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Cardiovascular haemodynamics and cardiac autonomic control in patients with subclinical and overt hyperthyroidism
M Petretta1, D Bonaduce, L Spinelli
1Department of Internal Medicine, Cardiology and Heart Surgery, Federico II University of Naples, Naples, Italy.
Insights
Thyroid disease impacts heart function, with overt hyperthyroidism causing significant cardiac changes. Subclinical hyperthyroidism shows subtle changes in relaxation and autonomic control, indicating early cardiac effects.
Area of Science:
- Cardiology
- Endocrinology
- Autonomic Nervous System
Background:
- Hyperthyroidism, a condition of excess thyroid hormone, affects multiple organ systems, including the cardiovascular system.
- Subclinical hyperthyroidism, characterized by suppressed TSH with normal free thyroid hormone levels, may also have cardiovascular implications.
- Understanding these effects is crucial for timely diagnosis and management.
Purpose of the Study:
- To comprehensively evaluate cardiac structure and function in patients with subclinical and overt hyperthyroidism.
- To assess cardiac autonomic control in these patient groups.
Main Methods:
- Two-dimensional Doppler echocardiography was used to assess left ventricular structure and function.
- 24-hour Holter monitoring with heart rate variability analysis evaluated cardiac autonomic control.
- A control group of 20 healthy individuals was included for comparison.
Main Results:
- Overt hyperthyroidism was associated with increased left ventricular end-diastolic volume and mass, and enhanced myocardial contractility (shortening velocity, ejection fraction).
- Subclinical hyperthyroidism showed a shorter isovolumic relaxation period and decreased heart rate variability, indicating parasympathetic withdrawal.
- No significant cardiac structural or functional differences were observed between normal subjects and patients with subclinical hyperthyroidism.
Conclusions:
- Thyrotoxicosis leads to structural cardiac changes and increased myocardial contractility, with subclinical hyperthyroidism primarily affecting left ventricular relaxation velocity.
- Both subclinical and overt hyperthyroidism demonstrate impaired cardiac autonomic control, specifically parasympathetic withdrawal.
- These findings highlight the progressive cardiovascular impact of thyroid dysfunction.
Objective:
To characterize cardiac structure and function and cardiac autonomic control in patients with subclinical and overt hyperthyroidism.
Design:
Thirty patients with subclinical hyperthyroidism and 30 with overt disease were selected from patients never previously treated for endocrinological disease in the outpatient clinic of our institution. Twenty normal individuals were studied as control group.
Methods:
Left ventricular structure and function and cardiac autonomic control were evaluated, respectively, by two-dimensional Doppler echocardiography and by 24-h Holter recording with heart rate variability analysis.
Results:
Patients with overt hyperthyroidism showed greater values of left ventricular end-diastolic volume (P<0.05) and left ventricular mass (P<0.05) than patients with subclinical disease. In addition, the mean velocity of left ventricular fibre shortening (P<0.05) and left ventricular ejection fraction (P<0.05) were greater in patients with overt hyperthyroidism than in patients with subclinical disease. No difference in any of these parameters was detectable between normal subjects and patients with subclinical disease. The isovolumic relaxation period was shorter in patients with subclinical hyperthyroidism than in control individuals (P<0.05) and in patients with overt hyperthyroidism (P<0.05). As regards cardiac autonomic control, all time and frequency domain measures decreased progressively from control individuals to patients with subclinical hyperthyroidism and those with overt disease (P<0.001).
Conclusions:
Thyrotoxic patients show changes in left ventricular structure and increased echocardiographic indexes of myocardial contractility, whereas the only echocardiographic feature detectable in patients with subclinical hyperthyroidism is an increased velocity of left ventricular relaxation. Cardiac parasympathetic withdrawal is evident in patients with overt hyperthyroidism and in patients with subclinical disease.