What is the treatment for heart block?

Treatment for Heart Block

For heart block, treatment depends on the type and severity, with permanent pacemaker implantation indicated for symptomatic bradycardia, all type II second-degree AV block (even if asymptomatic), and third-degree AV block. 1

Classification of Heart Block

Heart block is classified into three main types:

1. First-degree AV block: Prolonged PR interval (>0.20 seconds)

   • Generally benign and requires no treatment unless PR interval is severely prolonged (>0.30 seconds) causing symptoms 2
   • May cause symptoms similar to pacemaker syndrome when PR interval exceeds 0.30 seconds 3

2. Second-degree AV block:

   • Type I (Mobitz I/Wenckebach): Progressive PR prolongation until a P wave is not conducted
     • Usually occurs at AV node level
     • Often benign, especially in inferior MI
   • Type II (Mobitz II): Sudden failure of P wave conduction without PR prolongation
     • Usually occurs below AV node in His-Purkinje system
     • Higher risk of progression to complete heart block 4

3. Third-degree (complete) AV block: No atrial impulses conducted to ventricles 5

Acute Management

For Symptomatic Bradycardia:

1. First-line treatment: Atropine 0.5-1 mg IV every 3-5 minutes (maximum 3 mg) 1, 6

   • Atropine blocks vagal effects, increases heart rate
   • Most effective for sinus bradycardia and AV nodal blocks
   • Can prevent or abolish bradycardia and asystole 6

2. If atropine ineffective:

   • Epinephrine 2-10 μg/min IV infusion or
   • Dopamine 2-10 μg/kg/min IV infusion 1

3. Transcutaneous pacing for unstable patients not responding to medications 1

4. Temporary transvenous pacing for patients refractory to medical therapy 1

Indications for Permanent Pacemaker

1. Absolute indications (Class I):

   • Third-degree and advanced second-degree AV block with symptoms
   • Type II second-degree AV block (even if asymptomatic)
   • Symptomatic bradycardia regardless of type or site of block 1

2. Reasonable indications (Class IIa):

   • Asymptomatic persistent third-degree AV block with adequate escape rhythm
   • First-degree AV block with PR interval >0.30 seconds causing symptoms similar to pacemaker syndrome 4, 3

3. Special cases:

   • Bifascicular or trifascicular block with intermittent second or third-degree AV block 4
   • AV block associated with Lyme disease requires antibiotic treatment and may need temporary pacing 4

Special Considerations

1. First-degree AV block:

   • Generally requires no treatment unless PR interval >0.30 seconds with symptoms 4, 2
   • Consider exercise testing as symptoms may worsen during activity 3

2. AV block in myocardial infarction:

   • For inferior MI with AV block: Often transient and responds to atropine 4
   • For anterior MI with AV block: Higher risk, often requires pacing 4

3. Medication-induced AV block:

   • Identify and discontinue offending agents (beta-blockers, calcium channel blockers, digoxin)
   • Consider reversible causes before permanent pacing 1

4. Bifascicular and trifascicular block:

   • Higher risk of progression to complete heart block
   • Pacing indicated with syncope or evidence of severe conduction disturbance 4, 7

Effectiveness of Treatment

• Atropine is effective in approximately 50% of cases of symptomatic bradycardia 8
• Permanent pacing significantly improves survival in patients with complete heart block 4
• For first-degree AV block with left ventricular dysfunction, biventricular pacing may be preferred over conventional DDD pacing 3

Pitfalls to Avoid

• Delaying pacemaker implantation in patients with Mobitz type II block
• Using medications that worsen AV block without appropriate pacing backup
• Attributing AV block solely to medications when underlying conduction disease may be present
• Failing to monitor patients with bifascicular block for progression to complete heart block 1

Remember that heart block treatment should focus on preventing life-threatening bradycardia and its hemodynamic consequences, with permanent pacing being the definitive treatment for high-grade and symptomatic AV blocks.