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

Treatment of Second-Degree AV Block

Permanent pacemaker implantation is indicated for all patients with Mobitz Type II second-degree AV block, even if asymptomatic, due to the high risk of sudden progression to complete heart block and sudden cardiac death. 1, 2

Immediate Assessment and Stabilization

Distinguish Block Type and Location

• Mobitz Type II shows constant PR intervals before and after blocked P waves, representing infranodal (His-Purkinje) disease with unpredictable progression 2, 3
• Mobitz Type I (Wenckebach) shows progressive PR prolongation before the blocked beat, typically occurs at the AV node level, and has a more benign prognosis 2, 3
• 2:1 AV block cannot be definitively classified without additional testing (electrophysiologic study or stress testing may be needed) 2

Acute Hemodynamic Management

• Place transcutaneous pacing pads immediately for Mobitz Type II due to high progression risk 4
• Initiate continuous cardiac monitoring until definitive treatment 4
• For symptomatic bradycardia with hemodynamic compromise, begin transcutaneous pacing while preparing for transvenous temporary pacing 4
• Atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg total) may be attempted but do not rely on atropine in Type II second-degree or third-degree AV block with wide QRS complexes as these are unlikely to respond 5

Exclude Reversible Causes Before Permanent Pacing

• Electrolyte abnormalities (particularly hyperkalemia) 2
• Drug toxicity (digitalis, beta-blockers, calcium channel blockers) 2
• Lyme disease 2
• Transient vagal tone increases 2
• Hypoxia from sleep apnea (reversible with treatment) 2
• Perioperative hypothermia or inflammation near AV conduction system 2

Definitive Treatment: Permanent Pacemaker Indications

Class I Indications (Must Implant)

• Symptomatic second-degree AV block of any type with bradycardia symptoms 1, 2
• Mobitz Type II block, even if asymptomatic, because the block is infranodal with unreliable escape mechanisms and unpredictable progression 2, 4
• Asystole ≥3.0 seconds or escape rate <40 bpm in awake patients 1, 2
• Second-degree AV block during exercise in absence of myocardial ischemia 1
• Post-MI persistent Type II block with bilateral bundle branch block 2
• Postoperative AV block not expected to resolve after cardiac surgery 1
• Post-catheter ablation of AV junction 1
• Neuromuscular diseases (myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb dystrophy) with AV block 1

Class IIa Indications (Reasonable to Implant)

• Asymptomatic second-degree AV block at intra- or infra-His levels found at electrophysiological study 1
• First- or second-degree AV block with pacemaker syndrome symptoms or hemodynamic compromise 1

Class III (Do NOT Implant)

• Asymptomatic Type I (Wenckebach) second-degree AV block at the supra-His (AV node) level 1
• AV block expected to resolve (unless specific conditions like sarcoidosis, amyloidosis, or neuromuscular disease where progression risk remains) 1

Pacemaker Selection

Dual-chamber pacing (DDD) is the preferred mode for second-degree AV block Type II to maintain atrioventricular synchrony and prevent pacemaker syndrome. 2

Acceptable Alternatives

• Single-chamber ventricular pacing (VVI/R) only for sedentary patients, significant comorbidities, or permanent atrial fibrillation 2
• Single-lead VDD pacing for younger patients with normal sinus node function and isolated AV block 2
• Program dual-chamber devices to maintain native AV conduction when possible to prevent pacing-induced ventricular dysfunction 4

Special Clinical Scenarios

Post-Myocardial Infarction

• Persistent Type II block after acute MI with bilateral bundle branch block requires permanent pacemaker 2
• Transient advanced AV block with associated bundle branch block after MI warrants permanent pacing 2
• Long-term prognosis relates primarily to extent of myocardial injury rather than the AV block itself 2

Perioperative Management

• Even asymptomatic 2:1 AV block can progress to complete heart block with anesthesia induction 6
• Prophylactic temporary pacemaker should be implanted preoperatively in patients with 2:1 AV block, even without symptoms 6
• Most postoperative AV block recovers within 7-10 days; monitor during this period before permanent pacing 4

Type I (Wenckebach) Block at AV Node Level

• Chronic second-degree AV nodal block has a relatively benign course in patients without organic heart disease 7
• In patients with organic heart disease, prognosis is poor but related to severity of underlying disease rather than the block itself 7
• Permanent pacing indicated only if symptomatic bradycardia develops 1, 7

Critical Pitfalls to Avoid

• Do not delay pacemaker implantation in Type II block waiting for symptoms, as progression can be sudden and life-threatening 2, 4
• Do not confuse Mobitz Type II with Type I, as Type II requires pacing even when asymptomatic while Type I at the AV node level does not 1, 2
• Do not use atropine as definitive treatment for Type II block with wide QRS, as it is ineffective for infranodal block 5
• Do not use single-chamber atrial pacing (AAI) in AV block, as the conduction disease is below the atrium 2
• Limit total atropine dose to 0.03-0.04 mg/kg in patients with ischemic heart disease 5