PECULIARITIES OF HEART RHYTHM DISORDERS IN PATIENTS WITH MYOCARDIAL INFARCTION WITHOUT ELEVATION OF ST SEGMENT DEPENDING ON THE DEGREE OF CORONARY ARTERY LESIONS

The prevalence of myocardial infarction and its leading role in the structure of overall and cardiovascular mortality encourages the search for predictors of complicated course of disease and the search for optimal means to prevent adverse events. The aim of the study – to establish features of cardiac arrhythmias in patients with myocardial infarction without ST-segment elevation depending on the degree of coronary artery lesions. Materials and Methods. The study involved 156 patients with NSTEMI aged 38 to 80 years. All patients were examined according to the current treatment protocol for patients with acute coronary syndrome without ST segment elevation and daily Holter ECG monitoring was performed for 3-5 days after hospitalization. Results. It was found that the degree of coronary artery lesions is positively correlated with the likelihood of severe adverse ventricular arrhythmias and episodes of silent myocardial ischemia in the early period. Conclusions. By determining the total score of coronary artery disease, it is possible to stratify the adverse course of NSTEMI, in particular, the occurrence of fatal ventricular arrhythmias in the early period.


INTRODUCTION
Myocardial infarction (MI) is one of the leading causes of death and disability worldwide. In Ukraine, the frequency of registration of MI per capita is the highest in the European population, which puts this problem in the category of priority medical and social problems for our society [1].
In the last 20 years, there has been a trend of increasing incidence of myocardial infarction without ST-segment elevation (NSTEMI), which, according to some data, accounts for about half of all registered MI [2,3]. The main problem with NSTEMI is that the long-term prognosis of these patients remains unsatisfactory, and mortality one year after the disaster equals or even exceeds that of STEMI [4].
Of great scientific interest are studies that develop the concept of predicting the nature of coronary artery disease using clinical and various non-invasive instrumental parameters, which allows using simple and affordable research methods to stratify patients for invasive treatment [5]. In addition, the development of myocardial dysfunction on the background of acute ischemia leads to acute remodeling and potential electrical instability of the myocardium.
The aim of the study -to establish features of cardiac arrhythmias in patients with myocardial infarction without ST-segment elevation depending on the degree of coronary artery lesions.

MATERIALS AND METHODS
We conducted a comprehensive study of 156 patients with acute myocardial infarction without STsegment elevation (NSTEMI) aged 38 to 80 (mean 62.0 ± 0.71, median -62 and interquartile range -55 and 70) years, who are urgent demonstrations were hospitalized in the Municipal Non-Profit Enterprise "Vinnytsia Regional Clinical Medical and Diagnostic Center for Cardiovascular Pathology".
The criteria for including patients in the study were: 1. Verified NSTEMI, first diagnosed; 2. age up to 80 years; 3. the absence of contraindications to percutaneous coronary interventions and the use of the main groups of pharmacological agents included in the basic therapy of NSTEMI; 4. informed consent of the patient to participate in the study.
The criteria for exclusion from the study were: 1. STEMI, transferred in the past and recurrent acute myocardial infarction; 2. age of patients 80 years and older; 3. the presence of sinoatrial or atrioventricular block II-III degree, implanted or the need for implantation of an artificial pacemaker; 4. chronic heart failure NYHA-III, IV before the incident of acute myocardial infarction; 5. diseases of the respiratory system, kidneys and liver, which were accompanied by signs of pulmonary, renal and hepatic failure; anemic conditions with a hemoglobin level below 110 g / L; 6. the presence of rheumatic and congenital heart defects, idiopathic and inflammatory myocardial lesions; 7. malignancies, severe neuropsychiatric disorders, alcohol abuse; 8. the presence of contraindications to percutaneous coronary interventions and the use of the main groups of pharmacological agents included in the basic therapy NSTEMI; 9. reluctance and refusal of the patient to participate in the study.
All patients were examined according to the NSTEMI protocol [6] and daily Holter ECG monitoring was performed for 3-5 days after hospitalization.

RESULTS AND DISCUSSION
To assess the severity of damage to individual main arteries, we calculated the conditional score of coronary artery lesion (CA), where 0 points -the absence of any atherosclerotic plaques in the CA (intact artery), 1 point -the presence of atherosclerotic stenosis up to 50 %, 2 points -from 50 % to 90 % of the lumen of CA and 3 points -CA occlusion (atherosclerotic stenosis > 90 %) [7]. In addition, the total conditional CA lesion score was additionally calculated as the sum of the right coronary artery (RCA), left anterior descending artery (LAD), and left circumflex artery (LCx) lesions. According to the obtained data, it was observed that the mean conditional score of RCA was 0.74 ± 0.08, LAD -2.03 ± 0.10 and LCx -0.89 ± 0.09, respectively. The total conditional CA lesion score was 3.66 ± 0.17 [7].
It was observed that in the group of patients with NSTEMI and existing hemodynamically significant stenosis (HSS) CA, compared with the group without HSS CA, significantly longer total episodes of supraventricular tachycardia / atrial fibrillation (SVT / AF) were recorded during the day, against 50=90 0.03), an increase in the total number of paired / group ventricular extrasystoles (VE) (24 vs. 16, p=0.006) and the total duration of ventricular tachycardia (VT) episodes per day (103 vs. 51 s, p=0.02). In addition, with a tendency to increase the number of cases with registered episodes of silent myocardial ischemia (SMI) (19.4 % vs. 4.5 %, p=0.08) in the presence of HSS CA, compared with their absence, determined a significant increase the number of SMI episodes per day (4 vs. 2, p=0.04) and their total duration (28 vs. 10 min, p=0.01) and the decrease in heart rate (HR) in SMI episodes (114 vs. 125, p=0.03) ( Table 1).
The results of the following analysis, which assessed changes in the parameters of ECG monitoring by Holter depending on the value of the total score of the CA lesion (≤ and> 3 points) showed that in the group with milder (total score of CA ≤3 points), compared with more severe anatomical lesions CA (total score of CA> 3 points), there was a significant decrease in heart rate at night (58 vs. 64, p=0.02) with a higher circadian index (CI) ( In addition, in patients with more severe anatomical lesions of the CA observed a significant increase in the frequency of registration of episodes of SMI during the day (25.4 % vs. 12.4 %, p=0.04) and their total duration (18 vs. 9 min, p=0,03).
Thus, the results of the study showed that in patients with NSTEMI there is some association between the severity of anatomical lesions of the CA, as determined by CVG, and the increased incidence of various severe and prognostic ventricular arrhythmias detected by Holter ECG. Also, in the group with HSS CA, compared to its absence, there was a significant increase in the duration of asymptomatic episodes of SVT / AF per day (p=0.03).
We have established a connection between the degree of CA stenosis and the occurrence of ventricular tachyarrhythmias. Previous studies have been performed in various categories of patients to assess the prognostic impact of MI with or without ST-segment elevation in patients with ventricular tachyarrhythmias and sudden cardiac arrest on admission. In high-risk patients with ventricular tachyarrhythmias, non-MI had a higher mortality rate than MI, respectively, NSTEMI than STEMI, along with MI associated with VT ≥48 hours [8].