Heart rate variability in hyperthyroidism on sub Saharan African patients: a case–control study

OBJECTIVE: We aimed to determine heart rate variability in freshly diagnosed untreated hyperthyroidism patients. We enrolled 10 patients (9 females) and 10 matched controls for sex and age. Each eligible patient underwent five different tests according to Ewing battery tests for cardiac autonomic dysfunction assessment. HRV was assessed during each maneuver and on 24 h using a continuous electrocardiogram with automatic estimation of SDNN, RMSSD, LF HF and HF/LH ratio. Results of tests were compared between hyperthyroidism patients and matched controls using the non-parametric test of Mann-Whitney. RESULTS: Heart rate was significantly higher in patients with thyrotoxicosis (82.91 ± 10.99 vs 67.04 ± 6.80; 0.006) compared to their controls. On time-domain analysis, there was a trend towards reduction in SDNN (39.52 vs. 63.75; p = 0.2) as well as the RMSSD (30.44 vs 64.03; p = 0.09) in patients with hyperthyroidism. The frequency-domain analysis showed non-significant higher values for the LF (43.87 vs 38.85 ± 12.85; p = 0.8) and lower for the HF (32.54 vs 43.39; p = 0.3). Test's results were mostly impaired in hyperthyroid patients and all patients presented abnormal results for parasympathetic activity. Untreated and recently diagnosed hyperthyroidism is associated to an altered parasympathetic activity in sub Saharan African patients.