What is the treatment for 2nd degree heart block?

Treatment of Second-Degree Heart Block

Permanent pacemaker implantation is indicated for all patients with Mobitz Type II second-degree AV block regardless of symptoms, while Mobitz Type I (Wenckebach) requires pacing only when symptomatic. 1, 2

Immediate Assessment and Risk Stratification

The critical first step is distinguishing between Mobitz Type I and Type II, as they have fundamentally different prognoses and management:

Mobitz Type I (Wenckebach) Characteristics

• Progressive PR interval prolongation before a dropped beat, with PR shortening after the block 3
• Block typically occurs at the AV node level (supranodal) 3
• Generally benign prognosis, can be normal in athletes during sleep 3
• Does NOT require pacing unless symptomatic 1

Mobitz Type II Characteristics

• Constant PR intervals before and after blocked beats 2, 3
• Block occurs in the His-Purkinje system (infranodal) 2, 4
• High risk of unpredictable progression to complete heart block 2
• Requires permanent pacemaker even if asymptomatic (Class I indication) 1, 2

2:1 AV Block

• Cannot be classified as Type I or Type II 3
• Requires additional evaluation (stress testing or electrophysiology study) to determine the level of block 3
• Treat based on QRS width and clinical context 1

Treatment Algorithm

For Mobitz Type II or Advanced Second-Degree Block

Immediate Actions:

• Place transcutaneous pacing pads immediately due to high progression risk 2
• Initiate continuous cardiac monitoring 2
• Obtain echocardiography to assess for structural heart disease 2
• Check electrolytes (potassium, magnesium) to rule out reversible causes 2

Acute Symptomatic Management:

• Do NOT rely on atropine for Mobitz Type II with wide QRS complexes - these bradyarrhythmias are not responsive to cholinergic reversal 5
• If atropine is attempted (narrow QRS only), use 0.5 mg IV every 3-5 minutes to maximum 3 mg 2, 5
• Arrange urgent transvenous temporary pacing for hemodynamically unstable patients 2

Definitive Treatment:

• Permanent pacemaker implantation is mandatory (Class I indication) for all Mobitz Type II patients, even if asymptomatic 1, 2
• Do not delay pacemaker placement - progression to complete heart block can be rapid and unpredictable 2
• Dual-chamber pacemakers should be programmed to maintain native AV conduction when possible 2

For Mobitz Type I (Wenckebach)

Asymptomatic Patients:

• No treatment required 1
• Permanent pacemaker is NOT indicated for asymptomatic Type I second-degree AV block at the AV node level 1

Symptomatic Patients:

• Permanent pacemaker implantation is indicated for symptomatic bradycardia regardless of block type or site (Class I indication) 1
• Symptoms include fatigue, exercise intolerance, presyncope, syncope, or heart failure 1

For 2:1 AV Block

• If narrow QRS: likely AV nodal, treat as Mobitz Type I 1
• If wide QRS: likely infranodal, treat as Mobitz Type II 1
• Consider stress testing - exercise-induced worsening indicates His-Purkinje disease requiring pacing 6

Advanced Second-Degree (High-Grade) AV Block

Two or more consecutive blocked P waves with some preserved AV conduction:

• Generally considered infranodal 3
• Permanent pacemaker indicated (Class I) if associated with symptomatic bradycardia, ventricular arrhythmias, or asystole ≥3 seconds 1
• Also indicated if awake heart rate <40 bpm or drug therapy causing symptomatic bradycardia is required 1

Special Clinical Scenarios

Post-Cardiac Surgery or Ablation

• Permanent pacemaker indicated if AV block persists beyond 7-10 days postoperatively 1, 2
• Most postoperative AV block recovers within this timeframe 2
• After AV junction ablation, permanent pacing is mandatory (Class I) 1

Neuromuscular Diseases

• Permanent pacing may be considered (Class IIb) for any degree of AV block in myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb dystrophy, or peroneal muscular atrophy due to unpredictable progression 1

Exercise-Induced Block

• Second- or third-degree AV block during exercise (not due to ischemia) requires permanent pacing (Class I indication) 1, 6
• This indicates His-Purkinje disease with poor prognosis 6

Reversible Causes (Class III - Pacing NOT Indicated)

• AV block expected to resolve: drug toxicity, Lyme disease, transient vagal tone increases, or hypoxia in sleep apnea 1, 6
• Treat underlying cause and monitor for resolution 1

Critical Pitfalls to Avoid

Misdiagnosis of Mobitz Type II:

• Vagal surges can cause simultaneous sinus slowing and AV nodal block that mimics Type II 4, 7
• Atypical Wenckebach with minimal PR changes may appear as Type II 7
• Concealed His bundle or ventricular extrasystoles can create pseudo-AV block 4, 7
• True Mobitz Type II has NOT been reported in inferior MI or young athletes - these are typically vagal 4

Atropine Use:

• Doses <0.5 mg may paradoxically slow heart rate further 6
• Completely ineffective in Type II block with wide QRS 5
• Use with extreme caution in acute coronary ischemia 2
• No effect in heart transplant patients 5

Delayed Pacing:

• Do not wait for symptoms to develop in Mobitz Type II - progression can be sudden and life-threatening 2
• Continuous monitoring is essential until permanent pacemaker is placed 2