What is the treatment for a 2nd degree atrioventricular (AV) block?

Treatment for Second-Degree AV Block

Permanent pacemaker implantation is indicated for Mobitz Type II second-degree AV block even in asymptomatic patients, while Mobitz Type I (Wenckebach) typically requires pacing only when symptomatic. 1, 2

Critical First Step: Distinguish Block Type and Location

The treatment algorithm depends entirely on correctly classifying the block:

Mobitz Type II Block

• Constant PR intervals before and after blocked P waves with sudden failure of conduction 3, 2
• Almost always infranodal (His-Purkinje system), particularly with wide QRS 1, 3
• High risk of sudden progression to complete heart block and sudden cardiac death 3, 2
• Permanent pacemaker is Class I indication regardless of symptoms 1, 2

Mobitz Type I (Wenckebach) Block

• Progressive PR prolongation before the dropped beat with characteristic "group beating" 4
• Usually AV nodal location (supranodal) 1, 4
• Benign prognosis unless symptomatic 1
• Pacing indicated only if symptomatic bradycardia present 1

2:1 AV Block (Special Category)

• Cannot be classified as Type I or Type II from ECG alone 3, 4
• Requires exercise stress test or electrophysiologic study to determine anatomic level 1, 4
• If found to be infranodal at EP study, treat as Type II with permanent pacemaker 1

Definitive Treatment Algorithm

For Mobitz Type II Block:

Immediate Actions:

• Do not delay pacemaker implantation waiting for symptoms—progression is unpredictable and sudden 2
• Consider temporary pacing as bridge if hemodynamic compromise, syncope, or heart failure present 2
• Dual-chamber (DDD) pacing is preferred to maintain AV synchrony and prevent pacemaker syndrome 2

Class I Indications for Permanent Pacemaker:

• Type II block with symptomatic bradycardia (including heart failure or ventricular arrhythmias) 1
• Type II block requiring drugs that cause bradycardia 1
• Type II block with documented asystole ≥3.0 seconds or escape rate <40 bpm 1
• Type II block occurring during exercise (not due to ischemia) 1
• Asymptomatic Type II at intra- or infra-His levels found at EP study 1

For Mobitz Type I (Wenckebach) Block:

Observation is appropriate if:

• Patient is asymptomatic 1
• Block is at supra-His (AV node) level 1
• No hemodynamic compromise 1

Permanent pacemaker indicated if:

• Symptomatic bradycardia present 1
• Symptoms similar to pacemaker syndrome or hemodynamic compromise 1
• Found to be intra- or infra-Hisian at EP study (uncommon but possible) 1

Exclude Reversible Causes Before Permanent Pacing

Must rule out the following before proceeding with permanent pacemaker:

• Electrolyte abnormalities (particularly hyperkalemia) 2
• Drug toxicity: digitalis, beta-blockers, calcium channel blockers 2
• Lyme disease 2
• Sleep apnea with hypoxia (reversible with treatment) 2
• Perioperative causes: hypothermia, inflammation near AV conduction system 2
• Acute myocardial ischemia (if exercise-induced block) 1

Acute/Temporary Management

Pharmacologic Approach:

• Atropine may be used for acute symptomatic bradycardia, but is unreliable and may worsen infranodal block 5
• Atropine works by vagal inhibition and is most effective for AV nodal (Type I) block 5
• In complete heart block, atropine may occasionally cause AV block and nodal rhythm as an adverse effect 5
• Temporary transcutaneous or transvenous pacing is preferred over atropine for Type II block with hemodynamic compromise 2

Perioperative Considerations:

• Prophylactic temporary pacemaker should be placed before elective surgery in patients with 2:1 AV block, even if asymptomatic, as general anesthesia can precipitate complete heart block 6
• Progression from 2:1 block to complete block has been documented within minutes of anesthesia induction 6

Post-Myocardial Infarction Context

• Anterior MI with Type II block indicates extensive necrosis and has high mortality 3
• Persistent Type II block after acute MI with bilateral bundle branch block requires permanent pacemaker (Class I) 2
• Transient advanced AV block with associated bundle branch block after MI also warrants permanent pacing 2
• Long-term prognosis relates primarily to extent of myocardial injury rather than the AV block itself 2

Common Pitfalls to Avoid

• Do not misdiagnose atypical Wenckebach (with constant PR intervals before block) as Type II—this is a frequent error 7, 8
• Do not assume narrow QRS = benign—Type I block with narrow QRS can still be infranodal in 60-70% of cases with bundle branch block 7
• Do not wait for symptoms in true Type II block—sudden progression to complete block can occur without warning 2
• Vagal surges can cause simultaneous sinus slowing and AV nodal block that superficially resembles Type II block but is benign 7, 8
• Concealed His bundle or ventricular extrasystoles may mimic Type II block (pseudo-AV block) 7, 8

Pacemaker Selection

• Dual-chamber (DDD) pacing is the Class I recommendation for maintaining physiologic AV synchrony 2
• Single-chamber ventricular pacing (VVI/R) acceptable only in sedentary patients, significant comorbidities, or permanent atrial fibrillation 2
• Single-lead VDD can be useful in younger patients with normal sinus node function and isolated AV block 2