Management of Bradycardia Post-CABG
Atropine 0.5-1 mg IV is the initial treatment for symptomatic bradycardia after CABG surgery, repeated every 3-5 minutes as needed up to a maximum total dose of 3 mg. 1, 2, 3
Initial Assessment
Before initiating treatment, rapidly assess whether the bradycardia is causing hemodynamic compromise: 2
- Altered mental status
- Ischemic chest discomfort
- Acute heart failure
- Hypotension (systolic BP <90 mm Hg)
- Other signs of shock
Establish IV access, initiate continuous cardiac monitoring, obtain a 12-lead ECG, and ensure adequate oxygenation. 2
First-Line Treatment: Atropine
Administer atropine 0.5-1 mg IV bolus as initial therapy. 1, 2 This can be repeated every 3-5 minutes up to a maximum cumulative dose of 3 mg. 1, 2
Critical Dosing Considerations
- Never give doses <0.5 mg, as this may paradoxically worsen bradycardia through central vagal stimulation. 2, 3, 4
- Atropine works by competitive antagonism of muscarinic acetylcholine receptors, blocking vagal effects on the heart. 3
- Peak effect occurs 7-8 minutes after IV administration. 3
When Atropine May Be Ineffective
Atropine is likely to fail in: 2
- Type II second-degree AV block (infranodal block)
- Third-degree AV block with wide QRS complex (His-Purkinje level block)
- Post-cardiac transplant patients (denervated hearts)
In these scenarios, atropine may actually cause paradoxical worsening with ventricular standstill or high-degree AV block. 1, 2, 4
Second-Line Treatment: Chronotropic Agents
If bradycardia persists despite full-dose atropine (3 mg total), initiate IV infusion of β-adrenergic agonists while preparing for transcutaneous pacing. 1, 2
Dopamine
- Starting dose: 5-10 mcg/kg/min IV infusion 1, 2
- Titrate by 2-5 mcg/kg/min every 2-5 minutes based on heart rate and blood pressure response 2
- At 5-20 mcg/kg/min, provides both chronotropic and inotropic effects through β1-adrenergic stimulation 2
- Do not exceed 20 mcg/kg/min due to excessive vasoconstriction and arrhythmia risk 2
Epinephrine
- Starting dose: 2-10 mcg/min IV infusion 1, 2
- Alternative dosing: 0.1-0.5 mcg/kg/min 2
- Preferred over dopamine when severe hypotension requires both strong chronotropic and vasopressor support 2
- Use with extreme caution in acute coronary ischemia, as increased heart rate may worsen ischemia or extend infarct size 2, 5
Isoproterenol
- Dose: 1-20 mcg/min IV infusion 2
- Provides pure β-adrenergic effects (chronotropy and inotropy) without vasoconstriction 2
- May be preferable in ischemic cardiomyopathy with bradycardia, as it avoids the vasoconstrictive effects of epinephrine 2
Third-Line Treatment: Transcutaneous Pacing
Initiate transcutaneous pacing (TCP) immediately if the patient remains hemodynamically unstable despite atropine. 1, 2
- TCP is a Class IIa recommendation for unstable bradycardia unresponsive to atropine 1
- Serves as a temporizing measure while preparing for transvenous pacing if needed 1
- Requires sedation/analgesia in conscious patients due to pain from muscle contractions 2
- A randomized trial showed identical survival rates (~70%) between dopamine and TCP for atropine-refractory bradycardia 2
Special Considerations in Post-CABG Patients
Risk Factors for Severe Bradyarrhythmias
Post-CABG patients at highest risk for requiring permanent pacing include those with: 6
- Age >64 years
- Preoperative complete left bundle branch block (5-fold increased risk)
- Concomitant LV aneurysmectomy
- More leftward frontal plane QRS axis
Common Pitfalls
Avoid atropine in suspected infranodal block (Type II second-degree or third-degree AV block with wide QRS), as it may precipitate complete heart block or ventricular standstill. 2, 4
Do not delay TCP while giving additional atropine doses in hemodynamically unstable patients—TCP should be initiated simultaneously with second-line pharmacologic therapy. 2
Excessive atropine dosing (>3 mg total) may cause central anticholinergic syndrome with confusion, agitation, and hallucinations. 2, 3
Higher initial atropine doses (1.0 mg vs. 0.5-0.6 mg) and cumulative doses >2.5 mg over 2.5 hours are associated with increased adverse effects including ventricular tachycardia/fibrillation and sustained sinus tachycardia. 5
Monitoring
Continue cardiac monitoring during and after treatment, evaluating: 2
- Heart rate response
- Blood pressure stabilization
- Resolution of symptoms (mental status, chest pain, signs of shock)
Approximately 0.8% of post-CABG patients develop prolonged bradyarrhythmias (mean duration 10.5 days) requiring permanent pacemaker insertion. 6