TABLE OF CONTENTS
When I started writing this post, I wondered if it was redundant. After all, the AHA has a beautiful algorithm, and ACLS drills it into our heads repeatedly. We do know what to do.
But the more I read, and the more I thought about real patients, the more I realised something else. Maybe the algorithm was also narrowing our focus.
Bradycardia isn’t a single problem. And atropine isn’t the decision. It is just one possible response.
What is Bradycardia?
Bradycardia has traditionally been defined as a heart rate less than 60/min.
More recent guidelines (AHA 2018) recognise that clinically significant bradycardia is usually less than 50/min.
Why do we care?
- Cardiac output = heart rate × stroke volume
- Stroke volume cannot compensate indefinitely for a falling heart rate
- In severe bradycardia, cardiac output must be low. This is simple physiology
- A normal blood pressure does not exclude shock here
- If a patient is “bradying down” in front of you, don’t wait for hypotension. Act early
- Progressive bradycardia is often a pre-terminal rhythm
- Some patients may appear deceptively stable due to a strong sympathetic response
- One more reason to fear bradycardia: torsade de pointes
- Torsade de pointes is a pause-dependent arrhythmia
- Bradycardia prolongs the QT interval and increases the risk of malignant ventricular arrhythmias
- Leaving patients profoundly bradycardic is not benign
Firstly: Is this actually a rhythm problem?
Not all bradycardia is primary “electrical disease”.
Bradycardia may be:
- Physiologic (sleep, athletes)
- A response to metabolic, toxicologic, or ischemic stress
Before treating the rhythm, identify the cause.
Start by ruling out the dangerous and reversible causes:
- Hyperkalemia
- Cardiac ischemia
- Toxicologic causes
- Raised intracranial pressure (Cushing reflex)
This is how I remember the causes of bradycardia:
The BRADI mnemonic
B – BRASH / Hyperkalemia
R – Reduced vitals (hypoxia, hypoglycemia, hypothermia with or without hypothyroidism)
A – Acute coronary occlusion
D – Drugs (beta-blockers, calcium channel blockers, digoxin)
I – Intracranial pathology / Infection
Treat the cause whenever possible.
Bradycardia often improves when physiology improves.
Reversible causes to address early
Cardiac ischemia:
The primary goal is urgent reperfusion. Transfer to the cath lab as soon as possible.
- Bradycardia medications or transcutaneous pacing should be used only as a bridge while definitive management is arranged
- If vasoactive support is needed, use minimal doses of dopamine or epinephrine, as both can worsen myocardial ischemia
- Inferior MI: Nodal ischemia with increased vagal tone, typically producing narrow-complex, transient bradycardia that often responds to atropine.
- Anterior MI: Infranodal conduction system ischemia, more commonly producing wide-complex bradycardia that usually requires pacing.
Hypothermia:
Rewarming is the first-line treatment and often corrects the bradycardia without the need for medications or pacing.
Myxedema coma:
Treat with thyroxine. Bradycardia typically improves as the underlying endocrine abnormality is corrected.
Toxicological causes:
- Beta-blocker or calcium channel blocker toxicity:
- Consider high-dose insulin therapy, with or without lipid emulsion
- Consider glucagon when appropriate
- Pacing is often ineffective
A practical clue:
- Calcium channel blocker toxicity tends to cause hyperglycemia
- Beta-blocker toxicity tends to be normoglycemic or hypoglycemic
- Propranolol toxicity: Consider sodium bicarbonate due to sodium-channel blockade
- Digoxin toxicity: Can produce almost any bradyarrhythmia, from junctional rhythms to complete heart block. Consider digoxin-specific antibody fragments (DigiFab)
Special populations
Post-cardiac transplant /Spinal cord injury
- Aminophylline:
6 mg/kg IV in 100–200 mL over 20–30 minutes
- Theophylline:
- Typical total daily dose ~450 mg
- Target serum levels 10–20 mcg/mL
300 mg IV, then oral 5–10 mg/kg/day
Inferior MI with high-grade AV block
- Aminophylline: 250 mg IV bolus
Atropine should be avoided in transplant patients due to the risk of high-grade AV block or asystole.
