What is the appropriate treatment for a patient diagnosed with heart block?

Treatment of Heart Block

For symptomatic second-degree Mobitz Type II or third-degree (complete) heart block, permanent pacemaker implantation is the definitive treatment and should be pursued urgently, as these conditions carry high risk of sudden progression to asystole and death. 1

Acute Management Algorithm

Immediate Assessment and Stabilization

For hemodynamically unstable patients with second-degree or third-degree AV block:

• Apply transcutaneous pacing pads immediately upon recognition of Mobitz Type II or complete heart block, as these can progress unpredictably to asystole 2
• Assess for hemodynamic compromise: hypotension, altered mental status, chest pain, dyspnea, or signs of shock 1
• Establish continuous cardiac monitoring until permanent pacing is achieved 2

Pharmacologic Therapy (Temporizing Measures Only)

For AV nodal-level blocks (second-degree Mobitz Type I or some third-degree blocks with narrow QRS escape rhythms):

• Atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg total) is reasonable for symptomatic bradycardia at the AV nodal level 1
• Critical caveat: Atropine is often ineffective for Mobitz Type II and infranodal blocks (His-Purkinje system) and should not delay definitive pacing 2, 3
• Doses <0.5 mg may paradoxically worsen bradycardia 4

For refractory symptomatic bradycardia:

• Beta-adrenergic agonists (isoproterenol, dopamine, dobutamine, or epinephrine) may be considered if low likelihood of coronary ischemia exists 1
• In acute inferior MI setting, IV aminophylline may be considered 1

Temporary Pacing

For patients with symptomatic second-degree or third-degree AV block refractory to medical therapy:

• Temporary transvenous pacing is reasonable to increase heart rate and improve symptoms until permanent pacemaker can be placed 1
• For prolonged temporary pacing needs, externalized permanent active fixation leads are preferred over standard passive fixation temporary leads 1
• Transcutaneous pacing may be considered as a bridge until transvenous or permanent pacemaker is placed 1

Permanent Pacemaker Indications by Block Type

Third-Degree (Complete) Heart Block

Permanent pacemaker implantation is a Class I recommendation for:

• Any symptomatic third-degree AV block not attributable to reversible causes 1
• Asymptomatic third-degree AV block with documented periods of asystole ≥3 seconds or escape rhythm <40 bpm while awake 1
• Third-degree AV block associated with cardiac sarcoidosis (with defibrillator capability if meaningful survival >1 year expected) 1

Second-Degree Mobitz Type II

Permanent pacemaker is mandatory (Class I) for all patients with Mobitz Type II, even if asymptomatic, due to unpredictable progression to complete heart block 2

Second-Degree Mobitz Type I (Wenckebach)

• Generally does not require permanent pacing unless symptomatic or associated with structural heart disease 1
• Occurs at AV nodal level with more reliable escape rhythms compared to Mobitz Type II 2

First-Degree AV Block

Permanent pacemaker is NOT indicated for asymptomatic first-degree AV block with PR <300 ms (Class III recommendation) 5, 4

Permanent pacing is reasonable (Class IIa) when:

• PR interval >300 ms causes symptoms similar to pacemaker syndrome (fatigue, exercise intolerance, dyspnea) or hemodynamic compromise 5, 4
• Symptoms are clearly attributable to the profound first-degree block 5, 4

Management of Reversible Causes

Before proceeding to permanent pacing, identify and treat reversible causes:

Transient/Reversible Etiologies

• Lyme carditis or drug toxicity: Medical therapy and supportive care, including temporary transvenous pacing if necessary, should be provided before determining need for permanent pacing 1
• If AV block completely resolves with treatment of underlying cause, permanent pacing should NOT be performed (Class III: Harm) 1

Medication-Induced Block

• For patients on chronic stable doses of medically necessary antiarrhythmic or beta-blocker therapy with symptomatic second-degree or third-degree AV block, it is reasonable to proceed to permanent pacing without drug washout 1
• Evaluate for AV nodal blocking agents: beta-blockers, calcium channel blockers (verapamil, diltiazem), digoxin, amiodarone 5, 4

Special Populations

• Thyroid abnormalities: In symptomatic second-degree or third-degree AV block without clinical myxedema, permanent pacing without observation for reversibility may be considered 1
• Neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome): Permanent pacing may be considered even with first-degree AV block due to unpredictable progression 1, 5, 4

Pacemaker Mode Selection

For chronic symptomatic AV block:

• Dual-chamber pacing is preferred over single-chamber ventricular pacing to maintain AV synchrony and prevent pacemaker syndrome 1
• In patients with intact AV conduction and sinus node dysfunction, dual-chamber or single-chamber atrial pacing is recommended 1
• Program dual-chamber pacemakers to minimize unnecessary ventricular pacing when native AV conduction is intact 1

Critical Pitfalls to Avoid

• Do not delay permanent pacemaker placement for Mobitz Type II or complete heart block – these can progress rapidly and unpredictably to asystole 2
• Do not confuse Mobitz Type I with Mobitz Type II – Mobitz Type I shows progressive PR prolongation before blocked beats, while Mobitz Type II has constant PR intervals 2
• Do not rely on atropine for infranodal blocks (Mobitz Type II, complete heart block with wide QRS escape) – it is ineffective and delays definitive treatment 2, 3
• Do not implant pacemakers for isolated, asymptomatic first-degree AV block with PR <300 ms – this is potentially harmful (Class III) 5, 4
• Do not use atropine in acute MI with caution – increased heart rate may worsen ischemia 5

Post-MI Considerations

In acute inferior MI:

• Early AV block (within 6 hours) is usually vagally mediated, responds to atropine, and resolves within 24 hours 6
• Late AV block (>6 hours, especially >24 hours) is due to ischemic damage, responds poorly to atropine, and requires pacing 6
• Temporary pacing is reasonable for symptomatic bradycardia; permanent pacing indicated if block persists beyond 7-10 days postoperatively 2