990-46 Decreased Heart Rate Variability Precedes Daily Life Ischemia

Triggers of daily life ischemia remain undefined. Evidence suggests that vagal withdrawal may produce ischemia by coronary vasoconstriction. Heart rate variability (HRV) has been shown to be an indicator of vagal tone. Therefore, we analyzed 68 asymptomatic ambulatory ischemic events (>1 mm downsloping ST depression, for >60sec) in 19 men with documented coronary disease during 48 h Holter monitoring. HRV was examined using spectral analysis distinguishing low frequency (If=0.04–0.15 Hz) and high frequency (hf=0.15–0.40 Hz) HRV at 60-, 20-, 10-, 4-, and 2-minutes prior to, and 2-, 10-, 20-, and 60-minutes after ischemia. To control for heart rate, HRV was also assessed at similar heart rates during non-ischemic periods. A significant (p<0.05) decrease in hf-HRVwas observed in the 10–60 min periods prior to ischemia and a further drop emerged at both 4- and 2-min prior to ischemia. In addition, hl-HRV was significantly lower 10- and 4-min priorto ischemia (4.26±0.13 and 4.22±0.15) than in the heart rate controlled periods (4.96±0.29 and 4.93±0.26). Results for If-HRV were similar