Heart rate variability in heart disease. Evaluation of cardiac sympathetic modulation andmodification by interventions

Abstract

Reduced heart rate variability (HRV) has been shown to be an independent risk factor for cardiac death after acute myocardial infarction, in patients with chronic coronary artery disease and in patients with congestive heart failure (CHF). Furthermore, HRV has been proposed as a non-invasive tool for the assessment of cardiac autonomic tone, in particular vagal tone. The assessment of cardiac sympathetic activity by HRV is debatable. The aims of this thesis were to evaluate changes of HRV by interventions in patients with elevated risk of cardiac death with the underlying assumption that changes in HRV could be used as surrogate endpoint for mortality and furthermore to evaluate cardiac sympathetic tone by means of HRV.Methods: (1) HRV was measured before and after endoscopic transthoracic sympathicotomy in patients with severe angina pectoris and HRV changes were compared with QT dispersion in these patients. (2) In patients with CHF on placebo, on ß-blockers and after ß-blockade withdrawal, baseline HRV was compared with invasively measured cardiac nor-adrenaline(NA) spillover in a subgroup of patients. (3) In patients randomised to routine or intensive exercise training after a myocardial infarction or coronary artery bypass surgery, HRV was measured at base-line and after training.Results and conclusions: Sympathectomy increased total HRV including vagal tone and reduced QT dispersion over time indicating reduced risk for cardiac death. The proposed sympathetic marker LF/HF did not change in the supine position but was significantly reduced during 70° head up tilt test one month after surgery. Comparing HRV indices and cardiac NA spillover in patients with CHF also demonstrated a strong correlation with LF/HF in the standing (r=0.81) but not in the supine position and there was no correlation with other HRV indices. These results indicate that LF/HF during orthostatic stress could be used as an index of cardiac sympathetic nerve activity. Patients with CHF on ß-blockade had a significant increase in vagal HRV indices in contrast to patients 24-hours after ß-blocker withdrawal who had a significant vagal reduction in the level of the placebo group. This could imply a potential risk for malignant arrhythmias when ß-blockade medication is discontinuing abruptly. In patients participating in cardiac rehabilitation, exercise capacity increased significantly more after three months of training in the intensive training group and this difference remained one year later. Total HRV increased significantly more in this group, and one year later the differences was still significant.