Cardiac Sympathovagal Balance Research Articles

Changes in Cardiac Autonomic Control During Nocturnal Repetitive Oxygen Desaturation Episodes in Patients with Coronary Artery Disease

Periodic fluctuations in respiration such as Cheyne-Stokes respiration or the sleep apnoea syndrome are known to be associated with very-low-frequency oscillations in heart rate (cycle times about 30-120s), which may be related to periodic changes in sympathetic and vagal tone. Since disturbances in cardiac sympathovagal balance have been associated with increased cardiovascular morbidity and mortality, especially in patients with coronary artery disease (CAD), we investigated changes in cardiac autonomic control in patients with CAD during periodic breathing episodes. Thirty-five patients with a left ventricular ejection fraction (LVEF) of > 50% and 13 patients with an LVEF of < or = 35%, who were scheduled for coronary bypass surgery, were studied using a nocturnal Holter electrocardiograph (ECG) and pulse oximetric recordings. Heart rate variability was assessed by spectral analysis during cyclic oxygen desaturation episodes, indicating periodic breathing patterns, and during control episodes with normal oxygen saturation. Cyclic oxygen desaturation episodes with a duration of at least 20 min were observed in 17 patients with an LVEF of > 50% and in nine patients with an LVEF of < or = 35% (minimal oxygen saturation 83.9 +/- 3.1 versus 80.4 +/- 5.6%; cycle frequency between 0.0068 and 0.0294 Hz, no significant differences between groups), all of which were associated with very-low-frequency (0.0033-0.04 Hz) oscillations in the heart rate. During cyclic desaturation episodes patients with normal, as well as those with imparied left ventricular function, had marked increases (P < 0.01) in very low frequency power, low frequency (0.04-0.15 Hz) power and the ratio of low-to-high frequency (0.15-0.4 Hz) power. The low:high frequency ratio was significantly higher in patients with an LVEF of > 50% than in patients with an LVEF of < or = 35% during cyclic desaturation episodes, but not during control episodes. Repetitive oxygen desaturation episodes are associated with marked changes in heart rate variability which indicate cardiac sympathetic predominance in patients with CAD. Our results suggest differences in the modulation of cardiac sympathovagal balance during periodic breathing episodes between patients with normal and imparied left ventricular function.

Effect of heartmate left ventricular assist device on cardiac autonomic nervous activity

Clinical performance of a left ventricular assist device is assessed via hemodynamic parameters and end-organ function. This study examined effect of a left ventricular assist device on human neurophysiology. This study evaluated the time course change of cardiac autonomic activity of 3 patients during support with a left ventricular assist device before cardiac transplantation. Cardiac autonomic activity was determined by power spectral analysis of short-term heart rate variability. The heart rate variability before cardiac transplantation was compared with that on the day before left ventricular assist device implantation. The standard deviation of the mean of the R-R intervals of the electrocardiogram, an index of vagal activity, increased to 27 +/- 7 ms from 8 +/- 0.6 ms. The modulus of power spectral components increased. Low frequency (sympathetic activity) and high frequency power (vagal activity) increased by a mean of 9 and 22 times of each baseline value (low frequency power, 5.2 +/- 3.0 ms2; high frequency power, 2.1 +/- 0.7 ms2). The low over high frequency power ratio decreased substantially, indicating an improvement of cardiac sympatho-vagal balance. The study results suggest that left ventricular assist device support before cardiac transplantation may exert a favorable effect on cardiac autonomic control in patients with severe heart failure.

Perioperative Changes in Cardiac Autonomic Control in Patients Receiving Either General or Local Anesthesia for Ophthalmic Surgery

To investigate whether local (LA) or general anesthesia (GA) provides more perioperative stability in cardiac autonomic tone, we analyzed heart rate variability (HRV) by means of spectral analysis, intraoperatively and up to 3 h postoperatively, in otherwise healthy patients scheduled for cataract surgery. Fourteen patients received GA (premedication: clorazepate; anesthetic induction: propofol, alfentanil, atracurium; anesthetic maintainance: isoflurane, alfentanil; airway management: laryngeal mask airway), and 14 patients received LA (retrobulbar block with bupivacaine/mepivacaine). In the GA group, total power, as an indicator of cardiac autonomic activity, was significantly reduced intraoperatively and increased slowly during the postoperative period. The ratio of low frequency/high frequency (LF/HF) power, indicating cardiac sympathovagal balance, did not change significantly intraoperatively and remained stable in the postoperative period. The LA group showed no significant changes in total power intraoperatively. Postoperatively, heart rate and the LF/HF power ratio were significantly increased in the LA group compared to the GA group. GA as described above was associated with intra- or postoperative stability of the cardiac sympathovagal balance. Thus GA had no disadvantageous effects on the perioperative cardiac autonomic tone during ophthalmic surgical procedures compared to LA in otherwise healthy patients.

