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
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
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.
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 20 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.
Brandon says
DA (Dopamine) is a precursor to Epi. The reason some docs like to use one over the other is as follows: Your myocardium and nervous tissue transport DA into a vesicle that contains a specific enzyme that will convert it to Epi and then that vesicle must be trafficked to the proper receptor (typically on the outside of the cell) that will cause increased permeability to calcium and eventual muscle contraction. If you give Epi, you bypass this conversion system and get the effect you want sooner. Both are relatively quick processes, it just comes down to personal preference.
Kev says
In relation to the “Bainbridge Reflex”… would aggressive IV fluid treatment not be an effective way of raising heart rate in patients with symptomatic bradycardia? This is not what is indicated pre-hospital – so why not?
Jeff with admin. says
I’m not sure what the mean by brain bridge reflex but fluids will not stimulate the sympathetic nervous system. Atropine will increase heart rate. Transcutaneous pacing will increase heart rate.
Kind regards,
Jeff
sarfaraz says
Dopamine dose in bradycardia?
http://emedicine.medscape.com/article/2172085-overview
Jeff with admin. says
This document is from 2014. The AHA guidelines were released in late 2015. Prior to 2015, the AHA Guidelines for dopamine was 2-10 mcg/kg/min. This was changed to 2-20 mcg/kg/min in 2015. Kind regards, Jeff
Hilgendh says
What’s the major differences between Dopamine and Epinephrine besides the dose ranges? In my readings, i see that dopamine is a precursor to epi, and that both have a Beta- effect at low doses and an increasing Alpha effect at higher doses. Why is epinephrine prefered for everything? What would be reasons to choose one over another?
Thanks!!!
Jeff with admin. says
For the treatment of bradycardia, dopamine or epinephrine infusions are both classified equal in their effect (Class IIb LOE B) and either choice would be equally acceptable for the treatment of symptomatic bradycardia.
The major difference would be that if you have a patient who is hypotensive along with the bradycardia, epinephrine would probably be a better choice to start with. This is due to the fact that epinephrine can simultaneously increase the heart rate and blood pressure. Whereas with dopamine, you have to titrate different doses to achieve either an increase in heart rate or increased blood pressure.
I would not say that epinephrine is always preferred for everything. I have often seen a physicians first choice for hypotension or bradycardia be dopamine.
Kind regards, Jeff
SheilaK says
The dopamine infusion rate – on the algorithm chart it states 2-10 mcg/kg/mn but on the information above in bold it states 2-20mcg/kg/mn. Which is the correct dose?
Jeff with admin. says
Can you please let me know which “algorthm chart” you are asking about? The correct dosing is 2-20 mcg/kg/min.
Is the 2-10 mcg/kg/min dosing you referenced from this website or another chart you are looking at?
Kind regards,
Jeff
Ellen Mosca says
On the AHA ACLS Bradycardia Algorithm listed on this site
Jeff with admin. says
If you can provide the link to the algorithm you are looking at that would be great. I cannot locate any bradycardia algorithm on the site that lists dopamine infusion for bradycardia at 2-10 mcg/kg/min. The correct dosing is 2-20 mcg/kg/min. Kind regards, Jeff
Ren says
EPI is for if BP >100 systolic
Dopamine is used if BP <100 systolic
That is, if TCP is unavailable or treatment is contraindicated.