What are the treatments for first, second, and third degree (complete) heart blocks?

Treatment of Heart Blocks by Degree

First-Degree AV Block

First-degree AV block (PR interval >0.20 seconds) generally requires no treatment in asymptomatic patients, but permanent pacemaker implantation is reasonable when the PR interval exceeds 0.30 seconds and causes symptoms similar to pacemaker syndrome or hemodynamic compromise. 1, 2

Management Algorithm

Asymptomatic patients with PR <0.30 seconds:

• No treatment required 1, 2
• Monitor for progression, particularly in patients with structural heart disease 2

Symptomatic patients or PR ≥0.30 seconds:

• Assess for reversible causes first: medications (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics), electrolyte abnormalities (potassium, magnesium), or Lyme disease 2, 1
• Evaluate for symptoms of inadequate LV filling: fatigue, exercise intolerance, dyspnea, or pacemaker syndrome-like symptoms 2
• Check for hemodynamic compromise: hypotension or increased wedge pressure 2
• Permanent pacemaker implantation is reasonable (Class IIa) if symptomatic with hemodynamic compromise or pacemaker syndrome 1, 2

Acute symptomatic management:

• Atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg) may be considered for symptomatic bradycardia when the block is at the AV node level 2, 3
• Warning: Doses <0.5 mg may paradoxically slow heart rate further 2, 3

Critical Caveats

• Exercise-induced worsening of AV block (not due to ischemia) indicates His-Purkinje disease with poor prognosis and warrants permanent pacing 2
• Neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome, Erb dystrophy) may have unpredictable progression; permanent pacing may be considered even with first-degree block 1, 2
• First-degree block with wide QRS suggests infra-Hisian disease and requires closer monitoring 1

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Second-Degree AV Block

Mobitz Type I (Wenckebach)

Mobitz Type I second-degree AV block typically occurs at the AV node level and rarely requires pacing unless symptomatic, as it uncommonly progresses to complete heart block. 1

Management approach:

• Asymptomatic Type I at the AV node level: No pacing indicated 1
• Symptomatic bradycardia: Permanent pacemaker indicated 1
• If wide QRS complex is present, electrophysiological study should be performed to determine if block is infra-Hisian, which would warrant pacing 1

Acute management:

• Atropine 0.5 mg IV may improve AV nodal conduction temporarily 3
• Transcutaneous pacing patches should be applied for high-risk patients 1

Mobitz Type II

Mobitz Type II second-degree AV block is an infra-Hisian conduction abnormality with high risk of progression to complete heart block and requires permanent pacemaker implantation, even in asymptomatic patients. 1, 4

Management:

• Permanent pacemaker implantation is indicated (Class I) for all patients with symptomatic Mobitz Type II block 1
• Asymptomatic patients with Mobitz Type II should receive permanent pacing due to high risk of progression to complete heart block 4
• Temporary transvenous pacing is indicated as a bridge to permanent pacemaker 1

Key distinguishing features:

• Constant PR intervals before and after blocked beats 4
• Usually associated with wide QRS complex due to infra-Hisian location 4
• Common in anterior wall MI with extensive myocardial necrosis 4

Critical pitfall:

• 2:1 AV block cannot be classified as Type I or Type II by ECG alone; requires exercise testing or electrophysiological study to determine anatomic level 4

High-Grade Second-Degree Block

Advanced second-degree AV block (≥2 consecutive blocked P waves) should be managed similarly to third-degree block with urgent temporary pacing and permanent pacemaker implantation. 1

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Third-Degree (Complete) AV Block

Third-degree AV block is a cardiovascular emergency requiring immediate temporary pacing (transcutaneous or transvenous) followed by permanent pacemaker implantation in nearly all cases. 1, 5

Immediate Management

Unstable patients (hypotension, altered mental status, chest pain, heart failure):

1. Atropine 0.5-1.0 mg IV bolus (may repeat every 3-5 minutes to maximum 3 mg) 3, 5

   • More effective if escape rhythm has narrow QRS (suggesting AV nodal level block) 3
   • Less effective with wide QRS escape rhythms (ventricular escape) 5

2. Transcutaneous pacing immediately if atropine ineffective or while preparing for transvenous pacing 1, 5

   • Apply patches prophylactically in high-risk patients 1
   • Note: Transcutaneous pacing is painful; use for urgent stabilization only 1

3. Transvenous temporary pacemaker placement (via internal jugular, subclavian, or femoral vein) 1, 5

   • Preferred definitive temporary solution 1
   • Bridge to permanent pacemaker 5

Indications for Permanent Pacemaker (Class I)

Permanent pacemaker implantation is indicated for: 1

• Third-degree AV block at any anatomic level with symptomatic bradycardia, heart failure, or ventricular arrhythmias
• Third-degree AV block requiring medications that cause symptomatic bradycardia
• Asymptomatic third-degree AV block with:
  • Documented pauses ≥3.0 seconds OR
  • Escape rate <40 bpm OR
  • Escape rhythm below the AV node (wide QRS) OR
  • Cardiomegaly or LV dysfunction present
• Third-degree AV block in atrial fibrillation with pauses ≥5 seconds
• Post-catheter ablation of AV junction
• Postoperative AV block not expected to resolve
• Neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome, Erb dystrophy)
• Exercise-induced third-degree AV block without myocardial ischemia

Special Clinical Contexts

Acute myocardial infarction:

• Inferior MI: AV block usually at nodal level, may be transient; temporary pacing indicated if symptomatic 1
• Anterior MI: AV block usually infra-Hisian with extensive necrosis and high mortality; temporary pacing followed by permanent pacemaker indicated 1, 4
• Persistent second- or third-degree AV block with bilateral bundle branch block after MI requires permanent pacemaker 1

Lyme carditis:

• Hospitalization and continuous monitoring required for symptomatic patients or second/third-degree block 1
• Parenteral antibiotics (ceftriaxone) recommended initially for hospitalized patients 1
• Temporary pacemaker may be required but can be discontinued when block resolves 1
• Treatment duration: 14-21 days 1

Drug-induced block:

• Permanent pacing may be considered if block is expected to recur even after drug withdrawal 1

Prognosis and Risk Stratification

Escape rhythm characteristics predict stability: 5

• Narrow QRS escape (40-60 bpm): AV nodal or high His-Purkinje origin, more stable 5
• Wide QRS escape (20-40 bpm): Ventricular origin, less stable, higher risk of asystole 5

Mortality considerations:

• Complete heart block occurs in 8% of post-MI patients 5
• Anterior MI with complete heart block has particularly poor prognosis due to extensive necrosis 4
• Permanent pacing improves survival, especially in patients with syncope 1