Cardiac Sympathovagal Balance and Peripheral Sympathetic Vasoconstriction

Both epidural and general anesthetics alter autonomic balance. However, the relative differences between epidural (EA) and general anesthetics (GA) with regard to cardiac and peripheral sympathovagal balance have not been described. Twenty consecutive patients scheduled for radical retropubic prostatectomy were randomized to receive EA (n = 10) or GA (n = 10). Power spectral analysis was performed on the electrocardiographic recordings, with the ratio of low (0.05-0.125 Hz)/high (0.125-0.5 Hz) frequency power used an index of cardiac sympathovagal balance. The forearm minus fingertip skin-surface temperature gradient (> 4 degrees C) was used as an indicator of sympathetically mediated peripheral vasoconstriction. Patients in the EA group demonstrated a significantly greater low/high frequency power ratio and a more frequent incidence of peripheral vasoconstriction than the GA group during the intraoperative period. During the postoperative period, the GA group demonstrated an increase in the low/high ratio and the incidence of vasoconstriction relative to the intraoperative period. Intraoperatively, upper body vasoconstriction appears to be accompanied by a significant shift in cardiac sympathovagal balance toward sympathetic predominance with EA relative to GA. Postoperatively, GA is associated with a shift in the sympathovagal balance toward sympathetic predominance. Further research is required to determine whether this results in cardiovascular compromise in the high-risk patient.

Effect of thrombolysis on heart rate variability and life-threatening ventricular arrhythmias in survivors of acute myocardial infarction

Objectives. The aim of the present study was to determine the influence of early thrombolysis on ventricular tachyarrhythmias (clinical and inducible) and heart rate variability in survivors of myocardial infarction at high risk for life-threatening ventricular arrhythmias.Background, A greater electrical heart stability may be important in improving survival in patients treated with thrombolysis. Few data are available about the influence of fibrinolysis on postinfarction arrhythmic events and other prognostic variables, such as inducible ventricular tachycardia and heart rate variability.Methods. The study group comprised 51 consecutive patients who underwent electrophysiologic study within 30 days of infarction, owing to the presence of two or more of the following criteria: left ventricular ejection fraction <40%, late potentials and repetitive ventricular ectopic beats. Thirty patients underwent thrombolysis within 6 h of the onset of symptoms (Group A), and 21 received conventional treatment (Group B). Inducibility of sustained monomorphic ventricular tachycardia was tested in both groups, and the standard deviation of all normal RR intervals during 24-h Holter monitoring was calculated. All patients were prospectively evaluated for occurrence of arrhythmic events.Results. The two groups were similar with regard to left ventricular ejection fraction (mean ± 1 SD 38 ± 6% [Group A] vs. 36 ± 8% [Group B]). Ventricular tachycardia was induced in 6 (20%) of 30 Group A patients versus 14 (67%) of 21 Group B patients (p = 0.002). The standard deviation of normal RR intervals was higher in Group A than in Group B (113 ± 36 vs. 90 ± 39 ms, p = 0.05). In patients with anterior infarction, the standard deviation of normal RR intervals was higher in 19 patients with thrombolysis than in 16 patients with conventional treatment (118 ± 41 vs. 74 ± 24 ms, p = 0.0002). During a mean follow-up period of 23 ± 11 months, 4 (13%) of 30 Group A patients had an arrhythmic event versus 9 (43%) of 21 Group B patients (p = 0.04).Conclusions. After myocardial infarction, in high risk patients, thrombolysis significantly reduced the occurrence of arrhythmic events independently of left ventricular function. This effect may be related to both an improvement in electrical heart stability, as elucidated by electrophysiologic study, and a favorable action on the cardiac sympathovagal balance.

Neurocardiac responses to vagoafferent electrostimulation in humans.

To determine if cardiac vagal tone is enhanced by vagal electrostimulation (VES), we examined the heart rate autospectrum (HRA) in eight patients with implanted stimulators for complex partial seizures. In four patients the VES was activated at 30 Hz and 500-msec pulse (HiStim group) compared to 2 Hz and 130-msec pulse for the LoStim group (n = 4). Continuous ECG and respiratory waveforms were recorded for 45 minutes every 8 hours (7-8 AM; 3-4 PM 11-12 PM) during resting supine wakeful epochs both before and 15 days after surgical implantation. From the HRA cardiac sympathovagal balance was expressed as the ratio of the low frequency (LF) power to the high frequency (HF) power. There were no presurgical differences between the groups in heart rate, its variance, or the energies contained in any autospectral band. The LoStim group showed no significant change in heart rate (HR), HF peak power, or LF:HF ratios during 2 weeks of VES. Conversely, in the HiStim group, the LF:HF peak power ratio (an expression of sympathetic dominance) decreased from 2.5 +/- 1.5 preimplant to 1.5 +/- 0.49 (P < 0.02) with VES. During VES there was a significantly higher HF power in the HiStim compared to LoStim group. No diurnal variations in HRA values were seen for either group. (1) A relationship exists between selective vagal nerve electrostimulation and the HRA; and (2) high stimulation frequency of the vagus nerve in man is associated with sustained augmentation of cardiac vagal tone throughout a 24-hour cycle.