Is a heart rate of 37-45 beats per minute (bpm) concerning during sleep, specifically bradycardia?

Heart Rate of 37-45 During Sleep is Not Concerning

A heart rate of 37-45 beats per minute during sleep is not concerning and does not require treatment, as this represents a normal physiological response due to increased parasympathetic tone during sleep. 1

Physiological Bradycardia During Sleep

• Parasympathetic tone is more dominant than sympathetic tone during rest and sleep, causing significant sinus bradycardia (rates <40 bpm) or pauses (>5 seconds) which are common during sleep and have been observed across a wide age range 1
• Young individuals, especially well-conditioned athletes, have dominant parasympathetic tone at rest associated with resting sinus rates that can be well below 40 bpm 1
• Sinus bradycardia is seen in states of heightened vagal tone such as during sleep or deep rest, and is a normal physiological (not pathological) phenomenon 1
• Healthy young individuals, particularly athletes, can have sleeping rates as slow as 30 to 43 beats per minute with sinus pauses producing asystolic intervals as long as 1.6 to 2.8 seconds 1

Clinical Guidelines on Sleep-Related Bradycardia

• The ACC/AHA/HRS guidelines specifically state that in patients with sleep-related sinus bradycardia or transient sinus pauses occurring during sleep, permanent pacing should not be performed unless other indications for pacing are present (Class III: Harm recommendation) 1
• Nocturnal bradyarrhythmias are common in both health and disease, with sinus bradycardia being the most common bradyarrhythmia encountered during sleep 1
• In most circumstances, these are physiological, mediated, asymptomatic events which require no intervention 1

When to Be Concerned

• The key clinical question is whether there are symptoms associated with the bradycardia 2
• Symptoms that would warrant further evaluation include:
  • Syncope or dizziness associated with the bradycardia 1, 3
  • Exercise intolerance or inability to achieve appropriate heart rate with exertion (chronotropic incompetence) 3, 2
  • Chest pain, dyspnea, or fatigue that correlates with episodes of bradycardia 4
• Asymptomatic bradycardia, even with heart rates below 40 bpm during sleep, does not require treatment 1

Special Considerations

• If bradycardia occurs with sleep apnea, treatment should be directed at the sleep apnea rather than implanting a pacemaker 1
• In patients with sleep apnea and sleep-related bradyarrhythmias, frequency of episodes is decreased with continuous positive airway pressure and patients are unlikely to develop symptomatic bradycardia in long-term follow-up 1
• The normal range of heart rate during sleep can vary based on age and fitness level, with studies showing base heart rates during sleep in normotensive subjects averaging around 49±4 beats per minute 5

Common Pitfalls in Evaluation

• Overdiagnosis of pathological bradycardia can lead to unnecessary pacemaker implantation 3
• Although permanent pacemaker implantation is a relatively low-risk cardiac procedure, procedural complications can occur, and implanted leads have long-term management implications 1
• Failure to recognize sleep apnea as a cause of nocturnal bradycardia may lead to inappropriate treatment 1
• Day-to-day variation in minimum heart rate during sleep can be approximately 5±3 beats per minute, so isolated readings should be interpreted with caution 6

In conclusion, a heart rate of 37-45 beats per minute during sleep is within the normal physiological range and, in the absence of symptoms, does not require further evaluation or treatment.