**7. Clinical approbation of metrics of analysis of magnetocardiographic data on the basis of two-dimensional visualization of the solution of the inverse problem of magnetostatics. Multicenter studies**

The purpose of using any diagnostic parameter is to formulate a clinically significant diagnostic conclusion, i.e.:

a. decision on the presence or absence of a pathological process;

b. in the case of a process—determining the severity.

The set of features has higher diagnostic accuracy than a single feature. Thus, there is a problem with forming from a set of parameters of a single complex indicator, which synthesizes various aspects of the information contained in each individual indicator. Such an indicator can be created on the basis of the method of linear discriminant analysis (LDA). As a result, a discriminant function is automatically built. If the value of the function is greater than the threshold, the results of the MCG test are positive, if less—negative.

Another, empirical-statistical approach, which is used to form a comprehensive index, is calculated on the basis of scores. When using this approach, the values of all quantitative indicators are a priori divided into ranges. When the value of an individual indicator falls into the appropriate range, it is given a certain number of points.

Then the number of points of all indicators is summed. If the sum of points exceeds a certain threshold, the MCG test is considered positive, if on the contrary—negative. If the test is positive, the number of points determines the severity of the pathology on the principle—the higher the score, the more pronounced the pathology. Such scores are widely used in electrocardiography (Sylvester score, Freuleher score, CIIS and others), as well as to assess the results of the test with dosed exercise (Duke's index). We have created an integrated scoring criterion of the additive type for the diagnosis of myocardial ischemia using MCG. The value of this criterion was recently investigated by us in two multicenter studies involving foreign colleagues. A two-center study was conducted at the National Military Medical Clinical Center and at the Catholic Clinical Philippusstift (Essen, Germany) [12]. We examined 79 patients with complaints of chest pain and normal or non-informative results of ECG and echocardiography at rest, i.e., in difficult-to-diagnose cases. All patients underwent coronary ventriculography. According to the results of coronary angiography, patients were divided into subgroups with stenosis> 70% in at least one of the main coronary arteries (subgroup 1a) and a subgroup of persons without hemodynamically significant stenosis (subgroup 1b). Control group 2 consisted of 30 healthy volunteers close in age. **Table 1** shows the indicators of diagnostic value of the complex MCG index to detect significant stenosis of the coronary arteries in difficult-to-diagnose cases.

The goal of any diagnostic test is to reduce the uncertainty level and to increase the confidence of the investigator in valuable decision-making. The present study investigates a group of patients for whom this decision is performed on the basis of coronary angiography. The pretest probability of hemodynamically significant coronary artery stenosis in patients analyzed was about 50%; therefore, the degree of uncertainty is the highest in this case. Post-MCG probability to use analogous to post-ECG probability that a hemodynamically significant stenosis is absent is 85% in the case of negative result of MCG-study. In the case of a positive MCG result, the probability of haemodynamically significant stenosis is 93%.

Thus, the results of our MCG-study reduce uncertainty in decision-making. Coronary angiography should be considered for patients with positive MCG-results. In the case of negative MCG-results, the invasive procedure could be avoided.

An even larger multi-center study was conducted in three leading clinics in Beijing under the guidance of specialists from the main hospital of the Chinese Navy. A total of 133 people were examined (mean age 59 3.1 years). All surveyed individuals were divided into three groups. The first group (61 people) consisted of patients with severe myocardial ischemia who met the criteria for revascularization: the degree of coronary artery stenosis was ≥80% or was between 50% and 80%, with a margin of coronary blood flow ≤0.8.


#### **Table 1.** *Diagnostic value of complex MCG index.*

#### *Unshielded Magnetocardiography in Clinical Practice: Detection of Myocardial Damage… DOI: http://dx.doi.org/10.5772/intechopen.104924*

The second group (13 people)—patients whose myocardial ischemia is confirmed by the "gold standard"—invasive coronary angiography but has not yet met the criteria for revascularization. The third group (59 people) is the control group. The percentage of coincidence of ICG results and coronary angiography in each group was as follows: for severe coronary heart disease—85.45%, for mild coronary heart disease —77.78%, in the control group—87.10%.

