What is the recommended management for a patient with Mobitz type II atrioventricular block and left bundle‑branch block?

Management of Mobitz Type II AV Block with Left Bundle Branch Block

Permanent pacemaker implantation is mandatory for all patients with Mobitz Type II AV block, regardless of symptoms, and this indication is not altered by the presence of left bundle branch block. 1, 2

Immediate Stabilization

• Place transcutaneous pacing pads immediately upon recognition of Mobitz Type II, as this rhythm has unpredictable and potentially life-threatening progression to complete heart block 2
• Arrange for urgent transvenous temporary pacing if the patient is hemodynamically unstable, using femoral, internal jugular, or subclavian venous access to reach the right ventricular apex 2
• Atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg total) may be attempted for temporary stabilization, though it is often ineffective since Mobitz Type II occurs in the His-Purkinje system below the AV node 2
• Maintain continuous cardiac monitoring until permanent pacemaker placement 2

Diagnostic Evaluation Before Pacemaker

• Obtain serum electrolytes immediately (potassium, magnesium, calcium, sodium) and renal function to identify reversible causes, particularly in patients with acute kidney injury where hyperkalemia can worsen AV block 2
• Perform transthoracic echocardiography (Class I recommendation) to assess for structural heart disease, infiltrative cardiomyopathy (sarcoidosis, amyloidosis), or ventricular dysfunction 2
• Consider cardiac MRI if echocardiogram suggests infiltrative disease, myocarditis, or to assess for myocardial scar 2

Permanent Pacemaker Implantation

The combination of Mobitz Type II with LBBB represents infranodal disease in the His-Purkinje system and is a Class I indication for permanent pacing, even in asymptomatic patients. 1, 2

Key Points About Pacemaker Indication:

• The block occurs in the His-Purkinje system with slow, unreliable escape mechanisms, making progression to complete heart block unpredictable and potentially fatal 2, 3
• Historical data shows 75% of patients with Mobitz Type II experienced syncopal attacks, and prophylactic pacing prevents Adams-Stokes syndrome and sudden death 3
• Pacemaker placement should not be delayed even if electrolytes normalize, as the underlying conduction system disease remains 2

Device Selection:

• Dual-chamber pacemakers should be programmed to maintain native AV conduction when possible to prevent pacing-induced ventricular dysfunction 2
• Consider ICD capability (Class IIa recommendation) in patients with:
  • Neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome) requiring pacing with meaningful survival >1 year expected 2
  • Infiltrative cardiomyopathies (cardiac sarcoidosis, amyloidosis) 2
  • Hypertrophic cardiomyopathy at high risk for sudden cardiac death 1

Special Clinical Scenarios

Post-Procedural Mobitz Type II:

• Pacemaker implantation is recommended before discharge (Class I) for persistent Mobitz Type II after alcohol septal ablation, surgical myectomy, tricuspid valve surgery, or TAVR 1, 2
• Most postoperative AV block recovers within 7-10 days; if Mobitz Type II persists beyond this period, permanent pacing is indicated 2

Acute Myocardial Infarction:

• Mobitz Type II in the setting of acute MI represents a Class Ia indication for temporary transvenous pacing, followed by permanent pacemaker if block persists after a waiting period 1, 2
• The waiting period allows assessment for resolution of ischemia-related conduction abnormalities 1

Post-TAVR with New LBBB:

• New LBBB occurs in approximately 10% of patients after TAVR and resolves in approximately 50% at 6-12 months 1
• Patients developing Mobitz Type II with new LBBB post-TAVR require permanent pacing before discharge 4
• An HV interval ≥65 ms after TAVR modestly predicts development of high-grade AV block (sensitivity 80%, specificity 79%) 1

Critical Pitfalls to Avoid

• Do not confuse Mobitz Type II with Mobitz Type I (Wenckebach): Type II shows constant PR intervals before and after blocked beats, while Type I demonstrates progressive PR prolongation 2, 5
• Do not delay pacemaker placement for extensive workup if the diagnosis is clear and no obvious reversible cause exists 2
• Avoid exercise stress testing in confirmed Mobitz Type II, as exercise can worsen AV block in His-Purkinje disease and is potentially dangerous 2
• Do not rely on atropine for definitive management, as it rarely improves infranodal block 2
• Recognize that asymptomatic status does not change the indication: Mobitz Type II is a Class I indication for pacing regardless of symptoms due to unpredictable progression 1, 2, 3

Prognosis

• Permanent pacing improves survival in patients with high-grade AV block, especially if syncope has occurred 2
• Without pacing, Mobitz Type II carries high risk of progression to complete heart block with potential for sudden death 3, 5
• The site of block in the His-Purkinje system is the most important determinant of prognosis, making prophylactic pacing essential 3