[Circadian variations of sinus rate in subjects with normal or pathological sinus node (author's transl)].

Circadian variation of sinus rate (SR) is well described in subjects with normal sinus node (SN). On the other hand there are on data in literature concerning the SR daily variations in patients with SN disfunction. In order to clarify this problem we studied the SR circadian variation in normal subjects (12, and in patients with intermittent bradycardia (11), persistent bradycardia (9) and intermittent 2:1 seno-atrial block (7). SR was recorded utilizing ECG Holter monitoring. By histograms obtained every two hours, modal, maximum and minimum SR were evaluated. Time series were analyzed with a computer program for cosinor method. In the patients with normal SN, circadian periodicity in SR was confirmed with acrophase at 1626 (maximum SR), 1638 (minimum SR) and 1631 (SR mode), respectively. In patients with intermittent bradycardia a circadian rhythm was detected only in minimum SR (acrophase 1651) and in SR mode (acrophase: 1631). No statistically significant circadian variations of the 3 parameters of SR were observed in patients with both persistent bradycardia and sinoatrial block. These data suggest that: - the disappearance of circadian periodicity is proportional to the severity of SN dysfunction; - the patients with intermittent bradycardia show a more normal behavior at low rates than at high ones; - the disappearance of circadian rhythm in patients with marked SN disfunction can be related to SN intrinsic involvement and/or autonomic nervous system disfunction.