Sinus bradycardia is defined as a heart rate below 60 beats per minute originating from the sinoatrial node. It often occurs normally during sleep due to decreased metabolic demands or in trained athletes with well-conditioned hearts. While most adults can tolerate rates as low as 45 beats per minute, symptomatic bradycardia requiring treatment can include hypotension, dizziness, and syncope. The electrocardiogram of sinus bradycardia shows a normal rhythm with regular P waves, PR intervals, QRS complexes, and T waves within normal limits.

1. Sinus Bradycardia

2. Sinus Bradycardia
• Sinus rate below 60 beats/minute
• Regular rhythm
• Occurs normally during sleep
– Decreased metabolic demands
• Occurs normally in a person with a well-
conditioned heart
– Athlete
• Well-conditioned hearts can maintain a normal stroke
volume with less-than-normal effort

3. Sinus Bradycardia
• How it happens
– Normal response to a reduced demand for blood
flow
• Vagal simulation increases and sympathetic stimulation
decreases
– Automaticity in the SA node diminishes

4. Sinus Bradycardia
• A tolerable condition?
– Most adults can tolerate a sinus bradycardia of 45-
59 beats/minute
– Less tolerant of a rate below 45 beats/minute

5. Sinus Bradycardia
• Causes
– Non-cardiac disorders
– Conditions producing excess vagal stimulation or
decreased sympathetic stimulation
– Cardiac diseases
– Certain drugs

6. Sinus Bradycardia
• No symptoms? No problem
• Symptoms? PROBLEM
– Prompt attention is critical
– Can lead to more serious problems
• Hypotension and dizziness
• Ventricular tachycardia and ventricular fibrillation

7. Symptomatic Bradycardia
• If a patient can’t tolerate bradycardia, he may
develop these signs and symptoms:
– Hypotension
– Cool, clammy skin
– Altered mental status
– Dizziness
– Blurred vision
– Crackles, dyspnea
– Chest pain
– Syncope

8. Symptomatic Bradycardia
• When to call for help and what to do until help
arrives
– Look at the patient and ask how they are doing
– Call for help if heart rate is too slow and/or
symptomatic
• Compare it their normal heart rate and rhythm
– Stay with the patient
– If the patient is not breathing and does not respond
• Call code
• ABCs/CPR

9. Sinus Bradycardia
• Atrial & ventricular rhythms are regular, as are
their rates, except that they’re both under 60
beats/minute

10. Sinus Bradycardia
• Normal
– P wave preceding each QRS complex
– PR interval
– QRS complex
– T wave
– QT interval

11. Sinus Bradycardia
• P wave
– rounded, smooth, and upright in lead II, signaling
that a sinus impulse has reached the atria

12. Sinus Bradycardia
• PR interval
• Normal indicating that the impulse is following
normal conduction pathways
– 0.12-0.20 seconds

13. Sinus Bradycardia
• QRS complex
• Normal duration representing normal
ventricular impulse conduction and recovery
– Less than 0.12 seconds

14. Sinus Bradycardia
• T wave
– Upright in lead II, confirming that normal
repolarization has taken place

15. Sinus Bradycardia
• QT interval
– Within normal limits
• 0.36 to 0.44 seconds