Heart Rate Variability (HRV) As A Diagnostic Tool For Patients With Coronary Heart Disease (CHD)

Abstract

Berbalk et al. (2001) described a so called heart rate variability threshold (HVT) during an incremental bicycle ergometer test in healthy young people at the minimum of parameters of the vagal tone using analysis of heart rate variability parameters (RMSSD, stdb). The power at the HVT and the power at the individual anaerobic lactate threshold showed a significant positive correlation in the examined population. In patients with coronary heart disease (CHD) non-invasive diagnostic methods apart from lactate diagnostics, focusing on ECG monitoring are primarily searched to determine training intensities. PURPOSE The purpose of this study was to examine the use of HRV as a diagnostic tool to determine performance and training intensities for patients with coronary heart disease. METHODS 36 patients (5 female, 31 male, age: 65,6±9,1 years, height: 172,6±6,5 cm, weight: 75,9±9,3 kg) with known CHD were investigated. The subjects performed a cycle test with incremental intenisty (WHO-Scheme) until subjective exhaustion with permanent ECG-registration on an Ergoline Ergo-Metrics ER 900 bike. At the end of each level, blood lactate was taken and heartbeat was noticed. The power at 4 mmol/l lactate was determined by linear interpolation. This parameter was then correlated with parameters of HRV. HRV was continuously recorded and saved by a Polar watch S 810. The last minute of each level was evaluated and parameters of the short-time variability (RMSSD, stdb), which show the influence of the vagal tone, were taken from this time sequence. The minimum of short-time variabilty parameters determined during the ergometer test was then correlated with the power (Watt) at 4 mmol/l lactate concentration. RESULTS In 24 subjects HVT could not be determined according to an insufficient exhaustion and a maximal lactate concentration below 4 mmol/l. In the remaining group of 12 patients, HVT correlated highly (r=0.97, p < 0.01) with the power corresponding to 4 mmol/l lactate CONCLUSIONS The results of the study show that HVT can be used to determine training intensities in patients with coronary heart disease. As, however, two thirds (n=24) of the subjects did not reach a sufficient exhaustion to determine HVT, this diagnostic method is only useful for a selected subgroup of patients being able to reach higher metabolic exhaustion. One reason for the lower maximal lactate values could be the higher medication of β-blockers as compared to the other group. Another reason could be the lower extend of regular physical activity in these 24 subjects. Before using HVT measurements in cardiac patients on a regular basis, more subjects have to be included.