Characteristics of Circadian Blood Pressure Profile in Patients With Acute Coronary Syndrome and Their Association With Thyroid Function

Abstract

The paper presents the results of a study of circadian arterial blood pressure (ABP) profile in patients with Acute Coronary Syndrome (ACS) and their association with thyroid-stimulating hormone (TSH) levels.
 Aim. To conduct a comparative analysis of circadian BP monitoring (CBPM) indicators in patients with ACS and their association with the TSH level.
 Materials and Methods. The study includes 125 patients with ACS aged 36 to 81 (mean age - 60.98± 0.81 years old). The patients were divided into two groups according to thyroid function. Group one (I) included 51 individuals (40.8%) - hypothyroid patients (TSH level>4mIU/ml), mean age - 62.51±1.18 years old; Group II included 74 individuals (59.2%) - euthyroid patients (TSH level 0.4-4mIU/ml), mean age - 59.93±1.08 years old. The serum-free thyroxine (FT4) levels were within the normal range in both groups. In the general group, the proportion of individuals with unstable angina (UA) was 28.8%, and with myocardial infarction (MI) - 71.2%. In particular, in Group I, the proportion of individuals with UA was 23.53%, and with MI - 76.47%; in Group II, the proportion of individuals with UA was 32.43%, and with MI - 67.57%, p>0,05 between Groups I and II. The circadian BP monitoring was carried out using the Biomed ВАТ41-2 device after stabilization of the patient's condition (on the second day of hospital admission). The following indicators have been determined: systolic BP (SBP) - daytime, nighttime, and average daily (24 hours) (SBPd, SBPn, and SBPav); diastolic BP (DBPd, DBPn, and DBPav); pulse BP (PBPd, PBPn, and PBPav); time index (TI) for SBPd, SBPn, and SBPav (SBPd TI, SBPn TI, and SBPav TI) and DBP (DBPd TI, DBPn TI, and DBPav TI); variability of SBPd, SBPn, and SBPav (SBPd var, SBPn var, and SBPav var) and DBP (DBPd var, DBPn var, and DBPav var); average daily index for SBP (SBP AvDI) and DBP (DBP AvDI); average daily heart rate (HRav). To study thyroid function in patients enrolled, TSH and FT4 levels were determined by chemiluminescent immunoassay method on the ARCHITECT iSystem analyzer using reagent kits for the quantitative determination of TSH (ARCHITECT TSH) and FT4 (ARCHITECT Free T4).
 Results and Discussion. The comparison of the CBPM results in both groups of patients with ACS shows significantly higher mean nighttime (SBPn and DBPn) levels in Group I patients compared to Group II patients: SBPn - by 6.27% (125.44±2.98 mm Hg (I) versus 117.58±2.26 (II), p<0,05), DBPn - by 6.15% (73.65±1.91 mm Hg (I) versus 69.12±1.62 (II), p<0,05), in the absence of a significant between-group difference between the mean levels of respective daytime and average daily indicators. Mean DBPn TI value also turned out to be significantly higher in Group I patients compared to Group II patients - by 33.69% (42.47±4.60% (I) versus 28.16±3.60% (II), p<0.01). Significant difference was detected between mean SBP AvDI and DBP AvDI indicators in hypothyroid patients (I) versus respective indicators in euthyroid patients (II): SBP AvDI (I) 2.52±1.25% versus SBP AvDI (II) 5.99±0.98, p<0.05; and DBP AvDI (I) 4.69±1.38% versus DBP AvDI (II) 8.88±1.32, p<0.05.
 Conclusions. 1. Mean nighttime BP indicator (SBPn, DBPn, and DBPn TI) levels were significantly higher in the Group of hypothyroid patients with ACS, compared to euthyroid patients. In addition, the proportion of patients whose mean nighttime SBP and DBP levels exceeded the permissible values (SBPn<120, DBPn<70 mm Hg) was significantly higher in the Group of hypothyroid patients (I) compared to the Group of euthyroid patients (II). 2. Every third hypothyroid patient (I) (SBP AvDI: 37.25% and DBP AvDI: 31.37%) had a night-peaker circadian BP profile, characterized by nighttime BP increase instead of reduction, which suggests an extremely unfavorable prognosis. The findings may signal an additional adverse effect of thyroid dysfunction on arterial tone and, accordingly, BP regulation, which brings about a high risk of complications of ACS.