What is the appropriate management of a complete (third-degree) atrioventricular block?

Management of Complete Heart Block (Third-Degree AV Block)

Permanent pacemaker implantation is the definitive treatment for complete (third-degree) atrioventricular block and is a Class I indication that prevents sudden death and improves survival. 1, 2

Immediate Assessment and Stabilization

Evaluate Hemodynamic Status

• Assess immediately for symptomatic bradycardia including syncope, presyncope, heart failure symptoms, chest pain, hypotension, altered mental status, or dyspnea 2
• Determine the anatomic level of block, as this critically determines prognosis and urgency—infranodal blocks (His-Purkinje system) can progress rapidly and unpredictably with slower, unreliable ventricular escape rhythms, while AV nodal blocks have more stable junctional escape mechanisms 1, 2

Rule Out Reversible Causes First

• Patients with transient or reversible causes (Lyme carditis, drug toxicity, myocarditis, electrolyte abnormalities, acute MI, thyroid dysfunction) should receive medical therapy and supportive care, including temporary transvenous pacing if necessary, before determining need for permanent pacing. 1
• Note that 88% of patients with third-degree AV block still require permanent pacemaker even after correction of reversible causes 2
• Reversible conditions may unmask a preexistent conduction disorder, so recurrence after reversal may still warrant pacing 3

Acute Medical Management

Pharmacologic Therapy

• For AV nodal-level block with symptoms or hemodynamic compromise, atropine is reasonable to improve AV conduction and increase ventricular rate (note: infranodal blocks will NOT respond to atropine) 1
• Beta-adrenergic agonists (isoproterenol, dopamine, dobutamine, or epinephrine) may be considered when coronary ischemia likelihood is low 1
• In acute inferior MI setting, intravenous aminophylline may be considered 1

Temporary Pacing

• For symptomatic or hemodynamically compromised patients refractory to medical therapy, temporary transvenous pacing is reasonable 1
• For prolonged temporary pacing needs, use an externalized permanent active fixation lead over standard passive fixation temporary leads 1
• Temporary transcutaneous pacing may be considered for hemodynamic compromise refractory to medications until transvenous or permanent pacemaker is placed 1
• Infranodal blocks require continuous arrhythmia monitoring until pacemaker implantation due to risk of rapid, unpredictable progression 2

Permanent Pacemaker Indications (Class I - Definitive)

Absolute Indications

• Acquired third-degree AV block at any anatomic level not attributable to reversible or physiologic causes requires permanent pacing regardless of symptoms 1, 2
• Third-degree AV block with symptomatic bradycardia, heart failure symptoms, or ventricular arrhythmias presumed due to AV block 2
• Third-degree AV block requiring medications that cause symptomatic bradycardia 2
• Asymptomatic third-degree AV block in awake patients with high-risk features: documented asystole ≥3.0 seconds, escape rate <40 bpm, or escape rhythm below the AV node 2
• Third-degree AV block with atrial fibrillation and bradycardia with pauses ≥5 seconds 2
• Post-MI third-degree AV block that persists 2

Special Populations Requiring Permanent Pacing

• Neuromuscular diseases (myotonic dystrophy type 1, Kearns-Sayre syndrome) with evidence of third-degree AV block or HV interval ≥70 ms require permanent pacing with additional defibrillator capability if meaningful survival >1 year expected 1
• Infiltrative cardiomyopathies (cardiac sarcoidosis, amyloidosis) with third-degree AV block—permanent pacing with defibrillator capability if needed is reasonable 1
• Lamin A/C gene mutations with PR >240 ms and LBBB—permanent pacing with defibrillator capability is reasonable 1

Drug-Induced Block on Necessary Medications

• In selected patients on chronic stable doses of medically necessary antiarrhythmic or beta-blocker therapy with symptomatic third-degree AV block, proceed to permanent pacing without drug washout or observation for reversibility 1
• When symptomatic AV block develops as consequence of guideline-directed therapy with no alternative treatment, permanent pacing is recommended 1

Cardiac Sarcoidosis Exception

• In cardiac sarcoidosis with third-degree AV block, permanent pacing with additional defibrillator capability (if meaningful survival >1 year expected) without observation for reversibility is reasonable 1

Critical Pitfalls to Avoid

• Do NOT discharge asymptomatic patients with third-degree AV block and high-risk features (escape rate <40 bpm, ventricular escape rhythm, pauses ≥3 seconds) without pacemaker placement 2
• Do NOT perform permanent pacing in patients with complete resolution of AV block after treatment of known reversible and non-recurrent causes 1
• Do NOT perform permanent pacing in asymptomatic vagally mediated AV block 1
• Do NOT assume atropine will work for infranodal blocks—it only works at the AV nodal level 1
• Do NOT delay pacemaker placement in infranodal blocks, as they can progress rapidly and unpredictably to asystole 2