Heart Care Info - Heart Disease Prevention & Treatment

The influence of subclinical hyperthyroidism on blood pressure, heart rate variability and incidence of arrhythmia

GW Kamiński, K Makowski, D Michalkiewicz... - Thyroid, 2012 - Background: The impact of subclinical hyperthyroidism (s HT) on the cardiovascular system still needs to be elucidated. The aim of the study was to prospectively assess blood pressure, variability in heart rate, and the prevalence of arrhythmias in patients with s HT, ...

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Background: The impact of subclinical hyperthyroidism (s HT) on the cardiovascular system still needs to be elucidated. The aim of the study was to prospectively assess blood pressure, variability in heart rate, and the prevalence of arrhythmias in patients with s HT, both before and after they are restored to the euthyroid state. Methods: The study group consisted of 44 normotensive patients (37 women, 7 men), aged 22-65 years (mean±SD: 45.9±11.0) with s HT. Enrolled patients were drawn from 1080 patients referred to our department for treatment of hyperthyroidism. Study patients were treated with radioiodine treatment to restore the euthyroid state. Ambulatory blood pressure monitoring (ABPM) and Holter electrocardiography were performed (1) when s HT was diagnosed and (2) at least 6 months after they became euthyroid. Results: s HT in comparison to euthyroid state was associated with higher (109.3±7.1 vs 107.1±7.7 mm Hg) nocturnal systolic mean blood pressure (p=0.035) and blood pressure (BP) load (14.8 vs 10.2 %, p=0.033), mean diastolic BP (66.4±6.6 vs 64.8±6.6 mm Hg, p=0.047) and mean arterial pressure (80.8±43.1 vs 79.3±43.6 mm Hg, p=0.049). Moreover, significant changes in both the time and frequency domain measures of heart rate variability were observed: decrease of the square root of the mean squared differences of successive NN intervals (r MSSD) - 45.68±34.1 vs 65.09±50.6 ms (p=0.03) and the low frequency power (LF) - 5.71±0.99 vs 6.0±1.01 ms2 (p=0.049) as well as increase of QT interval dispersion - 58.25±28.5 vs 46.90±12.1 ms (p=0.020). This was accompanied by clinically insignificant increase in the frequency of ventricular extrasystoles (VES) - 3.1±7.4 vs 0.6±1.2 per hour (p=0.048) and increased mean heart rate - 78.4±6.8 vs 76.0±8.0 beats/min (p=0.004). Some of the parameters correlated positively with thyroid hormones: nocturnal diastolic BP with FT3 (r=0.397, p=0.008), r MSSD with FT4 (r=0.389, p=0.013) and QT interval dispersion with FT4 (r=0.450, p=0.004). Conclusions: The study suggests that s HT in comparison to euthyroid status may be associated with a statistically significant but probably clinically insignificant increase of QT interval dispersion, prevalence of VES, elevated nocturnal arterial BP and changes in heart rate variability. These findings broaden our understanding of the cardiovascular effects of s HT.