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Electrical properties of the myocardium in patients with arterial hypertension combined with subclinical hypothyroidism

Late atrial and ventricular potentials are non-invasive electrocardiographic criteria for presence of high arrhythmic readiness and risk of life-threatening arrhythmias. The electrical properties of the myocardium in patients with stage II arterial hypertension (AH) combined with subclinical hypothyroidism have not been studied previously. Aim. To study the changes of electrical properties of the atrial and ventricular myocardium in patients with AH combined with subclinical hypothyroidism. Materials and methods. The criteria for inclusion in the study were the presence of stage II AH without thyroid gland pathology and combined with subclinical hypothyroidism (SH) (for patients of the main group). Depending on the level of thyroid-stimulating hormone (TSH), the AH patients were divided into 2 groups – with normal (0.4–4.0 mU/ml) and moderately elevated level of TSH (4.0–15.6 mU/l, with normal levels of thyroid hormones). The group of patients with AH without SH included 92 patients (women – 81.52 % (75), men – 18.48 % (17)); the group of patients with AH with concomitant SH included 30 patients (women – 86.7% (26), men – 13.3 % (4)). All patients underwent 24-h BP monitoring and ECG (combined ECG and BP monitor “Kardiotechnica-04-AD-3”,St. Petersburg,Russia). A 40 Hz cutoff filter was used recording in the X, Y, Z orthogonal leads. Data were processed with the help of a program Statistica 6.0. Data were presented as the median and inter-quartile range of Me (25 %; 75 %). Results. In AH patients without concomitant subclinical hypothyroidism, unlike in relatively healthy patients, late atrial potential predominance was seen (63 % vs. 84 %; P = 0.0419) with a 16.4 times (P = 0.018) increase in the number of premature atrial contractions. Also, in patients with AH without concomitant subclinical hypothyroidism late ventricular potentials (LVPs) occurred 5.7 times more often (6 % vs. 34 %, P = 0.0302) and were associated with a significant (P = 0.004) increase in the number of premature ventricular contractions per day in this category of patients. In SH patients with a concomitant subclinical hypothyroidism, unlike in relatively healthy individuals, atrial ectopic activity was significantly more predominant (LAP was found in 87 %; versus 63 %, P = 0.0498), which was accompanied by a logical 27.2 times (P = 0.038) increase in the number of premature atrial contractions and ventricular ectopic activity. Changes in the electrical properties of the ventricles were accompanied by an increase in the percentage of detected LVPs (77 % versus 6 %, P = 0.0001), which was associated with a significant (P = 0.001) increase in the number of premature ventricular contractions per day in this category of patients (441.53 ± 1414.97 versus 0.00 ±0.00 inalmost healthy subjects, P = 0.001). AH patients with and without concomitant SH did not differ from each other in terms of indexes characterizing late atrial potentials. There was also no statistically significant difference in the number of premature atrial contractions (P = 0.527), paired premature atrial contractions (P = 0.449), salvos of atrial premature contractions (P = 0.314). However, in AH patients with concomitant SH there was a significant increase in the ectopic activity of the ventricles – LVPs were found in 77 % vs. 33 % in individuals without SH (P = 0.0001), changes in the electrical properties of ventricles in AH patients with concomitant SH were also associated with an increase in the number of premature ventricular contractions by 6.69 times (from 42.56 ± 36.96 to 441.53 ± 1414.97, P = 0.026) compared with the same index in patients with AH without concomitant SH, indicating the negative effect of SH on the electrical properties of the ventricles. Conclusions. In patients with stage II arterial hypertension in comparison to relatively healthy subjects, indicators that characterize the late potentials of the atria and ventricles are significantly changed, which is accompanied by an increase in the number of supraventricular and ventricular rhythm disorders. Subclinical hypothyroidism causes an additional pro-arrhythmic effect on the ventricular myocardium in arterial hypertension.