What are the treatment options for heart block?

Treatment Options for Heart Block

Treatment of heart block should follow a stepwise approach based on the type of block, symptoms, and hemodynamic stability, with permanent pacing indicated for symptomatic second-degree or third-degree AV block that is not due to reversible causes. 1

Initial Assessment and Management

Acute Medical Therapy for Symptomatic AV Block

1. First-line medication:

   • Atropine 0.5-1 mg IV is reasonable for patients with second-degree or third-degree AV block at the AV nodal level with symptoms or hemodynamic compromise 1, 2
   • Can be repeated every 3-5 minutes as needed (maximum total dose of 3 mg) 2
   • Caution: Atropine has limited effectiveness in infranodal block and may be ineffective in type II second-degree or third-degree AV block with wide QRS complexes 3

2. Second-line medications (if atropine fails):

   • Beta-adrenergic agonists may be considered for symptomatic second-degree or third-degree AV block with low likelihood for coronary ischemia 1:
     • Isoproterenol (2-10 μg/min IV infusion)
     • Dopamine (2-10 μg/kg/min IV infusion)
     • Dobutamine
     • Epinephrine

3. Special situations:

   • For AV block during acute inferior MI: IV aminophylline may be considered 1
   • For beta-blocker or calcium channel blocker overdose: Glucagon, high-dose insulin therapy, and IV calcium 2

Temporary Pacing

1. Transcutaneous pacing:

   • May be considered for patients with second-degree or third-degree AV block and hemodynamic compromise refractory to medical therapy 1
   • Used as a bridge until transvenous pacing or permanent pacemaker is placed 1

2. Temporary transvenous pacing:

   • Reasonable for patients with symptomatic second-degree or third-degree AV block refractory to medical therapy 1
   • For prolonged temporary pacing, an externalized permanent active fixation lead is preferred over standard passive fixation temporary pacing lead 1

Permanent Pacing

Indications for Permanent Pacemaker Implantation

1. Definite indications (Class I):

   • Symptomatic second-degree or third-degree AV block 1
   • Persistent second-degree AV block in the His-Purkinje system with bilateral bundle branch block 1
   • Third-degree AV block with symptoms 2
   • Symptomatic AV block attributable to a known reversible cause that does not resolve despite treatment 1

2. Reasonable indications (Class IIa):

   • Symptomatic patients on chronic stable doses of medically necessary antiarrhythmic or beta-blocker therapy causing AV block 1
   • Second-degree or third-degree AV block associated with cardiac sarcoidosis 1
   • Persistent second- or third-degree AV block at the AV node level, even without symptoms 1

3. May be considered (Class IIb):

   • Symptomatic second-degree or third-degree AV block associated with thyroid function abnormalities without clinical myxedema 1

Pacing Mode Selection

• Dual-chamber pacing is recommended for patients in sinus rhythm 2
• Single-chamber ventricular pacing is reasonable for patients with permanent atrial fibrillation or significant comorbidities 1, 2

Management Based on Type and Etiology of Heart Block

Reversible Causes

1. Drug-induced AV block:

   • Identify and discontinue medications that worsen AV conduction (digitalis, beta-blockers, calcium channel blockers) 2
   • For patients on chronic stable doses of medically necessary medications, permanent pacing may be reasonable without waiting for drug washout 1

2. Lyme carditis:

   • Medical therapy with antibiotics and supportive care, including temporary pacing if necessary 1
   • Parenteral antibiotics (e.g., ceftriaxone) recommended for hospitalized patients 1
   • Permanent pacing typically not needed as AV block usually resolves with treatment 1

3. Acute myocardial infarction:

   • Inferior MI: AV block usually occurs at AV node level and may respond to atropine 2, 4
   • Anterior MI: AV block usually infranodal, associated with extensive myocardial damage, higher mortality risk, and often requires permanent pacing 2

First-Degree AV Block

• Generally considered benign, but may warrant monitoring
• Permanent pacing may be reasonable when PR interval exceeds 0.3 seconds and causes symptoms similar to pacemaker syndrome 1, 5
• Recent evidence suggests first-degree AV block may be a marker for progression to higher-grade block in some patients 6

Pitfalls and Caveats

1. Do not delay pacing in hemodynamically unstable patients with high-grade AV block
2. Atropine ineffective in:
   • Type II second-degree or third-degree AV block with wide QRS complexes 3
   • Patients with transplanted hearts 3
   • Infranodal block 2
3. Early vs. late AV block in inferior MI:
   • Early AV block (within 6 hours) often responds to atropine and resolves within 24 hours 4
   • Late AV block (after 6 hours) typically has longer duration, responds poorly to atropine, and may require pacing 4
4. Permanent pacing should not be performed for transient AV block due to reversible and non-recurrent causes that have completely resolved 1

By following this structured approach to heart block management, clinicians can provide appropriate treatment based on the type, etiology, and clinical presentation of AV block to improve patient outcomes and quality of life.