What is the management plan for a new Mobitz (second-degree atrioventricular block) II block?

Management of New Mobitz II Atrioventricular Block

Permanent pacemaker implantation is recommended for all patients with newly diagnosed Mobitz type II second-degree atrioventricular block, regardless of symptoms, due to high risk of progression to complete heart block and sudden death. 1

Initial Assessment and Stabilization

• Hemodynamic stability assessment:

  • If unstable with symptomatic bradycardia: Administer atropine 0.5 mg IV (may repeat to maximum 3.0 mg) 1
  • Note: Atropine may be ineffective in Mobitz II block as the block is typically below the AV node 1
  • Consider transcutaneous pacing for immediate stabilization if medical therapy fails 1

• Diagnostic evaluation:

  • 12-lead ECG to confirm diagnosis and identify associated conduction abnormalities
  • Transthoracic echocardiogram to exclude structural heart disease 1
  • Laboratory tests to rule out reversible causes (thyroid function, electrolytes, pH) 1

Definitive Management

Indications for Permanent Pacing

• Class I recommendation (strong): Permanent pacemaker implantation for:

  • All patients with Mobitz type II AV block regardless of symptoms 1
  • Patients with high-grade AV block or third-degree AV block 1

• Important considerations:

  • Mobitz type II block is abnormal and not a normal physiologic finding (unlike some cases of Mobitz type I/Wenckebach) 1
  • The site of block in Mobitz II is almost always below the AV node (infranodal) 2
  • High risk of progression to complete heart block with potential for Adams-Stokes syndrome and sudden death 3

Special Circumstances

• Patients with neuromuscular diseases or infiltrative cardiomyopathies:

  • Permanent pacing with additional defibrillator capability if needed and meaningful survival >1 year is expected 1

• Distinguishing from other conditions:

  • Important to differentiate true Mobitz II from 2:1 Wenckebach physiology
  • Exercise testing may help distinguish between the two 1
  • Electrophysiology study may be required in rare cases to determine the level of block 1

Follow-up Care

• After pacemaker implantation:
  • Device check before discharge
  • Follow-up within 2-12 weeks of implantation
  • Regular device checks as per standard protocol (typically every 6-12 months)

Pitfalls and Caveats

• Misdiagnosis risk: "Apparent Mobitz type II block" can occur in vagally-mediated AV block, which has a more benign prognosis 4, 5

• Avoid delaying therapy: Do not delay permanent pacemaker implantation in confirmed Mobitz II block, even in asymptomatic patients, due to high risk of progression to complete heart block 3

• Ineffective treatments: Atropine is often ineffective in Mobitz II block as the block is typically located in non-nodal tissue (bundle of His or more distal conduction system) 1

• Pseudo AV block: Concealed His bundle or ventricular extrasystoles may mimic Mobitz II block and should be ruled out 5