SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY BEFORE AND DURING EPISODES OF NOCTURNAL ISCHEMIA IN PATIENTS WITH EXTENSIVE CORONARY-ARTERY DISEASE

Spectral analysis of heart rate variability was used to assess autonom ic nervous system activity associated with episodes of nocturnal myoca rdial ischaemia in 32 patients (20 men, age 58 +/- 9 years) with exten sive coronary artery disease. Twenty-four hour Holter tape recordings were analysed and spectral indexes of heart rate variability were comp uted by fast Fourier analysis on 2 min segments covering the period fr om 10 min before to 10 min after each nocturnal ischaemic episode, def ined as ST segment depression greater than or equal to 1 mm lasting at least 4 min. Spectral power was measured at low frequencies (LF: 0.06 - 0.10 Hz) and high frequencies (HF: 0.15 - 0.40 Hz) and the ratio LF /HF was calculated. Results A total of 30 episodes of nocturnal ischae mia were analysed. High frequency spectral power showed a clear decrea se during the 10 min before the onset of ischaemia, remained steady un til the end of the episode, and returned to normal by 6 min after. Low frequency spectral power fluctuated throughout the ischaemic episodes with no clear pattern of variation. The low/high frequency ratio refl ected mainly the changes in high frequency. Conclusions Sympathetic pr edominance due to parasympathetic withdrawal is the principal change i n autonomic nervous system activity associated with episodes of noctur nal ischaemia.