle. Within a free muscle wall the excited region moves from the endocardium to the epicardium. High-resolution vectorcardiogram  allows viewing of the region of the depolarization wave propagation during the cardiac muscle evolution, so provides an opportunity to detect even relatively small changes in electric activity of particular segments of the cardiac muscle caused by ischaemia, hypertrophy and/or administered drugs.

Figure 1: A standard vectorcardiogram a) constructed on the basis of the normal ECG recorded at rest (example of the electrode I) and a high-resolution vectorcardiogram constructed on the basis of a) with the resolution of the QRS complex enhanced by the method of linear transformation.

RESULTS

Within the research projects realised for a few years at the Institute of Physics AMU in cooperation with a few university hospitals of the Medical University in Poznań, about 3000 patients suffering from coronary artery disease (angina pectoris, previous myocardial infarction) were examined.

This paper presents research results concerning three separate groups of people :

1)       A group of 100 patients with a cardiac muscle infarct diagnosis, confirmed on the basis of  clinical examination (biochemical tests, ECG recordings, echocardiography, etc.).

2)       A group of 38 patients subjected to single photon emission computed tomography (SPECT) examination.

3)       A group of 49 healthy people

ECG records for each patient were made by Medea-cardiograph model 5012 made by MEDEA-GLIWICE.  The apparatus records averaged P-QRS-T complexes, its frequency band conforms to the AHA standard for analog filtration [0.05 - 100 Hz], its sampling frequency is 500 Hz. The ECG signals were subjected to the computer program processing in order to enhance their resolution. The amplitude of high-resolution signals was normalised so that a single, simulated, standarized peak of a Gaussian curve of 20 ms in width and 1 mV amplitude had the same final amplitude of 1 mV after processing. In the next step a high-resolution vectorcardiogram was procured, according to standard procedures from the ECG records of enhanced resolution [7].

Quantitative analysis of activities of particular regions of the cardiac muscle was made. In order to perform this analysis the left and right ventricle and septum were divided into particular walls and segments to which specific directions in the orthogonal Frank lead system were ascribed.

The activity of a given region of the cardiac muscle, e.g. inferior wall, was calculated within the bulk angle of 60⁰ about the directional vector of this region (directional cosines of the inferior layer: 0, 1, 0), according to the following equation:

Akty =  [R(t)] ² _* cos [R(t), F]                         (1)

where:

Akty- total electric activity of a given segment during a single cardiac muscle evolution,

cos[R(t), F] - cosine of the angle made by the direction of the transient depolarisation vector and the directional vector of a given cardiac muscle segment,

R(t)- transient depolarisation vector measured in 1ms,

F- directional vector of a given cardiac muscle segment.

The activity defined as above is measured in mV² [9].

TABLE 1
Linear transformation results - particular wall of the cardiac muscle infract

Linear transformation results Risk factor	Infarct
	Yes	No
Activity of particular wall of the heart drop below <50% of normal activity	100	2
Normal activity of particular wall of the heart	0	47

Sensitivity = 100%, Specificity = 96%, PPV=98%, NPV=100%

TABLE 2
Linear transformation results and SPECT examination results

Linear transformation results and SPECT examination results	SPECT examination
	Low perfusion of particular wall	Normal
Activity of particular wall of the heart drop below <50% of normal activity	35	5
Normal activity of particular wall of the heart	0	47

Sensitivity = 100%, Specificity = 90%, PPV = 88%, NPV = 100%

Electric activities of particular fragments of the cardiac muscle were measured by the linear transformation method for a group of healthy subjects and for the following groups of patients:

a) people with clinically recognised infarct of the particular wall of the cardiac muscle, table 1,

b) people subjected to SPECT examination, table 2

The specificity and sensitivity of the linear transformation method as well as the positive predictive values (PPV) and negative predictive values (NPV), were determined.

The study of people with clinically recognised infarct of the particular fragment of the cardiac muscle revealed a considerable decrease in electric activity of this wall, on the average to about 50% of the activity established for healthy subjects (Table 1). Statistical analysis of the results obtained for a group of 149 persons proved a high sensitivity and specificity of the method. 

The results obtained for people subjected to SPECT show a good correlation between the low perfusion of particular fragment of the heart and the decrease in electric activity of particular fragments of the cardiac muscle observed by the linear transformation method (Table 2)[9]. A similarly good correlation was obtained between the results of coronarography examination and the decrease in electric activity of particular fragments of the cardiac muscle observed by the linear transformation method [10].

It is expected that soon much more reliable diagnostic criteria of the linear transformation method would be developed, taking into account not only the absolute but also relative decrease in the electric activity of given fragments of the cardiac muscle, the latter relative to the total activity of the cardiac muscle corresponding to the QRS complex.

CONCLUSION

Preliminary analysis of the sensitivity and specificity of high-resolution vectorcardiogram in IHD diagnostics has proved the method much promising in the diagnostics of ischaemic disease. It also provides the information on electric activity of particular segments of the cardiac muscle so it should allow diagnosis in patients whose ECG is difficult for interpretation (bundle branch block), verify the positive result of exercise ECG test in patients with low initial probability of coronary disease or the negative result of ECG test in patients with choky pains and a high probability of coronary disease.

REFERENCES

[1]. J. Max, Methodes et techniques  de  traitement  du  signal  et  applications aux mesures physiques. Paris: Masson, 1981

[2]. A. Koper, R. Krzyminiewski, „Analysis of  resonance  excitations  by linear transformation technique theory”. Acta Magnetica II 3, 1985.

[3]. J. Masiakowski, R. Krzyminiewski, J. Pietrzak, „EPR study of free  radicals structure and conformation in pyridoxine hydrochloride single crystal”, Chem.Phys.Lett,, 116, 387, 1985

[4]. N.M. Atherton, W.A. Crossland,” A single-crystal ENDOR study of g-irradiated pyridoxine hydrochloride”,  J.Chem.Soc.Faraday Trans. I 83, 37,1987

[5].  R. Krzyminiewski,  Proc.XV  Conf.Radio  and  Microwave Spectroscopy RAMIS'93, 36, 1993

[6]. R. Krzyminiewski,”Computer enhancement of complex spectroscopic spectra resolution” Mol.Phys.Reports; 6, 174, 1994

[7]. Ch.L. Levkov,” Orthogonal electrocardiogram derived from the limb and chest electrodes of the conventional 12-lead system”, Medical & Biological Engineering & Computing, 25, 155, 1987

[8]. A. Hedberg, A. Ehrenberg,”Resolution enhancement of ESR spectra  from irradiated single  crystals  of  glycine”,  J. Chem.Phys., 48, 4822, 1968

[9]. R. Krzyminiewski, G. Panek, R. Stępień,”High resolution vectorcardiogram”, Journal of Medical Physics; 24, pp.181-185, 1999

[10] R. Krzyminiewski, G. Panek, R. Stępień, U. Schmidt, „Corelation of results of coronarographic examination and high-resolution vectorcardiography,” in Proceedings of 3^rd International Conference on Bioelectromagnetism, 2000, pp.121-122.