Circadian variations of sinus rate in subjects with sinus node dysfunction

Area of Science:

• Cardiology
• Chronobiology
• Electrophysiology

Background:

• Circadian variations in sinus rate (SR) are established in healthy individuals.
• Limited data exists on daily SR variations in patients with sinus node (SN) dysfunction.

Purpose of the Study:

• To investigate circadian variations of SR in patients with varying degrees of SN dysfunction.
• To compare SR circadian patterns between healthy subjects and patients with bradycardia or sinoatrial block.

Main Methods:

• ECG Holter monitoring was used to record SR in 12 healthy subjects and 39 patients.
• SR was analyzed using 2-hourly histograms (maximum, modal, minimum) and cosinor analysis.
• Patients included those with intermittent bradycardia, persistent bradycardia, and intermittent 2:1 sino-atrial block.

Main Results:

• Healthy subjects exhibited confirmed circadian SR periodicity.
• Patients with intermittent bradycardia showed circadian rhythm only in minimum SR and SR mode.
• No significant circadian SR variations were observed in patients with persistent bradycardia or sinoatrial block.

Conclusions:

• The loss of circadian SR periodicity correlates with the severity of SN dysfunction.
• Intermittent bradycardia patients exhibit more normal circadian behavior at lower heart rates.
• Marked SN dysfunction may lead to loss of circadian rhythm due to intrinsic SN or autonomic nervous system involvement.