What is the initial approach to managing a patient with 2nd degree Mobitz type 1 (Wenckebach) heart block?

Management of Second-Degree Mobitz Type I (Wenckebach) AV Block

Mobitz type I (Wenckebach) generally has a benign prognosis and does not require routine cardiac monitoring or immediate intervention in asymptomatic patients. 1

Initial Assessment

Determine if symptoms are present and directly attributable to the AV block:

• Look specifically for syncope, presyncope, transient dizziness, lightheadedness, heart failure symptoms, or confusional states from cerebral hypoperfusion caused by slow heart rate 1
• Assess whether the patient is an athlete or if the rhythm occurs during sleep, as Wenckebach is common and benign in these settings 1, 2
• Evaluate for reversible causes including medications (negative chronotropic agents), vagal stimulation, or acute myocardial infarction 1, 3

Risk Stratification Based on ECG Features

Examine the QRS complex and PR interval characteristics:

• If QRS is narrow and shortest PR interval is <0.3 seconds: This indicates AV nodal (proximal) disease with excellent prognosis 2
• If QRS is wide or shortest PR interval is ≥0.3 seconds: Obtain 24-hour ambulatory ECG monitoring to assess for progression to higher-degree block 2
• The progressive PR prolongation before the blocked beat confirms the diagnosis and typically indicates benign AV nodal disease 1, 2

Management Algorithm

For Asymptomatic Patients:

• No cardiac monitoring is required 1
• No pacemaker indication unless coexisting bundle branch block or other high-risk features are present 2
• Routine follow-up with periodic ECG monitoring is sufficient 2

For Symptomatic Patients:

If symptoms are clearly attributable to Wenckebach:

• Permanent pacing is indicated 2
• Establish symptom-rhythm correlation using ambulatory monitoring if the relationship is uncertain 2

If exertional symptoms are present:

• Perform exercise treadmill testing to determine if pacing would provide benefit 2
• Exercise testing helps assess whether AV conduction improves with increased sympathetic tone (favorable) or worsens (unfavorable) 4

Special High-Risk Scenarios Requiring Pacemaker:

• Coexisting bundle branch block or bifascicular block (suggests risk of progression to complete heart block) 2
• Neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome) regardless of symptoms 2
• Infiltrative cardiomyopathy with Mobitz I pattern 2

Critical Distinction: Rule Out Mobitz Type II

You must differentiate true Mobitz I from Mobitz II or 2:1 block masquerading as Wenckebach:

• Mobitz II has constant PR intervals before blocked beats and represents infranodal disease requiring pacemaker regardless of symptoms 1, 2
• In 2:1 AV block, the distinction cannot be made from surface ECG alone 2
• If uncertainty exists, perform exercise stress testing (Mobitz I improves with exercise, Mobitz II worsens) or electrophysiology study 2, 5

What NOT to Do

Do not place a pacemaker for:

• Asymptomatic vagally-mediated Wenckebach 2
• Wenckebach in trained athletes without symptoms 1, 4
• Wenckebach during sleep in otherwise healthy individuals 1

Acute Management if Symptomatic Bradycardia Present

If hemodynamically unstable while awaiting definitive therapy:

• Atropine 0.5 to 1 mg IV can temporarily improve AV nodal conduction 6
• Atropine is effective for AV nodal (Mobitz I) block but ineffective for infranodal (Mobitz II) block 6

Common Pitfalls

• Assuming all Wenckebach is benign: Rare cases have infranodal origin and require pacing despite typical Wenckebach pattern 5
• Missing coexisting conduction disease: Always assess for bundle branch blocks that increase risk 2
• Confusing nonconducted PACs with AV block: Look for premature P waves with different morphology 3