What is the management for a patient with a 3rd (third) degree heart block?

Management of Third-Degree Heart Block

Patients with third-degree atrioventricular block require immediate permanent pacing regardless of symptoms, as this condition poses significant mortality risk and should not be managed conservatively. 1

Initial Assessment and Stabilization

• Assess for signs of hemodynamic compromise including syncope, dyspnea, chest pain, hypotension, or altered mental status 1
• Establish IV access, provide supplemental oxygen if hypoxemic, and initiate continuous cardiac monitoring 1
• Obtain a 12-lead ECG to confirm the diagnosis and determine if the escape rhythm originates from the AV node (narrow QRS) or ventricles (wide QRS) 1, 2
• Evaluate for potentially reversible causes including acute myocardial infarction, drug effects, electrolyte abnormalities, or Lyme carditis 1, 3

Immediate Management

For Unstable Patients (Hypotension, Altered Mental Status, Chest Pain)

• Administer IV atropine 0.5-1.0 mg every 3-5 minutes up to a maximum total dose of 3 mg 1
  • Note: Atropine is often ineffective in third-degree AV block, especially with infranodal block (wide QRS), but should still be attempted while preparing for pacing 1, 4
• Initiate transcutaneous pacing immediately for symptomatic patients while preparing for transvenous pacing 1
• Consider vasopressor support (dopamine or epinephrine) if pacing is ineffective or unavailable 1

For All Patients with Third-Degree AV Block

• Arrange for urgent cardiology consultation for temporary transvenous pacing followed by permanent pacemaker implantation 1
• Hospitalize and continuously monitor all patients with third-degree heart block due to risk of sudden deterioration 1

Definitive Management

• Permanent pacemaker implantation is indicated for all patients with acquired third-degree AV block not attributable to reversible causes 1
• Even in cases where AV block is drug-induced, approximately 50% of patients will require permanent pacing due to persistence or recurrence of block after drug discontinuation 3
• For patients with third-degree AV block after myocardial infarction, permanent pacing is recommended regardless of symptom status 1

Special Considerations

Drug-Induced AV Block

• Discontinue potential culprit medications (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics) 3
• Despite medication discontinuation, 27% of patients may experience recurrence of AV block, necessitating permanent pacing 3
• Carvedilol-induced blocks tend to resolve permanently after drug discontinuation, while metoprolol-induced blocks often persist or recur 3

Lyme Carditis with Third-Degree AV Block

• For confirmed Lyme disease with third-degree AV block, parenteral antibiotics (ceftriaxone) should be initiated immediately 1
• Temporary pacing may be required until the conduction abnormality resolves 1
• Hospitalization and continuous monitoring are recommended for all patients with Lyme carditis and third-degree AV block 1

Post-Myocardial Infarction

• Third-degree AV block occurs in approximately 8% of patients following MI 2
• Permanent pacing is indicated for persistent third-degree AV block after MI regardless of symptom status 1
• Temporary pacing should be instituted immediately while arranging for permanent pacemaker implantation 1

Prognosis and Follow-up

• Without intervention, third-degree heart block carries significant mortality risk, especially with wide QRS escape rhythms (ventricular origin) 2
• After permanent pacemaker implantation, patients should be followed regularly to ensure proper device function 1
• Underlying causes (ischemia, infiltrative disease, etc.) should be addressed to improve long-term outcomes 1

Common Pitfalls to Avoid

• Relying solely on atropine for management of third-degree AV block, as it is frequently ineffective, especially in infranodal blocks 1, 4
• Delaying pacemaker implantation in asymptomatic patients with third-degree AV block 1
• Assuming drug-induced AV block will permanently resolve with medication discontinuation 3
• Failing to recognize third-degree AV block as a potential manifestation of acute myocardial infarction requiring urgent revascularization 2, 4