Title page for ETD etd-05262008-120839


Document Type Master's Dissertation
Author Grant, Catharina Cornelia
URN etd-05262008-120839
Document Title Heart rate variability and dysrhythmogenic potential in patients admitted to psychiatric institutions
Degree MSc
Department Physiology
Supervisor
Advisor Name Title
Prof M Viljoen Supervisor
Keywords
  • sympathetic tone
  • parasympathetic tone
  • stress response
  • heart rate variability
  • dysrhythmogenic potential
  • corrected JT-time
  • JT-dispersion
  • autonomic function
Date 2000-04-05
Availability restricted
Abstract
The aim of this study was to investigate the dysrhythmogenic potential in psychiatric patients at the time of admission to psychiatric hospitals and clinics and to look at the autonomic nervous system balance. In general, the possibility that psychiatric patients could be at an above normal risk for cardiovascular incidents is indicated by the well-known fact that various emotional states can influence cardiovascular function, as well as the fact that several antidepressants and other medications prescribed in psychiatry can influence the heart. In addition, the possibility of an increased dysrhythmogenic potential in selective diagnostic groups of psychiatric patients is already implicated by the results of a number of studies. In this study the potential dysrhythmogenic potential was assessed by means of heart rate variability, corrected JT-times and JT-dispersion between leads V1 and V6 of the ECG. The rationale for the investigation of the autonomic nervous system function in this study is situated in the fact that heart rate variability, i.e., the fluctuations in the intervals between consecutive heartbeats, is mediated largely by the autonomic nervous system with heart rate variability reflecting the interaction between sympathetic and parasympathetic influences on the pacemaker. Autonomic function was indirectly assessed by means of time domain analyses, frequency domain analyses, Poincaré and detrended fractal analyses of baseline and stressed tachogram recordings. In view of the fact that many psychiatric patients are stressed and that many psychiatric drugs can influence cardiac functioning it was argued that knowledge about the cardiovascular function of patients at the time of admission to psychiatric institutions might be of value for patient care.

The results of this study showed below normal heart rate variability, prolonged JTc-times and increased JT-dispersion in the psychiatric group. Low heart rate variability is associated with an increased risk for cardiovascular incidents and is generally a reflection of altered autonomic nervous system functioning. The lowered heart rate variability present in the patient group was statistically validated by a Fisher Exact test (p<0.0001). The means of the psychiatric group compared to the control group JTc-values (0.3960 vs. 0.3152, p = 0.0194), and the JT-dispersion (0.0986 vs. 0.0143, p = 0.0057), were significantly prolonged, pointing towards a prolonged ventricular repolarisation time, as well as inhomogeneity of ventricular repolarisation. All three indicators, (heart rate variability, JT-time and JT-dispersion), therefore suggested an increased dysrhythmogenic potential in the psychiatric admissions included in this group. Heart rate variability indicators determined by time domain, frequency domain, Poincaré and detrended fractal analysis of the patient group versus the control group baseline tachograms (RRSD = 0.0259 vs. RRSD = 0.0720, RMSSD = 28.072 vs. RMSSD = 88.948, pNN50 = 11.854 vs. pNN50 = 42.265, LF = 126.49 vs. LF = 1093.03, HF = 100.85 vs. HF = 578.68, Power = 229.47 vs. Power = 1678.94, SD1 = 19.983 vs. SD1 = 63.268, SD2 = 48.863 vs. SD2 = 111.165, and Alpha1 = 1.1218 vs. Alpha1 = 0.9558) confirmed the very low heart rate variability with highly significant differences (p<0.0001) in most cases.

The results obtained by heart rate variability analysis techniques further showed that the baseline (resting) autonomic nervous system alterations involved depressed parasympathetic and elevated sympathetic tone. The values obtained with moderate emotional stress showed an inability to mount the expected autonomic nervous system stress response, i.e., parasympathetic activity did not show the normal stress-induced decrease and sympathetic activity was lower, rather than higher, than baseline values.

In short, the study clearly showed an increased risk for cardiovascular incidents in acute psychiatric admissions, abnormal baseline autonomic nervous system functioning, as well as a markedly deficient autonomic stress response.

© University of Pretoria 2005

G561/ag

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