Management of Mobitz Type II Second-Degree AV Block
Immediate First Step
The first step is to place transcutaneous pacing pads immediately and arrange for urgent permanent pacemaker implantation, as Mobitz Type II carries high risk of unpredictable progression to complete heart block. 1
Initial Management Algorithm
Immediate Actions (Within Minutes)
- Apply transcutaneous pacing pads immediately upon recognition of Mobitz Type II, as the American College of Cardiology emphasizes the high risk of sudden progression to complete heart block 1
- Initiate continuous cardiac monitoring until permanent pacemaker placement 1
- Assess hemodynamic status for signs of compromise including hypotension or low cardiac output 1
Urgent Diagnostic Workup (Within Hours)
- Obtain transthoracic echocardiography (Class I recommendation) to assess for underlying structural heart disease 1
- Draw serum electrolytes and complete laboratory panel to identify reversible causes such as hyperkalemia 1
- Both tests should be performed, but neither should delay pacemaker placement 1
Definitive Management
- Arrange for permanent pacemaker implantation urgently - this is a Class I indication for all patients with Mobitz Type II, even if asymptomatic 1, 2
- The block occurs in the His-Purkinje system with unpredictable and potentially life-threatening progression, making pacemaker placement mandatory regardless of symptoms 1
Why Neither Echocardiogram Nor Electrolytes Alone Is the Answer
While both echocardiography and serum electrolytes are recommended in the initial workup 1, the true first step is immediate preparation for potential hemodynamic collapse by placing transcutaneous pacing pads. The echocardiogram helps identify structural disease but doesn't change the immediate management need for pacing capability 1. Electrolytes may reveal reversible causes like hyperkalemia 3, but Mobitz Type II typically represents infranodal conduction system disease 2, 4 rather than a metabolic derangement.
Critical Pitfalls to Avoid
- Never delay pacemaker placement - Mobitz Type II can progress rapidly and unpredictably to complete heart block with hemodynamic collapse 1
- Do not confuse with Mobitz Type I (Wenckebach) - Type II occurs in the His-Purkinje system with slower, unreliable escape mechanisms, while Type I occurs at the AV node with more reliable escape rhythms 1, 2
- Avoid AV nodal blocking agents including beta-blockers, non-dihydropyridine calcium channel blockers, and digoxin, as these can worsen conduction 5
Acute Temporizing Measures for Symptomatic Patients
- If hemodynamically unstable, arrange for urgent transvenous temporary pacing 1
- Atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg total) may be used temporarily for symptomatic bradycardia, though it is less effective for infranodal block 1
- Atropine should be used with caution in acute coronary ischemia 1
Special Clinical Scenarios
- Anterior wall myocardial infarction is a common acute cause, typically associated with extensive myocardial necrosis and high mortality 2
- Post-procedural Mobitz Type II (after alcohol septal ablation, surgical myectomy, tricuspid valve surgery, or TAVR) requires pacemaker implantation if block persists beyond 7-10 days 1
- Drug-induced cases (e.g., pembrolizumab) may require emergent temporary pacing and progression to complete heart block can occur within hours 6