NON-ISCHEMIC PHENOTYPES OF PATIENTS WITH ACUTE CHEST PAIN ON EXERCISING STRESS ECHOCARDIOGRAPHY
Authors:   Research Institute of Cardiology, Tomsk National Research Medical Center, Tomsk Russian Federation, Abramenko E. E. 
Published: October 2023

INTRODUCTION Acute chest pain is one of the most common caus­es for emergency medical care seeking. In some cases, it is considered as a manifestation of acute coronary syndrome (ACS). However, in patients with normal cardiac troponin (cTn) levels and a normal or non­diagnostic electrocardiogram (ECG) (non-ST eleva­tion ACS (NSTE-ACS) low-risk patients), the inci­dence of stenotic coronary atherosclerosis is not high. Stress echocardiography in this category of patients is indicated for ischemia visualization. Analysis of heart rhythm, ECG changes, systemic and intra­cardiac hemodynamics, in addition to assessing lo­cal contractility, allows us to identify other patholog­ical responses to stress. It is already known that their comprehensive assessment has predictive potential for long-term adverse events in patients with chron­ic coronary syndrome. THE AIM To identify non-ischemic phenotypes in low-risk patients with non-ST elevation acute coronary syn­drome. MATERIAL AND METHODS A single-center, prospective, continuous study included 70 patients aged 54 (45; 63) years (60% men) hospitalized in the department of the region­al vascular center in 2022—2023 with acute chest pain, normal or non-diagnostic ECG, normal cTn level, low (< 3 %) GRACE risk and no restrictions for exercise stress echocardiography. The patients had not previously verified coronary heart disease (which was an inclusion criterion) and had no wall motion abnormality at rest. Stress echocardiography on a horizontal bicycle ergometer was performed in the first 2 (0; 3) days of the hospital period. The tests were carried out in the absence of rhythm­slowing therapy. The results of tests completed ear­ly for subjective reasons (muscle fatigue, failure) were not included in further analysis. To determine patient phenotypes based on stress echocardiogra­phy data, pathological responses to stress in the form of dichotomous variables were used to perform clus­ter analysis. The final group consisted of 50 of a non­ischemic phenotype — those who did not belong to the cluster, which was characterized by the high­est frequencies of wall motion abnormality, ST seg­ment depression > 1 mm, and angina. To determine the potential significance of the identified pheno­types, the cardiac performance reserve (P/m) was ad­ditionally determined as the difference in P/m val­ues, calculated using the formula 0,222 - CO - APBmean LVM where CO — cardiac output; APBmean — mean arterial blood pressure; LVM — left ventricular mass), at peak load and at rest. RESULTS Four patient phenotypes were identified that dif­fered statistically significantly (p < 0.05) in terms of exercise tolerance, volumetric contractile reserve and heart rate reserve. Type 1 (n = 17) was character­ized by a high frequency of combined decreases in all 3 indicators; type 2 (n = 11) — by the decreased ex­ercise tolerance and heart rate reserve, normal con­tractile reserve; type 3 (n = 11) — by normal exercise tolerance and heart rate reserve, but decreased con­tractile reserve; type 4 (n = 11) — by normal exer­cise tolerance, contractile reserve and heart rate re­serve. The decrease in contractile reserve (types 1 and 3) was consistent with a statistically significant lower increase in left ventricular ejection fraction at peak exercise (5 (2; 7) vs. 12 (8; 13), respective­ly; p < 0.001) and P/m reserve (1.0 (0.6; 1.4) versus 1.3 (1.1; 1.6), respectively; p = 0.010). Patients with decreased contractile reserve were statistically signif­ icantly older (60 (48; 68) vs. 47 (43; 54) years, re­spectively; p = 0.003). Type 4 included predominant­ly men (91 %). For type 2, no statistically significant differences in the clinical and demographic data of pa­tients were identified. CONCLUSION In the structure of patients with low-risk pa­tients with NSTE-ACS, the phenotypes are identi­fied that are determined by a decrease in exercise tol­erance, contractile deficiency and chronotropic re­serve. Phenotypes are characterized by different levels of P/m reserve and may differ in the frequency of ad­verse events in the long-term period, and a decrease in contractile and heart rate reserve can be considered as potential targets for personalized therapy, however, in the diagnostic algorithm for ACS this remains a top­ic for further research.