What is the treatment for 2nd degree Atrioventricular (AV) Block Type 2?

Treatment of Second-Degree AV Block Type 2

Permanent pacemaker implantation is indicated for Mobitz Type II second-degree AV block, even in asymptomatic patients, due to the high risk of progression to complete heart block and sudden cardiac death. 1

Immediate Management Approach

Symptomatic Patients

• Permanent pacemaker implantation is the definitive treatment for Type II second-degree AV block with symptomatic bradycardia (Class I indication). 1
• Temporary pacing may be required as a bridge to permanent pacemaker if the patient presents with hemodynamic compromise, syncope, or heart failure symptoms. 1
• Atropine can be used acutely for symptomatic bradycardia, though its effectiveness is limited because Type II block is infranodal (below the AV node level) and less responsive to vagal manipulation. 2, 3
• Isoproterenol infusion may be considered as a temporizing measure in emergency situations while arranging for pacing. 4

Asymptomatic Patients

• Permanent pacemaker implantation is reasonable even in asymptomatic Type II second-degree AV block (Class IIa indication), as this represents a Class IIa recommendation in the 1991 guidelines and has been reinforced in subsequent updates. 1
• The rationale is that Type II block is almost always infranodal, carries poor prognosis, and frequently progresses to complete heart block without warning. 1, 3, 5
• Symptoms are frequent, prognosis is compromised, and progression to complete heart block is common with Type II block. 1

Critical Diagnostic Considerations

Distinguishing Type II from Type I Block

• Type II block shows constant PR intervals before and after blocked P waves, representing all-or-none conduction without visible changes in AV conduction time. 6, 5
• The site of block in Type II is almost always infranodal (within or below the His bundle), particularly when associated with wide QRS complexes. 1, 6, 3
• Type I block (Wenckebach) typically shows progressive PR prolongation and is usually AV nodal, carrying a more benign prognosis. 6

Special Situations Requiring Vigilance

• 2:1 AV block cannot be definitively classified as Type I or Type II and may require electrophysiologic study or stress testing to determine the level of block. 6
• Exercise-induced Type II block, even if transient, indicates severe conduction system disease and warrants permanent pacing. 1, 7
• Type II block has not been reported in inferior myocardial infarction or young athletes, where apparent Type II patterns are usually misinterpreted Type I block. 5

Exclusion of Reversible Causes

Before proceeding with permanent pacing, exclude:

• Electrolyte abnormalities (particularly hyperkalemia), drug toxicity (digitalis, beta-blockers, calcium channel blockers), Lyme disease, and transient increases in vagal tone. 1, 3
• Hypoxia in sleep apnea syndrome (reversible with treatment). 1
• Perioperative AV block due to hypothermia or inflammation near the AV conduction system. 1

Post-Myocardial Infarction Context

• Persistent Type II block after acute MI with bilateral bundle branch block requires permanent pacemaker (Class I indication). 1
• Transient advanced AV block with associated bundle branch block after MI also warrants permanent pacing. 1
• The long-term prognosis relates primarily to extent of myocardial injury and intraventricular conduction defects rather than the AV block itself. 1

High-Risk Features Requiring Expedited Pacing

Patients with the following features require urgent permanent pacemaker consideration:

• Pre-existing right bundle branch block (RBBB) with new Type II block carries 47% risk of progression to complete heart block. 8, 9
• New left bundle branch block after procedures (e.g., TAVR) with 14% progression to high-degree AV block within 30 days. 8
• Documented asystole ≥3.0 seconds or escape rate <40 bpm in awake patients. 1

Common Pitfalls to Avoid

• Do not delay pacemaker implantation in Type II block waiting for symptoms to develop, as progression to complete block can be sudden and unpredictable. 1, 5
• Do not misclassify Type I block with bundle branch block as Type II; Type I with wide QRS is infranodal in 60-70% of cases and also requires pacing. 5
• Do not assume atropine will be effective for Type II block, as the infranodal location makes it poorly responsive to vagal manipulation. 2, 3
• Do not dismiss exercise-induced Type II block as benign; this indicates severe His-Purkinje disease requiring permanent pacing. 1, 7

Monitoring After Procedures

• For patients at risk after cardiac procedures (TAVR, valve surgery), 30-day continuous ambulatory monitoring identifies delayed occurrence of high-degree AV block in approximately 8-9% of cases. 8
• Timing of delayed pacemaker requirement averages 5 days post-procedure. 9