Dynamics of low-frequency R-R interval oscillations preceding spontaneous ventricular tachycardia

Abstract

Background: Increased sympathetic activity is believed to be an important trigger of sustained ventricular tachyarrhythmias (VT) and is believed to be responsible for the increased heart rate that we and others have reported before the onset of spontaneous VT. However, in the patients reported herein, heart rate variability (HRV) indexes that reflect sympathetic activity unexpectedly declined, whereas heart rate increased. To explain this apparent paradoxic behavior, we tested the hypothesis that baseline levels of HRV determine its reaction to short-term autonomic perturbations before the onset of VT. Methods and Results: Holter electrocardiograms from 47 patients (ejection fraction 36% ± 15%) with recorded VT were analyzed. Frequency domain HRV indexes (low-frequency power [LFP] 0.04 to 0.15 Hz, high-frequency power [HFP] 0.15 to 0.4 HZ, and total power [TP] 0.01 to 0.4 Hz) were studied in 5-minute intervals and over a period of 24 hours. Patients were divided into those with a decrease in LFP in the 2-hour period before VT (group A, n = 32) and those with an increase or no change (group B, n = 15). The data were logarithmically transformed. Heart rate increased 15 minutes before the onset of VT compared with the 24- hour mean in both groups (group A: 80.3 ± 15.4 to 86.1 ± 20.0 beats/min, P = .005; group B: 80.6 ± 13.5 to 86.7 ± 14.0 beats/min, P = .017). Group A had higher TP, LFP, and LFP/HFP 2 hours before VT, and these variables decreased 15 minutes before the onset of VT (TP from 7.31 ± 1.28 to 6.88 ± 1.35, LFP from 6.09 ± 1.28 to 5.38 ± 1.33, LFP/HFP from 1.33 ± 0.89 to 0.96 ± 0.80, P