2.1 Patient group
The study was conducted on May 1st 2021, using the Kyiv Heart Institute of the Ministry of Healthcare of Ukraine facilities. The study was conducted in accordance with the guidelines of the Declaration of Helsinki and approved by the Ethics Committee of Shupik National Healthcare University of Ukraine, (protocol code №5 and date of approval 04/04/2021).
Written informed consent was obtained from all subjects involved in the study.
23 patients were examined with a mean age of 58.8 ± 11.2 years. All the patients underwent coronary artery stenting. Fifteen patients underwent PCI as a part of acute Q-infarction treatment, 8 as a treatment for chronic CAD, and stable angina CCS class II-III. All the patients received intraoperative analgesia. The mean duration of the intervention was 40.2 ± 21.1 minutes, while the number of stents was 1.8 ± 0.9.
The exclusion criteria were age > 75 years, liver dysfunction, progressive renal failure, acute and chronic infection, cardiac insufficiency, anemia, inflammation, peripheral vascular disease, pregnancy, suspected systemic thrombotic diseases, diabetes, cancer, other heart diseases, thyroid dysfunction, and autoimmune diseases.
Preoperative clinical and laboratory parameters as well as anthropometric values are presented in Table 1.
Table 1. Demographics and selected clinical features of the patients who have undergone coronary stenting.
Parameter
|
Value
|
Age (years)
|
63.4±5.3
|
Sex (m/f)
|
16/7
|
BMI (kg/m²)
|
28.4±5.2
|
AH (n (%))
|
20 (86.9%)
|
Hb (g/L)
|
136.3±17.1
|
Ht
|
41.2±4.4
|
Тr (*10^9/L)
|
231.3±38.2
|
PTI
|
93.4±10.5
|
Urea (mmol/L)
|
6.4±2.2
|
Cr (μmol/L)
|
94.7±22.5
|
Ischemic heart disease
|
23 (100%)
|
Heart failure
|
21 (91.3%)
|
Pulmonary hypertension
|
7 (30.4%)
|
Pulmonary disease
|
9 (39.1%)
|
Vessel disease
|
12 (52.2%)
|
Abbreviations: BMI, body mass index; AH, arterial hypertension; Hb, hemoglobin; Ht, hematocrit; Tr, platelet count; PTI, prothrombin index; urea, urea; Cr, creatinine.
2.2 ECG and heart rate variability scaling method
After the surgical intervention, all patients underwent a modified computer ECG with subsequent analysis using an innovative scaling method.
Recently, an innovative ECG and heart rate variability scaling method was developed by the Institute of Cybernetics of the National Academy of Sciences of Ukraine. The original software was developed using this method.
The program was developed on the basis of a hierarchical principle. It consists of the four levels listed below in ascending order:
1) The lowest level is comprised of multiple separate parameters describing a) various aspects of heart rate variability, b) amplitude and time parameters, as well as the shape of ECG waves, and c) the presence of main rate, rhythm, and sequence of myocardial contraction abnormalities (in other words, arrhythmias).
2) The second level is comprised of groups of related parameters with close to each other physiological sense:
3) The third level is represented by three integral sections, each of which represents a different aspect of cardiovascular system functioning that can be assessed through ECG: the sections of regulation assessment, state of the myocardium, and arrhythmia diagnostics.
4) The fourth, highest level — the collective integral criteria of the cardiovascular system’s functional status.
Multiple quantitative parameters registered by the program and used for analysis had different units of measurement (s, mV, etc.) or none at all. Naturally, there is a problem with converting data to compact and suitable analysis formats that would also be convenient for making conclusions and decisions, that is, switching to, for example, dimensionless parameters. To solve this problem, a functional scaling method was used. The interval scale from 0 to 100 notional points was divided into four equal intervals: 0–25, 26–50, 51–75, 76–100 is used. These intervals match four status grades: normal, mild, moderate, and severe abnormalities. The median value of the normal range of each parameter in absolute units (e.g., in seconds) was taken as 100 points on the interval scale of functional status used. Thus, for each parameter, four intervals of absolute values were determined, which matched four equally wide (25 points each) intervals on the scale we used. In the next step, linear relations between discrete parameter values in absolute units and the corresponding number of points for this discrete value are established within each interval. Consequently, a linear correspondence scale between the absolute parameter values and the number of points on the functional status scale was obtained for each parameter. With the transfer to higher analysis levels, generalization and aggregation of information obtained at the previous level occurs. The composite index, present in this software, was formed based on the evaluation of the conventional and original parameters of heart rate variability, as well as the characteristics of ECG waves and complexes.
The suggested scaling method was invented precisely for solving practical problems and already has widespread applications [12–14] in solving various tasks in different areas of clinical medicine, sports medicine, and large-scale population studies, including the analysis of large ECG data arrays of the Oxford Population Health study.
It is worth mentioning that the suggested scaling method includes both a series of adapted conventional algorithms for physician-led ECG assessment (cardiac rhythm abnormalities and morphological analysis of ECG figures) and ECG analysis algorithms that have proven prognostic value for predicting serious cardiovascular events in large international studies. Finally, an analysis of psychoemotional state was performed through HRV analysis using a modified R. McCraty algorithm based on the neurovisceral integration model [15].
2.3 Registration and analysis of ECG and heart rate variability
In this study, paired measurements were used — 3 minute-long ECG registration both prior to and several hours after the surgery. The examination was conducted using a fully certified “Cardio + P” innovative device, developed by V.M. Glushkov Institute of Cybernetics of the National Academy of Sciences and manufactured by “Metekol” LLC. A total of 23 pairs of electrocardiograms were analyzed. 240 primary and calculated ECG parameters were analyzed for each electrocardiogram, among which 11 were composite parameters (from 0 to 100 points).
Statistical processing of the results was conducted using the STATISTICA 10 software package. Quantitative values are presented as mean ± standard deviation (in the case of normal distribution). Anomaly detection in the data (presence of outliers) was conducted using the variance range criteria and Kolmogorov-Smirnov test. The Shapiro-Wilk's W test, recommended for small samples, was used to test the hypothesis about the type of distribution. Homogeneous groups were identified among patients using cluster analysis (K-means clustering algorithm). Repeated measures analysis of variance (repeated measures ANOVA) was used to analyze the impact of the stenting factor. The effect of this factor was determined in this study using partial eta squared (ɳ2). The statistical significance of mean value change in overall composite parameters before and after stenting was tested using a t-test for two dependent samples (in case of normal distribution), and in all other cases using a non-parametric Wilcoxon test. The P-value significance level was set to 0.05, in compliance with the conventional medico-biological study guidelines.