Cardiac autonomic function and vascular profile in subclinical hypothyroidism: Increased beat-to-beat QT variability

Abstract

Background:Patients with subclinical hypothyroidism (SH) may have higher incidence of coronary heart disease and autonomic dysfunction.Design of the Study:Prospective case control study.Aim and Objectives:To evaluate beat-to-beat QT variability and vascular stiffness in patients with SH compared to normal controls.Materials and Methods:We compared linear and nonlinear measures of cardiac repolarization liability using beat-to-beat QT intervals derived from the surface electrocardiogram during supine posture and vascular indices including pulse wave velocity and ankle-brachial index (ABI) during supine posture between female patients with SH and age- and sex-matched normal controls. Spectral analysis was done at very low frequency (LF) (0.003–0.04 Hz), Low frequency (LF) (0.04–0.15 Hz), and high frequency (HF) (0.15–0.4 Hz). The HF represents vagal regulation (parasympathetic) and LF represents both parasympathetic and sympathetic regulation.Results:We recruited 58 women with a mean age of 31.83 ± 8.9 years and 49 controls with mean age of 32.4 ± 9.9 years (P = NS). QT variability index (QTvi) was higher in cases compared to controls (P = 0.01). The ratio of LF/HF of R-R interval which is an index of sympathovagal tone was significantly more in cases compared to controls (P = 0.02). The difference in the left minus the right ABI was significant between cases and controls (P = 0.03).Conclusions:The cases had lower parasympathetic activity as compared to controls, and there was a predominance of sympathetic activity in cases. QTvi may be an important noninvasive tool in this group of patients to study the risk of cardiovascular mortality.

Non-invasive markers of cardiovascular risk in patients with subclinical hypothyroidism: A systematic review and meta-analysis of 27 case control studies

“… Author Year Country Participants (SCH/EU) Age (SCH/EU) Study design TSH cutoff value T4 measured? Measure outcomes NOS Score Ali Aydogdu 33 2017 Turkey 30/30 37.70 ± 13.54/40.96 ± 13.39 Case-control study ≥5.5 mIU/L + EAT thickness 7 Pramila Kalra 39 2016 Canada 58/49 31.83 ± 8.91/32.42 ± 9.98 Case-control study >4.5 mIU/L + PWV 5 Edip Unal 50 2017 Turkey 38/38 8.1 ± 3.6/8.9 ± 2.4 Case-control study >4.2 mIU/L + CIMT 8 Irmak Sayin 48 2016 Turkey 44/42 41.2 ± 15.9/42.1 ± 13.5 Case-control study >5.0 mIU/L + EAT thickness 8 Mustafa Altay 30 2017 Turkey 35/30 34.4 ± 10.3/32.5 ± 7.5 Case-control study — + CIMT 4 Yasemin Isik-Balci 38 2016 Turkey 53/31 9.25 ± 4.29/7.19 ± 5.15 Case-control study — + CIMT 4 Dilek Arpaci 31 2016 Turkey 41/35 34.07 ± 6.70/31.82 ± 5.57 Case-control study >5.4 mIU/L + EA...…”

Impact of subclinical hypothyroidism on frequency of premature ventricular contractions in elderly patients without structural heart disease

“…Cacciatori et al suggested that thyroid hormone deficiency was associated with an increased sympathetic influence on the autonomic cardiovascular system. Some studies demonstrated that SH increased the cardiovascular risk factors, including altered lipid profile, impaired cardiac contractility, decreased cardiac output, increased systemic vascular resistance and cardiac electrical abnormalities (16)(17)(18). Galetta et al showed that the patients with SH had a higher QTd and lower heart rate variability (HRV) measurements compared with the healthy control group, and that the QTd was positively associated with TSH value, with the measurements returning to normal after treatment (9).…”

O sistema nervoso autônomo no hipotireoidismo subclínico

“…O hipotireoidismo subclínico (HS), uma das disfunções tireoidianas existentes, é bioquimicamente definido pela concentração elevada do hormônio estimulador da tireoide associado a uma concentração normal de tiroxina livre, de acordo com o valor de referência populacional específico (KALRA et al, 2016).…”