Changes in frequency domain measures of heart rate variability in relation to the onset of ventricular tachycardia in acute myocardial infarction.

The imbalance of the autonomic nervous function has been shown to contribute to the genesis of ventricular arrhythmias. Power spectral analysis of components of heart rate variability has the potential to quantify the cardiac autonomic tone during ambulatory electrocardiographic recording. We analysed the power spectral components of total power, very low frequency power (0.0033-0.04 Hz), low frequency (0.04-0.15 Hz) and high frequency (0.15-0.40 Hz) power in 12 consecutive patients accompanied with 27 episodes of ventricular tachycardia in acute myocardial infarction. The spectral areas were measured in 5-min periods preceding the onset of ventricular tachycardias. The total power of heart rate variability increased progressively before the onset of ventricular tachycardia episodes (P < 0.05). The increase of total power was mainly due to higher, very low frequency power at the onset rather than before the onset of ventricular tachycardia (P < 0.05). The trend towards adrenergic predominance at the onset of ventricular tachycardia was observed by an increase of average heart rate (P < 0.05) without concomitant increase in high frequency power. Thus, the occurrence of ventricular tachycardia is associated with changes in the power spectrum of heart rate variability suggesting alterations in autonomic tone at the onset of ventricular tachycardia in acute myocardial infarction.