What is the management of second degree heart block?

Management of Second Degree Heart Block

Permanent pacing is recommended for patients with acquired second-degree Mobitz type II atrioventricular block, high-grade atrioventricular block, or third-degree atrioventricular block not attributable to reversible or physiologic causes, regardless of symptoms. 1

Types of Second Degree Heart Block and Initial Assessment

Second degree heart block is characterized by intermittent failure of atrial impulses to conduct to the ventricles. There are two main types:

1. Mobitz Type I (Wenckebach):

   • Progressive PR interval prolongation before a blocked beat
   • Usually occurs at the AV node level
   • Generally considered more benign than Type II

2. Mobitz Type II:

   • Constant PR interval in conducted beats with sudden failure of conduction
   • Usually occurs below the AV node (infranodal)
   • Higher risk of progression to complete heart block

3. 2:1 AV Block:

   • Cannot be classified as Type I or II based on surface ECG alone
   • May be nodal or infranodal in origin

Acute Management Algorithm

1. Assess hemodynamic stability and symptoms:

   • If unstable (hypotension, altered mental status, chest pain, heart failure):
     • Administer atropine 0.5 mg IV (may repeat to maximum 2.0 mg) for symptomatic bradycardia 1, 2
     • Consider beta-adrenergic agonists (isoproterenol, dopamine, dobutamine) if no response to atropine and low likelihood of coronary ischemia 1

2. Implement temporary pacing if medical therapy fails:

   • Transcutaneous pacing for immediate stabilization (though painful) 1
   • Progress to temporary transvenous pacing if needed 1

Chronic Management Based on Block Type and Symptoms

Mobitz Type II Second Degree AV Block:

• Permanent pacing recommended regardless of symptoms 1
• Higher risk of progression to complete heart block and sudden death 3, 4

Mobitz Type I (Wenckebach):

• With symptoms clearly attributable to AV block: Permanent pacing is reasonable 1
• Without symptoms: No permanent pacing needed, but close monitoring recommended 1
• Caution: Long-term studies show chronic Mobitz type I may have similar prognosis to Mobitz type II if left untreated 4

2:1 AV Block:

• Requires additional evaluation to determine level of block
• If symptomatic or evidence suggests infranodal block: Consider permanent pacing 1

Special Considerations

1. Reversible causes: Treat underlying cause first (medications, electrolyte abnormalities, myocarditis) 1

   • Permanent pacing should not be performed if block resolves with treatment 1

2. Vagally mediated AV block:

   • Permanent pacing should not be performed if asymptomatic 1

3. Neuromuscular diseases or infiltrative cardiomyopathies:

   • Permanent pacing recommended with second-degree AV block regardless of symptoms 1
   • Consider additional defibrillator capability if indicated 1

4. Pediatric patients:

   • Children with concerning second-degree block have ~30% risk of progression to complete heart block 5
   • Risk factors for progression: block at maximum sinus rate, below normal average heart rate, 2:1 block on initial ECG 5

Additional Testing for Chronic Management

1. Ambulatory ECG monitoring: Reasonable for patients with symptoms and first-degree or Mobitz type I block to establish symptom correlation 1

2. Exercise testing: Reasonable for patients with exertional symptoms and first-degree or Mobitz type I block at rest 1

3. Electrophysiology study: May be considered in selected patients with second-degree AV block to determine level of block 1

Common Pitfalls to Avoid

1. Misclassification of block type: Ensure correct diagnosis between Mobitz I and II, as management differs 6

2. Overlooking pseudo-AV block: Concealed His bundle or ventricular extrasystoles may mimic second-degree AV block 6

3. Assuming all Mobitz type I blocks are benign: Chronic Mobitz type I block may have similar long-term outcomes to Mobitz type II if left untreated 4

4. Delaying pacing in high-risk patients: Patients with Mobitz type II have high risk of progression to complete heart block and should receive prompt intervention 3, 4