ACLS Drugs for Bradycardia

ACLS Drugs for Bradycardia

When bradycardia is being treated in ACLS, if an underlying cause cannot be identified and corrected, medications are indicated.

There are three medications used in the bradycardia algorithm: atropine, epinephrine, and dopamine. Each drug and its use within the bradycardia algorithm is explained below.

Atropine

Atropine is the first drug used to treat bradycardia in the bradycardia algorithm. It is classified as an anticholinergic drug and increases firing of the SA Node by blocking the action of the vagus nerve on the heart resulting in an increased heart rate.

Atropine should be used cautiously in the presence of myocardial ischemia and hypoxia since it increases oxygen demand of heart and can worsen ischemia.

The dosing for Atropine is 0.5 mg IV every 3-5 minutes as needed, and the maximum total dosage that can be give is 3 mg.

Atropine should be avoided in hypothermic bradycardia and it will not be effective for Mobitz type II/Second Degree Block Type 2.

You may have read that Atropine is not effective for Mobitz II (2nd degree block type II) and Complete Heart Block (3rd degree block)
Click here to find out why

Epinephrine and Dopamine

Epinephrine and dopamine are second-line drugs for symptomatic bradycardia. They are both used as infusions in the bradycardia algorithm if atropine is ineffective.

New 2010 ACLS guidelines state that if bradycardia is unresponsive to atropine, an equally effective alternative to transcutaneous pacing is the use of an IV infusion of the beta-adrenergic agonists (dopamine or epinephrine).

Dosing:

Begin the epinephrine infusion at 2 to 10 mcg/min and titrate to patient’s response.

The goal of therapy is to improve the patient’s clinical status rather than target an exact heart rate.

Begin the dopamine infusion at 2 to 10 mcg/kg/min and titrate to the patient’s response.

Precautions

Prior to use of ACLS drugs in the treatment of symptomatic bradycardia, contributing factors of the bradycardia should be explored then ruled out or corrected.

Return to main ACLS Pharmacology page.


In your AHA Provider manual, you will see it stated under the bradycardia algorithm section that atropine is not effective for Mobitz II and Complete Heart Block. I have had a number of people ask why it is not effective. Here is an explanation:

First let’s look at atropine and how it works. Atropine increases firing of the sinoatrial node (atria) and conduction through the atrioventricular node (AV) of the heart by blocking the action of the vegus nerve.

With 3rd degree block there is a complete block and disassociation of the electrical activity that is occurring in the atria and ventricles. Since atropine’s affect is primarily on the SA node in the atria, 3rd degree block would prevent its affect on the SA node from influencing the rate of ventricular contraction which is needed to improve perfusion.

With Mobitz-II, aka, Second-degree AV Block Type II, the situation is similar. There is a partial block in the electrical impulses from the atria (SA) to the ventricles, and thus the affects of atropine would not significantly change the status of the ventricles.
This block can also rapidly progress to 3rd degree block.

To summarize, Atropine may speed the firing rate of the SA node (atria), but the ventricles are not responding to anything the atria (SA node) puts out. Thus, the heart rates will not increase.

There may be some action at the AV-node with atropine, but the effect will be negligible and typically not therapeutic. Atropine in most cases will not hurt the patient with 3rd degree block unless they are unstable and you delay pacing to give atropine.

It is important to note that Mobitz II and Complete Heart Block may be associated with acute myocardial ischemia. In this case, if atropine is used and it increases the heart rate there is a high potential for worsening of the myocardial ischemia due to the increased oxygen consumption. The increased heart rate will also reduce diastolic filling time which may worsen coronary perfusion.

Since new onset mobitz II and Complete Heart Block are commonly associated with myocardial infarction, it would be ideal to keep the HR slow (50-60) to increase diastolic filling time. Anytime you increase HR, the diastolic filling time is what takes the biggest hit.

Transcutaneous Pacing should be the first line in symptomatic Mobitz II and Symptomatic Complete Heart Block. It is very safe & less painful than in previous times due to technology improvements. Research has shown that most individuals can tolerate > 15min of transcutaneous pacing without too much difficulty.

Now back to the bradycardia drugs

Comments

  1. rob says

    So atropine is not to be used in a bradyarrhythmia when the etiology is presumed to be an AMI. How often is a bradycardic rhythms’ etiology not AMI. What are other causes of symptomatic bradycadia? Also could you direct me towards some literature that supports withholding atropine in the presence of bradycardia secondary to AMI. Thanks!

    • says

      It can be used but you should use it with caution. Here is the AHA quote and link to the reference:
      “Avoid relying on atropine in type II second-degree or third-degree AV block or in patients with third-degree AV block with a new wide-QRS complex where the location of block is likely to be in non-nodal tissue (such as in the bundle of His or more distal conduction system). These bradyarrhythmias are not likely to be responsive to reversal of cholinergic effects by atropine and are preferably treated with TCP or b-adrenergic support as temporizing measures while the patient is prepared for trans-venous pacing.” Reference: Pg. S749-750 Circulation Journal Nov. 2nd 2010

  2. goar0701 says

    I am a little confused here, please some help!!!

    For the treatment of Hypotension (Just for ACLS purpose), can we use:

    Dopamine infusion of 10-20 mcg/kg/min. OR,
    Epinephrine infusion of 0.1-0.5 mcg/kg/min OR,
    Epinephrine infusion of 2 – 10 mcg/min.

    Thanks for your help!

    • says

      Page 76 AHA ACLS Provider Manual states:
      Treat hypotension as follows:
      Epinephrine 0.1-0.5 mcg/kg/min
      Dopamine 5-10 mcg/kg/min

      For chemical pacing with bradycardia the provider manual page 113 states:
      Epinephrine: Initiate at 2-10 mcg/min and titrate to response
      Dopamine: Initiate at 2-10 mcg/kg/min and titrate to response
      Kind regards,
      Jeff

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>