ROLE OF CIRCADIAN RHYTHMICITY IN THE HEART-RATE-VARIABILITY PRECEDINGNONSUSTAINED VENTRICULAR-TACHYCARDIA

The difference in sympathovagal activity preceding non-sustained ventr icular tachycardia (NSVT) was examined between patients with and witho ut a circadian rhythm. Thirty-three patients' Holter monitoring data ( 41 NSVT episodes) were analyzed regarding the frequency domain measure s (low-frequency component [LF: 0.04-0.15 Hz], high-frequency componen t [HF: 0.15-0.4Hz], and the ratio of LF to HF [LF/HF]) for each 15-min average from 120 min before each episode of NSVT. The presence of a c ircadian rhythm was accepted when the rhythm adaptation was significan t by cosinor analysis and the acrophase was located at night (22.00-06 .00 h) in HF (HF-positive group, n=17), and during the daytime (10.00- 20.00h) in LF/HF (LF/HF-positive group, n=12). The negative groups wer e identified by the absence of a circadian rhythm (HF-negative group, n=16; LF/HF-negative group, n=21). The serial changes in the HF power before NSVT were significantly different between the I-IF-positive and -negative groups (p<0.05). The HF increased from 75-60 min before NSV T in the HF-positive group, whereas the HF decreased from 60-45 min in the HF-negative group. The serial changes in the LF/HF ratio were not significantly different between the LF/HF-positive and -negative grou ps. Thus, the circadian rhythmicity of vagal activity seems to have an important role in the genesis of NSVT.