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 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 vagas 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 and Complete Heart 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).
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.
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.
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.
First, it is important to note that Mobitz II and Complete Heart Block are commonly associated with acute myocardial ischemia.
It is not so much that the Atropine won’t increase the heart rate when given for Mobitz II and Complete Heart Block. In fact it will probably increase the HR, but this has a high potential of inducing more myocardial ischemia as the HR will double or triple. This will also reduce diastolic filling time which will worsen coronary perfusion.
Since Mobitz II and Complete Heart Block are almost always 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. Mobitz I is not usually associated with MI.
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