HEART RATE VARIABILITY IN PATIENTS WITH THYROID DYSFUNCTIONS
Background: Although cardiac automaticity is intrinsic, heart rate and rhythm, generated from the sinus node, are largely under the control of the autonomic nervous system. Thyroid dysfunctions generate an inbalance between the parasympathetic and sympathetic nervous system.
The aim of our study was to asses the influence of the vegetative nervous system on the heart in patients with hypo- and hyperthyroidism of different severities, even with subclinical forms. A secondary purpose was to determine wether heart rate variability analyse could predict the severity of arrhythmias in patients with thyroid dysfunctions, but with normal rest ECG.
Matherial and method: We studied 42 patients with hypo- and 54 with hyperthyroidism of different etiology and severity, without associated cardiovascular diseases, admitted in the Endocrinology Clinic of County Hospital Timisoara, between October 2009 and October 2012. All patients with normal rest ECG, except for sinus bradicardia or tahicardia, had 24 hours Holter monitoring with Holter Labtech ECG Holter. We used the Nevrokard Long-Term aHLV (L-aHRV V.5.0.0.) program for the heart rate variability analyse, performed on the 24 hours Holter ECG monitoring, in a subgroup of selected patients (23 with hypothyroidism and 30 with hyperthyroidism) without history of smoking, dyslipidemia or blood pressure values over 130/80.
Results: All parameters of heart rate variability were depressed in both hypo- and hyperthyroidism. Patients with severe overt forms had the lowest values. We found an association between the form of the Lorenz plots and the typ of ventricular or supraventricular arrhythmias present on the 24 ECG Holter monitoring.
Conclusion: Heart rate variability is depressed in thyroid dysfunctions. There is a correlation between the form of the Lorenz Plot ant the severity of the arrhythmias.