What is the management of heart block?

Management of Heart Block

The management of heart block depends on the type, location, hemodynamic consequences, and underlying cause, with temporary or permanent pacing indicated for symptomatic or high-risk cases. 1

Types of Heart Block and Initial Assessment

Heart block is classified into three main categories:

• First-degree AV block: PR interval >0.20 seconds
• Second-degree AV block:
  • Type I (Mobitz I/Wenckebach): Progressive PR prolongation until a beat is dropped
  • Type II (Mobitz II): Sudden failure of conduction without PR prolongation
• Third-degree (Complete) AV block: Complete dissociation between atria and ventricles

Key Assessment Parameters:

• Heart rate and blood pressure
• Presence of symptoms (syncope, pre-syncope, dyspnea, fatigue)
• ECG findings (QRS width, escape rhythm rate)
• Location of block (AV nodal vs. infranodal)
• Associated conditions (MI, myocarditis, medication effects)

Management Algorithm by Heart Block Type

First-Degree AV Block:

• Generally requires no treatment 1
• Monitor if PR interval is markedly prolonged (>0.30s) with symptoms 2
• Consider pacing only if hemodynamically compromised or with symptoms similar to pacemaker syndrome 1

Second-Degree AV Block:

1. Type I (Mobitz I):

   • If asymptomatic: Observation only
   • If symptomatic or with hypotension:
     • IV atropine 0.5-1mg (initial dose 0.3-0.5mg, may repeat up to 1.5-2.0mg) 1
     • If no response to atropine, temporary pacing 1

2. Type II (Mobitz II):

   • Temporary pacing electrode insertion regardless of symptoms 1
   • Urgent angiography with view to revascularization if no prior reperfusion therapy 1
   • Permanent pacing usually required 1

Third-Degree (Complete) AV Block:

• Immediate temporary pacing for symptomatic patients 1
• IV atropine 0.5-1mg if associated with inferior MI (may be ineffective if infranodal block) 1
• Permanent pacemaker for persistent block 1
• AV sequential pacing for patients with RV infarction and hemodynamic compromise 1

Special Considerations by Etiology

Acute Myocardial Infarction:

• Inferior MI: Heart block often transient and at AV nodal level

  • First-line: IV atropine for symptomatic bradycardia 1
  • Temporary pacing if no response to atropine or hemodynamic compromise 1

• Anterior MI: Heart block often infranodal with extensive damage

  • New bundle branch block or hemiblock indicates high risk for complete AV block 1
  • Prophylactic temporary pacing wire placement may be warranted 1
  • Permanent pacing for persistent block 1

Myocarditis:

• Temporary pacing for symptomatic heart block during acute phase 1
• Permanent pacing for persistent AV block 1
• Device selection should reflect LV dysfunction status 1
• Earlier impulse generator implantation may be considered for giant cell myocarditis or sarcoidosis 1

Drug-Induced:

• Discontinue offending medications if possible 3
• Temporary pacing until drug effects resolve 1
• Consider permanent pacing if no alternative therapy available (e.g., thalidomide) 1

Specific Interventions

Pharmacological Management:

• Atropine: First-line for symptomatic sinus bradycardia or AV nodal block
  • Dosage: 0.3-0.5mg IV, may repeat up to total of 1.5-2.0mg 1
  • Mechanism: Competitive antagonism of muscarinic acetylcholine receptors 4
  • Caution: May be ineffective or harmful in infranodal block 1

Pacing Indications:

• Temporary pacing:

  • Symptomatic bradycardia unresponsive to atropine 1
  • New or indeterminate age bifascicular block with first-degree AV block 1
  • Mobitz type II second-degree AV block 1
  • Complete heart block with hemodynamic compromise 1

• Permanent pacing:

  • Persistent advanced AV block after MI 1
  • Symptomatic AV block at any level 1
  • Transient advanced AV block with associated bundle branch block 1

Common Pitfalls and Caveats

• Avoid pacemaker implantation during acute phase of myocarditis 1
• Don't use atropine in infranodal blocks (may worsen block) 1
• Don't overlook reversible causes of heart block (electrolyte abnormalities, medication effects, ischemia) 3
• First-degree AV block is not always benign - may progress to higher-grade block requiring pacing 5
• Avoid verapamil in patients with AV block as it may worsen conduction 1
• Recognize that new bundle branch blocks or hemiblocks in anterior MI indicate high risk for developing complete AV block 1

Heart block management requires prompt recognition of the type and hemodynamic significance, with appropriate intervention based on symptoms, location of block, and underlying etiology. Temporary measures should be instituted for acute symptomatic cases, while permanent solutions address persistent conduction abnormalities.