Calcium
If the cause is unclear or hyperkalemia or toxicity is suspected, calcium is reasonable.
Calcium-responsive bradycardias include:
- Hyperkalemia
- Hypocalcemia
- Hypermagnesemia
- Calcium channel blocker overdose
Dose:
- Calcium chloride 1 g IV
- OR calcium gluconate 3 g IV
Calcium is relatively safe and reasonable when the etiology of bradycardia is unclear.
What Next: Is this a rhythm atropine actually works on?
Before giving atropine, ask two questions:
- Is the patient symptomatic?
- Is this a rhythm atropine can fix?
Is the patient symptomatic?
Symptoms suggesting unstable bradycardia (CHAAS):
- Chest pain
- Hypotension
- Acute heart failure
- Altered mental status
- Signs of shock, including syncope
Even without overt instability, some rhythms are high risk:
- Mobitz II AV block
- Complete heart block with wide QRS
- Ventricular pauses greater than 3 seconds
- Recent asystole
These patients require treatment in the emergency department.
In the absence of instability or high-risk rhythms, close monitoring and cardiology referral are appropriate.
In the absence of instability or high-risk rhythms, close monitoring and cardiology referral are appropriate.
Is this a rhythm atropine can fix?
Atropine blocks vagal tone at the AV node. It only works if the distal conduction system is intact.
Atropine is likely to respond to:
- Sinus bradycardia
- Vagal-mediated bradycardia
- Proximal AV block
Atropine is likely to fail in
- Mobitz II
- Complete heart block
- Wide-complex bradycardia
- Post-cardiac transplant patients
Proceed early to pacing or vasoactive support.
Only about 25–30% of patients have a meaningful response to atropine.
Failure is common and expected.
Atropine dosing and why the dose matters
For symptomatic bradycardia, give atropine 1 mg IV or IO.
Repeat every 3–5 minutes to a maximum total dose of 3 mg.
Why did we move from 0.5 mg to 1 mg?
Low doses can paradoxically worsen bradycardia:
- Below 0.5 mg, M1 receptor blockade may transiently slow the heart
- At higher doses, M2 blockade predominates and heart rate increases
This is why current practice starts at 1 mg IV.
When atropine should be avoided
Atropine is ineffective or potentially harmful in:
- Cardiac transplant patients
- Mobitz II or third-degree AV block with wide QRS
- Narrow-angle glaucoma
- Bladder outlet obstruction without catheterisation
- Ileus or obstructive GI disease
- Significant tachycardia or hypertension
- Fever or heat exposure
Atropine didn’t work: Now what?
Atropine commonly fails in sick bradycardias.
Options include:
- Chronotropic or vasoactive agents - such as epinephrine or dopamine
- Transcutaneous pacing
It is often difficult to predict which patients will respond best to medical therapy versus electrical pacing.
In peri-arrest states, stepwise pharmacology is often impractical. A single agent that supports both heart rate and blood pressure is usually preferred. Epinephrine often fulfills this role.
Prepare epinephrine and pacing simultaneously.
A randomized feasibility study comparing dopamine versus transcutaneous pacing in patients who failed atropine showed no difference in survival to discharge.
Why epinephrine works better than atropine.
Epinephrine:
- Increases heart rate
- Increases myocardial contractility
- Improves preload and afterload
- Acts above and below the AV node
In unstable bradycardia, epinephrine provides meaningful hemodynamic support.
Do not wait for atropine to “kick in.” If the first dose of atropine is ineffective, prepare epinephrine and pacing simultaneously.
Chronotropic or vasoactive agents
Epinephrine
- Dose: 2–10 mcg/min IV infusion
(or 0.1–0.5 mcg/kg/min, titrated to effect)
- Provides combined chronotropy, inotropy, and vasoconstriction
- Often preferred in peri-arrest or shock states, where global hemodynamic support is required
Dopamine
- Dose: Start at 5 mcg/kg/min IV
- Titrate by 5 mcg/kg/min every 2 minutes (usual range 5–20 mcg/kg/min)
- Doses above 20 mcg/kg/min increase the risk of vasoconstriction and arrhythmias
- Less predictable than epinephrine, particularly in severe conduction disease
Isoproterenol
- Dose:
- IV bolus 20–60 mcg, followed by 10–20 mcg boluses as needed
- OR infusion 1–20 mcg/min, titrated to heart rate
- Useful in selected settings, but requires close monitoring for ischemia
Transcutaneous pacing
Transcutaneous pacing is often the fastest way to increase heart rate in unstable bradycardia.
