What is the treatment for Mobitz (Second-Degree Atrioventricular Block) type 2?

Treatment 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 represents a Class I recommendation due to the high risk of unpredictable progression to complete heart block. 1, 2

Immediate Management

Initial Stabilization

• Apply transcutaneous pacing pads immediately upon recognition, as Mobitz Type II carries high risk of sudden progression to complete heart block 2
• Initiate continuous cardiac monitoring until permanent pacemaker is placed 2
• Assess hemodynamic stability including blood pressure, signs of hypotension, and evidence of low cardiac output 2

Temporary Pharmacologic Management

• For symptomatic patients requiring temporary stabilization, atropine 0.5 mg IV every 3-5 minutes up to maximum 3 mg total dose may be attempted, though atropine is often ineffective since the block occurs in the His-Purkinje system below the AV node 1, 2
• Use atropine with caution in acute coronary ischemia settings 2

Temporary Pacing

• Arrange urgent transvenous temporary pacing for hemodynamically unstable patients 1, 2
• Transcutaneous pacing serves as a bridge until transvenous access is obtained 1
• The femoral, internal jugular, or subclavian veins provide transvenous access to the right ventricular apex 1

Diagnostic Workup

Essential Testing

• Obtain 12-lead ECG to confirm diagnosis and assess for bundle branch blocks (commonly RBBB with left fascicular block or LBBB) 3
• Perform transthoracic echocardiography (Class I recommendation) to evaluate for structural heart disease 2
• Check electrolyte panel, particularly potassium, to rule out reversible causes 2, 4
• Review medication list for potential causative agents (e.g., lithium, beta-blockers, calcium channel blockers) 5

Distinguishing Features

• Mobitz Type II shows constant PR intervals before and after blocked P waves, distinguishing it from Mobitz Type I which demonstrates progressive PR prolongation 1, 2, 6
• The block occurs in the His-Purkinje system (infranodal), not at the AV node level 6, 3, 4

Definitive Management

Permanent Pacemaker Indications

• Pacemaker implantation is mandatory for all patients with acquired Mobitz Type II block not attributable to reversible causes, even if asymptomatic 1, 2
• This Class I indication exists because 75% of patients experience syncope and the condition carries high risk of sudden progression to complete heart block with potential for Adams-Stokes attacks and sudden death 3
• Dual-chamber pacemakers should be programmed to maintain native AV conduction when possible to prevent pacing-induced ventricular dysfunction 2

Special Clinical Scenarios

• For postoperative Mobitz Type II (after alcohol septal ablation, surgical myectomy, tricuspid valve surgery, or TAVR): monitor for 7-10 days as most cases recover; if block persists beyond this period, proceed with permanent pacemaker 2
• In acute MI setting: Mobitz Type II represents a Class Ia indication for temporary transvenous pacing, followed by permanent pacemaker if block persists 1
• Neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome): permanent pacing with defibrillator capability if meaningful survival >1 year expected 1
• Infiltrative cardiomyopathies (cardiac sarcoidosis, amyloidosis): consider pacemaker with defibrillator capability 1

Critical Pitfalls to Avoid

Diagnostic Errors

• Do not confuse with "apparent Mobitz Type II" which is vagally-mediated AV nodal block that mimics true Mobitz Type II but occurs with simultaneous sinus slowing and responds to atropine 7, 8
• Do not mistake for Mobitz Type I, as Type I typically occurs at the AV node with more reliable escape rhythms, while Type II occurs in the His-Purkinje system with slower, unreliable escape mechanisms 2, 6
• In 2:1 AV block patterns, the classification cannot be determined from surface ECG alone and may require exercise testing or electrophysiology study 6

Management Errors

• Do not delay pacemaker placement awaiting symptom development, as progression to complete heart block is unpredictable and potentially fatal 2, 3
• Do not rely on atropine for definitive management, as it rarely improves infranodal block 1, 2
• Do not discharge patients without pacemaker implantation or continuous monitoring capability 2

Prognosis

• Permanent pacing improves survival in patients with high-grade AV block, particularly those who have experienced syncope 2
• Without pacemaker, the natural history includes high incidence of progression to complete heart block with risk of sudden death 3, 4