For an elderly patient with a history of cerebral vascular accident (CVA) infarct, diabetes, and third-degree atrioventricular (AV) block with a narrow QRS complex, who has not responded to atropine, would epinephrine still be the recommended next step?

Third-Degree AV Block with Narrow QRS: Epinephrine After Failed Atropine

For third-degree AV block with a narrow QRS complex that has not responded to atropine, epinephrine is an appropriate next-line pharmacologic agent while preparing for transcutaneous or transvenous pacing. 1, 2, 3

Why the Narrow QRS Changes Management

The narrow QRS complex is critical because it indicates the block is likely at the AV nodal level (supranodal) rather than infranodal (His-Purkinje system), which fundamentally changes the response to medications 1:

• Nodal-level blocks are associated with a faster, more reliable junctional escape mechanism and will sometimes respond to catecholamines like epinephrine 1
• Infranodal blocks (wide QRS) are unresponsive to atropine and catecholamines, requiring immediate pacing 1, 2

In unusual circumstances, particularly at night with accompanying sinus slowing, a vagal etiology may be considered especially when the QRS is narrow, suggesting the block may still have some autonomic component 1

Pharmacologic Bridge to Pacing

While atropine remains first-line for symptomatic bradycardia, epinephrine serves as a reasonable temporizing measure when atropine fails 1, 3:

• Epinephrine dosing: 2-10 mcg/min IV (or 0.1-0.5 mcg/kg/min) titrated to desired heart rate and blood pressure effect 3
• Alternative beta-adrenergic agents include dopamine (5-20 mcg/kg/min) or isoproterenol (1-20 mcg/min), though isoproterenol carries higher risk of increasing myocardial oxygen demand 3

Critical Caveats in This Patient

Given the patient's history of CVA, diabetes, and elderly age, several important considerations apply:

Myocardial Ischemia Risk

• Epinephrine increases cardiac output and causes peripheral vasoconstriction, which may induce cardiac arrhythmias and myocardial ischemia, especially in patients with coronary artery disease 4
• Increased heart rate from any chronotropic agent may worsen ischemia or increase infarct size if acute coronary syndrome is present 1, 5
• However, bradycardia-induced hypoperfusion itself worsens ischemia, making treatment of symptomatic bradycardia essential despite these risks 5

Monitoring Requirements

• Monitor blood pressure frequently during epinephrine infusion, as individual response varies significantly and excessive hypertension can occur 4
• Continuous ECG monitoring is essential to detect progression of conduction abnormalities or development of arrhythmias 3

Definitive Management: Pacing

Epinephrine should never delay preparation for pacing 1:

• Transcutaneous pacing is the preferred immediate intervention for unstable patients and should be initiated while preparing for transvenous access 1, 2, 3
• Transvenous pacing is indicated for definitive management when third-degree AV block persists 1, 2
• Even with narrow QRS suggesting nodal-level block, third-degree AV block requires pacing as the definitive treatment, as pharmacologic support is only temporizing 1, 2

Why Not Just Pacing Alone?

While pacing is definitive, pharmacologic support with epinephrine provides several advantages:

• Transcutaneous pacing is painful in conscious patients and may not achieve consistent capture 1
• Epinephrine can stabilize hemodynamics while IV access for transvenous pacing is being established 3
• In the context of possible vagal-mediated block (narrow QRS), catecholamines may restore conduction temporarily 1

The key is to use epinephrine as a bridge, not a destination—prepare for pacing simultaneously. 1, 2