It is a temporary measure, used to stabilize the patient while preparing for more definitive management, such as transvenous pacing or correction of the underlying cause.
Think of TCP as buying time, not fixing the problem.
In patients with severe bradycardia and shock, pacing may be initiated while vascular access is being established.
Use it for:
- High-grade AV block
- Peri-arrest bradycardia
- Drug-refractory instability
Pad placement
Effective pacing depends heavily on pad position.
- Optimal pad placement continues to be an area of ongoing research
- Air is a poor conductor, so directing current through lung tissue is less effective
- Anterior–posterior placement is generally preferred and more likely to achieve capture
A prospective study of 20 patients undergoing elective cardioversion in an electrophysiology laboratory found that anterior–posterior pacing was more likely to achieve capture than the anterolateral position
Energy settings
Adjust energy based on patient stability:
- Crashing or unconscious peri-arrest patient:
Start at a high current to achieve rapid capture. If needed, increase immediately to maximum output (typically 140–200 mA), then titrate down once the patient is stabilized.
- More stable, conscious patient:
Start at a lower current and increase gradually in 5–10 mA increments until capture is achieved.
Once capture is obtained:
- Maintain pacing at 10–20 mA above capture threshold
- Capture typically occurs around 40–80 mA, though higher currents may be required
- If capture is not achieved, reposition pads and reassess the pacing vector
Rate: Set the pacing rate at 60 bpm.
Beware of pseudo-pacing
Electrical spikes on the monitor do not confirm myocardial capture.
Always confirm mechanical capture using:
- Palpable pulse, preferably distant from the chest
- Pulse oximetry waveform synchronized with pacing spikes
- Bedside echocardiography showing ventricular contraction
If there is no pulse, there is no pacing.
Transcutaneous pacing is often painful and should be accompanied by appropriate analgesia and sedation whenever the patient’s clinical status allows.
This is usually the point where I would place a flowchart.
But the purpose of this post is to think beyond arrows and boxes.
So here is a checklist instead
What matters
1️⃣Is this actually a rhythm problem?
Not all bradycardia is primary “electrical disease”.
Use the BRADI mnemonic to look for reversible causes:
- B – BRASH / Hyperkalemia
- R – Reduced vitals (hypoxia, hypoglycemia, hypothermia with or without hypothyroidism)
- A – Acute coronary occlusion
- D – Drugs (beta-blockers, calcium channel blockers, digoxin)
- I – Intracranial pathology / Infection
Treat the underlying cause whenever possible.
2️⃣Is this a rhythm atropine actually works on?
Is the patient symptomatic?
Unstable bradycardia?
- Chest pain
- Hypotension
- Acute heart failure
- Altered mental status
- Signs of shock, including syncope
High risk rhythm?
- Mobitz II AV block
- Complete heart block with wide QRS
- Ventricular pauses greater than 3 seconds
- Recent asystole
These patients require treatment in the emergency department.
Is this a rhythm atropine can fix?
- Sinus bradycardia
- Vagal-mediated bradycardia
- Proximal AV block
If not, proceed early to pacing or vasoactive support.
3️⃣ Atropine didn’t work : Now what?
- Chronotropic or vasoactive agents - such as epinephrine or dopamine
Or
- Transcutaneous pacing
Do not wait for atropine to “kick in.” If the first dose of atropine is ineffective, prepare epinephrine and pacing simultaneously.
Want to Read More?
- Wigginton, Jane G., et al. "Part 9: adult advanced life support: 2025 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care." Circulation 152.16_suppl_2 (2025): S538-S577.
- Kusumoto, Fred M., et al. "2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society." Journal of the American College of Cardiology 74.7 (2019): e51-e156.
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