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Autonomic nervous system activity and the spontaneous initiation of ventricular tachycardia

^a Cardiac Electrophysiology Program, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA

View larger version (14K): [in a new window]   Figure 1 Circadian distribution of ventricular tachyarrhythmias (VT) in the studied group.

View larger version (17K): [in a new window]   Figure 2 Heart rate (HR). Mean of 24-h and 30-min averages before the onset of ventricular tachycardia (VT). ***The differences are significant at p < 0.001 compared to the 24-h average.

View larger version (37K): [in a new window]   Figure 3 Frequency components of the heart rate variability signal, 24-h average and at 30-min intervals before the onset of sustained ventricular tachycardia. (a) Total power (TFP). (b) Ratio of low to high frequency power (LFP/HFP). (c) Low frequency power. (d) High frequency power. (e) Normalized low frequency power. (f) Normalized high frequency power. *p < 0.05 for comparison 30-min versus 24-h average. **p < 0.01 compared to the 24-h average. nu = normalized units. Significance of changes during 2-h period before ventricular tachycardia was assessed by analysis of variance and is discussed in the text.

View larger version (18K): [in a new window]   Figure 4 Changes in heart rate (top panel) and the low to high frequency power ratio (LFP/HFP) (bottom panel) during 4 h before ventricular tachycardia (VT) in an individual patient. See text for discussion.

View larger version (60K): [in a new window]   Figure 5 Spectral changes in the total (TFP) (a), low frequency (LFP) (b) and high frequency (HFP) (c) power and low/high frequency ratio (d) preceding the arrhythmia with respect to ectopic beat frequency. Power spectral analysis was repeated after removal of data segments not meeting the frequency threshold criteria: >50%, >75% and >85% normal beats. *p < 0.05 compared to the 24-h average. **p < 0.01 compared to the 24-h average.