Achieved a total sensitivity of 93.75%, a specificity of 87.10%, PPS was 88.24%, and NPV 93.10%.

Thus, magnetocardiographic examination is a reliable method of diagnosing chronic coronary heart disease, including in difficult-to-diagnose cases.

Analyzing the possibilities of using different methods for myocardial ischemia detection, it is necessary to take into account their position on the steps of the "ischemic cascade". For example, systolic myocardial dysfunction, which is detected by echocardiography under load, in the ischemic cascade manifests itself later than the heterogeneity of blood flow. Manifestation of myocardial ischemia in the form of changes in the ST segment on the ECG is manifested even later and therefore the possibilities of the ECG in the detection of myocardial ischemia, even under load, are limited. At the top of the ischemic cascade is the anginal syndrome. What is the place of the MCG in this context? In our opinion, in some cases, the ICG at rest is outside the ischemic cascade, recording the "history" of episodes of past myocardial ischemia that have occurred before. The rather high sensitivity of the MCG is due to the fundamental physical advantages of the method. The rather high values of diagnostic accuracy of MCG received in numerous research are reached at rest. The causes of electrophysiological changes at rest in patients with coronary heart disease are diverse. First of all, these are changes in repolarization as a result of apoptosis. Also, previous episodes of myocardial ischemia can lead to cell necrosis in limited areas of the myocardium, causing impaired electrogenesis. Several articles have shown that transient ischemia contributes to an increase in interstitial endocardial fibrosis in patients with a history of MI. It is also suggested that in coronary heart disease already at rest there is a significant alternative to the level of myocardial blood supply. This in turn can also lead to subtle electrophysiological changes that are already taking place at rest.

It is known that myocardial ischemia is accompanied by activation of free radical processes, and it is obvious that this should be manifested by disturbances in the functioning of ion channels, changes in TPD, and excitability of conductive cells and cardiomyocytes. It can be assumed that changes in MCG parameters in patients with coronary heart disease at rest are due to changes in electrophysiological characteristics such as resistance of membranes and intercellular connections, and the rate of conduction.

That is, we can conclude that due to its high sensitivity, the MCG at rest reveals the effects of episodes of transient ischemia (apoptosis, interstitial fibrosis, inhomogeneity of perfusion, and metabolism) [13].

Sufficiently high sensitivity of MCG is caused by fundamental physical advantages of the method. The result of these physical advantages is that the MCG signal more completely and accurately reflects electrical processes of the heart. MCG is much more sensitive than ECG to myocardial ischemia, thus MCG signal is changed even in cases when the shape of the ECG signal does not differ from normal. This advantage of MCG most clearly could be demonstrated by the shift of ST-segment (**Figure 14**).

Figure demonstrates standard ECG and MCG, registered on the same day almost simultaneously. There are no ST-segment shifts registered in any of the ECG leads. On the contrary, at points 14 and 20, there is a depression of ST-segment, and at points 4,5, and 6—an elevation of it.

**Figure 14.** *ECG in 12 leads (A) and MCG (B) of the patient with 2 vessels CAD (high-grade RCA and LCX stenosis).*

It is important to understand that the presence of depression and elevation simultaneously within the 36-point MCG grid has the same electrophysiological basis as reciprocal changes in ST-T interval of ECG leads. In the case above, there is an ST depression in the right-central quadrant of grid (points 14,20) and elevation in leftupper quadrant of MCG grid. In our opinion, this configuration may reflect ischemia of the inferior wall of the left ventricle. Naturally, the identified dislocations of the ST

#### *Unshielded Magnetocardiography in Clinical Practice: Detection of Myocardial Damage… DOI: http://dx.doi.org/10.5772/intechopen.104924*

segment will clearly appear on the CDV maps throughout this segment. We have developed the atlas of representative current density maps within ventricular repolarisation we have seen in patients with different variants of chronic CAD. We have selected "difficult-to-diagnose" patients with normal or uncertain, non-specific results of the routine tests. In that way, we would like we wanted to highlight the role of MCG in clinical routine—to feel out the gap between routine but non-sensitive diagnostic methods and much more expensive advanced non-invasive and invasive techniques [14].
