Sinus bradycardia (SB) is a sinus rhythm with a rate less than 60 bpm i.e.
Rate: Slow (<60 bpm)
Rhythm: Regular
P waves: Normal (upright and uniform)
PR interval: Normal (0.12-0.2 seconds)
QRS: Normal (0.06-0.1 seconds)
**Causes:**
1. Vagal stimulation, physiologic causes (in well-trained athletes), sleep
2. Hypothyroidism, hypothermia, electrolyte imbalances (eg. hyperkalemia)
3. Inferior wall myocardial infarction (MI)
4. Sick sinus syndrome
5. Medications (eg. beta blockers, calcium channel blockers,digoxin)
**Treatment:**
Sinus bradycardia can result in reduced cardiac output and breakthrough dysrhythmias. Treatment is guided by evaluation of the underlying cause and by whether symptoms are present.
1. Drug therapy (including atropine and epinephrine) should be considered for patients who manifest signs of hypoperfusion or are symptomatic (dizzy, weak, or hypotensive).
2. Pacemakers (temporary or permanent) may be required if drug therapy is ineffective.
