Q&A: Treatment of Bradycardia

The normal adult heart rate, arising from the SA node, has been considered historically to range from 60 to 100 beats per minute, with sinus bradycardia being defined as a sinus rhythm with a rate below 60 beats per minute. However, the "normal" heart rate is, in part, the result of the complex interplay between the sympathetic and parasympathetic nervous systems. It is affected by numerous factors and varies in part with age and physical conditioning. Sinus arrhythmia, changes in the sinus rate as a result of respiratory cycles, often accompanies sinus bradycardia.

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In this article:
Evaluation of bradycardia
MCQ exam: clinical scenario
MCQ exam: answer
MCQ exam: explanation

Evaluation of bradycardia

Sinus bradycardia is generally confirmed by ECG after a slow pulse is identified on physical examination, with the diagnosis usually being easy to establish from the surface ECG. An upright P wave in leads I, II, and aVL, and a negative P wave in lead aVR, indicates a sinus origin of the bradycardia. It is vital to exclude other causes of bradyarrhythmias such as AV block.

Sinus bradycardia should be distinguished from other bradyarrhythmias resulting in a reduced heart rate (ie, second or third degree atrioventricular [AV] block, junctional escape rhythm, ventricular escape rhythm). This is easily done by establishing the 1:1 relationship between P waves and QRS complexes on the surface electrocardiogram (ECG). Patients with more than one P wave for every QRS complex have second or third degree AV block, while patients with no discernible P waves will have an escape rhythm (either junctional or ventricular in origin).

For the majority of patients with sinus bradycardia, the underlying cause can usually be determined from history and physical examination alone.

MCQ exam: clinical scenario

A patient experiences serious signs and symptoms secondary to a bradycardia, and his 12-lead ECG shows no signs of an acute MI.

What is the treatment of choice?

a) Atropine
b) Bretylium
c) Dopamine infusion
d) Epinephrine infusion
e) Transcutaneous cardiac pacing
f) Norepinephrine

MCQ exam: answer

The correct answer is A.

MCQ exam: explanation

When a patient is experiencing serious signs and symptoms secondary to bradycardia, and his 12-lead ECG shows no signs of an acute MI, atropine is the initial drug of choice. Classified as a parasympatholytic or anticholinergic, atropine can restore normal SA nodal automaticity (increasing sinus node rate) and AV nodal conductivity through its direct vagolytic action. It's the initial drug of choice to treat symptomatic bradycardia in patients with a pulse.

TREATMENT OF BRADYCARDIA
For asymptomatic patients with sinus bradycardia, treatment is neither indicated nor required. For patients with symptoms who have evidence of hemodynamic instability, atropine (0.5 mg IV push, which can be repeated every three to five minutes, if needed, to a total dose of 3 mg) have taught. For patients who are hemodynamically stable, but have signs or symptoms of acute myocardial ischemia or infarction should be treated accordingly. Patients who are hemodynamically stable, with evidence of another systemic condition associated with sinus bradycardia (eg, hypothyroidism, infection, etc) should be treated accordingly. Patients in whom a medication is suspected to be causing the symptomatic bradycardia should have the medication withheld. Patients with no other evidence of a potential cause should be evaluated for sinus node dysfunction.

Reference(s)
1). UpToDate: Sinus bradycardia. Available online: https://www.uptodate.com/contents/sinus-bradycardia