ASSESSMENT OF TIME-DOMAIN AND SPECTRAL COMPONENTS OF HEART-RATE-VARIABILITY IMMEDIATELY BEFORE ISCHEMIC ST SEGMENT DEPRESSION EPISODES

In an attempt to study autonomic function during the 5-minute period p receding ischemic ST segment depression (down arrow ST) episodes, we s elected 138 down arrow ST episodes, without preceding down arrow ST du ring the last 15 minutes before each episode, from the Holter tapes of 35 patients with multivessel coronary artery disease. For the 5-minut e period preceding each down arrow ST episode, we calculated the follo wing heart rate variability (HRV) indices; the mean RR interval (RR5), the standard deviation of all RR intervals (SD Index5), the correspon ding coefficient of variation (CV5), and the natural log (Ln) of the s pectral components, total power at 0.000 to 0.400 Hz (TP5), low freque ncy power at 0.040 to 0.150 Hz (LF5), high frequency power at 0.150 to 0.400 Hz (HF5), and the ratio of the low to high frequency power (LF5 /HF5). As HRV indices of the 24-hour period, we calculated the respect ive RR, SD Index, CV, Ln TP, LnLF, LnHF, and Ln LF/HF. RR5, SD Index5, CV5, and Ln TP5 were all significantly lower than RR (t = -5.343, p = 3.7 x 10(-7)), SD index (t = -19.091, p = 1.99 x 10(-40)), CV(t = -15 .780, p = 1.28 x 10(-32)), and LnTP (t = -3.210, p = 0.0016), respecti vely. LnHF5 was inversely correlated with the magnitude of the down ar row ST; r = -0.174, P < 0.05, and CV5 was inversely correlated with th e natural log (Ln) of the ischemic event duration; r = -0.183, P ( 0.0 5. Analogous results were obtained for both the painful and silent dow n arrow ST episodes. It is concluded that HRV is decreased during the 5-minute period preceding down arrow ST episodes, and is inversely rel ated with the magnitude and the duration of the down arrow ST.