Management of Mobitz Type II Second-Degree AV Block
Permanent pacemaker implantation is indicated for all patients with Mobitz Type II second-degree AV block, regardless of symptoms, as this is a Class I recommendation. 1, 2
Immediate Actions
- Place transcutaneous pacing pads immediately upon recognition of Mobitz Type II block due to high risk of progression to complete heart block 2
- Initiate continuous cardiac monitoring until permanent pacemaker is placed 2
- For hemodynamically unstable patients, arrange urgent transvenous temporary pacing 2
- Atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg total) may be used temporarily for symptomatic patients, though Mobitz Type II typically does not respond to atropine 2, 3, 4
Diagnostic Confirmation
- Verify the diagnosis on 12-lead ECG: Mobitz Type II shows periodic nonconducted P waves with constant PR intervals before and after the blocked beat, without progressive PR prolongation 2
- Distinguish from Mobitz Type I (Wenckebach), which shows progressive PR prolongation before the blocked beat 2
- Note that the QRS complex is often wide in Mobitz Type II, indicating infra-His disease 3, 5
- In 2:1 AV block, surface ECG alone cannot distinguish Mobitz I from Mobitz II; electrophysiological studies may be required 3
Initial Workup
- Obtain transthoracic echocardiography to assess for structural heart disease 2
- Check electrolyte panel (particularly potassium) to rule out reversible causes 2
- Review medication list for AV-blocking drugs (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics) 3
- Consider thyroid function tests and assess for ischemic heart disease 3
Definitive Management: Permanent Pacemaker
Pacemaker implantation is a Class I indication for Mobitz Type II, even in asymptomatic patients, because the block occurs in the His-Purkinje system with unpredictable and potentially life-threatening progression to complete heart block 1, 2, 3
Pacemaker Programming Considerations
- Dual-chamber pacemakers should be programmed to maintain native AV conduction when possible to prevent pacing-induced ventricular dysfunction 1
- Regular device checks are needed after implantation to ensure proper function 2
Special Clinical Scenarios
Postoperative Mobitz Type II
- Pacemaker implantation is recommended for postoperative Mobitz Type II (after valve surgery, TAVR, alcohol septal ablation) that persists beyond 7-10 days 1, 2
- Most postoperative AV block recovers within 7-10 days; monitor during this period 1
Athletes with Mobitz Type II
- Comprehensive evaluation including echocardiogram and stress testing is required 3
- Exercise testing may reveal exercise-induced worsening of AV block 2, 6
- Even asymptomatic athletes require pacemaker implantation due to risk of prolonged ventricular pauses and potential neurological damage 7
Critical Pitfalls to Avoid
- Do not confuse with Mobitz Type I: Mobitz Type I (Wenckebach) typically occurs at the AV node with more reliable escape rhythms, while Mobitz Type II occurs in the His-Purkinje system with slower, unreliable escape mechanisms 1, 3, 5
- Do not delay pacemaker placement: Mobitz Type II can progress rapidly and unexpectedly to complete heart block with hemodynamic collapse 1, 3
- Do not rely on atropine: Unlike AV nodal blocks, Mobitz Type II does not respond reliably to atropine because the block is infranodal 3, 4
- Exclude pseudo-AV block: Concealed junctional extrasystoles can mimic Mobitz Type II; careful ECG analysis is essential 8